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If we restarted the Universe n Times from T=0.....

  1. Sep 17, 2015 #1
    Would it always be identical?
    Would it ever be identical?

    Essentially with the current state of physics and taking quantum fluctuations into consideration, would it always be the same?

    Is there motion at T=0?


    Another question:

    If we restarted the Universe from the big bang and let it play out in accordance with Bohmian mechanics(or any other deterministic interpretation), would it then follow that everything would be exactly the same as it is now?
    Or would it be different?

    Apologies for the philosophical questions, but I'm wondering what modern physics has for an answer for this question specifically, and also what the majority of you think.

    Thank you
     
  2. jcsd
  3. Sep 17, 2015 #2

    mathman

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    My guess - quantum fluctuations would make things different.
     
  4. Sep 17, 2015 #3

    mfb

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    Assuming you prepare the intial state in exactly the same way (no matter what exactly that means), it will depend on your favorite interpretation of quantum mechanics. In deterministic interpretations, it will be the same, in nondeterministic interpretations it will not (probably).

    I don't think that question is well-defined.
     
  5. Sep 17, 2015 #4
    Well quantum fluctuations cause reality time field to disapparate. My best guess.
     
  6. Sep 17, 2015 #5

    phinds

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    Uh ... what is a "reality time field"?
     
  7. Sep 18, 2015 #6
    In MWI it will be the same.
     
  8. Sep 18, 2015 #7
    Well MWI says nothing about the probability distribution of the evolution of the wave function in our own Universe. Just that all the possibilities within superposition do actually happen, just in other worlds.

    So who's to say that each individual Universe isn't probabilistic(as quantum mechanics demonstrates), with all the possibilities eventually being actualized somewhere.
     
    Last edited: Sep 18, 2015
  9. Sep 18, 2015 #8

    mfb

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    No, MWI gives you the amplitudes as well. In MWI that's all that exists. Same amplitudes => same universe.
    Quantum mechanics demonstrates that some things appear indeterministic to observers that are part of the universe. That's perfectly compatible with a deterministic universe with MWI.
     
  10. Sep 18, 2015 #9
    So you can predict with 100% certainty the outcome of every wave function collapse?

    If it quacks like a duck, walks like a duck, and looks like a duck...:wink:
     
  11. Sep 18, 2015 #10

    mfb

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    There is no wave function collapse in MWI.
    So every object you observe at very dim light is black or grey just because you are unable to see its color?
     
  12. Sep 18, 2015 #11
    Yes I am aware of this, all possibities occur in a branching multiverse. Do you know objectively where every subatomic particle within a superposition will be located within our Universe before measurement? Do you know where it will end up, and what we will observe in our Universe, before measuring? No, you don't, because we only know the probablity distribution.

    No it is an old metaphor. What I meant was if it appears to be probablistic, and experimentation yields results that lend credence to this. Perhaps it actually is indeterministic...rather than an infinite number of branching worlds with copies of everyone except one photon travels...a little to the right. :smile:
     
    Last edited: Sep 18, 2015
  13. Sep 18, 2015 #12

    mfb

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    With infinite computing power, sure.
    There is no such thing as "our universe", unless you mean the full universe with all worlds. Yes we can know where it will end up in this full universe.
    I know, and it is not applicable at all.
     
  14. Sep 18, 2015 #13
    Could you elaborate a bit more on this?

    This assumes the MWI is correct, and let me redefine what I had said and substitute "our universe" with "our world".


    That's a subjective statement in my humble opinion, and I feel as though what I wrote above holds up. However I can see why you would say that it doesn't apply here.

    Thanks for the interesting back and forth so far. What main reasons do you have for taking the MWI view, other than determinism, and perhaps getting rid of the wave function speculation?
    How do you derive the born rule/probability with MWI?

    Edited for clarification
     
    Last edited: Sep 18, 2015
  15. Sep 19, 2015 #14

    mfb

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    I don't know what would be left to elaborate. If you know the laws of physics, if they are deterministic, and know the initial state exactly, you can predict the evolution of the system. That is the definition of deterministic.
    No, the whole discussion is in the context of MWI.
    Also, we are talking about interpretations. "correct" is not a meaningful concept for interpretations. If I say "this tree is tall" and you say "it is small", who is correct? There is no objective definition of large and small - both are interpretations of "the tree has a height of 5 meters".
    tzimie and you started a discussion about MWI, I joined.
    This is beyond the scope of this thread. We have multiple threads about the MWI, you can check those.
     
