Digitalism said:
Are you serious? Doesn't that just push back the question of what happened "before" a singularity back one step? Also, how could you know -objectively- how many oscillations have occurred? Or are you saying it would be a time symmetric oscillation or something similar?
Nothing wrong with the one-bounce picture. That is the most common in the LQC research lit.
You can set it up, with zero cosmological curvature constant , so that it repeatedly bounces, but that is not the most common case to consider.
It seems to me that the theory does not address questions like "why does existence exist?" or "where did it all come from?". It studies what could have happened to geometry and matter right around the bounce. What implications for inflation? What features might carry over from prior collapsing region? What might be an OBSERVABLE signature of the bounce?
AFAIK it leaves completely open the question of where the prior collapsing phase could have come from!
You might say the attitude is first let's try to understand what really happened instead of that classical failure called "singularity". And let's try to TEST our model by determining its footprint on the CMB polarization map.
So it's very focused on what should replace the classical theory breakdown. When the classical theory is replaced by a quantum theory that recovers the classical shortly before and after its failure, they find that in the new version quantum effects at high density cause gravity to be repellent. The brief episode where gravity is repellent involves a period of faster than exponential growth called "super-inflation", which precedes the ordinary inflation era. Ordinary inflation has constant or slowly declining H, super-inflation has rapidly increasing H, driving H to around the Planck frequency. (H is Hubble growth rate, units of reciprocal time). Considerable inhomogeneity, or "structure" is wiped out during the period where quantum effects dominate and gravity is repellent instead of attractive.
there are some recent papers on the pre-inflationary period in LQC. In case you are interested I'll get some links. there's also the interesting question of
geometric entropy. How do you define it? When gravity is attractive, structure tends to increase, clumping, inhomogeneity grows, when repellent, the reverse. Different equilibrium states. New paper by Clifton Ellis Tavakol on geometric entropy, still no universally accepted definition.
BTW you are quite right that it pushes the frontier back a step. that is how science works I guess.
Model and test, figure out what was actually going on at the start of expansion, and immediately before. then, if you can do that, you still have another problem:what came before that. But I wouldn't call that *merely* pushing one step back in time. I think it is potentially a valuable accomplishment and very worthwhile striving for. (Though it fails to explain why existence exists
)
