How can photons have momentum if they have zero mass?

Question

I understand E = hv, but I’m not getting why photon collisions can “push” things instead of just producing heat. Thanks!

In: Physics

Answer 1

Photons have relativistic mass. While the photon itself doesn’t have mass in the conventional sense, it does have energy, and remember that E=mc^2; energy is mass and mass is energy. This means that a photon has a kind of ‘virtual’ mass. A photon can push on something like a solar sail by hitting the sail and imparting momentum, causing the reflected photon to have less momentum, and therefore less mass/energy (a longer wavelength).