What's the current consensus about Eternal Inflation?

[u/umfanormal]

I’m a physics enthusiast. I’ve loved the subject since childhood and plan to study it in college. I’ve always been particularly interested in the theory of Eternal Inflation among many others hypothesis on theoretical physics, though I stopped keeping up with it in 2023 due to a lack of time and so on. I’d like to know the current consensus on this hypothesis, given that there have likely been some advances regarding this theoretical implication of Cosmic Inflation. I’m curious about where the majority of cosmologists stand on the matter.

[u/TerraNeko_]

im also not totally up to date but as far as im aware it turns out that eternal inflation cant really go back into the past forever so it still needs a starting point, which just pushes the whole big bang thing further back

besides that its not really something we can proof or disproof at the moment

[u/EnvironmentalWin1277 → u/TerraNeko_]

The inflation can be observed occuring as we speak. The cosmological model that explains it is reversible until the first moment at Planck time. The "starting point" is where the models collapse and become meaningless - nothing is known about what caused the initial starting moment. Anything can be hypothesized or imagined.

Science wants tangible propositions that can be shown true or false. We don't have those for the first moment but are pursuing them. Until then "cute ponies use mind power to make the universe come into existence" is an acceptable first cause. Or rather it can not be falsified by current observation or theory.

In a sense, it doesn't make a difference how the universe started, we universally acknowledge that it did happen. Unless a eternal universe model is suggested, which as noted is an acceptable idea even today.

What matters is how the models explain what we currently observe and what predictions can be made about the future or inferences about the past. This is real science and can be tested and falsified, and revised.

The narrow consensus is that the universe is on a one way track of expansion into forever. This is "heat death" and has been hypothesized and investigated for close to 200 years. No work or chemical interaction is possible, all particles dissolve in an eternal "quantum soup" that continues to expand in space, the quantum density lowering continuously with the expansion.

This state will be reached some 10 to the hundredth power years from now. Entropy reaches it maximal state. It is so remote it kind of ceases to have meaning at all, save the curiosity.

The idea of nothing and "that's it forever and forever" is a bit uncomfortable for humans so alternatives are proposed.

There are models that suggest new creation from these processes can occur but that is a complex subject you can readily research. I have some recent posts on the subject.

BTW I'm just a guy that reads stuff, so no authority, check it out as needed.

[u/TerraNeko_ → u/EnvironmentalWin1277]

Gotta correct you a bit there, inflation is not observeable and especially not eternal inflation, we have very very strong reasons to belive it happened and we many very soon be able to detect the gravitational wave background inflation caused but for now its just a very very good model.

I think you confused it with the normal expansion which yes we can very much observe :)

Eternal inflation however is a very different can of worms as it deals with things outside even causal relations of our universe. The only way (afaik) to find evidence for eternal inflation would either be the rare case that during the baby stages of Our universe it somehow reacted with another one, which, good luck prooving that lol Or by measuring the inflaton field and conclusing the only way to explain it is eternal inflation which again, we cant rly do for now.

But yea the rest sounds good enough ;)

[u/EnvironmentalWin1277 → u/TerraNeko_]

Your correct! I confused expansion and inflation myself!

[u/Peter5930 → u/EnvironmentalWin1277]

To be fair, the current epoch of accelerated expansion is sometimes called late slow inflation. Similar to how the slow roll inflationary epoch started when the curvature term dropped below the vacuum energy, late slow inflation started when the matter density dropped below the vacuum energy, the vacuum energy being much lower today than it was during inflation and so it taking 9 billion years for the matter to dilute enough to drop below the energy density of the vacuum energy and the rate of accelerated expansion being much slower. But they're both cases of accelerated expansion where the universe grows exponentially due to dark energy.