Having trouble understanding the wave function collapse.

[Fredrik]

I am afraid you're a victim of a very common misconception about MWI. People ask: ok, there are 2 outcomes, cat alive and cat dead, but why *I* see only dead one (or alive one)? For *me* it is random, right?

This is wrong. In MWI an observer is not a line, it is a tree. It 'splits' when being decoherenced with an outcome. So MWI predicts that in one branch one observer is asking "but why cat is dead?" and in another one "but why cat is alive?"

Why would you define "me" as the entire tree rather than a short unbranched segment of that tree? I mean, the other branches of "you" might not even be asking themselves if the cat is dead or alive. If I'm asking myself that, then I wouldn't consider some version of me who isn't asking himself that question "me".

I don't have any objections at all to phrases like "to me, the cat is dead". They just need to be interpreted correctly. First of all, "me" needs to be as I described above. Second, the rest of the statement should be interpreted as saying that the probability that a measurement on the cat will give us the result "dead" is 1.

That's what it means. Nothing more, nothing less. Statements such as "the cat is dead" are only "neither true nor false" when the probability of measuring that result is neither 1 nor 0.

 

[Dmitry67]

I agree that my definition is "me" is fuzzy. Any observer is a tree, but as the same time there are 2 major effects affecting our consciousness:

1. We can remember the past, not the future
2. We can not 'feel' what our 'other' copies in another branches are experiencing (because of the decoherence)

So, all the functionality of my brain is based on just one 'slice' of the reality. My consioucness is always backwards-oriented, so I don't feel branching at all.

So an observer is a tree which is severily impared in terms of the communication between the branches. To the extent that every branch thinks that is is absolutely alone.

Well, in any case, it is just wording... I think we don't have a serious disagreement, right?

 

[Zarqon]

All this talk about trees and "feel the branching" seems strange to me, given the answers I got to a question earlier.

Is the analogy of a tree really accurate to describe MWI? Given what I have read here earlier, wouldn't a better analogy be parallel racetracks, that in total sum up all possibilities that could ever happen. But in each "track" you live alone without connection to the other tracks, and in fact, if the cat is observered to be dead in "your" branch, then it was always doomed to die for you, you just didn't know it yet.

A tree that branches as time goes on implies decisions being made continuously, and I don't see that being consistent with determinism. Is this analogy a better description, or did I missunderstand something earlier?

 

[Dmitry67]

1 Is the analogy of a tree really accurate to describe MWI?

2 But in each "track" you live alone without connection to the other tracks, and in fact, if the cat is observered to be dead in "your" branch, then it was always doomed to die for you, you just didn't know it yet.

3 A tree that branches as time goes on implies decisions being made continuously, and I don't see that being consistent with determinism. Is this analogy a better description, or did I missunderstand something earlier?

1 not really, it is a simplification

2 the word "you" is not well-defined in MWI. Depending on the clarification, answer to your question might be negative or positive

Regarding the "you just don't know it yet" - note that in modern MWI "splitting" is well-defined physical process (decoherence). In case of an ideal box, before you opened it, you are not decoherenced with what is inside, so for you there are really 1/2 alive cat + 1/2 dead cat inside! Only when you open it and exchange few photons you are decoherenced with it and "split". So (another misconception about MWI) quantum events don't split the whole universe. "Splitting" propagates at ligth speed (but it can be much much slower).

3 This is important. What decisions are you talking about? Decisions for cat being dead or alive? there are no such decisions, as all outcomes do occur.