4 ms·
There actually is a law of conservation of mass (it's the same law, because mass is energy) and it only appears violated if you forget about the particles that
by tardedmeme 5mo ago
There actually is a law of conservation of mass (it's the same law, because mass is energy) and it only appears violated if you forget about the particles that are zooming away at the speed of light. Of course the mass of a system changes if mass can flow in and out.
- mr_mitm 5mo agoMass is not the same as energy. Mass can be converted to energy or has energy, but a photon, for example, is massless while carrying energy.
- deleted 5mo ago[deleted]
- tardedmeme 5mo agoThat is incorrect. Photons have mass. They have no rest mass. They also cannot rest, so you might wonder how relevant that is.
- mr_mitm 5mo agoThe concepts of rest mass and relativistic mass are considered outdated. In modern physics, "mass" means what they meant by "rest mass". Here some indication I'm not making this up: https://hsm.stackexchange.com/questions/2465/when-and-why-did-the-concept-of-relativistic-mass-become-outdated https://hsm.stackexchange.com/questions/2465/when-and-why-di... In any case, I never use those concepts, and I know no professional particle physicist that does. By "mass", I mean rest mass.
- tardedmeme 5mo agoWhen you put a photon in a stationary box, the "relativistic mass" of the photon becomes part of the "rest mass" of the photon-box system. You can't ignore it.