Some new evidence that the Dark Energy Concept is wrong

[Buzz Bloom]

TL;DR Summary

From
https://phys.org/news/2020-01-evidence-key-assumption-discovery-dark.html
January 6, 2020
New evidence shows that the key assumption made in the discovery of dark energy is in error

The reference in the summary refers to an article which has been recently accepted by The Astrophysical Journal. A draft version of the article dated December 10, 2019 is

https://arxiv.org/pdf/1912.04903.pdf .​

​

The content of the draft article is way over my head, so I am hoping that participants in the PFs can provide some relatively simple "I" level evaluation of the conclusion that dark energy does not exist. As I understand this, it means that the cosmological constant is zero, and the average mass density of baryonic and dark matter is about five times larger than previously thought.

 

[mfb]

Where would all that mass be? Why don't we see anything like that in the CMB? So much mass should slow down the expansion much faster. But I don't see where you get that from, I don't find it in the abstract and I don't find it in the discussion section either. They discuss that the standard fits might need some adjustments, dark energy might turn out to be 30% larger or smaller or so if their analysis is correct, but they don't say "there is no dark energy" or anything like that.

 

[Buzz Bloom]

They discuss that the standard fits might need some adjustments, dark energy might turn out to be 30% larger or smaller or so if their analysis is correct, but they don't say "there is no dark energy" or anything like that.

Hi mfb:

Thank you for your post. I much appreciate your correcting my misunderstanding.

Regards,
Buzz

 

[mfb]

Here is a good discussion by an expert

 

[PeroK]

Hi mfb:

Thank you for your post. I much appreciate your correcting my misunderstanding.

Regards,
Buzz

I have noticed a frequent issue in science journalism. Let's say that a series of studies has put a quantity at $30-70$, say. A new study puts the quantity at $0-50$. Science journalists generally report these results as contradictory and that the second result casts doubt on the established evidence. When, in fact, they are not contradictory at all.

 

[fresh_42]

Science journalists generally report these results as contradictory and that the second result casts doubt on the established evidence.

I have the impression that eyecatchers and clickbaits have become more important than content, too. Advertisement changed a lot in the recent years.

 

[jedishrfu]

Theres a related issue in paper publishes where a team does numerous experiments that fail to show effect and one experiment that shows it may be true so they publish one result.

Positive results get published and negative results go nowhere. So you must find a way to make your results always positive.

My niece went through this her thesis work was to investigate an effect and extend our understanding of it. Instead she discovered a flaw in prior thesis papers that there was no effect to be shown. Resulting in a potential retraction issue for her advisor.

 

[Lord Crc]

From the phys.org post:

Commenting on the result, Prof. Young-Wook Lee (Yonsei Univ., Seoul), who led the project said, "Quoting Carl Sagan, extraordinary claims require extraordinary evidence, but I am not sure we have such extraordinary evidence for dark energy. Our result illustrates that dark energy from SN cosmology, which led to the 2011 Nobel Prize in Physics, might be an artifact of a fragile and false assumption."

That seems a lot stronger than what the paper claims, so perhaps not surprising some get the wrong idea.

 

[DEvens]

Cosmology has been the "missing top step in the dark" often enough that I have a radical policy of putting off opinions about new results. It may turn out that this new paper is right. Or that they've made some arithmetic error. Or that they have Vaseline on their lens. But I will refuse to get enthusiastic, positive or negative, until this has been kicked around by a bunch of experts and had the sharp corners removed. Usually that takes 5 to 10 years.

 

[kimbyd]

Summary:: From
https://phys.org/news/2020-01-evidence-key-assumption-discovery-dark.html
January 6, 2020
New evidence shows that the key assumption made in the discovery of dark energy is in error

The reference in the summary refers to an article which has been recently accepted by The Astrophysical Journal. A draft version of the article dated December 10, 2019 is

https://arxiv.org/pdf/1912.04903.pdf .​

​

The content of the draft article is way over my head, so I am hoping that participants in the PFs can provide some relatively simple "I" level evaluation of the conclusion that dark energy does not exist. As I understand this, it means that the cosmological constant is zero, and the average mass density of baryonic and dark matter is about five times larger than previously thought.

Ugh. There is much that is wrong with this article.

First, the science:
What they're claiming is that there is evidence that supernovas have changed in brightness over time, that earlier supernovae were dimmer than later ones. Their result is close to the boundary of what many would consider "significant" in a statistical sense. So it's definitely not strong evidence that these luminosities have changed over time. But it's conceivable that this is the case.

That said, when they claim that supernovae are the most direct and strongest evidence for dark energy, that's a matter of opinion that I most definitely do not share. Personally, I think the strongest evidence for dark energy stems from the integrated Sachs-Wolfe Effect.

In a universe with no dark energy, the gravitational potentials of large structures are constant with time. This means that when a photon enters a galaxy cluster, it picks up a blueshift, and then when it later leaves the cluster it redshifts by the exact same amount that it gained.

Dark energy, however, causes the gravitational potentials to get shallower over time. So when the photon leaves the potential it doesn't have to climb as high out, so it doesn't redshift by as much and picks up a small blushift from crossing the cluster.

Unlike supernovae, which are only sensitive to the rate of expansion over time, this is a direct effect that dark energy has on matter in the universe that is really hard to replicate by other means. And when we compare estimates of nearby structures with the CMB temperatures across the sky, there is quite significant evidence of dark energy.

 

[timmdeeg]

Personally, I think the strongest evidence for dark energy stems from the integrated Sachs-Wolfe Effect.

Thank, a very interesting hint, I wasn't aware of that. More about here:
Updated tomographic analysis of the integrated Sachs-Wolfe effect and implications for dark energy