Dark Matter Particle: Top Candidates

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In summary, dark matter is postulated to exist throughout all the universe, not just in galaxies. It appears to be more prevalent in clusters and on larger scales.
  • #36
Given the speed of light is invariant, the relative motion of galaxies in the foreground is of no consequence. Only mass need be considered for lensing effects.
 
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  • #37
Chronos said:
Given the speed of light is invariant, the relative motion of galaxies in the foreground is of no consequence. Only mass need be considered for lensing effects.
There are some pretty smart people who disagree with you. They think the speed of light might be determined by the texture of the space-time that the light has to cross.

http://arxiv.org/abs/hep-th/9408016

http://arxiv.org/abs/gr-qc/9504041

http://arxiv.org/abs/astro-ph/0001441

The fact that "empty" space is actually a sea of virtual particles is proof that there is an aether. Densification or polarization of this field has implications for the refractive properties of space-time. Lenses are arrangements of matter in which the speed of light is slower (in our real world) than that of the SOL in a "vacuum". By extension, the space-time properties in very massive clusters (caused by ZPE gradients) should produce refractive effects that cannot be explained by the visible matter in the cluster.
 
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  • #38
Chronos said:
Given the speed of light is invariant, the relative motion of galaxies in the foreground is of no consequence. Only mass need be considered for lensing effects.
Granted that if the first early galaxies were moving very slowly with respect to light, then lensing would not be affected by the motion of the foreground galaxy. But I do not know how fast early galaxies were moving, do you? But if there were moving at some portion of light, say 1/3 that of light, then the backgound photons would feel the force of gravity for a longer period of time and be deflected more. I don't see yet what invariance would have to do with anything. Not only that, but the galaxies would acquire some portion of relativistic mass and the gravitational field associated with that.
 
  • #39
Mike2 said:
Granted that if the first early galaxies were moving very slowly with respect to light, then lensing would not be affected by the motion of the foreground galaxy. But I do not know how fast early galaxies were moving, do you? But if there were moving at some portion of light, say 1/3 that of light, then the backgound photons would feel the force of gravity for a longer period of time and be deflected more. I don't see yet what invariance would have to do with anything. Not only that, but the galaxies would acquire some portion of relativistic mass and the gravitational field associated with that.


Surely the galaxies' own local motions were far less than c, and if you mean motion due to expansion, of course the galaxies were not and are not moving in that sense. Space is expanding, the remote galaxies are no more moving like that than we are.
 
  • #40
Mike2 said:
Granted that if the first early galaxies were moving very slowly with respect to light, then lensing would not be affected by the motion of the foreground galaxy. But I do not know how fast early galaxies were moving, do you? But if there were moving at some portion of light, say 1/3 that of light, then the backgound photons would feel the force of gravity for a longer period of time and be deflected more. I don't see yet what invariance would have to do with anything. Not only that, but the galaxies would acquire some portion of relativistic mass and the gravitational field associated with that.
Galaxies moving slowly with respect to light? Light does not have a preferred reference frame. That is why the speed of light is called 'invariant'. And yes, I do know, given what I have read, how fast galaxies were moving in the past. It is called red shift. Your photon deflection model is not supported. Photons entering a gravitational field are blue shifted. When they exit, they are red shifted. The net effect is... zero.
 
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  • #41
Turbo-1 said:
The fact that "empty" space is actually a sea of virtual particles is proof that there is an aether.
Really? That is a pretty bold assertion. Which version of aether do you have in mind, Lorentzian?
 
  • #42
Chronos said:
Really? That is a pretty bold assertion. Which version of aether do you have in mind, Lorentzian?
It's not bold at all. The vacuum of space is not empty, but is populated by zero-point energy fields. The EM ZPE field consists of a sea of self-annihilating virtual particle pairs, and this field exerts a measurable force, as demonstrated by the Casimir effect.

If you know anything about optics, you will know that light travels at different speeds in media of different densities. If you will glance at the papers I linked above, you will see that I am not the only person who has made the logical extension and arrived at the understanding that the speed of light can be affected by the density of the ZPE field through which it propagates. In fact, light propagating through a suppressed ZPE field (between the plates of a Casimir device) can be shown to travel faster than the speed of light in a "vacuum" (normal ZPE field).

"Empty" space isn't. The ZPE field predicted by QED has been proven to exist and its pressure has been measured using test equipment of various designs - not just the "two flat plates" configuration of the first model.
 
