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B Is MWI deterministic or not?

  1. Nov 23, 2016 #1
    I am just looking for an answer to this question--

    Does the Many-Worlds Interpretation demand that every physically possible scenario has to be played out somewhere in the Multiverse? David Deutsch has told me that yes this is true (including absurd/ unlikely scenarios...although those would happen with less frequency)

    And here is what Max Tegmark has said about Many Worlds--

    "Things inconsistent with the laws of physics will never happen - everything else will. However, to cheer you up: even if some of your twins hold up gas stations, most of your twins certainly don't, given what I already know about your personality; it's important to keep track of the statistics, since even if everything conceivable happens somewhere, really freak events happen only exponentially rarely".

    So that is my question. I would love to believe what someone posted earlier...that certain physically possible events WILL NOT happen in the multiverse, but that seems to be at odds with the strictly deterministic nature of this theory.
    Last edited: Nov 24, 2016
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  3. Nov 24, 2016 #2


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    MWI is deterministic in terms of the evolution of the universe.

    Every physically possible process happens in some branch, but the norm of branches where extremely "unlikely" things happen (like a broken glass reassembling) is negligible.
  4. Nov 24, 2016 #3
    Okay, thanks for the response. And this is consistent with what people like Tegmark have said...
    But I'm going to test the limits of what you've just said and ask you the same question that I asked David Deutsch...Is there a universal branch where George W. Bush and Bill Clinton get married? It seems like a silly question, but if absurd scenarios like that are actually physically taking place...it raises a million questions about ethics and the implications of living in a multiverse.
    Even though the absurd universes make up a negligible minority of overall universes, those negligible universes are themselves verging on infinite and increasing exponentially. The universal timeline where the shattered glass spontaneously reassembles is not just one universe but an incalculable number of branching timelines wherein the glass reassembles in trillions of slightly different ways. The universe where George Bush and Bill Clinton get married is not just one universe but trillions of constantly branching timelines where every possible version of their relationship is destined to be played out...
    So in that's sense, its not really a comfort to say that absurd/ highly unlikely scenarios are only happening to us in a small minority of universes, because that small minority of universes is actually an incalculably vast plethora of universes.....(and incalculably vast numbers of "you"s and "me"s who are experiencing what is going on in those universes)
  5. Nov 24, 2016 #4
    I keep going back and forth on mwi. The science seems to point to it being true...but my common sense tells me it doesn't add up (and of course my common sense is probably wrong...)
  6. Nov 24, 2016 #5


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    You cannot count them. And even if you could, it would not make sense.
    And philosophical discussions are not the scope of this forum.
  7. Nov 24, 2016 #6
    Okay then...here is a question that may belie my knowledge of the topic. But I have to ask--

    If what we perceive as "normal events" make up the overwhelming share of multiversal timelines..does this mean that there are duplicative universes to ensure that "normal timelines" are in the majority...

    Let me explain what I mean-- Assume there is one timeline where George W. Bush is married to Bill Clinton...that timeline then branches into EVERY POSSIBLE outcome that could arise from that relationship (the universes where they honeymoon in Maine, the universes where they honeymoon in NIagara Falls etc etc...) Everything that can possibly happen does happen.

    Now let's look at an initial "normal" timeline where George W. Bush is married to Laura Bush.....that timeline also branches into EVERY POSSIBLE outcome that could arise from that relationship (the universes where they honeymoon in Maine, the universes where they honeymoon in NIagara Falls so on and so forth)

    Wouldn't the "absurd" universes and the "normal" universes have the exact same number of timelines (i.e. one timeline branch per physically possible event)?

    The only thing I can think of that would change that ratio is if there are duplicative versions of the "normal timelines" i.e. there are several identical versions of that moment where George proposes to Laura for every one instance (or branch) where George proposes to Clinton...

    Are there duplicative copies of universes in order to weight the multiverse towards "normality"? Or am I missing something more obvious here?
  8. Nov 24, 2016 #7
    By the way, I would also be interested in hearing from people who believe in mwi but DON'T necessarily believe that absurd/ low density universes must be represented...
    Have any of you mwi proponents taken that position?
  9. Nov 24, 2016 #8


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    No, it means you cannot count them, and even if you could it would not make sense. See my previous post.

    "every possible outcome" is much more than what we would describe as individual outcomes for humans. "individual outcomes" are dominated by the level of individual atoms in different places.

    The existence of "odd" branches is a direct consequence of MWI, it doesn't make sense to like (believe is the wrong word) one thing but don't believe in its consequences.

