The Bouncing Universe
It has been known for a few decades that the universe is expanding. But it is also known that gravity is an attractive force. This implies that at some point it may be possible that the universe would stop expanding and start shrinking instead until a Big Crunch at the end which will end it all.
Or would it?
Leonard Susskind suggests that a Big Crunch would be followed by another Big Bang. And who knows? If it has happened once, it can happen again. And again. And again. Because matter and energy cannot be created or destroyed, there is no reason to assume that there will ever be a point where what has happened once cannot ever happen again.
Each time the Big Bang happens, it might be different. The distribution of matter/anti-matter might be different so that people like you and I see a universe that appears to be mostly matter, or the so-called “constants” of nature may be derived differently so that the electron orbits slightly closer to the atom, leading towards different star structures, different temperatures needed for fusion, different amounts of each element available for chemistry to work on.
There are an infinite possible configurations, and with an infinite number of Bang/Crunch cycles, there might be time to explore them all.