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 Originally Posted by OngBonga
Yeah and I'm assuming the guy going on a trip to the sun is moving at constant velocity, so yes, inertial frame of reference. I'm sure GR can handle non-inertial FoR, but my brain can't!
I think you mean "free-falling in a gravitational field," rather than "moving at constant velocity."
But maybe I'm forcing an assumption.
Originally Posted by OngBonga
That's a good question, not sure if it's essentially the same question, gonna mull this over for a bit.
I can settle on an answer that is both good and bad.
If the photon's existence in the plane bears some angular momentum (nevermind that without time, momentum cannot be defined, take it as an intrinsic value of photons)
then we can describe that angular momentum with a vector, a 2D object.
When that photon is viewed in 4D spacetime, it is still described by a 2D vector - it's Poynting vector (which is pointing where the photon is headed, conveniently enough).
So I can find a way to visualize some aspect of this conundrum.
The big problem is that not all photons have rotational polarization. Some have planar polarization.
Originally Posted by OngBonga
Interesting side note - light appears to travel at <c through a non-vacuum due to refraction. Apparently this is due to the photon exciting electrons, which in turn create EM waves, which interact with the photon. The sum of all these waves result in a lower observed value for c. But the photon still moves at c, it just appears not to. I'd be curious if you can explain this in language I can understand, because I'm not really getting it.
It comes down to phase lag and interference. The accelerated electrons (and other charged particles to a lesser extent) are accelerated by the photon, not moved by the photon. The phase lag between the acceleration and velocity of the charged particles results in new wave, with equal magnitude and direction, but a new phase.
As the phase is continually being shifted, the photon's location is moved "backward" a little bit... in a continuous manner.
It's important to note that phase velocity and group velocity are different. The phase change isn't changing the phase velocity, but it's changing the group velocity. So the E-M fields are still propagating at c, but the group velocity of the wave packet appears to move at less than c due to the interference.
(This one is difficult to explain, so don't count these answers as an expert opinion, but a good metaphor.)
Originally Posted by OngBonga
I do get this, but it doesn't really answer the question of how the photon observes two objects clearly separated by space to be occupying the same location. More than that, it observes ALL objects in the direction of travel, in both directions (behind and in front of) infinitely, to occupy the same location in space.
It's more a matter of physics not describing the photon's "rest" frame in a satisfying, intuitive way.
We have an easy time thinking of something with mass moving faster and faster, but a hard time accepting that no matter how fast it gets, it's still effectively infinitely slower than c, as no amount of acceleration could ever get an object with mass up to c. We have a hard time understanding that no matter how fast you're moving, you still measure c as much faster than you.
Moving at c is a totally different beast.
It just has to be that way, though, IMO, no matter how hard it is to visualize.
If light didn't move at c, which is the upper limit of all speeds in the universe, then causality is broken, and a cause no longer has to precede its effect.
Originally Posted by OngBonga
I mean the best I can do is to conclude that space emerges when something moves at <c, the photon doesn't "observe" anything because from its FoR it's stationary in a timeless spaceless universe, it occupies a singularity with everything in the universe. But that's akin to saying the photon's FoR is not valid. Not sure if that's a problem for GR.
It's not a problem for GR. It's a consequence of SR.
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