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Photons violate Uncertainty Principle?

  1. Feb 10, 2013 #1
    A photon is considered as a quantum particle, right?
    However since we know the speed of a photon(speed of light) and hence can predict its position, isn't it violating the Heisenberg Uncertainty Principle?
    Where am I going wrong? Is it false to believe that a photon is a quantum particle?
  2. jcsd
  3. Feb 10, 2013 #2


    Staff: Mentor

    isnt it momentum vs position? so even though we know its speed we might be limited in knowing its momentum (ie wavelength or its frequency) .
  4. Feb 10, 2013 #3


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    It's a bit difficult to talk about a photon's position since there doesn't exist a well-defined position operator for a photon.

    For massive particles, there is a position operator, fulfilling the Heisenberg algebra
    [tex][\hat{x}_i,\hat{p}_j]=\mathrm{i} \hbar \delta_{ij}.[/tex]
    Then for any pure or mixed state the Heisenberg-Robertson uncertainty relation,
    [tex]\Delta x_i \Delta x_j \geq \frac{\hbar}{2} \delta_{ij}[/tex]
    holds. I tells you that the position and momentum of the particle both are not fully determined but distributed with a finite standard deviation, and the product of these standard deviations cannot be smaller than [itex]\hbar/2[/itex] if you consider position and momentum components in the same direction.
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