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Sticks
2012-Oct-09, 05:43 PM
Every student of physics should know how the Michelson-Morley experiment sounded the death knell for the theory of Luminiferous aether, and rightly so because Luminiferous aether does not exist.

But I was wondering if there were any conceptual similarities between that old discredited concept of Luminiferous aether and that of the well established existence of Dark Matter?

Could those of long ago who subscribed to Luminiferous aether claim that our concept of Dark Matter is related? i.e those of long ago wrongly believed that the Earth was swimming in this Luminiferous aether, and today we have shown that dark matter is what keeps galaxies from flying apart when they spin.

Or are both concepts totally unrelated and I have too much time on my hands to even contemplate something so ridiculous? :o

caveman1917
2012-Oct-09, 06:29 PM
The two are unrelated. The aether was necessary because there was a clash between newtonian physics and maxwell's equations. Simplistically speaking maxwell's equations said that light travelled at a certain speed, c. This raised the question, speed with respect to what? In newtonian physics (and galilean relativity that came with it) speed adds up with changing reference frames, just like in everyday experience. If i am driving at 50 km/h and another car at 100 km/h, then changing the frame to myself the other car is going 50 km/h relative to me (and the earth's surface receding at 50 km/h the other way). But maxwell's equations didn't say a word about with respect to what exactly the speed of light would be c, it just said "the speed of light is c". So enter the aether, which people then thought was the supposed frame where light went at c (and in other frames would go at c+v or c-v). However this aether would be more accurately described as a preferred frame of reference, not something with mass or substance (it was heavily debated whether it had any sort of substance). It is a preferred perspective if you will, rather than an actual "thing".

Dark matter on the other hand is certainly a "thing" with mass, but more importantly it is not a frame of reference. It is not a stationary thing that equally fills the entire universe. It comes in lumps and bits of it go this way and other bits the other way. It doesn't have any properties that the aether would need to have.

Sticks
2012-Oct-09, 06:52 PM
Thanks for that, in essence I had an inaccurate idea of what they thought this aether was. The way a certain programme on one of the cable channels gave me a wrong idea.

:doh:

caveman1917
2012-Oct-09, 07:19 PM
Thanks for that, in essence I had an inaccurate idea of what they thought this aether was. The way a certain programme on one of the cable channels gave me a wrong idea.

:doh:

Well there were many diverse ideas about what exactly the aether was - and equally many counterarguments that it couldn't have been those things, the important thing is that it needed to have completely different properties than what dark matter needs to have.

Tensor
2012-Oct-09, 07:47 PM
Well there were many diverse ideas about what exactly the aether was - and equally many counterarguments that it couldn't have been those things, the important thing is that it needed to have completely different properties than what dark matter needs to have.

My favorite was that the LE needed to have properties that seemed to contradict each other. For instance, it had to be stiffer than any know substance (to allow the speed of c to be so high), but then had to be so tenuous that it didn't affect the orbits of astronomical objects.

Grey
2012-Oct-09, 07:59 PM
I would say that the aether wasn't thought of just as a frame of reference for the movement of electromagnetic waves. Rather, there was a sense that any such waves should be conveyed by a medium (just like water waves, sound waves, or any other waves that had been observed up to that point are all carried by a medium of some sort). So the aether was hypothesized to be the medium for electromagnetic radiation. Of course, it had to have some unusual properties. For example, since light waves were known to be transverse waves, it had to be a solid (a liquid or gas can only transmit longitudinal waves). And since the speed of light was so high, the rigidity of the aether had to be huge. And yet despite being an extremely rigid solid, it apparently was massless and did not impede objects passing through it in any way. Part of the reason it didn't survive Einstein's relativity is that there were a host of problems with the idea that had no satisfactory resolution.

Edited to add: And it looks like I took too long typing, and Tensor beat me to it. :)

Tensor
2012-Oct-09, 10:55 PM
Edited to add: And it looks like I took too long typing, and Tensor beat me to it. :)

Yeah, only because you put in all the necessary detail I didn't. :)

undidly
2012-Oct-10, 10:14 AM
I would say that the aether wasn't thought of just as a frame of reference for the movement of electromagnetic waves. Rather, there was a sense that any such waves should be conveyed by a medium (just like water waves, sound waves, or any other waves that had been observed up to that point are all carried by a medium of some sort). So the aether was hypothesized to be the medium for electromagnetic radiation. Of course, it had to have some unusual properties. For example, since light waves were known to be transverse waves, it had to be a solid (a liquid or gas can only transmit longitudinal waves). And since the speed of light was so high, the rigidity of the aether had to be huge. And yet despite being an extremely rigid solid, it apparently was massless and did not impede objects passing through it in any way. Part of the reason it didn't survive Einstein's relativity is that there were a host of problems with the idea that had no satisfactory resolution.

