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Cosmologist
2012-Dec-09, 04:40 AM
http://www.universetoday.com/98864/do-we-really-need-dark-matter/

I never understood the focus on dark matter and energy. science is supposed to be based on evidence.

Shaula
2012-Dec-09, 05:36 AM
It doesn't explain galactic rotation curves or elemental abundances so claiming dark matter doesn't exist is premature. Although to he be fair he has not made this claim. He has put forwards an interesting idea though - hope he does more work on it.

The rotation curves thing really is a big deal in this case because if there is more matter in the galaxies then it could support his idea or damage it quite badly depending on whether or not a baryonic fix can be found for these curves. So far it looks unlikely, relying on very, very tuned mass distributions or billions of billions of objects that are hard to form and harder to preserve. Detailed simulations of structure formation need to be done to see if his model can actually replicate our universe as we see it without a non-interacting fluid.

So, sensationalist topic title aside it is an interesting piece of work and if he is right could reduce the need for dark matter. It will mean a lot of other things need to be added to cosmological models though so any claims that it is simpler are on thin ice.

And BTW Science is based on evidence, that is why we have had to hypothesise dark matter and energy. At the moment they are the best fit to the evidence we have. If theory turns out to have legs then the consensus will change. That is how science works.

Cougar
2012-Dec-09, 02:57 PM
The paper itself says: (http://arxiv.org/abs/1212.1110)


According to Einstein’s special relativity, an observer moving at high velocity with respect to an external observer will measure time flowing at a slower pace than the outside observer.

Perhaps this is just poorly worded in the paper, but the "observer moving at high velocity" observes the time on his own clock as flowing normally. Only the outside observer measures the clock of the person moving at high velocity to be flowing slower than his own clock.

Jens
2012-Dec-10, 12:55 AM
I only read the blog entry, not the paper, but it sounds like he is mainly arguing against the need for dark energy. There is nothing mentioned about how to explain the rotation curves of galaxies without dark matter. . . Maybe it's in the paper.

Shaula
2012-Dec-10, 06:12 AM
I only read the blog entry, not the paper, but it sounds like he is mainly arguing against the need for dark energy. There is nothing mentioned about how to explain the rotation curves of galaxies without dark matter. . . Maybe it's in the paper.
It isn't - just cluster dynamics.

Cosmologist
2012-Dec-10, 11:08 PM
In a paper titled “An expanding universe without dark matter and dark energy” (arXiv:1212.1110) Pierre Magain, a professor at Belgium’s Institut d’Astrophysique et de Géophysique, proposes that the expansion of the Universe could be explained without the need for enigmatic material and energy that, to date, has yet to be directly measured.

Seems explicit enough.

Dark matter gets far too much attention. Its always on the cover of astronomy magazines and gets discussed like its real. I like the new estimate for the age of the universe at around 15.4 – 16.5 billion years old.


The benefit to a slightly older Universe, Magain posits, is that it’s not so uncannily close to the apparent age of the most distant galaxies recently found — such as MACS0647-JD, which is 13.3 billion light-years away and thus (based on current estimates, see graphic at right) must have formed when the Universe was a mere 420 million years old.

Could a stable galaxy form in just 420 million years? The earth took longer than that to cool down and settle into a semi-stable state. I agree with Magain that there should be a larger gap between the Big Bang and the formation of the first galactic structures.

Shaula
2012-Dec-10, 11:18 PM
Yeah, the pop-sci summary does seem pretty explicit. Shame the paper doesn't actually support that. It'd be better to base your comments on the paper, not the journalist's take on it. The paper admits it cannot deal with galactic rotation curves. Or nucleosynthesis. So it is not complete. As I said, it is an interesting paper, I'd like to see more come out of it but both your thread title and the article are sensationalist and inaccurate based on the paper.


Dark matter gets far too much attention. Its always on the cover of astronomy magazines and gets discussed like its real.
It is the current best fit to our observations. Would you also like to see less cover space give to quarks, the Higgs boson and just about anything else we cannot directly see? Alternative explanations are always being tested, and have been tested in the past. Until one of them has equal or better predictive power than the current models it is basically poor science to pick the model you happen to feel more comfortable with.

Van Rijn
2012-Dec-10, 11:20 PM
It isn't - just cluster dynamics.

Ouch. How can someone argue against dark matter and not cover galaxy rotation curves?

Van Rijn
2012-Dec-10, 11:21 PM
The paper admits it cannot deal with galactic rotation curves. Or nucleosynthesis. So it is not complete.


I read this after I posted. Good that the author admits to the issue at least.

Shaula
2012-Dec-10, 11:31 PM
It is a good paper actually. Refreshingly honest with what it can and cannot do, treats errors well and highlights where the data it uses for support is weak. I am glad the OP brought it to our attention, it is interesting to read. I just wish it wasn't being sensationalised by that article and the initial post.

Cosmologist
2012-Dec-10, 11:45 PM
Sensationalism is Universe Todays stock and trade. Can't blame the author of the article for that. He isn't even a scientist. as for my initial post all I did was link to an article on the main page here. My comment "I never understood the focus on dark matter and energy. Science is supposed to be based on evidence." is valid. The title reflects the core premise of the article. Dark matter is only a theory.

ASTRO BOY
2012-Dec-11, 12:34 AM
I once had an Astronomer named Geraint Lewis tell me we have more evidence for DM then we do for BH's.

He is the Professor of Astrophysics at University of Sydney and his reserach is in the areas of DE and DM.

TooMany
2012-Dec-11, 12:58 AM
I once had an Astronomer named Geraint Lewis tell me we have more evidence for DM then we do for BH's.

He is the Professor of Astrophysics at University of Sydney and his reserach is in the areas of DE and DM.

Assuming GR is correct, we have very good evidence that there is much unseen mass, hence the name "dark matter". There is also a need for a non-interacting mass to make BB nucleosynthesis match observed proportions of elements. Hence the usual conclusion is that the "dark matter" consists of some yet to be discovered particle. Super Symmetry (SUSY) theory (around since the 80's but undemonstrated) predicts a particle that could account for the dark matter. Lately though substantial doubt has been cast on super symmetry since the most popular expectations have been ruled out by the LHC.

Strange
2012-Dec-11, 01:06 AM
Dark matter is only a theory.

Only a theory? So you are convinced then. I might have gone for only a hypothesis.

Cosmologist
2012-Dec-11, 01:17 AM
Is that why the Aquatic Ape Theory was renamed the aquatic ape Hypothesis by its supporters? Semantics.

cjameshuff
2012-Dec-11, 01:32 AM
Sensationalism is Universe Todays stock and trade. Can't blame the author of the article for that. He isn't even a scientist. as for my initial post all I did was link to an article on the main page here. My comment "I never understood the focus on dark matter and energy. Science is supposed to be based on evidence." is valid. The title reflects the core premise of the article. Dark matter is only a theory.

It is actually a name for a particular departure of observation from theoretical predictions, leading to the development of an assortment of new theories attempting to explain and describe the appearance of excess mass. In other words, science, based on evidence.

Cosmologist
2012-Dec-11, 02:32 AM
We dont know why galaxies are holding themselves together as the observable mass is insufficient to do the job. Probably something to do with that giant black hole at the core of most galaxies. A theory based on meagre circumstantial observations. no evidence exists. Just coincidental happenstance. Dark exotic matter is just a brain fart.

Hornblower
2012-Dec-11, 04:07 AM
We dont know why galaxies are holding themselves together as the observable mass is insufficient to do the job. Probably something to do with that giant black hole at the core of most galaxies. A theory based on meagre circumstantial observations. no evidence exists. Just coincidental happenstance. Dark exotic matter is just a brain fart.

We infer the existence of black holes by their gravitational effects on their surroundings, and we infer the presence of diffuse dark matter in much the same way. If all of the additional mass was in the form of a central black hole, the orbital velocities of the outlying stuff would be much closer to Kepler's laws rather than being more nearly constant as a function of orbital radius. The dark matter has to be spread out over the full extent of the galaxy, at gradually decreasing density with larger radius, to account for the observed velocities.

ASTRO BOY
2012-Dec-11, 04:53 AM
Assuming GR is correct, we have very good evidence that there is much unseen mass, hence the name "dark matter". There is also a need for a non-interacting mass to make BB nucleosynthesis match observed proportions of elements. Hence the usual conclusion is that the "dark matter" consists of some yet to be discovered particle.


Hi Too Many.....I'm not arguing the existence or otherwise of DM...I agree that the accumalitive evidence we have, especially the "Bullet Cluster" observations gives it solid theoretical status at this stage......
I am sceptical of what the mentioned Astronomer told me about more evidence for DM then BH's. It was his pet project at the time and I'm convinced he was showing some slight bias.

cjameshuff
2012-Dec-11, 05:06 AM
We infer the existence of black holes by their gravitational effects on their surroundings, and we infer the presence of diffuse dark matter in much the same way. If all of the additional mass was in the form of a central black hole, the orbital velocities of the outlying stuff would be much closer to Kepler's laws rather than being more nearly constant as a function of orbital radius. The dark matter has to be spread out over the full extent of the galaxy, at gradually decreasing density with larger radius, to account for the observed velocities.

More, the mass of the central black hole can be measured by the motions of the stars in the immediate vicinity. In most cases, you need many times the total visible mass to explain the rotation rate of stars near the rim of the galaxy. The mass of that black hole? Typically on the order of a millionth or so of the overall mass of the galaxy. The black hole has almost no effect on the rotation curve of the galaxy as a whole. Somewhat of a problem for Cosmologist's suggested alternative...

And then there's galaxy cluster motions, gravity lensing observations, etc...

Shaula
2012-Dec-11, 08:09 AM
We dont know why galaxies are holding themselves together as the observable mass is insufficient to do the job. Probably something to do with that giant black hole at the core of most galaxies. A theory based on meagre circumstantial observations. no evidence exists. Just coincidental happenstance. Dark exotic matter is just a brain fart.
You may be right, you may be wrong. Whichever it turns out to be in the long run you have come to that conclusion via a non-scientific method. Which is why is it pretty pointless you trying to use it to justify your beliefs. The consensus is that DM is required. When a better theory comes along it may not be required any more. But until then trying to rubbish it based on your personal assessment and the discounting of data and work that disagrees with your belief is a very poor way to go about science.

As for your post not being sensationalist - what is the title? And what does the paper say? Sensationalist. You are stating as fact something the paper does not support.

TheTruthSeeker
2012-Dec-19, 03:04 PM
Hi everyone

I have a few questions about what i have read on this thread.

Is dark matter just ordinary matter that is not illuminated?
Is dark matter just matter that we can not observe either because the light is too dim for us to see or is absorbed by other objects before it reaches us?
Is it right to say that if a black hole contains matter - then a black hole has created dark matter because it does not allow us to see that matter?

antoniseb
2012-Dec-19, 05:12 PM
Hi everyone

I have a few questions about what i have read on this thread.

Is dark matter just ordinary matter that is not illuminated?
Is dark matter just matter that we can not observe either because the light is too dim for us to see or is absorbed by other objects before it reaches us?
Is it right to say that if a black hole contains matter - then a black hole has created dark matter because it does not allow us to see that matter?
No, Dark Matter is a technical term that refers specifically to matter which does not interact much with normal matter... so neutrinos are an example of dark matter. As to whether small black holes are a constituate of the observed (by its effects) Dark Matter, that has not been ruled out, but that doesn't appear to be what you were asking.

cjameshuff
2012-Dec-19, 06:48 PM
No, Dark Matter is a technical term that refers specifically to matter which does not interact much with normal matter... so neutrinos are an example of dark matter. As to whether small black holes are a constituate of the observed (by its effects) Dark Matter, that has not been ruled out, but that doesn't appear to be what you were asking.

