The Universe's Expansion May Be Slowing Down, Not Speeding Up ?

Pinball1970 said:
I try not post YouTube videos, here is a quote on PF from Sabine Hossenfelder (the Hoss)

"Basically, they say that it's wrong to conclude that the expansion of the universe is accelerating. It's just that younger galaxies have on average dimmer supernovae. They don't say why this might be the case. They simply say this is what the data really say. And this isn't one of those maybe results with low statistical significance. This is a whopping 5.5 sigma correlation which they call a serious systematic bias."

One interesting comment was that this factor is not new to the cosmological community, just that it is not as significant as this paper suggests.
We can expect more on this since so much is at stake.
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Yes, interesting that doubt about the validity of these standard candles seems to have been floating around for a while. Do you know anything about this baryon acoustic oscillation, or whatever it is, that they mention as corroborating, at least directionally, their findings?
 
geordief said:
if the acceleration is lessening,what happens when (if?) it becomes less than zero?

Does expansion gradually stop and if it does, does it turn into contraction or might it find an equilibrium which could look like the Steady State even if not the Steady State that Hoyle assumed?(well I am not really familiar with what the Steady State was actually meant to be)
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It's worth remember what the position was in cosmology before we found data that seemed to show that the expansion of the universe is accelerating.

Prior to that, we had relativistic models with cosmological constant set to zero. With that setting, the ultimate fate of the universe is determined entirely by the density of matter in the universe. More than a critical density means the expansion will slow, stop then reverse, and we get a Big Crunch. Less than the critical density means the expansion continues forever and we get an eventual heat death of the universe. With exactly the critical density, we also get an expansion that continues forever, but at an ever-decreasing rate.

Interestingly, it appears that the average density of the universe is right at the critical value, or at least so close that we can't tell whether it is slightly more or slightly less. That seems unlikely to be a coincidence, but I don't think it has been explained either.

The density has to include dark matter, of course. Even if we abolish dark energy, dark matter will still be a problem that needs a solution.
 
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James R said:
It's worth remember what the position was in cosmology before we found data that seemed to show that the expansion of the universe is accelerating.

Prior to that, we relativistic models with cosmological constant set to zero. With that setting, the ultimate fate of the universe is determined entirely by the density of matter in the universe. More than a critical density means the expansion will slow, stop then reverse, and we get a Big Crunch. Less than the critical density means the expansion continues forever and we get an eventual heat death of the universe. With exactly the critical density, we also get an expansion that continues forever, but at an ever-decreasing rate.

Interestingly, it appears that the average density of the universe is right at the critical value, or at least so close that we can't tell whether it is slightly more or slightly less. That seems unlikely to be a coincidence, but I don't think it has been explained either.

The density has to include dark matter, of course. Even if we abolish dark energy, dark matter will still be a problem that needs a solution.
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How can we know the average density of the universe if we only have the observable unierse to look at?

(I understand that it may be that the ratio of unobservable to observable could be anything -even some exponentially huge number)

Maybe the CMWB has information that applies to the unobservable universe and allows us to calculate its average density?
 
exchemist said:
Yes, interesting that doubt about the validity of these standard candles seems to have been floating around for a while. Do you know anything about this baryon acoustic oscillation, or whatever it is, that they mention as corroborating, at least directionally, their findings?
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Yes I have read up not or at least tried to. Simply put they are the sound waves of the plasma of the very early universe. These became "fixed" when the plasma cooled enough to hold onto the electrons.
 
exchemist said:
Yes, interesting that doubt about the validity of these standard candles seems to have been floating around for a while. Do you know anything about this baryon acoustic oscillation, or whatever it is, that they mention as corroborating, at least directionally, their findings?
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This is closely linked to the CMBR because that was the point when the oscillations were frozen. The separation of these sound waves are being measured in surveys like DESI.
These frozen sound waves are seen in the distribution of galaxies. They have worked out that the sound waves could have moved 150 Mpc before decoupling when the CMBR was produced.

Edit: the amount of separation "equates to" 150Mpc.
 
Thanks to C C , we now have, if not exactly a rebuttal then some reasons to doubt this finding. https://www.universetoday.com/artic...ng-heres-what-a-nobel-laureate-has-to-say-abo

I’ve copied this reference from her evergreen thread on “Compromised Science”.

Two objections. One is that while the supernova standard candle light curves don’t correct for galactic age they correct for galactic mass, which apparently correlates with age. The authors of the paper however went back to earlier versions without this correction, so their criticism of the light curves currently used is rather unfair. The other is that the authors assume young galaxies have supernovae produced by young progenitors. This, according to the critic, himself a Nobel Prize winner, is a false assumption.

So the empire strikes back already. It will be interesting to see how this plays out.
 
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