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ASTRO BOY
2013-Feb-18, 07:57 PM
I found the rather interesting article at .....

http://phys.org/news/2013-02-scientists-breakthroughs-dark-matter-mystery.html

Scientists sense breakthroughs in dark-matter mystery

Today, though, scientists believe that with the help of multi-billion-dollar tools, they are closer than ever to piercing the mystery—and the first clues may be unveiled just weeks from now.

"And the tantalizing thing on the cosmology side is that we have an airtight case that the dark matter is made of something new... there is no particle in the Standard Model that can account for dark matter."



More at the link.......

ASTRO BOY
2013-Feb-18, 07:59 PM
Another extract from the article interested me somewhat........

"The real question is why dark matter has six times the energy that is in ordinary matter," said Lisa Randall of Harvard University".

antoniseb
2013-Feb-18, 08:13 PM
Speculation is that there are some particular energies we are likely to see positrons having... including one or more that seem consistent with some family of WIMPs. The details will be published soon, but as to when exactly, that is secret.

ASTRO BOY
2013-Feb-18, 08:19 PM
Is the following extract from the article an example of poor journalism?

" Another big weapon is the Large Hadron Collider (LHC) near Geneva, the biggest particle smasher in the world. Its power, they insist, could allow them to break-up electrons, quarks or neutrinos to uncover dark matter."

ASTRO BOY
2013-Feb-18, 08:21 PM
Speculation is that there are some particular energies we are likely to see positrons having... including one or more that seem consistent with some family of WIMPs. The details will be published soon, but as to when exactly, that is secret.

Thanks for that info antoniseb......and is this related to my previous post?

antoniseb
2013-Feb-18, 08:31 PM
....and is this related to my previous post?

Until the paper comes out we won't really know. There's a rumor that they got some great information from the last runs before reconfiguring for 14 TeV... but it is just a rumor. I suspect that the reference to the LHC may be hopes for that new capabilities two years from now.

trinitree88
2013-Feb-19, 01:56 AM
I, ll bet chinese food that sam's paper from the ams results will find a null result...no dark matter, including wimps....and I have not been to the conference. .....pete

Swift
2013-Feb-19, 02:05 AM
The January 12 issue of Science News (http://www.sciencenews.org/view/feature/id/347258/description/Light_in_the_Dark) had a big article on the on the search for dark matter. It reviews some of the searches done so far and some of the planned ones.

This mystery matter apparently consists of tiny particles of some exotic species, but efforts to trap them (in underground detectors) or make them (in particle accelerators) have produced frustrating results: Some experiments find hints of such particles; others find nothing.

Yet despite the frustration, physicists offer a message of hope. With a deluge of new data already in hand, and more precise probes in the works, learning the identity of dark matter may just be a matter of time.

“My feeling,” says theoretical physicist Katherine Freese, “is that we’re on the edge of discovering it.”

By discovering it, she means directly detecting the existence of dark matter particles, determining their species and mass and then, ideally, figuring out how they fit into physicists’ broader theories of matter and energy. And as it turns out, the latest twists in the dark matter plot suggest that those particles might not fit where most experts had expected.

Cougar
2013-Feb-19, 02:31 AM
Is the following extract from the article an example of poor journalism?
"...could allow them to break-up electrons, quarks or neutrinos to uncover dark matter."

Ha ha. Yes. I don't think they "break up" any of those things, especially not neutrinos.

But as to "Will Dark Matter Finally Reveal Itself?" . . . . It better! It makes up a large percentage of the entire mass-energy of the universe. Much more than all the stars, gas, planets, and black holes. It's a 'problem' that will not go away until it is solved.

neilzero
2013-Feb-23, 06:38 PM
Think of the possibilities as a construction material if we can issolate dark matter for practical applications. Interesting properties are all but certain. Neil

Shaula
2013-Feb-23, 06:49 PM
Think of the possibilities as a construction material if we can issolate dark matter for practical applications. Interesting properties are all but certain. Neil
In the best current models for it the stuff doesn't interact electromagnetically. So it won't bond with anything or form structures (barring new physics). It will basically be a very low viscosity gas that escapes just about any container. So not the most interesting of materials.

borman
2013-Feb-25, 06:37 AM
Towards a resolution of the differences between the various Dark Matter searches

Modulation signals have been seen in some searches, namely DAMA/LIBRA, CoGeNT, and CRESST-II experiments. Meanwhile no signals have been monitored and constraints are established in other experiments such as Xenon10, Xenon100, and CDMSII.
To make issues more perplexing is that CDMS II and CoGeNT both operated in the same mine and both made use of Germanium detectors while CDMS II additionally used Si detectors. Aside from a mass difference (~250gms for CDMS vs 440 gms for CoGeNT), the main difference is the method of signal acquisition. CDMS II uses phonon detection while CoGeNT uses ionization detection.
The purpose of the experiments is to look for WIMP interactions with targets and further if such signals relate to the Earth’s orbit about the Sun to support the idea of a galactic WIMP wind.
Given the prior of the WIMP wind, the two families of experiments appear to disfavor each other and the search has been for systematic error that either causes or suppresses signal acquisition. To date a reliable source of error has not yet been found.
Another possibility to follow is that all experiments give valid observations and there is no sufficient source of experimental error to explain their differences. This may require a re-evaluation of the prior as the source of the differences.
As a trial proposal, a large amount of symmetry suppresses the signal. Xenon and the crystal lattices used for phonon signal acquisition have more symmetry than those who see a signal. A possible clue comes from the 1995 TOPEX/POSEIDON experiment to test general relativity. While relativity was supported to greater than 95% confidence, there were observed a “pass bias” (maximum of 10.2m) quite in excess of the theoretical rms error (23cm) only in the more eccentric orbits. The more circular the orbit, the more the signal disappeared. Eccentricity is related to orbit. So the question is whether what is WIMP “wind” is possibly related to eccentricity. If the anomaly is scale independent, then the effect can be shrunk to lattice, atomic, or even nuclear scales where lack of symmetry may lead to signal acquisition. Modulations in the radio-active decay rates have been monitored in some species while being reconfirmed as being absent in other species.
A test of the hypothesis could come with dark Matter detectors using superfluid He-4 and He-3 (ULTIMA). The expectation is that He-4 being symmetrical like Xenon will give null results while repeating the experiment with He-3 may allow signal acquisition.
References
Relativity in the Global Positioning System
http://relativity.livingreviews.org/Articles/lrr-2003-1/download/lrr-2003-1Color.pdf
Search for annual modulation in low-energy CDMS-II data
http://arxiv.org/pdf/1203.1309v2.pdf
CoGeNT: A Search for Low-Mass Dark Matter using p-type Point Contact Germanium Detectors
http://arxiv.org/abs/1208.5737
A Concept for A Dark Matter Detector Using Liquid Helium-4
http://arxiv.org/abs/1302.0534
DAMA/LIBRA results and perspectives
http://arxiv.org/abs/1301.6243
Concerning the Time Dependence of the Decay Rate of 137Cs
http://arxiv.org/abs/1211.2138

Jens
2013-Feb-25, 08:14 AM
Ha ha. Yes. I don't think they "break up" any of those things, especially not neutrinos.


I think it's probably loose journalism as well, but on the other hand, I'm not absolutely positive. I remember reading in SciAm last year about the possibility that quarks may not be fundamental, and for example in this article (http://www.nature.com/news/not-quite-so-elementary-my-dear-electron-1.10471), it says that electrons can be broken into "virtual particles," so I kind of wonder. I don't know if we know enough about neutrinos to make any determination there, we don't even know what their mass is.

John Mendenhall
2013-Feb-26, 03:49 AM
I, ll bet chinese food that sam's paper from the ams results will find a null result...no dark matter, including wimps....and I have not been to the conference. .....pete

With apologies to pete, I propose a fifth force, unifying the other four, and manifesting itself to us as undetectable 'dark matter'.

We can call the fifth force 'the dark side of the forces'.

Forgive me, gentle readers, chinese food has upset my stomach. Regards, John M.

Jerry
2013-Feb-26, 11:29 PM
"And the tantalizing thing on the cosmology side is that we have an airtight case that the dark matter is made of something new... there is no particle in the Standard Model that can account for dark matter."

Well, no.

Eliminating all the usual suspects doesn't mean that the devil did it himself. Eliminating every know type or matter means either there is an unknown force, or we don't understand the forces we think we have a good handle on.

We've been waiting for half a century for a reasonable explanation for Zwicky's observations. The answer has always been 'soon'

Shaula
2013-Feb-27, 06:23 AM
Well, no.

Eliminating all the usual suspects doesn't mean that the devil did it himself. Eliminating every know type or matter means either there is an unknown force, or we don't understand the forces we think we have a good handle on.
By this logic we never would have discovered neutrinos and instead would have assumed that our thoughts on conservation of energy/momentum were wrong. We also would have assumed that our ideas on EM were wrong and that there were no neutrons. Dirac would have been wrong and there would be no positrons.

lpetrich
2013-Mar-01, 10:43 PM
Another extract from the article interested me somewhat........

"The real question is why dark matter has six times the energy that is in ordinary matter," said Lisa Randall of Harvard University".
I think that she's referring to the overall density of the Universe -- the Universe has 6 times as much mass in dark matter as in ordinary, baryonic matter.

It's possible that dark matter could be something too difficult to detect, like gravitinos. The gravitino is the supersymmetry partner of the elementary particle of gravity, the graviton, and its interactions have essentially the same strength: VERY, VERY, VERY weak.

But if these experiments succeed in detecting dark matter, then we may get some important clues about its nature, especially if several of them do so. That's because the detectors use several materials:

DAMA/LIBRA - Na, I, Tl
CoGeNT - Ge
CRESST-II - Ca, W, O
Xenon10, Xenon100 - Xe
CDMS II - Si, Ge

How many protons and neutrons? I'll be assuming no isotope separation from Earth's-crust sources.
O: Z = 8, N ~ 8.02, N/Z ~ 1.00
Na: Z = 11, N = 12, N/Z ~ 1.09
Si: Z = 14, N ~ 14.1, N/Z ~ 1.01
Ca: Z = 20, N ~ 20.1, N/Z ~ 1.00
Ge: Z = 32, N ~ 40.7, N/Z ~ 1.27
I: Z = 53, N = 74, N/Z ~ 1.40
Xe: Z = 54, N ~ 77.3, N/Z ~ 1.43
W: Z = 74, N ~ 109.9, N/Z ~ 1.48
Tl: Z = 81, N ~ 123.4, N/Z ~ 1.52

For (WIMP de Broglie wavelength) > (size of nucleus), the interaction cross section is ~ (fproton*Z + fneutron*N)2 (coherent limit). If that de Broglie wavelength is much less, then the WIMP scatters off of the individual nucleons as if they were separate particles, in incoherent fashion. Since vDM ~ 10-3 c, the WIMP's' de Broglie wavelength will be larger than a nucleus unless its mass is at least a few hundred GeV.

So if one can see dark matter with silicon, germanium, and some of the heavy elements, one will be able to (1) disentangle the WIMP-proton and WIMP-neutron interactions and (2) get an idea of the coherence of the interaction, which will give a clue as to the WIMP's' momenta, and thus of their mass. That can be checked against the recoil energies that the nuclei get -- is it consistent?

Also, if one can get directional information, one may be able to test hypotheses of WIMP velocity distributions.

TooMany
2013-Mar-01, 11:24 PM
The DAMA/LIBRA folks seem confident that they have detected a signal. Does this directly contradict other experiments, so the victory flag cannot be raised?

ASTRO BOY
2013-Apr-03, 08:04 PM
Scientists report hint of dark matter in first results from $2 billion cosmic ray detector (Update 3) April 3, 2013

A $2 billion cosmic ray detector on the International Space Station has found the footprint of something that could be dark matter, the mysterious substance that is believed to hold the cosmos together but has never been directly observed, scientists say.

full article at....
http://phys.org/news/2013-04-scientists-hint-dark-results-billion.html

antoniseb
2013-Apr-03, 08:48 PM
Scientists report hint of dark matter in first results ...
I want there to be a definite observation of Dark Matter so we can see more of what makes up the universe, and what there is beyond the standard model of particle physics, but let's be clear this is only a hint, and it isn't unambiguous.

lpetrich
2013-Apr-04, 03:03 AM
They have identified both electrons and positrons in the cosmic rays that they detected - 6.8 million total out of 25 billion total cosmic-ray events, mostly protons.

But I agree that they are diffident on whether they have found evidence of dark-matter annihilation -- two DM WIMP's colliiding to make an electron-positron pair.


I'm skeptical about how much one can learn from low-energy charged cosmic rays, because they don't have a very large gyroradius. That's the Larmor radius, the radius of orbit around a magnetic field line.

r = 33.36 km * (p / 1 GeV/c) * (1/Z) * (1 gauss / B)
p = momentum, Z = atomic number, B = magnetic field

I'll use an energy of 1 TeV and a charge of 1 as a reference, since the putative gamma-ray annihilation line from the Fermi telescope is at 130 GeV.

The galactic magnetic field is about 10-6 gauss, meaning that that particle has a gyroradius of 3.3*1010 km or around 200 AU's or 10-3 parsecs.

Source: Particle Astrophysics Lecture 3 - Cosmic Rays - PA3.pdf (http://homepages.ulb.ac.be/~khanson/particle-astrophysics/w11/PA3.pdf)

From Interplanetary magnetic field - Wikipedia (http://en.wikipedia.org/wiki/Interplanetary_magnetic_field), the interplanetary magnetic field is 10-9 tesla or 10-5 gauss, about 10 times greater, making that particle's gyroradius about 20 AU.

ASTRO BOY
2013-Apr-04, 05:31 AM
I want there to be a definite observation of Dark Matter so we can see more of what makes up the universe, and what there is beyond the standard model of particle physics, but let's be clear this is only a hint, and it isn't unambiguous.



That is certainly the case at this point in time.........

from the article....
"But the evidence isn't enough to declare the case closed. The footprints could have come from another, more conventional suspect: a pulsar, or a rotating, radiation-emitting star".

Time and further research should reveal something more concrete........

lpetrich
2013-Apr-04, 07:35 AM
There is another possible detector of dark-matter decays: neutrino telescopes (Neutrino detector - Wikipedia (http://en.wikipedia.org/wiki/Neutrino_detector)). Identifying Dark Matter Annihilation to Neutrinos - Richardson-INFO11.pdf (http://alexfriedland.com/info11/info11talks/Richardson-INFO11.pdf)

From the looks of it, they hope to detect neutrinos from WIMP annihilation in the Sun and the Earth. This would happen by the WIMP's bouncing off of nuclei and getting captured. They would then accumulate and run into each other.

Galactic dark matter
Wind: ~ 250 km/s
Dispersion: ~ 250 km/s

Escape velocities at the surface:
The Sun: 620 km/s
The Earth: 11.2 km/s
Will be larger in the interior.

The WIMP's will travel at about 700 km/s in the Sun's interior until they collide with nuclei. Most of them will then be captured. A problem is that the Sun's interior is hot and gaseous and is supported by its pressure. That will give the nuclei velocities not much less than the local escape velocity, and that may kick out some of the WIMP's.

However, only a small fraction of the passing WIMP's will get captured by the Earth, because it is improbable that they will be traveling slow enough to make them easy to capture.

lpetrich
2013-Apr-04, 08:34 AM
As to DAMA/LIBRA, it seems like a rather weak signal, and I would not be surprised if it weakens with the collection of more data. No other experiment has reported anything similar.

Jerry
2013-Apr-06, 03:28 AM
"The positron fraction spectrum exhibits no structure nor time dependence. The positron to electron ratio shows no anisotropy indicating the energetic positrons are not coming from a preferred direction in space. Together, these features show evidence of a new physics phenomena." ... "Even with the high statistics, 6.8 million events, and accuracy of AMS, the fraction shows no fine structure."

Which is consistent with dark matter being everywhere; but it is also consistent with the statement 'we don't have a clue what is happening here.'

lpetrich
2013-Apr-06, 03:44 AM
There's also the gyroradius problem I mentioned -- low-energy particles, like what the AMS had detected, are likely to have their velocity directions thoroughly mixed up when they arrive here, meaning that one can't get a clue about their sources. So they could be from anywhere outside our Solar System.

TooMany
2013-Apr-06, 03:55 PM
As to DAMA/LIBRA, it seems like a rather weak signal, and I would not be surprised if it weakens with the collection of more data. No other experiment has reported anything similar.

The last paper I read claimed that they have substantially tightened the error bars in recent years. Their graph seems evidence that the are detecting something, but who knows for sure what, maybe the seasonal change in some part of the experimental environment?

After the neutrino fiasco, one has to be a little skeptical.

antoniseb
2013-Apr-07, 01:51 PM
... After the neutrino fiasco, ...
I am struggling to guess what you are referring to here.

trinitree88
2013-Apr-07, 02:22 PM
I am struggling to guess what you are referring to here.

antoniseb. I think he refers to the putative superluminal neutrino velocity implied last year..SEE:http://news.discovery.com/space/opera-leaders-resign-after-no-confidence-vote-120404.html ..and found to be the result of some loose cables in the timing apparatus. Dark matter allegedly interacts gravitationally but not electromagnetically, but is not found in samples of matter in a lab yet. It ought also interact inertially unless we invoke another new rule for a type of mass that no longer obeys the principle of equivalence. But tests of the Eotvos type or similar also show no such effect to date. I'll stick to Standard Model particles and hold my ground, betting the signals will disappear with the discovery of normal baryonic molecular hydrogen in larger quantities than previously expected or measured as we send satellites specifically designed to search for it into space.
It is interesting to note that such putative molecular hydrogen would respond to incoming galactic cosmic rays by emitting some gamma rays, and that the weak galactic magnetic field would slowly remove an isotropic bombardment into one more axisymmetric as happens to them locally, and more strongly with Earth's field.
Ought to look like this galactically...........SEE:http://www.nasa.gov/mission_pages/GLAST/news/new-structure.html

and SEE Stefano Gabici's paper, arxiv... SEE: http://arxiv.org/abs/1304.1172

TooMany
2013-Apr-11, 05:22 AM
Dark matter is commanded to appear, because it must be!!! Supersymmetry is not yet not found, despite the perfection of the theory! But it must be so! What will we do? We cannot give up!!! Supersymmetry and the answer to our prayers will come!

TooMany
2013-Apr-11, 05:30 AM
I am struggling to guess what you are referring to here.

Kidder.

Shaula
2013-Apr-11, 05:36 AM
Dark matter is commanded to appear, because it must be!!! Supersymmetry is not yet not found, despite the perfection of the theory! But it must be so! What will we do? We cannot give up!!! Supersymmetry and the answer to our prayers will come!
So assuming something is there because it fits observations well is bad? And as for SUSY - it is one of many alternative theories. None of which have any strong evidence for them yet. Or are you suggesting that developing new theories is something science should avoid?

TooMany
2013-Apr-11, 05:50 AM
So assuming something is there because it fits observations well is bad? And as for SUSY - it is one of many alternative theories. None of which have any strong evidence for them yet. Or are you suggesting that developing new theories is something science should avoid?

No, assuming something is there because you have a nice, satisfying theory is "bad" (whatever that means). I'm suggesting that making pretty theories without evidence for (I think) 30 years is not "science". Bring out the alternatives, because it appears that the best guess has flopped.

What are you doing up so late? My goodness, what time is it in the UK? Let's see, hmm... about 9 hours ahead. It's not even all that early! I'm the one who is up late!

Good morning!

(More seriously, I read your posts because I think you know what you are talking about.)

Shaula
2013-Apr-11, 06:34 AM
No, assuming something is there because you have a nice, satisfying theory is "bad" (whatever that means). I'm suggesting that making pretty theories without evidence for (I think) 30 years is not "science". Bring out the alternatives, because it appears that the best guess has flopped.
Good evening!

You mischaracterise the nature of science quite badly. Dark matter theory is often being tested. Just like MOND and all the baryonic ideas. People are always taking new measurements and comparing them to theory. There are always younger researchers trying to find ways to overturn the consensus. Why do you think you are always able to find papers discussing alternatives to dark matter then we are playing paper-conkers over it? Because that is the easiest way to make a name for yourself. Most young scientists would love to find good evidence to change the current paradigm. And no one I know who works the area has ever said dark matter is a satisfying theory. Until we have a beaker full of it on the lab bench it won't be satisfying. It is just the best fit as I have said over and over again to you.

Are you saying SUSY is the 'best' guess? Well, several issues. It is not the best. It is one speculation. There are others. Even a cursory Wikipedia search throws up loads. SUSY has gained ground because it is intrinsically a part of String Theory and that has some strong supporters. But ideas like Loop Quantum Gravity and Technicolor are still going strong. They get a bot less popular press but they are still being worked on. Next issue - it is not a guess. It drops out quite naturally from considerations of symmetry in current theories. Working through the ramifications of that leads to some neat results. And lastly there are loads of variants of SUSY. The MSSM has had big holes knocked through it, most other versions are still feasible to some degree.

Personally I am not a big fan of most SUSY approaches. I can see the justification for them, I even understand some of the maths behind them. So I feel pretty secure in coming to that conclusion. That said I would never say we should close off the avenue of research just because of that. There is no strong evidence for the shape of anything beyond the Standard Model physics. That is a problem. So people try to build new theories, look for clever ways to find good evidence. The alternative is to blunder around in the dark hoping we stumble over the answer. I consider that a rather foolish approach.

lpetrich
2013-Apr-13, 01:06 PM
About SUSY, I like it because it offers a solution of the conundrum of why there are spin-1/2 particles.

Spin-0 ones are easy. All one needs is a field with some value at each point in space-time.

Nonzero-spin ones are more difficult. Those are fields with some space-time-related degrees of freedom.

