> But we've only ever looked from inside the solar system. It doesn't matter where you are looking from, it matters what direction you are looking. If you look towards Polaris (the North Star) the cosmic background radiation is virtually identical in character to every other direction you look. That means light is traveling at the same speed through all regions of space. > You keep beating the same point that the measurments are consistent while ignoring that there could be major flaws in our assumptions. They're not assumptions. That's what's hanging you up. > You admit the stars would "look different" if the speed of light was not constant, which is exactly my point, they would look like they were closer or further away. No, stars wouldn't look different - the whole universe would look different in one direction versus another direction. Quasars would appear closer in one direction than the other. Light would be more redshifted from stars in one direction than from stars in another direction. Cosmic background radiation would appear closer in a direction that had some region(s) of space where light traveled faster, and it would appear further away in a direction that had some region(s) where light traveled slower. We don't see that. There isn't any evidence that the speed of light in the vaccuum of space varies by a meaningful amount.