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MWI and Contacting Other Worlds

  1. Jun 8, 2010 #1
    My first post!

    Hi there. I am definitely new to this stuff, so as basic an answer as you can provide would be much appreciated (although "basic" and QM are not necessarily friends..)

    Okay, so MWI hypothesizes that anything that can happen will, and that those happenings occur in parallel universes that we have no contact or communication with. I am wondering if anyone has hypothesized how communication with a parallel universe could be possible. And by "communication," I mean an actual person entering another world, either by "seeing" it for the first time, or crossing over into it.

    The way that I understand it, the concept of linearity prohibits this, because someone from world A cannot have an effect on any of the linear events that occur in world B. But I am wondering why not? If someone was to cross over from world A into world B, then why wouldn't their actions simply be new branches on the MWI tree? I hope I am explaining this correctly.

    Basically what I want to know is if contact with another universe, which exists amongst the one we are living in, is possible (or hypothesized to be possible). And if so, what is the hypothesis? Thanks!
  2. jcsd
  3. Jun 8, 2010 #2
    Im new at this as well...

    It seems to me that if you could communicate from Universe A to Universe B then in fact those are one universe, Universe C.
  4. Jun 9, 2010 #3
    1. MWI does not postulate the existence of parralel Universes. Instead, it does not add any new aioms at all, and the existence of these worlds comes from QM formalism (+Quantum Decoherence)

    2. There are no other 'universes' - everything happens in ours, and 'different worlds' occupy the same space - but they just lose an ability to communicate. So no, there is no way to communicate with them (Penrose has an idea that different confuguration of heavy bodies in another branches can cause the 'collapse', removing other branches. But he is not an MWI-er, he used that sort of communication to explain why they dont exist)

    3. I think you understand that 'splitting' minto branches is physical process. When I make a Schoedinge cat experiment here and I have 2 outcomes, I don't split anything on Andromeda: 'splitting' propagates there at speed of light, but in practice much much slower.
  5. Jun 9, 2010 #4
    I think MWI proponents might argue that we are in fact visiting those other paralell universes in a sort of inceremental step like fashion. So you make a decision in this unverse, whcih then causes you to branch off into another paralell universe. Of course you dont notice you are in a different universe.

    However,personally i think the whole idea is ridiculous. beware of any theories which necessitate an infintie number of anything.
  6. Jun 9, 2010 #5
    I find MWI troublesome, but I find collapse troublesome as well. Decoherence is Juuuuuuust right. For arbitrary numbers of things, it isn't easy to find theories which don't end in them at some point. Infinities are everywhere; I would amend this to "beware theories which necessitate infinite numbers of things we can never observe, directly or indirectly."
    From there we can remove infinite, and just get to "Falsifiable or Verifiable" and be done with it.
  7. Jun 9, 2010 #6
    Including Cosmology?
  8. Jun 9, 2010 #7
    Especially Cosmology. I love it, but I think "beware" isn't a terrible warning regarding it, compared to say, optics, or chemistry.
  9. Jun 9, 2010 #8
    yes, and a great example. Are you suggesting there is evidence the cosmos are infinite?
  10. Jun 9, 2010 #9
    I think "decoherence" is a reasonable FAPP way of dealing with qm without invoking foundational/philosophical issues. But even Zurek admits its no solution to the measurement problem.
  11. Jun 9, 2010 #10
    Based on the observations, space is almost flat, so both options are possible (finite and infinite). In both cases, the universe exists (whatever that word means) beyond the 'Hubble bubble'.

    It you limit yourself by positivism and strict version of falsiability, you can't even talk about 'what is beyond the cosmological horizon' or 'what is inside the black holes', or 'do alternative MWI worlds exist'
  12. Jun 9, 2010 #11
    I think there is more evidence to suggest that the universe, or the energy/matter contained within it is in fact finite, than infinite. But its true to say we just dont know.
  13. Jun 9, 2010 #12
    Thanks for the info guys. What is the fundamental difference between MWI and decoherence? As per my question, I am quite interested in the possibility of visiting an alternate universe, albeit occupying the same space, where you might be able to come in touch with yourself. Is there any place I should start (books, etc.) to research this possibility?
  14. Jun 10, 2010 #13
    There is no such possibility
    But you can start from here: http://en.wikipedia.org/wiki/Quantum_decoherence

    There is no 'difference' between MWI and Decoherence; all non-collapse interpretations (MWI and BM) are based on the decoherence. Decoherence is a machanism which showed that we don't need a 'collapse' to explain what we see.
  15. Jun 10, 2010 #14
    Different "universes" in MWI can communicate. Double-slit experiment is an example of such a communication. Universes can split and merge. This is actually an ugly description, I like to think that there is continuum of "universes" that change their relative probabilities.

    Consider an experiment with two half-mirrors. We throw a photon on the first half-mirror. Its wavefunction splits into two, so MWI says that a new universe has just been born. A photon travels one of the paths in the first universe, the second in the other. Now both photons of both universes reach the second half-mirror, one from each side. If the communication between universes were impossible, the two entangled photons would not feel each other. However, in reality, one photon leaves the second half-mirror via only one path. That means, the two universes have communicated and merged into one.

    In fact, this splitting and merging occurs continuously. There's no discrete moment that a new universe pops out. Rather, the probability of an already existing universe reaches nonzero level.
    Last edited: Jun 10, 2010
  16. Jun 10, 2010 #15
    I agree that the words are ugly
    But when we see the interference, we just dont call it 'different worlds'. After the Decoherence we call them 'different worlds' but at that moment the probability of communication (non-diagonal elements) is almost 0.
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