Is Dark matter real or just a fudge factor?

[NoelC]

Not sure if this has been discussed or if anyone is even interested.
But, doesn't this Guardian article imply that time dilation (the rate at which clocks slow with increased gravitation) alone accounts for the observed increase in the rate of expansion of the universe without the need for dark matter or the associated dark energy?

The implication here is that not only does dark energy not exist, but the universe is slowing in it's expansion rate. Is this a minority view or are we just seeing the latest views in cosmology changing direction?

Has anyone else looked into this?

https://www.theguardian.com/science/2023/jul/03/astronomers-observe-time-dilation-in-early-universe

This July 23 article suggests 'Time Dilation' due to the increased gravity forces in the early universe would mean time ran at 1/5th the current rate verses the time it runs in the current epoch.  Looking back at objects from that time frame would therefore make them look as if the universe was expanding slower in the past than it is now.

This article does not make it clear that time dilation will affect red shift (which I believe to be the case from other papers).

The following article appears to say that dilation can account for the acceleration and that the existing calculation (Friedmann-Lemaitre-Robertson-Walker - FLRW) when adjusted for time dilation accurately predicts the rate of expansion without the need for dark matter or the associated dark energy.

Cosmological Redshift and Cosmic Time Dilation in the FLRW Metric:
https://www.frontiersin.org/articles/10.3389/fphy.2022.826188/full
Final conclusion:-
"The conformal FLRW metric fits the SN Ia observations with no need to introduce dark energy into the Einstein and Friedmann equations. The dark energy is an artefact of the erroneous metric used for describing the evolution of the Universe. Consequently, no repulsive forces produced by dark energy and acting against gravity are present in the corrected Friedmann equations. Since the only force considered in the Friedmann equations is gravity, the expansion of the Universe is decelerating at the present epoch."
(i.e. dark matter doesn't exist)

Anyone else looked into this?

[Rick]

My gut says it's fudge factors all the way down, but I am not and never have been an expert cosmologist, nor have I played one on TV. However, I'm pretty sure it's a question at the core of a whole giga-heap of cosmology research, and there'll be Nobel prizes for anyone who cracks the problem incontrovertibly....

[NoelC]

Rick; yes I'm sure they will all get nobel prizes, but rather odd when you think that a host of researchers won it for finding dark matter in the first place.  Notably (of course) Vera Rubin never did.

I have to say that I am not against the premis that there is a great deal more matter in the universe than we can see (matter that does not radiate).  A large proportion of which may be in black holes.

w/r to Rubin's original proposal, that stars at the edge of galaxies appear to move at similar speeds to those in the centre, contrary to the model we see in the solar system:- Such a phenomona would also occur in the event that the black hole at the centre of the galaxy is very large (due to dilation affecting the red shift - spectroscopy was the basis of Rubins observations). Zwicky's observations I believe were that orbiting galaxies appeared to be moving too fast for the visible matter.  Again, his observations were made before it was realised that galactic cores normally contain large black holes.  In recent years the observed number and mass of these holes has been increasing. I am not familiar with all the arguments for dark matter put forward by other observers.

Astronomers have taken to equating red shift with distance due to the universal expansion rate.  But Einstien showed; high mass also = high redshift:
https://astronomy.swin.edu.au/cosmos/G/Gravitational+Redshift
As we know, galaxies with heavy black holes at their cores (like quasars) are heavily red shifted.  Which kind of makes a hash of the observations of those that insist redshift = distance.  Without knowledge of the mass, they can't correct for dilation.

It has always seemed slightly odd to me that in most of the pictures of gravitational lenses that we see, the core galaxy is visibly more redshifted than the galaxy it's lensing.

This image demonstrates that the front galaxy is heavily red shifted, while the galaxy whose light it's bending is blue shifted.  If red shift = distance, then surely the central galaxy should be behind the curved one.  If it's in front, then we have a problem; because it's clear the core galaxy is red shifting the light from it by time dilation.  Another explanation could be that the galaxy is moving away very fast; but I raise this because most of the gravitational lenses show orange galaxies in their core.
The explanation of this is that 'a cloud of dark matter' is curving space around the galaxy, but I've not seen consideration of dilation effects in their arguments.  IMHO it's just a very high mass galaxy which is curving space.

I suspect our view of the universe is being distorted by premises that are no longer valid.

[Hugh]

Thanks Noel ~ interesting ~ you have given me some reading to do here!

I did read some time ago (I am not sure where) that there was mounting evidence that the rate of expansion was/is likely to have varied in differing parts across the Universe? 

Overall, I tend to fall back on quotes from Neil deGrasse Tyson ("The Universe is under no obligation to make sense to you!"); and Sir Arthur Eddington ("Not only is the Universe stranger than we imagine, it is stranger than we can imagine!").

~ Hugh

[AndrewRamsay]

Noel -

It is a fascinating study.   I think I dimly understand the idea that dilation of space speeds up the apparent speed of light, without any need for a missing dark energy factor to account for accelaration.  However, the authors don't actually mention dark matter anywhere (I ran a search).  I think the case for dark energy has been well made by calculations demonstrating that most galaxies are held together by gravitational forces which exceed those expected from the measurable collected mass (including black holes).

But I may be wrong?

- Andrew

[NoelC]

Andrew
Thanks for your reply.  I'm just reading other's conclusions. But I thought the argument over galaxies holding together (Zwicky) was that he proposed that the galaxies had insufficient mass ergo dark matter was holding them together.  I think we now recognise there is probably enough matter (in black holes) to hold them together and account for the increased speed they show.

The argument for 'dark energy' (changes in the universal expansion rate) was effectively countered in the second paper I linked to.

Interestingly observations from the James Webb telescope tend to support the argument that there was a lot more matter in the early universe than we allowed for:-
https://phys.org/news/2023-02-discovery-massive-early-galaxies-defies.html
This article is on another topic (galaxy formation), but does tend to make me think that the numbers don't add up when it comes to the current view on the total amount of matter.

It will be interesting to see if Colin goes into this next week (torches, passing trains and atomic clocks at the ready).