Come on, help me out, someone who understands the science. It's a question I've posed before, but I'm still none the wiser more than five years later. The context of my question is the hypothesis that 'our universe may be just one in a vast collection of universes known as the multiverse'; and the question itself is prompted by this sort of thing:
Some physicists have theorized that only universes in which the laws of physics are "just so" could support life, and that if things were even a little bit different from our world, intelligent life would be impossible. In that case, our physical laws might be explained "anthropically," meaning that they are as they are because if they were otherwise, no one would be around to notice them.
There has to be a way of explaining this that saves it from its prima facie air of total unreasonableness. If such-and-such, no one would be around to notice does not normally establish that such-and-such can't be the case. For example: if a tree falls in a forest on an unpopulated island then no one would be around to notice. This doesn't prove the non-existence of unpopulated islands. For another example: if you read your book while hiding in a cupboard, then no one will see you reading. It doesn't show that you couldn't read while hiding in a cupboard. Provided, of course, you had a light of some kind. So come on, someone, explain it in terms that don't appear plainly absurd.