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Parallel universe: in every universe, you are presented with a different decision. Does that mean there are an infinite amount of parallel universes? I.e., if in one universe I choose to go left, I am then presented with different choices vs if i choose right, and that creates more universes with more decisions to be made.

Or does it mean that in the end of one's life we end up in the same place, meaning that its just one parallel universe that eventually collides with the other.

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Related: physics.stackexchange.com/q/14255/2451 –  Qmechanic Apr 1 '12 at 10:03
    
The way the question is framed, i.e. the observer "chooses" makes this question suitable for a metaphysical forum or a science fiction one. There exist metaphysical "theories" for example in the Seth series of Roberts en.wikipedia.org/wiki/Jane_Roberts that take the anthropic/consciousness pov as a prime mover, universes having a "reality" quotient according to the mover. This sort of "science" also found in fantasy science fiction as in the diskworld of Terry Pratchett en.wikipedia.org/wiki/Pratchett . –  anna v May 2 '12 at 5:42
    
continuing the fun: in the Seth universes a personality weaves in and out of them according to choice and could end up in the same one he/she started with at the end. fun but not science . –  anna v May 2 '12 at 5:44
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It is not your "choice" that produces a universe, but quantum events (in a certain philosophical view) which might affect your choice, but are not affected back. To apply a notion of causation from your consciousness to matter is backwards, and leads to all sorts of "The Secret" and "What the Bleep do We Know" verifiably false mystical nonsense. This is a level mixing--- the notion of causation at the level of consciousness, where the entity is data and computation, is different than the notion at the level of atoms, where the computation has not emerged, and must always be presented with a non-chaotic path through the atomic chaos in order to continue.

It is not clear exactly how meaningful parallel universes are. If you don't ask this by asking "what do I see if I do this or that?" you can easily ask nonsense questions. This is logical positivism.

In positivist terms, the parallel universes amount to little more than the statement that quantum mechanics allows for more parallel computation than classical mechanics, and certain classes of counterfactual measurements can be made in quantum mechanics (like the Elitzur-Vaidman bomb tester/Vaidman counterfactuals) which cannot be made classically.

The notion of consciousness is computational, and we don't know exactly how it is embedded in the physical description. This is the issue with both mysticism and quantum mechanics, at least in the Many-Worlds/Consciousness Causes Collapse/Decoherence interpretations, which deal with the issue of quantum mechanical observers. In order to say that worlds collide, or that your consciousness is the same in two parallel universe, in a positivistic way, you need to know how consciousnesses "chooses" to go along different paths, depending on which paths "exist", and these questions require you to identify consciousness in the world, and to answer certain questions about existence, questions which are probably meaningless, because they are hard to formulate in a positivistic way, as questions about "what do I see if I do this or that?"

To show you some of the difficulty, consciousness is a computational entity that is not necessarily confined to your body--- some parts of your consciousness might be in interactions of yourself and others you know or read, so that certain aspects are dormant until the right combination of other computing parts are present. If you view yourself as but a part of a larger computation, it is not clear that death is so important, since the computation keeps going in others. If you write a book, others can emulate you, if you read a lot of Einstein, you get to know Einstein. So is Einstein dead? I don't think so, not entirely.

Einstein, when facing death said he was not afraid of dying, since he felt his own internal life was sufficiently connected to the rest of the world, that it would not be much of a change. It is not clear where your soul-stuff is, because it is computation, it is software, and software is pattern, without mass, and doesn't really have a place. Most of the generative stuff is in your head, but that's not everything, because you might have external notes (like the guy in the movie Mememto), or books, or google, to look up things you forget. The whole computation is bigger than the individual, and it might be more accurate to place the source of our experience in the big collective rather than in our individual heads. This is the position of certain religious faiths, and it is not a question that is easily adressed by positivism or by science.

The above is a long-winded way of saying that this is more philosophy than physics, but you can get insight about this, as about everything else in philosophy, using logical positivism. Rudolph Carnap is a place to start, although I don't read him, or any other philosophers.

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