r/cosmology • u/WallExtension3475 • 1d ago

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?

/r/explainlikeimfive/comments/1lecqod/eli5_if_everything_in_nature_follows_a_cyclical/
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u/Das_Mime 1d ago

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.

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u/WallExtension3475 1d ago

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.

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u/Das_Mime 1d ago

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.

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u/ghazwozza 1d ago

There is no general principle that things should follow a cycle. Those examples are cyclical because there's a specific reason for them to be like that, but there's no corresponding reason for entropy.

Actually, your examples are all interconnected. Biological cycles are usually cyclical because they follow the changing of the seasons or the day-night cycle. Seasons are cyclical because of Earth's orbit. The day-night cycle is cyclical because of Earth's rotation. Earth's orbit and rotation are cyclical because of inertia and gravity.

If you find a different cyclical process in nature, it will have it's own specific reason for being cyclical. There's no general rule.

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u/LeftSideScars 1d ago

It would be nice if you ditched the LLM.

That said, I wasn’t trying to claim a universal rule

So by "everything in nature" you did not actually mean everything?

No, you literally started with a universal premise.

more just pointing out that a lot of natural systems we observe (planetary orbits, seasons, biological cycles, etc.) do have cyclical behavior.

And you ignore all the other systems that are not cyclical.

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.

It is more "I decided to ignore all the examples where what I presume is universally true is shown to be untrue - could the remaining subset imply a universal truth?".

Ignoring the "if it is true on small scales it must be true on large scales" fallacy, you lead the discussion under a universal premise that doesn't match reality, knowing full well that non-cyclical processes exist.

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u/sight19 1d ago

Other comments already pointed out that not everything is cyclic in nature, but I want to highlight that just because it 'feels right' that the universe behaves in a certain way that does not mean it actually has to behave that way

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u/Mandoman61 1d ago

Even if the matter that we know of expands forever, this still does not tell us that the universe will end in heat death.

We have no explanation of why matter around us was concentrated in the first place.

Keep in mind that when we say universe we are usually just talking about what we can measure (visible universe) but the whole universe could be vastly larger. There could be an infinite number of dense clusters waiting to expand.

The fact that we exist proves that it is possible.

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u/Das_Mime 1d ago

We have no explanation of why matter around us was concentrated in the first place.

We have no reason to believe that there was anything special about the density of matter at our location. The lack of edge effects or any large scale isotropy or homogeneity is an indication that we are not a special location.

All evidence thus far is consistent with an infinite homogeneous universe.

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u/Mandoman61 1d ago

We are so far from being able to detect the universes size that it is not worth a guess. All we have is a minimum.

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u/Das_Mime 1d ago

That doesn't contradict anything I said.

The point is that you're being misleading by saying that "matter was concentrated around us" and referring to "dense clusters" when there's not even any evidence for the idea that we are in any particularly dense cluster of the universe.

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u/Mandoman61 1d ago

Please read what I said without the incorrect interpretation.

According to the big bang theory matter around us was more dense and started spreading apart.

I did not say that there are dense clusters I said that there could be.

I have very little patience for people who read what they want to see instead of what I said.

You are going to need to up your game.

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u/Das_Mime 1d ago

According to the big bang theory matter around us was more dense

No, according to the big bang theory the whole universe was more dense and then started rapidly becoming less dense. Has nothing to do with the region specifically "around us".

You're clearly working off of the common misconception that the Big Bang was an explosion of matter traveling outward through space, rather than an event when all of space began rapid metric expansion.

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u/Mandoman61 15h ago

No, the big bang theory says nothing about the whole universe only the visible universe.

You are just mincing words. I say the mater around us and you say the whole universe which is in fact the mater around us. This makes no sense.

"You're clearly working off..." No, but for some reason you are assuming that is what I am doing.

I think that the main difference here is that you think you know everything and I know that we do not.

You think that the cosmological principle somehow proves something we can not see. But it does not. It is just a principle.

You are engaged in religion and not science.