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Everything in nature is truly random and unpredictable

  1. Dec 17, 2005 #1
    quantum mechanics basically says that everything in nature is truly random and unpredictable. However, isnt it just as likely that there are particles we are unable to detect that cause everything to happen. Because we can't detect them, everything would seem random.
  2. jcsd
  3. Dec 18, 2005 #2
    Individual quantum events are unpredictable. Random means unpredictable. QM places fundamental limitations on what can be experimentally determined. So, as far as we can be meaningfully (ie., unambiguously) concerned, nature, as it's revealed to us through experiments, is random.
    But is nature, as it exists and behaves independent of experiments, truly random? There's, apparently, at least wrt the current state of the art (and science) of physics, no way to know that.
  4. Dec 18, 2005 #3
    As we'd expect, some people are happy with having fundamental theory based on chance events but other people want to find a cause for why one thing happens and not another. Most famously, Einstein didn't like the idea of using chance events as fundamental.

    Hidden particles is one of the approaches to it. When you consider all the mysterious dark matter and other stuff making up much of the universe and which we didn't know about until recently, other kinds of hidden particles influencing events doesn't seem too outlandish. :biggrin:

    One problem is finding how to tell a theory based on chance events apart from a theory with hidden particles or other theories.

    It's quite interesting to wonder if there is really a cause to events. :smile:
  5. Dec 18, 2005 #4
    No QM DOES NOT say that.

    First of all the "everything in nature" part is wrong since QM only applies onto "atomic distance scales", not onto the macroscopic world.

    Secondly, the "random and unpredictable" part is also wrong. If this were true, than why would we need QM ? Since QM obviously is correct in predicting physical phenomena at small distance scales, your statement is fundamentally incorrect. What you want to say is this: "at atomic distance scales, nature becomes probabilistic". Being probabilistic is NOT the same as being a random event...

    The only "problem" with QM is this: as distance scale lowers from macroscopic to atomic phenomena, where (ie at what specific distance scale) do we make the actual transition from Newton to QM ?

  6. Dec 18, 2005 #5
    quantum effects can be taken to macroscopic levels, its just negligable. Also, probabalistic does mean unpredictable. what can you predict at a quantum level? You can only predict the average of a large group, not the outcome of a single event.
  7. Dec 18, 2005 #6
    Actually, QM isn't even "random" for some measurements. If you prepare a particle to be in an energy eigenstate, you will keep measuring the same energy. Similarly with momentum states in certain situations. The uncertainty only really arises when we start talking about multiple measurements or making measurements in eigenstates of incompatible observables.
  8. Dec 19, 2005 #7
    But, one does not need to do that. That was my point.

    Actually this is a classic interpretation error. You CAN predict the outcome of a measurement but the clue is that QM gives you the probability that this specific outcome shall occur.

    Also another thing, The HUP for momentum and position does NOT imply one cannot measure the position of a particle exactly. YOU CAN and this measurement is ONLY limited by the accuracy of your apparatus. For example, suppose you measure the position of an electron that has definite momentum. The spread on position is infinite. This means that if you would redo the measurement under the same conditions and measure that same electron, you would get a different value for the position.

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