Seems as good a thread as any.
Spread across two days, I heard this whole 45-minute discussion. It is both fascinating and horrible.
Briefly, Kaku -- one of the founders of string theory -- is a smirking nihilist, trafficking in nothing but arbitrary speculations, grounded in the bizarre Copenhagen interpretation of quantum physics.
Penrose is a dignified and rational thinker, fearlessly stating that the Copenhagen view is simply wrong and that there therefore is zero basis for even considering string theory or any "multiverse" talk.
Sabine is also very rational, mostly, in her criticism of Kaku's cookoo ideas, although she is too hung up in standard notions of testability and refutations.
In the end, this is not really a talk about physics but about philosophy. I have the impression, from other sources than this talk, that Penrose holds some Platonist views of mathematics -- but he is still an amazingly lucid, unpretentious, honest thinker. I like and admire him.
The "mystery of the multiverse" is really only that people take multiverse ideas seriously. As Sabine says, this is chiefly a sociological issue, not one of physics.
I even dislike the notion of the Multiverse in Marvel comics -- as it just disintegrates the whole wonderfully unified Marvel Universe into endless what-ifs (Stan Lee was known to disapprove of this development by later Marvel writers) -- but its far worse when we are seriously talking about the one and only Real Universe!
View: https://youtu.be/W39kfrxOSHg