What we call "mass" is actually "rest mass" - ie. the mass when the thing is not...

		Diggsey on Aug 10, 2021 \| parent \| context \| favorite \| on: How far could a spaceship go if we never ran out o... What we call "mass" is actually "rest mass" - ie. the mass when the thing is not moving. Photons don't have rest mass because they don't rest. What photons do have is momentum, and so due to conservation of momentum, hitting a photon will slow you down.