As a whole, we humans are pretty smart folks. We’ve figured out most of our planet’s mysteries, and a good many of them beyond our little blue orb, as well. One thing we’ll probably never be 100% sure about, however, is the creation of the universe—which, considering that it includes every known and unknown thing in the history of existence, is understandable. I’m still not sure how the jelly gets inside jelly donuts. (Remember, I said we’re smart as a whole; individual people can be pretty stupid).
We’re so unsure about how the universe came about that there are literally dozens of contradicting theories and models. Most of the older ones have been disproven, thanks to hundreds of years of additional research. But there are still a few hypotheses floating around that might be right. One of them is the cyclic model of the universe.
‘Round & ‘Round & ‘Round She Goes…
At its essence, the cyclic model hypothesizes that the universe in on an infinite self-sustaining life cycle. The cyclic model is considered an at least somewhat probably alternative to the (now) more widely accepted model of an infinitely-expanding universe.
For example, the oscillating universe theory that Einstein was kicking around in the 1920s postulated that the universe was continually moving from a Big Bang (not the Big Bang, because in this case there are more than one of them) to a Big Crunch, which is the same as a Big Bang but in reverse. Betwixt, the universe would expand for an unknown period of time before being pulled back in by the gravitational attraction of matter.
Einstein’s theory was disproved by American mathematical physicist Richard Chace “Big Dick” Tolman. His study of the Second Law of Thermodynamics led to the counter-hypothesis that entropy can only increase; ergo, successive cycles would grow both longer and larger. Flipped and reversed, these cycles going backward in time prior to the present cycle would become shorter and smaller, which would ultimately lead to, essentially, a single Big Bang, not one of many Big Bangs.
…Where She Stops, No One Knows
After that, the cyclic model was stuck in a “well I guess maybe it could be a thing but it’s hard to say” limbo until the early 21st century CE. The discovery of evidence of the existence of dark energy—an unknown form of energy long hypothesized to permeate all of space—offered new insights. After studying roughly 200,000 galaxies outside our own, covering 7 billion years of cosmic time, it was confirmed that dark energy is, in fact, expanding our universe at a constantly increasing speed.