A quibble: technically, "dark matter" is all matter that's not directly detectable by light (or other areas of the electromagnetic spectrum, like radio). We see that it's there, but we don't see it itself. Matter that's not illuminated does qualify, but there are strong limits to how much can be around without obviously blocking light, being directly visible itself, etc. The maximum amount of dark "normal" matter is a small fraction of what is required to explain the gravitational effects we see.

Various other alternatives have been ruled out, and the most successful theory remaining is that most dark matter is some completely different form of matter that only interacts via the weak and gravitational forces. There aren't enough neutrinos to account for dark matter, but they are proof that weakly interacting matter isn't a physically absurd suggestion. There is strong evidence that most dark matter is such a form of matter in some galaxy collisions, where we see the gravitational lensing of dark matter separated from normal matter.

The paper that the article Cosmologist linked was about an attempt to explain the expansion of the universe without dark matter, ignoring the other evidence that it exists. Magain is basically describing a universe with much less matter than the one we appear to be in, and he estimates an age that disagrees with the age estimated with other approaches. Cosmologist's comments about science being based on evidence seem to be aimed at the wrong target.

SRH
2012-Dec-19, 07:03 PM
Could someone please explain the details of the anomaly...

"There is also a need for a non-interacting mass to make BB nucleosynthesis match observed proportions of elements."


Thanks.

Shaula
2012-Dec-19, 09:17 PM
Basically nucleosynthesis occurs by a series of steps, building up from protons/neutrons to larger atoms (Helium, Deuterium and so on). The probability of these collisions is very sensitive to the density of the material. By diluting the hot proton/neutron soup with dark matter you can tune the amount of deuterium and helium produced. It so happens that the amount of dilution required agrees with the amount of DM we infer from other measurements.

TheTruthSeeker
2012-Dec-20, 11:16 AM
How much matter should there be in the universe compared to how much we can see?

Also how can we know how much matter is in the universe? and how can we know how much matter there should be?- if we could see the whole universe then the there would be no debate on wether or not its infinite.
if we cannot see the whole universe then we cannot say there is not enough matter in the universe because it may be in places that we cannot see.

Amber Robot
2012-Dec-20, 05:50 PM
A quibble: technically, "dark matter" is all matter that's not directly detectable by light (or other areas of the electromagnetic spectrum, like radio). We see that it's there, but we don't see it itself. Matter that's not illuminated does qualify, but there are strong limits to how much can be around without obviously blocking light, being directly visible itself, etc. The maximum amount of dark "normal" matter is a small fraction of what is required to explain the gravitational effects we see.


Which is why the term "non-Baryonic dark matter" is talked about by professionals.

Shaula
2012-Dec-20, 06:07 PM
How much matter should there be in the universe compared to how much we can see?

Also how can we know how much matter is in the universe? and how can we know how much matter there should be?- if we could see the whole universe then the there would be no debate on wether or not its infinite.
if we cannot see the whole universe then we cannot say there is not enough matter in the universe because it may be in places that we cannot see.
It is not about absolute volumes, it is about density. We can see only a small amount of the 'stuff' the universe (the observable universe) is made up of. In pure mass terms we can see about 10-15% of the matter that has to be out there. We know it out there from several lines of evidence - galactic rotation curves, galactic cluster dynamics, the abundances of different nuclei in the universe.

So we know it is there, we see its gravity and other effects it has had on matter through the universe's history. From these observations we can deduce some of the properties is must have, which rules out it all being baryonic matter.

TheTruthSeeker
2012-Dec-20, 09:50 PM
Thanks Shaula - that fits nicely into my own theory - i would like others to comment on whether these figures are accurate according to the mainstream and i will also check other sources. its not that i dont trust you its just that i prefer to have as many sources as possible :-)

just to be sure i do get what your saying ill put it into my own words.

current observations of the visible universe lead us to conclude that there must be more matter out there than we can see because there is more gravity than the visible universe could provide on its own. we call this "dark matter".

Cougar
2012-Dec-21, 12:20 AM
We dont know why galaxies are holding themselves together as the observable mass is insufficient to do the job. Probably something to do with that giant black hole at the core of most galaxies.

It definitely does not have anything to do with the supermassive black hole at the center of galaxies, as Hornblower explained. It's surprising that you're dissing dark matter, but you apparently know so little about it....

Shaula
2012-Dec-21, 08:27 AM
current observations of the visible universe lead us to conclude that there must be more matter out there than we can see because there is more gravity than the visible universe could provide on its own. we call this "dark matter".
Yes but with two caveats. One - there is not more gravity in the sense that just turning up gravity would work. The missing mass has the be distributed in the right way (luckily this right way is also physically plausible given its other properties - i.e. it ended up where it should have ended up). Two - there are other lines of evidence that would lead you to proposing dark matter even if the galactic rotation curves were purely Newtonian.

TheTruthSeeker
2012-Dec-21, 09:14 AM
I dont quite understand - given that dark matter has not actually been proven to exist yet - how anyone can say that it is distibuted in the right way and has ended up where it should be. From what i understand the models can only show you where the dark matter should be in order explain the observations. By saying it ended up where it should have ended up is the same as saying that you have direct proof that it is actually there rather than saying we believe its there because it makes sense that it is there.

is it proven to be there?
or is it belived to be there as a way to balance the equation?

antoniseb
2012-Dec-21, 11:44 AM
I dont quite understand -
...is it proven to be there?
or is it belived to be there as a way to balance the equation?
What do you think you mean by 'proven'? We observe where DM is by several methods, such as how its gravitational influence distorts the apparent shapes of background galaxies. We think perhaps we are seeing evidence of it from the center of the Milky Way in the form of gamma rays given off when two DM particles annihilate each other. Less direct but still worth calling evidence is the computer models of the early universe, and finding which ratios of DM and baryonic matter are required to get the CMB temperature variations that we see (as Shaula describes below). This is not just balancing an equation.

Shaula
2012-Dec-21, 11:44 AM
In order to produce the effects it does on galactic rotation curves dark matter needs to be non-interacting (only interacting via gravity and possibly the weak force) as otherwise we would see it, it also has to be fairly 'cold'. We can also deduce how much there would have been by looking at the density requirements for the early universe (from acoustic signatures in the cosmic microwave background radiation) and the baryon/photon ratio (which gives us a handle on how much non-baryonic stuff there must have been to achieve that density). Taking these we know roughly what was there at the start. We then plug these into models which work out how these fluids behave and evolve it forwards. What we see is remarkably similar to what is out there. A few tweaks to the deduced properties of dark matter and we get a universe that looks like our own. And this holds true for all the major pieces of evidence. You can deduce its properties from a subset of the evidence and then test it against the rest. It works.

Don't get me wrong there are some things left unexplained by current models, but so far dark matter is the best fit to the entire body of evidence out there.

TheTruthSeeker
2012-Dec-21, 07:20 PM
What do you think you mean by 'proven'? We observe where DM is by several methods, such as how its gravitational influence distorts the apparent shapes of background galaxies. We think perhaps we are seeing evidence of it from the center of the Milky Way in the form of gamma rays given off when two DM particles annihilate each other. Less direct but still worth calling evidence is the computer models of the early universe, and finding which ratios of DM and baryonic matter are required to get the CMB temperature variations that we see (as Shaula describes below). This is not just balancing an equation.

by proven i mean that there is direct evidence that it is there - an experiment that has captured one of these particles or the creation of one in an experiment etc. when you say "we think perhaps we are seeing " i take that as not having direct proof but more of an educated guess.

you can tell a lot by the way things are worded - for example when i watch documentaries such as the wonders of the universe. they start telling us a background story about the current theories - but then use phrases like "so we know" which annoys me because they have already said they in the introduction that its still just a theory and no one knows for sure.

Assuming that it does exist and if dark matter is different to normal matter then to have two particles annihilate each other would hint that either there is dark matter and anti - dark matter or the particles are travelling at very high velocity when they collide or dark matter particles can anihilate one or both normal matter or anti matter.
the relative size of space compared to the size of a particle would also suggest that there would need to be a great number of these particles and anti particles for there to be a collision in the first place. is that a reasonable assumption?

Shaula
2012-Dec-21, 07:26 PM
is that a reasonable assumption?
There are fairly stringent limits on how hot (fast moving) the dark matter particles can be. Note that also the gamma signatures were only found in the region of the galactic core where gravity has concentrated these particles (slowly). Since dark matter is only weakly interacting the cross section for any interaction is tiny.

TheTruthSeeker
2012-Dec-21, 08:42 PM
slowly releative to what?

from my understanding of relativity even though to us light slows down as you get closer to the EH locally all things will still travel at normal speeds relative to each other.

antoniseb
2012-Dec-21, 08:50 PM
slowly releative to what?

from my understanding of relativity even though to us light slows down as you get closer to the EH locally all things will still travel at normal speeds relative to each other.

As it happens, the 130 GeV gamma ray signature is coming from an extended place at least 800 light years from Sgr A*, so the event horizon isn't an issue.

Shaula
2012-Dec-21, 08:51 PM
slowly releative to what?

from my understanding of relativity even though to us light slows down as you get closer to the EH locally all things will still travel at normal speeds relative to each other.
Each other.

The velocity spectrum of a gas relative to its own centre of mass is the usual measure of hot or cold and this is what I am talking about.

TheTruthSeeker
2012-Dec-21, 11:12 PM
im interested to know what you both understand to happen in the this scenario.

two observers look out to each other - observer 1 is close to the EH of a black hole looking out - observer 2 is close to the outer edge of the galaxy.

does observer 1 see observer 2 moving fast and observer 2 see observer 1 moving slowly?

the reason for the question is that i want to know if we look at a point in space that is under a much greater gravitational effect than our own - will we see it as cold - because to us it is moving slowly - but locally it may be moving fast and be hot.

Shaula
2012-Dec-21, 11:50 PM
No it does not work like that. The key thing is to remember that the particles tend to a thermalised velocity distribution which has a fairly simple form. The shape of this changes with temperature so even if there were some reason to think that the mean velocities measured are wrong the shape of the distribution would give it away if it were.

Strange
2012-Dec-22, 12:25 AM
Also, the vast majority of dark matter is nowhere near the black hole (and neither are we) so it isn't really relevant.

Cougar
2012-Dec-31, 06:11 PM
you can tell a lot by the way things are worded - for example when i watch documentaries such as the wonders of the universe. they start telling us a background story about the current theories - but then use phrases like "so we know" which annoys me because they have already said they in the introduction that its still just a theory and no one knows for sure.

Yes, it is certainly annoying when such TV shows dumb down their message. I guess they think they're reaching a wider audience, and unfortunately, they're probably right. But as Tony Rothman said,


"More and more scientists are now engaging in the popularization of their own fields. I wholeheartedly support this trend for the simple reason that scientists know their turf better than journalists. At the same time I am disturbed to see a growing gap between the standards upheld by scientists when they face other scientists and the standards they uphold when they face the public... [saying] things they would never try to get away with among colleagues."

But the way part of your comment was worded also brings up some problems:


"just a theory.... no one knows for sure."

Just a theory? I suggest you never again use this phrase in the presence of scientists. This is what creationists famously say: "Oh, evolution is just a theory." Nevermind that there are MOUNTAINS of direct and hard evidence supporting this theory, making it one of the most well supported theories in science. Scientific theories have hard evidence supporting them. Examples of non-theories: "creation science" and "intelligent design." These have no supporting evidence. They do not rise to the level of an actual theory.

