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Poor explanation of 'random'

  1. Aug 14, 2009 #1
    It seems to me that when 'randomness' is referred to, the explanation is always describing what 'random' behavior is not. I would equate 'random' with: no history, no dependence on intial conditions, no pattern, no predictable order. It only argues that 'random' behavior or outcomes are based on something other than what is listed above. So, my question is: what 'is' randomness, without descriptions of what it is not???
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  3. Aug 14, 2009 #2


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    In probability theory, a "random variable" is simply a probability measure on some space -- a function that, among other properties, assigns a real number from 0 to 1 to each "event" of the measure space.

    (e.g. one might consider the discrete space {1,2,3,4,5,6}, and the measure P that assigns to each subset S the number |S|/6)

    In complexity theory, the "Kolmogorov complexity" of a string is its shortest representation (according to some reasonable scheme). It turns out (I hope I state this properly) that for any computable property Q, the proportion of incompressible strings that have property Q is the essentially the same as the proportion of all strings that have that property.

    In particular, this means incompressible strings have no "features" that make them stand out from other strings, and so this makes for a good measure of randomness.

    Unfortunately, this system is only really applies in bulk -- it cannot be used in any reasonable way to talk about individual strings.
  4. Aug 14, 2009 #3
    Randomness is simply a word that is defined in terms of a negative. There are many such words -- such as "unkind", "antisocial," "atypical"...the list goes on. By definition, these words are defined in terms of the lack of something else. So what?

    Randomness exists mostly only in Utopian statistical theory. The only potential source of randomness so-far known to man is in quantum theory...so this could be used as a positive example of randomness, but it doesn't change the fact that it is impossible to re-define a word that is defined in terms of a negative in terms of positive(s).
  5. Aug 14, 2009 #4


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    Alright, but how about a system that behaves almost exactly like a system that has no history, no dependence on initial conditions, etc? Chaotic systems have such sensitive dependence on initial conditions that, for all practical purposes, they behave like a random system would.
  6. Aug 14, 2009 #5
    A random event has no deterministic cause - not just no cause that we know of, but no cause period that can exactly explain the effect.
    Last edited: Aug 14, 2009
  7. Aug 14, 2009 #6


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    How can such an event occur at all then?
  8. Aug 15, 2009 #7
    macro chaotic systems are deterministic in principle, just not in practice. But, this doesn't seem to be 'random' as it is defined here, as future behavior is based on the initial conditions (in chaos theory), it's just not predictable. I think true randomness can have no ties to initial conditions, if it did, and the behavior of the system is dependent on these initial conditions, then this seems to be the cause, and therefore the system becomes determined (in principle).
  9. Aug 15, 2009 #8
    If there was a 'how', it wouldn't be random.
  10. Aug 15, 2009 #9
    In addition to JoeDawgs response... who said random events occur at all? :)

    Besides many (but not all) quantum physicists, of course.
  11. Aug 15, 2009 #10
    Correct... unless you consider that random events may be bound by initial conditions. Events with no definite cause may still be bound by preconditions, even if they are not determined by them. Such situations are proposed by some interpretations of quantum mechanics, for example.
  12. Aug 15, 2009 #11


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    My point is, it could not occur in the first place. A penny cannot fall - randomly or otherwise - if it has not first been tossed.
  13. Aug 15, 2009 #12
    It seems, then, that you believe in deterministic causation in nature. In this case, no event can be truly random. We can still have the word "random" and use it approximately in 2nd order macroscopic statements of cause and effect. We say that a coin flip is random, but it's understood that if we could have complete knowledge of the toss it would be, in principle, possible to determine the outcome ahead of time. This is the classical mechanized world view.

    QM is more fuzzy about random events occurring at the basic physical causal level.
  14. Aug 15, 2009 #13


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    I believe that the reason for decay of a nucleus will eventually be explainable. If the decay or any other random subatomic event truly had no causal event, then what is to stop it from decaying into multiple hydrogen atoms, or into a pot of petunias? See, there are causal rules around decay; it happens virtually the same way every time. The fact that the time delay (of an individual nucleus) doesn't seem to follow a rule suggests simply that we don't know it yet.
  15. Aug 15, 2009 #14
    At the quantum level we have absolutely no idea what forces are at play, and we can't predict what outcome will occur with any level of certainty at all. Arguments can surely be made for an assumption of determinism in nature... but it may be harder to get there than would initially be expected.

    Niels Bohr, based on Kantian ideas of the primacy of classical properties, simply denied that there is any underlying level of determinism to be uncovered. David Bohm, assuming the primacy of deterministic natural laws, came to the conclusion that such laws exist but we can in principle never know what they are. According to Bohm, we can only reveal lower and lower levels of an infinitely recursive reality, but we can never explain anything in terms of the deepest level of reality.
  16. Aug 15, 2009 #15


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    Agreed. But that is not tantamount to saying there is no causitive agent.
  17. Aug 15, 2009 #16
    This is a standard http://en.wikipedia.org/wiki/Argument_from_ignorance" [Broken] If its random, then yes, it could result in a pot of petunias, but thats really not just one random event, its quite a few. The hydrogen thing involves fewer.

    So yes, there could be a pot of petunias floating somewhere around Orion's belt. But there is no frequency to random events, and the universe is big, so the fact you haven't seen it happen doesn't mean much.

    All you've said here is you don't believe in random events.
    Last edited by a moderator: May 4, 2017
  18. Aug 16, 2009 #17
    Well, how about this.
    Determinism means a causal event chain. A chain that develops over several stages over a period of time.
    A random event would be an event that has no event chain.
    This would essentially mean it happened instantaneously and that there is no causal process for why it happened.

    Using this definition, is there really any way to understand such an event?
    I would say no.
    I'm not going to try to say that I have all the answers, but it does seem odd to me if such events exist in the universe, either in quantum physics or any other macro/micro level.
    The only way I can see it looking random is if something is injected into our universe from another dimension, or similar, because then the process would not have started in OUR universe.
    But this is of course speculation to the extreme. Just saying.
  19. Aug 16, 2009 #18


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    Or how about less extreme: simply a causal event occurring in a dimension we do not have access to - a la the higher 4 dimensions of string theory.
  20. Aug 16, 2009 #19

    I agree. It seems without a cause to determine (in principle) the outcome, then the outcome can be boundless and without order or structure. The fact that the decay of a nucleus occurs the same in multiple events leads one to the notion that there is a form and structure to the decay and this is essentially what determines it (in principle). However, the cause may never be known. Kind of like Chaos theory. If we go far enough down the causal chain we lose sight of the initial conditions, we know the result is caused by them, but the interactions that brought the result is too complicated to understand or it is simply hidden from our knowledge.
  21. Aug 17, 2009 #20
    It would seem that to predict just which atom will decay and when it will decay would assume that each atomic nucleus of a particular isotope is distinctive in some way. This would imply some hidden variable(s) involving nuclear properties. Does anyone have any idea what properties these might be? For example, are there different kinds or combinations of gluons? I think we know the quark structure of nucleons, and afaik, it is the same for all nucleons.
    Last edited: Aug 17, 2009
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