If the universe is expanding at an accelerated rate it would mean that the more we go in the past, the slower the speed of expansion must have been. Provided the acceleration was always non-zero and in the same direction, at some point in time in the past, it should have been stationary, and before that the speed should have been in the opposite direction, and the universe should have been contracting. Does this make any sense whatsoever? Assuming it does, and assuming that the point at which it was stationary was during the big bang, would this imply that there was a 'big crunch' before the big bang and possibly what actually initiated it?
2 Answers
FLRW models have two types of solutions. In one type, which requires a large value of the cosmological constant, you get a "big bounce." Such large values of the cosmological constant have been ruled out by observation.
In the other type of solution, which is the type that is consistent with observation, you get a singularity rather than a bounce, and there is never a stationary point or any contraction.
- 11
Re "In one type, which requires a large value of the cosmological constant, you get a 'big bounce'". https://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtre%E2%80%93Robertson%E2%80%93Walker_metric#Interpretation This says that: "The cosmological constant, on the other hand, causes an acceleration in the expansion of the universe." Therefore this does not seem to allow for a bounce.
- 364