As to "no one knows for sure." Just a heads up: In science, there is never absolute certainty. Scientific understanding lives and evolves as time goes on. There is never any absolute "truth" in science. That's what differentiates it from religion. Scientists certainly "seek truth," but they also understand they will never reach it in any absolute sense. They are quite satisfied to just get closer to it. That seems to have been happening a lot in the past 100 years.

noncryptic
2013-Jan-02, 05:27 PM
http://www.universetoday.com/98864/do-we-really-need-dark-matter/

I never understood the focus on dark matter and energy. science is supposed to be based on evidence.

I think you misunderstand what the dark matter claim is about: the claim is not that dark matter exists,

the claim is that something exists that causes certain as-of-yet unexplained large scale gravitational effects, and the working hypothesis (http://en.wikipedia.org/wiki/Working_hypothesis) is that it is caused by an as-of-yet undetected form of matter. It's because of 'something is there but we can't see it' that it is aptly called "dark matter".

ASTRO BOY
2013-Jan-02, 08:06 PM
I think you misunderstand what the dark matter claim is about: the claim is not that dark matter exists,

the claim is that something exists that causes certain as-of-yet unexplained large scale gravitational effects, and the working hypothesis (http://en.wikipedia.org/wiki/Working_hypothesis) is that it is caused by an as-of-yet undetected form of matter. It's because of 'something is there but we can't see it' that it is aptly called "dark matter".



Just playing the Devil's Advocate here.... plus also of course the unlikely event that we need a new model of gravity.

My thoughts on DM?
Although lacking evidence in the beginning when it was first proposed, investigations since have uncovered much evidence to support the concept, one of the most convincing being the "Bullet Cluster" observations.
So much so that I had an astronomer on another forum tell me we have more evidence for DM then we do for BH's....His work and research at that time was in DM and I think he, being human, was slightly biased toward that direction.......

Thanatos
2013-Jan-03, 06:06 AM
A promising dark matter candidate is the sterile neutrino. It has good theoretical and evidentiary support, has right the properties, and has drawn increasing interest over the past couple years. A very good treatise on the sterile neutrino is found here: http://arxiv.org/abs/1204.5379

quotation
2013-Jan-03, 07:00 PM
I happened to come across the following article while tracking down some info on two-fluid non-ideal MHD modeling and thought it might be interesting to those following this thread:

Falsification of dark energy by fluid mechanics
CARL H. GIBSON
Departments of MAE and SIO, Center for Astrophysics and Space Sciences, University of California at San Diego
http://arxiv.org/abs/1206.0218


At the plasma-gas transition, the plasma fragments into Earth-mass gas planets in trillion planet clumps (proto-globular-star-cluster PGCs). The hydrogen planets freeze to form the dark matter of galaxies and merge to form their stars. Dark energy is a systematic dimming error for Supernovae Ia caused by dark matter planets near hot white dwarf stars at the Chandrasekhar carbon limit...

The fatal flaw of the CC model [(standard (concordance) model of cosmology)] is its assumption that fluid mechanics can be ignored assuming ideal collisionless potential flow...Concordance cosmology rejects basic fluid mechanics as unnecessary. Flows are assumed to be ideal, resulting from gradients in a velocity potential. Gravitational structure formation is based on the Jeans analysis of 1902...

Jeans (1902) reduced the Navier Stokes equations to acoustics by neglecting viscosity (Euler’s equation), neglecting density (Jeans swindle), neglecting non-linearity by the application of linear perturbation stability analysis (no turbulence), and neglecting diffusion of weakly interacting massive particles (no neutrinos)...

Without fluid mechanics, cold dark matter is needed to explain structure formation during the plasma epoch...With fluid mechanics, it is only necessary to recognize that the low densities and high temperatures of the early H − He4 plasma and gas Universe give large kinematic viscosities v values that dominate self-gravitational structure formation, contrary to Jeans (1902) and all CDM cosmology models...
In some respects this is a very bizarre paper, in that it makes some bold claims in a very short space (6 pages) with a single paragraph conclusion:

The accelerating expansion rate of the Universe and Dark Energy concepts rewarded by the 2011 Nobel Prize in Physics are falsified by fluid mechanics. The standard model of cosmology must be replaced by HGD (hydro-gravitational-dynamics) cosmology.
And that's it. Like I said above, I was just looking around fluid dynamics, non-ideal MHD, and galaxy formation when I ran into this one and just thought it might be of some interest here. Okay, back to MRx cascades in collimated jets.

John Mendenhall
2013-Jan-03, 08:59 PM
I happened to come across the following article while tracking down some info on two-fluid non-ideal MHD modeling and thought it might be interesting to those following this thread:

Falsification of dark energy by fluid mechanics
CARL H. GIBSON
Departments of MAE and SIO, Center for Astrophysics and Space Sciences, University of California at San Diego
http://arxiv.org/abs/1206.0218


In some respects this is a very bizarre paper, in that it makes some bold claims in a very short space (6 pages) with a single paragraph conclusion:

And that's it. Like I said above, I was just looking around fluid dynamics, non-ideal MHD, and galaxy formation when I ran into this one and just thought it might be of some interest here. Okay, back to MRx cascades in collimated jets.

I read thru the whole paper (it's readily accessible) and although I think the author is out of his depth, it's a good read. And a fine example of how Science is conducted. Now the fun starts with peer reviews of his viscosity claims. And gas planets. And dimming. Unsoweiter.

Thanks, Quotation, a good link. Regards, John M.

A.DIM
2013-Jan-04, 04:00 AM
I read thru the whole paper (it's readily accessible) and although I think the author is out of his depth, it's a good read. And a fine example of how Science is conducted. Now the fun starts with peer reviews of his viscosity claims. And gas planets. And dimming. Unsoweiter.

Thanks, Quotation, a good link. Regards, John M.

Hear hear, interesting stuff!

A couple years ago I cited a Gibson paper and asked about his HGD cosmology. As per usual, it was poo pooed.
I too am out of my depth, but intuition tells me there's something to it...
Hydro-Gravitational Dynamics of Planets and Dark Energy (http://www.jafmonline.net/modules/htmlarea/myarchix/file-archive/JAFM-022035.pdf).

Shaula
2013-Jan-04, 07:51 AM
Actually that paper is a horrible read. The chip on the author's should is painfully obvious. He makes several patently ridiculous assertions like that the current models 'ignore' fluid mechanics. What he means is that he objects to the simplifications they use. His planets have some pretty special properties too. They can apparently dim things without causing an excess of lensing events, their atmospheres don't distort images in any way while doing this dimming. More than half his references are to his own papers.

I have no doubt at all that turbulence has some interesting things to say about structure formation - equally have no doubts that he is making a huge leap ahead of what the evidence and theory actually says. His model does not magically get rid of the problems CDM solves. It just replaces them with other problems.

TooMany
2013-Jan-04, 08:43 PM
Actually that paper is a horrible read. The chip on the author's should is painfully obvious. He makes several patently ridiculous assertions like that the current models 'ignore' fluid mechanics. What he means is that he objects to the simplifications they use. His planets have some pretty special properties too. They can apparently dim things without causing an excess of lensing events, their atmospheres don't distort images in any way while doing this dimming. More than half his references are to his own papers.

I have no doubt at all that turbulence has some interesting things to say about structure formation - equally have no doubts that he is making a huge leap ahead of what the evidence and theory actually says. His model does not magically get rid of the problems CDM solves. It just replaces them with other problems.

Ignoring the arrogance for a moment, he seems to be suggesting that current models are not properly taking fluid dynamics into account (he is a professor of fluid dynamics at UCSD). Maybe he's got something. It wouldn't be the first time models were incorrect. What do you make of his observational evidence in Hydro-Gravitational Dynamics of Planets and Dark Energy (http://www.jafmonline.net/modules/htmlarea/myarchix/file-archive/JAFM-022035.pdf)?

Shaula
2013-Jan-04, 09:19 PM
Ignoring the arrogance for a moment, he seems to be suggesting that current models are not properly taking fluid dynamics into account (he is a professor of fluid dynamics at UCSD). Maybe he's got something. It wouldn't be the first time models were incorrect. What do you make of his observational evidence in Hydro-Gravitational Dynamics of Planets and Dark Energy (http://www.jafmonline.net/modules/htmlarea/myarchix/file-archive/JAFM-022035.pdf)?
As I said I am not denying that it has a part to play.

I certainly don't really see his evidence as particularly strong. He requires you to accept a complete rewrite of just about everything we have deduced about planetary nebula, white dwarf stars and so on. Accepting his evidence lies are the end of a huge chain of "if, then ... if, then" statements - and I would challenge a lot of them. His mechanism for dimming is highly suspect.

So we have a few grainy pictures and some ideas about how the universe might be. In exchange we have to rewrite our lifecycles of stars, throw out standard cosmology, ditch the Standard model of physics because nucleosynthesis will break and several other things. I do not feel he has made anything like a compelling enough case to pretty much throw out everything and start over.

I think his ideas about vorticity and structure formation have merit - however I think his basing his whole cosmology on extrapolations from this is a big leap.

TooMany
2013-Jan-04, 11:12 PM
As I said I am not denying that it has a part to play.

I certainly don't really see his evidence as particularly strong. He requires you to accept a complete rewrite of just about everything we have deduced about planetary nebula, white dwarf stars and so on. Accepting his evidence lies are the end of a huge chain of "if, then ... if, then" statements - and I would challenge a lot of them. His mechanism for dimming is highly suspect.

So we have a few grainy pictures and some ideas about how the universe might be. In exchange we have to rewrite our lifecycles of stars, throw out standard cosmology, ditch the Standard model of physics because nucleosynthesis will break and several other things. I do not feel he has made anything like a compelling enough case to pretty much throw out everything and start over.

I think his ideas about vorticity and structure formation have merit - however I think his basing his whole cosmology on extrapolations from this is a big leap.

Whatever it might break does not matter if it is true. We need observations to decide what is. I have never seen his detailed argument for the formation of these cold bodies. It makes me wonder if he actually has one. On the other hand it's always seemed peculiar to me that astronomers think such bodies cannot form (I've see this argued in at least one paper, but the argument was very weak).

TooMany
2013-Jan-05, 01:26 AM
I found this paper (http://arxiv.org/abs/0906.5087) and this one (http://arxiv.org/abs/astro-ph/9904230) in which he presents some arguments with actual math.

It seems that his earlier papers were somewhat more modest and more populated with math. Maybe he's gotten PO'd at the mainstream astronomers for ignoring him over the years (he is not an astronomer AFAIK). His theory goes back to at least 1996 which is 17 years ago. It would seem that that correct analysis of baryonic interactions is vital in astronomy. So my question is not whether all of his claims are correct but rather whether he has some point about the behavior of matter that is not getting proper attention, perhaps because few astronomers are experts in hydro dynamics?

I noticed there were other threads on this Gibson's papers where he was thoroughly bashed as wrong about many things but no one took on the core of his argument. The thread was terminated as the whole idea was labeled ATM. So let's not have that happen.

But I'm still curious about what happens to hydrogen, helium and a bit of dust in an environment at 2.7K. We know in the case of planetary systems that gas planets form. Jupiter's atmosphere is 99% hydrogen and helium and is believed to have a hydrogen core. If such a planet can form in our system in proximity to a star, why could this not happen without the aid of a star? The triple point of pure hydrogen is 14K at a pressure of 1 psi (7 kPa). The measured temperatures of some known galactic clouds are similar.

StupendousMan
2013-Jan-05, 02:45 AM
I suggest you and other readers interested in this topic do a little reading about the "Jeans mass." It might help you to frame some of your questions on this topic.

Shaula
2013-Jan-05, 08:01 AM
Whatever it might break does not matter if it is true. We need observations to decide what is.
Of course it matters. Because we have good lines of evidence for a lot of things that get broken by this. Also the observations we make have to be interpreted by reference to a model. If, in order to get his model to work, we have to largely re-write physics as we know it then we are entering tricky ground. You end up with a situation where you have a choice: Accept his model, but agree than nothing in space works like it does in the lab. Reject his model and find another explanation more rooted in testable physics.