Edited to add: And it looks like I took too long typing, and Tensor beat me to it. :)

The aether is not a rigid solid.
Cannot add more because the explanation is ATM.

Ivan Viehoff
2012-Oct-10, 11:13 AM
The troubling bit about the dark matter hypothesis is that we need so much dark matter, and to account for so much of it we need it to be in exotic forms. Rather less of it and we could account for it as compact halo objects and the like. But despite apparently having a clear signal of it, we seem to have rather incredible difficulty actually getting a more tangible signal of the reality of this exotic matter, a situation which is unusual in relation to recent developments in astrophysics, usually we have managed to track things like this down more quickly, and the effort that goes into tracking things down is never greater.

People have attempted to construct alternative theories of gravity which would remove the need to hypothesize so much dark matter, but so far such attempts have failed. Moreover using conventional gravity theory to map the apparent dark matter haloes of galaxies results in substantially different haloes from one otherwise similar galaxy to another, which is going to be difficult to account for by any adjustment to gravity without still having a lot of dark matter. This is the sense in which dark matter is considered a more solid hypothesis than the alternative one of "there's something wrong with our theory of gravity". But assuredly there is something wrong with our theory of gravity, though.

There's dark energy, which really is a shorthand for "there is something very wrong with our theories when applied on cosmological scales". It would be surprising if the "something wrong" did not significantly affect gravity.

Cougar
2012-Oct-10, 12:36 PM
But assuredly there is something wrong with our theory of gravity, though.

Or maybe not. I wouldn't be too assured.


There's dark energy, which really is a shorthand for "there is something very wrong with our theories when applied on cosmological scales".

What theories do you mean? Instead of "something wrong," I'd just say "there's something, period." We may not have had it wrong, we just didn't have it all.

profloater
2012-Oct-10, 01:07 PM
Have been thinking about what Grey said and it seems a bit too easy to rubbish the aether as not being solid liquid or gas. Obviously it would have been thought of as a fine structure too small to see, and to carry transverse waves it could have been a kind of fluid with elasticity but no viscosity. tension would allow transverse waves, this is not an ATM suggestion but rather seeking to explain the aether history in the history of ideas. A fluid with no viscosity, i.e perfect offers only inertial resistance to a body passing through it and although it is was not formulated as such the aether would have to explain both EM transmission and fundamental inertia.

grapes
2012-Oct-12, 08:48 PM
Have been thinking about what Grey said and it seems a bit too easy to rubbish the aether as not being solid liquid or gas. Obviously it would have been thought of as a fine structure too small to see, and to carry transverse waves it could have been a kind of fluid with elasticity but no viscosity.
There are such things as non-Newtonian fluids that can exhibit elasticity, but, insofar as they are elastic, they act like a solid. They may have different behaviors over different time frames, but in the time frame of the transmission of light, the aether acted as a solid in transmitting transverse waves.


tension would allow transverse waves, this is not an ATM suggestion but rather seeking to explain the aether history in the history of ideas. A fluid with no viscosity, i.e perfect offers only inertial resistance to a body passing through it and although it is was not formulated as such the aether would have to explain both EM transmission and fundamental inertia.You can walk across oobleck if you're fast and forceful enough, but mush into it if you're not. Our oobleck universe? :)

trinitree88
2012-Oct-16, 03:46 PM
Every student of physics should know how the Michelson-Morley experiment sounded the death knell for the theory of Luminiferous aether, and rightly so because Luminiferous aether does not exist.

But I was wondering if there were any conceptual similarities between that old discredited concept of Luminiferous aether and that of the well established existence of Dark Matter?

Could those of long ago who subscribed to Luminiferous aether claim that our concept of Dark Matter is related? i.e those of long ago wrongly believed that the Earth was swimming in this Luminiferous aether, and today we have shown that dark matter is what keeps galaxies from flying apart when they spin.

Or are both concepts totally unrelated and I have too much time on my hands to even contemplate something so ridiculous? :o

Actually, Asimov's treatment of the MM experiment indicates that it never actually discredited the Luminiferous ether...it only showed that you could not find the ether using a MM experiment. It may yet be there. The concensus of the physics community swung towards disregarding it's need to exist, and it hasn't arisen since. pete

and Isaac is not ATM....

