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haushofer said:what exactly makes it more plausible that they correspond to different "universes" which are actually realized?
I think what is important, since it's a solid fact, is that it makes it possible. From here on, people tell campfire stories (campfire stories with arXiv numbers! :-).
The currently popular campfire story goes like this: If it is possible, it will happen once there is a mechanism that explores all possibilities. One such mechanism might be cosmic inflation, if thought of in the naive way as a small "bubble" (as they like to say these days) of spacetime within a larger ambient spacetime suddenly expanding rapidly. The campfire crowd imagines that each such bubble has a chance to go off with different values of those fields that fix the would-be "constants of nature".
That's fun as a campfire story, but it's not more than that. I wish people would focus more on actually figuring out stuff.
It is ridiculous that we don't even know for sure how much of the apparent cosmological constant deduced from supernova data is actually due to the observable universe not really being completely homogeneous, as assumed in the concordance model. The "backreaction debate" remains inconclusive. This is amazing, it means that potentially we are in for a much larger drama than the disappearance of the KKLT fatansy. Somebody should figure this out. But of course that's much harder than telling campfire stories.