Do dark matter and dark energy have an effect on the red shift?

[Teslascience]

Do dark matter and energy affect on red shift phenomena? If yes, what, and what is the consequence of it?

 

[rootone]

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.
Since these distant galaxies red shift indicates that they are receding away from 'here' at an accelerating rate, there must be some kind of energy which causes that.
It became known as dark since we have no clue what it is. .

 

[Teslascience]

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.

Thanks, so far is all correct, but does dark matter not causes an opposite effect on red shift as dark energy does?

 

[Ibix]

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.

 

[Teslascience]

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.

Thank you! Meanwhile I found in an another topic, that my question was not quite right here. Bapowell wrote:
"I think science can only speculate about Dark cosmology at this point so it is a legitimate area of discussion that may not be an agreeable topic in this forum since teaching what is known is the goal here - I think."
I shall agree with him, we can only speculate about Dark physics, but it is too interesting anyway.

 

[phinds]

Do dark matter and energy affect on red shift phenomena? If yes, what, and what is the consequence of it?

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

 

[Arman777]

Can we ask the question like this,
"We are only observing the galaxies as Edwin Hubble did, calculating their redshift values and plotting them. In this case, Is it possible to discover dark matter just by looking the redshift values ?"

 

[Teslascience]

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

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]

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.

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.

 

[jocarren]

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.

 

[Khashishi]

Dark energy is too small to have a significant effect on rest mass of individual particles. I guess it might factor into corrections in the 45th decimal place or so.

(I estimated 45 decimal places based on a dark energy density of 10^-27 kg/m^3, a particle mass of 10^-27 kg, and a particle size of 10^-15 m)

 

[Arman777]

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.

Well since expansion happens on megaparsec level I really doubt that.

 

[jocarren]

I was thinking of a cumulative effect on the higgs mechanism, let's say on a particle collection over cosmological time. It's an extremely vague speculation anyway.

 

[timmdeeg]

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?

“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]

“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.

I'm aware of that, just sharing a baseless speculation.

 

[phinds]

I'm aware of that, just sharing a baseless speculation.

Then you should go back and read the forum rules.

 

[jocarren]

Then you should go back and read the forum rules.

Missed that point, you are right. I apologize.

 

[ohwilleke]

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

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".

 

[phinds]

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".

Dark Energy causes expansion. Matter, both normal and dark, cause contraction, so no I don't believe you are correct.

 

[PeterDonis]

dark matter and dark energy have an effect no different from comparable mass-energy densities of ordinary matter distributed in the same places would

This is true for dark matter, but not for dark energy. Dark matter, like ordinary matter, causes light rays to converge, hence the phenomenon of gravitational lensing.

Dark energy, if it "clumped" as matter does, would cause light rays to diverge; I suppose one could call the phenomenon this would produce, if it occurred on a small scale, "gravitational anti-lensing". However, since the density of dark energy is uniform throughout the universe (unlike the density of dark matter and ordinary matter, both of which clump, though the former does so to a lesser extent than the latter), it has no effect on light rays at all, since any such effect requires a spatial variation in density.

 

[kimbyd]

Do dark matter and energy affect on red shift phenomena? If yes, what, and what is the consequence of it?

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.

Most of the observations related to dark matter stem from how it clusters, e.g. through gravitational lensing. These effects have no direct impact on the redshift, however, because dark matter doesn't interact with light (if it did, it wouldn't be dark).

Dark energy has one reasonably-direct impact on redshift: it changes how large dense and underdense regions evolve over time, by making gravitational potentials more shallow as time goes on. So if a photon enters an overdense region, it picks up a blueshift from falling into the gravitational potential well. If the region is large enough, by the time the photon climbs back out of the well, that well will be more shallow, so it picks up a net blueshift. The same thing happens in reverse for photons passing through underdense regions. This phenomenon is knows as the Integrated Sachs-Wolfe effect, and its impact is extremely subtle for most light sources, but makes a measurable difference for the cosmic microwave background (CMB), where we see a relationship between CMB temperatures and nearby large-scale structure which agrees with what we would expect from this effect.

 

[phinds]

The direct consequences of dark matter and dark energy on redshift are pretty minimal.

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

 

[kimbyd]

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

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]

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.

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.

 

[Teslascience]

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".

Yes, my question is about the impact of it, thanks.

 

[Ibix]

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".

Yes, my question is about the impact of it, thanks.

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.

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.

Dark energy acts differently. As far as I understand it, it doesn't clump at all, its density doesn't reduce with time, and it acts like a negative pressure, accelerating the expansion of the universe. Again, kimbyd explained one effect it had on cosmological redshifts; she clearly knows more about it than I do.

 

[kimbyd]

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.

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).

Dark matter doesn't cause any of these effects.

 

[timmdeeg]

Without dark matter, the expansion rate would be considerably larger than it currently is

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]

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.

Yes, my terminology was sloppy (I should have just said "recession", not "expansion rate"), but my point was valid.

 

[Bandersnatch]

Yes, my terminology was sloppy (I should have just said "recession", not "expansion rate"), but my point was valid.

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.

 

[timmdeeg]

Yes, my terminology was sloppy

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.

 

[kimbyd]

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.

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.

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.

 

[Arman777]

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.

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?

 

[kimbyd]

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?

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.

 

[Arman777]

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.

Hmm I understand it I guess , thanks. But what about "initial expansion rate". What it means ?