Jerry
2012-Oct-16, 04:35 PM
Actually, Asimov's treatment of the MM experiment indicates that it never actually discredited the Luminiferous ether...it only showed that you could not find the ether using a MM experiment. It may yet be there. The concensus of the physics community swung towards disregarding it's need to exist, and it hasn't arisen since. pete

and Isaac is not ATM....
There are unresolved paradox when a frame of reference is missing. The experiments excluded a medium that was not altered by the earth; and other experiments (interplanetary space flights) essentially rule out many other frames-of-reference. It is still a curious result, given that Maxwellian equations work so well with respect to the interaction of light with physical matter; and the way matter aligns magnetic fields and poles.

Hornblower
2012-Oct-16, 05:25 PM
If a large amount of dark matter of whatever stealthy type is needed, so be it. The cosmos is what it is and does what it does, and it does not care whether or not fallible human beings such as ourselves are troubled by it.

Ivan Viehoff
2012-Oct-17, 09:17 AM
What theories do you mean?
The standard model.

sirius0
2012-Oct-17, 10:27 AM
Could Sticks' opening post have been about the Higgs field? Are there any similarities between the two that those of old might latch onto to try and make a zombie life version of LE? It is quirky how it confers mass and inertia .'. setting up space-time for a limit of c speed (well i mean that via inertia, if defined as the energy needed to transfer an object with mass from one frame to a different one, it excludes objects with mass from getting to c) I guess in some ways the Higgs field is also the exact opposite to an LE too?

trinitree88
2012-Oct-17, 11:37 AM
Could Sticks' opening post have been about the Higgs field? Are there any similarities between the two that those of old might latch onto to try and make a zombie life version of LE? It is quirky how it confers mass and inertia .'. setting up space-time for a limit of c speed (well i mean that via inertia, if defined as the energy needed to transfer an object with mass from one frame to a different one, it excludes objects with mass from getting to c) I guess in some ways the Higgs field is also the exact opposite to an LE too?

sirius0. The neutrino sea also limits the velocity of particles. Neutral and charged currents, Z0, and W+,W-...reactions have cross sections that increase as the square of the velocity....so the "sea" becomes viscous indeed as you approach c. SEE:http://cupp.oulu.fi/neutrino/nd-cross.html pete

borman
2012-Oct-21, 09:38 PM
Einstein-Aether theories

There are some theorists who have looked to adding an aether for Dark Matter rather than postulating Dark Matter Particles such as WIMPs or modifying gravity. This aether is not the Luminiferous Aether of the 19th Century.
Here is an example where it has been used recently:
http://arxiv.org/abs/1209.0464
Testing Lorentz invariance of dark matter
This was a subject in another thread on the Astronomy forum started by trinitree88 about Lorentz Invariance Violation.

quantumlevel
2013-Nov-30, 05:33 AM
I'm just a humble amateur in physics. Lots of Wikipedia, some books, no knowledge of the mathematics. In my simplistic ignorance, I get the sense that the luminiferous aether and dark matter theories share notable conceptual connections; each theory "writes into existence" a universally predominant substance, that cannot be seen or even detected except, at best, by indirect evidence, e.g. the assumption that all waves must travel through a medium, or the effect of gravity on the motion of the arms of spiral galaxies. Facetiously, one could say the luminiferous aether is the dark matter.

Noclevername
2013-Nov-30, 04:43 PM
I'm just a humble amateur in physics. Lots of Wikipedia, some books, no knowledge of the mathematics. In my simplistic ignorance, I get the sense that the luminiferous aether and dark matter theories share notable conceptual connections; each theory "writes into existence" a universally predominant substance, that cannot be seen or even detected except, at best, by indirect evidence, e.g. the assumption that all waves must travel through a medium, or the effect of gravity on the motion of the arms of spiral galaxies. Facetiously, one could say the luminiferous aether is the dark matter.

But DM is not "universally predominant"; it has been measured only as haloes around galaxies, meaning it is gravitationally bound.

Strange
2013-Nov-30, 04:53 PM
Well, predominantly in/around galaxies. But gravitational microlensing shows that it appears to be more widely distributed - especially in the large scale structure of clusters and galaxies.

The other difference is that there was never any evidence for the luminiferous aether; just a baseless assumption that it ought to be there ("Oh. No it's not. Never mind. Move on.")

