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

Another silly one

  1. Nov 9, 2008 #1
    watching from earth frame, i see an electron lose a photon and get slower. but if i consider a frame still moving with initial velocity of electron, what do i see? the electron looses a photon,but moves faster. hence its relativistic mass is also greater than rest mass.total energy has increased in both ways. how is sum of mass and energy conserved here?
     
  2. jcsd
  3. Nov 9, 2008 #2
    Bravo, you have just shown a single free electron cannot emit a single photon.
     
  4. Nov 9, 2008 #3
    What if it is not free but oscillating due to an alternating electrical field? Does it still see itself in freefall, emitting photons for no reason? or does it "feel" itself accelerating since the field is not gravitational?
     
  5. Nov 9, 2008 #4

    Dale

    Staff: Mentor

    A stationary accelerometer in the oscillating electron's rest frame would register an oscillating acceleration, so you know that the frame is non-inertial and therefore the electron would "feel" itself accelerating.

    To the OP: you may want to look into the conservation of four-momentum, which encapsulates the conservation of energy and conservation of momentum in one nice convenient Lorentz-invariant package.
     
  6. Feb 2, 2009 #5
    well then let us assume electron and neutron moving in direction of electric field.then, with respect to nuetron, is electron gaining energy when it is actually becoming slower relative to earth?
     
  7. Feb 2, 2009 #6

    Dale

    Staff: Mentor

    What does conservation of the four-momentum tell you?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?