Solid evidence for true randomness in in the universe?

  1. Is there any solid evidence for true randomness in in the universe? Or is it with everything more the idea of "we could theoretically predict it if we had ALL the information"?

    Is everything thought to be essentially deterministic at some level?
     
  2. jcsd
  3. vanesch

    vanesch 6,236
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    On the contrary. Everything is thought to be essentially random in a fundamental way.

    cheers,
    Patrick.
     
  4. Can you give me a solid exmaple of this, and why it is thought to be so?

    Years ago I had thought that was the case, then I remember reading that that was a common misconception about QM theory.

    I am involved in a discussion with someone where their viewpoint rests solidly on the belief that the universe in completely deterministic, and true randomness does not exist in any form anywhere, anyhow. Only lack of information.

    If he is wrong, I wold like to be able to point to something solid to say so. If specific experimental evidence, then at least why and where exactly randomness is thought to occur.

    Thanks.
     
  5. The example that comes to mind is a single photon hitting a beam splitter. Does it go through or reflect?
     
  6. Yes, but why is that thought to be random, as opposed to there just being a lack of complete state information to know what will happen?
     
  7. ZapperZ

    ZapperZ 30,170
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    Because when there is a superpostion of states, QM doesn't tell you which state you will end up measuring when you actually make a measurement. As far as WE currently know within conventional QM, there are no underlying mechansim that selects these states. It is truly unknown and thus, randomly selected according to its probability coefficient.

    This is unlike throwing a coin, for example, where your ignorance of the intricate details of the mechanics causes you to lump them all into a probability. In such a situation, classical mechanics STILL dictate that if you do know all there is to know about the process, then the outcome of that coin toss is deterministic. No such description exists for the QM case. If your friends are saying that there has to be a similar underlying mechanism that causes a selection of states, then they are speculating beyond what is known conventionally. If one can do that, then all bets are off and you might as well speculate anything you want.

    Zz.
     
  8. Ok, thanks.
     
  9. vanesch

    vanesch 6,236
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    I would like to add to what Zapperz explained, that we have serious indications that even if there would ever be such a deterministic explanation for the randomness in QM, that this explanation has to satisfy some bizarre properties which make us believe that it is in principle impossible to know the state of these underlying properties.
    The reasoning goes as follows: Bell's theorem tells us that such a deterministic explanation (it is called "hidden variable theories") can only coincide with all QM predictions if it is "non-local". Experiments indicate strongly that cases where Bell's theorem plays a role, nature still seems to follow the QM predictions (I say "indicate strongly" because there are some rather implausible, but possible, loopholes in the experimental setup).
    But a "non-local" theory is a theory, according to special relativity, in which cause and effect can switch roles (if event A causes event B in a non-local way, then for another observer, B arrives before A arrives). So if we are not going to be able to influence the past, we better never have experimental acces to this underlying mechanism.
    But of course, it is always possible that QM is wrong, that special relativity is wrong (and that the moon really is made of green cheese), so there is always a scientific doubt to statements that contain a "never" or an "always".
    But for all what is known today, we really think that the randomness in quantum mechanics is fundamental.

    cheers,
    patrick.
     
  10. thanks, that was really helpful ... mentioning specific experimental evidence was just what I needed.
     
  11. in reality you can not think of the universe as completly random, but you can never know everything there is to know about it . even if you could obviously the predictions would eventually come to a horrible standstill
     
  12. ZapperZ

    ZapperZ 30,170
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    You obvously didn't get my example of a coin toss and WHY this is DIFFERENT than QM's description.

    Zz.
     
  13. How can we say that there is not deeper framework to physics behind that of QM. I'm not disputing what QM says about how the subatomic world behaves, just whether it is ultimately random or not. I don't believe it is. Randomness doesn't seem like a solution to me. I'm not saying it isn't, but I can't make any sense of the concept. To me if something exists it has to be confined in a system of rules, or laws. And out of rules and laws I can think of no way to create randomness, only the relative appearance of randomness.
     
  14. ZapperZ

    ZapperZ 30,170
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    You have the luxury to spew out what you BELIEVE in without any physical justification. Physics, luckily, has no such luxury. You don't have to show any proof, any observation, that would support your idea. Physics does! You merely have to believe something simply based on your own personal preference and tastes. Physics can't!

    Based simply on what we KNOW, what we can PROVE, and what has been OBSERVED and considered as scientific evidence, there are no underlying mechanism behind the apparent randomness in QM, and this includes the selection of states out of a superpostion. You may speculate as much as you want, but until and unless you are willing to provide solid evidence to contradict such assertion, you might as well speculate that bored angels on pinheads with nothing better to do are doing the selecting for us.

