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Special Relativity: Lenght contraction and a photon.

  1. Sep 24, 2015 #1
    Reading an old thread (wich is now closed or i would post the question there) there was a discussion about the size of a photon, and if it was an adequate question at all.

    The discussion on the other thread couldnt agree on a response. Yet there was some postulates that could work with this idea Im bringing to you now:

    In special relativity, one of the effects for a stationary viewer is lenght contraction, higher the speed, higher the contraction in the direction of the movement.
    So, can we assume since a photon travels at maximun velocity, it has maximun contraction?
    Maybe that could explain why we cant messure a size in a photon, and its duality? yet we can in an electron?

    What would this means? a photon's size would be relative to origin and destination?

    Am I talking nonsense? why?
  2. jcsd
  3. Sep 24, 2015 #2


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    An electron is a charged particle. While the electron itself is considered a point, its field extends over a distance. A photon is also a point particle, but has no charge.
  4. Sep 24, 2015 #3


    Staff: Mentor

    These types of questions are all misunderstandings of what relativity says. Relativity is about transformations between inertial frames. You cant attach an inertial frame to a photon since it moves at the speed of light so such musings are meaningless.

  5. Sep 24, 2015 #4
    Remember length contraction and time dilation do not apply to photons or any particle with a light-like spacetime interval because there does not exist a rest frame for the particle by which to relatively measure time. Boosts to light-like vectors do not rotate them in spacetime.

    Photons and electrons do not have sizes as the above poster said, they are point particles.
  6. Sep 25, 2015 #5


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    You can repeat it as often as you like, but photons are not point particles in any classical sense. They don't even have a well-defined position! I guess, it's really time that I write an Insight article on it!
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