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

Looking for explanation of randomness.

  1. Jul 16, 2006 #1
    Hi all, for some time I have been wondering about something I’m not too sure on. Please could someone tell me how randomness can exist? That is to say on a molecular level, or on any level things happening without cause or justification? Patterns may be too hard for us to currently understand or predict however it would be wrong to say because of that randomness exists.

    In a universe described by some driven by chance some have said anything can happen. I once heard a scientist say in all seriousness say there’s a chance we could disappear and reappear in mars then reappear here. Would like an explanation of how true randomness can exist.

    By saying that there’s a chance anything can happen your implying there is randomness on a large scale, also in a more Newtonian universe there can not be infinite dimensions, parallel universes because things can only ever happen one way.I believe that if something moves on a molecular level it’s because of forces acting on it.
     
    Last edited: Jul 16, 2006
  2. jcsd
  3. Jul 16, 2006 #2

    Danger

    User Avatar
    Gold Member

    Hi, Wartorious. Welcome to PF.
    On the macro scale, you are correct. Everything happens as a consequence of preceding events. The problem is that when you get down to the quantum level, where those preceding events take place, there is no predictability. (Clarification: you can predict the probability of something happening, but not the certainty of it.) Heisenberg showed that, and it hasn't been refuted. On a lesser scale than your Martian example, all of the gas molecules in a sealed container could end up on one side, leaving a vacuum on the other. The odds of it happening, however, are vanishingly small. When you get into stuff like quantum tunnelling, virtual particles, etc., there are simply too many variables to even consider tracking accurately. We don't even know, for example, how many different subatomic particles there are. Right now, they're trying to find the Higgs bosun and graviton and maybe a couple of others. Every time that a new 'brane or string or whatever theory comes up, it suggests new and more exotic particles. Bottom line, we are not even close to understanding how the Universe works. It seems pretty well established, though, that it is ultimately based upon randomness.
    This is not one of my more knowledgeable areas, so I'll leave any further discussion to the experts.
     
  4. Jul 16, 2006 #3
    Well how can anything exist? Randomness is just an instance of that particular problem. :smile:

    Why would it be wrong? :confused:
     
  5. Jul 16, 2006 #4
    We can assume we exist. Randomness is however much more hypothetical.

    So randomness is a tool, like numbers to make up our lack of understanding of the universe? If something’s hard currently to measure you would say it can never be measured or predicted because its random? I don’t deny the universe may be incredibly complicated and measuring things in chance a useful way of thinking yet the universe, I believe is balanced and acts without chaos or randomness. If partials were to react erratically without any kind of forces making them act that way then I don’t believe complicated structures could ever exist like they do now. We may call the sky blue, yet its not blue, its just a label we place on it, yet because we call the shy blue then we change the perception of the sky and start to corrupt the truth, I have seen the sky be every colour of the rainbow yet we still call it blue.

    If we call the universe random then surly we will put less effort into understanding the true cause of things. I would like to see the jar of gas becoming half unpressurised and even if it did I believe there would be a cause of it and would not prove randomness nesseraly.
     
    Last edited: Jul 16, 2006
  6. Jul 16, 2006 #5
    Your question was how can randomness exists.

    We are talking about if elements of nature have intrinsic randomness right? Then how is this question relevant? :confused:

    No.

    Well if you believe that then what is your question? You seem to have made up your mind that the universe cannot be random. So what then is there to discuss?

    Well if you postulate that nothing in the universe is random then it is logical that any person making a statement concerning the randomness of the universe has not "truly understood" it.

    So this topic does not seem to be a query but rather a sermon. "Nothing in the universe is random and anybody who says that something is not random simply does not truly understand it".

    :smile:
     
  7. Jul 16, 2006 #6

    vanesch

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    It is quite a subtle issue and people are still debating what randomness is. Part of the answer is rather simple: randomness is ignorance. When we assign probabilities to events, it is because we don't know them precisely. Randomness is the essential aspect of a signal (if you're on the receiving end): you will get one of different possible messages, but you don't know which one. This makes the "signal", before you received it, a "random quantity". And here we see the "ignorance" part: the emitter DID know, and for the emitter, the signal is of course NOT random.
    You can get quite far already with the view that randomness describes ignorance. However, the question remains: is ALL randomness, simply reducible toignorance ? Or are there other forms of randomness in nature ? (sometimes called irreducible randomness).
    Note that here, one should make a clear distinction between related concepts: determinism, causality, "free will", ... because often one confuses them when talking about randomness.
     
