Far out cosmology: Hubble tension resolved (Introduction)

by David Turell , Tuesday, May 28, 2024, 16:22 (177 days ago) @ David Turell

A new study:

https://mail.google.com/mail/u/0/#inbox/FMfcgzQVwnWSGHFcXjhPnJrmbsmZMnfp

"Physicists love talking about anomalies and tensions in their data because every such tension could mean new physics. In cosmology, we have had the “Hubble tension” that has attracted a lot of attention in the past decade. It might just have disappeared. Let’s have a look.

***

"Indeed, we can’t measure that the universe is expanding right now. What we do is, we look at distant galaxies. Because the light takes so long to reach us, we see them as they were in the past.

"And from that we calculate how the universe should be expanding today, according to Einstein’s equations.

"The rate at which the universe is expanding is known as the Hubble rate, denoted with a capital H, and the rate at which it is expanding today is H naught. The issue is now that cosmologists have used different measurements to determine this constant, H naught, and got different results. This is the so-called “Hubble tension”.

"The discrepancy is not huge, but the measurements are outside each other’s uncertainty range. There have been many different measurements by now but the ones that have the biggest discrepancy are those using data from the cosmic microwave background, and from supernovae. (My bold)

***

"It comes from the group of Wendy Freedman at the University of Chicago.

"They wrote a paper about this a few months ago but now just reported an update at the recent APS meeting in Sacramento. They used data from the James Webb Telescope for two types of stars, red giants and a type called carbon stars. It’s a little more difficult to extract information about the expansion rate from them, but the excellent data quality from the Webb telescope makes it possible.

"The result they get agrees with that of the cosmic microwave background.

"All of this fits neatly with the suspicion that there’s something wrong with the supernovae analysis."

Comment: follow-up papers will now vote for the solution or against it, but for now it looks settled.