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Heisenberg incertitude principe ? contradicting ?

  1. Oct 26, 2007 #1

    JPC

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    hey

    does the Heisenberg incertitude principe really show that there are random numbers in nature ? Because to me doesnt sound very logic that the future is not predefined. I mean that it would mean that if my magic we could "Roll back time , and press the play button", things wont happen the same, different events would occur. And, if there are random numbers, what determines these random numbers ? It would sound way more logic that a precise object/reaction/event leads to a precise object/reaction/event.

    And, what tells us that behind what we see as intercitudes, there is actually a billion lines long equation ?

    And, Heisenberg says that things do not have a precise location, properties , ect until they are measured ?
    But what does it mean to be measured ? why would everything be imprecise just because one being from one specie on earth hasnt measured it ? why would a rubber have an imprecise lenght until one type of complexly assembled object (human) put a ruler besides it.
     
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  3. Oct 26, 2007 #2
    Yes, this is exactly the major point of quantum mechanics. Events in nature occur as if there was a random noise that wouldn't allow them to be repeatable. Nobody knows what is the reason of this indeterminism.

    This is another important lesson of quantum mechanics: we should't even ask what are system's properties before they are measured. All we can know about physical system comes from measurements, and the goal of theory is to predict results of these measurements. That's what quantum mechanics does brilliantly. Questions about "what happens in reality?" (i.e., while we are not measuring) don't belong to science, because whatever answer is given it cannot be verified by experiment.

    Eugene.
     
  4. Oct 27, 2007 #3
    Well, the thing with measurement is that the observer will always affect the observed. A simplistic illustration is imagine being in a dark room. To observe the things around you, you lit your flashlight. The light from your flashlight however, has energy and this energy is transfered to the objects which you are observing. Obviously, by adding energy to what is observed, the observed is affecting the observed! That is why nothing can be determined precisely before being measured. It's just like Schrödinger's cat. From the reference frame of the observer, the cat is both dead and alive until the observer affects the observed by opening the box.

    This is why the position and speed of an electron may never be determined simultaneously. Imagine, if you want to observe the electron's position, you have to add energy to it in order to observe, and this will affect the speed. If measuring the speed however, position will be affected as the electron is being observed.

    Quantum theory does seem contradictory yes, but it's all about "stepping outside the box" and being willing to accept new ideas.
     
  5. Oct 27, 2007 #4
    QM predicts the classical result of very low energy experiments. It does not explain what actually happened, and we just don't know. We can only guess. Look up the difference between "Copenhagen interpretation" and "hidden variables".

    In a nutshell, part of the Copenhagen interpretation is "shut up and calculate", which can be interpreted as we may never know what "really happens", or maybe "all that happens is what we see classically and nothing more".

    The "hidden variables" interpretation assumes, just as you say, reality really is deterministic and there are things going on that we just don't know about. I'm a hidden variable-ist. I believe Mach's principle is manifested as continual interactions between all particles in the universe, and these are the hidden variables. (How silly to claim a particle can exist without interacting with the other particles of the universe!)

    However, one of the big reasons the jury is still out on this is because of superposition. Apparently energy need not be conserved until the results of an experiment is observed, and the definition of "observation" is debatable. So that's why the heated debate rages on what really happens.
     
    Last edited: Oct 27, 2007
  6. Oct 27, 2007 #5

    Hurkyl

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    Nothing you said here is logical; you haven't made any deductive or inductive arguments that derive a conclusion from stated hypotheses.

    The determinism / indeterminism question has been around for a long time; I think it goes back at least as far as the ancient Greeks. And, incidentally, pre-quantum mechanics doesn't imply determinism nor does quantum mechanics imply indeterminism.

    e.g. all of classical mechanics is perfectly consistent with the hypothesis that physical quantities are random variables. And the class of 'unitary evolution' interpretations of QM state that the 'wavefunction of the universe' evolves in a strictly deterministic fashion.



    By the way, it's the Heisenberg uncertainty principle.


    The point is that the classical description of the universe is not exactly correct. Quantum mechanics is not merely classical objects with random behavior; quantum mechanics is a whole new theory. And the easiest way to prevent yourself from understanding quantum mechanics is to insist upon describing things in classical terms.
     
    Last edited: Oct 27, 2007
  7. Oct 27, 2007 #6

    JPC

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    Yes, but I mean there should be a either Dead or Alive property for the cat ? Its not because we cannot determine if hes dead or alive that hes not either dead or alive ? Why couldnt things be without being measured ?

    Why couldnt there be hidden variables as fleem says ? Like equations that we dont know yet to calculate , but that to get the variables we need to use systems that modify these variables, so meaning we can only get aproximations.
     
  8. Oct 27, 2007 #7

    JPC

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    oh sorry, for the cat experience, i didnt see "From the reference frame of the observer,"
     
  9. Oct 27, 2007 #8

    Hurkyl

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    Because, as per the experimental confirmations of Bell's theorem, we have to give up some 'desirable' feature of the universe. If you want to keep hidden variables, then you have to give up some other 'desirable' property of the universe. (And you have to deal with the fact that it's quantum mechanics that has all of the empirical support, not the hidden variable theories)
     
  10. Oct 27, 2007 #9

    JPC

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    yes but where would these random numbers come from ?
     
