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New research puts age of universe at 26.7 billion years, nearly twice as old as previously believed (phys.org)

submitted 1 year ago by L4s@lemmy.world to c/technology@lemmy.world

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New research puts age of universe at 26.7 billion years, nearly twice as old as previously believed::Our universe could be twice as old as current estimates, according to a new study that challenges the dominant cosmological model and sheds new light on the so-called "impossible early galaxy problem."

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[–] moridinbg@lemmy.world 6 points 1 year ago (7 children)

Are there any constants that we actually know to have varied along the lifetime of the universe?

[–] h34d@feddit.de 2 points 1 year ago* (last edited 1 year ago) (2 children)

According to my understanding, yes. For example, it is usually assumed that there was a period of time shortly after inflation when matter was in a quark-gluon plasma, which would imply a larger strong coupling than today, since a small strong coupling is associated to confinement. There was also the electroweak-epoch, during which the electromagnetic and weak interactions were unified, and the corresponding gauge bosons were massless. The masses of the W and Z bosons can thus also be regarded as time-varying, as well as the electron charge. However, it should be noted that these changes are not all that significant on the cosmological scales under investigation here (e.g. the quark epoch ended at about 10^-6^ seconds after the big bang, which is much much less than the age of the universe, and it's assumed that it still took quite a while before the first stars formed). A time-varying cosmological constant could potentially be much more relevant (and some quantum gravity theories even predict it), and I've heard some people suggesting it as a potential solution for the H0 tension. However, I unfortunately can't access the paper and assess what precisely the author did there, and whether it is in any way similar to what I just mentioned.

[–] jalda@sopuli.xyz 2 points 1 year ago (1 children)

What you're talking about is the energy dependence of the coupling constants, which is a phenomenon that is very well understood theoretically, and also checked in experiments. The early universe was much hotter, and thus particles had much more kinetic energy and "felt" slightly different coupling constants. The neat thing is that, since this is a purely energy-dependent effect, we can recreate the conditions of the early universe: the collisions at LHC have an energy of the order of 1 TeV, which corresponds to a temperature of 10^16^K, the temperature 10^-12^ s after the Big Bang. Anything after the first 10^-12^ s we can directly recreate, and from 10^-12^ s to about 10^-30^ s-ish we can more or less reliably extrapolate. And of course this is all included in the standard Lambda-CMD cosmology.

Although the article is behind a paywall (which is somewhat strange in cosmology, but I digress), you can check other articles by the same author that also use the "varying constants" framework, for example https://arxiv.org/abs/2201.11667. His framework is that the speed of light c, the Planck constant h, the Boltzmann constant k and the Gravitational constant G depend directly on time, or to be more precise, on the expansion factor of the universe. There are two big differences with respect to what you were saying:

c, h and k are not coupling constants, and therefore they don't receive any energy-dependent corrections. In fact, you could think of these constants as "conversion factors" between units: c converts space-time coordinates in seconds to space-time coordinates in meters, k converts kinetic energy in Joules (or electronvolts) to kinetic energy in Kelvin, and h converts angular momentum or action measured in quanta to angular momentum or action measured in J·s (or eV·s). Honestly it doesn't make much sense to me that these constants could change (what does it means, in physical terms), that they could change in a correlated way, or that they could change in a correlated way to one, and only one, coupling constant, G.
Since this is a time-dependent change, there is no real way to significantly test the hypothesis (unlike the energy-dependent changes). We can not go back in time, or to wait to a different time when these constants would be different. He actually proposes to study how the experimental determinations of these constants in the last 10-20 years, which sounds very wild, as those tiny differences are very susceptible, by definition, to experimental uncertainties, and they are not very suitable for controlled tests.

[–] h34d@feddit.de 1 points 1 year ago

Thanks for giving additional explanation. I was trying to keep my reply relatively short and agree with most of what you said.

Although the article is behind a paywall (which is somewhat strange in cosmology, but I digress), you can check other articles by the same author that also use the “varying constants” framework, for example https://arxiv.org/abs/2201.11667. His framework is that the speed of light c, the Planck constant h, the Boltzmann constant k and the Gravitational constant G depend directly on time, or to be more precise, on the expansion factor of the universe.

Thanks for the arxiv link. I was aware that some people did stuff like this (time-varying fundamental constants), but the abstract only speaking of "coupling constants" made me think of Λ (and G), not fundamental constants. There are some theories that motivate a varying speed of light, for example (Hořava–Lifshitz gravity comes to mind), but this doesn't seem to be motivated by any theory in particular, as far as I can tell. I also agree with you that it seems quite weird to give c, h, and k a time dependence each, only to then have them all be functions of G.

Since this is a time-dependent change, there is no real way to significantly test the hypothesis (unlike the energy-dependent changes).

I'm not sure if I fully agree with this. Shouldn't varying c, h, and k with time clearly change any observable related to the dispersion of light and gravitational waves, or black body radiation (among many other things)? And if we had access to even just one of those from different times during cosmological evolution (where the change should be much larger than between a few decades in the present), we should in principle be able to check if the proposed scaling law holds quite easily. Of course, the author could always make the variation with time small enough to avoid contradicting experiment (which would make it indeed unfalsifiable in practice), but that seems to go against the main idea of using these time-varying fundamental constants to explain some aspects of cosmological evolution. My guess now would be that the paywalled paper modifies the relation between redshift and time to undo the "damage" done by modifying the constants. Nevertheless, it wouldn't surprise me much if this kind of scaling is already ruled out implicitly by some data, as I can't imagine it not affecting a lot of different observables, but maybe I'm also overestimating the experimental cosmological data available at present, or the strength of the variance the author proposes.

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