Ask Ethan: If The Universe Ends In A Big Crunch, Will All Of Space Recollapse?
“When you describe the Big Crunch, you talk about a race between gravity and the expansion of space. It’s not clear to me that if gravity wins that race, whether space stops expanding, or simply that the matter in space stops expanding. I’d love to hear your explanation of this.”
The Universe is expanding, and we can confirm this by looking at the relationship between how redshifted a galaxy’s light is compared with how far away it is from us. But if these galaxies, at some point in the far future, stop being redshifted and start moving closer and closer to us again, does that necessarily mean that the fabric of space is contracting? Is all of space necessarily recollapsing? Or could the galaxies simply be moving towards us, owing to some massive attraction, while the fabric of space doesn’t recollapse at all? Does a Big Crunch necessarily equate to a recollapsing Universe?
Even though we don’t know whether dark energy will reverse itself or not, we do know the answer to this question, and yes, a Big Crunch does mean recollapse! Find out why on this edition of Ask Ethan.