(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A photon decays into a positron and an electron - show why this is impossible. Under what conditions could this be possible?

2. Relevant equations

conservation of linear momentum:

[tex] P_{PHOTON} = P_{POSITRON} + P_{ELECTRON} [/tex]

conservation of energy:

[tex] E_{PHOTON} = E_{POSITRON} + E_{ELECTRON} [/tex]

3. The attempt at a solution

[tex] P_{PHOTON} = P_{POSITRON} + P_{ELECTRON} [/tex]

[tex] \frac{E_{PHOTON}}{c} = \gamma mu + \gamma mu = 2\gamma mu [/tex]

[tex] E_{PHOTON} = E_{POSITRON} + E_{ELECTRON} [/tex]

[tex] E_{PHOTON} = \gamma mc^{2} + \gamma mc^{2} = 2\gamma mc^{2} [/tex]

[tex] \frac{E_{PHOTON}}{c} = 2\gamma mu = \frac{2\gamma mc^{2}}{c} [/tex]

therefore:

[tex] u = c [/tex] â€¦which would be impossible. is this right? I'm a bit confused on how you apply conservation of energy and momentum in relativity. for instance i haven't considered any reference frames here and i'm not sure if it requires some kind of transformation.

any help is appreciated, thank you!

btw I've assumed that the product particles have equal rest mass and share the energy equally. and u is the velocity of the positron/ electron

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Relativity - photon 'decay'

**Physics Forums | Science Articles, Homework Help, Discussion**