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Teslascience
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Do dark matter and energy affect on red shift phenomena? If yes, what, and what is the consequence of it?
rootone said:Dark matter doesn't have much to do with red shift, but dark energy does.
The entire concept of dark energy arises from observations of red shifted light seen to be emitted by distant galaxies.
Ibix said:Dark matter contributes to the "normal" matter density of the universe. That isn't really an opposite effect to dark energy, just a different one.
Yes, both have a significant effect.Teslascience said:Do dark matter and energy affect on red shift phenomena? If yes, what, and what is the consequence of it?
Interesting, and I will think about. I think further that the relation of dark energy to dark matter has also some effect on red shift, but this is not an exact thing we don't have enough information yet.phinds said:Yes, both have a significant effect.
The rate of expansion of the universe depends on three things
1) the expansion rate after inflation
2) the amount of matter in the universe
3) the effects of dark energy
Since dark matter is by far the preponderance of matter in the universe it certainly has a significant effect on the expansion. If there were no dark matter, the acceleration caused by dark energy would have started much sooner than it did
There is no "relation of dark energy to dark matter". They have nothing to do with each other and only have the same "dark" name for unrelated reasons.Teslascience said:Interesting, and I will think about. I think further that the relation of dark energy to dark matter has also some effect on red shift, but this is not an exact thing we don't have enough information yet.
Well since expansion happens on megaparsec level I really doubt that.jocarren said:There is no relation betwen both concepts, but, I can't help wondering: can expanding spacetime have any impact on fundamental particles interaction, thus having some effect on rest mass? I fear my standard model kung fu is not strong enough.
“Expanding spacetime” means that comoving objects are getting farther apart from each other. This doesn’t effect their rest mass. Note, mass is invariant. The mass of a given object depends on its internal energy (adding heat increases the mass), not on its motion relativ to another object.jocarren said:There is no relation betwen both concepts, but, I can't help wondering: can expanding spacetime have any impact on fundamental particles interaction, thus having some effect on rest mass?
timmdeeg said:“Expanding spacetime” means that comoving objects are getting farther apart from each other. This doesn’t effect their rest mass. Note, mass is invariant. The mass of a given object depends on its internal energy (adding heat increases the mass), not on its motion relativ to another object.
Then you should go back and read the forum rules.jocarren said:I'm aware of that, just sharing a baseless speculation.
phinds said:Then you should go back and read the forum rules.
phinds said:Yes, both have a significant effect.
The rate of expansion of the universe depends on three things
1) the expansion rate after inflation
2) the amount of matter in the universe
3) the effects of dark energy
Since dark matter is by far the preponderance of matter in the universe it certainly has a significant effect on the expansion. If there were no dark matter, the acceleration caused by dark energy would have started much sooner than it did
Dark Energy causes expansion. Matter, both normal and dark, cause contraction, so no I don't believe you are correct.ohwilleke said:The answer to that question, I believe (and feel free to correct me if I am wrong), is that dark matter and dark energy have an effect no different from comparable mass-energy densities of ordinary matter distributed in the same places would. In other words, all matter and energy give rise to gravitational redshift in the same manner, whether or not it is "dark".
ohwilleke said:dark matter and dark energy have an effect no different from comparable mass-energy densities of ordinary matter distributed in the same places would
The direct consequences of dark matter and dark energy on redshift are pretty minimal. As others have noted, the primary relationship between these and redshift come through their impact on the expansion of the universe.Teslascience said:Do dark matter and energy affect on red shift phenomena? If yes, what, and what is the consequence of it?
I disagree completely. Without dark matter, the expansion rate would be considerably larger than it currently is, and without dark energy it would be considerably lower than it currently is. Thus for any given distant object, its red-shift would be noticeably different if either of those were missingkimbyd said:The direct consequences of dark matter and dark energy on redshift are pretty minimal.
When I said "direct" I was excluding how both interact with redshift through the expansion. I hoped my second sentence, which immediately followed the part you quoted, made that clear.phinds said:I disagree completely. Without dark matter, the expansion rate would be considerably larger than it currently is, and without dark energy it would be considerably lower than it currently is. Thus for any given distant object, its red-shift would be noticeably different if either of those were missing
I was so startled by the first sentence that the second one didn't much register. I think your use of "primary" as implied by the combination of sentences to apparently mean "not significant" is confusing. Anyway, I see now that you understand, we're just discussing how you expressed yourself, not about the underlying situation.kimbyd said:When I said "direct" I was excluding how both interact with redshift through the expansion. I hoped my second sentence, which immediately followed the part you quoted, made that clear.
Yes, my question is about the impact of it, thanks.ohwilleke said:This is correct, but I'm not sure that it is responsive to the question being asked in the OP.
