Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Points of energy

  1. Mar 12, 2007 #1
    My friend and me have reached an impasse. We can’t agree on the nature of whether a photon is a point (he says that). I tend to disagree with this assertion because this means that some energy would need to be stored in a point, which by simplistic math seems impossible to me. But there seems no way that something with size or mass to move at the speed of light while following those laws presented in relativity, the special and general theory. If someone has an answer to this question please tell me because it's been bugging me of late.
  2. jcsd
  3. Mar 12, 2007 #2
    It has bugged me for QUITE a while.I got some interesting replies!
  4. Mar 12, 2007 #3


    User Avatar
    Science Advisor

    Are these two separate questions?

    What simplistic math are you talking about? Perhaps if you explained why you think a photon can't be a single point? You might also explain what you or your friend means by a (physical) point!

    That's certainly true of mass- and the photon has 0 mass. I'm not at all sure about "size". Are you think of the length contracting to 0 in the direction of motion?
  5. Mar 12, 2007 #4


    User Avatar

    Staff: Mentor

  6. Mar 12, 2007 #5
    First of all saying something is contained with no size seems to indicate that it would have infinite density, in addition the simple math I referred to was the property of 0 which states any number times 0 is 0. It also seems that a photon that hits another object needs surface area to interact this that other object and from surface area I derive size.

    So I was thinking that this might make the idea of a photon in a point impossible, but that there seems to be some proof for it. In addition I don't see how I can be right either, as a photon, with size, that could moves along a path curved by gravity indicate one side gos faster than the other and therefore at least on the sub-photon level something to exceed the speed of light. We had worked out the math for a spinning photon but realized that this spinning action would cause the photon to gain mass. Making it impossible for it to move at the speed of light.

    He means, if I'm not mistaken, that a photon has no size or mass.

    oh I am so confused by this.
    Last edited: Mar 12, 2007
  7. Mar 12, 2007 #6


    User Avatar
    Gold Member

    Good logic. This applies to the electrons' charge density and was the subject of much discussion in the early days of the electron. Experiments show the the electron is not a point, but varies in size depending on how hard you hit it. It gets smaller as the probing collisions get more energetic.

    Not if it spins in a plane at right angles to the direction of motion.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook