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I had an idea on how to measure the one-way speed of light and need to be told why I’m horribly wrong. The entire problem is that you can’t synchronize two clocks, right? Well what if we just don’t use clocks? From what I understand (I’m not even graduated high school so not much) the Schwartzchild radius is the distance away from the center of a black hole where the escape velocity is $c$ (measured using the two-way mirror method). By analyzing how light behaves when being bent around bodies, could we then rule out some of the extremes of the one-way speed? We could prove that light couldn’t possibly be $c/2$ one direction and instantaneous in the other because then that would mean that light would always escape a black hole or any other body, even past where the escape velocity is $c$? Because we observe that light can always be captured by a black hole in any direction, could we get a reasonable estimate by just analyzing how gravity affects light as it nears an escape velocity of $c$? Someone tell me what I’m missing here please, thanks! I understand this would be very difficult or impossible to physically test but I was just wondering what about the actual concept is wrong.

Qmechanic
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Collin Frost
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The term "measurement of the one-way speed of light" refers to a very specific measurement scenario in which light is sent from a source at point A to a detector at point B. What you describe in your question - "analyzing how light behaves when being bent around bodies" - is not this type of measurement.

The constancy of speed of light is one of the core elements of the theory of relativity. Any deviation from it would imply violation of Lorentz symmetry and that could potentially have many observable effects. The fact that we cannot measure the "one-way speed of light" in the narrow sense described above, does not mean that we cannot infer it by other experimental means. We do not need black holes for that - there are many, many experimental tests of relativity that have been performed. (Of course, measuring how light is bent by massive objects is another important test of general relativity).

J. Delaney
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