https://www.google.com/url?sa=t&source=web&rct=j&url=https://m.youtube.com/watch%3Fv%3DpTn6Ewhb27k&ved=2ahUKEwjclump6dD4AhVbK0QIHflYARcQwqsBegQIJxAE&usg=AOvVaw3U3pMsYkj9kSdW08mERYF-
Here’s the link. I think...
It is very difficult to know for certain that basic constants (like the speed of light) have always been the same or are the same everywhere in the universe...