Markus Hanke
2013-Jan-05, 10:02 AM
perhaps because few astronomers are experts in hydro dynamics?

Actually, hydrodynamics are frequently employed by astrophysicists. An example would be the interior of stars, and the interior EFE solutions describing them, which are largely based on fluid dynamics.

TooMany
2013-Jan-05, 04:18 PM
Of course it matters. Because we have good lines of evidence for a lot of things that get broken by this. Also the observations we make have to be interpreted by reference to a model. If, in order to get his model to work, we have to largely re-write physics as we know it then we are entering tricky ground. You end up with a situation where you have a choice: Accept his model, but agree than nothing in space works like it does in the lab. Reject his model and find another explanation more rooted in testable physics.

Like WIMPs?

TooMany
2013-Jan-05, 05:08 PM
I suggest you and other readers interested in this topic do a little reading about the "Jeans mass." It might help you to frame some of your questions on this topic.

I read the Wiki article. I could not find any terms in Jeans' equations representing viscosity, turbulence or radiation of thermal energy. The analysis appears very simplistic treating the gas as adiabatic. The only things considered are density, gravitational potential, temperature (kinetic energy) and the speed of sound. What happens when other affects are considered?

Can anyone shed some light on why gas planets cannot form spontaneously but only form in the context of star formation?

Shaula
2013-Jan-06, 07:22 AM
Like WIMPs?
Principle of parsimony.

TooMany
2013-Jan-06, 06:27 PM
Principle of parsimony.

Parsimony? Not at all, it's the invention of a substance not known to exist to sustain a theory about the origin of the universe.

Anyway Shaula, I'm very interested in why we would not expect condensation of matter to occur outside of star formation. It does not make sense to me because the temperature of a black body not near a star is about 2.7K, which is far below the critical point of hydrogen. I had a hard time finding the vapor pressure of hydrogen below 13K. But I finally did here (http://www.aip.org/avsguide/refguide/vapor.html). It appears that below 9K, the vapor pressure is less than a couple of hundredths of a psi. At 5K it is miniscule. Further, we know that Jupiter exists and seems to by only 1% metal, but we assume it formed in an environment far warmer than interstellar.

Shaula
2013-Jan-06, 07:04 PM
Just for info - we have been around and around and around this one. I am not interested in repeating this. I know you don't like DM theories, I know you want to find an alternative and I know that you will keep trying to find a way to 'prove' it is all wrong. Go back and read any one of the half dozen other threads where we have banged heads fruitlessly on this to see how the argument will develop.

TooMany
2013-Jan-06, 10:44 PM
Just for info - we have been around and around and around this one. I am not interested in repeating this. I know you don't like DM theories, I know you want to find an alternative and I know that you will keep trying to find a way to 'prove' it is all wrong. Go back and read any one of the half dozen other threads where we have banged heads fruitlessly on this to see how the argument will develop.

Sorry, but I don't recall any detailed discussion of condensation and I'm genuinely curious as to the reason(s) astronomers believe it cannot happen. I don't think it's fruitless to examine that. Rather isn't this an important question to ask? What happens to matter at these low temperatures? We know about stars because they shine so brightly. We know about intergalactic hot gas because it emits X-rays. Despite that fact that it is that hot, it is so sparse that it is unable to transfer significant heat. I doubt that intergalactic gas could melt a snowball.

The only explanation for the assumed absence of smaller conglomerations of matter I ever stumbled upon was sad to say the least. The argument was that "snowballs" cannot exist because they would bump into each other and break up. Of course that's ridiculous because we have gas planets. I've been trying to find some information about the subject. Most of what I find concerns star formation which is a very large scale condensation, but I haven't found much about limiting factors on size. I know a little about fragmentation into Jeans mass but the scale of that is much larger than a star, it's more like a globular cluster.

Condensation of gas clouds would seem inevitable at present temperatures. As a cloud contracts, the pressure and temperate increase balancing the force of gravity, but, anything above 2.7K is going to loose heat through radiation and as it does, the cloud will continue to contract. By the time the temperature drops to 9K, there is so little vapor pressure that collapse is inevitable. You could try to argue that radiation prevents that but can it? In a large cloud the outer parts will absorb and re-emit leaving the inner parts to continue to cool.

In researching this I just came upon an interesting problem called "cooling flows" in clusters. We know that in the denser parts of these clusters that this hot gas should be cooling, and there is evidence that it is, but it does not seems to be forming stars because if it were, the galaxies would be brighter and contain more young stars. So what is happening to that cooling flow is an interesting question.

StupendousMan
2013-Jan-07, 01:14 AM
Earlier, I suggested that you do some reading about the "Jeans mass". You replied that you looked at the Wikipedia page, found an equation, and it seemed to leave a number of factors out. Above, you state correctly that the Jeans mass is much larger than the mass of, say, a snowball.

I was hoping that you would do some real reading about the Jeans mass. You know, find a good textbook or two, or check out a review article. If you did so, you'd find that Jeans was trying to figure out exactly what you've been asking: at what mass will a cloud of gas collapse due to gravitational forces? His answer: for conditions which are common in interstellar space, at a mass which is of order a solar mass. Much, much larger than the mass of a snowball. Two of the three effects you mentioned in one of your earlier message act to increase this mass. It's likely, then, that snowballs are unlikely to form from interstellar clouds due to gravitational collapse.

So, if you want to form snowballs, you'll need to find a different mechanism to form them. Perhaps they form due to the random collisions of molecules and dust particles. Why don't you start with the conditions inside a typical interstellar cloud and figure out -- very simple back-of-the-envelope estimates -- how long it might take for an object with the mass of a snowball to form from such random collisions? Then come back and tell us.

TooMany
2013-Jan-07, 01:46 AM
Earlier, I suggested that you do some reading about the "Jeans mass". You replied that you looked at the Wikipedia page, found an equation, and it seemed to leave a number of factors out. Above, you state correctly that the Jeans mass is much larger than the mass of, say, a snowball.

I was hoping that you would do some real reading about the Jeans mass. You know, find a good textbook or two, or check out a review article. If you did so, you'd find that Jeans was trying to figure out exactly what you've been asking: at what mass will a cloud of gas collapse due to gravitational forces? His answer: for conditions which are common in interstellar space, at a mass which is of order a solar mass. Much, much larger than the mass of a snowball. Two of the three effects you mentioned in one of your earlier message act to increase this mass. It's likely, then, that snowballs are unlikely to form from interstellar clouds due to gravitational collapse.

So, if you want to form snowballs, you'll need to find a different mechanism to form them. Perhaps they form due to the random collisions of molecules and dust particles. Why don't you start with the conditions inside a typical interstellar cloud and figure out -- very simple back-of-the-envelope estimates -- how long it might take for an object with the mass of a snowball to form from such random collisions? Then come back and tell us.

I need more real reading about Jeans mass? You're the expert. Where did you get that answer, that only stellar size objects can form? I've looked but not yet found an explanation of why substellar objects cannot form. Saying it is simply back of the envelope estimates sounds very suspicious. The process is far more complicated than Jeans equation. His equation completely ignores loss of heat, viscosity, magnetism and nucleation. It concludes that only gigantic clouds can condense (thousands of stellar masses), but it does not predict that when they do they form only stellar mass objects. His theory stops well short of the formation of anything in particular.

Water in moist air can condense in a variety of ways spanning microscopic drops to softball sized ice balls (from 10 um to 10^5 um, with a whole lot more forming at the low end).

TooMany
2013-Jan-07, 07:48 PM
If you did so, you'd find that Jeans was trying to figure out exactly what you've been asking: at what mass will a cloud of gas collapse due to gravitational forces? His answer: for conditions which are common in interstellar space, at a mass which is of order a solar mass.

Can you cite a paper or something with this conclusion that Jeans figured out that collapse mass was on the order of solar? I don't think that is correct.



Thus, the smallest possible mass capable of collapse at the time of decoupling was 10^5 Mo . That is about the mass of a present day globular cluster. Nothing smaller could have formed. By contrast in the interstellar medium of our Galaxy where T ~ 50K and the Jeans' Mass is 500 Mo.


However, this mass is not only dependent on temperature, it depends on the density of the gas you start with. *The higher that density, the smaller the mass. The lower the temperature the smaller the mass. Once you get high densities, radiation and turbulence become more important but are not even considered by Jeans equations.

I've done some more research about this condensation issue, reading a few recent papers on the subject. It appears is that the mechanism is hideously complex and not well understood at all. There is no back of the envelope calculation that explains the IMF, let alone the formation of substellar objects. Even numerical simulations are having great difficulty. The papers I've read indicate that turbulence is now seen as a critical issue. My conclusion is that we really do not know a whole lot about the behavior of gas and dust, yet.

However, we do know that substellar condensations occur in the star forming process including the trillion or so Oort cloud objects, the Kuiper belt the planets and the asteroids. The gas planets in particular are interesting. Somehow they form and they do so fairly quickly even in the presence of increasing thermal radiation. It's not like all this has been figured out, there are competing theories, but that's what makes astronomy so exciting these days. You never know what will turn up next.

Reality Check
2013-Jan-08, 01:57 AM
Can you cite a paper or something with this conclusion that Jeans figured out that collapse mass was on the order of solar? I don't think that is correct.

I suspect that StupendousMan mistyped.
Start with Jeans mass (http://en.wikipedia.org/wiki/Jeans_instability#Jeans_mass) (Jeans, J. H. (1902). "The Stability of a Spherical Nebula". Philosophical Transactions of the Royal Society of London. Series A 199: 1–53. JSTOR 90845.)
Once typical values for molecular coulds are plugged in to his equation, the Jeans mass is of the order of thousands to tens of thousands of solar masses (http://en.wikipedia.org/wiki/Star_formation#Cloud_collapse). The Wikipedia page cites Prialnik, Dina (2000). An Introduction to the Theory of Stellar Structure and Evolution. Cambridge University Press. 195–212.

I agree that the mechanism is hideously complex but the conclusions seem clear - gas clouds will not spontaneously collapse to create snowballs, planets or other rocks that can be candidates for dark matter. Even collapses that are triggered, e.g. by novae, will not do this.

A real problem with the idea that dark matter is rocks is that dark matter has been detected in the intracluster medium (http://en.wikipedia.org/wiki/Intracluster_medium) (ICM). The ICM is much less dense than the interstellar medium and much, much hotter (10 to 100 million K!). So not only do you need a bit of magic to create the rocks, you also need additional magic to move them out of galaxies and even out of clusters :D .

TooMany
2013-Jan-08, 02:29 AM
I agree that the mechanism is hideously complex but the conclusions seem clear - gas clouds will not spontaneously collapse to create snowballs, planets or other rocks that can be candidates for dark matter. Even collapses that are triggered, e.g. by novae, will not do this.


How do we know that? How did we reach these clear conclusions? How do comets form? How did Jupiter form?



A real problem with the idea that dark matter is rocks is that dark matter has been detected in the intracluster medium (http://en.wikipedia.org/wiki/Intracluster_medium) (ICM). The ICM is much less dense than the interstellar medium and much, much hotter (10 to 100 million K!). So not only do you need a bit of magic to create the rocks, you also need additional magic to move them out of galaxies and even out of clusters :D .

You shouldn't use the term "rocks" because there isn't enough metal for rocks. But ice or gas planets are possible. The ICM gas that we detect by X-ray emission is so tenuous that regardless of this high temperature, it could not melt a snowball. There is a lot of dust in galaxies (in fact there are metals even in the ICM) that can cause nucleation where matter sticks to the dust and then these dust particles coated with hydrogen and helium can stick together and gain mass attracting more gas and dust and so. How can you prevent this from happening when it's so cold for a billion years? About 80% of the mass in galaxies is not seen. It is not in the stars, it is not in the form of gas and dust, but it must be somewhere.