    There is an approach to develop a different theory (not interpretation) called mangled worlds, which would introduce a physical process to remove those worlds.
  10. Nov 24, 2016 #9
    Trust your common sense
  11. Nov 24, 2016 #10
    ha...yes perhaps I should. But there seem to be problems with all of the other Interpretations as well...
    I think I need to take a second look at the Bohm/ pilot wave Interpretations...
  12. Nov 24, 2016 #11
    I wonder if it is like the path integral formulation of QM in that the multiple worlds which are close re-inforce each other and those that are radically divergent cancel out leaving the observer to observe the most likely universes forming the experience.
  13. Nov 25, 2016 #12


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    Assuming that this is physically possible, yes. :wink:

    But a lot of other things in this branch are probably different from our branch as well. This is left out in virtually all discussions of this topic that I have seen; alternate branches are always talked about as though they are exactly like our branch except for one small change (or one small change plus the obvious implications of it--for example, obviously the same Bush and Clinton children would not exist in a branch where GWB married Bill). But the MWI does not say that; more precisely, the MWI does not require that such a branch--not just one where GWB and Bill marry, but one where they marry and everything else except that and the obvious consequences is the same as ours--is physically possible. It could be that any physically possible GWB-Bill marriage branch differs from ours in lots of other ways as well, going back not just to the meeting or even the births of GWB and Bill but hundreds or thousands of years or even more. It could be that in this hypothetical branch no one exists corresponding to Hillary Clinton (or Monica Lewinsky or Gennifer Flowers or any other of Bill's paramours); it could be that there isn't even a United States of America in this branch, or any office even close to President; it could be that GWB and Bill are not politicians and have life stories very different from the ones they have in our branch (even though they are DNA and personality identical); it could be that the entire history of Western civilization is different--perhaps male homosexuality has been the norm since the 5th century BC in this branch. We have no way of knowing without being able to model the microphysics of human beings and human history at a leven many orders of magnitude more detailed than our current models.

    Of course you could object that the people I was calling "GWB" and "Bill" in this hypothetical completely different branch don't really qualify for those labels (for one thing, it might not be physically possible for them to be DNA and personality identical to our versions). But that just means that the original premise, that there is a branch where GWB and Bill marry, is physically possible, was false--there might be no physically possible world in which two people that are close enough to our GWB and Bill to deserve those labels, marry. In other words, such claims might be drastically underestimating the extent to which what we see as contingent facts about people, like whom they are attracted to and whom they marry, are actually physically determined by the specifics of the world/branch in which they exist.
  14. Nov 26, 2016 #13
    But that's the thing...I think mwi does require this...For example I think that is required that right now, as I'm writing this, our universe is going to branch into a timeline where Bill Clinton suddenly decides that he is in love with Bush and jumps up to book a flight to Texas (or wherever GWB lives) As far as I can tell, Clinton's own personality and the previous nature of the Bush/ Clinton relationship would be immaterial. If determinism is real there would be a kind of “quantum insanity” which would force us to do ridiculous and irrational things.
    That's the problem with mwi. We know that these things are impossible from a common sense perspective...but like mfb said earlier, determinism is kind of an all or nothing proposition
    But the thing I wonder is...if human behavior arises from biology, biology arises from chemistry and chemistry arises from physics..etc...etc. Is some human behavior so ridiculous and/or counterproductive that it would effectively violate the laws of physics? I doubt it but I often wonder if any mwi proponents have ever explored this idea?

    By the way I like your avatar...
  15. Nov 26, 2016 #14
    are there any academic papers or writings on this theory? It seems like an interesting idea...
  16. Nov 26, 2016 #15


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    I don't see this at all. But in any case, the question whether it is physically possible for, say, Clinton and Bush to suddenly decide to get married tomorrow, is not really a question of quantum mechanics; it's a question of cognitive science, psychology, etc. And we certainly don't know anywhere near enough about those disciplines to be able to say that quantum superpositions play any role in our mental processes, much less that there are superpositions possible that would lead to "quantum insane" branch points such as you describe. So for MWI proponents to claim that there must be branches where such things take place seems to me to be going way beyond what the theory actually says.

    What do you mean by "effectively violate"? Nothing can violate the actual laws of physics, by definition. If we saw something that seemed to violate what we thought were the laws of physics, we would have to revise our understanding of the laws; we wouldn't say the laws were violated.
  17. Nov 26, 2016 #16


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  18. Nov 27, 2016 #17
    It may be similar to the mangled worlds idea mentioned above by mfb, but we must be careful here to not violate the charter. I am not suggesting this as a theory only as a way of thinking about things, this may be philosophy. The problem with all Quantum mechanical interpretations is that they all seem to be philosophy.
  19. Nov 27, 2016 #18
    Well, my common sense tells me your right but many of the experts say that that psychology doesn't really enter it...They would say that subatomic determinism overrides any psychological or social norms.

    Yeah that's what I'm saying...mwi proponents say that everything happens somewhere in the multiverse...with the exception of events that violate the laws of physics. So I'm proposing that perhaps some human behavior is so counterproductive that it can not possibly happen. This human behavior would actually violate the laws of physics and would therefore not be allowed to happen under the mwi framework...

    But unfortunately it's a pretty weak argument for several reasons. One reason is that we see bipolar/ schizophrenic doing absurd and counterproductive things on a regular basis. So we see that physics will allow counterproductive behavior to occur.

