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Bob S
May18-10, 03:03 PM
P: 4,663
For simplicity, let's consider the total absorption of a photon by an electron in the lab frame, where the electron is initially at rest. For a photon of energy Eγ = pc and momentum p = Eγ/c , the final total energy of the recoiling electron would be

Ee= m0c2 + Eγ.

But the momentum of the recoiling electron would be p = Eγ/c,

leading to a total energy of

[Ee]2= [m0c2]2 + [pc]2= [m0c2]2 + [Eγ]2

These two equations are irreconcilably different, because energy and momentum cannot both be conserved..

Bob S