A fairly simple one is a vector: a space-time direction. More complicated ones have multiple space-time directions: higher-order tensors.
A spin-1 particle is a vector.
A spin-2 particle is a 2-tensor. A symmetric traceless one, to be more precise.
A spin-1/2 particle is a spinor in space-time, a more complicated sort of entity.

The known spin-1 particles emerge from "gauge symmetries", continuous local symmetries of non-space-time degrees of freedom.
The only spin-2 particle, the graviton, emerges from space-time coordinate arbitrariness, a sort of gauge symmetry involving space-time.

So all the known integer-spin particles are associated with various symmetries.

That leaves the known spin-1/2 particles. Could their nonzero spin also be associated with a symmetry? The only symmetry that can make that happen is SUSY, a symmetry which relates particles with different spins. So there you have it.

antoniseb
2013-Apr-13, 01:42 PM
... because it appears that the best guess has flopped. ...
In what way do you think it has flopped? If actual SUSY particles are difficult to detect, or very massive and short-lived (TeV or higher), then we would not have detected them yet. The process is looking for possible low-hanging fruit. I'm not calling SUSY a glorious success, it isn't, we haven't seen it, but it is very much in the running. All of the alternatives are at least as difficult to observe directly. By your measure, they've all flopped, but my claim is that none of them have flopped until evidence is found about how one in particular can't be the answer. Money is going into what can be tested with possible technical development.

Shaula
2013-Apr-13, 04:27 PM
That leaves the known spin-1/2 particles. Could their nonzero spin also be associated with a symmetry? The only symmetry that can make that happen is SUSY, a symmetry which relates particles with different spins. So there you have it.
The issue is that the symmetry cannot be exact. It has to be really, really badly broken. And there simply is no easy way to do that without introducing a lot of extra particles or a mechanism for which there is no obvious cause (no background field that can easily become asymmetric). It is different with the electroweak and condensed matter broken symmetries, with supersymmetry this is a real problem. For me it is one of those solutions that looks really promising at first glance but gets more and more complex when you try to make it work. I would not rule it out, I just don't think it is as neat a solution as it seems at first.

lpetrich
2013-Apr-14, 03:21 AM
Back to SUSY and elementary-particle symmetries.

Gauge symmetries: its generators are scalars, spin 0 -> their fields have spin 1 -- particles like the photon, the W, the Z, and the gluon
Space-time symmetries: its generator is a vector, spin 1 -> its field has spin 2 -- the graviton
Supersymmetry: its generator is a spinor, spin 1/2 -> its field has spin 3/2 -- the gravitino

Supersymmetry applied to gravity is supergravity or SUGRA. The graviton has a SUSY counterpart: the gravitino, complete with gravitational-strength interactions. That is, super super super weak by the standards of familiar elementary particles.

SUSY is related to space-time symmetries, and like space-time symmetries, it is independent of any other interactions or other features a particle may have. Thus, members of a SUSY multiplet must share gauge interactions, any other quantum numbers, and masses.


But we clearly don't observe that, and as Shaula noted, SUSY must be a broken symmetry. The easiest SUSY partners to recognize in the LHC are the squarks and the gluino, and from LHC observations, their masses are at least 1 TeV. When the LHC restarts in 2015, it should be able to go up to 2 TeV.

Even worse, it's hard to get SUSY breaking out of the Minimal Supersymmetric Standard Model. So it's usually proposed that it happens in some "hidden sector" of additional particles, and then gets transmitted to the MSSM particles in some way or another. Ways like "gravity mediation", "gauge mediation", and "anomaly mediation".

lpetrich
2013-Apr-14, 09:15 AM
As to what dark matter might be, we can be sure of some things that it is almost certainly not.

Not SIMPS -- strongly interacting massive particles
Not CHAMPS -- charged massive particles

That leaves WIMPS -- weakly interacting massive particles
And possibly MACHOS -- massive compact halo objects, like interstellar planets and brown dwarfs and black holes

A positively-charged CHAMP will act like a nucleus
A negatively-charged CHAMP will act like an electron, and if massive enough, will orbit inside a nucleus
A SIMP will stick to a nucleus, making it an unusually heavy isotope

There are some very strong upper limits for CHAMPS and SIMPS:
[hep-ex/0102033] The Search for Stable, Massive, Elementary Particles (http://arxiv.org/abs/hep-ex/0102033)
Phys. Rev. Lett. 87, 231804 (2001): New Experimental Limits on Strongly Interacting Massive Particles at the TeV Scale (http://prl.aps.org/abstract/PRL/v87/i23/e231804)

antoniseb
2013-Apr-14, 12:26 PM
... And possibly MACHOS -- massive compact halo objects, like interstellar planets and brown dwarfs and black holes...
Thanks for a very readable summary!
Just as a follow-up, there are also some very strict limits on MACHOs from the OGLE and related projects and other efforts. Interstellar (unbound to stars) brown dwarfs, planets, asteroids, and comets cannot be more than one percent of the missing mass in any size range. This pretty much only leaves black holes, and for these there are only a few very unexpected size ranges not ruled out yet. They would need to be at the mass of a small asteroid. These can't form by collapsing stellar interiors, but some models of inflation don't rule out things like this having formed as inflation came to a halt. To me WIMPs seem much more likely, but these tiny primordial black holes are what's left for MACHOs as the main contributor to galactic dark matter.

lpetrich
2013-Apr-14, 03:44 PM
There are several sorts of possible dark-matter WIMP's.

The Lightest Supersymmetric Particle (LSP). There are several possible types.

The sneutrino (scalar neutrino; spin 0), the SUSY partner of the neutrino (spin 1/2). Usually considered unlikely.
The neutralino (spin 1/2), a mixture of the SUSY partners of neutral Higgs particles (spin 0) and the photon and the Z (spin 1).
The gravitino (spin 3/2), the SUSY partner of the graviton (spin 2).

These are only a little bit of the zoo of SUSY-related particles, though most of that zoo is unlikely to be dark-matter WIMP's.

Sterile neutrinos, like right-handed ones, as opposed to ordinary, left-handed ones.

Hidden-sector particles.

The axion. This is a particle proposed to keep strong interactions from getting CP violation. That can happen as a result of the structure of the QCD vacuum, something that is rather nontrivial.


These particles have varying degrees of detectability, in fashions like:

Decay -- into detectable particles
Annihilation -- two WIMP's run into each other and make detectable particles -- the Fermi gamma-ray telescope may have detected gamma rays from WIMP annihilation: its 130-GeV line in the direction of our Galaxy's center
Interaction with laboratory materials -- several experiments mentioned earlier in this thread



Lightest Supersymmetric Particle - Wikipedia (http://en.wikipedia.org/wiki/Lightest_Supersymmetric_Particle)
Neutralino - Wikipedia (http://en.wikipedia.org/wiki/Neutralino)
Sfermion - Wikipedia (http://en.wikipedia.org/wiki/Sfermion) -- mentions sneutrinos
Sterile neutrino - Wikipedia (http://en.wikipedia.org/wiki/Sterile_neutrino)
Axion - Wikipedia (http://en.wikipedia.org/wiki/Axion)
[1211.6739] The 130 GeV gamma-ray line and generic dark matter model building constraints from continuum gamma rays, radio and antiproton data (http://arxiv.org/abs/1211.6739)
[1205.6811] Implications of a 130 GeV Gamma-Ray Line for Dark Matter (http://arxiv.org/abs/1205.6811)
Doubt cast on Fermi's dark matter smoking gun - space - 06 November 2012 - New Scientist (http://www.newscientist.com/article/dn22466-doubt-cast-on-fermis-dark-matter-smoking-gun.html)

lpetrich
2013-Apr-14, 04:03 PM
Doubt cast on Fermi's dark matter smoking gun - space - 06 November 2012 - New Scientist (http://www.newscientist.com/article/dn22466-doubt-cast-on-fermis-dark-matter-smoking-gun.html)
From re-analyzing the data and correcting for a glitch caused by a damaged instrument.

"The feature's gotten a little smaller," she says. "It hasn't gone away completely, but we do not see it to be very significant. At this point, we have to cast doubt on this being a dark matter line."

The signal also showed up in the ring of gamma rays around Earth, but it seems to account for only half of that detected from the galactic centre, and there is no good way to explain why it is there. "There is nothing obvious, at least to me, that connects the galactic centre and the [gamma-ray ring]," Weniger says.

Probing the 130 GeV gamma-ray line with ground-based gamma-ray telescopes - Abstract - Journal of Physics G: Nuclear and Particle Physics - IOPscience (http://iopscience.iop.org/0954-3899/40/3/035202)

The evidence of a monochromatic γ-ray line-like structure at ~130 GeV, recently obtained from Fermi Large Area Telescope (Fermi-LAT) data, poses serious challenges for standard astrophysical processes. It is generally believed that the narrow profile of the spectral line is very likely to be originated from dark matter annihilation or decay. Further careful observations with either satellite detectors or ground-based detectors are necessary. Here we suggest that ground-based γ-ray telescopes, such as High Energy Stereo System-II (HESS II) (under construction) and the forthcoming high performance experiment Cerenkov Telescope Array (CTA), will be very effective in testing the monochromatic nature of the tentative 130 GeV γ-ray line. With approximately 10-h exposure, HESS II (CTA) may reach a 9σ (100σ) detection of the line, if it is indeed a γ-ray line.

So that Fermi-telescope discovery is still up in the air.

borman
2013-Apr-16, 12:23 AM
CDMS II sees three more events with Si-Ge detectors.

http://cdms.berkeley.edu/CDMSII_Si_DM_Results.pdf

Will the Xe experiments continue to not see events?

lpetrich
2013-Apr-16, 11:17 AM
Three more or some original three events? Hard to tell from that paper, though it looks like some original three.

trinitree88
2013-Apr-16, 06:03 PM
antoniseb. I think he refers to the putative superluminal neutrino velocity implied last year..SEE:http://news.discovery.com/space/opera-leaders-resign-after-no-confidence-vote-120404.html ..and found to be the result of some loose cables in the timing apparatus. Dark matter allegedly interacts gravitationally but not electromagnetically, but is not found in samples of matter in a lab yet. It ought also interact inertially unless we invoke another new rule for a type of mass that no longer obeys the principle of equivalence. But tests of the Eotvos type or similar also show no such effect to date. I'll stick to Standard Model particles and hold my ground, betting the signals will disappear with the discovery of normal baryonic molecular hydrogen in larger quantities than previously expected or measured as we send satellites specifically designed to search for it into space.
It is interesting to note that such putative molecular hydrogen would respond to incoming galactic cosmic rays by emitting some gamma rays, and that the weak galactic magnetic field would slowly remove an isotropic bombardment into one more axisymmetric as happens to them locally, and more strongly with Earth's field.
Ought to look like this galactically...........SEE:http://www.nasa.gov/mission_pages/GLAST/news/new-structure.html

and SEE Stefano Gabici's paper, arxiv... SEE: http://arxiv.org/abs/1304.1172

I'm updating this post as a result of a recent search for papers on carbon monoxide, whose chemistry, stability, and relative presence as a tracer gas of molecular hydrogen (not atomic) in giant,... and smaller,..molecular clouds is key to inferring galactic masses. It seems that the localized physical chemistry of the cloud can have a significant impact on converting carbon monoxide...CO...to carbon dioxide...with the key player being oxygen. Oxygen is generally believed to be the third most common element in the universe, following hydrogen and helium.
SEE:http://m.iopscience.iop.org/0067-0049/182/1/1?rel=sem&relno=6

SEE:http://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements

Point being?...as evidenced in the experimental work...carbon monoxide can be converted to both carbon dioxide (efficiently)...and to suprathermal carbon and atomic oxygen. The atomic oxygen is highly reactive and can initiate further conversions, while the carbon can form nanotubes, the blackest black. This process can occur slowly even in cold clouds. Then the tracer of molecular hydrogen, CO, is essentially gone, but the column density remains. Baryonic dark matter. pete


Notice Michael Richmond's last graphic in pink and green (molecular hydrogen)...and overlay to the Fermilat gamma ray "bubble" SEE:http://spiff.rit.edu/classes/phys230/lectures/ism_gas/ism_gas.html

trinitree88
2013-Apr-16, 06:43 PM
I'm updating this post as a result of a recent search for papers on carbon monoxide, whose chemistry, stability, and relative presence as a tracer gas of molecular hydrogen (not atomic) in giant,... and smaller,..molecular clouds is key to inferring galactic masses. It seems that the localized physical chemistry of the cloud can have a significant impact on converting carbon monoxide...CO...to carbon dioxide...with the key player being oxygen. Oxygen is generally believed to be the third most common element in the universe, following hydrogen and helium.
SEE:http://m.iopscience.iop.org/0067-0049/182/1/1?rel=sem&relno=6

SEE:http://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements

Point being?...as evidenced in the experimental work...carbon monoxide can be converted to both carbon dioxide (efficiently)...and to suprathermal carbon and atomic oxygen. The atomic oxygen is highly reactive and can initiate further conversions, while the carbon can form nanotubes, the blackest black. This process can occur slowly even in cold clouds. Then the tracer of molecular hydrogen, CO, is essentially gone, but the column density remains. Baryonic dark matter. pete


Notice Michael Richmond's last graphic in pink and green (molecular hydrogen)...and overlay to the Fermilat gamma ray "bubble" SEE:http://spiff.rit.edu/classes/phys230/lectures/ism_gas/ism_gas.html


and finally, the bond dissociation enthalpys in kilocalories per mole for carbon dioxide is ~ 192 vs, ~ 111 for water. With oxygen present in a GMC surely some of the oxygen will be in water, particulary with the large hydrogen concentrations, but like seagulls scavenging tidbits from the beach....pretty soon it's food free, and oxygen will scavenge CO to CO2, and the equilibrium can leave it there.
SEE:http://www.cem.msu.edu/~reusch/OrgPage/bndenrgy.htm

Shaula
2013-Apr-16, 09:20 PM
Point being?...as evidenced in the experimental work...carbon monoxide can be converted to both carbon dioxide (efficiently)...and to suprathermal carbon and atomic oxygen. The atomic oxygen is highly reactive and can initiate further conversions, while the carbon can form nanotubes, the blackest black. This process can occur slowly even in cold clouds. Then the tracer of molecular hydrogen, CO, is essentially gone, but the column density remains. Baryonic dark matter. pete
Now you just need to work out why clouds that are apparently subject to a fairly uniform flux (since this is not a UV based thing) deviate so wildly from each other. And fix nucleosynthesis. And the scattering due to dust. And explain why you don't see the effects of these clouds impinging on different radiation domains. Any what process produced this excess carbon and oxygen without enriching the other metals. And a load of other issues. Non-baryonic dark matter is still the best fit to observations. It may turn out not to be the answer eventually but right now the evidence is simply not there to get rid of it.

Jens
2013-Apr-17, 01:43 AM
Not SIMPS -- strongly interacting massive particles
Not CHAMPS -- charged massive particles
That leaves WIMPS -- weakly interacting massive particles
And possibly MACHOS -- massive compact halo objects, like interstellar planets and brown dwarfs and black holes


Sorry, I can't comment on the contents, but just wanted to say that I'm of a mixed mind whether the people who made up those terms should be awarded for their humor or shot for it.

trinitree88
2013-Apr-17, 12:51 PM
Now you just need to work out why clouds that are apparently subject to a fairly uniform flux (since this is not a UV based thing) deviate so wildly from each other. And fix nucleosynthesis. And the scattering due to dust. And explain why you don't see the effects of these clouds impinging on different radiation domains. Any what process produced this excess carbon and oxygen without enriching the other metals. And a load of other issues. Non-baryonic dark matter is still the best fit to observations. It may turn out not to be the answer eventually but right now the evidence is simply not there to get rid of it.

True. There's lots to do yet. Wild deviations can arise from the differing environmental histories of clouds. I'm not positing a new nucleosynthesis scheme...hoyle did that decades ago....fluxes, cross-sections, rates. I'm just positing the known abundances universally that come from spectroscopic line intensities. Oxygen Is number three in abundance. Environments generally have lots of it. Nothing reacts with helium. So oxygen chemistry in various phases is an important consideration. I believe there is no known mix of isotopes for bigbangnucleosynthesis that will yield the presently observed mix without some being off by about an order of magnitude....close, but no cigar.nevertheless, I'll chug along and see what develops. A difference of opinion makes a horse race. Pete

Shaula
2013-Apr-17, 01:20 PM
I believe there is no known mix of isotopes for bigbangnucleosynthesis that will yield the presently observed mix without some being off by about an order of magnitude....close, but no cigar.nevertheless
That is not a Big Bang issue though, that is a post bang stellar nucleosynthesis problem linked to uncertainties in the rate of formation of stars and their lifetimes. BBN fixes the relative abundances of the isotopes of the light elements H/He (which we can get from primordial clouds) and the baryon density. If you massively increase the baryon density then these abundances go horribly wrong, you also have to fix the acoustic peaks in the CMBR. So if you limit the search to what the theory predicts then it is in excellent agreement. Baryonic dark matter theories are not in anything like as good agreement on either of these points. The outstanding issue in BBN is the Lithium problem - and that is widely acknowledged to be where there is a gap. Baryonic dark matter actually makes the Lithium problem worse IIRC.

antoniseb
2013-Apr-17, 01:36 PM
On the original topic, the last paper in today's "Fun Papers" from arXiv is about a group claiming to have observed a Dark Matter particle in a mine experiment with Silicon and Germanium detectors at about 9 GeV.

lpetrich
2013-Apr-18, 08:18 AM
That's from CDMS II -- three events. RÉSONAANCES: More mess with dark matter detection (http://resonaances.blogspot.com/2013/04/more-mess-with-dark-matter-detection.html)

It roughly agrees with CoGent's results, but it is above the upper limits from the Xenon-10 and Xenon-100 experiments. Xenophobic dark matter? Or else either some experiments are getting false positives or else some other experiments are getting false negatives. However, some experimenters are hoping to get much larger quantities of detector material working, and that may help resolve that issue.

kzb
2013-Apr-19, 11:43 AM
Thanks for a very readable summary!
Just as a follow-up, there are also some very strict limits on MACHOs from the OGLE and related projects and other efforts. Interstellar (unbound to stars) brown dwarfs, planets, asteroids, and comets cannot be more than one percent of the missing mass in any size range. This pretty much only leaves black holes, and for these there are only a few very unexpected size ranges not ruled out yet. They would need to be at the mass of a small asteroid. These can't form by collapsing stellar interiors, but some models of inflation don't rule out things like this having formed as inflation came to a halt. To me WIMPs seem much more likely, but these tiny primordial black holes are what's left for MACHOs as the main contributor to galactic dark matter.

It seems to me there is still some parameter space free in which more normal baryonic matter could exist. My understanding is that clouds would've been rejected by the search algorithm in the MACHO progammes, and a highly heterogenous distribution (imagine something like cold starless globular clusters) could've been missed.

There also seems room for reasonable doubt about the mass of gas that is estimated via tracers (along the lines that Trinitree is saying).

You could say we are moving the goalposts, but it is no different to what the particle searches are doing. DM particle properties are predicted, these particles searched for, not found, so then we move on to a fresh prediction. No different. Where there IS a difference is the relative amount of resources devoted to each area.

Shaula
2013-Apr-19, 01:05 PM
You could say we are moving the goalposts, but it is no different to what the particle searches are doing. DM particle properties are predicted, these particles searched for, not found, so then we move on to a fresh prediction. No different. Where there IS a difference is the relative amount of resources devoted to each area.
No, I would say you are picking and choosing what evidence you use. You are ignoring the other lines of evidence that say it is very hard to reconcile a lot of well founded physics with huge amounts more baryonic dark matter. That is why the effort devoted to this is small. It is rather like complaining that there is not enough aether physics going.

And for info the basic properties of dark matter as deduced from cosmological models have remained fairly constant (there is a debate on temperature distributions, that is about all). What is changing is that they are testing and throwing away candidates based on very theoretical particle physics. That doesn't change the basic parameters taken from observations.

Grey
2013-Apr-19, 02:13 PM
You could say we are moving the goalposts, but it is no different to what the particle searches are doing. DM particle properties are predicted, these particles searched for, not found, so then we move on to a fresh prediction. No different. Where there IS a difference is the relative amount of resources devoted to each area.Actually, I pretty much accept this attitude. It is reasonable to at least explore the possibility of dark matter being baryonic, and to go about it in a systematic manner. The fact that the resources devoted to that are much smaller than those dedicated to the search for non-baryonic matter makes sense, though, too.

Given what we know, non-baryonic matter is a much more likely fit to all of the observations, for a variety of reasons. Dark matter really does behave very much like a cold gas of particles that don't interact much, other than gravitationally. Now, individual astronomers have a lot of choice in what kinds of research they'll pursue, what kinds of theories they'll propose, and what kinds of evidence they'll look for to try to back up those theories. The fact that a lot of astronomers and physicists are looking for non-baryonic dark matter candidates is simply a natural result of the fact that it looks very much like that's the way the evidence is pointing. If that ever changes, and a larger number of astronomers become convinced that baryonic matter could account for the observations, we'll see more resources put in that direction.

As far as I'm concerned, that's all good science. Most scientists will pursue the direction that (to them) seems most likely to be successful, and there will usually be a more or less consensus view among them, with lots of different details discussed and debated. And there will probably always be a few scientists around the edges that will favor a differing view, and there's nothing wrong with them trying to come up with sufficient evidence to support that view. Maybe they'll even find that evidence eventually. But in this case, it's probably not the way to bet. ;)

trinitree88
2013-Apr-20, 06:36 PM
Actually, I pretty much accept this attitude. It is reasonable to at least explore the possibility of dark matter being baryonic, and to go about it in a systematic manner. The fact that the resources devoted to that are much smaller than those dedicated to the search for non-baryonic matter makes sense, though, too.

