Possible cause of cosmological redshift observations?

rod

Oct 22, 2019
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KC Strom. From what I understand the answer is likely *yes* because of the principle of equivalence in Einstein GR. Photons are said to redshift as 3D space expands. There may be some other math here but GR is used. I do note however, QM has not directly observed in the lab, photons redshift as 3D space expands. The redshift of galaxies is explained using GR math.
 
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Feb 3, 2020
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Thank you, Rod.

I am under the impression that, by observing cosmological redshift, we have determined that, with the exception of a small handful of galaxies close to us, every galaxy is moving away from us.

Any thoughts as to why some galaxies are not behaving appropriately?
 
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rod

Oct 22, 2019
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KC Strom, ref post #3. "Any thoughts as to why some galaxies are not behaving appropriately?"

Do you have some specific examples referencing NGC numbers or Messier numbers?
 
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Rod, ref post #4.

Unfortunately, no. I recall reading a general article in Live Science that mentioned that a handful of galaxies "near us" were not moving away from us. This struck me as odd.

To be honest, I'm looking for actions in our universe that do not fit well with current cosmological understanding. Just fishing...
 
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Rod, ref post #4.

Unfortunately, no. I recall reading a general article in Live Science that mentioned that a handful of galaxies "near us" were not moving away from us. This struck me as odd.

To be honest, I'm looking for actions in our universe that do not fit well with current cosmological understanding. Just fishing...
One of the first redshift observations (V. Slipher) of nebulae -- back then there were no "galaxies" per se -- was of the only galaxy visible to the human eye -- the Andromeda galaxy. It was found to have a blueshift. We now know its distance and that in a few billion years we will collide, though its extremely rare that stars would smash into one another when they fly through one another.

There are several other galaxies in our group that are moving more toward us than away from us.
 
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Thanks. This is quite interesting. A couple of assumptions:

1. The blueshift of these galaxies is explained by GR math.
2. These galaxies are orbiting something massive and just happen to be headed toward us at "this moment in time" as they proceed along their orbital path.

A couple of questions:

1. Do we know what is being orbited?
2. If space itself is expanding is the amount of blueshift we observe "offset" or "reduced" by the redshift driven the expansion?

Clear as mud?
 
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Thanks. This is quite interesting. A couple of assumptions:

1. The blueshift of these galaxies is explained by GR math.
That's a part of the equation, and it's a good question.

The few blueshifted galaxies will all be local. The cosmological redshift per GR is caused by actual expansion of space between two objects. There is little expansion of space that takes place for local galactic clusters as their gravity holds them together so they don't drift away in the Hubble Flow. I suppose this little bit must be taken into account for greater accuracy. The blueshift, therefore, we observe is a Doppler effect, no doubt.

The Doppler effect for the more distant galaxies is also likely a factor, but here the roles are reversed - Doppler is a small portion of the shift and the cosmological redshift is the main portion.

2. These galaxies are orbiting something massive and just happen to be headed toward us at "this moment in time" as they proceed along their orbital path.
Yes, we are in what is known as the "Local Group", and we are one of the larger members.

1. Do we know what is being orbited?
Yes, we know their distance thanks to things like Cepheid Variables and other techniques, and we know their radial velocities. Their transverse velocity is important as well but I think this may be inferred from all the other galaxie's information and a determined c.g. for the cluster. Perhaps another will address this.

2. If space itself is expanding is the amount of blueshift we observe "offset" or "reduced" by the redshift driven the expansion?
Yes, as mentioned above.[/quote][/QUOTE]
 
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Perhaps someday, we will see a list like the confirmed exoplanet lists showing all here :)
I found this article that states there are over 7000 blueshift galaxies in the NED1 catalog. Apparently, 90% of these are found in two groups.

The last estimate for the number of galaxies in the observable universe is around 2 trillion, so a little more than 7k isn't all that much.
 
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rod

Oct 22, 2019
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Helio, your post #11 looks like fun :) "BLUE SHIFTED GALAXIES There are more almost 7000 blue-shifted galaxies listed in the NED1 web site. Being blue-shifted means that they are approaching the earth. The velocities ranges from just-above-zero to 8000 km/sec. The vast majority of velocities is less than 200 km/sec."
 