  8. Jul 16, 2006 #7
    I am of a beleif that although we can observe randomness, it is only so because we lack the resolution or understanding of the mechanisms underlying that variation.

    Admitedly i dont fully understand things, but this is my stance untill i can prove firmly to myself otherwise or that my hypothesis/beleif is true or false.

    When i consider this, i think the universe to be ultimatley entireley deterministic. Randomness is then just a psuedo randomness brought about by a lack of complete knowlage of the process, that is the Seed or source and the function or equations that generate that randomness.

    I take the anthropic principle and the big bang as possible mechanism that, although i admitedly dont fully understand, will help me decide if this stance is correct or not.

    Take for example the flip of a coin.

    When we toss a coin, the outcome is said to be random, with a 50/50 chance of either outcome. I dispute this, i would say that the outcome of the toss is entirley determined by the initial variables that go into the "flick" and that these variables are essentially deterministic, however extremley chaotic and difficult to predict.

    I look more at probabillity as a way of describing situation where we lack complete information.

    I know that this is most likley an incorrect model, but i look forward to learning the outcome regardless.
     
  9. Jul 16, 2006 #8
    i see we use words as determinism and initial variables and randomness. I think we make assumed understood connection in our posts. They are related but in physics very different level than in spoken everyday language. Plus there is pure mathematical randomness (for which i recommend mr chaitin's book, meta math).

    Chaos theory which may connect determinism, randomness and initial variables is in simple word non-linearity. Such systems may be deterministic, but unpredictable and mainly unrepeatable in reality.

    nope, one may know completely equations governing a system but still get unpredictability.

    Given that we may never know with infinite precision initial conditions of a system, we are bound by certain unpredictability in certain systems.
     
  10. Jul 16, 2006 #9
    yes im afraid my maths is too weak to fully understand these terms, thanks for the explanation though.
     
  11. Jul 16, 2006 #10
    I did find the above quote slightly insulting, however I don’t mind. Was trying to justify my opinion and understand others.

    Thanks, I do feel I understand better, although I’m not sure why it’s in the philosophy bit however nearly all the modern theories involve as much Rationalism as empiricism so im not too insulted.

    Thanks all
     
  12. Jul 16, 2006 #11

    -Job-

    User Avatar
    Science Advisor

    An important variable is the degree of freedom of these random events. If events are random, but over a finite interval, then some structure may arise out of it.
    For example, a given particle's position 1 second from now might be considered a random variable, but this random variable is over a finite interval. The reason is that the particle can't travel faster than the speed of light, so 1 second from now its position is random but within a given radius of the original position. So the particle, whose position 1 second from now is random, is guaranteed to be within a certain finite region of space.
    There is then the possibility of some certainty arising out of an underlying randomness.
    At a more macroscopic scale, it might be that any given random variable's "freedom" is so small, by comparison, that the Universe, from this macroscopic perspective behaves as a deterministic Universe; even though there is an underlying randomness to events.
    I think, to go further, it might be possible to show that for every Universe in which no random variables have "infinite freedom", there must be a scale large enough, such that, at that scale, that Universe behaves deterministically. This could be due to what we might call "loss of precision".

    Loss of precision happens in computers because computers have a finite amount of storage for each number causing numbers to be truncated/rounded. If a number's randomness freedom is tiny, then an eventual loss of precision will eliminate the randomness of that number. Similarly at a large enough scale, if an event's randomness freedom is tiny, an eventual loss of precision will eliminate the randomness of that event.
     
    Last edited: Jul 16, 2006
  13. Jul 17, 2006 #12

    vanesch

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    As I said, "randomness", "causality" and "determinism" are usually mixed with eachother.

    Determinism means that there is some causal structure (each event has its own past and future), and that, given all there is to know about an events past, the laws of nature determine uniquely what happens at said event ; in other words, there is no freedom of any choice anymore.

    However, there's a difference between determinism and randomness. Determinism has something to do with "predicting the future", while randomness has a priori no link with any causal or temporal flow. Randomness applies as well to the past as to the future. Randomness means "one out of many". You have one corpse, and 6 potential murderers. Who did it, is random, until you find more evidence.
    The outcome of a football game is random (even if the game is over), until you learn about it (by watching the video or hearing it on the radio or something).

    For instance: is the assignment of your telephone number "random" ?
    Are numbers from a pseudo-random number generator algorithm "random" ?


