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

Center of momentum frame with photons?

  1. Mar 21, 2012 #1
    Is it possible to have a center of momentum frame in a system with a photon and a massive particle?

    If you were to do so in a system with two massive particles, this would involve redefining the velocity of the particles in the CM frame. E.g. if A moves towards B with speed 2v, in the CM frame, A and B would move towards each other at v.

    Since the photon will have speed c in all frames, is it possible to have a unique frame in which the massive particle has momentum -E/c (where E is the energy of the photon)?
     
  2. jcsd
  3. Mar 21, 2012 #2

    Dale

    Staff: Mentor

    Yes, it is possible. Remember that as you change reference frames the photon will red-shift or blue-shift. The Doppler shift will change the energy and therefore the momentum of the photon. There will be a unique frame where it is opposite that of the massive particle.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook