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Homework Help: Heisenberg's Momentum-Position Uncertainty Principle

  1. Apr 17, 2010 #1
    I was reading about how Heisenberg found out that it is "impossible to determine simultaneously with unlimited precision the position and momentum of a particle" (Serway/Moss/Moyer, 174)

    [tex]\Delta p\Delta x \geq[/tex][STRIKE]h[/STRIKE]/2 (where [STRIKE]h[/STRIKE] is plank's constant over 2pi.)

    My question is why is this true? I read that it had something to do with the large wavenumbers [tex]\Delta[/tex]k, but I'm unsure exactly how that affects anything. I'm just a little hazy on the reason for why, even ignoring the error caused by measuring insturments, it would be impossible to measure two precise things at once.
  2. jcsd
  3. Apr 18, 2010 #2


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    One way of gaining some intuition is to consider Fourier transforms. It is impossible to exactly know the frequency of a sine wave unless you have an infinitely long interval to measure it. To know its frequency (energy) you give up all localization in time. The same holds in the quantum world.
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