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The few blueshifted galaxies will all be local. The cosmological redshift per GR is caused by actual expansion of space between two objects. There is little expansion of space that takes place for local galactic clusters as their gravity holds them together so they don't drift away in the Hubble Flow. I suppose this little bit must be taken into account for greater accuracy. The blueshift, therefore, we observe is a Doppler effect, no doubt.

Thanks, no more questions. Well, maybe one (or two). Any thought as to how far (away from us) a galaxy would have to be before there is meaningful redshift (perhaps there is a better way to ask this question)?

Secondly. So, to clarify. Space doesn't expand between objects held together by gravity?
 
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Thanks, no more questions. Well, maybe one (or two). Any thought as to how far (away from us) a galaxy would have to be before there is meaningful redshift (perhaps there is a better way to ask this question)?
Well, "meaningful" is a great word but it is very subjective. There are no redshifts or blueshifts for galaxies that threaten us due to their vast distance, but if you are studying, say, a bright star in another galaxy, then it is critical to get an accurate distance to better understand just how bright it really is (ie luminosity).

The most distant objects are so redshifted that their light is mostly in the IR band, so you can't see them in a regular telescope.

The most distant thing currently available to us is the CMBR, which can only be "seen" in the microwave band, though it originally was the same wavelengths as cooler stars (~ 3000K).

Secondly. So, to clarify. Space doesn't expand between objects held together by gravity?
I think the view is that spacetime expands everywhere. But it is an incredibly small amount locally. It only increases by about 70kps after you look at regions 1 million parsecs (3.26 million lightyears) away from us, so a few light years is trivial.

But the gravitational pull that keeps a galaxy together easily overcomes this expansion. As a star attempts to move away with expansion, IOW, then it moves back due to the surrounding gravity.
 
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But the gravitational pull that keeps a galaxy together easily overcomes this expansion. As a star attempts to move away with expansion, IOW, then it moves back due to the surrounding gravity.

Thank you, Helio. RE; Post #15

This surprises me a bit. My mind wants to think that "leftover BB acceleration" in combination with DM/DE might overcome gravity. But, no matter. To me, gravity is a very localized force. I'll call it strong. DM, if it exists, is ubiquitous. It must be weak by comparison to gravity.

Thanks for your time.
 
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Thank you, Helio. RE; Post #15

This surprises me a bit. My mind wants to think that "leftover BB acceleration" in combination with DM/DE might overcome gravity. But, no matter. To me, gravity is a very localized force. I'll call it strong. DM, if it exists, is ubiquitous. It must be weak by comparison to gravity.

Thanks for your time.
Historically, the Big Bang had something that behaves like negative gravity and at that early density, the expansion rate was super incredible. [Inflation period of a <<1 nanosecond was really nuts.]

So, after 13.8 billion years, and negative gravity should be long gone, the thought was that the universe must be getting slower and slower as the gravity of the universe would slow everything down. The end result would be either we keep expanding forever, but slower and slower, or we would begin to contract, which would accelerate us back into a single particle-like size.

But the 1995 observations showed we are accelerating more and more. Thus, a mysterious (dark) negative gravity (energy) -- hence DE -- is causing the acceleration and was likely there all along, but the weaker gravity causing DE effects to become greater and greater.

DM is everywhere but it's not homogenous; it clumps around galaxies. Did DM cause the galaxies to form or did DM join galaxies after they started forming? I don't know.
 
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I am very sceptical about the BB. Especially approaching infinitely high temperatures, and infinitely high densities. (The exaggerations are mine). I definitely tend towards the idea that instead of this thoroughly unscientific straight line extrapolation backwards to (IMHO) to a totally unbelievable BB, it is much more likely that "we" passed through a nexus (like a figure 8 on its side) and the so-called BB is just the narrow part. This also has interesting implications for the fate of the Universe. The so-called BB is then just a transition point in a cycle.

