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Is this a Deterministic Universe

  1. Aug 21, 2013 #1
    Does the seemingly random nature of QM mean that the Universe is very non deterministic and does this mean that our existence is completely as a result of random chance, or am I significantly misunderstanding the nature of QM?

    I am new to QM and the idea of determinism, and I just wanted to get an idea for the current mainstream view. I also read a quote recently, I forget who, that said that no one really understands QM and wondered if that plays a part also..
     
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  3. Aug 21, 2013 #2

    DrChinese

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    You can really go all over the place with this topic, a lot of it being more philosophical than about physics.

    A deterministic universe is a viable possibility even with QM as it is. There is a non-local theory called Bohmian Mechanics in which QM's predictions are replicated, and everything is fully deterministic too.

    Also, a deterministic universe means "our existence is completely as a result of random chance" just as much as an indeterministic one does. The difference being that in one, our future has just one (random) possible outcome. In other interpretations of QM, there are many possible outcomes and none is more favored over another (although I guess some outcomes might be more likely in a sense).
     
  4. Aug 21, 2013 #3
    Thanks Dr, please let me ask this in a slightly different way. If the exact same universe were to be reproduced or started over n times from t=0 i.e. the BB, what are the chances that I would be here typing this in every one? I have heard answers from other Physicists ranging from n to 1 and even 0.

    Since I didn't do well in my QM class and it is so long ago, I am unable to judge which answer is most likely and so I wondered what most experts in modern QM think?

    I am not looking for a philosophical take or bias, just an understanding of the Physics and QM facts, which perhaps are not sufficiently well understood to be certain of the answer to a question like this?
     
    Last edited: Aug 21, 2013
  5. Aug 21, 2013 #4

    DrChinese

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    As I follow the more indeterministic branch: zero.

    But as mentioned, there are those pesky Bohmians too!
     
  6. Aug 21, 2013 #5
    And not 1? Am I not really here? :) My answer remains 1.

    Anyway thanks for replying. I hope that other QM people can weigh in on this, perhaps a poll? - again, on the Physics only.
     
    Last edited: Aug 21, 2013
  7. Aug 21, 2013 #6
    #Limited knowledge noob response warring#
    Well if the position an electron in space is based on probability and is somewhat random, and the big bang started on the quantum level, then the outcome of that big bang is a probability.

    On a more science fiction side of things, Backwards time travel is theoretically possible, so..

    Deterministic universe backwards time travel = paradox
    undermined universe backwards time travel = paradox free :), except for maybe running into your self.
     
    Last edited: Aug 21, 2013
  8. Aug 21, 2013 #7
    lyncsta, I don't believe in HG Wells time travel. You cant travel to a place that does not exist and the wave functions of everything in the past have all collapsed and do not exist. Lets leave this for the Sci-Fi thread. :)
     
  9. Aug 21, 2013 #8
    You would have a probability associated with what you typed, but also a probability to reply differently.

    Whether what you actually typed was predetermined or not (i.e. QM supplemented with hidden variables (non-local, mind you)) is really hard to say right now. I don't even know if an experiment can be performed that can differentiate between Bohmian Mechanics (deterministic version of QM) and standard QM, but there are a few articles published that try and do such.*

    *For clarity: QM = Quantum Mechanics
     
    Last edited: Aug 21, 2013
  10. Aug 22, 2013 #9
    Ever notice the correlation between logic, computability and causality? Basically the idea that every cause has a preceding cause that 'caused' it into existence is the basis for logic, which we use to discern the natural of the universe. In other words, it's the guiding principle (along with observation) through which we discover scientific truth. The idea that something can be 'uncaused' is a little ridiculous in my opinion because it not only goes against the very tenants we use to discern truth, but because it also holds the unfortunate reality of being logically impossible.

    No one in the world can explain to you how an uncaused cause could possibly come into existence, because it would be impossible and our logical minds simply can't comprehend it as a result. Given that, I think it's fair to say that either the observations made in regards to 'spooky' action at the sub-atomic level are incorrect, or there is a non-local, superluminal deterministic system at work. Or, perhaps the universe simply isn't inherently logical. Being of rational/logical minds though, we instinctively rebel against anything that isn't.

    With that said, the idea of inherent probability without an underlying deterministic system is rubbish in my opinion. If the quantum universe were inherently probable, what then makes one effect more probable than another? What's the cause of it?

    Any system of probability necessitates an underlying deterministic system.
     
    Last edited: Aug 22, 2013
  11. Aug 22, 2013 #10
    Its not predicted by "HG Wells time travel", but by albert einsteins theory of relativity - time dilation.

    http://en.wikipedia.org/wiki/Time_dilation


    If all matter exists at once, then so too must all time. hence spacetime.
     
  12. Aug 22, 2013 #11
    There is the multiverse theory :) That would explain the cause. But I suppose that just kicks the can down the road. We would be left asking what caused the multiverse.
     
