Circularity problem:
Since you can’t observe anything about it directly, the multiverse must be justified in terms of another theory that can be tested and this is string theory. But if you talk to string theorists these days about how they’re going to test the unified theory that string theory is supposed to provide, their answer is that, alas, there is no way to do this, because of the multiverse. You see, the multiverse implies that all the things you would think that string theory might be able to predict turn out to be unpredictable local environmental accidents.
So, the multiverse can’t be tested, but we should believe in it since it’s an implication of string theory, but string theory can’t be tested because of the multiverse.