    The other reason that it's a weak argument is because... even if there is an “emergent impossibility factor” (i.e. it so unlikely for me to say---gouge out my own eyes, from a rational/ commonsensical perspective that this event becomes effectively impossible... it may be irrelevant under the mwi framework because of recherché events like quantum tunneling and classically improbable subatomic activity.

    Thats the main problem-- Quantum tunneling seems to indicate that extremely improbable subatomic interactions (and thus extremely improbable real world events) are inevitable under the mwi framework.

    So the whole mystery of the mind/ body split may be irrelevant….Even if human logic is somehow able to override the determinism of mwi it wouldn't even matter in the face of absurd quantum physics. I may not want to poke out my own eyes but in trillions of universes my arm will involuntarily spasm and stab them out just the same…in some universes I will black out and when I come to my eyes will be gone…in some universes a pre-programmed robot will suddenly materialize out of the ether and force my arm to to perform the stabbing motion….
    Determinism would always override our "free will"
  20. Nov 27, 2016 #19
    Yeah that's what's amazing...after all these years, there is still is not an Interpretation which makes sense. Like David Deutsch has said, if mwi is not true then something REALLY WEIRD is going on...
  21. Nov 27, 2016 #20
    Yeah there are so many problems with mwi but I'm still open to it because so many of my heroes seem to favor it...David Deutsch, Max Tegmark, Frank Tipler, Richard Feynman...these are some of the brightest minds of our time...not to mention household names in the world of physics like Neil DeGrasse Tyson, Stephen Hawking, Murray Gell-Mann etc etc
    Then again there are many bright people who favor opposing Interpretations...but they definitely seem to be in the minority.
  22. Nov 27, 2016 #21


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    Can you give some actual examples? By which I mean, actual textbooks or peer-reviewed papers that argue for this viewpoint and give evidence to support it? I know physicists say lots of things in pop science articles, TV shows, etc., but that's because they can get away with stating their personal opinions in such venues even if those opinions are not supported by the actual physical theories.

    I don't think that whether a particular hypothetical human behavior is "productive" in human terms has any significant bearing on whether or not it violates the laws of physics. That seems to me to be just anthropomorphism.

    I'm also not sure that you have understood my argument. I wasn't arguing that a multiverse branch in which GWB and Bill marry might violate the laws of physics because such behavior would be "unproductive", or even because it would be so far out of sync with their personalities as we know them. I was arguing that the idea that there could be a multiverse branch in which GWB and Bill married but everything else (except for direct consequences of that change) was exactly the same as our branch, might not be correct, because such a branch might not be physically possible; there might be no physically possible way for an alternate branch to evolve such that only that one thing changed from ours. And the more things are changed from our branch, the less reason we have to call the individuals that marry in that branch "GWB" and "Bill", because a significant part of the personal identity of those individuals is their history--the particular facts of the branch they exist in.

    Perhaps another way of putting my objection is that, in order to imagine a branch in which GWB and Bill marry but nothing else changes, we need to know how to identify "GWB" and "Bill". What constitutes the personal identity of those individuals? Any MWI proponent who claims that we can do this purely based on our knowledge of quantum physics is, to put it bluntly, full of it. (AFAIK no MWI proponent claims this explicitly, but many of the claims they do make, if you went into the details, would, I suspect, turn out to implicitly assume that something like this is possible.) The question of what constitutes personal identity is not a question of physics, or at least not physics alone.

    As I said before, this matters for our discussion here only if quantum superpositions turn out to play a significant part in determining what human beings do. But we have no evidence that this is the case. The only concrete speculation I'm aware of along these lines, Penrose & Hameroff's idea about quantum superpositions in microtubules, didn't pan out when it was tested, AFAIK. As far as we can tell, our brains are classical objects and can be described perfectly well by classical physics, which means that there are no significant quantum superpositions involved.
  23. Nov 27, 2016 #22
    MWI is far from proven, it's not even fully defined yet. Problems exist in accounting for Born probabilities and the actual experience of the experimenter, which can bring in difficult questions involving exactly how consciousness is supposed to "branch". In fact a recent study showed that MWI may possibly be twaddlish.
  24. Nov 29, 2016 #23


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    Many of those most definitely do NOT favor MWI - they favor consistent histories.

    It is true they are open to it because CH has been described as MW without the MW.

    Last edited: Nov 29, 2016
  25. Nov 29, 2016 #24


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    It's an interesting question what Feynman was thinking about "interpretation". I think he'd be very critical and refer to "shut up and calculate". I can't help it to find this the wisest advice ever given concerning this rather philosophical side. I can't however agree with his criticism against Bell whose work precisely anabled a clearly physical approach, but my personal conclusion is that indeed the empirical facts concerning this work more and more solidifies the minimal probabilistic interpretation. There are probabilities, and that's it. There's no more than that behind QT, and as it seems that's how nature can be described as real and not somehow more.
  26. Nov 29, 2016 #25
    Please can you supply evidence that Feynman said to "shut up and calculate"?
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