  16. Sep 19, 2015 #15
    What is your personally preferred interpretation of quantum mechanics?

    Do you feel as though the Universe is deterministic or indeterminate?

    Edit:
    Also I wanted to reiterate that by "universe" I had meant the MWI meaning of the word "world". In essence I was making the observation that MWI is only deterministic from a birds eye view, and makes no statement on how probabilities function within our individual world, and as such it would be best to say each individual world is indeterminate.

    Thanks
     
    Last edited: Sep 19, 2015
  17. Sep 19, 2015 #16

    mfb

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    I like MWI, it is simple and elegant.
    That is philosophy, and I ignore philosophical discussions about the universe.
    There are no probabilities within a single world, because all measurements performed in the past have a certain outcome. People in this world can make theories about probabilities or amplitudes based on those observations.
     
  18. Sep 19, 2015 #17
    I could see your point up until you said this; I believe this statement to be a complete non sequitur. This is the same thing as me turning it on it's head and simply declaring that because we cannot be sure of the outcomes of future measurements, and can only determine the probability before hand, the world is inherently indeterminate.Therefore people in this world can only make theories or interpretations about the deterministic nature of the amplitudes, based on our observation.

    Not to get into a philosophical debate here or be outwardly tendentious, but you're being locally incoherent. To explain further that's like me saying because the 2007 New England Patriots lost the Superbowl, that they never had any chance to win in the first place. This is known as circular reasoning and this is inherently not a very scientific means of arriving at a non-biased conclusion. You're begging the question, so to speak. Many religious types perform this same fallacy when defending their "faith". You're basically saying that because the world is deterministic their are no probabilities.

    Also the error here is MWI does not say the single world is deterministic, only the total structure is deterministic, because all possibilities happen, somewhere. It doesn't say where, or how it would work however, and is agnostic on that point, and to say otherwise is a logical fallacy in itself. So as I said before it is deterministic only from a birds eye view, MWI is not deterministic in the since that our individual world itself is as it cannot predict(doesn't say anything about) the outcomes of the probability distribution.

    So I presume we can agree to disagree, unless you or someone else has something to add?
     
  19. Sep 19, 2015 #18

    mfb

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    I am not.

    I also think this discussion gets pointless. Read the MWI threads if you are interested in the topic.
     
  20. Sep 19, 2015 #19
    No explanation as to why you feel that way?

    I agree with you, and will do. Thanks again for the interesting discourse.
     
  21. Sep 20, 2015 #20
    Something In progress and I meant to say reality field. Abstract quantum science. I,ll explain more later.
     
  22. Sep 20, 2015 #21

    Nugatory

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    But please do be mindful of the PhysicsForums rule prohibiting speculative and personal theories that have not been published in an acceptable peer-reviewed journal....
     
  23. Sep 20, 2015 #22

    phinds

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    If you do explain more later, take care that you are not violating the forum rules on personal theories.
     
  24. Sep 20, 2015 #23
    Endan Rarity, looks like the QEnergySpa folks use the phrase "quantum reality field"... hoping your explanation has something else in mind? :)

    Mentor note: removed link (also in quote below)
     
    Last edited by a moderator: Sep 20, 2015
  25. Sep 20, 2015 #24

    phinds

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    AAAACCCKKK ! I do hope that's not what he has in mind.
     
    Last edited by a moderator: Sep 20, 2015
  26. Sep 21, 2015 #25
    I don't think there is an answer. But what I THINK is no, it would be different every time. To be the same, there have to be deterministic rules for things that I don't think there are rules for. Radioactive decay, in particular seems to be inherently unpredictable. It is JMO, but, for example, while the total C14 population must decay at a certain rate, the clock for an individual atom seems probabilistic, not mechanistic. Vacuum energy would also seem inherently unpredictable.

    If there is an exact, deterministic rule for everything, then the Universe would only depend on the starting conditions at T=0. And despite the complexity, it would always be exactly the same. I don't think that is the case, though that is JMO. So if you are counting/surveying, I vote "no".
     
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