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

Photon aceleration

  1. Feb 22, 2005 #1


    User Avatar

    I have been wondering wether a photon has acceleration or not, how does it reach the 300,000 km/s? does a photon even need to accelerate?

    I would also appreciate your telling me about rest mass, how does it work, what does it cause, etc.

  2. jcsd
  3. Feb 22, 2005 #2
    The photon has no rest mass, so it doesn't need to accelerate.
  4. Feb 22, 2005 #3
    An acceleration is a change in velocity. Photons always move at the speed of light, as do all massless particles.
  5. Feb 23, 2005 #4
    There's one thing though. A photon does have momentum, so when an atom emits a photon it has to recoil slightly.
  6. Feb 24, 2005 #5


    User Avatar

    Well, what Woz is trying to ask is, how does it start moving in the first place... maybe.

    It takes an infintesimal amount of energy to accelerate a luxon, a particle with no rest mass, such as a photon, but not zero. Once it gets accelerated to the exclusively luxonic speed of the speed of light in a vacuum, from that infintesimal amount of energy, it needs no more, it doesn't slow down or speed up, unless of course it goes through a medium.
    Last edited: Feb 24, 2005
  7. Feb 24, 2005 #6
    It may be absorbed or scattered but always propagates at C.
  8. Feb 24, 2005 #7
    The photon is propagating at c as soon as it is created. It is not that there is initially a photon 'at rest' that needs to be accelerated to c.
  9. Feb 24, 2005 #8


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    When was this "luxon" experimentally discovered or verified? Oh wait... it hasn't?

    Then why are you using a hypothetical particle to contradict something that HAS been experimentally verified, and has an unbelievably accurate theory (QED)? That's like using a pseudoscience to disprove a science!

    Take note of the statement already mentioned, that if a photon has to accelerate, it means that over some finite time, it IS NOT travelling at c in vacuum! This violates SR! We need to shake a few people up so that they somehow can get free from the classical newtonian mechanics here...

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook