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Would the universe be the same if it was reset?

  1. Jul 6, 2012 #1
    Exactly like the title says, Would the universe be the same if it was reset?

    Meaning, if we were to reset time to the big bang, and then fast forward to present, would the universe look the same, or would it be different?

    I thought it would be different, because of all the randomness in Quantum Mechanics, but my friend insists it would be the same.

    Who is right?
     
    Last edited: Jul 6, 2012
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  3. Jul 6, 2012 #2

    DaveC426913

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    You are correct.

    Current understanding of the universe is that it is non-deterministic.

    Your friend is thinking of a classical Newtonian deterministic universe, which has been deprecated by QM.
     
  4. Jul 6, 2012 #3
    Here is my friends argument for why the universe would be the same

    Does he have a case? What do you think?
     
  5. Jul 6, 2012 #4

    cepheid

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    In my opinion, your friend's statement is not so much an argument as it is a bunch of random words strung together. Seriously, there is no coherent point there.
     
  6. Jul 6, 2012 #5
    i think You are correct.
    http://gobackto.tk/signature.jpg [Broken]
     
    Last edited by a moderator: May 6, 2017
  7. Jul 6, 2012 #6

    DaveC426913

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    Concur with Cepheid. Your friend has not made an argument, he has simply voiced a personal (and unsubstantiated) opinion.

    It isn't about randomness, it's about the Heisenberg Uncertainty Principle. Suggest to your friend to read up on it.
     
  8. Jul 6, 2012 #7
    I am having difficultly explaining how it can not possibly be the same if it was reset.
     
    Last edited: Jul 7, 2012
  9. Jul 7, 2012 #8

    mfb

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    This depends on the interpretation.
    Take the most simple example: A photon reaching a half-reflecting mirror. It can either go through it or be reflected.
    - With non-deterministic interpretations, both can happen - but in each "run" of the world, just one thing happens, and it is not always the same.
    - With some deterministic interpretations (especially deBroglie-Bohm), you will always get the same result
    - With some deterministic interpretations (especially many worlds), both will happen in every "run", and you get separate observers for both results.
     
  10. Jul 7, 2012 #9
    I think the OP’s friend makes perfect sense.

    He is saying that truly random events do not occur. What appears random to us is only due to our limitations of measurements of all variables for an event. If we pick up a grain of sand at the beach we might speak of the randomness of how it came to be there. We have no way of knowing the millions of years of wind and wave action and all the physics that contributed to the position of that particular grain of sand. Yet we know that those causes exist (reasons for everything).

    As Dave said in post #2, this is a classical Newtonian deterministic view of the universe. So you can tell the OP’s friend to go read up on HUP and QM if you like. That’s fine, but I don’t think he deserves to be insulted. In my opinion he is much smarter than the average idiot on the street.
     
  11. Jul 7, 2012 #10

    cepheid

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    This seems like a coherent thought to you? What does entropy have to do with anything? What does it mean to measure something that you can't exactly measure? For that matter, what does it mean to "obtain randomness?" Your *interpretation* of what he said is reasonable, but it doesn't really follow from what he said, in my opinion.
     
  12. Jul 7, 2012 #11

    DaveC426913

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    Nobody insulted anyone and nobody called anyone an idiot.

    This is at heart a discussion of science, and the OP's friend is not talking science.

    eg. "everything happens for a reason" is not scientific.
     
  13. Jul 8, 2012 #12

    phinds

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    Yes, but at the quantum level they DO. This is NOT a measurement problem the way the OP's friend thinks it is, it is the way nature works.
     
  14. Jul 8, 2012 #13
    Are you sure it is truly random and does just not appear random due to some unforeseen variable we have yet to identify?
     
  15. Jul 8, 2012 #14

    mfb

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    It does not depend on variables which we could possibly have access to (it is not due to our limited knowledge).
    As stated before, there are interpretations where the path is determined by parameters we cannot access. It really depends on the interpretation.
     
  16. Jul 8, 2012 #15
    Summarizing, in an answer to the original question: some respectable physicists say "yes", others say "no"; it's an unsettled issue to date.

    For the moment being, I would say "yes".
     
  17. Jul 8, 2012 #16

    DaveC426913

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    I'd like to see these modern physicists who say yes.

    Modern physics - QM - says no.

    It's all fine and well to speculate about what might be underlying our correct understanding of the universe, but that does not make it an unsettled issue.
     
  18. Jul 8, 2012 #17
    So what does the same mean?

    That I would be replying at about 15 minutes past 10pm central standard time on a computer?

    Just from a biology/evolutionary point of view it is very unlikely the earth (if everything up to this point was exactly the "same") would ever even formed a multicellular organism, much less a eukaryotic one. Animals with a notochord... no way. Rerun it a billion times, no way.

    The same... I am horribly confused about what exactly would be the same.
     
  19. Jul 9, 2012 #18
    Dave, the indeterministic interpretation of QM is just as much a "speculation" as the deterministic one.

    I agree that not all interpretations are on equal footing a priori, but you seem to be implying that there are no arguments for the deterministic interpretation except taste (or even a sort of unwillingness to accept indeterminism). Am I interpreting you correctly? If so, I disagree on that one. There are a lot of respectable physicists who support the pilot-wave theory (if I really have to throw out one name, it's J.S. Bell; his name seems most obvious to say first since he's the most famous) and their arguments are all but poor in my view. The arguments concern matters such as a minimal set of axioms, or for example an absence of ambiguity (the main problem with the orthodox interpretation), even pratical issues like new (and sometimes better!) numerical approximations. Another argument might be that the pilot-wave theory was actually one of the very first versions of QM, implying it's not at all far-fetched (de Broglie put it forward, but Schrödinger -when writing down his equation- only afterwards left out the point particle, but for reasons we now know are wrong (at that time Schrödinger was not aware of the phenomenon of collapse which destroyed his interpretation) and Born, when putting forth his probabilistic law, for some unknown reason only based himself on Schrödinger's research, although the probabilistic law was already a consequence/theorem from de Broglie's theory).

    Literally the same, as in for example a Newtonian world view: if the laws are deterministic, then a certain set of fixed initial conditions (this is of course very important; even the slightest change in initial conditions will lead to a dramatically different universe) will lead to exactly the same evolution.
     
  20. Jul 9, 2012 #19

    mfb

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    This is wrong.
    The Copenhagen interpretation (and some others) says no. Other interpretations say yes.

    Count me in. And the ~60 others here, too (multiply a "physicist fraction" to this number of you like). And of course all other physicists supporting these interpretations.
     
  21. Jul 9, 2012 #20
    I'm not speaking on behalf of the validity of his statements, because it is very much an opinion and string of unfounded conclusions he seems to be talking about.

    But, I think entropy was relevant to his opinion because entropy is a way to describe systems that we cannot account for microscopically because they simply have too much information and too many variables and interactions. We describe it statistically, much as random events are described statistically. His point is that even though we can treat it as randomness, it is more as a result of our inability to account for all possible interactions, variables, etc. than it is that the universe is truly random.

    I think he is missing the mark though, because we have shown that single particles and interactions are only described mathematically using probability at best. My thought is that the universe would not be identical at small detail, but perhaps macroscopic properties such as total energy and entropy in the universe could be the same at a given time.
     
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