  13. Aug 22, 2013 #12

    I see time as a thin slice (Planck time) of the present in which particles interact. Other past planck times have no further effect and thus no longer exist. To go back to a point in the past would require recreating a whole new Universe in full, which is quite impossible.
     
    Last edited: Aug 22, 2013
  14. Aug 22, 2013 #13
    I agree, every time you think you have found first cause you can always ask what caused that?
    First cause and final effect therefore do not exist, just like a place at infinity cannot.
     
    Last edited: Aug 22, 2013
  15. Aug 22, 2013 #14

    Did you not mean the opposite? If you cant tell what the outcome of one single random event is then the Universe is already non-deterministic.



    I hope those that know QM better than me can weigh in on trying to understand whether QM means that the Universe is non deterministic with probabilities involved at every cause and effect, and at every planck time step.
     
    Last edited: Aug 22, 2013
  16. Aug 22, 2013 #15

    DrChinese

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    There is no evidence to support this statement, and plenty of evidence to indicate it is false. Are you familiar with delayed choice quantum erasers? These appear to change the past. There are a number of interpretations of QM in which past time is treated no differently than future time. These are the "time symmetric" class. The Transactional Interpretation and Relational Blockworld are examples.
     
  17. Aug 22, 2013 #16
    No, I meant what I said. I think you're confusing predictability with determinism. Just because something might be unpredictable and 'seemingly' random, doesn't mean it isn't deterministic. No worries though, pretty much everyone gets these two ideas mixed up. True randomness is impossible.

    You really have to ask yourself what makes one probable outcome more likely than another in a probability system.
     
  18. Aug 22, 2013 #17
    As Dr. Chinese hinted, there are a lot of interpretations about what QM means. Books upon books upon books. We have the math and it works, but what does it mean? [See the Penrose quote below] What does superposition, action at a distance, delayed choice, uncertainty, 'mean'....??

    For interesting insights, check out prior discussions in these forums on Heisenberg Uncertainty Principle.

    Sounds like Richard Feynman.

    A corollary is "Shut up and calculate" which means the math of QM as laid out is clear [See Penrose below]...what it means, how to interpret it is 'not so clear".




    http://en.wikipedia.org/wiki/Deterministic_system

    for a prior discussion, which I liked:

    [They take a statistical range of values.]

    more detail on this:

    from Roger Penrose celebrating Stephen Hawking’s 60th birthday in 1993 at Cambridge England.....this description offered me a new insight into quantum/classical relationships:

    and he goes on to relate this linearity and superposition to the double slit experiment.
    You can associate the imaginary aspect of complex quantum numbers with virtual particles as an initial perspective.
     
  19. Aug 22, 2013 #18
    Upon rereading all the above, seems like briefly discussing HUP would be of interest to you.

    Regard 'uncertain' as 'non deterministic' in descriptions below. [I bet someone will object to that!!]

    These are from my notes, so, thankfully, I can just copy and paste:

    Synopsis: If you search HUP in these forums you can rummage through many pages of disagreements and clarifications. The quotes below are slightly edited posts [for brevity, clarity] from those discussions. [I had little idea myself what HUP REALLY meant until arguments/discussions/and some research papers were dissected in these forums.]


    My own single sentence explanations :

    A] Get a better instrument and you'll get better measurement results to any accuracy.

    B] Quantum theory does not predict the outcomes of single measurements, it only predicts the ensemble [statistical] properties of multiple measurements.

    C] In classical mechanics we can predict with absolute precision, to arbitrary accuracy, the future position and momentum [for example] of a single particle; The HUP says no you can't: you can only make a statistically based prediction!


    Summary Details:

    It IS possible to simultaneously measure the position and momentum of a single particle. The HUP doesn't say anything about whether you can measure both in a single measurement at the same time. That is a separate issue.


    Fredrik:
    A quantum state (pure or otherwise) represents an ensemble of similarly prepared systems. For example, the system may be a single electron. The ensemble will be the conceptual (infinite) set of all single electrons which have been subjected to some state preparation technique (to be specified for each state), generally by interaction with a suitable apparatus.
     
    Last edited: Aug 22, 2013
  20. Aug 22, 2013 #19
    No one completely understands QM simply because they can't find an underlying deterministic system at work. Physicists can offer probable predictions based off of the data they've gathered, but that it's. They can't describe exactly how everything works because they simply don't have accountability of all of the variables involved.

    No offense to anyone, but if someone says they have a complete understanding of QM... Well, let's just say they have an extremely large, self-assuaging ego.
     
  21. Aug 22, 2013 #20

    DrChinese

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    Not sure how you get this. As far as anyone knows, every quantum measurement of a previously unknown observable yields a completely random outcome.

    It looks random, tastes random, smells random, so it must be a duck. :smile:

    The idea that "true" randomness does not exist in nature is purely by assumption.
     
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