Is there a real chance that there is a multiverse?

[Mister Agenda]

And you know the parameters of the universe can be tinkered with how? Not disputing, but I thought it was as yet unknown whether the cosmological constants could have been different from what they are.

To me it doesn't matter so much whether they can actually be tinkered with - after all what would that even mean. Whether they could have been different, the meaning of that question seems similarly hard to nail down, and depending on how I answer it, I find different related questions. So I don't think that distinction matters to me a lot. The physical parameters as we observe them seem to lie not entirely at random choices but such that matter can form, chemistry can exist, there are stars that actually work.

If that's not the only way they can be set, the question is, why were we so lucky that there is a universe at all where they are set in a sweet spot where there is chemistry and stars.

If for some reason the way they are set is the *only* way they can possibly be, the question becomes - why are we so lucky that the only way the universe can be is such that there is matter, and chemistry, and stars?

Conceptually, the latter is even more problematic than the former if you ask me...

I'm only a layman, but I thought Krauss made a somewhat compelling case that if the origin of the universe is due to a vacuum fluctuation, the 'energy budget' of the universe would need to be at or extremely close to zero, a 'flat' universe (and we have some evidence that this is the case). It doesn't seem more problematic to me that a universe that essentially has to 'add up to zero' would be extremely limited in the range of possible values its constants can have.

That's only one specific origin scenario; but I think it illustrates that we shouldn't be surprised to find ourselves in a universe so much like ours before we know how likely or unlikely a universe like ours is.