The aether would also have required physically implausible properties while there is nothing implausible about the nature of dark matter.

quantumlevel
2013-Nov-30, 06:37 PM
Maybe not predominant, but overwhelmingly more massive than baryonic matter.

quantumlevel
2013-Nov-30, 06:41 PM
Is there not some level of implausibility in that visible and detectable matter mysteriously constitutes only a small fraction of the mass in the universe?

cjameshuff
2013-Nov-30, 06:47 PM
Luminiferous aether:
Created because intuition and common experience leads us to expect waves to require a medium. Massless, frictionless, and otherwise unlike anything else we know of, and by definition required for the propagation of electromagnetism. It must be quite uniform, judging from our clear view of the sky and the observed uniformity of physics across the universe (consider that atomic interactions are mainly electromagnetic, weirdness would be expected if the medium carrying electromagnetism wasn't uniform). Experiments have been devised to detect it, none have been successful.

Dark matter:
Created because various measurements showed substantially more mass than was visible. Additionally found to improve models of matter production at the beginning of the universe. Very non-uniform in distribution, allowing it to be distinguished from a simple gravitational effect by observations of lensing in systems that separate it from normal matter, such as multiple galaxy cluster collisions. A good number of theoretical possibilities for composition, and particles similar to what would be required are known to exist.

The two are really not at all alike.

quantumlevel
2013-Nov-30, 07:12 PM
The similarity is that both theories postulate(d) the existence of an exotic form of matter that is (was) undetectable. To be clear, I am not arguing against the existence of dark matter. I know there are multiple reasons to believe it exists. I am a physics amateur, and I am unqualified to have an informed opinion on the subject. As someone who knows next to nothing, I simply find the comparison between luminiferous aether and dark matter interesting and, on some level, troubling.

StupendousMan
2013-Nov-30, 10:49 PM
I am a physics amateur, and I am unqualified to have an informed opinion on the subject. As someone who knows next to nothing, I simply find the comparison between luminiferous aether and dark matter interesting and, on some level, troubling.

I'm a physics professional. The fact that you find the comparison troubling means nothing to me. Why should it? Should a heart surgeon feel concerned if a plumber worries about the similarity between the aortic valve and a plunger?

quantumlevel
2013-Nov-30, 11:21 PM
I'm a physics professional. The fact that you find the comparison troubling means nothing to me. Why should it? Should a heart surgeon feel concerned if a plumber worries about the similarity between the aortic valve and a plunger?

Fine. As someone who wishes he had a deeper understanding of cosmology, thank you for your thoughtful reply.

Strange
2013-Dec-01, 12:32 AM
The similarity is that both theories postulate(d) the existence of an exotic form of matter that is (was) undetectable.

But, again, the difference is that the aether was never detected; there was never any evidence for it. While dark matter is detected; there is evidence for it.

wd40
2013-Dec-01, 01:26 AM
Did Einstein accept a non-luminferous ether?
Tesla and Einstein Were Both Right (http://milesmathis.com/tesla.html)

cjameshuff
2013-Dec-01, 01:52 AM
The similarity is that both theories postulate(d) the existence of an exotic form of matter that is (was) undetectable.

Dark matter is detectable: it wouldn't have even been postulated without observations that indicated more mass than was directly visible. Though poorly understood, particles with similar properties to those needed are known, it's not that exotic. Direct detection should be possible with sufficiently sensitive equipment, and multiple attempts are under way.

The aether was an appealingly intuitive model which wasn't necessary to explain any existing observations, required a substance with characteristics unlike anything else known, and never found observational support, despite being something that should be rather easier to detect than even neutrinos.

I don't see the similarity. It's not more comfortable or appealing to think that most of the universe is some weakly interacting matter that is only really relevant on galactic scales. If there's any sort of emotional bias involved, it'd be against it...as illustrated by the many people trying to replace dark matter with things like MOND which only work in particular special cases, if at all. (Now, you might draw a comparison between MOND theories and the aether...both apparently being driven primarily by philosophical objections to the alternative.)

Strange
2013-Dec-01, 01:54 AM
Did Einstein accept a non-luminferous ether?

No he did once (foolishly) use the word ether as an analogy for space-time. Many other people have used the word as an analogy for many other things. It has become meaningless.


Tesla and Einstein Were Both Right

Good grief.

LaurieAG
2013-Dec-01, 06:31 AM
But I was wondering if there were any conceptual similarities between that old discredited concept of Luminiferous aether and that of the well established existence of Dark Matter?

That's an interesting idea Sticks, it may be possible to build a conceptual bridge from each side to the benefit of the structural integrity of both sides.

If you regard the 'luminiferous aether' conceptually as the elusive preferred Euclidean/Newtonian 'time space' frame (x, y & z axis measured in light secs or years etc) at a discrete point in time you could use it as a classical mechanical reference point for a translated/transformed SR frame (and by extension GR) that can be used as a tool for the further analysis of the phenomena of dark matter.

