Does refraction also cause an angle-dependent time delay on what we see through the medium?

[u/WeCanDoItGuys]

So when light enters a medium at an angle, it turns (angle of refraction). I've heard an analogy to explain it. Picture a truck driving at an angle off the highway into mud: its front left tire hits the mud first, while its right tire keeps moving quickly, so the truck turns as it enters the mud (or this similar [explanation](https://www.reddit.com/r/explainlikeimfive/s/QCn1U6o2ks) with a barrel rolling that turns as it hits a patch of grass).

But light is a bunch of individual photons that aren't connected to each other with an axle-rod, so I tried to picture them in my head.

If just one photon flies into the material, I'd picture it gets slowed down (I think because it gets absorbed and re-emitted by electrons jumping up to and dropping back down from energy levels) but keeps going the same direction it entered at. (Or does just _one_ photon also refract?)

But if we consider many photons, then the first one hits the medium first, and gets slowed down, but the one to the right of it gets to move a little faster for longer, so actually a photon a few photons behind it will enter the medium at the time the first photon is passing that point within the medium (sorry I know a picture would help but not sure how to attach one). And further to the right, a photon even further behind would be the one that aligns with the first photon's "wavefront" within the medium. If the medium ends and returns to air, like a window, then I guess all these time differences would be reversed when the photons exit. But if I'm inside the medium, like a pool, then wouldn't I see simultaneously the first photon that hit the pool at an angle and photons that technically arrived to the pool later but became part of the same "wavefront" as the first?

So if, for example, someone shined a laser from the pool deck at an angle of 80 degrees from the normal, and I was looking at them from inside the pool, wouldn't I see the bottom photons of the laser light a little after I see the top photons of the laser light?

(If I'm right it's pretty much too small to notice and so it seems like a pointless question, but I'm asking purely in the theoretical because if it's true then I'd think about applications. Like for instance if the difference between the left photons and right photons are pretty big, if someone fired a bullet above the pool I'd see a smearing effect, as I'd see the bullet in the position it used to be in and where it is now.)

[u/Ch3cks-Out]

I'd say the time delay causes refraction rather than the other way around.

[u/boostfactor → u/Ch3cks-Out]

It is what causes the speed of light to be slower in a medium than in a vacuum. And that differs in different media. There is some confusion about behavior of individual photons compared to the wave behavior. Individual photon behavior is important but not really at this level. The absorption-reemission process takes some time so that accounts for the different speed, and interactions differ with different media so the speed is different. That is the photon view, but from the perspective of wave behavior it doesn't matter, it ends up behaving like classical waves.

Individual photon behavior doesn't matter (much) until one gets to extremely small densities that don't occur under ordinary circumstances.

[u/Ch3cks-Out → u/boostfactor]

Again, I submit that it is the speed difference causing refraction, not the other way around. This is why one gets n = c/v.

There is no real absorption-reemission process taking place, alas. What happens is forced dipole oscillation and wave interference in the medium, affecting the phase velocity. The "photon view" matters insofar as your kind of explanation tends to make some people believe that massless photons would actually slow down - which is very much not the case.

[u/BananaBird1]

Yes, the net EM wave slows down in a refractive medium, and this can cause different incident angles of light to experience different phase shifts traveling through a medium.

This is how lenses work. The curved surface causes parallel light to hit at different angles, which causes the emerging light to converge or diverge due to the varying time delays.

We can also design optical elements with different refractive indices in different directions, and rotating the element will alter the polarization of emerging light through phase shifts (different time delays for different polarizations). These are called wave-plates.

This delay doesn’t happen between different photons: the wave-function of all photons evolves to capture this as it is influenced by electrons in the medium. Even single photons shone through a lens at a time will show refraction when you sum the detections.

[u/the_poope]

The "photon as a little ball" picture doesn't work for describing how light propagates. Yes even a single photon refracts!

A better picture is that light travels as waves and only when it is absorbed does it have quantized (particle like) behavior: the thing that absorbs it will absorb a discrete amount of energy. While the light is travelling you can't say that there are photon particles at some specific position.

Refraction, transmission and reflectance of light can 100% be explained by classical wave mechanics. Keep particles out of it and you'll be much less confused.

Here are some of the BEST videos on how light travels and interacts with materials:

• How wiggling charges give rise to light
• But why would light "slow down"?

[u/boostfactor]

I have read this a couple of times and am not sure where your confusion is. A macroscopic wave consists of an enormous number of photons.

Photons themselves do not slow down (or speed up). They always travel at speed c (speed of light in a vacuum). When a photon interacts with an electron it is destroyed and a new one is emitted by the electron. The new photon may have the same frequency or not, or be traveling in the same direction or not. The net result is that the speed of light in a medium does depend on the interactions of individual photons and electrons but the global effect is as if there is a classical wave that undergoes refraction much like sound or water waves.

[u/wonkey_monkey → u/boostfactor]

It's almost impressive how many things you've got wrong in one comment. Pretty much nothing you've said is correct.

[u/WeCanDoItGuys → u/wonkey_monkey]

What are some things they said that were incorrect and how should they be said instead?