    Zz.
     
  15. I find it to be speculation to say that just because something appears to be random that it is.
     
  16. ZapperZ

    ZapperZ 30,170
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    Then maybe you need to reread what I wrote, especially when I described the coin toss, and when I mentioned about the "underlying mechanism" and the lackthereof behind the selection of a state. You are asking for things BEYOND what we know. All I'm saying is that those are BEYOND our knowledge, and THAT is what I meant as speculation.

    Till there are evidence to the contrary - till you can show that the superposition principle is wrong and that those SQIUDS experiment and H2 molecule bonding-antibonding energy gap can be explained by something else, you have no evidence to contradict what we know. All you have argued so far are simply based on a matter of tastes.

    Zz.
     
  17. QM is an incomplete theory of the universe. It makes specialized predictions. In every other instance where a theory was incomplete that I can think of it has always been because it was an approximate way of viewing a situation that allowed it to be effective for making predictions at a certain scale but was ultimately a part of a larger framework that worked differently. What QM precisely shows is that according to its inaccurate perspective that happens to be quite good at specialized predictions things appear to be random. Probability happens to be quite good at predicting that a coin flip will be 50/50 as well, but it turns out it is more deterministic than that. Every instance of probability that I can think of can be explained, except in QM. And as far as I know it is impossible to explain actual randomness. For these reasons it would be a leap of faith for me to believe what was happening on the QM level was ultimately random.
     
    Last edited: Oct 23, 2004
  18. ZapperZ

    ZapperZ 30,170
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    None of what you have said is based on ANY evidence. Read again. It is obvious that you do not understand the difference between scientific evidence and simply a matter of taste. You have offered ZERO evidence.

    If QM is "incomplete" then there would be tantalizing evidence that it is wrong, or unable to describe a phenomena. Look back at the history of science. At any instant when a theory is incomplete, there are obvious experimental evidence which it cannot explain! Pick ANY experimental evidence that we have so far and point to me where QM failed. The fact that there is a wide-ranging application of QM and large impact of its validity made it rather strange that you would claim that QM is only valid for "specialized" area. You don't think that the semiconductor in your electronics depends on QM, or the MRI that we use in medical physics made use of our knowledge of QM?

    Why is it that this thing has deteorated into another "QM is not valid/complete" discussion? In case you haven't discovered already, such issues have gone NOWHERE in the past. This isn't the first time someone has brought this up.

    Let's get back to the original question : is there ANYTHING that we know of (NOT speculate) in which the outcome of a result of a measurement is not based on some underlying mechanism that can predict with certainty that outcome? If you cannot show that the outcome of a Schrodinger cat-type experiment, such as those SQUIDs experiments, are based on some definite underlying mechanism that made it deterministic, then all your arguments are unverified speculation and we have nothing more to talk about.

    Zz.
     
  19. What I'm actually trying to argue is that both viewpoints are equally speculation, QM does not show evidence one way or another for natures deepest properties. QM has shown a way of making accurate predictions using probability at a certain level, that is all it can claim to say. If QM was a theory of everything it may be able to say something inherent about the universe at large, but it is not. For instance it does not describe gravity, space, or time.
     
  20. ZapperZ

    ZapperZ 30,170
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    But it still can! I mean, since we are SPECULATING, I can play that game too.

    BTW, the fact that QM STOP at describing something that we have no ability to measure or detect is NOT speculation. It only says what it can, and NOT go beyond that. This is NOT speculation. It is simply knowing when not to act foolish.

    You are still avoiding the issue. The fact that, unlike throwing a coin where even classical physics indicated that this is a deterministic event, a measurement of state out of a superposition has no such thing! This is the whole issue here! So if one wants to answer the original question of this thread based on what is accepted and verified and NOT based on speculation, there is only one way to answer this.

    I am NOT saying QM is the end of all theories. Let's be clear on that. As an experimentalist, I love nothing better than to prove a theory wrong. However, what I "suspect" or "believe" or "want to happen" is NOT the same as what we know of and accepted today. I can make such distinction and would not want to answer this thread based on MY preferences. That was what I was pointing out to your original reply. You have not separated what you "believe" or think should happen with what is known and accepted.

    Furthermore, let's not get into this "theory of everything" fallacy. I have written enough about this that it would be funny if you think that I would push for such a thing.

    Zz.
     
    Last edited: Oct 23, 2004
  21. My answer is no. It was good discussing this with you however, you definitely know your QM.
     
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