# How can a Photon apparently transfer Momentum without any Mass?

• I
KBon
Due to Compton - Scattering it seems that a Photon changes the Momentum of the electron, although it doesn't have any mass. How should I imagine this?

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vanhees71
Gold Member
2019 Award
A photon is massless but has energy and momentum. It's the mode of an electrodmagnetic field, and you have
$$E=|\vec{q}|c,$$
where ##\vec{q}## is the momentum of the photon.

In relativistic physics you don't need a mass to have a momentum!

jtbell
Mentor
Relativistically, the general relationship between energy, momentum, and mass is ##E^2 = (pc)^2 + (mc^2)^2## where p is the magnitude of the momentum. For a photon, m = 0 which gives vanhees71's formula, in different notation.

vanhees71
Nugatory
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