At any discrete instance in time the speed of light c, time and any distances based on c and time will all be rigidly consistent with each other (which may not necessarily be the case at other discrete instances in time) in this frame allowing for accurate comparisons between current relativistic models and astronomical observations made of the captured photon paths produced by continuously emitting sources rotating in Euclidean space.

Shaula
2013-Dec-01, 07:09 AM
Tesla and Einstein Were Both Right (http://milesmathis.com/tesla.html)
Why would you even link such a laughable article?

David Sims
2013-Dec-10, 12:50 PM
The troubling bit about the dark matter hypothesis is that we need so much dark matter, and to account for so much of it we need it to be in exotic forms. Rather less of it and we could account for it as compact halo objects and the like. But despite apparently having a clear signal of it, we seem to have rather incredible difficulty actually getting a more tangible signal of the reality of this exotic matter, a situation which is unusual in relation to recent developments in astrophysics, usually we have managed to track things like this down more quickly, and the effort that goes into tracking things down is never greater.

People have attempted to construct alternative theories of gravity which would remove the need to hypothesize so much dark matter, but so far such attempts have failed. Moreover using conventional gravity theory to map the apparent dark matter haloes of galaxies results in substantially different haloes from one otherwise similar galaxy to another, which is going to be difficult to account for by any adjustment to gravity without still having a lot of dark matter. This is the sense in which dark matter is considered a more solid hypothesis than the alternative one of "there's something wrong with our theory of gravity". But assuredly there is something wrong with our theory of gravity, though.

There's dark energy, which really is a shorthand for "there is something very wrong with our theories when applied on cosmological scales". It would be surprising if the "something wrong" did not significantly affect gravity.

I doubt that there is a WIMP component to dark matter. I'm skeptical about any hypothetical new particle, and I think that the neutrino is about as close to one as you'll ever find.

Instead, I believe that the excess matter is something like plain cold matter in forms ranging from sand-sized grains and gravel to perhaps the size of a minor planet, such as Ceres or Pluto. Oort cloud material, considerably more dense than we've supposed it to be, but not dense enough to observe in interstellar space.

Seeing this stuff might be challenging. In the general neighborhood of the sun, the Orion spur, but not near any of its stars, the integrated apparent magnitude is about −6.7, which corresponds to a radiant flux of 0.00001225 Wm⁻≤ and to an equilibrium blackbody temperature of 2.71K.

Although the atoms and molecules in the interstellar medium will have been kicked around by photons until they've acquired an average kinetic temperature of about 5000K, these larger bits of mass are too heavy to be affected like that, and their observed temperatures will therefore be about the same as the cosmic microwave background radiation. I don't think that the density of this material needs to be high enough to create a low-temperature fog that would cause a significant noise in front of the CMBR signal.

We have trouble enough observing brown dwarfs at any distance. However, at the distances we can see brown dwarfs, we see a lot of them. It appears that the trend in the general distribution of number density vs. mass, rising toward the lower masses, decreasing toward the bigger masses, continues past the red dwarfs, through the brown dwarfs, and likewise for even smaller stuff.

Our galaxy has about as much of its stellar mass in red dwarfs alone as it does in all other main sequence stars. It may have a similar amount packed away in brown dwarfs, another similar amount in rogue planets too small to be considered brown dwarfs, another similar amount in icy asteroids, etc. Maybe the total of all this material could account for dark matter. Then there wouldn't need to be any as-yet undiscovered particle that interacts only by gravity.

trinitree88
2013-Dec-10, 07:53 PM
Dark matter is detectable: it wouldn't have even been postulated without observations that indicated more mass than was directly visible. Though poorly understood, particles with similar properties to those needed are known, it's not that exotic. Direct detection should be possible with sufficiently sensitive equipment, and multiple attempts are under way.

The aether was an appealingly intuitive model which wasn't necessary to explain any existing observations, required a substance with characteristics unlike anything else known, and never found observational support, despite being something that should be rather easier to detect than even neutrinos.

