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How Random Is Random ?

  1. Mar 17, 2006 #1
    Is there any limit to randomness?
    Can anything in the universe be completely random at all levels of observation ?

    I feel otherwise. But doesn't that also lead to the conclusion that everything we do is definite and predetermined in some way (including the fact that I am posting this thread and that you are reading it)?
  2. jcsd
  3. Mar 17, 2006 #2
    "Random" is really a human perception based on human values.
  4. Mar 17, 2006 #3


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    Female logic...

    <runs and hides from the Sisterhood>
  5. Mar 17, 2006 #4


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    Arunbg, I found myself asking this question for an A level physics project some moons ago.

    While I can't give you an answer (mainly because there are far too many people here who know far more about it than myself), you want to be thinking about issues with deterministic, but not necessarily predictable effects. The roll of a dice has a number of well understood physical interactions (distance thrown from, spin, air resistance, initial orientation, interactions with whatever surface it hits) which mean that theoretically, its outcome is predictable. But such tiny differences in any of these can affect the outcome in such a significant manner than to be able to model the system to get accurate predictions would be an extremely tall order. The same goes for why every game of snooker is different, and why we can't really predict the weather. Read up on chaos theory!
  6. Mar 17, 2006 #5
    But Brewnog, for chaotic systems like a dice roll, it's clearly not random- it's just so complicated that we can't predict what will happen. Still, if we had a fast enough computer and an accurate measurement of the initial conditions, we could in principle determine exactly how the dice roll would land, or what the weather would be like 5 years from now.

    For true randomness, there would have to be literally no pattern whatsoever. No matter how fast your computer, no matter how good your data, you would be unable to make any predictions at all.

    For that criteria, I think human consciousness is the best bet. You could keep track of everything a person has done their whole life, and use an infinitely fast computer, and still not be able to predict (perfectly) what they would do in a situation. Free will makes it hard to find patterns.
  7. Mar 17, 2006 #6
    Is your question one of perception of randomness, or the mathematics behind randomness (sp?)

    If I was to write a progam in C for example that produced a random number after you click a button. The result for you would be random, since you cannot predict the output because you cannot see the source.... Off course you could take a data sample and backward engineer the result to find my algorthim, however if my algorithm was strong enough you would have to take many many many (approaching infinity) results...
  8. Mar 17, 2006 #7
    A computer program is not random. It follows a repetative cycle (only a big one). In real life, random is random. A quantum computer can make random numbers, and nature itself makes random "numbers".
  9. Mar 17, 2006 #8
    "Free will" is a pretty primitive, and also religious, term for people's decision making processes. You could, in principle, create a program that ran on the same dynamics if you could actually pinpoint what those were. The trouble is there can easily be a massive amount of information needed to understand why a person makes one choice and not another, and the decision making processes themselves evolve as the person learns more and is altered by experiences. None of this is random, just unbelievably complex.
  10. Mar 17, 2006 #9


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    No, not so.

    Even in bounded chaos, one can have randomness (stochastic phenomenon) that is not predictable.

    The best models and predictions are simply approximations, and always will be.
  11. Mar 17, 2006 #10
    The output of a program can be random from the view point of someone looking at it's output if you can not see/understand/decrypt the alogorthm used to create the stated output.

    the output is percieved as random!

    I never said a computer program was random!

    (This is basic cryptography)
    Last edited: Mar 17, 2006
  12. Mar 17, 2006 #11
    It may be a primitive term, but that's because it's directly observable. We're getting in to philosophy now :yuck: , but I don't think it reguires believing in religion to recognize that you have control over your thoughts and actions in a way that, say, a computer does not. Science might be able to one day explain how the brain generates this free will phenomenon, but it can't get escape the fact that it exists. Although, I suppose "random" isn't really the right word to use... "non-deterministic" would be better. My main point was that, no matter how much you knew about a person's brain, you'd never be able to perfectly predict their decisions.
  13. Mar 17, 2006 #12
    I'm not sure what stochastic phenomenon means. But how can something which is completely determined by physics (eg, a dice roll) be really random? Nonpredictable, sure, because we're limited in our knowledge of both the system and of physics. But that's not the same as truly random.
  14. Mar 17, 2006 #13
    I agree with your last sentence.

    "Free will", though, is a term that originated in religion and which retains religious connotations. The phenomenon you're refering to is just a matter of the minds sophisticated ability to sort through a tangle of desires, values, and information. The reason this would be so hard to predict is that it would be so difficult to simply uncover what they all are in a given individual, and also, to understand the complex dynamics by which a person sorts things out. On top of it all, since a person is constantly recieving information from the world around them all of the factors are in constant flux: their desires are modified, and their values shift.
  15. Mar 17, 2006 #14


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    Merriam-Webster online dictionary.

    Now with respect to - "something which is completely determined by physics" - Nature is random and chaotic - Nature determines the 'Physics'. As far as people are concerned, physics is just the study of nature, and at best we develop approximate models as to how we think Nature works. That's all. Sometimes we do a good job, and other times, we fall short.

    The result of a die roll or dice roll is still random.
  16. Mar 18, 2006 #15
    Let me repeat my question.
    Is anything in the universe completely random at all levels of observation?
    The apparent randomness of your algorithm to an outsider
    is because of his level of observation.On the other hand the output of the program is not random to the programmer.
    I feel that the term random is unfortunate and should be replaced with something like undetermined (especially in case of probability and the like)
    From a more scientific point of view, aren't randomness and probability the building blocks of quantum physics?
    Doesn't the uncertainty principle refute our views on absence of absolute randomness (it is impossible to measure with absolute certainty the momentum and position of an object)?
  17. Mar 18, 2006 #16
    I would think the diffraction experiment is random. We have no way to know where the electron goes. We just know a probable distribution of it from a statistical standpoint.

    The uncertainty principle says that we cannot know with 100% certainty the position or the momentum of any object, because we disturb the object when we measure it. I do not see how this refutes absolute randomness; it just means we have no way to know exactly position or momentum. That's a measurement issue, which for the double slit experiment, does not help us any. We can see where the photos go when they make the diffraction pattern, (That’s measurement issues) we CANT say what happens along the way. It is acting as a wave; we don’t know where the photon is. When it does interact it no longer behaves as a wave, it interacts as a particle. Meh, my explanation sucks.
  18. Mar 18, 2006 #17
    I don't think anything is random at any level of observation. I don't think cause and effect ever just cuts out and allows anything to perform any action without a cause. Things appear random to us when we don't understand the causes.
  19. Mar 18, 2006 #18
    I quote my textbook(high school national syllabus text mind you)

    So then why is the object disturbed and is there no way to measure the magnitude of this disturbance ?
    If there is indeed no way, then it becomes completely random and all our arguments are in vain.

    P.S: I have never understood the uncertainty principle as taught in school.
    Then again, it must be because I just don't know enough.
  20. Mar 18, 2006 #19
    What's the context of this statement?
  21. Mar 18, 2006 #20
    Yes. What I am saying is that by using the instrument, you must disturb what you measure. It is a fundamental issue. It does not matter how 'good' your instrument is, it HAS to distrub/interact with what its measuring.

    Here, perhaps this will help:

    Let's put it another way, suppose I am trying to measure the location of a particle. I try to do this by using a wavelength of photon. Well, when that photon meets the particle, it is going to interact with it, thereby changing the state of the particle, and thus its momentum in the process. So the better I measure its position, the less I know its momentum.
    Last edited: Mar 18, 2006
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