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Truly Random?

  1. Jul 8, 2008 #1
    1. Is thermal noise truly random?
    By truly random I mean can you not predict the next value even if you knew everything permitted about the electrons producing the effect.

    Does this follow from the math of quantum physics?

    2. What about nuclear decay is it truly random?
  2. jcsd
  3. Jul 8, 2008 #2


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    I don't think there is such a thing as truly random. Maby something could be so random we could never hope to work out the pattern.
  4. Jul 8, 2008 #3


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    Yes to both 1 and 2.
    Whether or not anything is "truly random" is a philosophical question. However, QM does not allow us predict e.g. when a decay even will occur even in principle .
    Hence, from a formal and mathematical point of view the answer is yes to both questions.
  5. Jul 9, 2008 #4
    Is there anything else we know to be truly random?
  6. Jul 9, 2008 #5


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    Sure. In accordance with the Heisenberg Uncertainty Relations, there are plenty of things that will take on a random distribution of values when a non-commuting attribute is held constant.

    A common example is taking a photon of known polarization and passing it through a polarizing beam splitter aligned 45 degrees from the known value. This will yield a truly random stream of photons (as to their new polarization). As far as anyone knows, the input photons are identical and there is no known "cause" that leads any photon to go one path or the other through the beam splitter.

    Of course, that doesn't stop folks from speculating that there is a cause. Other than our desire to have a cause for explanatory purposes, there is no supporting evidence for quantum causality in these cases.
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