But when you think about light’s speed in medium it seems like absorption and re emission which shifts light’s net velocity. The speed of light between the interaction is still c. That becomes obvious if you zoom into matter and find its mostly empty likr vaccum
No, that’s not really a useful way of modeling it for the case of light traveling through a linear medium.
The absorption/re-emission model implicitly localizes the photons, which is problematic — think about it in an uncertainty principle (or diffraction limit) picture: it implies that the momentum is highly uncertain, which means that the light would get absorbed but re-emitted in every direction, which doesn’t happen. So instead you can make arguments about it being a delocalized photon and being absorbed and re-emitted coherently across the material, but this isn’t really the same thing as the “ping pong balls stopping and starting again” model.
Another problem is to ask why the light doesn’t change color in a (linear) medium — because if it’s getting absorbed and re-emitted, and is not hitting a nice absorption line, why wouldn’t it change energy by exchanging with the environment/other degrees of freedom? (The answer is it does do this — it’s called Raman scattering, but that is generally a very weak effect.)
The absorption/emission picture does work for things like fluorescence. But Maxwell’s equations, the Schrödinger equation, QED — these are wave equations.
I wouldn’t say its a useful way, but if you think about it, everything is vaccum if you zoom enough. Also absorption can mean different things though so keep that aside and think of it as some interaction going on which in effect slows it down.
Now i looked up on youtube and this is what i meant (timestamp included). I was looking for 3b1b explaination but this one works too. It’s arguable if we can call it absorption or not, and what I said before might be ambiguous. But this guy explains it well
Edit: The 3b1b explaination is either in this video or in this one or maybe a combination of both
Since an observer traveling through space at the speed of light experiences no time from the beginning of their journey until they decelerate (since their 4-velocity vector has non-zero values only in the 3 dimensions of space), photons don’t just arrive precisely when they mean to, from the moment they are emitted, they have already arrived.
*in vacuo
But when you think about light’s speed in medium it seems like absorption and re emission which shifts light’s net velocity. The speed of light between the interaction is still c. That becomes obvious if you zoom into matter and find its mostly empty likr vaccum
No, that’s not really a useful way of modeling it for the case of light traveling through a linear medium.
The absorption/re-emission model implicitly localizes the photons, which is problematic — think about it in an uncertainty principle (or diffraction limit) picture: it implies that the momentum is highly uncertain, which means that the light would get absorbed but re-emitted in every direction, which doesn’t happen. So instead you can make arguments about it being a delocalized photon and being absorbed and re-emitted coherently across the material, but this isn’t really the same thing as the “ping pong balls stopping and starting again” model.
Another problem is to ask why the light doesn’t change color in a (linear) medium — because if it’s getting absorbed and re-emitted, and is not hitting a nice absorption line, why wouldn’t it change energy by exchanging with the environment/other degrees of freedom? (The answer is it does do this — it’s called Raman scattering, but that is generally a very weak effect.)
The absorption/emission picture does work for things like fluorescence. But Maxwell’s equations, the Schrödinger equation, QED — these are wave equations.
I wouldn’t say its a useful way, but if you think about it, everything is vaccum if you zoom enough. Also absorption can mean different things though so keep that aside and think of it as some interaction going on which in effect slows it down.
Now i looked up on youtube and this is what i meant (timestamp included). I was looking for 3b1b explaination but this one works too. It’s arguable if we can call it absorption or not, and what I said before might be ambiguous. But this guy explains it well
Edit: The 3b1b explaination is either in this video or in this one or maybe a combination of both
Yes, but light always travels at the speed of light, regardless of its speed. It travels at c in a vacuum.
Light is never late, nor is it early, it arrives precisely when it means to.
Since an observer traveling through space at the speed of light experiences no time from the beginning of their journey until they decelerate (since their 4-velocity vector has non-zero values only in the 3 dimensions of space), photons don’t just arrive precisely when they mean to, from the moment they are emitted, they have already arrived.
Dispersion and nonlinearities would like to have a word ;)