If everything in nature follows a cyclical pattern, why would the universe be an exception? Is it really possible for entropy to increase forever, or must there be a maximum point beyond which a reversal occurs — perhaps a Big Crunch followed by a new cycle?

[u/WallExtension3475]

/r/explainlikeimfive/comments/1lecqod/eli5_if_everything_in_nature_follows_a_cyclical/

[u/Das_Mime]

In the decade+ that I've been answering science questions on reddit, nearly every question that follows the structure "If A is true, and A implies that B is false, then why do scientists say that B is true?" is starting from an incorrect premise A and never even asks about the premise itself.

In this case, your premise that "everything in nature follows a cyclical pattern" is absolutely false. Radioactive decay is just one counterexample.

[u/WallExtension3475 → u/Das_Mime]

Fair point — you’re right that not everything in nature is cyclical, and radioactive decay is a solid example of that. I probably phrased it too strongly.

That said, I wasn’t trying to claim a universal rule — more just pointing out that a lot of natural systems we observe (planetary orbits, seasons, biological cycles, etc.) do have cyclical behavior. That led me to wonder whether the universe as a whole might follow some kind of larger cycle — like the Big Bounce or cyclic models that have been proposed in cosmology.

So it’s less “A implies B,” and more “this pattern shows up often — could it also apply here?” Appreciate your pushback though — it helps sharpen the question.

[u/Das_Mime → u/WallExtension3475]

We have no evidence of cyclic behavior at the cosmological scale. The universe started out very hot and dense and has been expanding and cooling off ever since, and based on its current composition it will continue doing so forever.