1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Mass of a photon.

  1. Jun 5, 2014 #1
    Photon is the sub-atomic particle that light is made of. The properties of Photon:
    Mass = 0, Charge = 0, Spin = 1.

    According to Einstein's relativity, light travels fastest at 300,000 km / sec. When any other object travels at the speed of light, the universe shrinks to zero distance. But, we know that it takes 8.3 minutes for light from the sun to reach earth. So, even for sun light, the universe does not shrink to zero.

    I find it hard to believe that photon has no mass. The energy of a photon is h x λ (Planks constant multiplied by Frequency) is roughly 10-20 Joules, small but finite.

    According to Einstein, E = mc2. In a nuclear reaction, the mass lost is converted to energy which is carried by photon. Consider a hypothetical experiment, where photon is converted to a truly mass-less energy "particle". In the experiment, the mass of a photon is converted to pure energy. In short, the mass of the photon is lost. The lost mass is equivalent to the energy calculated by Planks formula (proportional to its frequency). So, the mass of a photon is 10-36 (small but finite).

    If there was a mass-less particle, it would travel at infinite speed and can move from one end of the universe to the other end of the universe in zero time. For a truly mass-less particle, the universe would truly shrink to zero.
  2. jcsd
  3. Jun 5, 2014 #2
    You seem to be working in the frame of a photon. This is not possible in physics.

    This is not the actual formula. The formula is fine for slow moving objects, but not for things like photons.

    This is completely false and contrary to mainstream physics. Please do not write things like that.

    Some things to read:
    https://www.physicsforums.com/showthread.php?t=511175 [Broken]
    Last edited by a moderator: May 6, 2017
  4. Jun 5, 2014 #3


    User Avatar

    Staff: Mentor

    The full form of the equation is e2 = m2c4 + p2c2, where p = the momentum of the an object. Photons do not have mass, but they do possess momentum. So even when the mass is zero, you still have a finite amount of energy.

    You can check that here: http://en.wikipedia.org/wiki/Photon#Physical_properties
  5. Jun 5, 2014 #4
    Thank you, micromass, Drakkith. It is 17 years since I last read a formal textbook in physics. I recently got interested in Particle Physics. One of the YouTube video misled me to come to the above conclusions.

    As you rightly pointed out, I should have warned the reader that I was trying to prove a claim.
  6. Jun 5, 2014 #5


    User Avatar
    Gold Member

    You better avoid youtube videos and watch some nice lectures. Sometimes, youtube videos tend to mislead others
  7. Jun 5, 2014 #6
    You should phrase your statements as questions. That way it doesn't sound like you think you understand something that you really don't.
  8. Jun 5, 2014 #7
    I vote for less avoidance and more participation so that more people are exposed to real Science. Granted, it can seem an often thankless "job" but it's difficult to argue that it is ignore-worthy.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook