Infinite Universes: The Science & Limits of the Theory

[Redblue88]

TL;DR Summary

For example - https://www.theguardian.com/science/across-the-universe/2017/may/17/multiverse-have-astronomers-found-evidence-of-parallel-universes . The explanation of infinite universes sounds bonkers. What's missing?

I've read in several places that some cosmological theories posit the existence of an "infinite number of universes" with laws of physics different from our own. I'm sure there's a lot of shortcutting in the reporting and "infinite" can't really mean infinite, can it? Wouldn't an infinite number of universes with laws of physics untied to our own necessarily prove itself?

Here's what I mean (and I know I'm wrong, I just want to know why): truly infinite universes would suggest there's at least one universe capable of communicating with all other universes, and in a manner that the receiving universes would be capable of knowing what they were receiving. Doesn't the absence of such a signal in our universe prove that an "infinite number of universes" don't exist? Do the theories contain bounding conditions that just aren't reported? I can think of other consequences of an "infinite" number of universes, but they all sound more like science-fiction stories than science. I've read the "Mulitiverse" article in Wikipedia, so I know there are other multiple universe theories that are bounded, but this doesn't explain how a true "infinite number" theory works. Thanks.

 

[PeterDonis]

truly infinite universes would suggest there's at least one universe capable of communicating with all other universes, and in a manner that the receiving universes would be capable of knowing what they were receiving

Why do you think this?

 

[Redblue88]

An infinite number of universes with an infinite number of possible physical laws suggests there must be one universe with physical laws that satisfy the condition. To say otherwise means there is some unspoken (in the popular press) bounding condition, which is what I think is going on. I've just never heard what that bounding condition is and I'm curious as to what it is.

 

[PeterDonis]

An infinite number of universes with an infinite number of possible physical laws suggests there must be one universe with physical laws that satisfy the condition.

Why?

 

[PeterDonis]

I've read in several places

Are any of them textbooks or peer-reviewed papers?

 

[Redblue88]

Are any of them textbooks or peer-reviewed papers?

Please re-read the title of the post - I'm asking for what the popular press is leaving out (I provided a link and wikipedia entry as examples). As a lay person, I may not have access to the textbook or peer-reviewed article with the answer.

I can't find anything for the proposition that if there are an infinite number of universes with an infinite number of possible laws of physics, there's some constraint that prevents what I've postulated in my original question.

 

[Ibix]

An infinite number of universes with an infinite number of possible physical laws suggests there must be one universe with physical laws that satisfy the condition

I don't think that follows. For example, a universe with a different fine structure constant would have different physics. One can posit infinitely many universes with different fine structure constants. That's infinitely many universes, but it isn't obvious that any of them allow the kind of physics you are demanding.

I don't know what constraints there are (and it's almost certainly all speculation anyway), but "infinitely many" doesn't necessarily mean "anything goes".

 

[jbriggs444]

If I understand the unspoken reasoning here, it is that "infinitely many universes" means that "every possible universe". But that is not necessarily so. Especially when one is including the properties of the multiverse (connectivity between universes) in the description of a particular member universe.

One can have infinitely many things without having every thing.

 

[Redblue88]

This is very helpful and exactly the insight I was looking for. This is the kind of "unspoken" constraint that is missing from what I've seen in the lay press. I assumed it was there, but I've been curious whether it's baked into the theories. Thank you very much @Ibix and @jbriggs444

 

[PeterDonis]

I'm asking for what the popular press is leaving out

There's no way to answer that unless we have an actual textbook or peer-reviewed paper to compare to. The Guardian article you linked to does not reference any actual textbook or peer-reviewed paper, so we have no idea what "infinite universes" model it is talking about.

As a lay person, I may not have access to the textbook or peer-reviewed article with the answer.

Neither do any of us if we don't know which one it is.

 

[PeterDonis]

This is the kind of "unspoken" constraint that is missing from what I've seen in the lay press. I assumed it was there, but I've been curious whether it's baked into the theories.

And the answers that @Ibix and @jbriggs444 gave you do not tell you whether it is or not. They're not telling you about any actual theoretical model. They're just guessing about what some hypothetical model might say. We can't possibly say anything about any actual theoretical model if we don't have any reference to one.

 

[PeterDonis]

Since no valid reference has been provided, this thread is closed.