Given what we know, non-baryonic matter is a much more likely fit to all of the observations, for a variety of reasons. Dark matter really does behave very much like a cold gas of particles that don't interact much, other than gravitationally. Now, individual astronomers have a lot of choice in what kinds of research they'll pursue, what kinds of theories they'll propose, and what kinds of evidence they'll look for to try to back up those theories. The fact that a lot of astronomers and physicists are looking for non-baryonic dark matter candidates is simply a natural result of the fact that it looks very much like that's the way the evidence is pointing. If that ever changes, and a larger number of astronomers become convinced that baryonic matter could account for the observations, we'll see more resources put in that direction.

As far as I'm concerned, that's all good science. Most scientists will pursue the direction that (to them) seems most likely to be successful, and there will usually be a more or less consensus view among them, with lots of different details discussed and debated. And there will probably always be a few scientists around the edges that will favor a differing view, and there's nothing wrong with them trying to come up with sufficient evidence to support that view. Maybe they'll even find that evidence eventually. But in this case, it's probably not the way to bet. ;)

Grey. Life's a gamble. I'll bet a hot fudge sundae that Neils Bohr and Mme. Marie Curie regretted for a long time abandoning the law of Conservation of Momentum in explaining beta decay, and that the following paper will roll a few eyes towards a more mundane resolution of missing mass. SEE:http://arxiv.org/abs/0705.1356 Bournard, Alain-Duc, Brinks, Boquien, Amran, Lisenfeld, Koribalski, Walter, and Charmandaris...heretofore B3, A2LKWC.....

In other words.."recycled dwarf galaxies can form in the collisions of massive galaxies. Theory predicts that such dwarf galaxies should be free of non-baryonic dark matter...(since it should reside in the massive galaxy halos, and the collision occurs between material in rotating disks). Any baryonic dark matter is thought to be mostly in the diffuse warm/hot intergalactic medium (WHIM), which also should not be appreciably accumulated in the debris from rotating disk collisions. Therefor recycled dwarves are believed to be essentially, both non-baryonic and baryonic, dark matter-free.
They investigate NGC5291.....and conclude that the most likely candidate for dark baryons cannot be in low luminosity old stars, that are known to be absent from the dwarf galaxies around NGC5291 (M.Boquien et al.,A&A 467,93 (2007)...but most likely in cold molecular hydrogen.
QUOTE"To account for the missing mass in the recycled galaxies, however, a change of at least a factor of ten would be needed"....talking here of the conversion factor of observed CO emission /to molecular hydrogen.
This means dealing either with H2 traced by CO less efficiently than assumed, or a sizeable fraction of cold H2 not traced at all by CO....(D. Pfenniger, F.Combes, L. Martinet, A&A 285 , 79 (1994).

and finally, paraphrasing....collisional debris appears to contain roughly twice as much dark matter as visible matter. Though it could be explained by MOND, it indicates that significant dark matter resides in spiral galaxies' disks, with molecular hydrogen the likely candidate. pete

Shaula
2013-Apr-20, 08:16 PM
and finally, paraphrasing....collisional debris appears to contain roughly twice as much dark matter as visible matter. Though it could be explained by MOND, it indicates that significant dark matter resides in spiral galaxies' disks, with molecular hydrogen the likely candidate. pete
That paper is about hard to see baryonic matter in one particular type of galaxy whose evolutionary path has left it with little to no non-baryonic dark matter. It suggests that the matter contributes significantly to the missing baryons in the standard model. It does not replace or remove the need for non-baryonic matter as is clearly stated in the paper. As it acknowledges just having baryonic dark matter does not lead to a universe that looks like the one we observe. Large scale structure, elemental abundances - they do not work. The paper is a nice piece of work that shows a plausible repository for baryonic matter we already knew about but were having trouble finding. The simplistic picture of us just mapping CO and claiming that is all the baryonic matter out there is simply not true - that is why there was the problem of the missing baryons in the first place.

Grey
2013-Apr-21, 12:18 AM
Grey. Life's a gamble. I'll bet a hot fudge sundae...Your bet is a pretty convoluted one, especially since it includes whether or not Bohr and Curie had specific regrets, something we can probably never be sure about one way or the other. I'd be happy to make a more explicit one. I'll bet a hot fudge sundae (heck, a whole dinner, including a hot fudge sundae as dessert, payable in the form of a gift card to the winner's choice of restaurant, within reason) that we'll have discovered a new weakly interacting particle or particles that will account for the majority (since we're being specific, let's say any amount more than 50%) of the missing mass needed to account for galactic rotation curves and cluster dynamic observations within say, ten years from today. I could certainly be mistaken (even if dark matter is composed mostly of some unknown type of particle, we might not find it in ten years; neutrinos took more than 25 years), but I think it's there's a reasonable enough chance that we'll find it that I'm willing to take the risk. Want to take me up on it?

trinitree88
2013-Apr-21, 01:58 AM
Your bet is a pretty convoluted one, especially since it includes whether or not Bohr and Curie had specific regrets, something we can probably never be sure about one way or the other. I'd be happy to make a more explicit one. I'll bet a hot fudge sundae (heck, a whole dinner, including a hot fudge sundae as dessert, payable in the form of a gift card to the winner's choice of restaurant, within reason) that we'll have discovered a new weakly interacting particle or particles that will account for the majority (since we're being specific, let's say any amount more than 50%) of the missing mass needed to account for galactic rotation curves and cluster dynamic observations within say, ten years from today. I could certainly be mistaken (even if dark matter is composed mostly of some unknown type of particle, we might not find it in ten years; neutrinos took more than 25 years), but I think it's there's a reasonable enough chance that we'll find it that I'm willing to take the risk. Want to take me up on it?

Grey. Yep. Bet's on. I did read somewhere that both bohr and curie expressed publicly and repeatedly their regrets....but the issue of dark matter is ours and I think it will be resolved within the decade. Pete.
Nothing ventured nothing gained in the world...and my intuitive friend says I'll live to see 100, so if you win I'll still be alive and kicking...lol.

TooMany
2013-Apr-21, 06:42 PM
The powerful "evidence" that dark matter must be non-baryonic lies in the theoretical framework of cosmology rather than in direct observation. To meet the nucleosynthesis results required from the BB theory, there cannot be large additional amounts of baryonic matter. It is the firm belief in this theory of creation that drives the claim that there is no possibility other than non-baryonic weakly interacting matter. It is a near heresy to think otherwise, because the "evidence" is considered so compelling.

The observation of pure molecular hydrogen is difficult because it is incredibly transparent. And, despite MACHO studies, there remains the possibility of substellar condensed matter that has not been detected. Cosmologists appear anxious to dismiss the possibility of unobserved ordinary matter while at the same time bolstering the slightest hint of exotic dark matter particles. Problems such a dwarf galaxies with large quantities of dark matter that should not be present are swept under the rug. Objectivity is in the mind of the beholder.

Shaula
2013-Apr-21, 07:36 PM
The powerful "evidence" that dark matter must be non-baryonic lies in the theoretical framework of cosmology rather than in direct observation.
The theoretical model which best fits observations. Which, by the way, was not specifically derived to fit the same observations as dark matter. And which, as I have said over and over to you and others, is the current best fit to the data. Cosmologists and physicists don't 'want' to dismiss bayonic dark matter. The evidence points us away from it. Heresy has nothing to do with it. It is poor science to take the side of the model which fits the data badly but appeals to you.

You know, if you could marshal any better evidence than not liking dark matter I'd be more inclined to listen. As it is the root of every argument I see on here against non-baryonic dark matter is not "This model fits the data better" but "I don't like it so here are lots of attempts to discredit it". That is poor science.

TooMany
2013-Apr-21, 08:59 PM
It's not really a matter of not liking dark matter, the question is whether it is properly motivated by evidence. Or rather is the motivation to support a theory which cannot stand without the introduction of unknown physics? No matter how nice a theory may be, nor how many things it appears to explain, when reconciling the theory with observation requires the invention of things not yet detected, there should be at least some skepticism concerning that theory. And it's not just non-baryonic dark matter that's needed, there is also inflation invented to smooth the observable universe (and eliminate monopoles) and now dark energy to explain the apparent misbehavior of the expansion.

You may call that good science, but I have my own opinion. These constructions of new physics shed doubt on the underlying assumptions about how the universe has evolved. I was just reading this paper (http://arxiv.org/abs/1304.2785) (cited by antoniseb in Fun Papers) that says Planck2013 results are in conflict with models of inflation. In the light of the Planck results current models are subject to a new "unlikeliness problem". In fact according to the paper, the assumptions necessary to explain the observables concerning inflation are more demanding than an assumption of inherent smoothness that inflation was invented to account for.

Did you notice how handily you dismissed the dwarf galaxy evidence concerning the existence of dark ordinary matter? This problem (of dwarf galaxies stripped of non-baryonic dark matter) has been repeatedly emphasized by Pavel Kroupa. The apparent lack of interest is quite remarkable. To quote your dismissal:


It does not replace or remove the need for non-baryonic matter as is clearly stated in the paper. As it acknowledges just having baryonic dark matter does not lead to a universe that looks like the one we observe.

My translation: It does replace or remove the need to support the existing theory of creation which cannot account for our universe with only baryonic dark matter. No, I don't have a better theory, but what's the use insisting on a flawed theory, even if it is the best theory you can come up with? Better IMO to say, we have an idea for a theory, but it requires belief in things not observed.

Jens
2013-Apr-22, 03:46 AM
It's not really a matter of not liking dark matter, the question is whether it is properly motivated by evidence. Or rather is the motivation to support a theory which cannot stand without the introduction of unknown physics? No matter how nice a theory may be, nor how many things it appears to explain, when reconciling the theory with observation requires the invention of things not yet detected, there should be at least some skepticism concerning that theory.

I don't think it's a question of theory though. The problem is the observation that the rotation curves of galaxies are flat, which they shouldn't be. So trying to explain that observation requires something, and dark matter is one way to attempt to explain the observation. It might not be the correct explanation, but some explanation is required.

Shaula
2013-Apr-22, 05:42 AM
You may call that good science, but I have my own opinion. These constructions of new physics shed doubt on the underlying assumptions about how the universe has evolved. I was just reading this paper (http://arxiv.org/abs/1304.2785) (cited by antoniseb in Fun Papers) that says Planck2013 results are in conflict with models of inflation. In the light of the Planck results current models are subject to a new "unlikeliness problem". In fact according to the paper, the assumptions necessary to explain the observables concerning inflation are more demanding than an assumption of inherent smoothness that inflation was invented to account for.
The big problem I have with that paper is that it makes a huge assumption underlying the entire argument. That there are an infinity of potential inflation potentials and that each potential has an equal likelihood both of being the underlying form and of trigger anywhere on the potential. We can turn the problem around and ask "why should this be?". We simply do not know enough about the underlying mechanisms of inflation to justify these assumptions. They are assuming it is vacuum decay, assuming it is a random tunnelling seed and assuming both type one and two many worlds scenarios.


Did you notice how handily you dismissed the dwarf galaxy evidence concerning the existence of dark ordinary matter? This problem (of dwarf galaxies stripped of non-baryonic dark matter) has been repeatedly emphasized by Pavel Kroupa. The apparent lack of interest is quite remarkable.
Dismissed it by reading it and point out that the paper explicitly does not support the idea that all dark matter is baryonic? By pointing out that the numbers and the details in the paper explain the missing baryonic matter and do not replace the non-baryonic dark matter? Well I do apologise if being willing to actually read the papers cited makes me a horribly dismissive person with no interest in the subject. Not sure how that works, but hey.


My translation: It does replace or remove the need to support the existing theory of creation which cannot account for our universe with only baryonic dark matter. No, I don't have a better theory, but what's the use insisting on a flawed theory, even if it is the best theory you can come up with? Better IMO to say, we have an idea for a theory, but it requires belief in things not observed.
By this logic we should ditch GR. Ever seen warped spacetime? We should have given up on the Higgs mechanism (Higg boson), we should have given up on the Standard Model (pesky top quarks). And so on. Theories are always the best fit to the data available and often postulate things we then need to find ways to observe. You cannot find these ways to test a theory without a lot of work on it. Which you won't do it you thrown anything away which has anything you have no evidence for. Until something better comes along the current theory is the best fit to data. When that does I will defend it from this sort of sniping just as vigorously. If the critics of it had anything like as good a model I'd listen to them. But so far no one has managed to develop one.

TooMany
2013-Apr-22, 04:35 PM
The big problem I have with that paper is that it makes a huge assumption underlying the entire argument. That there are an infinity of potential inflation potentials and that each potential has an equal likelihood both of being the underlying form and of trigger anywhere on the potential. We can turn the problem around and ask "why should this be?". We simply do not know enough about the underlying mechanisms of inflation to justify these assumptions. They are assuming it is vacuum decay, assuming it is a random tunnelling seed and assuming both type one and two many worlds scenarios.


I have to agree with that. All we know is that we invented inflation to explain the smoothness which does not arise naturally from a simple theory of an expanding universe. The requirements for inflation are incredibly contrived. We can get this smoothness by assuming that at 10-33 seconds after creation, the expansion increased volume by a factor of 1078 over an interval of 10-36 seconds. Since no mechanism is known to account for it, it's open season for speculation about how this occurred. But surely it needs to have occurred to retain the theory as correct.



Dismissed it by reading it and point out that the paper explicitly does not support the idea that all dark matter is baryonic? By pointing out that the numbers and the details in the paper explain the missing baryonic matter and do not replace the non-baryonic dark matter? Well I do apologise if being willing to actually read the papers cited makes me a horribly dismissive person with no interest in the subject. Not sure how that works, but hey.


No, dismissing it by failing to observe the problem it creates for non-baryonic matter as dark matter. Instead you observe that the author does not claim to have found that all the missing mass is baryonic.



By this logic we should ditch GR. Ever seen warped spacetime? We should have given up on the Higgs mechanism (Higg boson), we should have given up on the Standard Model (pesky top quarks). And so on. Theories are always the best fit to the data available and often postulate things we then need to find ways to observe.


Of course not, these things are well supported by observation. They don't need additional speculations to make them work.

A theory may fit with observations A, B and C. But if it completely fails for D and E, why continue to act as if it is certainly true?



You cannot find these ways to test a theory without a lot of work on it. Which you won't do it you thrown anything away which has anything you have no evidence for. Until something better comes along the current theory is the best fit to data. When that does I will defend it from this sort of sniping just as vigorously. If the critics of it had anything like as good a model I'd listen to them. But so far no one has managed to develop one.

But what is the need to defend so vigorously a theory with serious problems? Just because there isn't a better theory? Even the "best fitting" theory is not a "good" theory if conflicts with observations. Conjuring up new things to support the theory doesn't strengthen the theory, but perhaps it helps to create an illusion of strength.

TooMany
2013-Apr-22, 04:37 PM
I don't think it's a question of theory though. The problem is the observation that the rotation curves of galaxies are flat, which they shouldn't be. So trying to explain that observation requires something, and dark matter is one way to attempt to explain the observation. It might not be the correct explanation, but some explanation is required.

I agree completely. Unless we are wrong about gravity there is a lot of unseen mass.

kzb
2013-Apr-22, 05:14 PM
I'm a bit skeptical about betting. Who is the referee? Who makes the call that a non-baryonic DM particle has been definitely discovered, and further, that what was discovered makes up most of the mass of the universe?

Something tells me it will never be that cut and dried.

Shaula
2013-Apr-22, 05:41 PM
No, dismissing it by failing to observe the problem it creates for non-baryonic matter as dark matter. Instead you observe that the author does not claim to have found that all the missing mass is baryonic.
It doesn't create any problem for non-baryonic dark matter. Which is quite obvious if you read the paper and look at the wider context.


Of course not, these things are well supported by observation.
You mean like non-baryonic dark matter? You are cherry picking what you regard as a good theory or a bad theory according to some internal specification. Poor science.


But what is the need to defend so vigorously a theory with serious problems? Just because there isn't a better theory? Even the "best fitting" theory is not a "good" theory if conflicts with observations. Conjuring up new things to support the theory doesn't strengthen the theory, but perhaps it helps to create an illusion of strength.
What I am defending is the scientific method used to come to the conclusions we have. Every time there is a new observation other ideas are tested, people are always working on other ideas. Your position is simply not tenable - it seems to be that any theory with holes in should be thrown out. GR and QM are not compatible. Should we be throwing them away?

Anyway, this is a pointless debate. We have had it before. And I really don't want to keep having it - it is boring. I have repeatedly acknowledged that there are issues with the current theory, that something better may come along. But you will not compromise away from your core belief and take unrealistic stances that would not hold for other theories. All to try to get rid of a theory you don't like.

Grey
2013-Apr-22, 06:27 PM
I'm a bit skeptical about betting. Who is the referee? Who makes the call that a non-baryonic DM particle has been definitely discovered, and further, that what was discovered makes up most of the mass of the universe?

Something tells me it will never be that cut and dried.We'll do the best we can, and the community of CQX (or wherever this board is living by then) can adjudicate. I'd say that for a particle or particles to account for the dark matter observations, it needs to interact primarily via gravity, with a very small interaction cross section, more or less comparable to a neutrino. However, unlike a neutrino, it needs to be fairly massive, so that it doesn't always travel at nearly the speed of light. There should be some reasonable evidence that this particle is present in the solar system, in something like the quantity we'd predict from dark matter models. If we do find such a particle in an accelerator, then we should be able to learn enough about it to design a detector that is sufficiently sensitive to pick it up, just like we can detect solar neutrinos even though they almost never interact. If we find such a thing by April 20, 2023, I'll insist that trinitree owes me that dinner (with a hot fudge sundae for dessert - that part is very important). If not, I'll owe him dinner. If there's some middle ground (for example, an ideal candidate in the right mass range is found, with exactly the kind of interaction profile it would need, but we don't yet have any evidence that it exists outside of the accelerator experiments where it is discovered), maybe we'll negotiate an extension while they try to figure out whether it's right.

I'd say that a successful discovery of a dark matter particle is almost certain to win a Nobel as quickly as the committee is convinced that the discovery is genuine. If a Nobel is granted, I think it would be hard for trinitree to argue that he hasn't lost the bet. Interestingly, because of the nature of discovery, it's a bit of a lopsided bet, given the time frame. That is, if no dark matter candidate is found in ten years, but there's still not a solid alternate theory, then I (and probably the rest of the physics community) will probably go right on thinking that there is such a particle, even though we haven't found it yet. I'd still have lost the bet, though.

antoniseb
2013-Apr-22, 07:12 PM
... Interestingly, because of the nature of discovery, it's a bit of a lopsided bet, given the time frame. That is, if no dark matter candidate is found in ten years, but there's still not a solid alternate theory, then I (and probably the rest of the physics community) will probably go right on thinking that there is such a particle, even though we haven't found it yet. I'd still have lost the bet, though.
We'll see if this new 9GeV dark matter particle pans out. The initial paper sounded fairly promising. The bet could be over in a few years, allowing time to build a 100 times sized detector and wait another year to collect statistically significant numbers.

trinitree88
2013-Apr-22, 07:18 PM
We'll do the best we can, and the community of CQX (or wherever this board is living by then) can adjudicate. I'd say that for a particle or particles to account for the dark matter observations, it needs to interact primarily via gravity, with a very small interaction cross section, more or less comparable to a neutrino. However, unlike a neutrino, it needs to be fairly massive, so that it doesn't always travel at nearly the speed of light. There should be some reasonable evidence that this particle is present in the solar system, in something like the quantity we'd predict from dark matter models. If we do find such a particle in an accelerator, then we should be able to learn enough about it to design a detector that is sufficiently sensitive to pick it up, just like we can detect solar neutrinos even though they almost never interact. If we find such a thing by April 20, 2023, I'll insist that trinitree owes me that dinner (with a hot fudge sundae for dessert - that part is very important). If not, I'll owe him dinner. If there's some middle ground (for example, an ideal candidate in the right mass range is found, with exactly the kind of interaction profile it would need, but we don't yet have any evidence that it exists outside of the accelerator experiments where it is discovered), maybe we'll negotiate an extension while they try to figure out whether it's right.

I'd say that a successful discovery of a dark matter particle is almost certain to win a Nobel as quickly as the committee is convinced that the discovery is genuine. If a Nobel is granted, I think it would be hard for trinitree to argue that he hasn't lost the bet. Interestingly, because of the nature of discovery, it's a bit of a lopsided bet, given the time frame. That is, if no dark matter candidate is found in ten years, but there's still not a solid alternate theory, then I (and probably the rest of the physics community) will probably go right on thinking that there is such a particle, even though we haven't found it yet. I'd still have lost the bet, though.

I have found a peer-reviewed, journal article that indicates a much less efficient CO/H2 coupling in lower density clouds, to the effect that it underestimates the hydrogen mass by as much as 4 orders of magnitude compared to the standard value. I'll post it later today from my cellphone. pete... it's mnras 2011 volume 412 (3): 1686-1700.doi: 10.1111/j.1365-2966.2010.18005.x

Rahul shetty, simon c. Glover, cornelius p. Dullemond and ralf s. Klessen


Modeling co emission-I.co as a column density tracer and the x factor in molecular clouds.

trinitree88
2013-Apr-24, 06:36 PM
I have found a peer-reviewed, journal article that indicates a much less efficient CO/H2 coupling in lower density clouds, to the effect that it underestimates the hydrogen mass by as much as 4 orders of magnitude compared to the standard value. I'll post it later today from my cellphone. pete... it's mnras 2011 volume 412 (3): 1686-1700.doi: 10.1111/j.1365-2966.2010.18005.x

Rahul shetty, simon c. Glover, cornelius p. Dullemond and ralf s. Klessen


Modeling co emission-I.co as a column density tracer and the x factor in molecular clouds.

