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Parallel universes make quantum sense?

  1. Sep 25, 2007 #1
    Parallel-universes-make-quantum-sense
    The Everett, or many-worlds, interpretation
    newscientist

    ? wouldn't this run out off energy extremely quickly
     
  2. jcsd
  3. Sep 25, 2007 #2
    No, energy is irrelevant. The conservation laws you're thinking of obviously apply to macroscopic states individually. Would you claim energy is borrowed (from where?) every time we do a double-slit experiment (putting the photon into a superposition of being in multiple places at once)?

    The experts seem to think the problem remaining with many-worlds is something to do with the interpretation of probability. I'm inclined to think the interpretation of probability remains a problem regardless of ones interpretation of QM.
     
  4. Sep 26, 2007 #3
    One would assume,that the energy was divided upon the split (but this couldn't happen)
    If a particle held a virtually infinite amount of positions in a virtually infinite amount of universes wouldn't this would become problematic once the energy was released from these particles in one of a virtually infinite amount of universes
     
    Last edited: Sep 26, 2007
  5. Sep 26, 2007 #4

    JesseM

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    There is no definite "split" in the many-worlds interpretation, just a universal superposition evolving continually according to the usual quantum rules. For complex systems like people, my understanding is that decoherence will cause different elements of the superposition to have almost no interference so there's no way for each version to notice the effects of the others in practice, but in theory there is always some small amount of interference so they are never truly isolated, the apparent split is just a subjective consequence of our limited ability to notice these effects. See Why do worlds split? from The Everett FAQ (which also deals with the question of energy conservation in question 22) or What is "A World"? from The Stanford Encyclopedia of Philosophy's entry on the many-worlds interpretation.
     
    Last edited: Sep 26, 2007
  6. Sep 26, 2007 #5
    This is very interesting:
    That multiverse=> QM
    Anyone has the original paper?
     
  7. Sep 26, 2007 #6
    Thanks for the replies & links

    But I still have an issue with the energy

    lets see if I can put it another way, I'm fine with superposition & conservation of energy

    Thing is this, say you have an atom, a hydrogen atom in a sun, the atom is converted into energy via nuclear fusion, bye-bye atom, this hydrogen atom no-longer exists anywhere

    Now as you have a virtual infinite amount of suns in a virtual infinite amount of alternative universes all sharing the same atom's all converting atom's into energy, wouldn't the energy be used up rather quickly, ie finite amount of atoms, divided by an infinite amount of energy extraction
     
  8. Sep 26, 2007 #7

    JesseM

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    Do you understand how superpositions work in quantum mechanics? The fact that one element of the superposition gives up its energy in the form of high-energy photons or something does not somehow rob the other elements of the superposition of their energy, even if we are talking about a superposition of states for a single atom. And you can't confuse the number of actual atoms which are involved in the superposition with the number of distinct elements (eigenstates of whatever variable you're interested in) in the superposition--a single atom can be in a superposition of a huge number of different states. And if you're talking about states with well-defined energies (energy eigenstates), the different states aren't drawing from a common "pool" of energy, each one has its own energy. Conservation of energy in QM just means that the expectation value for energy--the sum of the energy of each state times the probability of that state--doesn't change over time for a closed system that's not receiving energy from outside or giving up energy to the outside.

    Make sure you read question 22 of the Everett FAQ:
     
  9. Sep 26, 2007 #8
    this is exactly what Deutsch's press release was about [here is another source btw ] he was announcing that he has shown mathematically that the "bush-like branching structure created by the universe splitting into parallel versions of itself " exactly reproduces the probabilities predicted by the Born rule- which is why Andreas Albrecht said: "This work will go down as one of the most important developments in the history of science"
     
    Last edited: Sep 26, 2007
  10. Sep 27, 2007 #9

    Demystifier

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    But can we actually see (on-line if possible) the details of the Deutsch's proof?
     
  11. Sep 27, 2007 #10

    we are still waiting for the paper- this was just a press release
     
  12. Sep 27, 2007 #11
    Hopefully you can enlighten me, ? how far does the empirical evidence go
     
  13. Sep 27, 2007 #12

    JesseM

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    This is a pretty big question, since the idea of quantum states being superpositions of eigenstates (the states a system is in when you make a measurement and get a definite answer) is very fundamental, basically any calculation you do in ordinary QM will involve superpositions of eigenstates, and thus every experimental confirmation of QM's predictions would count as a type of empirical evidence for this. For starters you might read Part 1 and Part 2 of this page's primer on QM, or you might want to read a book like What Is Quantum Mechanics? which tries to introduce the basic math of QM without textbook-level detail, or the slightly more advanced Structure and Interpretation of Quantum Mechanics...maybe others here could recommend other introductory websites/books.
     
  14. Sep 27, 2007 #13

    xantox

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  15. Sep 28, 2007 #14

    Demystifier

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    These results have also been criticized. See e.g.
    http://lanl.arxiv.org/abs/gr-qc/9703089
    http://lanl.arxiv.org/abs/quant-ph/9907024
     
  16. Sep 28, 2007 #15

    xantox

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  17. Sep 28, 2007 #16

    Demystifier

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    Indeed. Nevertheless, I believe it is safe to say that neither of the sides presented an absolutely convincing proof. The question is: whose arguments one finds more convincing?
     
  18. Sep 28, 2007 #17
    MWI interpretation is speculative. Considerations of it can be wonderful exercises :rolleyes: -- and if one does these exercises well enough one might even make some money (or a career :rolleyes:) from doing these exercises.

    But for most of us I should think that worrying about all the metaphysical mumbo jumbo surrounding quantum theory is pretty much a waste of time? Isn't learning about the real world, and the way that quantum theory is used by physicists doing physics difficult enough? :smile:
     
  19. Sep 28, 2007 #18

    Demystifier

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    No! :smile:
     
  20. Sep 28, 2007 #19

    xantox

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    Yes, there is still no general agreement on the subject. The main difficulty being to decide whether the proof is (subtly) circular, or not.
     
    Last edited: Sep 28, 2007
  21. Sep 28, 2007 #20
    that's quotable (not specifically to Wallace and Saunders, but when I'm thinking about anyone's 'theory')
     
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