Algodoo

Quote: "now we don't really know if the speed of light is equal in all directions,"

Reply: Well, actually we DO! According to Professor Einstein, the velocity of light in a vacuum is the same for all observers. Therefore, we need not worry if light moves faster or slower in different directions. Problem solved!

Xray - But, the act of measuring is, itself, also influenced by this hypothetical bias. trying to measure light travelling back and forth assumes light travels the same speed both directions. Veritasium has a good video explaining this in YouTube. He shows that it's impossible to know, for example, exactly when a signal sent to Mars is recieved. If you no longer assume light travels both ways at the same speed, and instead takes all back-and-forth trips such that the average speed is c, the moment at which a signal reflects cannot be known. However, if there are three satellites in an equilateral triangle formation, this may make it possible to detect a speed bias. While it's super unlikely that light travels at different speeds during a round trip, it is impossible to prove that light doesn't do such a thing, while using a straight-line round trip measurer.

Yes, I've seen that excellent video by Veritasium. I have just a basic understanding of Einstein's special and general theories of relativity which is barely enough required to have an intelligent discussion with another science enthusiast like yourself. So, I'd better quit at this point before I say something which is untrue or inaccurate. I avoid that as much as possible!