Archive for July, 2013

July 1, 2013

A note on cosmology

For a long time, I wanted to do a post here on Louise Riofrio’s cosmology, because it was part of Sheppeard’s synthesis, but I felt I couldn’t do it justice. It’s a varying speed-of-light cosmology, in which there is no dark energy or accelerating expansion; light is just slowing down, because of the mass of the universe, according to the formula “GM=tc3.

But I could never quite grasp the logic whereby the density fractions were being predicted, and that was the big empirical claim to success. I also thought I saw a similarity to the Milne universe, but again, I never quite got it clear in my own head.

Much later I came to understand that the model was empirically problematic, because dark matter and dark energy density fractions evolve with time, so any numerology based on present-day observations is just picking out one moment in the history of the universe. It remains possible that the present-day values are special, e.g. perhaps they are the asymptotic values. One should also bear in mind that for Sheppeard, Riofrio’s handful of equations are a classical ansatz to be derived from a theory of quantum gravity.

The Planck satellite has in any case given us new values for the density fractions, that are no longer close to Riofrio’s numbers, so it’s an open question as to whether Riofrio’s ideas are still part of Sheppeard’s thinking. However, Sheppeard continues to champion another item of astrophysical numerology, which I believe was co-discovered by her collaborator Graham Dungworth – that the temperature of the cosmic microwave background equals the rest mass of a certain “mirror neutrino”, as predicted by a version of Brannen’s formula for Koide mass triplets.

This would be even more “problematic” than Riofrio’s numbers. The CMB temperature varies with the expansion, but that’s not fatal to the idea; quintessence models show that it’s possible to have mirror neutrino masses evolving with the size of the universe. The real difficulty lies in explaining the connection between CMB photons and mirror neutrinos at the level of particle physics and cosmic history.

One normally supposes that the CMB photons are simply photons which decoupled from the primordial plasma, once it had thinned out enough for neutral atoms to form, and which, ever since that time, have been travelling without scattering again. Neutrinos, mirror or otherwise, feature nowhere in this story, and yet they ought to, if the posited relationship is supposed to be real. Either the mirror neutrino ought to play a role in photon decoupling, or a completely different origin must be ascribed to the CMB photons, one with room for the mirror neutrinos to play a role. (Or the connection is spurious, which is what I think; but the ideas are still interesting to play with.)