Cat :)
 
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I am very sceptical about the BB. Especially approaching infinitely high temperatures, and infinitely high densities. (The exaggerations are mine).
Yes, I too don't think a beginning must be at a singularity with infinite everything. Science also doesn't like it, though many scientists will make the claim in spite of the equations completely breaking down at near that point. No doubt it helps sell books because saying "singularity" has wit - a singular one. :)

BBT has never began at that singularity and expanded from there, but more the opposite given its history. It started today and shrunk as we worked backwards with time, always improving the physics to explain what we observed. It's amazing that the equations seem to work up until you reach about t=10^-40 sec. or so, but never t = 0.
 
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KC Strom, ref post #3. "Any thoughts as to why some galaxies are not behaving appropriately?"

Do you have some specific examples referencing NGC numbers or Messier numbers?
We can look back to:
Kraken accretion, 11 billion years ago,
Helmi Stream merger, 10 billion years ago,
Gaia-Enceladus merger, 9 billion years ago,
Sagittarius encounter, 6 to 8 billion years ago,
and forward to:
Large Magellanic Cloud, 1.6 to 3.6 years in the future,
Andromeda collision, 4.5 to 5.8 years in the future.

Source: "All About Space" February 2021, page 50, A New View of the Milky Way by Kulvinder Singh Chadha.

Rod, I believe you take Sky and Telescope (which I do not). Do you take All About Space? Despite its title, I now rate it the best magazine I have seen. I rate it at least the equal of Astronomy, and ahead of Astronomy Now, and The Sky at Night, all of which I take regularly.

Note: This is just my personal opinion. I have no vested interests, and only wish to help members to very worthwhile sources of information, including information on red shift..
Cat :)
 
Yes, I too don't think a beginning must be at a singularity with infinite everything. Science also doesn't like it, though many scientists will make the claim in spite of the equations completely breaking down at near that point. No doubt it helps sell books because saying "singularity" has wit - a singular one. :)

BBT has never began at that singularity and expanded from there, but more the opposite given its history. It started today and shrunk as we worked backwards with time, always improving the physics to explain what we observed. It's amazing that the equations seem to work up until you reach about t=10^-40 sec. or so, but never t = 0.
Helio, you know that I favour the "figure 8 nexus" idea, and I don't see why the maths cannot accommodate, where t = 0 would simply cover the tangential shape of the nexus. That is in the usual diagram of time versus expansion size. What lies on the other side of the nexus is anybody's guess!

Cat :)
 

rod

Oct 22, 2019
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This discussion is fraught with peril :) Here is something to ponder about cosmology.

The One-Way Speed of Light and the Milne Universe, https://arxiv.org/abs/2012.12037, December 2020. "In Einstein's Special Theory of Relativity, all observers measure the speed of light, c, to be the same. However, this refers to the round trip speed, where a clock at the origin times the outward and return trip of light reflecting off a distant mirror. Measuring the one-way speed of light is fraught with issues of clock synchronisation, and, as long as the average speed of light remains c, the speeds on the outward and return legs could be different."

My observation. Measuring the age of distant objects in an ASC universe and the age of the universe - you cannot do :) "5 CONCLUSION In his formulation of the special theory of relativity, Einstein chose the convention that the speed of light is isotropic and so equal in all directions. He also acknowledged that the physical predictions of his theory will be unchanged if the speed of light was anisotropic, as long as the average round-trip speed is equal to c. In this paper, we have considered the question of the impact of the one-way speed of light on cosmological observations, addressing the suggestion we should observe different sides of the sky possessing different ages if light speed was unequal. By examining the simplest FRW universe, namely the empty Milne universe, it is seen that the anisotropic speed of light results in anisotropic time dilation effects that compensate for the differing light travel times..."
 
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There is no known experiment that I'm aware that can demonstrate a change in the speed of light in space. That is the basis of Special Relativity. Clock synchronization is tricky but comparing orbiting atomic clocks has demonstrated that the round trip for an average value of c isn't a requirement, IIRC.
 
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rod

Oct 22, 2019
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Helio, your post #23 still uses a round trip clock measurement, even at the atomic level :) The one-way velocity of c is not a measured quantity but uses ESC for simplicity. ASC, if true, collapses all the light-time one-way to Earth for distant stars, etc.
 

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