When I read the question, I see not a question about the impact of dark matter and dark energy on the rate of expansion of the universe, but instead a question about whether dark matter and dark energy impact the amount of red shift that we perceive from our vantage point given a particular rate of expansion of the universe, in a manner different that we would in a universe with the same expansion rate in which dark matter and dark energy were absent.
The answer to that question, I believe (and feel free to correct me if I am wrong), is that dark matter and dark energy have an effect no different from comparable mass-energy densities of ordinary matter distributed in the same places would. In other words, all matter and energy give rise to gravitational redshift in the same manner, whether or not it is "dark".
ohwilleke said:When I read the question, I see not a question about the impact of dark matter and dark energy on the rate of expansion of the universe, but instead a question about whether dark matter and dark energy impact the amount of red shift that we perceive from our vantage point given a particular rate of expansion of the universe, in a manner different that we would in a universe with the same expansion rate in which dark matter and dark energy were absent.
The answer to that question, I believe (and feel free to correct me if I am wrong), is that dark matter and dark energy have an effect no different from comparable mass-energy densities of ordinary matter distributed in the same places would. In other words, all matter and energy give rise to gravitational redshift in the same manner, whether or not it is "dark".
The problem is that the question isn't really separable like that. The universe is expanding the way it is because of the various matter/radiation/dark energy densities, so if the densities were different the expansion would be different and the cosmological redshift would be different. This is the point that @kimbyd made in #21 about the "primary impact" of the densities on redshift.Teslascience said:Yes, my question is about the impact of it, thanks.
Regular matter actually does impact redshift a bit more than that, because regular matter interacts with light. For example, cold CMB photons passing through the hot gas of a galaxy cluster will tend to pick up a bit of energy on the way, making them a little hotter (this is known as the Sunyaev-Zel'dovich effect). Dust will tend to interact with shorter wavelengths a bit more than longer wavelengths, filtering out the shorter wavelengths. Magnetic fields can also have an impact: magnetic fields can cause the polarization of light to rotate (this is known as the Faraday effect).Ibix said:Regular matter and dark matter are indistinguishable for this purpose. Their effect on expansion is the same so their effect on cosmological redshift is the same. There's only a difference at small scales - regular matter tends to clump more into things like galaxies, while dark matter tends to be more diffuse.
I think you want to say that without dark matter the accelerated expansion of the universe would be larger or in terms of the scale factor the value of its second derivative (which is positive in case the universe expands accelerated) would be larger. Usually "expansion rate" means the Hubble constant, which is decreasing however.phinds said:Without dark matter, the expansion rate would be considerably larger than it currently is
Yes, my terminology was sloppy (I should have just said "recession", not "expansion rate"), but my point was valid.timmdeeg said:I think you want to say that without dark matter the accelerated expansion of the universe would be larger or in terms of the scale factor the value of its second derivative (which is positive in case the universe expands accelerated) would be larger. Usually "expansion rate" means the Hubble constant, which is decreasing however.
I think your original response was correct, actually.phinds said:Yes, my terminology was sloppy (I should have just said "recession", not "expansion rate"), but my point was valid.
I was confused myself when I came across this sloppyness in a pop science cosmology book by Prof. Harald Lesch some time ago. So from this point of view you are in good company.phinds said:Yes, my terminology was sloppy
I'm really not sure this kind of comparison is meaningful. The problem is that the initial conditions aren't fixed, and there's no good way to fix them. Certainly, a universe will more matter will have a lower expansion after a time t than a universe with more matter, provided that they both start with the same initial expansion rate.Bandersnatch said:I think your original response was correct, actually.
After all, the rate of expansion (i.e. the Hubble parameter) falls as 1/t in an empty universe, and falls faster than that in a universe with matter in it. So, given two universes with identical initial expansion rates, but different matter contents, the one with less matter in it will result in higher H after time t from the start of the expansion.
What do you mean by same initial expansion rate?kind said:But it's not at all clear that they would have the same initial expansion rate. Less dark matter means different high-energy laws of physics, which means lots of things would be different.
The amount of dark matter we have is likely due to the nature of some kind of high-energy symmetry breaking event in the early universe. A change in that event which would have resulted in less dark matter would likely have changed many other things about our observable universe, which makes doing the thought experiment very, very tricky.Arman777 said:What do you mean by same initial expansion rate?
Also, Is it really makes that difference? Without matter and dark matter we can model universe (empty space with lambda case). For example, If we had less/more baryonic matter the physics rules would be the same. So why would it change for less dark matter?
Hmm I understand it I guess , thanks. But what about "initial expansion rate". What it means ?kimbyd said:The amount of dark matter we have is likely due to the nature of some kind of high-energy symmetry breaking event in the early universe. A change in that event which would have resulted in less dark matter would likely have changed many other things about our observable universe, which makes doing the thought experiment very, very tricky.
What we can say is that matter (whether normal or dark) tends to slow the rate of expansion. Radiation tends to slow the rate of expansion faster. A cosmological constant makes the rate of expansion tend towards a constant rate.