  11. Oct 27, 2007 #10
    Well what do you mean "come from"?

    Quantum theory describes that it's a matter of probability. Like rolling a die, you can't really say that the outcome "comes from" anywhere. The outcome is a matter of probability, like the energy levels around a nuclues where there is a high probability that an electron can be found. Basically, it's a matter of probability.
     
  12. Oct 27, 2007 #11

    Gokul43201

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    Where is the logical flaw?

    This is mostly correct, though it is not really what the Heisenberg Uncertainty Principle deals directly with.

    'Random' or 'stochastic' is the exact opposite in meaning to 'deterministic'. In other words, if something occurs randomly, then by definition, there is nothing that determines when it occurs. Your question is akin to asking: "if there are uncountable numbers, how are these numbers counted?"

    It seems you do not understand the meaning of the word 'logic'. A thing is either a logical result of the chosen axioms under the rules that make up the logic, or it is not. Besides, logical correctness is not a function of how an assertion "sounds" - so unless you provide an argument for your assertion, your statement is empty.

    A very tiny fraction of scientists actually do believe there is something like this involved - look up theories of "hidden variables" but also look into "Bell's Theorem".

    Actually, this is not from Heisenberg. This is part of what is called the Copenhagen Interpretation of Quantum Mechanics, but the basic idea is right.

    This is not easily answered and there are many threads here devoted to the measurement problem in QM.

    Because it is that one being of that one species that is pondering the precision.

    This has nothing to do with the species doing the measurement. If giraffes were describing the length of the object, they too would have to use a distribution until one of them made a measurement.
     
    Last edited: Oct 27, 2007
  13. Oct 27, 2007 #12
    "Randomness" is "following no rules". "Logic" is "rules".

    We can certainly use the concept of randomness in logical thought, but obviously we cannot use something that is random in logical thought--for when we do the thought becomes illogical (it follows no rules).

    For example, consider the sequence -12, 902, .037, 41, -4.5e17

    I can make the logical statement, "That sequence appears to be random". However, if the sequence really is random, then i cannot use the numbers, themselves as a part of a logical statement.

    I believe JPC is saying that the random values, themselves, are illogical (they follow no rules).

    Therefore if you believe there is true randomness in reality, then you believe there is an illogical component of reality. That is, you believe there is a subset of reality that follows no rules.
     
  14. Oct 27, 2007 #13

    JPC

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    Yes,

    and with the dice, calculator, ect for example they dont really give really random numbers, there actually a logic for the random number they give (with the dice depends how you throw it, how it its the surface, the characteristics of the surface, ect ; and for the calculator there is a algorithm behind it)

    And, some ingeneers have spent years trying to find algorithm to produce numbers as random as possible, and Heisenberg says random numbers actually exist in a pure form in nature

    But , now , how can nature produce random numbers in a pure form ? is infinite a random number ? Where does the next random number come from ? is it affected by the preceding ? Simply, how can nature produce a pure random number ? How can there be not a single rule behind it ? (apart from the probability) ? I mean the random numbers must come from somewhere , something must generate them ?
     
    Last edited: Oct 27, 2007
  15. Oct 27, 2007 #14
    Right. "Logic" says that it is impossible for there to be an algorithm that produces (truly) random data, yet we claim the universe is capable of doing just that. That is illogical--we can't have it both ways.
     
  16. Oct 27, 2007 #15

    JPC

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    but, since a lot of scientist believe the universe can create random numbers , what arguments do they give to explain it ?
     
  17. Oct 27, 2007 #16

    russ_watters

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    It is not claimed that an "algorithm" produces random results. Yes, that would be illogical.
    That is also incorrect. And it is also a little misleading to call the predictions of QM "random". They are probability based.
     
  18. Oct 27, 2007 #17

    JPC

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    But if there are probabilities, wouldnt that mean that there some kind of control on what numbers turn out ? Meaning that there is a part of determinism inside this Indeterminism ?

    And even if they are probability based, it still has a part of random numbers of a different type (instead of having the same probability for each random number, different probabilities for each random number) ?? And here i could ask the same questions , what generates these probability based random numbers ?
     
    Last edited: Oct 27, 2007
  19. Oct 27, 2007 #18

    Hurkyl

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    Those scare quotes are essential, because that 'explanation' has little or nothing to do with the technical meaning of the word "randomness" and of "logic".
     
  20. Oct 27, 2007 #19
    To prove this, you must now give an example of a random sequence that follows certain rules, and an example of logic that is not based on rules.
     
    Last edited: Oct 27, 2007
  21. Oct 27, 2007 #20
    You're right. The modern definition of "randomness" is "that which cannot be compressed". If a set of data has any correlation at all with an orderly set (for example, a Gaussian distribution correlates with a Gaussian curve), then that data set can be compressed and is therefore not "random". Some might call such a set "bounded random data" or "partly random". I don't mind it being called that too much as long as it is not called simply "random".

    BTW, for other readers, let me point out that the term "random" is sometimes used in mathematics to indicate a variable whose randomness is not yet known or was presumed random. For example, the term is sometimes used to refer to two variables being examined for correlation--and if a correlation is proven, it is wrong to refer to the variables as "random". That is not the definition we are using in this context.
     
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