    Yes, what a deterministic time evolution does, is to link the randomness of the outcome with the randomness of the initial state. Your ignorance of the outcome is equal to your ignorance of the initial state.
    And if you apply the deterministic time evolution in the -t direction, it works in the other way: what is the randomness of the initial state, given that I know the outcome.

    However, we are confronted also with quantum mechanics, which seems to indicate that there is some irreducible random element in nature. And then, it doesn't even make sense to say so, because every theory which is random, can be replaced with a theory which is deterministic and which has "hidden variables". So be careful when asking what is "randomness" while thinking about "the laws of nature".

    So maybe your question is: "is nature deterministic" ?
     
  14. Jul 17, 2006 #13
    Im aware of this, but lacking enough knowlage to really comment to deeply on it so i omitted it for simplicity.

    I apreciate your comments and ill try and reflect on them a bit more.

    Indeed, that is one of the underlying questions.
     
  15. Jul 18, 2006 #14
    I find this discussion rather interesting.
    With deterministic theory, there is a demand on value reproducibility. In other words, independent research must exhibit some tangible aspect of reproducible results; else the theory might be considered invalid, undeveloped or even a "sham"(such as supposed "free-energy" devices)

    With "randomness", the methodology of verification takes a striking twist:

    Randomness can not be "proven" because it is not possible to define exactly what constitutes the differance between randomness-vs-highly convoluted determinism.
    A mathematical model for randomness does not exist, nor can it ever exist, as it can not inherently self-validate.
     
  16. Jul 18, 2006 #15

    Claude Bile

    User Avatar
    Science Advisor

    On a quantum level, true randomness exists - you can get two different results for the exact same initial conditions. Psuedo-randomness, even chaotic systems do not share this quality.

    It is an interesting question, how randomness can exist, but consider the inverse proposition - how can it not exist? In other words, given our apparent freedom of choice, how can the universe be deterministic? While we have yet to reconcile quantum randomness with conscious choice, the mere fact that it opens up the possibility of choice seems to (at least in my opinion) validate the existance of randomness over pure determinism.

    Claude.
     
  17. Jul 18, 2006 #16
    You cannot use this as a scientific argument unless you can demonstrate that we have a freedom of choice.

    I think it much more plausible that we simply think that we have freedom of choice, but thinking something does not make it so. :smile:
     
  18. Jul 18, 2006 #17

    Doc Al

    User Avatar

    Staff: Mentor

    I don't see how randomness can possibly preserve freedom of choice. If something is random, how could you have chosen it?
     
  19. Jul 18, 2006 #18

    vanesch

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Because your choice is random ?
    I think the point is that in a deterministic universe, it's clear that there's not such a thing such as freedom of choice (given that everything is already determined since the initial conditions). So the only *hope* to have the *possibility* of a freedom of choice is an element of "randomness", here, of non-determinism : meaning: what happens at an event is not determined by initial conditions of the past.
    But it doesn't mean that because there is no temporal determinism, that the random outcome is a result of some free will. It only doesn't forbid it (as determinism does).
     
  20. Jul 18, 2006 #19

    Danger

    User Avatar
    Gold Member

    Claude, that is one of the best explanations that I've seen in print.

    Despite your claim of atheism in another thread, you certainly seem to take the 'Jesus Freak' approach to things (including in that thread, as evidenced by your hostility toward homosexuality). I'm a true atheist, and therefore 'superdeterminsm' is totally unacceptable. That condition could not exist without a 'supreme being' of whatever denomination. As a side note--Freudian slip?--I just caught that typo in time. My first approach was 'demonination'. Hmmm...
     
  21. Jul 19, 2006 #20

    vanesch

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Eh, sorry, this has nothing to do with religion. I'd rather say that, if the brain is governed by essentially classical laws (with some noise, which is however not on purpose), there's not much room for free will outside of the laws of nature: what your brain decides is what is determined by these classical laws and the noise (which, I take it, was not "on purpose"). Afterwards, you get the illusion that that is what you "really decided".
    Of course, the noise being random, it could be that your "free will" resides in a careful tuning of this at first sight random noise, in order to influence decisions in the right direction. This would then imply that the essence of our brain function doesn't reside in the structure of our brain, but in the thermal noise, which is a strange proposition.
    It is only when postulating a soul intervening in the laws of nature that you can really talk about free will.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Looking for explanation of randomness.
  1. Vacuum explanation (Replies: 4)

  2. Randomness ? (Replies: 8)

Loading...