The Cosmic Web at DIAS
Yesterday evening found me at the Dublin Institute for Advanced Studies, complete with scary Hallowe’en beard, to give a talk.
Picture Credit: Prof. Luke Drury
It was a nice friendly audience and we had a lot of interesting discussions afterwards. As usual on such occasions I’ve put up the slides in case anyone wants to see them:
After the talk I headed back to Maynooth. It was a very rainy night, but at least some of the fireworks were going off despite the potential for damp squibs.
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November 2, 2019 at 6:54 am
Peter: any comments/thoughts on https://physicsworld.com/a/dark-energy-debate-reignited-by-controversial-analysis-of-supernovae-data/
November 5, 2019 at 9:19 am
Where to start?
First, this is an old claim, though apparently there is now a new paper. Second, even if there is some problem with the supernova data, weakening their conclusions, why do they agree with other, independent, cosmological tests? It’s easy to come up with something which could change the results of one study. If they seriously believe that the universe is not accelerating, then they also have to explain what is wrong with the CMB analyses and all other cosmological tests which, for a quarter of a century or so now, are converging on the concordance values (hence the name). Until they do so, it is no wonder that people give them short shrift. And, no, the problem is not hidebound defenders of the orthodoxy. One good thing about the concordance model is that at first few people believed it; they were convinced by the data. Many of them had been hidebound defenders of the orthodoxy before, supporting the Einstein-de Sitter model, which became the standard model of the time for many wrong reasons. Hopefully they have learned their lesson.
More than a quarter of my own papers point out mistakes in other papers, so I do appreciate the concept. Actually, science needs more of this, and also results which confirm other results should be published. How many wrong results are there because no-one has bothered trying to reproduce them (perhaps because, if confirmed, it would be difficult to publish them)? But if they really believe that there is no cosmic acceleration (as opposed to saying that the supernova data don’t support it), then they have to explain why other lines of evidence also indicate that there is.
Finally, let me comment on this:
“The CMB does not directly measure dark energy,” he says. “That is a widely propagated myth.
True. But (drumroll, please!): neither do the supernova data. I have read claims that the supernova data “directly” measure acceleration, or even “directly” measure dark energy. No, they don’t. At best, one could argue that the chain of evidence is shorter than with, for example, the CMB.
November 5, 2019 at 10:04 am
“More than a quarter of my own papers point out mistakes in other papers”
I don’t have that many papers, so we are talking about 5 rebuttals. In one case, the other side has come around. In another, the claim has not been repeated. Two others haven’t seen the light personally, but the consensus is that the claims are wrong. One is still in progress, but the tide is turning. Bonus points if you can match the descriptions to the papers.
November 5, 2019 at 5:15 pm
” But if they really believe that there is no cosmic acceleration (as opposed to saying that the supernova data don’t support it), then they have to explain why other lines of evidence also indicate that there is.”
If their claim is that the supernova data are wrongly interpreted and do not strongly support an accelerating universe, then, considering the balance of other evidence, the logical approach would be to assume that the concordance model is correct and then figure out what is wrong with the supernova data.
In other words, people with axes to grind are often cut by them.
😐
Actually, the idea of the concordance model had been around for almost 10 years before the supernova data came along, so it would have been a surprise if acceleration had not been discovered. The idea that it completely surprised the cosmological community is very wrong.
Interestingly, the Supernova Cosmology Project initially claimed, on the basis of a few data points and thus with correspondingly large uncertainties, that the universe was decelerating. The wrong result was later seen to be due to an outlier.