Whenever I read about the multiverse, it is always presented in such a way that it, potentially, could account for the just right nature of this universe, because infinite universes would present every potential kind of universe.
Is this necessarily so? Should we assume that infinite universes would encompass every possible kind of universe? Does not the vehicle responsible for such a universe generating mechanism have a great deal to say about how many different types there are (even if they are infinite in number?)
Well, I sure hope so, that would mean that I’m a mutant in some universe far far away. But with shape shifting or telepathy, no optic blasts. That’s just stupid.
This depends on what sorts of multiverse you are talking about. There are many contexts in physics in which the word “multiverse” appears. Check out the many types in the wikipedia page for multiverse: Multiverse - Wikipedia
If I am assuming you are talking about multiverse in the inflationary cosmological sense, then there would be as many kinds of universes as there are initial conditions for the hot big bang, as this would depend on when that particular universe bubble exits inflation. What this actually entails in terms of the kinds of Universe that we can get is a technical question that is difficult to answer. By this I mean that I can give you some examples of the different kinds of universes that one can get, but to give an exhaustive list is difficult. It suffices to say that universes with varying values of physical constants (such as the gravitational constant, electron charge, etc) are not only possible but likely.
Note that just because there are an infinite number of a certain kind of universe, it does not mean that we cannot compute how probable that kind of universe is. For example, while there are infinitely many universes that are akind to ours, the probability of our universe occurring versus a different universe (that does not support life, for example) occurring is extremely small. This is what I meant when in this thread: Is Earth a Privileged Planet? - #7 by T.j_Runyon I call the multiverse as being misanthropic.
Crucially, there is no evidence and most probably no way to test the multiverse hypothesis directly.
However, this comes out directly from inflationary theory, which does have some evidence (evidence in the Bayesian sense, not proof!). If you are convinced that inflation happens (as most cosmologists circa 2018 do), then you will be hard pressed to not believe in the multiverse (It is possible to have inflation without multiverse, but it is difficult). Note my tenses: inflation happens not happened, because if you mix quantum mechanics with inflation, it is always happening.
To some this means that inflation itself is untestable, which renders it problematic. To others the fact that inflation can potentially explain any cosmological observations is a feature and not a bug.
Thanks very much for the explanation. That’s what I was getting at. I’m not certain that I completely understand, but I appreciate you responding. That’s really what I was getting at by asking. Often I see the multiverse put forth as a solution to the Goldilocks problem. So I was curious if those who formulate what the disparate universes might be like have any idea. It seems to be suggested that infinite universes would be of infinite kinds. I realized that it doesn’t need to be the case. There may be a narrow range of universe types that they might necessarily have to fit within. So it could be no response to the Goldilocks problem, or it could be an infinite number of answers to the Goldilocks problem.
With regards to the Goldilocks problem: that our Universe seem fine tuned for life, I would say that the multiverse is an answer to the Goldilocks problem. The range of universe types that can be produced by the inflationary is not narrow at all, but rather quite wide. Of these infinite kinds of universes, certainly some can harbor life (actually, infinitely many do).
I’m not a finitist, so personally I don’t have problems with infinite universes.
This is the correct way to think about it. Perplexingly, infinitely many universes that can harbor life can still mean that universes “almost never” harbor life.
How about the conundrum that if the multiverse is infinitely old, we have astonishingly arrived at Day infinity, and tomorrow is infinity +1. Or to look at it another way, if we move forward the same (infinite) number of days into the future as there are in the past, we shall arrive at the last day. That seems absurd.
This gets to the distinction between a countable and an uncountable infinity. A potential infinity is countable, and does not have an infinite number of days before, but could have an infinite number ahead.
