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Many Worlds - What drives the parallel branching?

  1. Nov 12, 2015 #1
    There is one segment of this interpretation that has always nagged at my mind. It's the part where a separate branch splits off at each individual choice. For a simple example; I have a choice to turn left or right, I choose to turn right, so now according to this interpretation another version of myself branched off and turned left in a parallel dimension/world, as well as every other possible direction.

    I get that part. What is nagging me is what drives the branching itself? How would a parallel world KNOW that it's time to branch off? What sparks the branch to occur? If the branching occurs at a natural constant rate, does it have discreet intervals in time or is it organic/analog?

    If the branch/split occurs based on certain events and choices, would that not mean that it is driven by conciousness or some observer?

    Wouldn't every single atom have a possible "choice", and if that is so that would mean seven billion billion billion separate parallel universes get created at some interval that is unknown, maybe even a billion times a second for all we know.

    It seems like this interpretation is cherished more because of how creative and exotic it is, rather than anything scientific.

    This creative interpretation is a candidate for Occam's razor if I've ever heard one, yet the many worlds theory seems to be more and more a thing. Help me my brothers.
     
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  3. Nov 12, 2015 #2

    andrewkirk

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    My impression is that there is no branching.The number of worlds does not change over time. Quantum superpositions are across worlds, not within worlds. When a measurement is made, we are not branching to create a new world, we are doing a test to find out which world we are in. If the experimental result is 'spin up' then we have just discovered that we are now, and always have been, in that 'spin up' world.

    I don't know if that's how Everett envisaged it, but that's how I've seen it presented a few times recently, and it seems much more intuitive and plausible than the branching idea. It dissolves the measurement problem entirely.
     
  4. Nov 12, 2015 #3

    DaveC426913

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    Inasmuch as I've tried to reconcile the MWI in my own thoughts, this is the interpretation I came up with too.
    Presumably, every subatomic particle will fork at every Planck unit (which is 10-43 seconds).
     
  5. Nov 13, 2015 #4

    bhobba

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    Its an entirely quantum process. Basically via a process called decoherence a quantum state becomes what is called a mixed state. This mixed state has a number of parts - each part is interpreted as a world.

    Thanks
    Bill
     
  6. Nov 13, 2015 #5

    Nugatory

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    It depends on which excrescence you most want to cut off with the razor :smile:
    There's something not to like about every interpretation, and this extravagant multiplication of worlds is the thing not to like about MWI. On the other hand, MWI's appeal comes from the way that it does not require an extra assumption (namely, that unitary evolution of the wave function is somehow magically aborted by a measurement)... and not requiring a extra assumption is what Occam's razor encourages.

    The important thing to remember here is that the choice of interpretation in quantum mechanics is largely a matter of personal taste, and there's no objective way of settling a debate over matters of taste.
     
  7. Nov 13, 2015 #6
    I thought maybe this might be relevant with respect to this:
    Source

    From the last (quoted) paragraph I can deduce that there is no actual superposition, only lack of knowledge. This means the cat is in only one (!) state, and there is an unambiquous reality. So it all seems, as usual, a matter of point of view and interpretation. I hope I am not off limits here, if I am, I apologize to the mod.
     
    Last edited: Nov 13, 2015
  8. Nov 13, 2015 #7

    stevendaryl

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    Bell's theorem shows that we can't have a "lack of knowledge" interpretation of quantum probabilities unless we allow for faster-than-light influences.
     
  9. Nov 13, 2015 #8

    Nugatory

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    That is indeed the most natural conclusion with regard to Schrodinger's cat, although many popular sources misunderstand Schrodinger's thought experiment. He wasn't seriously suggesting that the cat existed in a superposition of dead and alive, he was pointing out a problem in the then-current understanding of quantum mechanics: No one thought the cat could be in that state, yet there was nothing in the theory that said that it wouldn't.

    It took many decades to come to an even slightly satisfactory answer to this problem. Google for "quantum decoherence" (but I have to caution you that the math becomes somewhat daunting very quickly) or give David Lindley's excellent and layman-friendly book "Where does the weirdness go?" a try.
     
  10. Nov 13, 2015 #9
    That is the "hidden variable" hypothesis, and it was proven wrong by Bell experiments. My favorite way of seeing it is:

    Yes, the scientist will see either alive cat, or a dead one; never a mix. However, if the scientist and the cat are themselves in the bigger box, and yet another observer will open it sometime later, he *must* assume that "scientist+cat" are in the superposition of two states until the bigger box is opened. The theory that it is not so has been disproved by experiments.
     
    Last edited by a moderator: May 7, 2017
  11. Nov 13, 2015 #10
    Isn't such a scheme prone to decoherence, thereby introducing a system of entangled mixed states? I think of this: only a pure state can be in superposition. I am not sure though (layman). Please enlighten me!:smile:
     
  12. Nov 13, 2015 #11

    Nugatory

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    You are correct. Decoherence rapidly (very very rapidly) kills macroscopic superpositions of cat-sized systems, so these are properly treated as mixtures (some definite macroscopic state that we don't know until we look) instead of superpositions (no definite state unless a measurement collapses the superposition).
     
    Last edited: Nov 13, 2015
  13. Nov 13, 2015 #12

    andrewkirk

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    They didn't prove that. Even leaving aside the existence of loopholes, experimental violation of the Bell inequalities leaves open the possibility of non-local hidden variables, as well as the possibility of local ones if there is no counterfactual definiteness.
     
  14. Nov 15, 2015 #13
    Where have you sen this presented a few times recently? I presented it in this forum about half a year ago and everyone considered it pretty much a moot point. I know Alastair Wilson has done work on this, but other than him I rarely see it discussed.
     
  15. Nov 15, 2015 #14

    andrewkirk

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    The place I saw it first is this post that occurred in a philosophy discussion. I'm pretty sure I've seen it at least once somewhere else since then, but can't remember when.
     
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