11:11 <Greys> smart people time, the engineers at my job, who have degrees in physics and know shit better than me, say that photons travelling at speed of light speeds have mass because of speed

11:11 <Greys> how does that work

11:16 <Greys> my understanding is that light has energy and momentum; momentum is normally a feature of mass but it doesn't need to be; but having mass makes the math easier so maybe it's simpler to say photons have the mass that explains their momentum

11:17 <Greys> kinda like centerfloople force, one of them "isn't real" but it's still useful

11:27 <egg|cell|egg> They have mass, just no rest mass

11:27 <Greys> how does this work?

11:28 <egg|cell|egg> Mass-energy equivalence

11:28 <Greys> that sounds like the thing I said about the math being easier

11:30 <Greys> do they literally shooting through space have actual mass, or is it possible to treat them as if they have mass in a useful way?

11:30 <egg|cell|egg> Well photon pressure is a thing

11:32 <egg|cell|egg> https://en.m.wikipedia.org/wiki/Radiation_pressure

11:33 <Greys> right because they have momentum and they get absorbed and reabsorbed by matter so the momentum as at least temporarily given the matter and then the photon reemits at a different angle so it wouldn't by logic I understand leave with the same momentum

11:34 <Greys> judging by that image I think I'm fairly right about that.... cool

11:35 <egg|cell|egg> Read the Radiation pressure by reflection section

11:36 <egg|cell|egg> Also see https://en.m.wikipedia.org/wiki/Mass_in_special_relativity#Relativistic_mass

11:36 <Greys> " they have the properties of energy and momentum, and thus exhibit the property of mass as they travel at light speed" this is the kind of wibbly language that makes me suspicious of verdict statements

11:37 <Greys> exhibiting the property of mass sounds like a complicated way of not saying that photons have mass

11:38 <egg|cell|egg> They do, because it's the same thing as having energy

11:39 <Greys> so, you can't go the speed of light, if you have rest-mass, is that the correction I should make to my understanding of physics?

11:40 <egg|cell|egg> Yeah nonzero rest mass means your speed is less than c, and zero rest mass means it is always c

11:40 <Greys> I think I can function with this

11:41 <Greys> leaving the realms of actual discourse, any idea what the current theoretical state of tachyons is?

11:41 <egg|cell|egg> Considered useful for patching plot holes?

11:42 <Greys> I haven't read up on them in about five years but they were kind of like wormholes 10 years ago, a theoretically valid idea that we would probably never do much with

12:15 <Greys> that'll stick now

12:27 <Greys> acc, that happened because I tried to add you to the access list, and you weren't registered