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Why is photon massless particle?

  1. Mar 4, 2015 #1
    i'm still wondering,
    i know a bit of quantum mechanics and general relativity. well... very very little, if photon is a particle, it must be "something" right? i mean, something that exist in this space and time. why is "something" that "exist" don't have a mass? what is it consist of? or something that really small is different with something big like table? or is photon just a wave that going through space and time? but if it is just a wave, how does it come through vacuum space? please help me, i've done browsing but i got nothing. i am still at high school and the farthest thing i got is classical physics and really excited to modern one but too dumb-_-. and i am new here. thank you
  2. jcsd
  3. Mar 4, 2015 #2


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    This is a very familiar question, and I suggest you browse the forums, especially the Quantum Physics forum, for a bit to see all the ad nauseum answers that have been given.

    A photon isn't an ordinary "particle". Rather, it has been defined as having a clump of energy. It has not been defined as having a definite physical boundary in real space, the way we see a ball, for example.

    Secondly, for something to "exist", it must be detectable. We must be able to detect and measure its characteristics. That's it. Nothing here says that for something to exist, it must have a mass. Before quantum mechanics and special relativity came along, we detected light regularly. Yet, none of the theories at that time showed a "particle" picture of light, and thus, no question on whether it has a mass.

    The lesson that you should learn here is to think carefully what your logic and sequence of thinking is. Is the existence of A automatically implies the existence of B?

    I can already anticipate your subsequent questions on this (if it has "energy", then https://www.physicsforums.com/threads/do-photons-have-mass.511175/ [Broken]"). You should also read, before you go any further, the FAQ that we currently have on this topic.

    Last edited by a moderator: May 7, 2017
  4. Mar 4, 2015 #3
    In the book "Beyond the God particle" Lederman try to explain in a simple manner why photon is massless. The responsable is the Higgs field that permeates all the universe: for example in the case of the weak interaction, being a beaking simmetry, the bosons interact with it acquiring mass. He says that for the particles with mass the chirality oscillates from a right to left handedness while for massless ones it is unique and then they can't interact with Higgs field: so the photon cant't obtain mass and they are free to go at maximum speed.
  5. Mar 6, 2015 #4


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    I don't know that we can truly rule out that the photon has a very small mass that we simply can't measure. I doubt that is the case, but it will be hard to theoretically show that it must be massless without assuming that it is massless.
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