Comments by "" (@jmitterii2) on "Why No One Has Measured The Speed Of Light" video.

I think this undefined thing about one direction of speed of light is at the heart of allowing relativity of simultaneity to be a thing; that two observers in different inertial reference frames may not agree the order in which something happened such as length contraction or time contraction. Something that should be simultaneous might not be and this undefined characteristics on the direction of light is just another aspect of this; we're measuring it from two different reference frames, the light and us.... or something.
1