I have had this question in my mind for ages. You say that these counterfactual universes don't actually exist. But, according to Many-Worlds, don't all lawful Universes actually really really exist? I mean, isn't there some amplitude for Mr. Oswald to not have shot Kennedy, and then you get a blob where Kennedy didn't get murdered?

I've been banging my head against a wall on this and still can't come to a conclusion. Are the decoherent blobs actually capable of creating multiple histories on the observable level, up here? It looks, to me, that they should be. I mean, if these particles have each an amplitude to "be" here and there, then there is some amplitude for the combination of all particles in the Universe to correspond to a completely different macro Universe.

On the other hand, that seems to also imply that there's some amplitude for things like President Kennedy being shot, and then suddenly his wounds closed and he was up and running again. And that doesn't sound okay at all.

So... I am very, very confused.