Question

What's the timescale until the Medium Crunch?

Answer 1

clusters of galaxies drift apart due to space expansion until they all pass out of each other's cosmic event horizon. Gravitationally bound clusters overcome the space expansion, but they keep moving away - and once beyond Event Horizon of our cluster they cease to exist for all practical purposes for us - we can still observe their past image for a while but there is no power in the universe for us to reach them, ever. We, in our local cluster, become ultimately alone. But then, our local cluster is very, very big...Masses within the cluster are attracted to each other. Black holes suck in all available matter and eventually the whole local cluster becomes one supermassive black hole.

That would be the effective end of the world: universe of sparse supermassive black holes drifting apart faster than speed of light thanks to space expansion between them and beyond each other's cosmic event horizon, with no chance to influence each other.

Now, knowing the Hubble constant (and possibly in the future its variance in time) and distances between local clusters of galaxies finding the time until ours becomes the lonely island is a matter of simple calculations.

Now though, what would be the timescale for our local cluster of galaxies (defined as the gravitationally bound entity not subject to space expansion) to undergo its own Big Crunch - since it's not the Big Crunch of the whole universe - let me call it Medium Crunch 

Answer 2

Hey !

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In the big crunch theory, the universe will stop expanding and start shrinking. Read about the big crunch and what it means for you and the universe.

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Thanks !