It is! I also found this video later that I think does a better job of explaining reflection: https://youtu.be/1n_otIs6z6E

That was always my assumption about why it happened, but it turns out that’s not the case at all: https://youtu.be/CUjt36SD3h8

Reflections involve the material absorbing and re-emitting photons back the other direction.

The curvature of light from gravity is actually space-time itself being curved by mass. The light continues on a straight path through a curved space-time. It looks like it changes direction from the outside, but that’s just the shape of the universe in that area.

That’s why we feel gravity. The space-time around earth is curved inward, so going forward in time would actually mean falling towards the center if we were stationary in space. The ground is constantly accelerating us upwards. Light does not get accelerated that way, so it follows the curvature.

If you want to get really deep into the reflection topic: https://youtu.be/rYLzxcU6ROM

In aggregate, yes, but any individual wave of light is still traveling at c. You get the appearance of a slower wave because secondary waves are generated that cancel the original one in such a way that it makes a combined wave that appears to be slower.

I’ve been trying to wrap my head around this part and what it means for cause and effect for a while. I think Feynman said something like a photon is only ever emitted when the source and destination agree to exchange one. Which makes sense if the exchange is instantaneous to the photon. But how can billions of years pass for us in the mean time?

To be pedantic, photons never accelerate. They only ever travel at one speed in one direction