SEE:http://arxiv.org/abs/1011.2019

Shaula
2013-Apr-24, 08:19 PM
SEE:http://arxiv.org/abs/1011.2019
Worth noting that they find that the MC-averaged X factor is actually a pretty good tracer unless you are looking at very homogeneous or really, really dense clouds. What they are really showing is that mapping structure using the CO tracer is really not that accurate.

Jerry
2013-Apr-26, 06:01 PM
What I am defending is the scientific method used to come to the conclusions we have. Every time there is a new observation other ideas are tested, people are always working on other ideas. Your position is simply not tenable - it seems to be that any theory with holes in should be thrown out. GR and QM are not compatible. Should we be throwing them away?


No. You are defending a theory. The scientific method uses data to test a theory. When the theory fails the test, you either reject the test, reject the theory or modify the theory. The scientific debate is, or should be: Are the current modifications of the grand theories justifiable? There is tension in the small box dark matter has been lassoed into - tension meaning the data and the theory are no longer compatible. It is necessary to either reject (or modify) the new data; or yet again add another unanticipated property to the orthodox theory.

Your firm stand defending this orthodoxy is not a scientific position. A new, workable theory is not necessary before rejecting an old one. The existing theory is so elaborate that it is likely impossible for a fledgling theory to cover all of the attributes described by the orthodox theory. The condition that a new warm fuzzy theory be found before the old one is rejected is not a scientific position - science does not demand answers - science only rejects what is proven wrong and poses new tests and new questions.

A good example of this principle is found in Darwin's approach to the origin of species. He had seven main tenents. They were broad-brush - there was no detail. Four of the seven turned out to be wrong. (Although one of the four is making a surprising resurgence). The strength of Darwins theory as originally presented, was not what it explained; but how he exposed the flaws in the orthodox definitions of species.

Shaula
2013-Apr-26, 06:25 PM
Your firm stand defending this orthodoxy is not a scientific position.
That would be true if I were not defending the mainstream (it is not an orthodoxy, thanks, belief is not required) based on the best available evidence.


The scientific debate is, or should be: Are the current modifications of the grand theories justifiable?
Wrong. It should be: Does the theory work. Has it been falsified. The answers are yes and no respectively. You have no way to determine what is 'justifiable' - that is a judgement call. Which we try to keep out of science. The theory still stands as the best answer we currently have. And as for grand theories - there isn't really one. It is a pastiche of several theories pieced together slowly. That is why the way these theories are glued together has some flex.


A new, workable theory is not necessary before rejecting an old one.
It requires one of two things: either the old theory becomes incompatible with observations (not happened so far) or a more powerful theory comes along (not happened so far). Your claim that the current theory is incompatible with the evidence is simply wrong. Observations have allowed us to refine the properties of the material and the theory. It has not become impossible to reconcile things - new observations are reducing the number or scope of the unconstrained variables in the original theory. If new evidence actually made the model untenable I would happily discard it. People here are acting like I actually like dark matter theory. I don't. I would actually be delighted if it were replaced by something else. But I am not going to let my personal preferences cause me to adopt an unsupported position.


science only rejects what is proven wrong and poses new tests and new questions.
And so far the theory has not been proven wrong. And it is always being tested. New questions are being asked. It may fall, it may not. But so far all the other ideas proposed here are worse fits to the data as a whole.

TooMany
2013-Apr-26, 08:48 PM
That would be true if I were not defending the mainstream (it is not an orthodoxy, thanks, belief is not required) based on the best available evidence.

Wrong. It should be: Does the theory work. Has it been falsified. The answers are yes and no respectively.

And so far the theory has not been proven wrong. And it is always being tested. New questions are being asked. It may fall, it may not. But so far all the other ideas proposed here are worse fits to the data as a whole.

But it already has been proven wrong. It's predictions were wrong (nucleosynthesis and smoothness) but rather than fault the theory, new physics was invented to keep it afloat, namely CDM and inflation. This is correcting nature to fit a theory. The theory cannot be "disproven" so long as it is fair game to invent things that have not been observed to sustain it. When you do that, it becomes more of a belief than a theory. Hence the tendency to call it orthodoxy. It seems odd that the theory gets so much respect when it requires profound conjectures to make it work.

Shaula
2013-Apr-26, 09:38 PM
Now you are getting things very much the wrong way around. We are talking about CDM theory here. That was proposed to account for observed galactic dynamics. Within the observations there were a lot of degrees of freedom, aspects of dark matter not constrained by its use to explain galactic dynamics. Inflation and the Big Bang were developed totally separately. When people did the calculations they found that by including CDM in the Big Bang theory they got a better fit to observations.

Nucleosynthesis was a prediction of the BB model that was improved by adding in Dark matter. Then they used these new observations to tune the parameters of dark matter that were not constrained by the galactic dynamics.

Inflation was added to the BB theory to better fit what we saw. It has very little to do with CDM other than the fact that both are used in the explanations of structure formation, another model that was developed separately at first.

So you are grossly mischaracterising the way these theories have grown and how they have interplayed with each other. It is not at all as you are portraying things - there was never one monolithic theory that started out and had all this stuff added to it for some dogmatic reason. There were several lines of evidence that came together and supported each other.

And you claim that a theory can never be disproven if you just keep adding to it? Rubbish. There are constraints in the theory that, if broken, would invalidate it entirely. But so far we are still within an acceptable parameter space for it.

So far steady state, HDM, baryonic DM, MOND and hundreds more variants - they have all been tested and found to be a worse fit to observations. In fact all of these models have had just as much extra stuff added to them as the CDM model has to make them work (MOND, TVS and so on, the ridiculously hard to form super-black snowballs with unrealistic elemental abundances, MACHOs - the list goes on).

The thoery gets respect for the predictions it has made and the results you get out of it. No matter how much you attempt to dismiss them they are pretty accurate so far. Has the model been tuned? Yes, like every model ever. Have things been added to refine it? Yes. As has happened with every model ever. Maybe we will get to the point where it is disproven and discarded. Quite probably. You keep claiming that this is some sort of belief system. Then why does its apparently fanatical supporter here keep saying "It may be wrong, it may be replaced"? Could it be because it is not a belief system? I know, shocking thought.

Jerry
2013-Apr-28, 02:32 PM
Now you are getting things very much the wrong way around. We are talking about CDM theory here. That was proposed to account for observed galactic dynamics. Within the observations there were a lot of degrees of freedom, aspects of dark matter not constrained by its use to explain galactic dynamics. Inflation and the Big Bang were developed totally separately. When people did the calculations they found that by including CDM in the Big Bang theory they got a better fit to observations.

Nucleosynthesis was a prediction of the BB model that was improved by adding in Dark matter. Then they used these new observations to tune the parameters of dark matter that were not constrained by the galactic dynamics.


Inflation was added to the BB theory to better fit what we saw. It has very little to do with CDM other than the fact that both are used in the explanations of structure formation, another model that was developed separately at first.Inflation is married to CDM because the inflation accessory was predicted to have a signature in the CDM spectrum. When that signature did not emerge in the COBE and Balloon studies, another crutch was needed. Fortunately, the same bandage Einstein used to create a stable cosmos could also be used to accelerate the expansion and make the signature of inflation predicted go away. It was especially nice, because the amount of acceleration was consistant with the disturbing evidence of accelerated growth emerging in the supernova extensions of the distance ladder.


So you agrossly mischaracterising the way these theories have grown and how they have interplayed with each other. It is not at all as you are portraying things - there was never one monolithic theory that started out and had all this stuff added to it for some dogmatic reason. There were several lines of evidence that came together and supported each other.They converged to a singular and unique solution set. But they did so, because the values chosen allowed this conversion - otherwise they would not have been chosen. It needs to be pointed out here, that this is a mathematical exercise, and it is dangerous because adding epicycles to match new observations improved the precision of the astrolab. It is dangerous, because someone can look at the mechanics of the model and say 'what a great theory we have because we can make great predictions, and - if we take the earth out of the center, all of the precision breaks down'. We have been there, and we have done that.


And you claim that a theory can never be disproven if you just keep adding to it? Rubbish. There are constraints in the theory that, if broken, would invalidate it entirely. But so far we are still within an acceptable parameter space for it.Nope. At the moment, the tension in the Planck data - the smaller Ho value needed is too small to overlap the supernova data set.

It has been documented that when the Supernova distance ladder project published a value for Ho; the results of other families of observations started to converge upon this same value with remarkable precision - published precision that exclude the lower value favored by the Planck data. (There is one exception: Tulley-Fisher data did not converge, but predicted a much lower value of Ho. It was easy to discard though, because no one has an accepted theory about how the Tulley-Fisher relationship works in the first place.)


So far steady state, HDM, baryonic DM, MOND and hundreds more variants - they have all been tested and found to be a worse fit to observations. Yes, there are a lot of bad theories on the pile. It shouldn't hurt anyones feelings to throw on one more.


In fact all of these models have had just as much extra stuff added to them as the CDM model has to make them work (MOND, TVS and so on, the ridiculously hard to form super-black snowballs with unrealistic elemental abundances, MACHOs - the list goes on).Copernicus had to add epicycles, and they were god-awful ugly. He didn't have a good mathematical model, but he had a better basic theory.


The thoery gets respect for the predictions it has made and the results you get out of it. No matter how much you attempt to dismiss them they are pretty accurate so far. Has the model been tuned? Yes, like every model ever. Have things been added to refine it? Yes. As has happened with every model ever. Maybe we will get to the point where it is disproven and discarded. Quite probably. You keep claiming that this is some sort of belief system. Then why does its apparently fanatical supporter here keep saying "It may be wrong, it may be replaced"? Could it be because it is not a belief system? I know, shocking thought.The church has power because the church has money. It is a fact that in 1995 when Nillson proposed a new supernova model that ran contrary to theory, his funding was pulled. The Danes have been vindicated, but it is a soured prize.

So why won't the Planck data converge with such a precise platform? Something is wrong. It may be something little, but it can also be one of many basic premises. How do we find out? The first step in any twelve step program, is to admit that something is wrong. Fundamentally wrong. Why does the Tulley-Fisher relationship work, and what is it trying to tells us about the fundamentals of galaxy growth and formation?

Shaula
2013-Apr-28, 03:45 PM
It needs to be pointed out here, that this is a mathematical exercise, and it is dangerous because adding epicycles to match new observations improved the precision of the astrolab. It is dangerous, because someone can look at the mechanics of the model and say 'what a great theory we have because we can make great predictions, and - if we take the earth out of the center, all of the precision breaks down'. We have been there, and we have done that.
This is the crux of your argument and I think it is a misguided one. All models need refinement and improvement. And other models are being investigated. No one is saying we have all the answers. We have a best fit and we have other models and ideas. When a better fit comes along that will be mainstrream. If we just threw away every model whenever there was any need to tune it then science would go nowhere.


Nope. At the moment, the tension in the Planck data - the smaller Ho value needed is too small to overlap the supernova data set.
It is not too small to overlap, it is at about 2.5 sigma. So it is something like 5% chance that the two central values came from the same distribution. Not game breaking. Both results contain assumptions that may need to be changed.


It has been documented that when the Supernova distance ladder project published a value for Ho; the results of other families of observations started to converge upon this same value with remarkable precision
Except they don't. There is scatter from about 70-80.

This is a tired old argument and far from the point of the OP. It comes down to this: I don't think anyone is saying that the current models are perfect. I don't think that anyone is saying time spent looking at other models is wasted. The current models are being tested all the time. Every unexpected result opens up the arena for new ideas. But what an unexpected result does not mean is that we should throw everything away.

So a challenge: If you had your way what would you have researchers all over the globe do? Stop all science until we have a perfect model? Give up? What exactly is the point of your post here?

Jerry
2013-Apr-28, 03:53 PM
That would be true if I were not defending the mainstream (it is not an orthodoxy, thanks, belief is not required) based on the best available evidence.

The scientific debate is, or should be: Are the current modifications of the grand theories justifiable?

Wrong. It should be: Does the theory work. Has it been falsified. The answers are yes and no respectively. You have no way to determine what is 'justifiable' - that is a judgement call. Which we try to keep out of science.
Curious statement.

Fundamental science is all about judgement. We train scientists by exposing them to the great body of knowledge. Specialists in the various disciplines can tell you both the epistomologies of their fields and degeneracies that have been exposed.

When new evidence emerges, these experts first bounce this evidence against the knowledge in their lockers and then weigh the new evidence accordingly. The Tulley-Fisher relationship is given little weight, because it does not mesh well with prevailing theories about how galaxies form. This is a judgement call; and at the fundamental level, that is the best we can do.

What is worrisome to me, when new evidence emerges that won't flow the way we expect it to; is that somewhere in the well-worn corridors a path was walled off that should not have been. That is what is hardest to fix, because when you take down those walls there will be a lot of chaos. It can mean rejecting tons of flawed data. Wouldn't it be fun, if now is the time to do just that?

Shaula
2013-Apr-28, 04:10 PM
What is worrisome to me, when new evidence emerges that won't flow the way we expect it to; is that somewhere in the well-worn corridors a path was walled off that should not have been.
You act like old ideas are never revisited. They are. There is always someone out there trying something new or old to see how it fits. Scientists want to be proven wrong, they want to be surprised. Because that is how new things are discovered.


Wouldn't it be fun, if now is the time to do just that?
Yes - but only when there is enough evidence to do that. I think it is premature to do that now and I think most people would agree.

Jerry
2013-Apr-28, 10:55 PM
Except they don't. There is scatter from about 70-80.
The last time I checked, the preferred Tulley-Fisher value was about 58. I haven't had the time to beat down the Planck data and see if I think the tolerance bands are too wide.

I guess if you are an optimist, a 95% chance of discord is tolerable. There is a 99.99% chance we have failed to observe gravitational waves, and this does not seem to bother anyone.


This is a tired old argument and far from the point of the OP. It comes down to this: I don't think anyone is saying that the current models are perfect. I don't think that anyone is saying time spent looking at other models is wasted. The current models are being tested all the time. Every unexpected result opens up the arena for new ideas. But what an unexpected result does not mean is that we should throw everything away.Agreed - it is a tire old argument.




So a challenge: If you had your way what would you have researchers all over the globe do? Stop all science until we have a perfect model? Give up? What exactly is the point of your post here?
About every three months or so, the popular press quotes some physicist somewhere (usually Australian or Scotish); that new physics might be needed to explain this or that set of data; followed by a rush of apologist who insist nothing is broken. I'm looking forward to the day when everyone says, dang, the model is broken and nobody is quite sure how to fix it.

If I have a main point, it is that we shouldn't be waiting for the next Newton or Einstein - it is the great man worship that is killing progress in astrophysics. DM theory insists our concept of gravity is essentially complete. Let's build a deep space mission that can validate that assumption.

neilzero
2013-Apr-29, 12:46 AM
I favor the deep space mission, even if it is unlikely to PROVE anything leading edge. Data from 1/10 th light year by 2099 may be practical if we spend a lot of money. More than 1/10 light year is likely more than a century away unless we get an incredible breakthough. Neil

NoChoice
2013-Apr-29, 10:30 PM
About every three months or so, the popular press quotes some physicist somewhere (usually Australian or Scotish); that new physics might be needed to explain this or that set of data; followed by a rush of apologist who insist nothing is broken. I'm looking forward to the day when everyone says, dang, the model is broken and nobody is quite sure how to fix it.

If I have a main point, it is that we shouldn't be waiting for the next Newton or Einstein - it is the great man worship that is killing progress in astrophysics. DM theory insists our concept of gravity is essentially complete. Let's build a deep space mission that can validate that assumption.

I am glad to hear a voice of reasoning in this debate, Jerry.
I agree with this and your points in other posts.
As is so often the case mainstream advocates forget that what we call mainstream is a work in progress.
Current mainstream cosmology is at best a swiss cheese model: it stinks and is full of holes...

Shaula
2013-Apr-30, 05:12 AM
As is so often the case mainstream advocates forget that what we call mainstream is a work in progress.

You act like old ideas are never revisited. They are. There is always someone out there trying something new or old to see how it fits. Scientists want to be proven wrong, they want to be surprised. Because that is how new things are discovered.

Yes - but only when there is enough evidence to do that. I think it is premature to do that now and I think most people would agree.

I don't think anyone is saying that the current models are perfect. I don't think that anyone is saying time spent looking at other models is wasted. The current models are being tested all the time. Every unexpected result opens up the arena for new ideas.

All models need refinement and improvement. And other models are being investigated. No one is saying we have all the answers. We have a best fit and we have other models and ideas. When a better fit comes along that will be mainstrream.

Every time there is a new observation other ideas are tested, people are always working on other ideas.

The theoretical model which best fits observations... And which, as I have said over and over to you and others, is the current best fit to the data. Cosmologists and physicists don't 'want' to dismiss bayonic dark matter. The evidence points us away from it
And that is just from this page. So I am guessing you didn't read what was written and just assumed. If you are going to implicitly accuse me of something try to at least make sure it is not something contradicted an average of once every other post in this thread..

NoChoice
2013-Apr-30, 06:06 AM
And that is just from this page. So I am guessing you didn't read what was written and just assumed. If you are going to implicitly accuse me of something try to at least make sure it is not something contradicted an average of once every other post in this thread..

Oh, I did read! I read you giving the lip service. What you do, however, is rather different.

As Jerry said and I agree 100% with this: "Your firm stand defending this orthodoxy is not a scientific position. A new, workable theory is not necessary before rejecting an old one."

I follow the developments in especially astrophysics and cosmology very closely. I have a PHD in physics (even taught for while) but don't do physics professionally any longer because I just couldn't stand the orthodoxy and their tight control of the money (and thereby to a large degree what can be researched properly and what can't).

I very much appreciate Jerry's rather refreshing take on things and I despise the way he is often treated and ridiculed on this board.
I may get an infraction or two for this but it's for a good cause! :-)

Jerry, I very much admire your patience in the face of the dominant orthodoxy on this board. A trait I lack and a reason why I try to stay out of those debates. But sometimes I just can't help it, especially when a kindred spirit is mistreated in the way you often are.

Jerry
2013-Apr-30, 06:11 AM
According to Sheldon on the Big Bang Theory, there hasn't been any progress in physics since quantum chromodynamics in the 1960's; but lord knows we've tried.

This comic televison over-simplification has some merit. It is wrong to characterize the search for Dark Matter particles as successful. We are going to continue the billion- dollar search for gravitational waves again this year with more detectors supercharged and once again, there will be no affirming results. No one in the Ivory towers is willing to concede failure, or even draw a meaningful line in the sand as to what evidence of failure would be evidence enough.

I don't even think it is time to give up yet, but I think more funding should be redirected towards less popular research. Did we throw out baryonic solutions too soon? Is there a low field strength property of gravity that we can wrap our arms around?

The days of precision cosmology - predicted by Sagen and egged on by Peebles have never materialized. It is the declarations of success, rather than the admissions of failure, that are perturbing. It is time to accept that.

Shaula
2013-Apr-30, 04:31 PM
As Jerry said and I agree 100% with this: "Your firm stand defending this orthodoxy is not a scientific position. A new, workable theory is not necessary before rejecting an old one."

It requires one of two things: either the old theory becomes incompatible with observations (not happened so far) or a more powerful theory comes along (not happened so far).


Oh, I did read! I read you giving the lip service. What you do, however, is rather different.
Lip service... Riiight. By consistently and repeatedly stating that the current model is a best fit and that it may well turn out to be wrong, but that given the weak nature of the evidence compared to the strength of the theory and the far less good fits you get from other models that I
think it is premature to throw it all away. Do you think I am lying when I say that that is my opinion?


I don't even think it is time to give up yet, but I think more funding should be redirected towards less popular research.
The problem is that there is so much of it. Where to direct the cash? It is not like there is a bottomless pit of it. New ideas and novel work is funded to a degree but to ask for a billion dollar space mission just on the off-chance seems a bit hopeful.


It is the declarations of success, rather than the admissions of failure, that are perturbing.
I have made no just absolute declarations of success as far as I am aware. I have said, again and again and again, that this is the current BEST FIT. But for some reason both you and NoChoice seem to think that this means I slavishly defend an untenable orthodoxy so that the gods of science continue to shower me with money. If either of you could present me with better or show me where there is a irrefutable and unreconcilable inconsistency in the theory (rather than something that could be down to previously unconstrained parameters) then I'd be happy to listen. As would all scientists I know (and I have worked as one for more than a decade).

TooMany
2013-Apr-30, 07:42 PM
If either of you could present me with better or show me where there is a irrefutable and unreconcilable inconsistency in the theory (rather than something that could be down to previously unconstrained parameters) then I'd be happy to listen. As would all scientists I know (and I have worked as one for more than a decade).

That's the key point. A sigma 2.5 deviation is merely an indication of "tension" (a currently popular euphemism for disagreement with theory) that can be reconciled via some reinterpretation of the data or, if need be, with some new physics. Making the theory fit is the source of countless speculative papers about new physics. Defenders have a habit of pointing to "fundamental successes" (like nucleosynthesis and the CMB) while ignoring the fact that new physics were conjectured to obtain those successes.

