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Quantum suicide/immortality

  1. Feb 7, 2014 #1
    I just stumbled across this paper and I'd like someone to translate it for a layman. Just a paragraph or so if that's possible? Basically I just want to know how true quantum suicide is.

    http://xxx.lanl.gov/PS_cache/quant-ph/pdf/9709/9709032v1.pdf

    Also can you explain what this video actually means? Because as far as I can see I am not in two places at the same time. http://science.howstuffworks.com/48141-through-the-wormhole-quantum-rules-all-video.htm

    Are these related somehow?
     
  2. jcsd
  3. Feb 7, 2014 #2

    bhobba

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    The first paper is a bit of a tongue in cheek look at a slightly controversial interpretation of QM called Many Worlds. You can do a bit of a search about it if you want, but the bottom line is MW is a very beautiful interpretation of QM but with consequences many find outlandish - hence the slightly whimsical tone of the paper. At the lay level I wouldn't worry too much about it. If you really are taken by it it will first be necessary to learn a bit about QM.

    The video is simply one of those popularization's of QM that seem to abound these days. I watched it when it was shown here and like all such things it bought a smile to my face. Particles are not in two places at once and the other stuff such programs promulgate to get across the weirdness of QM.

    Here is what QM is ACTUALLY about:
    http://www.scottaaronson.com/democritus/lec9.html

    Basically QM is simply an extension to standard probability theory. Particles are not in two places at once etc etc. When particles are in what is called a superposition of position (this is the situation they call being in two places at once) what it means is when you observe it all you can predict is the probability it will be in a certain position. What its position is when its not being observed the theory is silent about. But some want to read more into it than the theory says and say its in two places at once etc etc. It isn't - simple as that.

    Once you understand its simply an extension of standard probability theory a lot of populist hand-wavy rubbish such as consciousness causes collapse, particles being in two places at once, and other 'misconceptions' disappear.

    Now I do not want to suggest no issues remain. That would be incorrect - but populist accounts rarely mention the REAL issue with QM.

    The real issue is that its a generalized probability model about 'marks' (outcomes of observations etc etc) left here in an assumed common sense classical world. But that world is in fact quantum - so exactly how does a theory that at its very foundations assumes such a world explain it:
    http://scitation.aip.org/content/aip/magazine/physicstoday/article/58/11/10.1063/1.2155755

    'The other mistake that is widely attributed to Einstein is that he was on the wrong side in his famous debate with Niels Bohr over quantum mechanics, starting at the Solvay Congress of 1927 and continuing into the 1930s. In brief, Bohr had presided over the formulation of a “Copenhagen interpretation” of quantum mechanics, in which it is only possible to calculate the probabilities of the various possible outcomes of experiments. Einstein rejected the notion that the laws of physics could deal with probabilities, famously decreeing that God does not play dice with the cosmos. But history gave its verdict against Einstein—quantum mechanics went on from success to success, leaving Einstein on the sidelines.

    All this familiar story is true, but it leaves out an irony. Bohr’s version of quantum mechanics was deeply flawed, but not for the reason Einstein thought. The Copenhagen interpretation describes what happens when an observer makes a measurement, but the observer and the act of measurement are themselves treated classically. This is surely wrong: Physicists and their apparatus must be governed by the same quantum mechanical rules that govern everything else in the universe. But these rules are expressed in terms of a wavefunction (or, more precisely, a state vector) that evolves in a perfectly deterministic way. So where do the probabilistic rules of the Copenhagen interpretation come from?

    Considerable progress has been made in recent years toward the resolution of the problem, which I cannot go into here. It is enough to say that neither Bohr nor Einstein had focused on the real problem with quantum mechanics. The Copenhagen rules clearly work, so they have to be accepted. But this leaves the task of explaining them by applying the deterministic equation for the evolution of the wavefunction, the Schrödinger equation, to observers and their apparatus. The difficulty is not that quantum mechanics is probabilistic—that is something we apparently just have to live with. The real difficulty is that it is also deterministic, or more precisely, that it combines a probabilistic interpretation with deterministic dynamics.'

    As Weinberg points out a lot of progress has been made in resolving that, but a few issues remain. If you are interested in pursuing that further, at your level a good book is Omnes - Understanding Quantum Mechanics:
    https://www.amazon.com/Understanding-.../dp/0691004358

    Thanks
    Bill
     
    Last edited by a moderator: May 6, 2017
  4. Feb 7, 2014 #3

    Ken G

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    The other problem with quantum suicide is that it is not scientifically verifiable, and is not even a falsifiable hypothesis. In other words, let's say you set out to test if our universe obeys a "quantum suicide" principle (which means, you cannot successfully commit suicide from your own perspective, your consciousness will always find a branch where you survive). How would you actually be able to test that principle? All you could do is try committing suicide (the ethics of such an experiment are highly questionable), but would this allow you to conclude anything? No it wouldn't, because in either type of world, you would either die, or not die. In either type of world, if you die, it is not an experimental outcome for you, from your perspective. Hence, the only possible experimental outcome for you is that you live. Thus, living is not evidence that the universe obeys quantum suicide, and indeed, no experimental outcome is evidence of that, because the alternative outcome could not refute the hypothesis, for you, nor could watching anyone else attempt the experiment tell you anything about quantum suicide. A hypothesis that cannot be refuted by any experimental outcome is simply not a scientific hypothesis, so "our universe obeys a quantum suicide principle" is not a scientific hypothesis.
     
  5. Feb 8, 2014 #4
    That's true it's sort of like a catch 22. However hopefully if we detect another universe and conclude that the MW theory is correct, could we then somehow indirectly prove / disprove quantum suicide?
     
  6. Feb 8, 2014 #5

    Bill_K

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    Aren't you confusing MWI with the Multiverse? The paper you cited emphasizes strongly that they are not the same.
     
  7. Feb 8, 2014 #6

    mfb

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    I highlighted the important part.

    In the same way a character in a single-player computer game will never see other instances of it, we cannot see other worlds in the many-worlds interpretation - if we could they would not be other worlds!
     
  8. Feb 8, 2014 #7

    Bill_K

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    Again, I have to quote the paper referred to above, which seems like a reliable source, and suggests the opposite...

     
  9. Feb 8, 2014 #8

    Ken G

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    All the same, decoherence does break the wave function up into effectively non-interacting sectors, so I never knew why people object to the "branching" characterization-- it seems accurate enough as pictures go! Yes they are not "metaphysical" branches, they are in the equations, but they are branches all the same, and we do not experience the other branches. So then what it comes down to is this: which do you believe, the equations, or your experiences? Should we interpret our experiences to be consistent with our equations, or regard the whole point of the equations as being an attempt to make sense of our experiences?
     
  10. Feb 8, 2014 #9

    mfb

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    @Bill: Okay, I guess that is a matter of definition. As long as interference is a realistic outcome, I wouldn't call them "different worlds".
    A person at two locations at the same time (with a notable difference between them) would certainly be incoherent in such a way that interference between the states is completely negligible.
     
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