  • #43
selfAdjoint said:
Surely the galaxies' own local motions were far less than c, and if you mean motion due to expansion, of course the galaxies were not and are not moving in that sense. Space is expanding, the remote galaxies are no more moving like that than we are.
Well, let's see... durring inflation all matter was moving very fast, right? Then the force of gravity slowed matter even while it condensed to galaxies. I still don't know how fast those first galaxies were moving? Or was everything moving very slowly in comoving coordinates even during inflation?
 
  • #44
If DM is cold and dark, how can it be proven, detected, if something most
think of as invariable isn't "c" for instance, please forgive my ignorance, but
it seems to me that this is a circular argument.
 
  • #45
Mike2 said:
Well, let's see... durring inflation all matter was moving very fast, right? Then the force of gravity slowed matter even while it condensed to galaxies. I still don't know how fast those first galaxies were moving? Or was everything moving very slowly in comoving coordinates even during inflation?
Agreed. They were moving very slowly in comoving coordinates even during inflation. As selfAdjoint pointed out, there is no evidence to suggest relativistic contributions to the mass of distant galaxies are any greater than for local galaxies [which is insignificant]. Cosmological red shift does not affect relativistic mass. Returning to the question of lensing of the CMBR, which is also relevant, see here.
http://home.fnal.gov/~scranton/LensedCMB/effect.html [Broken]
Wolram said:
If DM is cold and dark, how can it be proven, detected, if something most think of as invariable isn't "c" for instance, please forgive my ignorance, but
it seems to me that this is a circular argument.
Agreed. If 'c' is not invariant, a lot of modern theory turns into a mess. On the other hand, there is good evidence that 'c' has not detectably changed for billions of years, if ever [there are some possible anomalies if you go back 12 billion or so years].
 
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  • #46
Chronos said:
Agreed. If 'c' is not invariant, a lot of modern theory turns into a mess. On the other hand, there is good evidence that 'c' has not detectably changed for billions of years, if ever [there are some possible anomalies if you go back 12 billion or so years].
C may be invariant over time. Time (history) may be irrelevant. C must be variable, however, based on the density of the media through which light propogates (basic optics). If the vacuum of space is not truly a "void", but in fact contains fields defined by the base-level energies predicted by QED (the zero-point energy fields), we must expect that the light propogating through these fields can be effected by the properties of these fields.

C as defined as "the speed of light through a vacuum" may only be an ideal, never to be reached. The real C (as a cosmological speed limit) may only be a virtual entity, with a serious dependence on conditions.
 
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  • #47
Chronos said:
Returning to the question of lensing of the CMBR, which is also relevant, see here.
http://home.fnal.gov/~scranton/LensedCMB/effect.html [Broken]
This seems to suggest that the CMB is a backdrop farther away than the most distant galaxies? I didn't catch how much farther they assume the CMB to be. Nor did they explain how all this light got that far out? But, then again, they admit that this is only a simulation and that we do not yet possesses the capability to measure the CMB accurately enough to confirm this lensing of the CMB.

But wait, if the CMB photons were traveling since the beginning without scattering, then the photon that WE receive from the CMB must be the oldest photons of all. The photons from the photon soup that originate at every point and has been redshifted by expansion have photons originating at all points of space, but we only see those that are as old as recombination. CMB photons that were emitted nearer to us at the time of recombination have already past us by and are now headed away from us. We only see the oldest of the CMB. So we are seeing a backdrop. Is this right? Why does it seem that I have to be the one to explain everything?

What confuses me is if we can see these photons emitted so far away by the CMB, then how can there be any kind of horizon that is closer to us behind which galaxies are disappearing? Or is it that the CMB that we see IS the horizon. If so, then shouldn't it be even colder, in fact zero? Or will there come a time when we will no longer see the CMB? Or will the faint, red light of other galaxies take its place as the universe expands?
 