Shaula
2013-Apr-30, 08:02 PM
Defenders have a habit of pointing to "fundamental successes" (like nucleosynthesis and the CMB) while ignoring the fact that new physics were conjectured to obtain those successes.
And detractors ignore the fact that old physics was tried first. But hey hum, I am not going to win this one. Believe what you want to believe

TooMany
2013-Apr-30, 08:38 PM
And detractors ignore the fact that old physics was tried first. But hey hum, I am not going to win this one. Believe what you want to believe

That's what it seems to come down to, unfortunately. "We don't know" is a perfectly acceptable answer, better than a claim of well-established fact.

lpetrich
2013-Apr-30, 09:11 PM
According to Sheldon on the Big Bang Theory, there hasn't been any progress in physics since quantum chromodynamics in the 1960's; but lord knows we've tried.
Who's Sheldon?

It is wrong to characterize the search for Dark Matter particles as successful.
Who claimed that?

I don't even think it is time to give up yet, but I think more funding should be redirected towards less popular research. Did we throw out baryonic solutions too soon? Is there a low field strength property of gravity that we can wrap our arms around?
There's been a lot of work on that, so you might want to study the professional literature and try to find out what you think had gone wrong.


The days of precision cosmology - predicted by Sagen and egged on by Peebles have never materialized. It is the declarations of success, rather than the admissions of failure, that are perturbing. It is time to accept that.
Did Carl Sagan ever do any professional work on cosmology?

Where did Jim Peebles make that prediction? What prediction did he make? What do you mean by "precision cosmology"?

Noclevername
2013-Apr-30, 09:17 PM
Who's Sheldon?


A fictional character on a TV comedy.

NoChoice
2013-Apr-30, 11:06 PM
By consistently and repeatedly stating that the current model is a best fit and that it may well turn out to be wrong, but that given the weak nature of the evidence compared to the strength of the theory and the far less good fits you get from other models that I
think it is premature to throw it all away. Do you think I am lying when I say that that is my opinion?

Not at all. It seems to me you truly believe what you say. And there's nothing inherently wrong with that.

It's just as Jerry said: "It is the declarations of success, rather than the admissions of failure, that are perturbing."

Even a layman with a bit of wits can see immediately that current cosmology is basically fishing in the dark. Literally.
Yes, you say the current model may change but you also immediately say it was a best fit. The fit is so loose, however, that you can't really call it a fit.
And that's the point that some of us are trying get across.

That's all that's to it as far as I am concerned. There isn't a fit that deserves to be called a fit.

And it really is time to admit it.

ETA: And there's absolutely nothing wrong with current cosmology fishing in the dark. That's part of the scientific process. Nobody's to blame. I'm certainly not blaming anybody for it.
It is just the failure to admit it and the staunch insistence of some "mainstream" position that doesn't deserve to be called a position that smells a bit funny. It smells like stuffy orthodoxy to me...

Jerry
2013-May-01, 02:13 AM
[quote]I have made no just absolute declarations of success as far as I am aware.
True - this was a general, not personal statement - sorry.


The problem is that there is so much of it. Where to direct the cash? It is not like there is a bottomless pit of it. New ideas and novel work is funded to a degree but to ask for a billion dollar space mission just on the off-chance seems a bit hopeful.
You are correct, and the funding situation is not improving.


I have said, again and again and again, that this is the current BEST FIT.
The best fit is not always the best judgement call. This debate is not even worth reconducting at our level, unless someone is listening: Those who control the funding; those who make the decisions as to when it is time to pull the plug in one area, and focus more in another. I don't mean the politicians (although it could be them); but the principles who in many cases have focused their whole careers into one aspect or the other of ACDM cosmology.

It is said, that when Einstein was watching the fortieth year of the US Navel Research Center runnning Michelson Morley tests for aether, he stated that 'when you keep running the same tests and expecting different results, you are being stupid'. Keep in mind, he was talking about a series of tests that were always being conducted under new conditions and returning higher levels of precision. We have studied dark energy for more than eighty years now; and the only property on the table is that in a weak field environment, gravity still appears to behave badly. There has got to be a better set of solutions, and a way to find them.

Shaula
2013-May-01, 04:52 AM
It's just as Jerry said: "It is the declarations of success, rather than the admissions of failure, that are perturbing."
Do I have to keep quoting my replies to Jerry on this? I point out, with caveats, where the models works and it does not on this board over and over again. I try to explain to people what the current mainstream is without overselling it. I take the time to read papers people quote here and to point out things like misunderstanding (on both sides of the fence) or hidden assumptions. A few of the arguments I get parroted back to me against current cosmology were first mentioned by me in old threads to the people saying them.

And you know what? I am not exceptional at all. Just about all the scientists I know have the same attitude. Sure there are some who are strongly wedded to an idea. There are others with pet theories, people who are backing one of the less favoured ideas.


Yes, you say the current model may change but you also immediately say it was a best fit. The fit is so loose, however, that you can't really call it a fit.
And that's the point that some of us are trying get across.
And I hear your point and say it is wrong. I have no problem at all understanding what point you are trying to get across. I just disagree with it completely. Here is how the debate seems to go: "Well the current model explains the abundances of H/De/He really well" "But what about Lithium? Stop trumpeting your successes! It does not work for Lithium so throw out all your ideas!" "The model works well for large scale structure giving a realistic universe is a reasonable time" "Your orthodoxy does not explain low luminosity dwarf galaxies! Stop trumpeting your successes! It does not work for low luminosity dwarf galaxies so throw out all your ideas!" "Well, the model does a good job of explaining the CMBR and the BAOs in it." "Your model does not explain inflation from first principles! Stop trumpeting your successes! It does not work for inflation so throw out all your ideas!" You see why I hate this argument? It is unwinnable.

Personally I prefer positive science. Look for the gaps, look for other theories but don't expect a titanomachia over every gap or tweak to the model. One may come, in a way I hope it does. I have said several times on here that I actually don't like most of the mainstream components of cosmology. I find DE and DM unsatisfying. It has only been with the advent of things like CDT and CST that I even started to like the concept of a beginning at all. But it does not change the fact that what we have is the best fit, and has a number of notable successes to its name. Maybe this is due to overfitting, maybe not.

Anyway, I am done here. There is nothing constructive going on now. I just wanted to make sure that any visitor to the thread knew that the points on DM are not uncontested, and that the actual state of science is pretty far from the insulting way it is often referred to here. That the alternative solutions are not as easy as people make out and that criticism of the model and testing of it is a reflex built into most scientists. The community is not perfect at all, there are dogmatic elements to it. But mischaracterising it as a monolithic brake to progress is grossly oversimplifying things.

kzb
2013-May-01, 12:14 PM
This is from the Fun Papers in Arxiv thread:

*Cosmic Opacity* http://arxiv.org/abs/1304.7317 Yesterday I highlighted a paper about H2 because DM opponents use H2 to offer a 'possible' alternative to WIMPs. Today, we see a paper about Cosmic Opacity (which presumably has been decreasing). This paper debunks Cosmic Opacity as an alternative explanation for Dark Energy.

I'm essentially too thick to understand most of this paper. Plus, I've only tried to read it once so maybe I'm getting the wrong impression. I think what they are trying to say is that they have two sets of observations, one of which excludes cosmic opacity as the cause of supernova dimming with distance ,with high confidence. But the other does not? To me, that the two are not in accord would raise suspicion about the whole project, not that it debunks one theory or the other.

Anyway here is another recent arxiv paper:

http://arxiv.org/abs/1303.1375
Peaks in the CMBR power spectrum. II. Physical interpretation for any cosmological scenario
Authors: Martin Lopez-Corredoira

Again, I do not pretend to understand most of this. However, the conclusions seem to be that current DM/DE cosmology is the best fit to the six-parameter model. The point is also made (again) that if you have a model with six parameters that you are free to adjust between wide ranges, you could probably get almost anything to fit. However it is also concluded:

...[ origin of CMBR anisotropies]...
Here and in Paper I, it has been shown that it is a rather normal characteristic expected from any fluid with clouds of
overdensities that emit/absorb radiation or interact gravitationally with the photons, and with a finite
range of sizes and distances for those clouds.....

From some of his other publications, I also believe M Lopez-Corredoira to be a bit of a contrarian. He is professionally employed in the field so surely his points should be at least engaged with seriously.

TooMany
2013-May-01, 10:06 PM
The Corredoria paper was interesting in attempting to compare the successfulness of the standard model in predicting the CMB with an arbitrary polynomial with 6 free parameters. He concludes that the physical theory produces a better fit. He suggests that this toy analysis adds confidence to the standard model. The implication that the BAO could arise without the prescribed physical cause was interesting too.

I don't know whether he should be considered a contrarian just because he views the theory with some skepticism. Actually isn't it healthy to have some scientists examine the theory in a critical light? People (I'm not saying this is necessarily true for cosmologists) sometimes become convinced of things that are not true and apply rational arguments in support of false views by cherry picking successes and avoiding failures.

Since current theory has both successes and failures, my contention is that it should not be described to the public as if it is fact. Perhaps it's not the scientific community that is responsible for this public presentation, but every time I read a lay summary of cosmology, I cringe at the lack of disclaimers and the assurance with which speculative aspects such as inflation are described. There are many things in astronomy that are well-established, however what happened at 10-33 seconds from the beginning is not one of them.

Jens
2013-May-01, 11:04 PM
I sympathize other the idea that there is surely something beyond the standard physics. But I also think Shaula is right that people don't simply defend the orthodoxy. What about the issue of antimatter? Everybody knows it's a mystery, and people are trying to find some symmetry breaking, but haven't succeeded. Now just suppose we can't find any? Where would one go from there? It's hard to think of what experiments we might try? Actually, it's a limitation of cosmology that we can't bring what we are observing into a lab to investigate.

NoChoice
2013-May-01, 11:30 PM
Actually isn't it healthy to have some scientists examine the theory in a critical light? People (I'm not saying this is necessarily true for cosmologists) sometimes become convinced of things that are not true and apply rational arguments in support of false views by cherry picking successes and avoiding failures.

Since current theory has both successes and failures, my contention is that it should not be described to the public as if it is fact. Perhaps it's not the scientific community that is responsible for this public presentation, but every time I read a lay summary of cosmology, I cringe at the lack of disclaimers and the assurance with which speculative aspects such as inflation are described. There are many things in astronomy that are well-established, however what happened at 10-33 seconds from the beginning is not one of them.

Spoken from my heart.
Especially in cosmology we know so very little and yet think we already know so much.
That's why I think it is very important to make that clear to the public.
And that's the main reason I am posting on this rather exposed forum: To make sure that it is understood that cosmology is to a large degree conjecture and speculation.
There is absolutely nothing wrong with that. In the absence of better data and theories that is part of the scientific process.
It just needs to be understood for what it is.
"Mainstream" science - while it deserves some respect, for sure - is very much a work in progress, especially in cosmology and not to be taken all too seriously.
It certainly requires very clear and strong disclaimers. I absolutely agree.



What about the issue of antimatter? Everybody knows it's a mystery, and people are trying to find some symmetry breaking, but haven't succeeded. Now just suppose we can't find any? Where would one go from there? It's hard to think of what experiments we might try? Actually, it's a limitation of cosmology that we can't bring what we are observing into a lab to investigate.

Exactly. Our data is very sparse and taken from great distance - in both time and space.

In addition to that limitation (and causally connected) we lack a comprehensive theoretical framework that could make sense of the data we have.
Nobody's to blame. It's inherent in the subject.
Again: That's why it requires very clear disclaimers and is only to be taken with a large grain of salt.

And yet many mainstreamers preach from their high horses as if we already knew it all or even had a solid understanding. We really do not!

Jens
2013-May-02, 03:51 AM
So getting back to dark matter, we do have the anomalous observations of galaxy rotation curves, and so something has to give there. Either it's a physical problem, where dark matter seems like an obvious solution (what else could it be?) or it's an observational error, meaning that red shift and blue shift are not really showing velocity (but then what would they be showing?). So it seems that dark matter is a proposed way of explaining something that seems very difficult to explain in any other way.

NoChoice
2013-May-02, 04:29 AM
So getting back to dark matter, we do have the anomalous observations of galaxy rotation curves, and so something has to give there. Either it's a physical problem, where dark matter seems like an obvious solution (what else could it be?) or it's an observational error, meaning that red shift and blue shift are not really showing velocity (but then what would they be showing?). So it seems that dark matter is a proposed way of explaining something that seems very difficult to explain in any other way.

Yes, it is a big puzzle. I am not sure if even observational errors or misunderstandings can be entirely ruled out.
To extrapolate doppler shift to cosmic dimensions seems reasonable at first glance but we only have real verifiable data for it within our own solar system. The probes we have sent out show the expected doppler shifts. But cosmic distances are many orders of magnitude larger. At the end of the day, we do not really know. It seems a fair assumption but we don't know. A lot of cosmology is based on the extrapolation of the doppler effect to cosmic scales to be valid. If that pillar crumbles we would have to re-evaluate our entire cosmology. Probably a very scary thought for many and very few want to go there.

I am not saying it is wrong. I am only saying we don't actually know for sure. At this point it is conjecture.

And yes, DM seems an obvious solution.
Many of our theoretical tools like GR and quantum mechanics are tantalizingly precise in their predictions. My GPS for example works pretty well...

And yet - there are contradictions all over the place.
You mentioned the matter / antimatter asymmetry. No satisfying explanation.
Quantum gravity. No theory.
What about the fundamental problem of consciousness? After all, that's where all of this is happening! We just assume it's a result of brain function. At this point in time nothing but conjecture.
The list is long and disturbing and it indicates fundamental holes in our understanding (not just some minor details here and there).

I think nothing (or very little) should be off the table in terms of re-evaluation.
I was very glad to read that some physicists actually investigate whether antimatter is subject to the same gravitational laws as standard matter. We should not assume anything.

Strange
2013-May-02, 08:05 AM
Since current theory has both successes and failures, my contention is that it should not be described to the public as if it is fact. Perhaps it's not the scientific community that is responsible for this public presentation, but every time I read a lay summary of cosmology, I cringe at the lack of disclaimers and the assurance with which speculative aspects such as inflation are described.

This is largely a problem of journalism (including by science journalists who should know better) and popularizations. I think this is partly because people want to make their stories as simple as possible, but also because they know that the vast majority of people reading these popular descriptions have no interest in the caveats and uncertainties. I guess the writers think it may just confuse (some of) their readers. In addition they like dramatic headlines and exciting stories.

For some reason, New Scientist magazine prefers a headline like Darwin Was Wrong! over something like Some evidence may indicate that evolution could be somewhat more complex than suggested by the current model. Further work is required.

One the other hand, you need to be careful about throwing the baby out with the bathwater. There are unknowns and problems with (all) current theories but that doesn't mean that those theories should be scrapped. After all that is inherent to the nature of science. In the case of dark matter (and dark energy) many different possibilities are being explored. In terms of funding for, e.g. direct detection, the effort is going into the possibilities that we know how to detect (if they exist). But that doesn't mean that other avenues are being ignored. The ones that get reported in the press most often are the ones that are (a) currently most successful and (b) relatively easy to understand (or mashed into a form that is at least partially digestible).

kzb
2013-May-02, 12:25 PM
Jens - I believe the galactic rotation curve (in our own galaxy) has also been found via proper motion measurements, not just by Doppler shift. The proper motion of masers backs up the apparently too-high velocity in the outer regions of the galaxy. So it's unlikely to be due to some unknown issue connected to the Doppler effect. What else could it be? Well don't forget MOND. I don't like that either, but it is a competing theory to DM. Also some of us on here have this feeling that won't go away: there could be a lot of baryonic matter still not found. And astronomers have stopped trying to find it. Possibly we need psychiatric treatment for this condition, but let's see.

TooMany -I agree with you pretty well. I was saying M. L-C is probably viewed as a contrarian. The point I took from his paper was that a rather simple idea can account for much of the pattern of the CMB anisotropies, that is, clouds of the same size and at the same distance reproduce a lot of the observations. Considering that his model is undoubtedly oversimplified as it stands....well you see where I'm going on that.

I also am not suggesting that DM/DE should be abandoned by all. Absolutely not. I think it is also obvious there is a long list of scientists who are actively pursuing other ideas, and that it is the scientific press and press releases that give the wrong impression. I can also live with the fact that some lines of enquiry are more expensive than others, simply because of their nature, and therefore should get more resources. I'd also hope that scientists pursuing other ideas would also be supported, if only because negative results in these areas can be just as valuable scientifically.

trinitree88
2013-May-02, 03:45 PM
Sometimes, the classic spiral galaxies where the rotation curves first seemed to cry out for dark matter.....don't cry out after all. SEE:http://www.newscientist.com/article/dn13280-galaxy-without-dark-matter-puzzles-astronomers.html

Yep. I'm going to cherry pick this a bit...but not a lot. This paper finds no dark matter in spiral galaxies, and references MNRAS, A&A, Nature, Ap.J, articles (mainstream)with many names I've seen before, along with a few references I've not...(a little less mainstream). But, he talks physics, and in a forum still growing on the net....so I'm dropping it here to see how it sits with the pros who know more about galactic dynamics than I. If he's right, a lot of people will be up late toniight....thinking. pete


SEE:http://vixra.org/pdf/1112.0014v3.pdf

borman
2013-May-03, 02:02 PM
In a follow up study of Abell 520, Clowe et al found galaxies behind Cluster 5 that were also missing their Dark Mattr Halos creating some tension with the current paradigm.

Meanwhile latest results from XENON100 found no Dark Matter.

Cougar
2013-May-03, 02:15 PM
And that's the main reason I am posting on this rather exposed forum: To make sure that it is understood that cosmology is to a large degree conjecture and speculation.

On the other hand, there is a lot about current cosmology that is not conjecture and speculation. Are you describing your own personal understanding of the subject? On what basis are you making this claim? How well have you studied this subject?

StupendousMan
2013-May-03, 02:25 PM
Sometimes, the classic spiral galaxies where the rotation curves first seemed to cry out for dark matter.....don't cry out after all. SEE:http://www.newscientist.com/article/dn13280-galaxy-without-dark-matter-puzzles-astronomers.html

Yep. I'm going to cherry pick this a bit...but not a lot. This paper finds no dark matter in spiral galaxies, and references MNRAS, A&A, Nature, Ap.J, articles (mainstream)with many names I've seen before, along with a few references I've not...(a little less mainstream). But, he talks physics, and in a forum still growing on the net....so I'm dropping it here to see how it sits with the pros who know more about galactic dynamics than I. If he's right, a lot of people will be up late toniight....thinking. pete


SEE:http://vixra.org/pdf/1112.0014v3.pdf

I didn't stay up late after scanning this paper. The author postulates that spiral arms are created when material is ejected from the centers of galaxies. This basic notion conflicts with so much observational evidence that I just stopped reading.

trinitree88
2013-May-03, 06:34 PM
I didn't stay up late after scanning this paper. The author postulates that spiral arms are created when material is ejected from the centers of galaxies. This basic notion conflicts with so much observational evidence that I just stopped reading.

Stu. Thanks for the input....helps me channel my time and energy. I know John Middleditch from previous work and some private communications....perhaps you'll find his paper more cogent. SEE:http://arxiv.org/abs/1205.5107
It is interesting to note that his focus on the geometry, or morphological characteristics of supernovae, has led him to believe that selection effects in the Local population of them may have led many astray in both the dark matter and the dark energy regime. He was one of the first to note that the beaming factor in SN1987a was ~ 10,000, and is now backing up his issues with their "standard candle-ness", questioning their reliability in a few surveys. pete

P.S. It's something I questioned in my first A.A.P.T. physics talk at Vassar, Nov. 1992...."Parity, Pulsars and Supernovae Remnants".

NoChoice
2013-May-03, 11:13 PM
On the other hand, there is a lot about current cosmology that is not conjecture and speculation. Are you describing your own personal understanding of the subject? On what basis are you making this claim? How well have you studied this subject?

Yes. I am not trying to throw out the baby with the bathwater. I hope my posts cannot be misinterpreted like that.
I have stopped teaching and practicing physics a while ago, so I do not consider myself a cosmologist.
I do read the occasional paper that seems particular interesting but my main source are old friends and colleagues who are experts actively publishing in the field of cosmology and who I meet regularly.

I would consider myself very well informed with a pretty good understanding of the problems.

I tend to favor a more radical (in the original meaning of "going to the root") approach and I'm not afraid to question holy cows like our understanding of the doppler effect on cosmic scales.
The holes in our understanding are so fundamental (despite very precise predictions by some of our theoretical framework - a very fascinating conundrum!) that such an approach seems warranted.

Jerry
2013-May-04, 02:17 PM
Even a layman with a bit of wits can see immediately that current cosmology is basically fishing in the dark. Literally.
Yes, you say the current model may change but you also immediately say it was a best fit. The fit is so loose, however, that you can't really call it a fit.
And that's the point that some of us are trying get across...

That's all that's to it as far as I am concerned. There isn't a fit that deserves to be called a fit.


Perfect.

I believe it is Fermi who, late in his brilliant carreer, deflated a young physicist who came to him with a working model with only 'five free parameters' and stated, "yes, you only used five free parameters. I can build an elephant with five free parameters." Fermi would not be happy with the six loose cogs that have been added in his absence.

The irony is, we don't know how many parameters nature is using. We don't know whether it is five, fifty or fifty-five to the fifty-fifth power. We like simple, rigid and elegant, but we always have to include the caution that nature has thrown us curves. We may have the mathematical tools we need, we may be tooling up nature in places where random chaos rules.

Newton started his great thesis stating the simple axiom that he assumes there are no forces governing the heavens that are not native to the earth. In that one statement, Newton rejected angels, demons, Atlas and turtles - all the way down. We should, too...except we don't have to. We can't line up the planets as well as we would like to; and we desparately want to understand why. We can go out there with our precise rulers. We can zero-base a lot of things that Newton couldn't.

