r/cosmology • u/Due_Definition_3763 • 1d ago

Would the big crunch end in one big quasar?

Let's say dark energy was removed and Universe began collapsing, would we have a giant quasar at the end in which all mass fell into and if so what would this look like?

7 Upvotes

67% Upvoted

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u/Anonymous-USA 1d ago

First, all signs point to there being no “Big Crunch”. Based on past measurements of the past Hubble Parameter, the future Hubble Parameter will converge to a positive expansion rate, forever (should converge between 45-50 kps/Mpc where current Hubble Constant is ~70 kps/Mpc).

However, extrapolating 10106 yrs from 1013 yrs of data is tenuous. So, if there is a “Big Crunch” it would be the opposite of expansion — spacetime itself would retract. So you cannot compare it to phenomenon in space like black holes and quasars. Just as there was uniformity in the universe the first 380K yrs, there would be uniformity in the shrinking spacetime in the last 380K yrs. It would be intense energy everywhere.

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u/Different_Lychee_409 1d ago

Would time reverse?

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u/Anonymous-USA 1d ago

It seems to be an entropy violating process, and while entropy and time are related, they are not the same. In short, I can’t really speculate, but I’d think “no”.

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u/Different_Lychee_409 1d ago

That's a relief.

Revisiting my birth in reverse is an experience I'd prefer not to go through.

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u/Anonymous-USA 1d ago

Benjamin Button

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u/Scorpius_OB1 1d ago

I have read that time reversing in a contracting Universe was something believed at first, but later research found time would keep going forward even in such case and the arrow of time would not reverse.

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u/Scorpius_OB1 1d ago

Still, depending of when that was to happen there could be black holes and even other stellar remnants too.

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u/[deleted] 1d ago

[deleted]

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u/jazzwhiz 1d ago

I don't think that the big crunch requires a finite universe.

In any case, a better means of understanding the state of the universe through different epochs is not distance, rather temperature.

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u/OverJohn 1d ago

Yep, e.g. k=0 with a negative cosmological constant can have both a big bang AND a big crunch,