I don't see the similarity. It's not more comfortable or appealing to think that most of the universe is some weakly interacting matter that is only really relevant on galactic scales. If there's any sort of emotional bias involved, it'd be against it...as illustrated by the many people trying to replace dark matter with things like MOND which only work in particular special cases, if at all. (Now, you might draw a comparison between MOND theories and the aether...both apparently being driven primarily by philosophical objections to the alternative.)

cjameshuff. I think I'd take exception to that. The well established part of dark matter is that the rotation curves of galaxies indicate that they are non-Keplerian and the outer stars in the periphery are apparently exceeding escape velocity at their relative distances from the galactic bulge.
There are no known particles that have been seen and confirmed as "dark matter" yet, in the annals of the Particle Data Group, whose job it is to list them all. SEE: http://pdg.lbl.gov/ Much has been speculated about them as it is still observationally confirmed, based on mass / luminosity ratios which have been pretty good through the decades, with the exception of the protests of Zwicky long ago, and Vera Rubin in the interim.
That said, no SUSY particle has ever reared it's ugly head, like some Medusa, in over thirty years of searching....nor any of the other candidates for non-SM baryonic dark matter. It'd put the issue to rest, if they did. If, and when, any such candidate is found , good reason needs to exist why the stuff doesn't gravitationally clump in the middle of regular spirals like the Milky Way or in the detectors built for accelerator labs, cosmic ray studies, or neutrino detectors.
New sensors designed to look for difficult to detect molecular hydrogen stand a better chance of changing galactic mass profiles as the tracers used ( CO, HCN) are subject to nuclear photodisintegration in the galactic halo from impinging gamms ray bursts. It takes ~10-20 Mev to pop out a proton or a neutron from these light atoms, and GRB's far exceed that. With a beaming factor of ~ 10,000, (Middleditch) we only see the ones aimed at us, which runs ~ 1/day, but the galaxy feels 10,000 times that.
Photodissociated neutrons decay in ~ 14 minutes to atomic hydrogen. If hot it ionizes, if cool it undergoes an exothermic conversion to molecular hydrogen. So the molecular hydrogen in the periphery of a galaxy loses it's tracers of CO, and HCN over time. Scant fusion occurs there,( it's not nil, because an occasional thermal neutron can recombine with ambient nuclei),so you end up with a giant molecular hydrogen halo, devoid of tracer gases. Very tough to see with contemporary instrumentation.
Betcha a hot fudge sundae, new satellites will find it around these DM-loaded spirals. pete

Shaula
2013-Dec-10, 08:42 PM
cjameshuff. I think I'd take exception to that....
Well if you are right it will be interesting trying to fix all the other problems the matter being baryonic will cause.

Jean Tate
2013-Dec-10, 10:54 PM
I doubt that there is a WIMP component to dark matter. I'm skeptical about any hypothetical new particle, and I think that the neutrino is about as close to one as you'll ever find.

Instead, I believe that the excess matter is something like plain cold matter in forms ranging from sand-sized grains and gravel to perhaps the size of a minor planet, such as Ceres or Pluto. Oort cloud material, considerably more dense than we've supposed it to be, but not dense enough to observe in interstellar space.

Seeing this stuff might be challenging. In the general neighborhood of the sun, the Orion spur, but not near any of its stars, the integrated apparent magnitude is about −6.7, which corresponds to a radiant flux of 0.00001225 Wm⁻≤ and to an equilibrium blackbody temperature of 2.71K.

Although the atoms and molecules in the interstellar medium will have been kicked around by photons until they've acquired an average kinetic temperature of about 5000K, these larger bits of mass are too heavy to be affected like that, and their observed temperatures will therefore be about the same as the cosmic microwave background radiation. I don't think that the density of this material needs to be high enough to create a low-temperature fog that would cause a significant noise in front of the CMBR signal.

We have trouble enough observing brown dwarfs at any distance. However, at the distances we can see brown dwarfs, we see a lot of them. It appears that the trend in the general distribution of number density vs. mass, rising toward the lower masses, decreasing toward the bigger masses, continues past the red dwarfs, through the brown dwarfs, and likewise for even smaller stuff.

Our galaxy has about as much of its stellar mass in red dwarfs alone as it does in all other main sequence stars. It may have a similar amount packed away in brown dwarfs, another similar amount in rogue planets too small to be considered brown dwarfs, another similar amount in icy asteroids, etc. Maybe the total of all this material could account for dark matter. Then there wouldn't need to be any as-yet undiscovered particle that interacts only by gravity.
Aren't there rather severe constraints on the space density of massive compact objects, in our region of the Milky Way and along various sight-lines out several tens/hundreds of thousands of pc (from the many microlensing surveys, MACHO, OGLE, MOA, etc)? And don't these survey results pretty much mean that massive baryonic objects cannot be more than a minor component of any missing mass (for various regions of our galaxy and its halo)?

For smaller stuff - "from sand-sized grains and gravel to perhaps the size of a minor planet" - doesn't our solar system's relative velocity pretty much guarantee that we'd see an awful lot of this, in the form of hypervelocity meteorites? If so, the size and velocity distribution of any compact baryonic matter would have to be extremely peculiar for it to have been missed so far, wouldn't it (if it's to comprise more than a minor fraction of any missing mass)?