In the cooling flows in galactic clusters, where does all that in-flowing matter end up? We know that it does not all end up in stars. :confused:

noncryptic
2013-Jan-08, 04:57 PM
it's the invention of a substance not known to exist to sustain a theory about the origin of the universe.


It's not an invention, it's like a lead that investigators follow up on.
It's a hypothesis. It's not by long shot a foregone conclusion that it exists.

TooMany
2013-Jan-08, 05:58 PM
It's not an invention, it's like a lead that investigators follow up on.


It's an invention in the sense that it is hypothesized to exist to fill a hole, but there is as yet no direct evidence of it's existence.



It's a hypothesis. It's not by long shot a foregone conclusion that it exists.

I agree with that. The situation is that we cannot account for all the mass in what we are able to observe. What bothers me is the idea that nothing but gas, dust and stars can exist as forms of normal matter. The bias in favor of non-baryonic matter comes only partly from the failure to observe the matter; it is also driven by the need to explain abundance of primordial elements in BBT. The nucleosynthesis theory is rather speculative in the first place, so being stuck with satisfying that need seems presumptive.

antoniseb
2013-Jan-08, 06:09 PM
... there is as yet no direct evidence of it's existence. ...
You seem to be confusing the words evidence and proof. There is lots of direct evidence that it exists, and a lot of that evidence has been discussed in this thread. Saying there isn't any is just wrong.

noncryptic
2013-Jan-08, 09:02 PM
It's an invention in the sense that it is hypothesized to exist to fill a hole, but there is as yet no direct evidence of it's existence.

Contrary to what some seem to think, that's a perfectly valid way to advance science.
And it means the premise of the OP implied by the topic title -'science claims DM exists'- is false.

Reality Check
2013-Jan-08, 09:55 PM
How do we know that? How did we reach these clear conclusions? How do comets form? How did Jupiter form?

Read the article.
Planets: During the formation of stars (really needs a duh since this is basic astronomy).
Comets: From billions of years of accumulation of gasses on dust particles (the sort of accumulation that you fantasize about making enough comets to be dark matter).


It is not in the stars, it is not in the form of gas and dust, but it must be somewhere.

It is also not in the form of ice or gas planets because comets (or 'ice planets'?) and gas planets are a tiny percentage of each stellar system (0.2%?) and your 80% figure requires them to be much greater than the mass of each stellar system.

There are no cooling flows in galactic clusters (http://en.wikipedia.org/wiki/Intracluster_medium#Cooling_flow). The ICM should be cooling in theory but there is no sign of the flows that this will induce.
ETA: The cooling gas ends up closer to the center of the cluster: "As material in the centre of the cluster cools out, the pressure of the overlying ICM should cause more material to flow inwards (the cooling flow)." (http://en.wikipedia.org/wiki/Cooling_flow)

We may agree on one point: There should be baryonic dark matter in the universe for the simple reason that fitting cosmological models to the WMAP data gives that ~4% of the universe is baryonic matter but we have only accounted for about half the baryonic matter in the universe.
But this missing matter (the usual term) is probably in undetected gas rather than planets or comets.

That still leaves ~23% of the universe in non-baryonic dark matter and the rest in dark energy.

TooMany
2013-Jan-08, 10:45 PM
You seem to be confusing the words evidence and proof. There is lots of direct evidence that it exists, and a lot of that evidence has been discussed in this thread. Saying there isn't any is just wrong.

Well, it depends what you consider direct evidence. Evidence that there is unseen mass is just that. We know of only a certain set of particles with mass. DM theory proposes a new kind of massive particle that has never been directly detected. It's really hard to invalidate a theory based on a hypothetical (and thus far undetectable) particle.

LHC hasn't had success in validating SUSY and the standard model is now complete, particle wise. I heard LHC is going to be shut down for two years while they upgrade the magnets to reach higher power. Maybe something will show up then. Has an upper limit been placed on the mass of the proposed DM particle(s)?

I heard something amount gamma emissions coming from the center of the galaxy that might be indicative of some new particle and some sort of unusual microwave signal "galactic haze" has been detected by Planck which some people have proposed indicates non-baryonic DM.

TooMany
2013-Jan-08, 10:49 PM
Contrary to what some seem to think, that's a perfectly valid way to advance science.
And it means the premise of the OP implied by the topic title -'science claims DM exists'- is false.

I don't see anything wrong with having such a hypothesis, but by it's a tough one to refute.

Reality Check
2013-Jan-08, 11:26 PM
Well, it depends what you consider direct evidence. ...
I would think that knowledgeable people would consider the observations of colliding clusters such as the Bullet Cluster to be direct evidence (for astronomy :)). This is evidence that there is unseen non-baryonic mass.
The existence of dark matter is not a theory - it is an set of observations.

antoniseb
2013-Jan-08, 11:26 PM
...DM theory proposes a new kind of massive particle that has never been directly detected. It's really hard to invalidate a theory based on a hypothetical (and thus far undetectable) particle.

LHC hasn't had success in validating SUSY and the standard model is now complete, particle wise. ...

"DM Theory"? where have you ever seen one unified theory of Dark Matter? The OP says Dark Matter doesn't exist. You want to change the premise to "Neutralinos don't exist"? Go ahead (in a new thread). But the fact is that there are many models of Dark Matter constituents, but the evidence is that the mass is there, and it is not a collection of Baryons. Is it neutralinos? sterile neutrinos? axions, magnetic monopoles? primordial black holes (in some limited range of masses that haven't been ruled out yet)? These and others are still all open for discussion, and some of them could possibly be confirmed by more exacting efforts at detection, and some cannot be directly detected with anything yet imagined. The 130 GeV signal from the center of the galaxy has been used as evidence for a few of these, though the neutralino seems most favored by it.

TooMany
2013-Jan-09, 12:00 AM
There are no cooling flows in galactic clusters (http://en.wikipedia.org/wiki/Intracluster_medium#Cooling_flow). The ICM should be cooling in theory but there is no sign of the flows that this will induce.
ETA: The cooling gas ends up closer to the center of the cluster: "As material in the centre of the cluster cools out, the pressure of the overlying ICM should cause more material to flow inwards (the cooling flow)." (http://en.wikipedia.org/wiki/Cooling_flow)


I think you are misinterpreting. There is evidence for the cooling flows. In fact they required for the formation of massive galaxies within the cluster. The following is from the first source in that wiki article (emphasis mine):



This idealized picture represents the main features of cooling flows, which are found to be common in massive elliptical galaxies, groups, and clusters of galaxies through X-ray observations. The surface brightness and spectrum of the X rays show that the gas particles lose much of their thermal energy to X-radiation in the central region of many of these objects, implying that the cooling process necessary for the formation of galaxies has extended until the present time and that the central massive galaxies are continuing to grow now. Most of this growth is not in terms of visible stars, however, since the radiative cooling rates in nearby rich clusters of 10s to 100s M yr-1 would then make the central galaxies much bluer and brighter than even a superficial optical inspection allows. The cooled gas must somehow condense into optically dark objects, or some other process must come into play. Detailed observations at optical and other wavebands do reveal anomalies in the centers of cooling flows and confirm that the gas has a high density, a high pressure, and short cooling time, but so far do not reveal the cooled component. The only thing we know for certain is that gas is leaving the hot phase, where it is detectable in X rays, and is becoming some form of dark matter.
...
We review the evidence, derived from X-ray images and spectra, that the gas really cools and that cooling flows are common. Therefore they must be long-lived and steady. Recent data clearly show the temperature of the gas dropping towards the center of many clusters.


The cooling flow problem is that they don't see the cold matter forming stars. A simple solution is that much of it condenses without forming stars.

The wiki article you referenced suggests that the cooling flows aren't there:


as there is little evidence for cool X-ray emitting gas in many of these systems

However, the same reference I quoted above points out that the softer X-rays from cooled gas are strongly absorbed:


The X-ray data also show that the cooling-flow emission is absorbed, providing evidence for widespread cooled gas. The inferred mass of the absorbing matter is comparable to that expected from a persistent cooling flow.

Why isn't condensation seriously considered?

TooMany
2013-Jan-09, 12:14 AM
I would think that knowledgeable people would consider the observations of colliding clusters such as the Bullet Cluster to be direct evidence (for astronomy :)). This is evidence that there is unseen non-baryonic mass.
The existence of dark matter is not a theory - it is an set of observations.

I'm not saying that dark matter does not exist. I just question whether it must be some new as yet undetected particle. The Bullet Cluster is evidence that like the stars, the dark matter does not collide. That does not require the dark matter to be an non-interacting particle. If the dark matter is condensed baryonic matter, it would behave the same way.

TooMany
2013-Jan-09, 12:55 AM
"DM Theory"? where have you ever seen one unified theory of Dark Matter? The OP says Dark Matter doesn't exist. You want to change the premise to "Neutralinos don't exist"? Go ahead (in a new thread).

Sorry. If the thread is restricted to "is there unseen mass" then there is not much to discuss unless the OP wants to discuss whether General Relativity is incorrect about gravity.

antoniseb
2013-Jan-09, 01:07 AM
Sorry. If the thread is restricted to "is there unseen mass" then there is not much to discuss unless the OP wants to discuss whether General Relativity is incorrect about gravity.

Right, well the OP made a provocative claim and couldn't really back it up. If you want to discuss that it isn't what people think, or that it is the plentiful supply of dark planets, or some other such thing, you should do that in a thread that is labelled well enough that people can find your arguments when they go back to look in a few months or years.

matt.o
2013-Jan-09, 02:50 AM
I think you are misinterpreting. There is evidence for the cooling flows. In fact they required for the formation of massive galaxies within the cluster. The following is from the first source in that wiki article (emphasis mine):



The cooling flow problem is that they don't see the cold matter forming stars. A simple solution is that much of it condenses without forming stars.

The wiki article you referenced suggests that the cooling flows aren't there:



However, the same reference I quoted above points out that the softer X-rays from cooled gas are strongly absorbed:



Why isn't condensation seriously considered?


Much work has been done on the "cooling flow problem" in clusters since Fabian wrote that article in 1994. For instance, based on what we now know, your emphasis "The cooled gas must somehow condense into optically dark objects, or some other process must come into play." is on the wrong part of the sentence! The "some other process" that comes into play is AGN feedback. For example, you can see the review articles by McNamara and Nulsen (http://adsabs.harvard.edu/abs/2012NJPh...14e5023M or http://adsabs.harvard.edu/abs/2007ARA%26A..45..117M) and the references thereto and therein.

TooMany
2013-Jan-09, 05:22 PM
Much work has been done on the "cooling flow problem" in clusters since Fabian wrote that article in 1994. For instance, based on what we now know, your emphasis "The cooled gas must somehow condense into optically dark objects, or some other process must come into play." is on the wrong part of the sentence! The "some other process" that comes into play is AGN feedback. For example, you can see the review articles by McNamara and Nulsen (http://adsabs.harvard.edu/abs/2012NJPh...14e5023M or http://adsabs.harvard.edu/abs/2007ARA%26A..45..117M) and the references thereto and therein.

Yes it is an old paper, but if you read it you don't get any sense that the cooling flows do not exist. The problem is what happens to the in-falling matter. This paper (http://arxiv.org/abs/astro-ph/0210662)is from 2002 and suggests that the expected soft X-rays during cooling are missing while at the same time offering a variety of possible reasons for this, including the AGN heating. That paper doesn't lend much support to the AGN idea. It does however point out that radiation in UV and especially in IR are more than sufficient to account for the energy lost. It also points out how dust may be involved in the process. It seems like the problem is real and astronomers are looking for ways to make it go away. I've yet to see anyone propose condensation as the repository for the cooled matter.

