Kaj - there is a more cheerful answer. And this is it: Many-Worlds isn't true. Although Eliezer may be confident, the final word on the issue is still a long way off. Eliezer has been illogical on enough of his reasoning that there is reason to question that confidence.

Err, how can two copies of a person be *exactly* the same when the gravitational forces on each will both be different? Isn't the very idea that you can transfer actual atoms in the universe to a new location while somehow ensuring that this transfer doesn't deterministically guarantee being able to determining which person "caused" the *copy* to exist (I.E. the original), physical nonsense?

While molecules may not have invisible "unique ID" numbers attached to them, they are unique in the sense of quantum evolution, preserving the "importance" of one atom distinguished from another.

I am interested in the answer to John Maxwell's question as well.

In that vein, let me re-ask a question I had in a previous post but was not answered:

How does MWI not violate no-faster-than-light-travel itself?

That is, if a decoherence happens with a particle/amplitude, requiring at that point a split universe in order to process everything so both possibilities actually happen, how do all particles across the entire universe know that at that point they must duplicate/superposition/whatever, in order to maintain the entegrity of two worlds where both posibilities happen?

Question: how does MWI not violate SR/no-faster-than-light-travel itself?

That is, if a decoherence happens with a particle/amplitude, requiring at that point a split universe in order to process everything so both possibilities actually happen, how do all particles across the entire universe know that at that point they must duplicate/superposition/whatever, in order to maintain the entegrity of two worlds where both posibilities happen?

Dustin: "Good God, he's even making up his own contradictions now."

That is a meaningless comment, and adds nothing to this discussion. The whole point I believe, of Caledonian's argument is that the statement "MWI -is- collapse" is not a contradiction, so long as the differences in the theories/interpretations of QM can never be substantiated with experimental evidence, ever, because the theories themselves don't allow for it, rather than we just haven't seen those experiments yet.

That said, I don't think that's the case with MWI. If you are saying something about reality that supposedly is true, and has an effect on the rest of reality, I find it unlikely that if it were true, it wouldn't eventually result in experimental evidence that proved that.

But if it can not be shown that MWI would result in experiments that explicitly differentiated it from non-local collapse, than Caledonian's point remains valid, or at least valid enough that there's no reason to be nasty about it (Eliezer, Dustin).

Bob: But multiple worlds are observed, in subatomic phenomena. That's what superposition is. There is experimental evidence for multiple worlds.

How does the experimental evidence favor MW over a possible collapse function with non-GR-violating non-locality?

4 points:

If collapse actually worked the way its adherents say it does, it would be: 1. The only non-linear evolution in all of quantum mechanics. 2. The only non-unitary evolution in all of quantum mechanics. 3.... WHAT DOES THE GOD-DAMNED COLLAPSE POSTULATE HAVE TO DO FOR PHYSICISTS TO REJECT IT? KILL A GOD-DAMNED PUPPY?

Not a valid argument. The physics of the universe are what they are, at the microscopic and macroscopic levels. If it so happens that there is some non-GR-violating non-locality going on (don't complain, just cause you can't imagine it, doesn't mean it's not possible), then your list above simply would be wrong, and there would be no violation of "traditional physics" to complain about.

In any case, since from the perspective of each world we have non-determinism, and the only world we are acting on is our own, why is it necessary to explain many worlds for the purposes of AGI?

Well, first: Does any collapse theory have any experimental support? No.

Neither does MW, they are both interpretations.

I'm going out on a limb on this one, but since the whole universe includes separate branching “worlds”, and over time this means we have more worlds now than 1 second ago, and since the worlds can interact with each other, how does this not violate conservation of mass and energy?

Wiseman, there's only one amplitude distribution. One. Not two. Not three. One, in all the physics we know.

I do understand this Eliezer. But my point is even though it's just one distribution, there is still a description of differentation within that one distribution, otherwise the universe would be just one electron, or something like that. So since there is differentation within the distribution, and since those differentations are tracked and consistent due to the non-random laws of this universe, isn't that really the same as "identity", in that the "differentations" are always 100% unique?

Isn't each particle or amplitude configuration unique because only it has its exact relationship to every other amplitude configuration in the universe? Doesn't that sufficiently make each amplitude configuration at a specific spatial-temporal locality different from every other one, in that the universe can "tell" one from the other?

Ben Jones: Well that's just plain wrong.... QM is the most experimentally validated theory we have, but one of its implications is the relative identity of quanta.

The experiments show specific results, but it may be possible that some properties of the particles aren't interacting with any aspect of the experiment, thus QM would still be correct in the explanation for the original experiments, but not complete, as they don't explain the additional properties. So it is entirely possible.

The generality "invalidating one aspect of a theory can't invalidate the whole" may be a bit too extreme, but for practical purposes most theories are complex enough that that usually won't happen, it and it certainly wouldn't in the case of QM and particle identity.