Jean Tate
2013-May-04, 05:05 PM
Yes. I am not trying to throw out the baby with the bathwater. I hope my posts cannot be misinterpreted like that.
I have stopped teaching and practicing physics a while ago, so I do not consider myself a cosmologist.
I do read the occasional paper that seems particular interesting but my main source are old friends and colleagues who are experts actively publishing in the field of cosmology and who I meet regularly.

I would consider myself very well informed with a pretty good understanding of the problems.

I tend to favor a more radical (in the original meaning of "going to the root") approach and I'm not afraid to question holy cows like our understanding of the doppler effect on cosmic scales.
The holes in our understanding are so fundamental (despite very precise predictions by some of our theoretical framework - a very fascinating conundrum!) that such an approach seems warranted.

I've been following this thread with interest.

I must say that I am very puzzled by this: "The holes in our understanding are so fundamental ...". What, may I ask, are you referring to?

Given that, as of today, the only thing we know about the universe beyond our own solar system (with the possible exception of some neutrinos and some cosmic rays) is based on analysis of detected light (a.k.a. photons), are you claiming that QED is deeply flawed? Or is it, perhaps, the more mundane "we ain't been to 3C 273 yet, much less some z=7 galaxy, so we are basically totally clueless about everything beyond where Voyager has reached"?

NoChoice
2013-May-04, 10:38 PM
I've been following this thread with interest.

I must say that I am very puzzled by this: "The holes in our understanding are so fundamental ...". What, may I ask, are you referring to?

I mentioned a few in my post #102 above.

Jean Tate
2013-May-05, 02:05 AM
I've been following this thread with interest.

I must say that I am very puzzled by this: "The holes in our understanding are so fundamental ...". What, may I ask, are you referring to?I mentioned a few in my post #102 above.

Thanks!

In an earlier post you said that you once taught physics, and that you once 'practiced physics' (which I take to mean you did research in physics, and published papers in journals like Physics Review Letters; is that correct?), so I was a bit surprised to read, in post #102, that you seem to consider "observational errors" among these fundamental holes! I mean, isn't that the same as saying physics (and all of science?) is fundamentally flawed? And how in the world can 'the problem of consciousness' be considered a fundamental problem of cosmology?

Please don't misunderstand me, but my impression is that CQ is not the right place for this sort of discussion; wouldn't a philosophy or religion forum be more appropriate?

Perhaps this might help: if you're interested in "our understanding of the doppler effect on cosmic scales" (whatever you mean by that), what would you suggest might be a way to research this, as a physicist?

NoChoice
2013-May-05, 03:16 AM
[Note to moderator: I am happy to leave it at my following response as it would probably lead to a derailing of the thread. I only respond because of the direct question.
Is there any place in this forum you would consider appropriate for such a discussion?]



And how in the world can 'the problem of consciousness' be considered a fundamental problem of cosmology?
Please don't misunderstand me, but my impression is that CQ is not the right place for this sort of discussion; wouldn't a philosophy or religion forum be more appropriate?

From the way you worded your questions it seems you consider this an absurd proposition.

Consider this, tho:
Where does any of this take place? The content of the discussion, the concepts used, the reasoning used to operate with said concepts? In consciousness.

Quantum physics has pretty much made it official: The way nature reveals itself is very much depended on the question (and thereby the questioner).
You cannot simply leave the subject out of the equation.

There is nothing that indicates the validity of the usual approach of science to regard the subject as inherently separate and independent of the objects it studies.

Well respected scientists like Eugene Wigner and David Bohm (just to name two physicists; there are many others, including well-respected neurologists) see consciousness and matter as intrinsically linked, even as different manifestations of the same "phenomenon".

I agree with them. My own studies and explorations (although I started out as materialist) have led me to the same conclusions.

I'll leave it at that. Just as food for thought and to illustrate that the inclusion of consciousness in science is not as absurd as commonly assumed.

ETA: another aspect of this discussion I forgot to mention - maybe slightly more accessible for most - is the problem of the emergence of consciousness.
A link may suffice for the moment: http://en.wikipedia.org/wiki/Quantum_mind

Jean Tate
2013-May-05, 06:58 AM
[Note to moderator: I am happy to leave it at my following response as it would probably lead to a derailing of the thread. I only respond because of the direct question.
Is there any place in this forum you would consider appropriate for such a discussion?]


And how in the world can 'the problem of consciousness' be considered a fundamental problem of cosmology?
Please don't misunderstand me, but my impression is that CQ is not the right place for this sort of discussion; wouldn't a philosophy or religion forum be more appropriate?


From the way you worded your questions it seems you consider this an absurd proposition.

Consider this, tho:
Where does any of this take place? The content of the discussion, the concepts used, the reasoning used to operate with said concepts? In consciousness.

Quantum physics has pretty much made it official: The way nature reveals itself is very much depended on the question (and thereby the questioner).
You cannot simply leave the subject out of the equation.

There is nothing that indicates the validity of the usual approach of science to regard the subject as inherently separate and independent of the objects it studies.

Well respected scientists like Eugene Wigner and David Bohm (just to name two physicists; there are many others, including well-respected neurologists) see consciousness and matter as intrinsically linked, even as different manifestations of the same "phenomenon".

I agree with them. My own studies and explorations (although I started out as materialist) have led me to the same conclusions.

I'll leave it at that. Just as food for thought and to illustrate that the inclusion of consciousness in science is not as absurd as commonly assumed.

ETA: another aspect of this discussion I forgot to mention - maybe slightly more accessible for most - is the problem of the emergence of consciousness.
A link may suffice for the moment: http://en.wikipedia.org/wiki/Quantum_mind

Thanks for this.

Perhaps you could also expand a bit on some of the other items on both your stated long and disturbing list (http://cosmoquest.org/forum/showthread.php?142253-Will-Dark-Matter-Finally-Reveal-Itself&p=2126180#post2126180), and on the ones you didn't mention?

Back to how 'the problem of consciousness' can be considered a fundamental problem of cosmology.

If I may paraphrase, and extend a bit: you claim that the nature of CDM cannot be understood, with any degree of certainty (assurance, comfort, ...), unless and until 'the problem of consciousness' is solved; is that a fair summary?

Putting it another way, there is the possibility - of a serious, scientific (physics) kind - that the nature of CDM is closely related to what happens inside the brains of animals here on Earth, of the species Homo sapiens (and perhaps some closely related species too); is that a reasonable interpretation of what you're claiming?

To be clear on this last: you are not claiming this is a philosophical question akin to "If a tree falls in a forest and no one is around to hear it, does it make a sound?", but a serious question amenable to being addressed by the tools and techniques of physicists and astronomers. One whose answer might take a form something like "the mass of CDM in the observable universe is a function of the consciousness of Homo sapiens, and can be approximated by an inverse hyperbolic Bessel function of the Hilbert kind" (the last bit is nonsense, of course, but you get my meaning, right?)

Jean Tate
2013-May-05, 07:05 AM
Since current theory has both successes and failures, my contention is that it should not be described to the public as if it is fact. Perhaps it's not the scientific community that is responsible for this public presentation, but every time I read a lay summary of cosmology, I cringe at the lack of disclaimers and the assurance with which speculative aspects such as inflation are described. There are many things in astronomy that are well-established, however what happened at 10-33 seconds from the beginning is not one of them.

I found this particularly interesting, because my first thought was "if you replace 'cosmology/astronomy/what happened at ...' with equivalent words and phrases from almost any branch of science, won't the statement also be just as valid?" And especially for those which deal with regimes not amenable to controlled lab experiments, such as geology, paleontology, and climate science. Or is there something particularly special about a branch of science based almost entirely on the interpretation of detected light/photons from the sky?

NoChoice
2013-May-05, 08:02 AM
Thanks for this.

Perhaps you could also expand a bit on some of the other items on both your stated long and disturbing list (http://cosmoquest.org/forum/showthread.php?142253-Will-Dark-Matter-Finally-Reveal-Itself&p=2126180#post2126180), and on the ones you didn't mention?

Back to how 'the problem of consciousness' can be considered a fundamental problem of cosmology.

If I may paraphrase, and extend a bit: you claim that the nature of CDM cannot be understood, with any degree of certainty (assurance, comfort, ...), unless and until 'the problem of consciousness' is solved; is that a fair summary?

Putting it another way, there is the possibility - of a serious, scientific (physics) kind - that the nature of CDM is closely related to what happens inside the brains of animals here on Earth, of the species Homo sapiens (and perhaps some closely related species too); is that a reasonable interpretation of what you're claiming?

To be clear on this last: you are not claiming this is a philosophical question akin to "If a tree falls in a forest and no one is around to hear it, does it make a sound?", but a serious question amenable to being addressed by the tools and techniques of physicists and astronomers. One whose answer might take a form something like "the mass of CDM in the observable universe is a function of the consciousness of Homo sapiens, and can be approximated by an inverse hyperbolic Bessel function of the Hilbert kind" (the last bit is nonsense, of course, but you get my meaning, right?)

No, I'm afraid this is not at all an accurate summary of what I tried to communicate.
But - as I said - I will leave it at that for this thread.

Maybe I will start a thread about it someday but I doubt it.

Jean Tate
2013-May-05, 09:26 AM
No, I'm afraid this is not at all an accurate summary of what I tried to communicate.
But - as I said - I will leave it at that for this thread.

Maybe I will start a thread about it someday but I doubt it.

Fair enough, thanks for the clarification.

Does that apply to each and every other item mentioned in your long and disturbing list (http://cosmoquest.org/forum/showthread.php?142253-Will-Dark-Matter-Finally-Reveal-Itself&p=2126180#post2126180) too?

Hlafordlaes
2013-May-05, 04:37 PM
Yes. I am not trying to throw out the baby with the bathwater. I hope my posts cannot be misinterpreted like that.
I have stopped teaching and practicing physics a while ago, so I do not consider myself a cosmologist.
I do read the occasional paper that seems particular interesting but my main source are old friends and colleagues who are experts actively publishing in the field of cosmology and who I meet regularly.

I would consider myself very well informed with a pretty good understanding of the problems.

I tend to favor a more radical (in the original meaning of "going to the root") approach and I'm not afraid to question holy cows like our understanding of the doppler effect on cosmic scales.
The holes in our understanding are so fundamental (despite very precise predictions by some of our theoretical framework - a very fascinating conundrum!) that such an approach seems warranted.

Everything is provisional. But I think popular science ought to simplify for the same reasons a doctor might not tell his patient, "Well, it's either deadly or nothing, I'm working on it and I'll let you know." Announcing what seems fairly reliable according to the current state of due diligence seems OK to me.

As for the workings of observers and reality, true, it seems that way now. I wonder, though, how the first eggs depended on chickens watching them, if you get my poor analogy. That is, it seems we introduce the need for a cosmic observer, and I don't know where we have evidence for that.

Anyway, this last is, as you say in another post, off-topic, so perhaps best for a thread of its own.

TooMany
2013-May-05, 06:54 PM
I found this particularly interesting, because my first thought was "if you replace 'cosmology/astronomy/what happened at ...' with equivalent words and phrases from almost any branch of science, won't the statement also be just as valid?" And especially for those which deal with regimes not amenable to controlled lab experiments, such as geology, paleontology, and climate science. Or is there something particularly special about a branch of science based almost entirely on the interpretation of detected light/photons from the sky?

The comparison of these sciences is completely invalid. The sciences of geology, paleontology and climate are entirely driven by observation and application of known laws of physics. They do not propose any theory which is upheld by speculations concerning new physics. By contrast, present day cosmology assumes a theory (indeed based on evidence) but then proposes new physics to explain major disagreements of the theory with observation.

TooMany
2013-May-05, 07:32 PM
Announcing what seems fairly reliable according to the current state of due diligence seems OK to me.


Announcing as fact, conjectures (such as inflation) conceived to validate a theory is not OK to me. I would be fine with "we have a theory of evolution of the Universe that fits many observations. We attribute the CMB to the occurrence of transparency in the expanding universe when the universe was still very hot, but we discovered that this radiation has an unexpected characteristic. The CMB was far smoother than expected from our theory. However, we have found that a brief period of enormous inflation, during the first millionth of a millionth of a millionth of a millionth of a millionth of a second into creation, which expanded the dimension of a proton to 100 million kilometers can explain this smoothness. We have adopted this as part of our theory and are exploring possible new physics to account for the inflation."

Shaula
2013-May-05, 07:48 PM
Announcing as fact, conjectures (such as inflation) conceived to validate a theory is not OK to me. I would be fine with "we have a theory of evolution of the Universe that fits many observations. We attribute the CMB to the occurrence of transparency in the expanding universe when the universe was still very hot, but we discovered that this radiation has an unexpected characteristic. The CMB was far smoother than expected from our theory. However, we have found that a brief period of enormous inflation, during the first millionth of a millionth of a millionth of a millionth of a millionth of a second into creation, which expanded the dimension of a proton to 100 million kilometers can explain this smoothness. We have adopted this as part of our theory and are exploring possible new physics to account for the inflation."
Ironically enough that is pretty much what is taught and what is done. Announcing it as fact is something that happens mostly in popularisations of science. But hey, don't let that get in the way.

Strange
2013-May-05, 08:20 PM
By contrast, present day cosmology assumes a theory (indeed based on evidence) but then proposes new physics to explain major disagreements of the theory with observation.

Surely it is only the (so far) unsuccessful explanations such as MOND which propose new physics?

TooMany
2013-May-05, 08:38 PM
Ironically enough that is pretty much what is taught and what is done. Announcing it as fact is something that happens mostly in popularisations of science. But hey, don't let that get in the way.

If indeed it is only the popularizers, then perhaps the actual researchers should step forward and inform the public that some of these announcements are simply speculations in support of a theory which has run into disagreement with observations. Of course public impressions have no bearing on the validity of theory. However, it appears that the researchers themselves have become unduly convinced of the reality of these additions to physics.

Jean Tate
2013-May-05, 08:38 PM
I found this particularly interesting, because my first thought was "if you replace 'cosmology/astronomy/what happened at ...' with equivalent words and phrases from almost any branch of science, won't the statement also be just as valid?" And especially for those which deal with regimes not amenable to controlled lab experiments, such as geology, paleontology, and climate science. Or is there something particularly special about a branch of science based almost entirely on the interpretation of detected light/photons from the sky?The comparison of these sciences is completely invalid.
Thank you for your response. Most certain, and assured, it is.


The sciences of geology, paleontology and climate are entirely driven by observation and application of known laws of physics.

The sciences of astronomy, astrophysics, and cosmology are entirely driven by observation and application of known laws of physics, are they not? I mean, it all begins with the detection of light/photons, and the application of the laws of physics to the data derived from those detections.

Clearly, you disagree! But how? and why?


They do not propose any theory which is upheld by speculations concerning new physics.

Well, to keep the parallel accurate, one would have to write something like "They do not propose any theory which is upheld by speculations concerning new geology, paleontology or climate science", would one? And if viewed in this light, that's exactly what they do, don't they (replacing "speculations" with a somewhat less loaded word, of course)? After all, isn't that how all science works? Indeed, you might go so far as to say that if this sort of thing stopped, then science would be dead, wouldn't it?


By contrast, present day cosmology assumes a theory (indeed based on evidence) but then proposes new physics to explain major disagreements of the theory with observation.

I see Strange beat me to it; it's really only MOND (and its relativity-consistent extensions) which are new physics, wouldn't you say? (well, there are also lots of other 'new theories' of gravity, with names like 'chameleon f(R)'). I mean, the cosmology I know is based on GR, with some nuclear physics and atomic physics sprinkled on the top.

TooMany
2013-May-05, 08:40 PM
Surely it is only the (so far) unsuccessful explanations such as MOND which propose new physics?

You mean non-baryonic dark matter and inflation are based on known physics?

Jean Tate
2013-May-05, 08:54 PM
Ironically enough that is pretty much what is taught and what is done. Announcing it as fact is something that happens mostly in popularisations of science. But hey, don't let that get in the way.If indeed it is only the popularizers, then perhaps the actual researchers should step forward and inform the public that some of these announcements are simply speculations in support of a theory which has run into disagreement with observations. Of course public impressions have no bearing on the validity of theory. However, it appears that the researchers themselves have become unduly convinced of the reality of these additions to physics.

From reading this thread, I see that you and Shaula have expressed this sort of disagreement many times.

For what it's worth, my view is that Shaula is far closer to having accurately portrayed the way things work, in today's astronomy and astrophysics, than your characterizations are.

Might I suggest a way to resolve this?

The heart of the matter seems to be your personal belief that "the researchers themselves have become unduly convinced of the reality of these additions to physics". Leaving aside, for now, what seems to me to be a somewhat over-the-top characterization ("these additions to physics"), the key is what "the researchers themselves" have become convinced of (whether unduly or not), wouldn't you say? If so, then the most important thing to do is to deeply appreciate what sorts of things convinces these researchers, and how they go from being convinced of one thing to convinced of another, right?

In this regard, Shaula would seem to have made by far the stronger case; after all, he is one of the researchers himself, isn't he? And you are not, are you?

Jean Tate
2013-May-05, 09:06 PM
Surely it is only the (so far) unsuccessful explanations such as MOND which propose new physics?You mean non-baryonic dark matter and inflation are based on known physics?

It's a pity, I think, that you did not quote the statement of yours which Strange was responding to. Here it is: "By contrast, present day cosmology assumes a theory (indeed based on evidence) but then proposes new physics to explain major disagreements of the theory with observation."

I - and perhaps Strange too - assumed that, by "theory", you meant General Relativity. Did you? If not, what did you mean?

Anyway, you seem to be using important words in rather strange ways (well, strange to me anyway). For example, you go from "proposes new physics" to "not based on known physics" as if they are equivalent. For me at least, this is confusing. For me, chameleon f(R) gravity is new physics, as is MOND; in this context, non-baryonic CDM is not. So, for me, the answer to your question "Is non-baryonic dark matter based on known physics?" is "yes, it is."

Which nicely, I think, also illustrates a theme that has been running through this thread for a long time; namely, that you seem to have a quite different understanding of the nature of physics (and, perhaps, science in general) than almost everyone else who's been active in it.

Shaula
2013-May-05, 09:09 PM
If indeed it is only the popularizers, then perhaps the actual researchers should step forward and inform the public that some of these announcements are simply speculations in support of a theory which has run into disagreement with observations. Of course public impressions have no bearing on the validity of theory. However, it appears that the researchers themselves have become unduly convinced of the reality of these additions to physics.
They are more than speculations but less than a fully validated and worked out theory. As almost every researcher I know would say if asked. I note that, again, you just make these gross generalisations about researchers. So again I have to say: Having worked as a physicist for more than a decade, having studied astrophysics - your portrayals of hidebound, dogmatic researchers clinging to a theory do not align at all well with the people I have worked with and the people I know.

As for stepping forwards to inform the public - scientists do, via blogs and forums like this (like, in fact I am doing here). If you mean why don't they get into more pop-sci publications - well they do. Under headlines like "Current model of cosmology an unfounded theory: Is this the person who will revolutionise cosmology?". The slution for bad reporting is rarely more reporting.

Strange
2013-May-05, 09:16 PM
If indeed it is only the popularizers, then perhaps the actual researchers should step forward and inform the public that some of these announcements are simply speculations in support of a theory which has run into disagreement with observations.

I'm sure some of them would love to. But as the popular press is only interested in dramatic headlines, I doubt they would be listened to. Some of them write their own books, blogs and articles where they give a more nuanced approach. Those turn out not to be so popular for some reason...

And I think you mean "hypotheses" not "speculations".


However, it appears that the researchers themselves have become unduly convinced of the reality of these additions to physics.

perhaps it appears that way because that is the way the popular press report it?

TooMany
2013-May-05, 10:11 PM
I'm sure some of them would love to. But as the popular press is only interested in dramatic headlines, I doubt they would be listened to. Some of them write their own books, blogs and articles where they give a more nuanced approach. Those turn out not to be so popular for some reason...

And I think you mean "hypotheses" not "speculations".

Can you explain the difference? I'm happy to call inflation a hypothesis if you prefer.


perhaps it appears that way because that is the way the popular press report it?

Perhaps in part. I have no argument with the failings of the popular press.

I think I get the impression of conviction from the sheer quantity of scientific papers concerning inflation. As though it is quite real. Inflation theories are undergoing a pruning process due to Planck and perhaps other observations. But even if a nicely matching theory is found, how can it be corroborated? What will it predict, beyond what we have already observed?

TooMany
2013-May-05, 10:22 PM
It's a pity, I think, that you did not quote the statement of yours which Strange was responding to. Here it is: "By contrast, present day cosmology assumes a theory (indeed based on evidence) but then proposes new physics to explain major disagreements of the theory with observation."

I - and perhaps Strange too - assumed that, by "theory", you meant General Relativity. Did you? If not, what did you mean?

Anyway, you seem to be using important words in rather strange ways (well, strange to me anyway). For example, you go from "proposes new physics" to "not based on known physics" as if they are equivalent. For me at least, this is confusing. For me, chameleon f(R) gravity is new physics, as is MOND; in this context, non-baryonic CDM is not. So, for me, the answer to your question "Is non-baryonic dark matter based on known physics?" is "yes, it is."


All you are doing is stating your disagreement with MOND which is fine. But the popularity of non-baryonic CDM and inflation cannot disguise the fact that both require new physics, in the first case a new particle with certain properties and in the second, a new force with special conditions of action.

Strange
2013-May-05, 10:36 PM
You mean non-baryonic dark matter and inflation are based on known physics?

I have been thinking about this. Perhaps it depends what you mean by "new physics". For example, there are various attempts to make direct detection of various proposed particles which could make up dark matter. I'm not sure how experiments and detectors could be developed if it was new (in the sense of unknown) physics. As far as I know, all the proposed possibilities for dark matter as "stuff" (particles) are based on the standard model or other pre-existing theories. (I may be wrong about that, because I am not familiar with all the proposals, obviously.)

