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Multiple universes in cosmology and quantum mechanics

  1. Mar 23, 2014 #1

    Are the multiverses that come up in some cosmological theories, e.g. inflation, in any way related to the worlds in the many-worlds interpretation?
  2. jcsd
  3. Mar 23, 2014 #2


    Staff: Mentor

  4. Mar 25, 2014 #3
  5. Mar 30, 2014 #4
    No, they're not.

    Regarding inflation, the idea is that (i) space is infinite in standard models and (ii) the arrangement of matter gives way to dull uniformity on large scales, with no coherent structures larger than about 10^24 meters. Assuming the pattern in (ii) continues then our hubble volume will likely repeat itself somewhere. Max Tegmark claims that your nearest duplicate lives about 10^10^29 meters from you.

    Regarding many worlds interpretation, the idea is that a measurement of a superposed particle will correlate the state of the measuring device and the observer to that particle, and thereby magnify the superposition up into the device and the observer, thereby "splitting" them. As the observer is correlated with her environment, Earth, solar system, etc. the entire universe branches, and this happens continually.

    One could reject one while accepting the other, so they're logically independent.

    This might be useful: http://arxiv.org/pdf/0905.1283v1.pdf
    Last edited: Mar 30, 2014
  6. Apr 2, 2014 #5
    I thought that was one of the primary mainstream ideas. It's really the only one that makes sense to me.

    How mainstream or fringe is it really?
  7. Apr 2, 2014 #6


    Staff: Mentor

    Its not fringe in the sense its a legit idea rather than some of the mystic nonsense that is occasionally touted as science.

    It is fringe in the sense it's way outside the mainstream with few if any active researchers of the idea.

  8. Apr 3, 2014 #7
    It is a mainstream idea, but there are many different notions of a multiverse in which the wavefunction isn't considered to play a role.

    To unite the Everettian interpretation with a cosmological multiverse hypothesis requires a certain type of positional and temporal invariance, in which an observer doesn't have a specific location in the cosmos, rather each quantum event causes a selection effect.

    I think it's mathematically sound, though position and time in the wavefunction take on a non-traditional interpretation. For many this may be considered too big of an assumption.

    How fringe is it? That's a difficult question. More physicists take an interest in the MWI now, than before, but it's far from unanimous. Tegmark regularly conducts a straw poll of the favoured interpretations of QM amongst physicists that he speaks to, if you want a more detailed analysis. Of those what percentage take the cosmological multiverse seriously? I'm not sure, but even then they need to make the leap to consider them equivelant. So I would say that it's certainly a minority opinion, even amongst theoretical physicists, but then I suspect that many unproven ideas in theoretical physics have minority support.

    You can do virtually all physics without making a call on the MWI or a cosmological multiverse. So it's not clear how significant any support that they have or don't have across the broad physics community actually is.
    Last edited: Apr 3, 2014
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