More generally, don't the various CMB analyses, combined with BBN ones, put extremely strong limits on how much baryonic matter there can be, irrespective of what form it's in and where it's located? And don't those limits rule out anything more than a quite minor fraction of any missing mass being baryonic?

StupendousMan
2013-Dec-11, 12:18 AM
So the molecular hydrogen in the periphery of a galaxy loses it's tracers of CO, and HCN over time. Scant fusion occurs there,( it's not nil, because an occasional thermal neutron can recombine with ambient nuclei),so you end up with a giant molecular hydrogen halo, devoid of tracer gases. Very tough to see with contemporary instrumentation.


Interesting idea.

Have you gone through the calculations to see if the rate at which heavy atoms should be spallated into hydrogen by the known gamma-ray background is high enough to destroy the expected amount of, say, oxygen, within a Hubble time?

WayneFrancis
2013-Dec-11, 02:25 AM
I doubt that there is a WIMP component to dark matter. I'm skeptical about any hypothetical new particle, and I think that the neutrino is about as close to one as you'll ever find.

Instead, I believe that the excess matter is something like plain cold matter in forms ranging from sand-sized grains and gravel to perhaps the size of a minor planet, such as Ceres or Pluto. Oort cloud material, considerably more dense than we've supposed it to be, but not dense enough to observe in interstellar space.

Seeing this stuff might be challenging. In the general neighborhood of the sun, the Orion spur, but not near any of its stars, the integrated apparent magnitude is about −6.7, which corresponds to a radiant flux of 0.00001225 Wm⁻≤ and to an equilibrium blackbody temperature of 2.71K.

Although the atoms and molecules in the interstellar medium will have been kicked around by photons until they've acquired an average kinetic temperature of about 5000K, these larger bits of mass are too heavy to be affected like that, and their observed temperatures will therefore be about the same as the cosmic microwave background radiation. I don't think that the density of this material needs to be high enough to create a low-temperature fog that would cause a significant noise in front of the CMBR signal.

We have trouble enough observing brown dwarfs at any distance. However, at the distances we can see brown dwarfs, we see a lot of them. It appears that the trend in the general distribution of number density vs. mass, rising toward the lower masses, decreasing toward the bigger masses, continues past the red dwarfs, through the brown dwarfs, and likewise for even smaller stuff.

Our galaxy has about as much of its stellar mass in red dwarfs alone as it does in all other main sequence stars. It may have a similar amount packed away in brown dwarfs, another similar amount in rogue planets too small to be considered brown dwarfs, another similar amount in icy asteroids, etc. Maybe the total of all this material could account for dark matter. Then there wouldn't need to be any as-yet undiscovered particle that interacts only by gravity.

You can't have your cake and eat it to. It can't be planets etc because it total mass is about 5 times the amount of baryonic matter we observe. You can't say it would be lost in the noise of the CMB because the amount of energy it would produce is still very significant. The idea that MACHOs can make up the bulk of missing matter is pretty much ruled out by observation. Though these objects may not be very luminous in the visible spectrum they still would radiate a significant amount of energy in other ranges far above the CMB. Last I heard they constrained MACHOs to like less then 1% of the missing mass that is currently labelled as dark matter. We also don't just need radiation from these types of objects. They'd create microlensing events which are not observed in the quantities you would expect.

trinitree88
2013-Dec-11, 05:54 PM
Interesting idea.

Have you gone through the calculations to see if the rate at which heavy atoms should be spallated into hydrogen by the known gamma-ray background is high enough to destroy the expected amount of, say, oxygen, within a Hubble time?

StupendousMan. Let me PM you. pete

wd40
2013-Dec-12, 01:31 AM
Has any progress been made in Dark Mattter detection since Lammerzahl wrote this in 2006?


"Dark matter is needed if one assumes Einsteinís field equations to be valid. However, there is no single observational hint at particles which could make up this dark matter. As a consequence, there are attempts to describe the same effects by a modification of the gravitational field equations, e.g. of Yukawa form, or by a modification of the dynamics of particles, like the MOND ansatz, recently formulated in a relativistic frame. Due to the lack of direct detection of Dark Matter particles, all those attempts are on the same footing."

