The current state of cosmological theory has some aspects to it that are, at a bare minimum, puzzling. Near the beginning of the Big Expansion, aka the Big Bang, a period of what is called cosmic inflation occurred, this is a label slapped on a period of rapid expansion of space-time. I am reading that some think that a period of cosmic inflation also occurred just before whatever triggered the Big Expansion. And, quite recently, we have learned that the expansion of the universe is accelerating. No explanations for these mysterious expansions has yet been provided, at least with any physical support. As usual, speculation abounds.

I can remember reading in high school a speculation that the universe was expanding, but the dominant force in the universe, gravity, had to slow that expansion and eventually cause the universe to contract. I was enthralled with this speculation, but alas, studies now show that the expansion if the universe is not only not slowing, but is speeding up. (I think I am "oh for whatever" in theories I took a liking to.)

And, why religious apologists haven't claimed that their god is responsible for these expansions and accelerations of expansions yet (C'mon, God of the Gaps people, pick up the slack!), since we don't have a physical explanations for these yet, one can still speculate.

So, if the universe can go through phases in which its foot is on the accelerator, could it also not be the case that it could go through phases with its foot on the brakes? Ah, didn't see that coming, did'ja?

My theory lives! (Bwah, hah, hah!)

So, at some undetermined time in the future, the rate of expansion of the universe slows and gravity re-exerts its place as the dominant force in the universe. Instead of galaxies separating from one another over time, they then began to get closer. Closer and closer they get, until galaxies merge . . . and merge . . . and merge. (I have to wonder if entropy decreases during this phase as it increased during the expansion.) Then stars get so close they merge with other stars and black holes. On and on this goes until the universe is crunched (this phase of the universe's life cycle was called "the Big Crunch") into a tiny point. All matter is turned into energy and the tiny universe is immensely hot as well as being immensely small, just like the universe before the Big Expansion we currently observe. Then, Bam!, off it goes again.

This cycle continues over and over and over. Why? Because it can.

This is the likely scenario had no cosmic inflation occurred in the first place, or the rate of expansion of the universe had not accelerated. Since we do not yet have reasons for why those phases occurred, then an equally bewildering contraction seems possible.

Maybe our universe is in a universe growth chamber and the entities running it occasionally tweak the process to make to go in direction of their choice. "Reality" has shown us over and over that it can be weirder than we can imagine.

Ah, but a man's reach should exceed his grasp, or what's a heaven for?
(Robert Browning)