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  • #48
Mike2 said:
This seems to suggest that the CMB is a backdrop farther away than the most distant galaxies? I didn't catch how much farther they assume the CMB to be. Nor did they explain how all this light got that far out? But, then again, they admit that this is only a simulation and that we do not yet possesses the capability to measure the CMB accurately enough to confirm this lensing of the CMB.
Agreed. The CMB is a backdrop to the most distant galaxies yet observed. The current suspect for most distant observed galaxy is z = 10. The CMB is around z = 1100.
Mike2 said:
But wait, if the CMB photons were traveling since the beginning without scattering, then the photon that WE receive from the CMB must be the oldest photons of all. The photons from the photon soup that originate at every point and has been redshifted by expansion have photons originating at all points of space, but we only see those that are as old as recombination. CMB photons that were emitted nearer to us at the time of recombination have already past us by and are now headed away from us. We only see the oldest of the CMB. So we are seeing a backdrop. Is this right?
Agreed.
Mike2 said:
Why does it seem that I have to be the one to explain everything?
That is just the way it works. You shouldn't believe anything until you can explain it to yourself.
Mike2 said:
What confuses me is if we can see these photons emitted so far away by the CMB, then how can there be any kind of horizon that is closer to us behind which galaxies are disappearing?
Agreed. It's not possible.
Mike2 said:
Or is it that the CMB that we see IS the horizon.
Yes.
Mike2 said:
If so, then shouldn't it be even colder, in fact zero?
No. It is exactly as cold as it should be given the age of the universe. The CMB photons we now detect had a temperature of about 3000k at the time they were emitted. The only thing that cools them down is red shift. Since they now are about a temperature of 2.75K, we know that recombination occurred at around z = 1100 [which blue shifts them back to the time they had a temperature of about 3000k].
Mike2 said:
Or will there come a time when we will no longer see the CMB? Or will the faint, red light of other galaxies take its place as the universe expands?
The CMB will gradually grow cooler and cooler, always approaching but never quite reaching absolute zero. No new galaxies will emerge from behind the CMB barrier.
 
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  • #49
Chronos, you seem to be saying on the one hand that there is no horizons beyond which galaxies disappear. But on the other hand, you're saying that there is an expansion of the universe that can be faster than light. Or are you denying that the universe can expand faster than light? Where would that leave inflation? But if the universe can expand faster than light, then the photons from those regions will never reach us, right?
 
  • #50
We have had this discussion before in the thread “Time Dilation & big bang Question”

First the CMB is not an event or particle horizon, in that radiation from beyond the surface of last scattering (SLS) still reaches us, it is just continuously scattered until it finally reaches the SLS. That is why the temperature of the CMB is not zero.

Whether objects in front of that scattering, whose red shifts are finite, are actually traveling faster than light or not depends on how you measure their velocity. That is, how you define and measure distance and time across the space-time curvature and cosmic expansion. One standard convention is to say you can observe cosmologically super-luminal objects. See http://bat.phys.unsw.edu.au/~charley/papers/0310808.pdf
Garth
 
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<h2>1. What is dark matter?</h2><p>Dark matter is a hypothetical form of matter that is thought to make up about 85% of the total matter in the universe. It does not interact with light or other forms of electromagnetic radiation, making it invisible to telescopes and difficult to detect.</p><h2>2. What are dark matter particles?</h2><p>Dark matter particles are theoretical particles that are believed to make up dark matter. They are thought to be different from the particles that make up normal matter, such as protons and electrons.</p><h2>3. What are the top candidates for dark matter particles?</h2><p>There are several top candidates for dark matter particles, including weakly interacting massive particles (WIMPs), axions, and sterile neutrinos. However, none of these candidates have been confirmed as the true dark matter particle.</p><h2>4. How are scientists searching for dark matter particles?</h2><p>Scientists are using a variety of methods to search for dark matter particles, including underground detectors, particle accelerators, and telescopes. These methods look for indirect evidence of dark matter, such as its gravitational effects on visible matter, or attempt to directly detect dark matter particles interacting with normal matter.</p><h2>5. What is the significance of finding the dark matter particle?</h2><p>Finding the dark matter particle would be a major breakthrough in our understanding of the universe. It would help us better understand the composition and evolution of the universe, as well as potentially revealing new physics beyond the Standard Model. It could also have practical applications, such as in the development of new technologies.</p>

1. What is dark matter?

Dark matter is a hypothetical form of matter that is thought to make up about 85% of the total matter in the universe. It does not interact with light or other forms of electromagnetic radiation, making it invisible to telescopes and difficult to detect.

2. What are dark matter particles?

Dark matter particles are theoretical particles that are believed to make up dark matter. They are thought to be different from the particles that make up normal matter, such as protons and electrons.

3. What are the top candidates for dark matter particles?

There are several top candidates for dark matter particles, including weakly interacting massive particles (WIMPs), axions, and sterile neutrinos. However, none of these candidates have been confirmed as the true dark matter particle.

4. How are scientists searching for dark matter particles?

Scientists are using a variety of methods to search for dark matter particles, including underground detectors, particle accelerators, and telescopes. These methods look for indirect evidence of dark matter, such as its gravitational effects on visible matter, or attempt to directly detect dark matter particles interacting with normal matter.

5. What is the significance of finding the dark matter particle?

Finding the dark matter particle would be a major breakthrough in our understanding of the universe. It would help us better understand the composition and evolution of the universe, as well as potentially revealing new physics beyond the Standard Model. It could also have practical applications, such as in the development of new technologies.

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