Before THE BIG BANG | Ch 4. The Bouncing Universe

The idea is that the universe came out of another collapsing universe. This notion, sometimes called the Big Bounce, predicts that another universe collapsed inward, into a point of infinite gravity called a singularity, and then bounced back to produce our own universe.
It’s possible there have even been multiple bounces; an expand-and-contract cycle full of Big Bang like a universe accordion.

[Image source: wikipedia CC BY-SA 2.0 licensed]

Big Bounce theories have issues: namely, the idea of singularity just blowing up violates Einstein’s General Relativity, the rules for how gravity works. Physicists believe that singularities probably exist inside black holes
But physical laws don’t give a mechanism by which another universe, once collapsed into a singularity, should Bang. A Big Bounce, then, would require adding new particles and fields and coming up with new theories. There’s nothing in general relativity that says the universe would bounce if it turned into a singularity.

[image credit: Andrea Danti/Shutterstock]

And there’s an even bigger problem: bouncing universe require forward moving time with decreasing entropy (disorder-ness), and entropy always increase with time. That means as far as our established laws of physics are concerned, a bouncing universe can’t happen.

[Image source: dhushara]

[The big bounce in loop quantum gravity.]

That doesn’t mean a bouncing universe didn’t happen- it could just mean our current theories are incomplete. The laws we’ve established only cover the universe we can observe, after all.

References for further reading

• what existed before the bigbang
• Big Bounce
• The Big Bounce Theory: What is it?

Thanks for reading and learning