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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 http://www.ipod.org.uk/reality/reality_quantum_intro.asp and http://www.ipod.org.uk/reality/reality_quantum_casino.asp of http://www.ipod.org.uk/reality/reality_quantum_intro.asp 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.
     
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  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')
     
  22. Sep 28, 2007 #21
    Sorry to interrupt you scientists, but what does existance of parallel universe means for the lay person like myself?

    Now if you again consider the movie "what the bleep do we know" does it all connect now?
    Can you now give some attention to what the metaphysicts think?

    Thanks,
    Viva diva
     
  23. Sep 28, 2007 #22

    JesseM

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    Well, in theory it means that for any outcome that could have gone differently if certain apparently random quantum events had gone differently--which thanks to the butterfly effect would probably include most events in history and in the lives of individuals--there should be a "world" where the outcome was different, like one where you went to a different school or where the British won the revolutionary war. But in practice, you can't visit these worlds so it doesn't make much difference to your life even if it's fun to think about (although you should consider that any time you take a risk which could lead to disastrous consequences, even if things turn out all right in your world, there's another where some poor version of you or the people around you have to suffer the worst-case consequences, so maybe that would make you less inclined to take such risks out of sympathy!) In any case, the new results discussed on this thread don't actually provide any evidence that the many-worlds interpretation is correct, if the press release is accurate they just solve some internal conceptual problems with the interpretation that were a barrier to some physicists being willing to take it seriously.
    Nah, the many-worlds interpretation totally goes against the "observers can alter reality" thing that movie was promoting, since it dispels the idea of a "collapse of the wavefunction" upon observation which that idea was based on, and treats human observation as no different from other physical interactions. And as I understand it the many-worlds interpretation also removes the idea of a "nonlocal" connection between distant particles which I think the movie may also have been trying to draw metaphysical conclusions from. "What the Bleep" should not be taken too seriously as a guide to quantum physics, see here, here, http://dir.salon.com/story/ent/feature/2004/09/16/bleep/index.html [Broken] and here for criticisms from a scientific point of view.
     
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  24. Sep 29, 2007 #23
    Lets say that somebody went back in time 100 no 1000 years and did a lot of messing around with time.

    Come back to the world today and its a very different place today, ok we all get that.

    Well so what.

    Its only made a difference on this bubble of a planet, it has not changed a single thing in this solar system or Galaxy so I guess in the grand scale of things it would not change anything.

    What is the problem?
     
  25. Sep 29, 2007 #24

    JesseM

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    Actually the many-worlds interpretation doesn't have anything specifically to do with time travel, it's basically just a consequence of trying to make the laws of quantum mechanics as simple as possible (avoiding the need for wavefunction collapse). David Deutsch is one many-worlds advocate who thinks if time travel were possible, it would take you to a different world as you describe, but other many-worlds advocates would say either that time travel is impossible or that you would always stay in the same history you started from, it would be impossible to "change" anything.
     
  26. Oct 1, 2007 #25


    All said and done, I have been able to attract small and big things into my life just by changing my thinking. It is so spooky and works like magic. I have a scientific rational mind too, but I tried this only when I had hit rock bottom in my life. Thats when I said, well since nothing is working let me try this metaphysics thing. And lo and behold, it worked!
    I don't know the reason behind it. I don't even know if any science is involved in this phenomenon. But it worked for me, so I am not complaining :-)

     
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