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

Killjoy

Killjoy

Propelling The Farce!!
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Would this lend credence to the idea that there are Big Bang - Big Crunch cycles ?

The Universe's Expansion May Be Slowing Down, Not Speeding Up, Remarkable New Findings Suggest​


“Type Ia supernovae are the cosmic rulers we use to measure how fast the universe expands. If their brightness depends on the age of the stars that produce them, that ruler becomes unreliable – especially since younger stars dominate at greater distances,” Dr Chul Chung, a research professor at Yonsei University and co-corresponding author of the paper, told IFLScience.

“This age effect can mimic the signal of an accelerating universe, so correcting for it gives us a very different view of dark energy and the history of cosmic expansion.”

The standard model of cosmology sees the universe being made of dark energy (70 percent), dark matter (25 percent), and regular matter (5 percent). Dark energy acts like antigravity, pushing galaxies apart. Our best understanding to date saw it as a cosmological constant, unchanging and everywhere, responsible for the accelerated expansion of the universe.

We found that the universe is no longer in a phase of accelerating expansion, but has already entered a phase of decelerated expansion.
Dr Chul Chung

These new findings instead suggest that dark energy changes with time, and that the universe is not on an accelerated expansion – its expansion is actually slowing down. This is not the first evidence of this idea. The largest-ever map of galaxies published earlier this year suggested that dark energy might be weakening. The new work agrees with that data.
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Wow. If the standard candles are flawed then we are in for a major paradigm shift in cosmology. New hope for bounce theories.
 
White holes could allow to confirm Big Crunch - as there is tendency to form black holes after Big Bang, before symmetric Big Crunch there should be tendency to form our white holes - some might survive to our time as very lone shining points.

But what e.g. spectrum to expect from white holes?


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Here's the paper: https://academic.oup.com/mnras/article/544/1/975/8281988.

Indeed pretty dramatic if confirmed. A couple of things strike me.

One is that it is curious that, after applying all the corrections to the rate of acceleration they think may be needed, the cosmos would be in or close to a phase of zero acceleration at the present day. This seems a rather suspicious coincidence. I find myself wondering if it could indicate that the whole concept of accelerating and deceleration expansion is flawed. That might help resolve the whole Dark Energy conundrum. Very tantalising.

The other thing is that they don't go at all into the supernova physics. This is an exercise only in applying statistical methods to the observations. Won't the physicists be scratching their heads a bit to account for why the age of the progenitor star should affect the brightness of the supernova? This seems to cry out for comment at least.
 
exchemist said:
Won't the physicists be scratching their heads a bit to account for why the age of the progenitor star should affect the brightness of the supernova? This seems to cry out for comment at least.
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I looked into this. Younger star systems yield brighter SN, older dimmer. Lee too this into account, Perlmutter did not.
 
exchemist said:
The other thing is that they don't go at all into the supernova physics. This is an exercise only in applying statistical methods to the observations
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Lee is claiming that the data agrees with CMBR and BAO data which does not rely on standard candles.
Independent cross ref, which is nice in science
 
exchemist said:
The other thing is that they don't go at all into the supernova physics. This is an exercise only in applying statistical methods to the observations. Won't the physicists be scratching their heads a bit to account for why the age of the progenitor star should affect the brightness of the supernova? This seems to cry out for comment at least.
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The age of the star may affect its element distribution, which could possibly affect the brightness.
 
Pinball1970 said:
I looked into this. Younger star systems yield brighter SN, older dimmer. Lee too this into account, Perlmutter did not.
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OK but why then does standard cosmology assume brightness of these supernovae is independent of the age of the star, as is apparently the case according to abstract of this paper?

I had assumed the physics of the supernova process must predict it is independent, or they would not have been adopted as standard candles. Or am I missing something (it’s not a subject I know much about so forgive the naïvety of the question)?

P.S. Perhaps Janus58 can also comment if he sees this.
 
exchemist said:
OK but why then does standard cosmology assume brightness of these supernovae is independent of the age of the star, as is apparently the case according to abstract of this paper?

I had assumed the physics of the supernova process must predict it is independent, or they would not have been adopted as standard candles. Or am I missing something (it’s not a subject I know much about so forgive the naïvety of the question)?

P.S. Perhaps Janus58 can also comment if he sees this.
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As I've understood it, the homogeneity is based on theories about the evolution of stars and galaxies, so it's always been prone to uncertainty.

For the most luminous of the SCs, the Type Ia supernovae, this homogeneity always was questionable.

When I was in an astronomy club, the Cepheid variables were the cautionary tale. In the 1950s, they found that the nearby Cepheids used as the SC were of a different type than the ones used to measure distances to nearby galaxies. The nearby Cepheids were population I stars with much higher metal content than the distant population II stars. So the population II stars were actually much brighter than believed, and when corrected, this had the effect of doubling the estimates of distances to the nearby galaxies. That's no small adjustment.
 
Afterthought:

The search for a supernova progenitor had been going for longer than a century.

For a deep dive, look up Phillips Relationship. Basically, gets into the light curve of a SN and the low probability you will see the entire light curve, i.e. start to finish. So the Phillips was to provide a way to figure the peak luminosity from a section of the light curve. So, again, this is all pretty wobbly stuff in getting at any supposed homogeneity of the type 1A.
 
TheVat said:
Afterthought:

The search for a supernova progenitor had been going for longer than a century.

For a deep dive, look up Phillips Relationship. Basically, gets into the light curve of a SN and the low probability you will see the entire light curve, i.e. start to finish. So the Phillips was to provide a way to figure the peak luminosity from a section of the light curve. So, again, this is all pretty wobbly stuff in getting at any supposed homogeneity of the type 1A.
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Blimey! So we have all built our model of cosmology on a flimsy foundation, then.
 
exchemist said:
Blimey! So we have all built our model of cosmology on a flimsy foundation, then.
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Not exactly. This was the data and models available at the time.
It seems odd to me now in 2025 as a layman, that an expert researcher in the field in the 1990s, did not take this into account.
However the 1990s was thirty years ago and the models have improved as the data has come in from spectroscopy from better and better telescopes, better computer power, more refined models.
My understanding is that Lee used a lot of the same data but has factored this in.
I am not sure where this progenitor factor came in. Is there consensus on it's significance?
We have seen this before on the Gaia data, same numbers, different crunching, one favours MOND the other DM.
 
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Wizard of Whatever said:
The age of the star may affect its element distribution, which could possibly affect the brightness
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Maybe but that is not what I have got from going through the literature.
Some of the papers are tricky to say the least and I have had to use Ai to compare. I had cite this on PF as per the rules as this was posted there as well.
 
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