See SEP on Bohmian Mechanics for the main rival view.

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 had the same reaction... Can this be the same Eliezer who authored the sequences, and gave such strong support for the reality of Many Worlds?

I was half-expecting the other shoe to drop somewhere in the article... namely that if you are prepared to accept that the Many Worlds really exist, it makes the Great Reductionist Project a whole lot easier. Statements about causality reduce to statements about causal graphs, which in turn reduce to statements about counterfactuals, which in turn reduce to statements of actual fact about different blobs of the (real) quantum state vector. Similarly, statements about physical "possibility" and "probability" reduce to complicated statements about other blobs and their sizes as measured by the inner product on the state space.

Maybe Eliezer will be leading that way later... If he isn't I share your confusion.

Abstractions like probability and number are constructed by us; they don't strictly exist, but it's useful to act as though they do, since they help organize our reasoning. It could be that by coincidence that some part of the Real World corresponds precisely to the structure of our modal or mathematical reasoning; for instance, the many-worlds interpretation of QM could be true, or we could live in a Tegmark ensemble. But this would still just be an interesting coincidence. It wouldn't change the fact that our abstractions are our own; and if we discovered tomorrow that a Bohmian interpretation of QM is correct, rather than an Everettian one, it would have no foundational implications for such a high-level, anthropocentric phenomena as probability theory.

Thinking in this way is useful for two reasons. First, it insulates our logical fictions from metaphysical skepticism; our uncertainty as to the existence of a Platonic realm of Number need not undermine our confidence that 2 and 2 make 4. Second, it keeps us from being tempted to slide down the slippery slope to treating all our fictions (like currency, and intentionality, and qualia, and Sherlock Holmes) as equally metaphysically committing.

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.

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.

There are, though, a few blocks...

For one, I'm not financially independent, and my parents so happen to be Catholic-ish, so they think my dreams of immortality are foolishness of young age, and that cryonics wouldn't work because of "souls", whatever they may mean by that.

Also, I happen to live in the southeastern corner of Brazil. I'm... not positively sure that Alcor can reach me, let alone the CI.

I cannot, also, just quit college and teleport to the US and hope for the best. And I will, obviously, sign up as soon as I have the ability to do so and move to the US, and hope that I'm not hit by a car in the meantime.

Still, it's not exactly a dream I can achieve right now. Sadly.