I've read where "The Big Crunch" hypothesis has been all but rejected (thanks to dark energy), but if it does occur sometime in the far far distant future, would time go backwards as space shrinks back in on itself?
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I've read where "The Big Crunch" hypothesis has been all but rejected (thanks to dark energy), but if it does occur sometime in the far far distant future, would time go backwards as space shrinks back in on itself?
Order of Kilopi
Would space "shrink back in on itself"?Originally Posted by Spacedude
"I'm planning to live forever. So far, that's working perfectly." Steven Wright
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^^^ Perhaps a simple description (shrink), would crunch be any better?
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^^^ Oh wait, do you mean that space would stay in place (not shrink) but that just all the matter in it would collaspe/crunch?
Order of Kilopi
For matter to "crunch" would require a central location. If the Universe's mass is evenly distributed on large scales, as to our observations it appears to be, where would it collect for this crunch?
"I'm planning to live forever. So far, that's working perfectly." Steven Wright
Order of Kilopi
It doesn’t need a central location, it just needs to become denser. It’s the same way metric expansion can work whether the universe is spatially finite or infinite - no center required.
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Order of Kilopi
No, I don't think there is any reason to think that time would reverse if the universe starts contracting rather than expanding.
As above, so below
Order of Kilopi
But I was answering the post #4 that asked about just matter and not spacetime.
"I'm planning to live forever. So far, that's working perfectly." Steven Wright
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Thx for the replies, I was prompted to ask due to a semi related post on space/time slowing down etc.
Order of Kilopi
AFAIK entropy is one-way only. Time's arrow and all that. For time to reverse would take something other than a gravitational pull, which is what would account for a Big Crunch.
"I'm planning to live forever. So far, that's working perfectly." Steven Wright
Order of Kilopi
The universe contracting with time running backward is already happening right now.
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Yes. I thought I had seen your post tomorrow.
Order of Kilopi
I suspect that the Big Crunch would manifest simply as a universe getting denser as it gets smaller.
No matter where you started out on a journey, you would find yourself back at your starting point if you travelled long enough.
Eventually (before it got too hot and dense for life) you would find the universe to be only a billion light years across before you arrived back at your starting point.
So, like the expansion, there is no centre. The contraction is happening everywhere all at once.
And I don't see how time would run backwards simply because it's contracting. How would a distributed universe hundreds of billions of light years across "know" that it had - just this moment - stopped expanding and started the contraction phase, and then switch time over to 'backward'?
Events can only affect each other locally. Any given observation point observes that, at just this moment galaxies are (on average) static relative to each other - gravity just balancing expansion - and then tens of millions of years later, all galaxies are (on average) advancing toward each other. It's a continuum; there's no cusp - no 'time switch'.
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