VSl as an alternative to cosmic inflation

[windy miller]

It has been proposed that a varying speed of light can resolve certain cosmological problems thought to be solved by cosmic inflation. An example is this paper here by Albrecht and Magueijo:
https://arxiv.org/pdf/astro-ph/9811018.pdf
and this paper by Moffat
https://arxiv.org/abs/gr-qc/9211020
I would be interested to hear peoples thoughts on the strengths and weaknesses of this approach.

 

[kimbyd]

I haven't looked into it in detail, but I actually talked with Andy about this very model back when I was a grad student (~2006 or so). His conclusion at the time was that he felt the model just wasn't very useful and wasn't interested in working on it further. At the time, I took that to mean that he felt the idea both unlikely and didn't seem to offer room for interesting new theoretical ideas.

My personal feeling for this kind of model is that it's really, really difficult to reconcile its full implications. It's such a radical change to how we understand basic physics that it would change everything. It would require coming up with both a new theory of gravity and a new theory of quantum mechanics which allowed for the possibility of a variable speed of light. And then we'd have to go back and make sure that the new, modified models matched with existing observations. This is a monumental task.

 

[windy miller]

I haven't looked into it in detail, but I actually talked with Andy about this very model back when I was a grad student (~2006 or so). His conclusion at the time was that he felt the model just wasn't very useful and wasn't interested in working on it further. At the time, I took that to mean that he felt the idea both unlikely and didn't seem to offer room for interesting new theoretical ideas.

My personal feeling for this kind of model is that it's really, really difficult to reconcile its full implications. It's such a radical change to how we understand basic physics that it would change everything. It would require coming up with both a new theory of gravity and a new theory of quantum mechanics which allowed for the possibility of a variable speed of light. And then we'd have to go back and make sure that the new, modified models matched with existing observations. This is a monumental task.

Thank you for your reply.Im wondering if it could be embedded into Horava gravity? as on the wikipedia page it says: "Also, the speed of light goes to infinity at high energies." https://en.wikipedia.org/wiki/Hořava–Lifshitz_gravity

 

[kimbyd]

I don't think it could be embedded into it. But I could imagine somebody trying to estimate the past behavior of our universe using Hořava–Lifshitz gravity, and it's conceivable it would show behavior that is sort-of similar to the older VSL models.

The simple concept would be that in the very early universe, plasma temperatures would have been high enough that the effective speed of light would have been higher than its current value. There are some immediate questions that come to mind with this idea:
1) The speed of light would be particle-specific. What would it mean for the expansion with many particles of different energies, each behaving as if there were a different speed of light?
2) How would the changing speed of light impact temperature? Would the temperature still monotonically increase when looking backward in time, or would it level off at some finite temperature?
3) Does the theory predict a nearly scale-invariant spectrum of primordial density perturbations? Current measurements of the cosmic microwave background provide a very precise picture of the statistical properties of the density variations in the early universe, and any competing theory will have to match these observations.