Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is a-causality necessary for randomness?

  1. Aug 11, 2012 #1
    What is the relationship between a-causality and randomness?

    Let's look at the argument below:

    For something to be (truly/inherently) random there cannot be a cause.

    Because, if there is a cause then the cause can be studied and the result/output can be predicted and hence there would no randomness.

    True Randomness means something that cannot be predicted.

    We can predict whether will be an interference pattern or not, however we cannot predict the location of any individual/single photon/electron on the screen.

    We can, in principle, predict the results of a roll of a dice (or toss of a coin) if we took into account all the factors such initial forces on the dice during the toss, effect of air molecules etc. Since the roll of a dice has a cause its predictable.
     
    Last edited: Aug 12, 2012
  2. jcsd
  3. Aug 12, 2012 #2

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    An observation causes a quantum system to change state - we just can't predict what that state will be - but 100% for sure it caused it to change state - the change was not a-casual.

    In classical 100% deterministic systems chaotic behaviour abounds meaning since it is impossible to know with 100% accuracy the initial conditions there will always be some imprecision in knowledge that will grow to the point prediction is meaningless.

    Thanks
    Bill
     
  4. Aug 13, 2012 #3
    This seems a tad philosophical but... at the very least, it seems like you could have a perfectly reasonable "cause" for a "random" process, but the cause is necessarily hidden. I think that's the same as Hidden Variable Theory, which is I guess wrong because of Bell's Theorem, but I don't know exactly why.
     
  5. Aug 13, 2012 #4
    This isn't true. Nothing is truly random, even quantum mechanics. Although QM may seem completely random it isn't, it's just that we can never acquire the necessary information to determine precisely how the system will evolve.
     
  6. Aug 13, 2012 #5
    This is not known. All we can say is that we measure what appears to be a truly random phenomena when we measure quantum states. Although there exists deterministic explanations these are just speculations and have not been proven. At this point it is still an open question on whether the universe is really random or deterministic.
     
  7. Aug 13, 2012 #6

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    What can be said is a process that passes all tests for randomness may be truly random but of course we can never know if its the result of some deterministic process that has not been discovered yet and that process just happens to mimic randomness - tests for true randomness are pretty good these days and only some very sophisticated algorithms can actually pass it. If you believe nature just happens to be that 'good' - well it is a logically valid position - but I do not ascribe to it. Occams razor would suggest if we know of no underlying deterministic process and it passes randomness tests then the simplest explanation is it really is random.

    And as far as we can tell today QM is utterly and truly random eg random number generators based on thermal noise which is quantum in origin I am pretty sure pass every known test for randomness that even some reasonably sophisticated pseudo generators fail - although pseudo generators do exist that do pass those tests.

    Thanks
    Bill
     
    Last edited: Aug 13, 2012
  8. Aug 13, 2012 #7
    Shouldn't 'truly random' be regarded as the approximately 50/50 distribution of outcomes of hundreds of trials? If you toss a coin 222 times and it lands on tails approximately 111 times, it means it is truly random because nothing unobservable can be said to be affecting its 50/50(1 of 2) possibile outcomes. Does anyone object to this definition?

    Electrons and other fundamental particles do not obey the 50/50 statistics so they cannot be truly random. For reference, just look at the interference pattern from single electrons in a double slit experiment. I don't see how we could observe a newtonian(-like) universe based on a truly random quantum foundation. It would fall apart immediately, wouldn't it?
     
    Last edited: Aug 13, 2012
  9. Aug 13, 2012 #8
    Each of the fringes has a fixed probability of the electron/photon landing up on it, I thought.......for a given experimental setup (slit width and distance, electron distances etc).

    So conceptually the 50/50 i.e. fixed probability (totaling to 1), concept applies.
     
  10. Aug 13, 2012 #9


    The subtlety lies in the fact that the fringes are formed by the accumulation of thousands of single dots(landings). It's as if the electron travels as a wave through the slits but lands on the detection screen as a particle. After many many landings accumulate, we get the interference pattern and this is anything but random. It's so much more on the holistic side, that calling it random seems to require a re-definition of "randomness".
     
  11. Aug 13, 2012 #10

    unpredictability does not imply the lack of a cause, we cant confound determinism with predictability (or indeterminism with unpredictability)
    a-causality have to do with indeterminism but indeterminism does not have a relationship with randomess.

    by the way there are deterministic theories without being computable i.e. nopredictable outcomes and indeterministic process can produces a non-random sequence of outcomes.
     
