It seems the logic is as follows:
- A multiverse is possible.
- No one has proved it is impossible.
- Therefore, a multiverse is true.
No, that's not the logic.
The various multiverses are predictions or implications of physical theories. The logic is something like:
1. Theory X is a good explanation for a significant set of observations.
2. Theory X predicts or implies a multiverse.
3. If theory X is correct, the predicted multiverse is very probably correct.
According to (atheist) scientist Stephen Weinberg, American theoretical physicist and Nobel Laureate
in Physics,
Theory of Multiverse is merely a speculative with no mathematical underpinnings.
That unreferenced Weinberg quote doesn't give any indication of which theory he's talking about, so
¯\_(ツ)_/¯
Opinions vary, though most cosmologists now take it seriously. He is one of those less taken with the idea, but
he is quoted as saying it should be taken seriously, and why:
"I am not a proponent of the idea that our Big Bang universe is just part of a larger multiverse. It has to be taken seriously as a possibility, though.
...
It’s not part of the requirement of a successful physical theory that everything it describes be observable, or that all possible predictions of the theory be verifiable.
...
...string theory, which predicts a multiverse, can’t be verified by detecting the other parts of the multiverse. But it might make other predictions that can be verified. For example, it may say that in all of the big bangs within the multiverse, certain things will always be true, and those things may be verifiable. It may say that certain symmetries will always be observed, or that they’ll always be broken according to a certain pattern that we can observe. If it made enough predictions like that, then we would say that string theory is correct. And if the theory predicted a multiverse, then we’d say that that’s correct too. You don’t have to verify every prediction to know that a theory is correct."
He even published a paper titled "
Living in the Multiverse", where he mentions one should keep an open mind about it, and talks about the confidence that his colleagues have about it:
"About the multiverse, it is appropriate to keep an open mind, and opinions among scientists differ widely. In the Austin airport on the way to this meeting I noticed for sale the October issue of a magazine called Astronomy, having on the cover the headline “Why You Live in Multiple Universes.” Inside I found a report of a discussion at a conference at Stanford, at which Martin Rees said that he was sufficiently confident about the multiverse to bet his dog’s life on it, while Andrei Linde said he would bet his own life. As for me, I have just enough confidence about the multiverse to bet the lives of both Andrei Linde and Martin Rees’s dog."
I can't say whether he's a dog lover or not, but I don't think he harbours ill will towards Linde.
I hope that puts things in perspective for you.