I'll read your references, thanks.

antoniseb, I'll start a new thread.

Reality Check
2013-Jan-09, 09:25 PM
Can we move the cooling flow discussion to the other thread I started to avoid the topic confusion? Thanks.
Perhaps also move the discussion of dark matter = "ice or gas planets"?
TooMany, you can then present your evidence that there are enough "ice or gas planets" to explain the observations of dark matter (even between galaxy clusters!).

antoniseb
2013-Jan-10, 02:22 AM
Perhaps also move the discussion of dark matter = "ice or gas planets"?...

I'll be willing to move it IFF someone provides a list of numbers for posts that go with it. I don't plan to take the time to sort them myself.

Cougar
2013-Jan-10, 04:13 AM
The bias in favor of non-baryonic matter... is also driven by the need to explain abundance of primordial elements in BBT. The nucleosynthesis theory is rather speculative in the first place, so being stuck with satisfying that need seems presumptive.

I think these claims qualify for being not even wrong.

neilzero
2013-Jan-10, 05:15 AM
How about compact stars = white dwarfs, nuetron stars, quark stars (if any) black holes under 1000 solar mass and brown dwarfs. Accetion disks may be very thin. These block very little light, but have considerable mass. If our region of the galaxy, up to 10 parsecs has anomosly few of these 1800 to 2013, then could they total half of the dark matter needed? Possibly a dozen of them will pass though our solar system at about 0.1c in the next millenium? I know that is not good Occum's razor, but Occum's razor is not proven. Neil

Grey
2013-Jan-10, 03:17 PM
How about compact stars = white dwarfs, nuetron stars, quark stars (if any) black holes under 1000 solar mass and brown dwarfs.Microlensing studies have specifically looked for this type of dark, compact object, to try to determine how much mass is out there in this form. It turns out that the upper limit is much less than the required dark matter halo mass.

grapes
2013-Jan-10, 05:16 PM
Sensationalism is Universe Todays stock and trade. Can't blame the author of the article for that. He isn't even a scientist. as for my initial post all I did was link to an article on the main page here. My comment "I never understood the focus on dark matter and energy. Science is supposed to be based on evidence." is valid. The title reflects the core premise of the article. Dark matter is only a theory.
The author isn't a scientist? What do you mean by that? The UT article says he is a professor, an astronomer, at an institute in Belgium, no?

It may well be true that "(you) never understood the focus on dark matter and energy" and "science is supposed to be based on evidence" but the article doesn't come close to proving a case that dark matter doesn't exist.


It is a good paper actually. Refreshingly honest with what it can and cannot do, treats errors well and highlights where the data it uses for support is weak. I am glad the OP brought it to our attention, it is interesting to read. I just wish it wasn't being sensationalised by that article and the initial post.
I think it's going to get shot down on review, just because of what it doesn't treat. Yes, in his conclusion, he says "Of course, our model has to be tested against other observations, such as the flat rotation curves of spiral galaxies or...", but I would think that would be a pretty easy thing to test, and from what I understand of his model, the model would fail completely. I'm guessing he's already done that, and knows that it fails.

TooMany
2013-Jan-10, 11:58 PM
I think these claims qualify for being not even wrong.

How's that?

Cougar
2013-Jan-11, 04:56 PM
How's that?

You claimed:


The bias in favor of non-baryonic matter... is also driven by the need to explain abundance of primordial elements in BBT. The nucleosynthesis theory is rather speculative in the first place, so being stuck with satisfying that need seems presumptive.

Your first sentence is backward. Your second sentence builds on the backwardness of the first sentence. That's how you get to the other side of wrong, which is sometimes referred to as "not even wrong." I'm just letting you know. I am not going to explain the entire big bang theory for you. It has been developed from various independent approaches for about 90 years now. There's a lot to it. There's also a lot of literature explaining it. Whether you take advantage of past astronomical observations, that's up to you.

TooMany
2013-Jan-11, 08:04 PM
Your first sentence is backward. Your second sentence builds on the backwardness of the first sentence. That's how you get to the other side of wrong, which is sometimes referred to as "not even wrong." I'm just letting you know. I am not going to explain the entire big bang theory for you. It has been developed from various independent approaches for about 90 years now. There's a lot to it. There's also a lot of literature explaining it. Whether you take advantage of past astronomical observations, that's up to you.

I'm honestly don't know what you mean by "backward" in that sentence. What would the correct statement be? The "not even wrong" cliché adds nothing informative, just pejorative.

Shaula
2013-Jan-11, 08:15 PM
The correct statement would be Nucleosynthesis is a fairly well understood phenomenon that is a strong piece of evidence for non-baryonic matter. But that is not what you want to hear so...

TooMany
2013-Jan-11, 09:39 PM
The correct statement would be Nucleosynthesis is a fairly well understood phenomenon that is a strong piece of evidence for non-baryonic matter. But that is not what you want to hear so...

Right, at least we think we understand what happens based on the standard model, but when you put that together with the fact that the standard model doesn't account for 80% of the mass, how much confidence should you have in your understanding of that phenomenon? My understanding of the reason it "must" be non-baryonic is that the nucleosynthesis model limits the amount of baryonic matter produced far below the observed mass. I'm not sure however exactly what observations impose this limit. Is it the ratio's of primordial elements or is it something else?

Shaula
2013-Jan-11, 09:46 PM
The Standard Model is a particle physics model, not a cosmological one. So it does not have to account for cosmological missing mass. It is tested and confirmed in labs to a high degree of precision. But in your eagerness to disregard all evidence that does not agree without your dislike of dark matter you are treating what is actually a series of interlocking models as one monolithic one, and claiming that any flaw with this larger system invalidates every part of it.

I'm pretty sure I have discussed nucleosynthesis on here before and provided links. Doubtless they will not be good enough.

TooMany
2013-Jan-11, 11:12 PM
The Standard Model is a particle physics model, not a cosmological one. So it does not have to account for cosmological missing mass. It is tested and confirmed in labs to a high degree of precision. But in your eagerness to disregard all evidence that does not agree without your dislike of dark matter you are treating what is actually a series of interlocking models as one monolithic one, and claiming that any flaw with this larger system invalidates every part of it.


How can you make such a separation of particle physics from the cosmological missing mass? Nucleosynthesis is based (I assume) on well understood laboratory nuclear physics. But cosmologists assert that 80% of the mass existing during the nucleosynthesis resides in some particle(s) not known to physics. Yet cosmologist still think that nuclear physics is correct in spite of this unknown mass. The outcome is assumed to be the same regardless of the properties of this unknown particle. Or is it more accurate to say that it is assumed that the unknown particle has no effect on nuclear physics, but just adds some "dead" weight?

The only very weakly interacting particles I'm aware of are the neutrinos, but have at most an extremely small mass. What leads physicists to the idea that a very heavy particle could interact so weakly?

No, I'm not claiming that everything is wrong. I'm just skeptical about the level of credence given to these theoretical interpretations. I'm certainly not claiming that observations are wrong. It's just that it's a very curious situation. It seems like something is wrong. Isn't it just a bit self-contradictory to claim that the physics of nucleosynthesis is thoroughly understood, but 80% of the mass involved is a complete mystery to physics? If not, why not?

Shaula
2013-Jan-12, 08:35 AM
It is pretty simple. The matter we see was generated from something we do understand and can reproduce and model in the lab. There are tunable parameters (density, photon-baryon ratio etc) that we can explore and model. It is explaining those tuned parameters, how they had the values then from what we see now, that is where the Dark matter comes in.

Whereas your stance requires all matter outside our lab (including in stars and so on) to behave radically differently depending on where it is. If we follow your beliefs to their conclusion then we may as well stop particle physics, roll up research and give up because unless we put a probe in the middle of a star/at the moment of nucleosynthesis we can not know what is going on.


What leads physicists to the idea that a very heavy particle could interact so weakly?
Do you understand what weakly interacting means? Your question makes no sense at all.


Yet cosmologist still think that nuclear physics is correct in spite of this unknown mass.
Because we can test and measure things locally. Isn't your whole objection to DM that we have not done this? And yet as soon as a piece of evidence conflicts with your beliefs you immediately disregard lab work! This is why I find arguing with you so fruitless on this topic. You pick your evidence and throw stuff out based solely on how strongly it backs you up. It is an argument we can never win with you.

Cougar
2013-Jan-12, 01:15 PM
If you admit to being ignorant about this:


My understanding of the reason it "must" be non-baryonic is that the nucleosynthesis model limits the amount of baryonic matter produced far below the observed mass. I'm not sure however exactly what observations impose this limit.

Then on what basis do you make the following claim?


The nucleosynthesis theory is rather speculative in the first place...

TooMany
2013-Jan-12, 08:00 PM
It is pretty simple. The matter we see was generated from something we do understand and can reproduce and model in the lab. There are tunable parameters (density, photon-baryon ratio etc) that we can explore and model. It is explaining those tuned parameters, how they had the values then from what we see now, that is where the Dark matter comes in.


Non-baryonic dark matter is more than "tuning". With tunable parameters, we take the physics we know and adjust conditions of the early universe to match observation, fine. But this failed. We could not make it match observation. So we added an unknown substance that comprises 80% of all matter. Then we assume that the properties of this unknown substance are such that it has no effect on the application of known physics to the problem. That's certainly a possibility, but there is no basis for such an assumption (unless you can explain one). It's a conjecture but it is taken so seriously that it runs theoretical cosmology and astronomy.



Whereas your stance requires all matter outside our lab (including in stars and so on) to behave radically differently depending on where it is.


No, absolutely wrong. Stars per se work just fine without non-baryonic dark matter. What doesn't work without it is the theory of creation of the elements. So we claim we can add something not found in our lab and presumably not existing in our lab experiments and still have our known physics behave that exact same way as it does in the lab.

You are also wrong that I think this is an impossible conclusion. If we find this non-baryonic matter, great. But, do we let this guess drive all of our thinking about processes in the Universe to the exclusion of a more mundane explanation of dark matter - dark baryons? True if it is just baryons then there is something wrong with our thinking about the creation of elements, but that is a possibility as well.



If we follow your beliefs to their conclusion then we may as well stop particle physics, roll up research and give up because unless we put a probe in the middle of a star/at the moment of nucleosynthesis we can not know what is going on.


Oh but we have a very good idea about what's going on in stars using what we actually know. It works, no reason to discard that. What doesn't work is the application of what we know to the idea that the Universe started as an extremely hot soup of energy in which at some point it cooled enough for atomic nuclei to form. It doesn't come out right, unlike stars. So not understanding this failure, we hypothesize a new substance was there in great abundance but assume it has no effect on our nucleosynthesis calculations. It is not the same conditions as in the lab. It has a brand new condition - 80% of the mass is an unknown substance.

It certainly is possible that this non-baryonic particle actually exists, but it is hard to find.



Do you understand what weakly interacting means? Your question makes no sense at all.


I think the term "weakly interacting" speaks for itself. This new particle fails to have any substantial interaction with baryonic matter. The new particles pass directly through dense atomic nuclei but nothing happens (in 99.99999999% of cases), like neutrinos. However as mass it interacts gravitationally. Have I got that right? Physicists have been assuming that it has a large mass (in the Gev). Why such a large mass? Because we would have found it in collisions if it had a smaller mass? Or perhaps because if the mass was small, it would be too hot to form halos? I just read a lay article suggesting it might have a small mass like 10 Mev???



