Independent Inflationary Regions in an Infinite Universe?

[mister i]

TL;DR

In an infinite universe, could different inflationary processes have occurred in different regions, each giving rise to its own local universe?

In an infinite universe, could different inflationary processes have occurred in different regions, each giving rise to its own local universe? (differents observed universes), independent and not causally connected to the others? I have read the Multiverse entry on Wikipedia, but this possibility does not seem to be mentioned there.

 

[PeterDonis]

For reference, the Wikipedia page you mention is here:

https://en.wikipedia.org/wiki/Multiverse

 

[PeterDonis]

And from that Wikipedia page (thanks to @renormalize for the quote):

Proponents and skeptics
Modern proponents of one or more of the multiverse hypotheses include Lee Smolin, Don Page, Brian Greene, Max Tegmark, Alan Guth, Andrei Linde, Michio Kaku, David Deutsch, Leonard Susskind, Alexander Vilenkin, Yasunori Nomura, Raj Pathria, Laura Mersini-Houghton, Neil deGrasse Tyson, Sean Carroll and Stephen Hawking.
Scientists who are generally skeptical of the concept of a multiverse or popular multiverse hypotheses include Sabine Hossenfelder, David Gross, Paul Steinhardt, Anna Ijjas, Abraham Loeb, David Spergel, Neil Turok, Viatcheslav Mukhanov, Michael S. Turner, Roger Penrose, George Ellis, Joe Silk, Carlo Rovelli, Adam Frank, Marcelo Gleiser, Jim Baggott and Paul Davies.

So there does not seem to be any consensus on the question you're asking.

 

[javisot]

TL;DR: In an infinite universe, could different inflationary processes have occurred in different regions, each giving rise to its own local universe?

In an infinite universe, could different inflationary processes have occurred in different regions, each giving rise to its own local universe? (differents observed universes), independent and not causally connected to the others? I have read the Multiverse entry on Wikipedia, but this possibility does not seem to be mentioned there.

"A Level II multiverse, defined by Max Tegmark, consists of distinct, distant "bubble" universes formed through chaotic eternal inflation, where space expands forever. " (google)

 

[PeterDonis]

"A Level II multiverse, defined by Max Tegmark, consists of distinct, distant "bubble" universes formed through chaotic eternal inflation, where space expands forever. " (google)

Sure, but the OP's not asking how to define a multiverse. He's asking whether inflationary theory actually says a multiverse exists. And, as has already been posted, there is no consensus on that. Of course Tegmark thinks it does: he's listed as one of the proponents in the Wikipedia article that was quoted. But "Tegmark says so" doesn't guarantee that it's true.

 

[renormalize]

In an infinite universe, could different inflationary processes have occurred in different regions, each giving rise to its own local universe? (differents observed universes), independent and not causally connected to the others? I have read the Multiverse entry on Wikipedia, but this possibility does not seem to be mentioned there.

Yes, the possibility is mentioned in the Wikipedia article, namely as the "inflationary multiverse", in which multiple "bubble universes" arise due to Eternal Inflation.

 

[Jaime Rudas]

Yes, the possibility is mentioned in the Wikipedia article, namely as the "inflationary multiverse", in which multiple "bubble universes" arise due to Eternal Inflation.

As a supplement, this Andrei Linde's paper contains a good description of the eternal inflation hypothesis.

 

[javisot]

Sure, but the OP's not asking how to define a multiverse. He's asking whether inflationary theory actually says a multiverse exists. And, as has already been posted, there is no consensus on that. Of course Tegmark thinks it does: he's listed as one of the proponents in the Wikipedia article that was quoted. But "Tegmark says so" doesn't guarantee that it's true.

I agree that all of this is theoretical and possibly has no relation to reality, and that the informal proposal of bubble universes might not even be theoretically true.



What is the hierarchy of sizes?

Multiverse-universe > bubble universe > observable universe

I understand that the concepts of "observable universe" and "bubble universe" refer to different things, right?

 

[Jaime Rudas]

Sure, but the OP's not asking how to define a multiverse. He's asking whether inflationary theory actually says a multiverse exists.

The OP's not asking whether inflationary theory actually says a multiverse exists. He's asking whether different inflationary processes could have occurred in different regions, each giving rise to its own local universe. This is similar to the eternal inflation hypothesis that Tegmark includes in his classification.

 

[PeterDonis]

The OP's not asking whether inflationary theory actually says a multiverse exists. He's asking whether different inflationary processes could have occurred in different regions, each giving rise to its own local universe.

That's how Tegmark defines a Level II multiverse. It's true that he defines other levels as well. But the OP appears to be asking about that one. Asking whether the processes could have occurred that give rise to a Level II multiverse is the same as asking whether a Level II multiverse exists. The answer is that nobody knows for sure.

This is similar to the eternal inflation hypothesis that Tegmark includes in his classification.

Yes, which he says gives rise to a Level II multiverse.

 

[PeterDonis]

I understand that the concepts of "observable universe" and "bubble universe" refer to different things, right?

Yes.

 

[Jaime Rudas]

Asking whether the processes could have occurred that give rise to a Level II multiverse is the same as asking whether a Level II multiverse exists.

It's not the same to ask whether something could have happened as to ask whether it actually did happen. Moreover, the question seems to be aimed more at finding out whether this particular type of multiverse is among those described in the Wikipedia article.

 

[PeterDonis]

It's not the same to ask whether something could have happened as to ask whether it actually did happen.

It is when you're talking about multiverse hypotheses. That's the whole point of them: that every possible universe that could happen, does happen. The question is, is that actually true?

 

[Jaime Rudas]

The question is, is that actually true?

The OP isn't asking that.

 

[PeterDonis]

The OP isn't asking that.

How do you know? Why don't we let the OP decide what he's asking, and whether the posts in this thread are useful to him? We've each expressed our opinions, but it's up to him.

 

[Jaime Rudas]

the OP's not asking how to define a multiverse.

How do you know? Why don't we let the OP decide what he's asking?

 

[javisot]

Personally, I think the OP's question is answered by referencing Tegmark's Level 2 multiverse. On the other hand, Peter's point is appropriate, since the "bubble universe" proposal is far less formalized than it seems.

 

[mister i]

How do you know? Why don't we let the OP decide what he's asking, and whether the posts in this thread are useful to him? We've each expressed our opinions, but it's up to him.

My question was: In an infinite universe, could different inflationary processes have occurred in different regions, each giving rise to its own local universe?

In the Wikipedia article on the Multiverse, Level II effectively answers part of the question, although its title is Level II: Universes with different physical constants, and it discusses eternal inflation (which is somewhat beyond what I had in mind).

In any case, it seems clear that the answer is yes: in an infinite universe, different inflationary processes could have occurred in different regions.

If you allow me, within my limited knowledge, I would go a bit further and say that in an infinite universe, even before any inflation began, the universe already had an infinite volume. Therefore, it seems likely that there were more than just a single small homogeneous region. The Wikipedia article on cosmic inflation (theory) says: “The inflation solution starts with a tiny universe in thermal equilibrium, then expands…”

Of course, it may also be that the universe is not infinite but slightly curved and finite, in which case this discussion would largely disappear.