TooMany
2013-May-05, 11:50 PM
I have been thinking about this. Perhaps it depends what you mean by "new physics". For example, there are various attempts to make direct detection of various proposed particles which could make up dark matter. I'm not sure how experiments and detectors could be developed if it was new (in the sense of unknown) physics. As far as I know, all the proposed possibilities for dark matter as "stuff" (particles) are based on the standard model or other pre-existing theories. (I may be wrong about that, because I am not familiar with all the proposals, obviously.)

I would ask Shaula. All I know is that one hypothesis (beyond the standard model) called supersymmetry could potentially provide a WIMP, but as yet, the LHC has not provided evidence that confirms this hypothesis.

I think what lends credence to CDM and inflation is primarily that they supply potential solutions to theoretical problems. To say that these are based on observation is only true in the indirect sense that there were invented to explain observations that otherwise contradict physics. No need to repeat the neutrino story, a particle without which conservation of energy would collapse.

I guess the bottom line is that I wonder if we are barking up the wrong tree in our understanding of cosmology. Perhaps if I were as knowledgeable as Shaula I would understand the reasons for the apparent certainty that the the theory of expansion from an unbounded density and temperature is correct. For surely you would only invent new particles and inflation if you had no other choice.

Strange
2013-May-06, 12:07 AM
I would ask Shaula. All I know is that one hypothesis (beyond the standard model) called supersymmetry could potentially provide a WIMP, but as yet, the LHC has not provided evidence that confirms this hypothesis.

And that is basically what puzzles me. Supersymmetry is not "new physics"; it's not like it was invented to solve the dark matter problem. It has been around for decades. It is unconfirmed physics (as are a lot of ideas) but hardly "new".

But even if it is new physics, that is a good thing surely. The reason I love science is because it keeps discovering new things. There have been at least three major paradigm shifts in my lifetime. It's great!


To say that these are based on observation is only true in the indirect sense that there were invented to explain observations that otherwise contradict physics.

Isn't that true of every new and unexpected observation? (I'm not crazy about "contradict physics"; I would go with something more like, "don't fit current models" but never mind.)


No need to repeat the neutrino story, a particle without which conservation of energy would collapse.

Which is, of course, the perfect parallel to the current situation. Various hypotheses were proposed (*) and one eventually won out because of other observations.

(*) including abandoning, or at least seriously modifying, conservation of energy


I guess the bottom line is that I wonder if we are barking up the wrong tree in our understanding of cosmology.

As does everybody.


Perhaps if I were as knowledgeable as Shaula I would understand the reasons for the apparent certainty that the the theory of expansion from an unbounded density and temperature is correct.

Because it was predicted by general relativity (which is an incredibly well-tested theory) and confirmed by observation. You don't get much better than that in physics. (Not sure where you get the "unbounded density and temperature" from though.)


For surely you would only invent new particles and inflation if you had no other choice.

Absolutely. (Incidentally, I am far less convinced by inflation than dark matter.)

TooMany
2013-May-06, 12:56 AM
Supersymmetry is not "new physics"; it's not like it was invented to solve the dark matter problem. It has been around for decades. It is unconfirmed physics (as are a lot of ideas) but hardly "new".

But that is exactly what I am calling new physics, an unconfirmed conjecture about a property of nature. The fact that supersymmetry was proposed 30 years ago isn't evidence that it is real.



But even if it is new physics, that is a good thing surely. The reason I love science is because it keeps discovering new things. There have been at least three major paradigm shifts in my lifetime. It's great!


Sure it's a good thing if it's true. But if it is a crutch for a wrong idea, then it's not so good.



Which is, of course, the perfect parallel to the current situation. Various hypotheses were proposed (*) and one eventually won out because of other observations.

(*) including abandoning, or at least seriously modifying, conservation of energy


Well, no one wanted to abandon conservation of energy because it is so fundamental in physics. I don't think BBT is quite as fundamental.



Because it was predicted by general relativity (which is an incredibly well-tested theory) and confirmed by observation. You don't get much better than that in physics. (Not sure where you get the "unbounded density and temperature" from though.)


I'm not sure that is a fair claim. General relativity did not "predict" expansion of the Universe, the Universe could be doing the exact opposite (contracting) and still be consistent with GR. GR was around for a long time before the big bang theory was considered the "correct" interpretation of the red shift. It was around about a decade before the red shift was discovered and interpreted as expansion. Originally of course Einstein had proposed a cosmic constant to keep the Universe from collapsing. He declared that a big mistake after the red shift was discovered. Ironically, it has been revived in an attempt to incorporate dark energy into GR.

Retrospective prediction is an abuse of the word.



Absolutely. (Incidentally, I am far less convinced by inflation than dark matter.)

Then you need some other way to explain the smoothness.

Jean Tate
2013-May-06, 04:59 AM
All you are doing is stating your disagreement with MOND which is fine.

Ya know, it's difficult to hold a meaningful conversation when you summarize what I wrote like this.

Did I really come across like that to you? Did anyone else interpret what I wrote the same way?


But the popularity of non-baryonic CDM and inflation cannot disguise the fact that both require new physics, in the first case a new particle with certain properties and in the second, a new force with special conditions of action.

Hmm, after all this time, and all the hard work that others have put in to trying to explain this to you ... I know that much of today's physics is very difficult to wrap your mind around, and if all you read are the popularizations, it's very easy to misunderstand that physics in subtle yet profound ways. And I'm not sure what to do about it, that hasn't (apparently) already been tried (in this thread, to explain certain key aspects of astrophysics, and physics itself, to you).

I'll end with just this, before I go back to doing original research on spiral galaxies (which I must say is a lot more fun than engaging in what seems like sterile debate): we may, both of us (and all other readers of this thread today), live long enough to learn what the nature of DM is; some new particles? a modified form of GR? a radically new theory of gravity? all of the above? none of the above? Whatever it is, it will be interesting, likely very interesting. It is possible, but not very likely, that the key players will get Nobels. And maybe, just maybe, it will turn out to be a cruel combination of subtle aspects arcane corners of textbook physics. Whatever it is, it will surely be, in your words, new physics.

Shaula
2013-May-06, 06:10 AM
I guess the bottom line is that I wonder if we are barking up the wrong tree in our understanding of cosmology. Perhaps if I were as knowledgeable as Shaula I would understand the reasons for the apparent certainty that the the theory of expansion from an unbounded density and temperature is correct. For surely you would only invent new particles and inflation if you had no other choice.
The last sentence really sums it up. That is exactly what has happened. Every time one of these observations has come up old theories and new ones were rolled back out and tested. They did a worse job. You seem to have this idea that physicists generally enjoy just making stuff up so they can hang on to their old models. That is untrue. The LHC is a great example. Every scientist I know was saying to it "Come on, BREAK THE MODEL!". It was widely hoped that it would give us results that led to something new, something better. Its greatest disappointment is that it has not. Oh look, no strong CP violation. Oh look, a boring Higgs. The same is true of a lot of cosmological work. Trouble is that this is hard to get large grants for because generally with cosmology it is a longshot that this will happen for any one result - mainly because we just don't know what we are looking for there.


I think I get the impression of conviction from the sheer quantity of scientific papers concerning inflation. As though it is quite real. Inflation theories are undergoing a pruning process due to Planck and perhaps other observations. But even if a nicely matching theory is found, how can it be corroborated? What will it predict, beyond what we have already observed?
Inflation is part of the mainstream, obviously it will appear in a lot of publications. This does not mean no other work is being done and shared. The big journals have limited space. They tend to publish things that a lot of people can use, not another paper saying "This model does not work". As for how it can be tested? That is the point of developing a good theory. Inflation made a lot of predictions - signatures left in structure and the CMBR - that were tested for and used to better understand the basic model. As the theory gets better or more constrained more tests will be developed. There are some late peaks in the BAO that might be interesting, structure in the distribution of matter and abundance data that will provide tests. And those are just the ones we know of now.

Believe me, inflation is not just accepted and never tested. Ditto CDM And all the other bits of our cosmological model. Just because the default assumption is that it is a good model does not mean it is not tested. Every new piece of work has to start somewhere, has to assume that a certain body of physics is right. Otherwise every paper would start with re-proving GR and the Standard Model.

Strange
2013-May-06, 12:50 PM
Well, no one wanted to abandon conservation of energy because it is so fundamental in physics.

But it was considered. (Just to demonstrate that scientists are willing to make bold leaps if necessary.


I don't think BBT is quite as fundamental.

maybe not. But you would need "new physics" to replace it.



I'm not sure that is a fair claim. General relativity did not "predict" expansion of the Universe, the Universe could be doing the exact opposite (contracting) and still be consistent with GR. GR was around for a long time before the big bang theory was considered the "correct" interpretation of the red shift. It was around about a decade before the red shift was discovered and interpreted as expansion. Originally of course Einstein had proposed a cosmic constant to keep the Universe from collapsing. He declared that a big mistake after the red shift was discovered. Ironically, it has been revived in an attempt to incorporate dark energy into GR.

Retrospective prediction is an abuse of the word.

It is not a retrospective prediction. GR predicts expansion or contraction. The evidence gits with that. And not just in a general "handwavy" way but quantitatively.

TooMany
2013-May-06, 03:47 PM
But it was considered. (Just to demonstrate that scientists are willing to make bold leaps if necessary.



maybe not. But you would need "new physics" to replace it.




It is not a retrospective prediction. GR predicts expansion or contraction. The evidence gits with that. And not just in a general "handwavy" way but quantitatively.


The dictionary definition of "predict" is: to declare or indicate in advance; especially : foretell on the basis of observation, experience, or scientific reason.

There is an ordering in time. Finding a consistency of a theory with an observation is not a "prediction" by this definition. For example GR predicted that the path of light would be affected by a particular amount by a gravitational field. Subsequent to this prediction, the effect of the Sun on starlight was measured during an Eclipse and found to agree. However, GR did not predict the precession of Mercury's orbit; it was already well known.

Does it make sense to tune a theory with free parameters to observations and then say that the theory predicts those observations?

TooMany
2013-May-06, 04:15 PM
But you would need "new physics" to replace it.

I agree. There would have to another explanation using as yet undiscovered physics. The question in my mind is whether we have chosen a theory that matches some observations but is actually wrong. Could there be alternative new physics that explains redshift? I suppose that Shaula and other scientist in the field are quite convinced of the expansion due to multiple independent observations that are consistent with expansion. I'll come around for sure if JWT can show us in much greater detail the evolution since the CMB.

Shaula
2013-May-06, 04:38 PM
... I suppose that Shaula and other scientist in the field are quite convinced of the expansion due to multiple independent observations that are consistent with expansion...
Did you miss the bit where I said it was not a fact set in stone? That it was the best theory we have now? In short did you even read any of my responses qualifying what I thought of the theory? Or are you just simplifying the situation to make it easier to argue? If all you are going to do is insinuate that I am some dogmatic member of a cabal of scientists wedded to an untenable idea, while presenting nothing more than vague feelings, then this is not a useful discussion.

StupendousMan
2013-May-06, 04:58 PM
Strange wrote: GR predicts expansion or contraction.



The dictionary definition of "predict" is: to declare or indicate in advance; especially : foretell on the basis of observation, experience, or scientific reason.

There is an ordering in time. Finding a consistency of a theory with an observation is not a "prediction" by this definition. For example GR predicted that the path of light would be affected by a particular amount by a gravitational field. Subsequent to this prediction, the effect of the Sun on starlight was measured during an Eclipse and found to agree. However, GR did not predict the precession of Mercury's orbit; it was already well known.


Please read about the history of the cosmological constant. Then come back and post here again.

TooMany
2013-May-06, 06:04 PM
Please read about the history of the cosmological constant. Then come back and post here again.

I read this one The history of the cosmological constant problem (http://arxiv.org/pdf/gr-qc/0208027v1.pdf) that actually was not very clear as a history per se. However, it did clarify that the idea has been repeatedly offered to explain observations and then abandoned when a more satisfying explanation was found and then again proposed to solve yet another unexpected observation. Right now it is being applied as a possible way to incorporate the observed "dark energy" into GR. Apparently it has been in and out of favor a few times.

What is your point about this history?

trinitree88
2013-May-06, 06:08 PM
I agree. There would have to another explanation using as yet undiscovered physics. The question in my mind is whether we have chosen a theory that matches some observations but is actually wrong. Could there be alternative new physics that explains redshift? I suppose that Shaula and other scientist in the field are quite convinced of the expansion due to multiple independent observations that are consistent with expansion. I'll come around for sure if JWT can show us in much greater detail the evolution since the CMB.

"could there be alternative new physics that explains redshift.."? There is no doubt that velocity is involved in Doppler shifting light....but I just found a small article, that indicates we may be overlooking another contributor....SEE:http://arxiv.org/abs/1305.0427 the soft photon process. The energy cannot disappear, but ought to make itself known as a fairly uniform background hiss..

TooMany
2013-May-06, 06:23 PM
Did you miss the bit where I said it was not a fact set in stone? That it was the best theory we have now? In short did you even read any of my responses qualifying what I thought of the theory? Or are you just simplifying the situation to make it easier to argue? If all you are going to do is insinuate that I am some dogmatic member of a cabal of scientists wedded to an untenable idea, while presenting nothing more than vague feelings, then this is not a useful discussion.

No I did not miss that. You have stated that repeatedly. When new observations demand a change in theory, scientist will change it (there is of course a long history of changing theories). I don't think that the theory is untenable, it just seems a bit shaky, particularly with the inflation conjecture.

You may have misinterpreted my sentence that you quoted above. My meaning was this in other words: You and other scientist may be aware of multiple independent observations that corroborate the basic big bang theory that I am not aware of. (The basic BBT being: the entire universe was once extremely hot and dense, so much so that even nuclei could not yet exist and the Universe has been expanding, cooling and evolving ever since.) Such strongly corroborating evidence may provide the firm basis for sticking with the expansion theory.

TooMany
2013-May-06, 07:03 PM
"could there be alternative new physics that explains redshift.."? There is no doubt that velocity is involved in Doppler shifting light....but I just found a small article, that indicates we may be overlooking another contributor....SEE:http://arxiv.org/abs/1305.0427 the soft photon process. The energy cannot disappear, but ought to make itself known as a fairly uniform background hiss..

I heard a theory quite similar to that one to explain redshift. Some people in this forum suggested it was junk. The argument has always been that there is no known way for light to loose energy without scattering, implying that new physics would be required.

I'd never heard of a "soft photon" before. I'm trying to understand what that's about. Apparently it is mainstream.

StupendousMan
2013-May-06, 07:38 PM
I read this one The history of the cosmological constant problem (http://arxiv.org/pdf/gr-qc/0208027v1.pdf) that actually was not very clear as a history per se. However, it did clarify that the idea has been repeatedly offered to explain observations and then abandoned when a more satisfying explanation was found and then again proposed to solve yet another unexpected observation. Right now it is being applied as a possible way to incorporate the observed "dark energy" into GR. Apparently it has been in and out of favor a few times.

What is your point about this history?

My point was that when Einstein developed his theory of general relativity, he found that the equations of GR predicted that (depending on the average density of matter in the universe) space would be expanding or contracting -- or, if the density was _just_ the right value, static. He knew that the observations of the time showed no evidence for expansion or contraction. So, he added a constant of integration to the equations of motion which had _just_ the right value to cause the universe to be static.

Roughly 14 years later, Hubble published observational evidence for the expansion of the universe.

Hence, the theory of GR predicted the expansion of space.

TooMany
2013-May-06, 08:59 PM
My point was that when Einstein developed his theory of general relativity, he found that the equations of GR predicted that (depending on the average density of matter in the universe) space would be expanding or contracting -- or, if the density was _just_ the right value, static. He knew that the observations of the time showed no evidence for expansion or contraction. So, he added a constant of integration to the equations of motion which had _just_ the right value to cause the universe to be static.

Roughly 14 years later, Hubble published observational evidence for the expansion of the universe.


Hence, the theory of GR predicted the expansion of space.

You mean someone jumped out of their chair after reading GR and said "hey folks, the equations say the universe is expanding, let's go have a look and see if it's true"? That is not my understanding of what happened.

TooMany
2013-May-06, 09:08 PM
space would be expanding or contracting -- or, if the density was _just_ the right value, static

That's interesting. Are you saying that if you apply GR to static universe in which matter is distributed evenly but the density is low, it will start expanding? That's kind of counter intuitive because it implies a mysterious source of energy, continuous creation of energy as opposed to conservation. Is there any easy way to understand why that would be? What exactly is the critical density?

StupendousMan
2013-May-06, 09:32 PM
You mean someone jumped out of their chair after reading GR and said "hey folks, the equations say the universe is expanding, let's go have a look and see if it's true"? That is not my understanding of what happened.

Please read a bit about George Lemaitre. (http://en.wikipedia.org/wiki/Georges_Lema%C3%AEtre)

TooMany
2013-May-06, 09:51 PM
Please read a bit about George Lemaitre. (http://en.wikipedia.org/wiki/Georges_Lema%C3%AEtre)

Impressive guy. I didn't know that he had suggested the expansion solution in GR prior to Hubble's discoveries. Took a bit of observational convincing to get Einstein on board.

Jerry
2013-May-07, 08:47 AM
Did Carl Sagan ever do any professional work on cosmology?
...Where did Jim Peebles make that prediction? What prediction did he make? What do you mean by "precision cosmology"?Actually, Jim gave a speech at a conference stating we have entered the age of precision cosmology about the same time the WMAP team was giving us three sig figs on the age of the universe.

http://arxiv.org/abs/astro-ph/0208037

I gave away my Sagen CD's a long time age; and it would be difficult to tell whether Carl Sagan did any original work on cosmology or not simply because he wasn't strong on citing sources. Sagen was a champion of a well-defined universe; and his "universe in 31 day" calendar should be remembered by all. The are a lot of gaps in that calendar today, that did not appear in 1985.

Strange
2013-May-07, 10:48 AM
That's interesting. Are you saying that if you apply GR to static universe in which matter is distributed evenly but the density is low, it will start expanding? That's kind of counter intuitive because it implies a mysterious source of energy, continuous creation of energy as opposed to conservation. Is there any easy way to understand why that would be? What exactly is the critical density?

This might help: Expanding Space: the Root of all Evil? (http://arxiv.org/abs/0707.0380) The first part is non-mathematical and even some of the math can be followed "intuitively".

Strange
2013-May-07, 10:52 AM
Impressive guy. I didn't know that he had suggested the expansion solution in GR prior to Hubble's discoveries. Took a bit of observational convincing to get Einstein on board.

You might like this, as well:
http://blogs.nature.com/news/2011/07/letter_sheds_light_on_alleged.html
http://www.thehistoryblog.com/archives/13534

StupendousMan
2013-May-07, 12:41 PM
I gave away my Sagen CD's a long time age; and it would be difficult to tell whether Carl Sagan did any original work on cosmology or not simply because he wasn't strong on citing sources. Sagen was a champion of a well-defined universe; and his "universe in 31 day" calendar should be remembered by all. The are a lot of gaps in that calendar today, that did not appear in 1985.

It's not that hard to answer the question, "Did Carl Sagan do original research in the field of cosmology".

Go to the ADS Abstract Service:

http://adsabs.harvard.edu/abstract_service.html

Enter "Sagan, C" into the "Authors" field. Check the box for "require author for selection".

Enter "cosmology" into the "Abstract words" field. Check the box for "require text for selection".

Click on "Send Query".

Cougar
2013-May-07, 02:04 PM
...the sheer quantity of scientific papers concerning inflation. As though it is quite real.

Do you deny that inflation, or something like it, is needed to explain the universe we observe?

TooMany
2013-May-07, 07:02 PM
This might help: Expanding Space: the Root of all Evil? (http://arxiv.org/abs/0707.0380) The first part is non-mathematical and even some of the math can be followed "intuitively".

I read this article once before (and again just now). It was the first time that I could make sense of "expanding space" (or rather the first time I decided it did not make sense). I prefer not to think of it that way. In a situation without a cosmological constant, the expansion is inertial. If there are two comoving particles (e.g. galaxies distant from one another) and one is brought to rest with respect to the other, the distance between them will cease to expand. Thus to me "expanding space" seems like a misleading analogy. Some claim that the expansion is not experienced locally, e.g. in the solar system, because gravity works against it, as if the expansion is a force that must be countered to prevent local expansion. But after reading this paper I'm fairly certain that this is an incorrect understanding.

TooMany
2013-May-07, 07:17 PM
You might like this, as well:
http://blogs.nature.com/news/2011/07/letter_sheds_light_on_alleged.html
http://www.thehistoryblog.com/archives/13534

It's nice to know that Hubble is off the hook of an accusation of egotism. But they are separate discoveries. One was theoretically derived (and I believe quite a bit off the correct value due I suppose to poor data) while the other was achieved through dedicated work at the telescope without foreknowledge of a theoretic framework for the expansion. Both theoreticians and experimentalists deserve credit. Without observation, theory is worthless and without theory, there is no science, only taxonomy.

lpetrich
2013-May-07, 07:20 PM
Actually, Jim gave a speech at a conference stating we have entered the age of precision cosmology about the same time the WMAP team was giving us three sig figs on the age of the universe.

http://arxiv.org/abs/astro-ph/0208037
Seems to me that he's right about that.


I gave away my Sagen CD's a long time age; and it would be difficult to tell whether Carl Sagan did any original work on cosmology or not simply because he wasn't strong on citing sources. Sagen was a champion of a well-defined universe; and his "universe in 31 day" calendar should be remembered by all. The are a lot of gaps in that calendar today, that did not appear in 1985.
Constructing such a calendar is NOT the same thing as doing research into cosmology -- it's a form of popularization. I could easily do that myself, and Jerry, you also may be able to do that.