Because we can test and measure things locally. Isn't your whole objection to DM that we have not done this? And yet as soon as a piece of evidence conflicts with your beliefs you immediately disregard lab work!


If we did find it in the lab and could establish that it exists in the proper quantities then of course the conjecture is correct. No I don't disregard lab work as I've made clear I hope.



This is why I find arguing with you so fruitless on this topic. You pick your evidence and throw stuff out based solely on how strongly it backs you up. It is an argument we can never win with you.

What did I throw out? I think you are overreacting to my skepticism. What really bothers me is that this constructed framework of CDM appears to dominate all mainstream thinking about the Universe. Whenever some non-conforming observation is made, everyone seems to work very hard to continue to make this model fit. I guess they have decided collectively that it's the only possibility.

Take the cooling flows I was trying to discuss in another thread. Simple analysis suggests that large amounts of baryonic matter should be falling into the center of galaxies and cooling. But astronomers don't like that possibility because it does not fit with what they think they know about star formation. They expect all of this matter to end up as stars, but since it does not and does not appear to be gas, it must not exist. Hence they look to AGN to stop the cooling flows. In spite of tons of papers about this theory, there is no convincing mechanism (as yet) for AGN to stop the cooling flows in all clusters.

But suppose the cooling flows actually exist, then ordinary matter would be falling in at perhaps 10 times the rate indicated by star formation. Well, that's kind of nice because you add that up over time and it accounts for the DM. How could that happen? Perhaps in the frigid outskirts of these galaxies the matter condenses into sub stellar objects. Almost every paper I've read about this points out that if it is in-falling it must end up in some non-visible form. But this possible solution is given virtually no attention. Perhaps in part because it would mean that DM must be largely baryonic which contradicts the nucleosynthesis model.

So in a way, the tail wags the dog. The highly theoretical and virtually un-observable early nucleosynthesis trumps the findings from direct observations of clusters. That's what bugs me. I see a bias against simple explanations because they don't jive with the theoretical model of creation of the elements.

TooMany
2013-Jan-12, 08:20 PM
If you admit to being ignorant about this:
Then on what basis do you make the following claim?

The nucleosynthesis theory is rather speculative in the first place...

Well there is the assumption that this big bang started out with arbitrarily high density and temperature, raising the unanswered question what was there at t0. Oh, don't worry about that, let's just look at a temperature that we know something about and explain the formation of the elements. (Do we also explain the formation of protons, neutrons, electrons and photons also or is that something we don't know enough about?) It's speculative that this nucleosynthesis ever happened in this way. Maybe the expansion did not start from infinite density and temperature. That's what I'm mean by speculative. The phenomenon is not observed, it's just conjectured to have occurred.

On the other hand we observe stars and have been able in the lab to produce at the particle level the conditions in stars. We know about fusion, we do some calculations and viola, it works, stars run on fusion! This is not the case with nucleosynthesis. Although we know what we expect to happen in the same way as in stars, it does not work without adding something we do not even know to exist.

It's fun to speculate about origin, but we also need to understand what's going on in the Universe now. Why should speculation about the beginning force us to limit our solutions to direct observations?

Shaula
2013-Jan-12, 11:28 PM
What did I throw out? I think you are overreacting to my skepticism. What really bothers me is that this constructed framework of CDM appears to dominate all mainstream thinking about the Universe.
And so you know why that is? Would you like to hazard a guess as to why? Well I can tell you. It is because other models do not match observations and the DM theory is the best fit. Other theories are always being developed and tested. They do not work as well. That is the simple, crux, of the matter that you refuse to accept and keep picking at. That is why I react to your 'scepticism' - because it is not actually scepticism. You do not like Dark matter and you would rather hint that the entire body of scientists, every one out there, is somehow failing to spot or ignoring models that are not based on Dark Matter.

Anyway, we are back to the exact spot I thought we would be at. There is no argument or piece of theoretical work that will convince you. I'd wager money that if they ever got a jar of dark matter and gave it to you, with a bow around it, you would still be 'sceptical'.


No, absolutely wrong. Stars per se work just fine without non-baryonic dark matter.
Stars confirm our models of nucleosynthesis. The abundances and metalicity of stars is based on the SAME cross sections as we use to work out things about the early universe. That is why I said things had to behave differently everywhere - stars somehow have to obey the same rules the we have extrapolated from the lab based stuff but not the same rules as the primordial plasmas. They have to somehow match our predictions but also be able to change the rules at some arbitrary point to satisfy your dislike of dark matter. It was badly worded but to be honest I don't really care. It could be brilliantly expressed, you will just keep on insisting that it has to be dark snowballs.

TooMany
2013-Jan-13, 06:22 AM
And so you know why that is? Would you like to hazard a guess as to why? Well I can tell you. It is because other models do not match observations and the DM theory is the best fit. Other theories are always being developed and tested. They do not work as well. That is the simple, crux, of the matter that you refuse to accept and keep picking at. That is why I react to your 'scepticism' - because it is not actually scepticism. You do not like Dark matter and you would rather hint that the entire body of scientists, every one out there, is somehow failing to spot or ignoring models that are not based on Dark Matter.


It [non-baryonic DM] may be the best fit when you focus on the theoretical origin of elements. That's what bothers me. The rest of the time the "fit" isn't so good. It's not that I don't like non-baryonic dark matter, it's just that it's (so far) an invention to serve a highly theoretical purpose and that is to explain how nucleosynthesis can be correct while the baryonic mass predicted doesn't match the mass we see.

What I'm trying to express is that theorists are cornered by this need to make the nucleosynthesis work and have gone out of their way to make it work. It makes me suspicious that they might be barking up the wrong tree. I could make a long list of issues with current theory, but you should already know what they are. I just found a new one today. A large scale structure has been found that surpasses the maximum expected size of structure in LCMD by a factor of 4. Astronomers have found a filament-like structure of quasars at z~1.27 that is 4 billion light years long.

This theoretical explanation of the origin of the Universe is held dearly and does not yield to contrary observations. In the case of cooling flows, the assumption continues to be that the cooling flow cannot exist when there is every indication that it should. But there is a certain stubbornness or at least reluctance to consider obvious alternatives. Why? Perhaps because it would not be consistent with this creation model that has emerged?



Anyway, we are back to the exact spot I thought we would be at. There is no argument or piece of theoretical work that will convince you. I'd wager money that if they ever got a jar of dark matter and gave it to you, with a bow around it, you would still be 'sceptical'.


Did I make a spelling error?

But here's the problem with convincing me of your understanding. If you have other strong evidence for non-baryonic CDM, besides the theory about creation of elements, you should site it. You seem to think that I should be absolutely convinced that a theory with many weaknesses is correct. Clearly you are convinced but I am not.

You are wrong concerning my view of this jar of dark matter. If we found evidence of some particle say in the HLC that might fill the bill, that would be encouraging, but not itself enough to settle the issue. We need to know if the particle has sufficient lifetime (much more than the age of the Universe) and we need to show that it actually exists in sufficient quantity. Otherwise it is forever just a conjecture.



Stars confirm our models of nucleosynthesis. The abundances and metalicity of stars is based on the SAME cross sections as we use to work out things about the early universe. That is why I said things had to behave differently everywhere - stars somehow have to obey the same rules the we have extrapolated from the lab based stuff but not the same rules as the primordial plasmas.


Yes, but why is it that you cannot admit that the proposed primordial plasma is not like stars or any particle experiment we have ever performed because it is supposed that 80% of the mass in this primordial plasma is a new unknown particle? Please at least admit that given the assumption (of this new particle) the conditions are not the same as in the lab, so the expectation that things proceed as in the lab is not solid science, it's a speculation. It may be true, but it should be a highly suspect hypothesis rather than doctrine.



They have to somehow match our predictions but also be able to change the rules at some arbitrary point to satisfy your dislike of dark matter. It was badly worded but to be honest I don't really care. It could be brilliantly expressed, you will just keep on insisting that it has to be dark snowballs.

Come on Shaula. I don't know if DM is dark snowballs or not. I just suspect that it is a possibility (for many reasons). Just like non-baryonic DM is just a possibility until we get some proof. When we do get some proof the argument is over, done, kaput. You are teed-off at me because I don't accept this CDM theory as correct. I'm a bit teed-off at you because that's all you will even consider.

Shaula
2013-Jan-13, 08:15 AM
Did I make a spelling error?
Nope, I would never stoop so low (in debating terms) as to attack a typo or spelling error.


But here's the problem with convincing me of your understanding. If you have other strong evidence for non-baryonic CDM, besides the theory about creation of elements, you should site it. You seem to think that I should be absolutely convinced that a theory with many weaknesses is correct. Clearly you are convinced but I am not.
And here is my problem: there are numerous lines of evidence for the various properties we ascribe to dark matter, which you have seen over and over. But you don't like the conclusions drawn from them so you persist in adding more and more unlikely properties to normal matter to make it work. I do not claim that dark matter theory is correct, I claim it is the best fit to observations.


Please at least admit that given the assumption (of this new particle) the conditions are not the same as in the lab, so the expectation that things proceed as in the lab is not solid science, it's a speculation.
What I am saying is that the rules that govern them are the same, what you are saying is physics was different back them. We can simulate and test a range of densities. That is what is being 'tuned' here. You are now claiming that we cannot, that our models break down at temperatures and densities close to what we have achieved and similar to those in stars. Which is why I find your opinion unlikely.


You are teed-off at me because I don't accept this CDM theory as correct. I'm a bit teed-off at you because that's all you will even consider.
No, I am teed off at you because in every thread you can possibly find a link to dark matter you leap in and loudly proclaim that current theories are rubbish, that they are full of holes, that there are way more 'reasonable' theories out there and so on. You then refuse to accept anything that disagrees with that and make people play whack-a-mole with papers and snippets of them you have dug up. You implicitly insult and offend the community by suggesting that they are too focused on dark matter and unable to consider 'out of the box' ideas like dark snowballs and normal matter. You also keep implying that science is massively dogmatic, cannot adapt to new ideas and that it implicitly 'needs' people like you to come along and show it how ridiculous and wrong it is. Then admit or reveal you don't know the underlying physics. For example:

I think the term "weakly interacting" speaks for itself. This new particle fails to have any substantial interaction with baryonic matter.
No. Weakly interacting means it only interacts via the weak force. Just like neutrinos. Something that anyone who has done a reasonable level of background reading on the theories you are trying to attack here would know.

Anyway I am bowing out again. We are exactly where I knew we would end up.

Cougar
2013-Jan-13, 02:18 PM
Anyway I am bowing out again. We are exactly where I knew we would end up.

Ditto.

TooMany
2013-Jan-13, 06:09 PM
Nope, I would never stoop so low (in debating terms) as to attack a typo or spelling error.

Good.



And here is my problem: there are numerous lines of evidence for the various properties we ascribe to dark matter, which you have seen over and over. But you don't like the conclusions drawn from them so you persist in adding more and more unlikely properties to normal matter to make it work. I do not claim that dark matter theory is correct, I claim it is the best fit to observations.


You know I do keep looking for reasons for the non-baryonic interpretation and the ones I'm aware of are nucleosynthesis, failure to detect large quantities of hydrogen gas, failure to detect MACHOs. Perhaps theory of star formation is involved (e.g. more stars would form), I'm not sure. What do you mean by "unlikely properties of normal matter". Do you mean condensation is unlikely?



What I am saying is that the rules that govern them are the same, what you are saying is physics was different back them. We can simulate and test a range of densities. That is what is being 'tuned' here. You are now claiming that we cannot, that our models break down at temperatures and densities close to what we have achieved and similar to those in stars. Which is why I find your opinion unlikely.


