RE: Probably the most popular alternative is the cyclical universe where it contracts to a tiny ( but not infinity small volume ) only to re-expand.
The The Steinhardt–Turok model has been proposed for a long time.
It is not without its problems.
Mathematical physicist and physical chemist (who worked with Einstein at Caltech), showed, the earlier cyclic model failed because the universe would undergo inevitable thermodynamic heat death.
I know that the newer cyclic model evades this by having a net expansion each cycle, preventing entropy from building up. However, there remain major open issues in the model. Foremost among them is that colliding branes are not understood by string theorists, and nobody knows if the scale invariant spectrum will be destroyed by the big crunch.
Moreover, as with cosmic inflation, while the general character of the forces (in the ekpyrotic scenario, a force between branes) required to create the vacuum fluctuations is known, there is no candidate from particle physics.
I know they all have problems. Problems attract physicists.
Apparently the inflation aspect of BB started falling apart when they started analyzing the Wilkinson Microwave Anisotropy Probe data.
Again, kind of talking over my head here.
I pride myself to be a reasonably educated person in the sciences with acceptable reading comprehension, but I confess I could not understand most of that post, upon several re-readings.
Some of it seems to say that each cycle would cause losses that would diminish subsequent cycles, and so it could not be everlasting.
My biggest problem with the cycles theory is that there are no forces to recollect all the matter that disperses to its outer limit of the cycle. I’m sure these theories postulate some impenetrable outer boundary for some reason, or else the outer limit is also the centerpoint so that all matter flows back into the center even as it breaches the outer limit.
It is all preposterous to me.