It is said that we don’t know the actual speed of light going from a source to a target; we know only the two-way speed going from a source to a target and reflecting back to the source. Conceivably light is faster in one direction than the other. Perhaps one could test whether light has the same speed in opposite directions by use of the spinning photosensitive disc illustrated below.
The idea is to send a pulse of light simultaneously leftward and rightward from a single, middle source over a fast spinning photosensitive disc. If the disc spins fast enough, the light pulse should leave an arc shaped mark on each side, left and right. If light’s leftward and rightward speeds differ, then the arc will be flatter on the side of faster light speed, like the purple-dot path compared to the green-dot paths. One will not know which side is faster unless the light leaves a side-specific signature, eg a left-right color difference.
In this illustration, the disc made one quarter rotation as a light pulse (green dots) went from center to left edge and from center to right edge. It is depicted as it was at the end of that quarter turn. The purple dots show the path of the right-side pulse if it were twice as fast. They advanced with the disc as the slower and later (green) exposures occurred. Considering the speed of light relative to the speed of a matter disc, this experiment would require extremely fine resolution, since the disc would advance only a few atoms as the light pulse traveled from middle to edge. But such resolution may be possible, as it was achieved in the LIGO gravity-wave sensor.
An analogous experiment could be done with a fast-sliding photo-sensitive sheet instead of disk, or with a fast-rotating photo-sensitive cylinder as illustrated below. Perhaps the moving photo-sensitivity could be electronic rather than massive, given the speeds implied.