  12. Aug 13, 2012 #11
    My position isn't necessarily that QM isn't "truly random" but what it means to be truly random. For instance we cannot know both the position and momentum of a particle precisely because observing it changes it; in other words the very act of observation constrains the observer to how much information can possibly be extracted from any given system. Because of this information constraint we cannot know precisely the initial conditions of any system to predict a precise outcome. Does this mean that the universe is intrinsically deterministic? Not necessarily because no observer could possibly compute the future--the future remains completely hidden. The universe isn't exactly deterministic or truly random in this sense.
     
  13. Aug 13, 2012 #12
    Randomness is really just chaos. Where predicting the outcome in a chaotic system requires hefty computation. True Randomness is where a chaotic system cannot have a predicted outcome because of a fundamental computational limit.
     
  14. Aug 13, 2012 #13


    another confusion,
    Chaos involves deterministic process i.e. no random.

    A deterministic system will have an error that either remains small (stable, regular solution) or increases exponentially with time (chaos). A stochastic system will have a randomly distributed error*, these systems are deterministic, meaning that their future behavior is fully determined by their initial conditions, with no random elements involved**.


    *Casdagli, Martin. "Chaos and Deterministic versus Stochastic Non-linear Modelling", in: Journal Royal Statistics Society: Series B
    **Kellert, Stephen H. (1993). In the Wake of Chaos: Unpredictable Order in Dynamical Systems. University of Chicago Press.
    Lorenz, Edward N. (1963). "Deterministic non-periodic flow". Journal of the Atmospheric Sciences 20 (2): 130–141
     
  15. Aug 13, 2012 #14
    That's literally what I am saying. Randomness is really just a deterministic system with an error that increases exponentially. True Randomness is when that error exceeds all computational possibilities on a fundamental physical level.
     
  16. Aug 14, 2012 #15
    You have to be careful with your statements. I don't think this has been shown at all. It might work like that but you can't make a statement saying it's certain that it does work like that because it has not been proven (and if you think it has been proven could you find some sources for your claim?).
     
  17. Aug 14, 2012 #16

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    Indeed.

    Thanks
    Bill
     
  18. Aug 14, 2012 #17
    You are correct I do not think it has been proven. Which is precisely why I am going to explore this avenue. I'll get back to you on what I find :)
     
  19. Aug 14, 2012 #18
    "Random" is a thirteenth century word, it was never brought into human language to be used in science. Randomness cannot be created using mathematics and I don't believe it takes place in nature, all my spidey senses say its impossible.

    If a radioactive particle decays and you say it just happened "randomly" then it would be an effect without a cause, that's insane. I don't know what gave the signal for the particle to decay but it makes more sense to me to say I'm unable to see what gave the signal and therefore (to me) its unpredictable.

    Mathematics produces statistically random numbers so why wouldn't nature just use them instead of performing a magic trick. If they would just throw away the word random and replace it with unpredictable or unknowable I could sleep at night.

    Pseudo randomness is real, random is a figment of the human imagination.

    Either that or I'm just a nut job :biggrin:
     
  20. Aug 14, 2012 #19

    bhobba

    User Avatar
    Science Advisor
    Gold Member

    You are not a nut job - simply very ingrained in classical thinking. It has a cause - the act of interacting with the environment causes it to decohere and for the particle decay to manifest in some kind of observational apparatus. This is exactly the same as any other quantum observation with decoherence taken into account. It has a property before observation such as a particle present or not present - the theory simply does not predict it with certainty - only probabilities. Do you consider flipping a coin insane because you cant predict if its heads or tails - but you know its a head or tail. I don't and most people (actually everyone) I know doesn't. This is purely a matter of getting used to a world view that is slightly different - that's all - nothing mind boggling weird to the point its insane weird - weird yes - insane - no.

    Thanks
    Bill
     
  21. Aug 14, 2012 #20
    I can accept that 13.7 billion years ago space and time sprang into existence even though it didn't have a place to happen. I can believe that every time the universe needs to make a decision it splits in two. And I can believe in the existence of multiple realities just so long as none of them can generate a random number :smile:

    Imagine a universe where a small plastic computer is in charge of creating motion in some particles, the computer runs its program and instructs all the various particles to start moving. It gets so hot with all this movement that the computer melts. From that moment in time it would look like the particles were moving randomly. In reality the motion would be pseudo random and the cause no longer exists.

    I could invent dozens of ways to create the illusion of randomness but not one to create true randomness.

    For the universe to be able to create randomness it has to be capable of making a decision, since I view the universe as mathematical then its impossible for it to make a "choice"

    The difference between something being truly random or just unpredictable is colossal.

    What possible mechanism could the laws of nature use to make a "choice"
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Is a-causality necessary for randomness?
  1. Evolving Causality (Replies: 11)

  2. Causality question (Replies: 61)

  3. Quantum causality (Replies: 5)

  4. Quantum causality (Replies: 5)

Loading...