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I Many Worlds - Superdeterministic?

  1. Sep 6, 2015 #1
    Forgive me if this question has been asked previously on this board, but I cannot seem to find anything similar having searched around earlier.



    I suppose this blog entry written by the Physicist Robert Oerter linked below has accurately reflected how I feel about Many Worlds:

    "But now you see the problem: the future, in the normal sense of the word, involves the cat being either alive or dead, not both. And the MWI does not determine which future we will see. Indeed, from the point of view of the MWI, there is not even any sense in asking which outcome actually occurred, because both actually occurred, in different "worlds."

    So in the case of the cat, the future (in the normal everyday sense) is undetermined. But it's much worse than this: anything that occurs because of quantum effects has an indeterminate outcome. But in the MWI, everything that occurs at all occurs because of quantum effects. So (almost) everything is indeterminate."

    http://somewhatabnormal.blogspot.ca/2010/10/many-worlds-interpretation-is-not.html



    In opposition there's also this post written by Sean Carrol on his awesome science blog PreposterousUniverse:

    "What I like about Many-Worlds is that it is perfectly realistic, deterministic, and ontologically minimal, and of course it fits the data perfectly."
    http://www.preposterousuniverse.com/blog/2015/08/03/hypnotized-by-quantum-mechanics/



    Questions:

    1. So is Many Worlds open to interpretation?

    2. Is The Many Worlds interpretation Superdeterministic in the sense that if it is deterministic within each Universe, then all universes are a portion of a larger Superdeterminstic entity(Multiverse), and how crazy does that sound?

    3. Is there a branched copy of each Universe per each wave function collapse, meaning there is a Universe identical to this one, except ONE photon happens to travel in another direction, once? Am I just talking nonsense, or is this how Everett's Many Worlds actually works?

    Thanks everyone
     
  2. jcsd
  3. Sep 6, 2015 #2

    mfb

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    That applies to all interpretations.

    It is an interpretation.
    The deterministic evolution applies to the whole universe, which has many parts that are often called worlds.
    Yes.
     
  4. Sep 6, 2015 #3
    Hey thanks for the reply mfb; I guess 3. is where I have a bit of an issue with Many Worlds, as it appears an unlikely scenario and seems to be just as likely to me that at some point in "time" another Universe could exist within the Multiverse exactly like this one but with that one photon/electron/etc traveling in another direction, once, and that being the only difference. It seems unlikely to me I guess that they "branch" off instantly, and would be more logical, at least in my mind, that the Universes would exist either before or after this one where this would occur, rather than instantly pop into existence per each wave function "collapse", which I presume doesn't happen anyway in Many Worlds as all possibilities are realized.

    It's not that I doubt Many Worlds, it is that I doubt the way it is commonly put forth, it just makes more sense(at least in my mind) to say that the Universe "copys" with changes happen either "before or after" this Universe, then happen to branch off over time instantly.
     
  5. Sep 6, 2015 #4

    mfb

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    It does not happen instantly. It happens within the decoherence time.
    Well, one universe splits into two (or more) parts that quickly evolve so differently that their mutual interaction becomes negligible.

    Many worlds just lets the wavefunction evolve - no collapses, the splitting is natural result of the evolution of the wave function.
     
  6. Sep 6, 2015 #5
    Alright I see what is being presumed here, but still think it's most logical to say that there's a collapse and it's simply in-deterministic, but that's just my layman opinion.

    This sounds fairly different than the multiverse that's posited within string theory(which I believe to be very plausible), so is it possible that the many worlds interpretation and string theory are both correct?

    If so would that imply that there's "multiple-many world universes", so to speak?
     
  7. Sep 6, 2015 #6

    Nugatory

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    "Collapse" is an attractive way of thinking about QM because it works well in many local problems and provides a clear intuitive picture of how measurement changes the wave function. However, it is an awkward fit with the mathematical formalism, and MWI was developed as a collapse-free interpretation to avoid these difficulties.

    You are free to think that MWI or any other interpretation of quantum mechanics is "most logical". None of them are required by the mathematical formalism of the theory, none of them are inconsistent with that formalism, they all yield the same results for all experiments (at least so far) so there's no experiment (at least so far) that would tell us that any one is more right than another, and all of them stretch credulity when applied to some problems (different for different interpretations). Thus, there is a very strong element of personal taste in claiming that one is "more logical" than another.

    There's nothing wrong with personal taste, but "De gustibus non disputandum est".... With no objective standard for preferring one interpretation over another, these discussions tend to go in circles until they are closed. I'm leaving this one open for now, but I'll ask people to please not post into it unless they're saying something new.
     
