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I Expanding universe and quantum wavefunctions

  1. Aug 26, 2017 #1
    In a dark energy dominated universe, it seems that all the particles get away from each other and that the final state will be one with one or zero particles per horizon. This sounds very intuitive, but it is based on classical physics and GR. Particles have wavefunctions and this is whar confuses me in the context of expansion (and leaving the horizon). In the very far future, due to expansion particles will interact rarely and therefore there will be no decoherence really, all of the wavefunctions will spread. However, due to spreading, it would be possible that their wavefunctions interact and decohere again (paradoxically) or overlap and form something like a Bose Einstein condensate. Both options are of course strange so this serves rather as a reduction an absurdum. My real question is, quantum mechanically, what can we expect regarding the behavior of particles and their lack of interactions?

    Does it make sense to call them particles or will they really be spread out wavefunctions?
    If the final state is one of one particle per horizon, will the wavefunction of the particle cover all of the horizon?

    Thanks for the patience.
     
  2. jcsd
  3. Aug 26, 2017 #2

    PeterDonis

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    No, that's not correct. Bound objects, like tables, chairs, people, planets, stars, and even things like solar systems and galaxies, will continue to be bound; dark energy doesn't and can't break them apart into their constituent particles. You might be confusing the dark energy dominated scenario with the "Big Rip" scenario, which is driven by something called "phantom energy" that can rip apart bound systems (hence the name), but which has no evidence to support it.
     
  4. Aug 26, 2017 #3
    By "final state", are you referring to thermodynamic equilibrium or "heat death" of the universe?
     
  5. Aug 27, 2017 #4
    Yes, I was wondering what will happen with wavefunctions of the particles in the dark energy dominated universe approaching heat death. Will they spread due to lack of interaction between particles or will they have some meaningful wavelength that stays constant because of dark energy?
     
  6. Aug 27, 2017 #5
    This thread reminds me, that several years ago, the priest of my high school, asked me if the universe had an origin and an end, because he was explaining the creation to the boys. I told him about the Big Bang and entropic death, and that I believed that this was so.

    So he told me that it is very important. That it is very important that the universe had an origin and an end.
    When I asked him why, he replied: because Buddhists do not think so !!! (I don't know if he would not be a friend of Lemaitre)
    I don't know why I remember this conversation often

    *I edit because I try to correct grammar (I'm not native)
     
    Last edited: Aug 27, 2017
  7. Aug 27, 2017 #6
    I would expect the final state to be wave function collapse, @kimbyd could probably speak more to this.
     
  8. Aug 28, 2017 #7
    Just wondering, could you elaborate on what you were thinking with the Bose Einstein condensate?
     
  9. Sep 14, 2017 #8

    Grinkle

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    Asking a B question in an I thread - if something as bound as a black hole evaporates, how can anything else not? Won't any bound set of particles eventually disperse due to quantum effects?
     
  10. Sep 14, 2017 #9

    PeterDonis

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    Thinking of a black hole as "more bound" than other objects is not helpful here, since it's leading you to an incorrect inference. The reason black holes evaporate while other bound objects don't is that black holes have a horizon. An ordinary bound object does not. Quantum effects in the neighborhood of the horizon are what cause the evaporation, at least according to our best current understanding.

    Technically, yes, but not quite the way you might think--at least, according to the best guess we have right now, which might not be very good since we don't have a good theory of quantum gravity. According to that best guess, what will happen, on a long enough time scale, is that any bound object will eventually quantum tunnel into a black hole, and then the hole will evaporate. But we're talking really, really long time scales here--much longer than the time scale on which the accelerated expansion due to dark energy will take all objects not part of our local bound system beyond our cosmological horizon.
     
  11. Sep 20, 2017 #10

    mfb

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    And much longer than timescales where most of the objects in these systems will be ejected or fall into the central black hole. It is only relevant for the stuff that gets ejected, and then is isolated from everything else.
     
  12. Sep 20, 2017 #11

    Grinkle

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    What is our local bound system considered to be in this context?

    All the matter that is in the Milky Way? The Local Group? More? Something much less that may not include all the particles currently making up you and I?
     
  13. Sep 20, 2017 #12

    PeterDonis

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    Possibly our Local Group of galaxies; possibly even the Virgo cluster, which I believe our Local Group is orbiting. The Milky Way at the very least.

    No, much, much more than that--see above. The only way this would be a possibility is if a "Big Rip" scenario is correct, and that is extremely unlikely according to our best current model and data.
     
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