TooMany
2013-May-07, 07:23 PM
Do you deny that inflation, or something like it, is needed to explain the universe we observe?

That sounds like a cross examination by a prosecutor.

Do you deny that it is necessary only if many aspects/assumptions of BBT are in fact correct and there are no other possible explanations within the theory? Yes or no?

Jerry
2013-May-07, 11:17 PM
Do you deny that inflation, or something like it, is needed to explain the universe we observe?

????????

Inflation is a place holder - it is a difference between what was predicted; or what a well-reasoned extrapolation to the initial synthesis would have yielded and what we truly observe. How do you 'deny' something that is not understood? - something that cannot be checked using first principles?

Nothing is needed except a working model that works on first principles. We don't have one.

NoChoice
2013-May-07, 11:59 PM
Do you deny that inflation, or something like it, is needed to explain the universe we observe?

Deny?
Are you serious?

Inflation raises more questions than it answers and it adds another particle to the zoo (the inflaton), for which we don't even have a hint that it might exist.

Mystics and wise men over the millenia (and interestingly independent of social and/or religious background) have taught us that our view of the universe and "reality" in general, is all but an illusion.
They have all said that time doesn't exists (which conveniently throws that pesky little bugger called "causality" right out of the window).
They say that all that is is ever only now (that timeless eternal moment) and arises ever fresh (i.e. with no relation to what apparently arose "before").

Frankly, I find that hypothesis much more believable than most of contemporary cosmology. One could even elevate it to a theory since it matches all observations.

I am only half-serious but I am serious in saying that it seems much more consistent with observations than contemporary cosmology is!

Strange
2013-May-08, 12:33 AM
Thus to me "expanding space" seems like a misleading analogy.

Which is exactly the point of the paper. The trouble is that not only is the analogy (like all analogies) misleading but popular articles never explain that it is an analogy.


Some claim that the expansion is not experienced locally, e.g. in the solar system, because gravity works against it, as if the expansion is a force that must be countered to prevent local expansion. But after reading this paper I'm fairly certain that this is an incorrect understanding.

Another way of thinking of it is that the evolution of the scale factor ("expanding space") only happens in that way for the FLRW metric which requires a homogeneous distribution of mass. The universe is homogeneous on very large scales and so we see the expansion on those scales. Locally it is definitely not homogeneous and so the same simple approximation cannot be applied and hence no expansion expected.
(Or something like that.)

trinitree88
2013-May-08, 12:56 AM
Which is exactly the point of the paper. The trouble is that not only is the analogy (like all analogies) misleading but popular articles never explain that it is an analogy.



Another way of thinking of it is that the evolution of the scale factor ("expanding space") only happens in that way for the FLRW metric which requires a homogeneous distribution of mass. The universe is homogeneous on very large scales and so we see the expansion on those scales. Locally it is definitely not homogeneous and so the same simple approximation cannot be applied and hence no expansion expected.
(Or something like that.)
Ummm...the universe has most recently been seen not to be homogeneous on very large scales....the spins of galaxies indicate axisymmetry.

See:michael longo

Jens
2013-May-08, 02:07 AM
Ummm...the universe has most recently been seen not to be homogeneous on very large scales....the spins of galaxies indicate axisymmetry.


Has is? I would like to see the citation. I think it's a good question, but my impression from my own studies is that the universe has not been shown either to be homogenous or non-homogenous at large scales, i.e. there are papers arguing both sides of the issue. For example, this paper (http://arxiv.org/abs/1205.6812) argues it is homogeneous.

Shaula
2013-May-08, 05:26 AM
Ummm...the universe has most recently been seen not to be homogeneous on very large scales....the spins of galaxies indicate axisymmetry.

See:michael longo
Homogeneous distribution of mass is what was required. The possible parity violation on largest scales is perfectly capable of leaving that homogeneity intact. So that is not an argument against Strange's point.

Shaula
2013-May-08, 05:29 AM
Frankly, I find that hypothesis much more believable than most of contemporary cosmology. One could even elevate it to a theory since it matches all observations.

I am only half-serious but I am serious in saying that it seems much more consistent with observations than contemporary cosmology is!
The day they can make quantitative predictions in which a single fitted parameter explains loads of other phenomena is the day this statement is even close to being correct. As it stands this is complete hyperbole.

NoChoice
2013-May-08, 05:46 AM
The day they can make quantitative predictions in which a single fitted parameter explains loads of other phenomena is the day this statement is even close to being correct. As it stands this is complete hyperbole.

Well, the hypothesis I mentioned postulates time as illusion. Without time there is no causality and therefore inherently no predictions.
And yes, it was meant to be half hyperbole and half serious in the sense that it fits all observations. Inherently. To me, it seems a much better fit than inflation...
:evil:

Shaula
2013-May-08, 06:13 PM
Well, the hypothesis I mentioned postulates time as illusion. Without time there is no causality and therefore inherently no predictions.
And yes, it was meant to be half hyperbole and half serious in the sense that it fits all observations. Inherently. To me, it seems a much better fit than inflation...
:evil:
So you would rather have no model, no predictions and no way to make any. If every scientist who did not like an idea/theory took that line we'd probably still be trying to work out how fire worked.

The other important point is that by discarding any ability to predict you are outside the scientific method. So that idea is a far worse scientific model than even the most contrived, epicycle-filled lash-up would be.

Cougar
2013-May-08, 07:40 PM
Do you deny that inflation, or something like it, is needed to explain the universe we observe?

That sounds like a cross examination by a prosecutor.

It's a simple question, which I note you did not answer. Do I need to submit a Motion to Compel? :p


Do you deny that it [inflation] is necessary only if many aspects/assumptions of BBT are in fact correct and there are no other possible explanations within the theory? Yes or no?

Yes, I deny that. How else can the Horizon Problem be answered if not for "inflation, or something like it"?


The Horizon Problem: If one were to look at a galaxy ten billion light years away in one direction, say "west", and another in the opposite direction, "east", the total distance between them is twenty billion light years. This means that the light from the first has not yet reached the second, because the 13.8 billion years that the universe has existed simply isn't a long enough time to allow it to occur.


The Horizon Problem is not an assumption of the Big Bang. It is a simple observation. I repeat my question: Do you deny that inflation, or something like it, is needed to explain the universe we observe?

Jean Tate
2013-May-08, 09:04 PM
(snip)
I'll end with just this, before I go back to doing original research on spiral galaxies (which I must say is a lot more fun than engaging in what seems like sterile debate):
(snip)

Ummm...the universe has most recently been seen not to be homogeneous on very large scales....the spins of galaxies indicate axisymmetry.

See:michael longo

Not so fast! Wednesday, 13th July, 2011: What do you think of this? (http://www.galaxyzooforum.org/index.php?topic=279300.0)

A Galaxy Zoo forum (http://www.galaxyzooforum.org/index.php) thread, in the Object of the Day (http://www.galaxyzooforum.org/index.php?board=5.0) section, by me.

Anyone interested in joining me in my research into what the Longo (http://adsabs.harvard.edu/abs/2011PhLB..699..224L) and Land et al. (2008) (http://adsabs.harvard.edu/abs/2008MNRAS.388.1686L) research really found?

TooMany
2013-May-08, 09:04 PM
Yes, I deny that. How else can the Horizon Problem be answered if not for "inflation, or something like it"?

Cougar, I am not at all convinced that inflation is necessary. It was invented to make the model chosen continue to work in the face of unexpected observations. According to BBT the initial condition of the universe must be singular. That is, there is no limit on how great the energy density was as you approach time zero. That is just an assumption that we find pleasing, because we like to think that our expansion model can be worked backwards to such a state. What happened at T 0? We are clueless, but we are happy to play with any time after T 0.

An alternative theory of expansion is that, at the beginning of expansion, the universe had a finite density and inherent smoothness. You may say "nonsense, that just an arbitrary assumption", but so is the BBT idea of limitless density. In BBT you talk about astoundingly early periods like 10-33 seconds. We can't seriously claim to know physics under those conditions, so speculating about an inflation field is just playing theoretical games to make this model work. Inflation theory is not some evidence that supports BBT, but it seems to be interpreted by some as support for the theory.

Demanding that I accept inflation as a necessary consequence of observation is demanding that I accept the BBT model as absolutely correct and that I agree that there is no other possible solution in the context of that model. I'm not convinced of either.




The Horizon Problem: If one were to look at a galaxy ten billion light years away in one direction, say "west", and another in the opposite direction, "east", the total distance between them is twenty billion light years. This means that the light from the first has not yet reached the second, because the 13.8 billion years that the universe has existed simply isn't a long enough time to allow it to occur.


The Horizon Problem is not an assumption of the Big Bang. It is a simple observation. I repeat my question: Do you deny that inflation, or something like it, is needed to explain the universe we observe?

The horizon problem is created by BTT model. The smoothness of the CMB and perhaps the distribution of matter is assumed to require thermodynamic equilibrium among distant parts of the visible universe. Because the BBT assigns a finite age to the universe, and because it is expanding so fast, it is difficult to find a way to explain the equilibrium. The inflation conjecture, with appropriately chosen parameters, is used to eliminate the contradiction with observation. It says that the tiny part of the "ultra early" universe that contained us was in thermodynamic equilibrium. But that's not enough because the expansion rate observed is insufficient to make that tiny part the size of the visible universe. But, if the universe expanded by a factor of 1078 (nearly a google) in brief period at 10-33 seconds, then the part that was in thermal equilibrium would exceed the size of the visible universe today.

I'm compelled to believe this?

My play expansion theory is simpler. The Universe began expanding with finite density and smoothness over that volume which has since expanded to become the visible universe. We don't know how the expansion began anyway, so what's the difference?

I certainly cannot state that a particular unobserved event is required to explain the universe we observe. I think for even the greatest cosmologists, that would be a profound claim.

Jean Tate
2013-May-08, 09:17 PM
TooMany,

In the very first part of this post of yours, you say stuff that I'm 99.9% sure you know is quite untrue.

Yet you write it anyway!

Why? Did you simply not read the many posts by others, carefully explaining this to you? Or read it, but completely fail to understand it? Or understand it, but were determined to ignore it anyway?


According to BBT the initial condition of the universe must be singular. That is, there is no limit on how great the energy density was as you approach time zero. That is just an assumption that we find pleasing, because we like to think that our expansion model can be worked backwards to such a state.

Must every response to posts of yours contain a full recap of the core concepts of GR and QFT (in particular the Standard Model), before they can even begin to address the much finer points under discussion?

Question for other CQuestians: how - politely, rationally, succinctly - do you respond to this sort of (willful?) ignorance?

trinitree88
2013-May-08, 10:00 PM
Not so fast! Wednesday, 13th July, 2011: What do you think of this? (http://www.galaxyzooforum.org/index.php?topic=279300.0)

A Galaxy Zoo forum (http://www.galaxyzooforum.org/index.php) thread, in the Object of the Day (http://www.galaxyzooforum.org/index.php?board=5.0) section, by me.

Anyone interested in joining me in my research into what the Longo (http://adsabs.harvard.edu/abs/2011PhLB..699..224L) and Land et al. (2008) (http://adsabs.harvard.edu/abs/2008MNRAS.388.1686L) research really found?

I find it interesting that you focus on the outliers in the study, and not the general statistics in order to attempt a discreditation. It is clear that he increased his sample size in order to improve the reliability of his stats and that his initial results hold. Looks to me like somebody is running scared. As to schaula'sreply that it is the homogeneity of the mass distribution that is critical, not the parity symmetry....that was shown to fail when the hubble deep field photos showed that the southern field had twice as many galaxies as the northern field per steradian.

Are cosmologists now going to insist that the average mass is just half of the northern counterparts??...or will they now insist that there just happens to be twice as much dark matter in the northern galaxies. Getting pretty ludicrous. Pete

Strange
2013-May-08, 10:00 PM
Cougar, I am not at all convinced that inflation is necessary.

Interestingly, neither is Steinhardt (one of the developers of inflation theory). However, I don't know whether you would find the alternatives any more palatable.


According to BBT the initial condition of the universe must be singular. That is, there is no limit on how great the energy density was as you approach time zero. That is just an assumption that we find pleasing, because we like to think that our expansion model can be worked backwards to such a state.

That is what happens if you wind the model back to t=0 but I'm not sure anyone thinks that is a meaningful thing to do.


What happened at T 0? We are clueless, but we are happy to play with any time after T 0.

Exactly.


An alternative theory of expansion is that, at the beginning of expansion, the universe had a finite density and inherent smoothness.

That doesn't solve anything, though.


You may say "nonsense, that just an arbitrary assumption", but so is the BBT idea of limitless density.

Except the big bang theory doesn't include (or require) such an assumption.


In BBT you talk about astoundingly early periods like 10-33 seconds. We can't seriously claim to know physics under those conditions

The earliest times that are discussed in detail are those where it is thought the physics does still work. Of course, that may turn out to be wrong when, for example, we have a quantum theory of gravity.


My play expansion theory is simpler. The Universe began expanding with finite density and smoothness over that volume which has since expanded to become the visible universe.

To me, that explanation is equivalent to "magic happened". I know you think the same about inflation theory, but at least that is an attempt to explain the conditions we see. It may be wrong. But surely it is better than saying, "that's just the way it was".

Shaula
2013-May-08, 10:00 PM
According to BBT the initial condition of the universe must be singular
No. This is a very common misconception that has been corrected on this forum many times. BBT does not go back to a singularity because the theories it is based on break down before that point it reached and become invalid. BBT states that the observable universe evolved from a hot, dense state a finite time ago. And that is all. It does not include singularities, the theory becomes invalid before that.

Shaula
2013-May-08, 10:05 PM
As to schaula'sreply that it is the homogeneity of the mass distribution that is critical, not the parity symmetry....that was shown to fail when the hubble deep field photos showed that the southern field had twice as many galaxies as the northern field per steradian.
Reference? And did this show up in the EDF? And, of course, what is the statistical significance of this over such a tiny area of sky? Really need a deep sky survey to show a meaningful result.

Jean Tate
2013-May-08, 10:31 PM
I find it interesting that you focus on the outliers in the study, and not the general statistics in order to attempt a discreditation.

Hmm ... are we reading the same material?

The RA distribution of <A> of the galaxies with the greatest 'certainty' (i.e. those with >95% of votes for CW or for ACW) is consistent with a constant, the group mean (reduced chi2 =1.22±0.47, 9 dof). It's the galaxies which were less certainly classified that create the entire 'signal' in RA (and the two subsets are not correlated).


It is clear that he increased his sample size in order to improve the reliability of his stats and that his initial results hold.

Did you read the Longo paper? There no controls, multiple instances of the same object were not removed (this is a challenge doing this sort of work with SDSS images; one solution is discussed in Land et al.), and so on.


Looks to me like somebody is running scared. (snip)

If I may channel TooMany, looks to me like somebody didn't bother to read the material before making a snap judgement.

Jean Tate
2013-May-08, 11:11 PM
As to schaula'sreply that it is the homogeneity of the mass distribution that is critical, not the parity symmetry....that was shown to fail when the hubble deep field photos showed that the southern field had twice as many galaxies as the northern field per steradian.Reference? And did this show up in the EDF? And, of course, what is the statistical significance of this over such a tiny area of sky? Really need a deep sky survey to show a meaningful result.

Like COSMOS (http://arxiv.org/abs/astro-ph/0612306).

I don't remember reading anything in any papers which reported the sort of thing trinitree88 is claiming. And isn't the (expected) variation in number of galaxies per unit of sky real estate called 'cosmic variance'? Something which is very much on the minds of those who plan deep surveys ...

TooMany
2013-May-08, 11:35 PM
TooMany,

In the very first part of this post of yours, you say stuff that I'm 99.9% sure you know is quite untrue.

Yet you write it anyway!

Why? Did you simply not read the many posts by others, carefully explaining this to you? Or read it, but completely fail to understand it? Or understand it, but were determined to ignore it anyway?



Must every response to posts of yours contain a full recap of the core concepts of GR and QFT (in particular the Standard Model), before they can even begin to address the much finer points under discussion?

Question for other CQuestians: how - politely, rationally, succinctly - do you respond to this sort of (willful?) ignorance?

If you want to lay it on that thick, you should be more specific.

TooMany
2013-May-09, 12:36 AM
Interestingly, neither is Steinhardt (one of the developers of inflation theory). However, I don't know whether you would find the alternatives any more palatable.

Probably not, but as long as there is no verification, it really doesn't matter. I know we all want a good theory, but if we haven't got one, so be it. We just keep trying, maybe even try to think out of the box, which is the current theory.



That is what happens if you wind the model back to t=0 but I'm not sure anyone thinks that is a meaningful thing to do.


I agree that it's not meaningful to get so close that we have no empirical data to use. The inflation hypothesis takes it incredibly close to t=0. -33 is a big exponent. Nucleosynthesis happens (according to Wiki) between 0.1 sec and 1,000 seconds.



That doesn't solve anything, though.

No, but what does inflation solve when it's not based on any known physics?



Except the big bang theory doesn't include (or require) such an assumption.

I was trying to suggest that having detected expansion now, does not tell us that it must have started from a condition of unbounded density. That is an assumption that was chosen in building the theory. Perhaps we can attribute the idea to George Lemaitre who talked about a primordial atom. (To his credit he refused to consider his theory as creationism.)



The earliest times that are discussed in detail are those where it is thought the physics does still work. Of course, that may turn out to be wrong when, for example, we have a quantum theory of gravity.


Except that the calculations using known physics work only when we add that 75% of mass was made of something we haven't detected yet that does not interfere with our known nuclear physics. This is thought to also be a solution for the missing mass problem, so that makes it quite a bit more attractive as a conjecture than inflation.



To me, that explanation is equivalent to "magic happened". I know you think the same about inflation theory, but at least that is an attempt to explain the conditions we see. It may be wrong. But surely it is better than saying, "that's just the way it was".

The universe increasing in size by a factor 1078 in 10-36 seconds, without a reason that it should have, is not much less magical.

In defense of my toy theory, perhaps the universe is cyclic and only compresses to a finite density. If it's been doing that forever maybe it's OK that it's just smooth and stays that way. Of course I can't back this up, but maybe such a theory could be formed.

There is one really big advantage that an expansion theory has over steady state - maintaining a steady state is a very complicated business (hard to address with a theory).

TooMany
2013-May-09, 12:48 AM
Homogeneous distribution of mass is what was required. The possible parity violation on largest scales is perfectly capable of leaving that homogeneity intact. So that is not an argument against Strange's point.

Required for what? Describing the expansion, nucleosynthesis? One of the tenants is the Cosmological Principle which requires isotropy on large scales. In this recent paper by Longo (http://arxiv.org/abs/1104.2815) it is claimed that it is violated in addition to parity. A number of large scale anomalies have been found in the CMB. Will they all be whisked away, as in Land's attempt (http://arxiv.org/abs/0803.3247) to do so with spiral direction?

Cougar
2013-May-09, 04:26 AM
Cougar, I am not at all convinced that inflation is necessary.... According to BBT....

Don't change the subject. I'm talking about the Horizon Problem. You just waved that off with stuff like....


In BBT you talk about astoundingly early periods like 10-33 seconds....

That is a specific proposed detail of the theory that we obviously know little about. I'm talking about something we can observe and measure and something we do know about -- the Horizon Problem.


The horizon problem is created by BTT model....

No, it's not. It's created by our measurement of distance, and you have not addressed the problem. You think there's something wrong with the way distance is measured? You think we should measure distance differently? Let's hear it.


Because the BBT assigns a finite age to the universe....

You think there's something wrong with the current estimate of the Universe's age? If that's a yes, then there is seriously no reason to engage in any further discussion with one, as Jean noted, so wilfully ignorant. Fact is, the current age estimate is refined and confirmed by about 5 different, completely independent methods for estimating the age, most of which are big-bang independent. So, are you going to actually address the Horizon Problem or what?

Shaula
2013-May-09, 05:33 AM
I was trying to suggest that having detected expansion now, does not tell us that it must have started from a condition of unbounded density.
Did you miss my other post? The one where I pointed out that this is not what the BBT says. It is not required for the theory, not a part of the theory, not a requirement of nucleosynthesis and so on and so on.


Required for what? Describing the expansion, nucleosynthesis?
Suggest you actually read the post in context. Trinitree first tried to claim that a possible parity violation invalidated a previous argument. So I pointed out that this counter was totally irrelevant to the actual argument he was trying to counter. I am not even arguing, as you have now tried to claim, that there is no inhomogeneity. I am doing what a scientist or anyone interested in science should do. Checking the data behind the assertions being made, pointing out logically flawed arguments and generally highlighting that while people here are complaining that the current models are full of suppositions and epicycles their own arguments have little to no scientific merit and are fundamentally based not on healthy scepticism but a determination to find something that discredits an idea they don't like.

Swift
2013-May-09, 01:57 PM
This thread is closed pending moderator discussion.

Swift
2013-May-10, 12:49 PM
TooMany,

In the very first part of this post of yours, you say stuff that I'm 99.9% sure you know is quite untrue.

Yet you write it anyway!

Why? Did you simply not read the many posts by others, carefully explaining this to you? Or read it, but completely fail to understand it? Or understand it, but were determined to ignore it anyway?

Question for other CQuestians: how - politely, rationally, succinctly - do you respond to this sort of (willful?) ignorance?
The moderation team is struggling to come to a consensus on responses (if any) for this thread, but I wish to make it clear that posts like this are not acceptable. If you feel another member's posts are ATM or otherwise inappropriate, you Report the post(s). You do not make assumptions about others' motives and you do not try to raise a posse of members against them.

Meanwhile, this thread remains closed