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Interaction across many-worlds

  1. May 29, 2012 #1
    I was reading a description of the many-worlds interpretation and it stated that the separate universes cannot interact with each other. But in the double slit experiment isn't the interference pattern that is seen when both slits are open, specifically caused by this interference?

    How can the author state categorically that continuing interference cannot occur? Perhaps it still occurs but we are simply unaware of it. Just as the other universes are still there, but we can no longer see them. Wouldn't entanglement mean that the separate universes are in some way still connected. Or does entanglement and thus interaction, necessarily cease when coherence or whatever it is breaks down. I understand that we no longer see evidence of it, but does that disprove the possibility?

    I don't know a lot about physics, but this statement puzzled me, and I was hoping that someone could explain it.

    Thanks in advance for your patience in answering my question.
  2. jcsd
  3. May 29, 2012 #2
    About the interference pattern bit, I think it's just that the vast majority of Universes one could potentially branch off into have an interference pattern.
  4. May 29, 2012 #3


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    I would say that you are right. Without that interaction between worlds phase difference between two paths would have no effect on result.

    But then I have never taken many-worlds interpretation very seriously so maybe you should wait till some proponent of that interpretation will comment about your question.
  5. May 30, 2012 #4

    "No interaction between universes" means that one universe can not make a mark on another universe.

    When universes are fusing together we see interference patterns. And the inhabitants of the fusing universes say that information decreases in their universes when this fusing is happening.

    An universe acts like an eraser on another universe, not like a pen.

    It's expained here too:https://www.physicsforums.com/showthread.php?t=188476
    Last edited: May 30, 2012
  6. May 30, 2012 #5


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    Interference between different "worlds" (or more precisely - branches of the wave function) exists forever, but after decoherence the effect of such interference is negligible for all practical purposes. The probability of observing a lost branch is comparable to the probability of seeing the thermodynamic time arrow in a reversed direction.
  7. May 30, 2012 #6


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    The double slit in MWI does not produce multiple branches - the wave function is still within one branch, and can give interference.
    The branching happens at the screen, where the different positions of the detection lead to decoherence (the different branches evolve so differently that their connections become extremely small extremely quick). But that is unrelated to the initial question here.
  8. May 30, 2012 #7


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    The many-worlds interpretation explains the interference. But the many worlds interpretation is along the lines of "what if there was a magical fairy in a parallel dimension we can't see...."

    The problem isn't the waves, or the interference patterns. It's when the waves collapse. They collapse as a single particle in one place. And the question is, why aren't we seeing lots of particles - an infinite number - collapsing with an even distribution, across all the possible locations. There's an evenness in the waves, but when it hits the detector, it drops all its energy at a single point, not as an even distribution as what you might expect.

    How the many-worlds interpretation explains this, is that we are parallel to an infinite number of parallel universes. So, when the wave drops it's energy at a single point in our universe, then in an infinite number of parallel universes, the drop is at all the other infinitely possible points.

    And since we can't interact with these parallel universes, the interpretation is impossible to disprove.

    But as theories go.....it's one of the most absolutely dreadful there is. In mathematical theory, there is no limit to the size of infinity. In the many-worlds interpretation, for every wave front opened, an infinite number of parallel universes must pop into existence to satisfy an even collapse of the wave. And it's not just there is a set number of infinite universes - the infinite number of infinite parallel universes must expand at an infinite rate over an infinitesimal time frame.

    In one of those universes, you will be Lady GaGa.....In this universe, unfortunately my friend, you are not.

    The theory is impossible to prove, at the same time there is absolutely no proof for it's correctness.

    And it is probably not even wrong.

    It's more likely that it is just mathematicians yanking everyone's chain.
  9. May 31, 2012 #8


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    Not really. Use the same quantum mechanical description for all particles (not just the few which are part of your current experiment), and you naturally get MWI.

    Now that requires a magical fairy which performs this collapse.

    Like every other major interpretation of QM.

    The number is finite.

    Interpretations are not theories.
  10. May 31, 2012 #9
    How so? I think most other interpretations treat all quantum entities (meaning wave/particle thingies) pretty much the same.

    I think krd's point, though, was they thought MWI was ridiculous. And while I wouldn't call it a "magic fairy" to perform the collapse, could we not start a flamewar over interpretations of QM?
  11. May 31, 2012 #10


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    If you treat every particle the same, you have to do the same for all the particles in any "detector". The evolution of the wave functions then gives many branches of the wave function which have (nearly) no influence on each other, and every possible "measurement" has branches where it is realized.
    That is the basic concept of MWI. Let the wave function evolve.
  12. May 31, 2012 #11
    Yes, but you are assuming that the only alternative interpretation is the Copenhagen Interpretation. de Broglie–Bohm has a similar basic concept. Relational QM has nothing about wave function collapse, either.
  13. May 31, 2012 #12


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    Well, they are quite similar in the way they let the wave function (or pilot wave) evolve. And I did not say that you cannot get other interpretations here. My point was to show that MWI (which was mentioned by krd in the quoted part) does not have any magic fairies in that respect.
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