Low Entropy big bang , models that explain it

skydivephil

Hi
As I understand it there are several attmepts to explain the low entropy configuration of the universe at the big bang.
Is seems to me the choices on the table that Im aware of are a mutliverse as in the Caroll/Chen model . A cyclic universe as in the CCC model or some hybrid of the two as in the Baum/Frmapton model.
Are there any other explanations to this and if so how do they work?

Also why does the dense state of the unvierse not work as an explanation? After all I would have thought if the unvierse is so incredibly compressed then the number of allowed configurations should be less, obviously this is not the case , but why not ?

bcrowell

I wouldn't say that CCC attempts to explain the low-entropy big bang. Penrose takes the Weyl curvature hypothesis as an assumption. That means assuming the low-entropy big bang, not explaining it. I also don't think CCC is viable at this point. It predicted nonstandard particle physics, which turned out to be incompatible with observation. (The CMB evidence also turned out to be completely bogus.)

Chalnoth

Bear in mind that our current universe and the early universe are just two different states of the same system. So if you want to examine the entropy of the situation, you have to consider our current state to be just as relevant a configuration of the system as its early state. The total number of configurations available is not limited by the small size of the early system, because it is possible for such a small system to evolve into a large one like the one we observe.

However, it naively seems like the small size of the early universe must have something to do with the answer, whatever that answer happens to be. Carol and Chen proposed an explanation where a small piece of a large universe which has high entropy but very low entropy density could start off a new universe: it isn't a huge drop in entropy because of the low entropy density of the "parent" universe.