  8. Sep 9, 2015 #7
    The term "superdeterministic" I think is generally used for a set of explanations of apparently non-local correlations with some sort of conspiracy of the initial conditions, etc. It does not seem you really meant that meaning, you just mean normal determinism. That it is applied to a "larger" model than usual does not change it or suppose adding arbitrary adjectives.

    Incidentally, many-worlds handling (or failure to handle) exactly those non-local correlations is the reason I personally consider it a completely redundant extension or complication of the other models.
     
  9. Sep 9, 2015 #8

    mfb

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    Many worlds doesn't have any problem with those correlations. They naturally pop out of the evolution of the wave function.
     
  10. Sep 9, 2015 #9
    But when you try to explain when does a branching occur, you can not. You can not point to a space-time event that starts the branching and that has all resulting differences in its future. So you still get spatialy-separated differences, so it is still a non-local model.
    EDIT: But anyway, this is getting off-topic. If you disagree you can just ignore my post instead of answering. Or imagine that you've convinced me already.
     
    Last edited: Sep 9, 2015
  11. Sep 9, 2015 #10

    mfb

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    There is no need for such a thing.

    It is local - if you want to evaluate the correlations you need information from "far away" (spacelike separated), but to evaluate those correlations in the experiment you need classical information transfer. Your local part of the wave function (properly defined) evolves purely local and independent of the evolution "far away".

    Locality and determinism are not so unrelated, so I think it is not too off-topic.
     
  12. Sep 9, 2015 #11
    Ok, I'll bite. How can you say the state right before Alice's measurement evolving to the state (or branching into the states) right after her measurement is independent of Bob's detector settings?

    I guess the key is in the fine print. "local part of the wave function (properly defined)"... is there even such a thing for an entangled state? Can you point me at what to read about that?
     
  13. Sep 9, 2015 #12

    mfb

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    Calculate it, that will be the result.
    The laws of quantum mechanics are local. This is a very fundamental part of QFT, actually.
    Not if you care about correlations, but for Alice alone (using the typical photon example) the photon looks like one with a random polarization.
     
  14. Sep 9, 2015 #13
    Now you're just being quantum on me - you are telling me two opposite things at once.
    If we tried and calculated everything based on local evolution only, we'd not get a correlation, not match observed reality, and be wrong. So to calculate it properly, I have to calculate over the complete system. So Alice's measurement is not really independent of Bob's settings. So MW is not local.
     
  15. Sep 9, 2015 #14

    Demystifier

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    As I already said once, MW is neither local nor non-local. It is a-local. This means that MW does not live in the ordinary 3-space, so you cannot say that it is either local or non-local in the 3-space.
     
  16. Sep 9, 2015 #15

    Nugatory

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    You have to be careful about what you're calculating when. If you're trying to calculate the value of the correlation, then you can include everything in the past light cone of the event at which we compare Alice's and Bob's readings without any locality concerns - and as mfb says, the correlated result just pops out when you calculate the evolution of wave function to that point.
     
  17. Sep 9, 2015 #16
    Yes, but wouldn't this kind of reasoning imply that the experimental records for Alica and Bob are actually undetermined until they are compared? (Or until they become time-like separated)?
     
  18. Sep 9, 2015 #17

    mfb

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    Well, both possible outcomes (for both) are realized. They are determined in their respective world.
     
  19. Sep 9, 2015 #18
    Not quite, however after looking into it further you have all assisted in answering my question. If the MWI interpretation is correct then wave function would instantiate in every possible world. This implies an ontological "superdeterminism" for the wave function with an epistemic indeterminism for individuals within each universe.

    Ergo, each individual Universe would be functionally indeterminate, however the entire "Multiverse", or "Universe" containing the many/transfinite worlds is classically determinate in the sense that all possibilities are realized/eventually realized. So the correct answer is both, and also subjective based on your point of view.

    Ironically it doesn't make any difference if everything is deterministic or indeterministic, the philosophical and even scientific conclusions you would draw are exactly the same, rendering every debate about the topic futile.

    Thanks guys

    Edit:

    Also You claimed "both possible outcomes", when in effect they're calculated using a vector(s) in Hilbert space. Simply put there can be more than two possibilities.

    http://www.preposterousuniverse.com...hanics-is-given-by-the-wave-function-squared/
     
    Last edited: Sep 9, 2015
  20. Sep 9, 2015 #19
    I'm going to bite too (though its only more words). The worlds are already separate but Alice straddles two worlds. In one world she has photon 1 and Bob has photon 2, and in the other world vice-versa. For Alice the branching occurs when the photon is measured. The Bob in her world must have photon 2 if she has photon 1 etc.
     
  21. Sep 9, 2015 #20

    mfb

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    Sure. I used the classical example of photon polarization where you just have two outcomes for a detector. That example is sufficient to explore all features of quantum mechanics here.
     
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