Ken G
2013-Dec-12, 04:24 AM
cjameshuff. I think I'd take exception to that. The well established part of dark matter is that the rotation curves of galaxies indicate that they are non-Keplerian and the outer stars in the periphery are apparently exceeding escape velocity at their relative distances from the galactic bulge.
There are no known particles that have been seen and confirmed as "dark matter" yet, in the annals of the Particle Data Group, whose job it is to list them all. I believe cjameshuff may have been referring to the fact that neutrinos should be considered "dark matter," so we do have dark matter already in standard physics, it's just not "the" dark matter because it doesn't have the right properties and there isn't enough of it. I think this is an important point-- postulating dark matter is really nothing new, it's just that we are in the period between when something is postulated and when it is confirmed. Neutrinos themselves went through a phase like that. Now I'm not claiming to know that we will ever confirm it, or even that it is right, I'm just saying it's not really all that new of a way for physics to proceed. Not that all the other avenues should be shut off, they should certainly be pursued... but at a lower priority.

Shaula
2013-Dec-12, 06:51 AM
Has any progress been made in Dark Mattter detection since Lammerzahl wrote this in 2006?

"Dark matter is needed if one assumes Einstein’s field equations to be valid. However, there is no single observational hint at particles which could make up this dark matter. As a consequence, there are attempts to describe the same effects by a modification of the gravitational field equations, e.g. of Yukawa form, or by a modification of the dynamics of particles, like the MOND ansatz, recently formulated in a relativistic frame. Due to the lack of direct detection of Dark Matter particles, all those attempts are on the same footing."
Actually those attempts are not quite on the same footing. There are a whole list of other pieces of evidence that something like dark matter is needed. a simple tweak to gravity doesn't help with stuff like the BAO spectrum, nucleosynthesis, large scale structure formation and so on. These are not impossible to account for, but fixating on the gravitational effect rather misses the point of why the dark matter suggestion is more attractive than other ideas.

caveman1917
2013-Dec-13, 11:37 AM
I believe cjameshuff may have been referring to the fact that neutrinos should be considered "dark matter," so we do have dark matter already in standard physics, it's just not "the" dark matter because it doesn't have the right properties and there isn't enough of it. I think this is an important point-- postulating dark matter is really nothing new, it's just that we are in the period between when something is postulated and when it is confirmed. Neutrinos themselves went through a phase like that. Now I'm not claiming to know that we will ever confirm it, or even that it is right, I'm just saying it's not really all that new of a way for physics to proceed. Not that all the other avenues should be shut off, they should certainly be pursued... but at a lower priority.

As Tensor's signature line says: "Neptune: the original dark matter." (if i recall correctly, haven't seen him around in a while).

wd40
2013-Dec-20, 02:07 AM
Harold Aspden (http://peswiki.com/index.php/Harold_Aspden) died in 2011.

Has his super-dense aether theory (http://www.haroldaspden.com) been throughly discredited? Was there anything acceptable to mainstream of practical value in his writings?

Shaula
2013-Dec-20, 06:52 AM
I flicked through two of his works on that site. I saw absolutely nothing that has not been debunked over and over on this forum. There was little detail, lots of chains of speculation and a hefty dose of crying over the apparent beastliness of scientists for not appreciating his genius. Strawman attacks on Einstein, electric Sun arguments, vague appeals to logic - junk science, and not that convincingly written junk at that.

Weingeist
2014-Aug-07, 01:49 PM
I posted this link a couple years ago on references which provide absolute indisputable proof that the aether exists. It has since been updated.

http://sciliterature.50webs.com/RelativityDebates.htm

Swift
2014-Aug-07, 04:48 PM
I posted this link a couple years ago on references which provide absolute indisputable proof that the aether exists. It has since been updated.

http://sciliterature.50webs.com/RelativityDebates.htm
Weingeist,

If you wish to advocate a non-mainstream position, such as the existance of the aether, you will do so in our ATM forum or you won't do it on CQ. But you should know that, since you've been a member since 2007, and you will thus earn an infraction.

Weingeist
2014-Aug-08, 09:37 AM
Weingeist,

If you wish to advocate a non-mainstream position, such as the existance of the aether, you will do so in our ATM forum or you won't do it on CQ. But you should know that, since you've been a member since 2007, and you will thus earn an infraction.


I posted something over here years ago
http://cosmoquest.org/forum/showthread.php?66904-Does-the-electromagnetic-aether-exist
and as you can see I was harrassed and insulted.

Swift
2014-Aug-08, 12:41 PM
I posted something over here years ago
http://cosmoquest.org/forum/showthread.php?66904-Does-the-electromagnetic-aether-exist
and as you can see I was harrassed and insulted.
You weren't harrassed and insulted, you were questioned about your ATM idea (as per our rules) and you were instructed by moderators to follow our rules, an inability you continue to demonstrate. That will earn you another infraction.

As this thread seems to outlived its usefulness, I'm closing it.