You are refusing to understand my simple point and I don't understand why. My point is (and this is my last attempt) that we use what we know to predict results of nucleosynthesis, but it does not work. So we add that 80% of the mass at that time is some unknown particle, but claim that this new unknown particle has no effect on what we see in the absence of the unknown particle. That's all, nothing more. There is no rejection of good physics here, just skepticism of conjectured physics.




No, I am teed off at you because in every thread you can possibly find a link to dark matter you leap in and loudly proclaim that current theories are rubbish, that they are full of holes, that there are way more 'reasonable' theories out there and so on. You then refuse to accept anything that disagrees with that and make people play whack-a-mole with papers and snippets of them you have dug up. You implicitly insult and offend the community by suggesting that they are too focused on dark matter and unable to consider 'out of the box' ideas like dark snowballs and normal matter. You also keep implying that science is massively dogmatic, cannot adapt to new ideas and that it implicitly 'needs' people like you to come along and show it how ridiculous and wrong it is.


Well I admit that I do have a bias toward explaining astronomical observations based on things we know exist. Baryonic matter is just an alternate hypothesis. I have no proof of it's correctness, I just think it's a possibility bolstered by much published evidence of shortcomings in the non-baryonic CDM idea, which you should be well aware of. When considering theories it is important to recognize failures as well as successes.

Scientists cannot make nucleosynthesis work without non-baryonic matter, but I don't think this issue (creation) should be top priority in understanding what is around us. Maybe astronomers are too focused on solving the problem of creation. What's wrong with suggesting that? I don't know that I am correct about that, but it's a possibility. At one time astronomers were stuck on explaining planetary movements with epicycles but then Galileo found a much simpler explanation. It did not go down easily with the astronomers of the time. These things happen in science, old theories sometimes fail. It is neither arrogant nor insulting to suggest such a possibility.


Then admit or reveal you don't know the underlying physics. For example:

No. Weakly interacting means it only interacts via the weak force. Just like neutrinos. Something that anyone who has done a reasonable level of background reading on the theories you are trying to attack here would know.


You've got me on my limited knowledge of nuclear physics, but the weak force has that name for a reason and neutrinos indeed interact very "weakly" (in the literal sense) with baryons.



Anyway I am bowing out again. We are exactly where I knew we would end up.

OK. You expect me to say uncle, but no that's not going to happen until a lot of the current issue are resolved. I look forward to all the knowledge that continues to flow in from our observatories and hard working observational astronomers. That is where the rubber hits the road, not in hypothetical derivations concerning un-observable events.

Reality Check
2013-Jan-14, 01:15 AM
You know I do keep looking for reasons for the non-baryonic interpretation and the ones I'm aware of are nucleosynthesis, failure to detect large quantities of hydrogen gas, failure to detect MACHOs.
This sounds like you have not bothered to even read the Wikipedia article on dark matter (http://en.wikipedia.org/wiki/Dark_matter)!
The main evidence comes from fitting cosmological models to the WMAP data to get that the universe is made of ~4% baryonic matter, 23% non-baryonic matter and the rest dark energy.
The next evidence is the collision of galaxy clusters where two kinds of matter separate.
The next evidence is the simulations of the large scale strutuce of the universe that need dark matter to match observations.
The non-detection of enough baryonic matter to explain even the 4% baryonic matter let alone dark matter (or even dark energy since I suspect that you will not like that either) is evidence for dark matter.



My point is (and this is my last attempt) that we use what we know to predict results of nucleosynthesis, but it does not work. So we add that 80% of the mass at that time is some unknown particle,
We use what we know to predict results of nucleosynthesis and it works. This gives us a limit on the amount of baryonic matter. It is the addition of the observation that the universe is flat from thw WMAP data that shows that we are missing 96% of the universe's energy content.


Well I admit that I do have a bias toward explaining astronomical observations based on things we know exist.

The problem is that you do not seem to have that 'bias'. You want to try to explain non-baryonic matter using speculations about baryonic matter!
The astronomical observations based on things we know exist like ice and gas planets are that they exist around stars and have a tiny percentage of of stellar masses (not the several times needed to even explain the missing matter). There is observational evidence of rogue planets (http://en.wikipedia.org/wiki/Rogue_planet) (about 2 per star).


Scientists cannot make nucleosynthesis work without non-baryonic matter,
...stuff about creation...

Sorry but you are wrong: Scientists make nucleosynthesis work with specific quantities of baryonic matter. No dark matter is used.
I am not sure what you mean by 'creation' but it seems obvious to me that the primordial nucleosynthesis is important to explain what is around us.

TooMany
2013-Jan-14, 11:44 PM
This sounds like you have not bothered to even read the Wikipedia article on dark matter (http://en.wikipedia.org/wiki/Dark_matter)!

The main evidence comes from fitting cosmological models to the WMAP data to get that the universe is made of ~4% baryonic matter, 23% non-baryonic matter and the rest dark energy.
The next evidence is the collision of galaxy clusters where two kinds of matter separate.
The next evidence is the simulations of the large scale strutuce of the universe that need dark matter to match observations.
The non-detection of enough baryonic matter to explain even the 4% baryonic matter let alone dark matter (or even dark energy since I suspect that you will not like that either) is evidence for dark matter.


Oh, but I have read it, more than once. I do not deny the existence of "dark matter", I'm just not sure that it is non-baryonic. The arguments for non-baryonic seem to be these:


Study of nucleosynthesis in the Big Bang produces an upper bound on the amount of baryonic matter in the universe,[9] which indicates that the vast majority of dark matter in the universe cannot be baryons, and thus does not form atoms.


It also cannot interact with ordinary matter via electromagnetic forces; in particular, dark matter particles do not carry any electric charge.

The reason for this immediately following previous conclusion is not stated, but perhaps it is saying that the dark matter particles cannot interfere with nucleosynthesis and this is achieved by no EM interaction? Or maybe they are referring to the invisibility of the substance in general implies that it has no EM interaction.


In clusters such as Abell 1689, lensing observations confirm the presence of considerably more mass than is indicated by the clusters' light alone. In the Bullet Cluster, lensing observations show that much of the lensing mass is separated from the X-ray-emitting baryonic mass.

The missing mass is shown not to be in the X-ray gas which interacts strongly (collides). The missing mass remains associated with the visible galaxies. This is not necessarily evidence for non-baryonic matter. Condensed baryonic matter is also non-collisional.



The anisotropies in the CMB are explained as acoustic oscillations in the photon-baryon plasma (prior to the emission of the CMB after the photons decouple from the baryons at 379,000 years after the Big Bang) whose restoring force is gravity.[52] Ordinary (baryonic) matter interacts strongly with radiation whereas, by definition, dark matter does not—though both affect the oscillations by their gravity—so the two forms of matter will have different effects. The power spectrum of the CMB anisotropies shows a large first peak and smaller successive peaks, with three peaks resolved as of 2009.[51] The first peak tells mostly about the density of baryonic matter and the third peak mostly about the density of dark matter (see Cosmic microwave background radiation#Primary anisotropy).

I guess what this is saying is that fully baryonic matter is not consistent with the power spectrum of the CMB. And some separate measurement of the BAO is also inconsistent with baryonic matter but consistent with the CMB power spectrum? I admit to not knowing enough about these different expectations depending on ratio of baryonic to non-baryonic to fully understand how this conclusion is reached.

On the other hand, I take derivations based on the CMB structure with some degree of skepticism. When the CMB was discovered, it was attributed to cooling after the BB when recombination allowed the universe to become transparent. This was the trump card for the BB theory over others. But, the uniformity of this background was not what was expected from simple expansion and that demanded an explanation. The explanation emerged as a hypothetical period of inflation driven by some hypothetical new field which acted over an unimaginable short period of time to change the density of the universe by a factor bigger than the cube of Avagadro's number. Amazing is too weak a word for this conjecture. Here there are several new hypotheticals, added to the hypothetical non-baryonic dark matter:

1. A new type of repulsive force existed in the extremely-early universe.
2. This force acted at about 10-34 seconds into the existence of the universe for a period of 10-36 seconds and then shut down.
3. This force caused an expansion by a factor of 1078 during this time.

Before you tell me I am arguing from incredulity (concerning these numbers), I admit that is partly true. But part of the skepticism is simply that these are designed conjectures about new physics to fix a problem. None of these conjectures can easily be falsified. Why should anyone be convinced this happened? I guess because they are already convinced that the universe was arbitrarily dense and hot in the past and they are trying to make that explanation work to explain observations not consistent with the simple picture of thermal expansion from an extremely hot, dense state.

This is an accumulation of hypothetical physics, not just hypothesis about the state of known matter at high temperature and density based on known physics, but hypothesis demanding new physics, a new particle (not in the standard model and as yet undetected as a particle) and a new field acting on a minute time period with a fantastic power tailored to solve the magnetic monopole and uniformity problems.

So, my position is that I am skeptical that the interpretation of the CMB is correct. Certainly it may be correct, but to suggest the CMB interpretation has a solid foundation is misleading. Rather, a combination of speculations have been chosen to make the original BB hypothesis work in the face of non-conforming evidence.

Now you will blow your top at me for not admitting that this CMB theory is correct, or at least the only scientifically valid possibility, all others having been eliminated. You are telling me that my speculations about large amounts of condensed baryonic matter in the universe are ridiculous and unsupported, but you expect me to accept all of the above speculations as accurate instead and accept that MACHO micro lensing work done so far has conclusively proven there is not substantial additional dark baryonic matter.

I am not an unreasonable person. But speculations are just that. Current LCDM theory rests on new physics, not just known physics. I feel every right to have some healthy skepticism about it until we have further observations to confirm or deny than we do now. There are a number of ongoing issues with LCDM that astronomers are trying to dispose of: missing dwarf galaxies, large scale structures and anisotropies, dark flows, high-speed cluster collisions, galaxies stripped of DM, lack of DM in globular clusters, oddities in the CMB, cooling flows, galactic evolution through mergers, central DM cusps and growth rates of black holes. I'm well aware that astronomers are working to explain these issues while preserving LCDM, but the issues are not yet disposed of. Before I jump on board I'd rather wait for more observations. That is not an unreasonable position. Planck's results ought to help bolster ideas about the CMB, but if they don't work out right, then what? New physics?



Sorry but you are wrong: Scientists make nucleosynthesis work with specific quantities of baryonic matter. No dark matter is used.


But that's exactly what I said. They conjecture that the dark matter was present at five times the density of the baryonic matter during BB nucleosynthesis, but presume that this non-baryonic matter has no effect at all on the nucleosynthesis as observed in the lab. I suppose the argument is that the non-baryonic matter does not interact and that leaves it with no effect on nucleosynthesis? In actual nucleosynthesis experiments in the lab, the ambient non-baryonic density approaches zero, correct?



I am not sure what you mean by 'creation' but it seems obvious to me that the primordial nucleosynthesis is important to explain what is around us.

Sure that's important, but there are a whole lot of other things needing explanation too (some listed above).

You mentioned "dark energy" and you are correct, I am skeptical, but astronomers have already rewritten the textbooks to say that 73% of the universe is dark energy. Wow. I would have preferred to wait for more observations and analysis of other possible effects before making such a declaration. So I have not jumped on that bandwagon either.

I watch (with great interest) from the sidelines. I just wish we didn't have to wait till 2018 to launch JWST because I think will learn a lot from that observatory. There may be some big surprises. Everybody loves a surprise, right?

P.S. You have noted that the expected 4% of baryonic matter has not been detected. In fact the shortfall percentage wise is quite large. Now if you believe that it does exist, as required by theory, then what form is it in and why haven't we detected it?

tusenfem
2013-Jan-15, 09:07 AM
Okay Toomany that is enough "just asking questions," you are going well away from the mainstream.
Thread closed, if you want to discuss the "baryonic part" of dark matter then take it to ATM.