As a reminder, I’m open to requests to discuss any popular physics articles or videos, to append to my “I read popular physics” series. This video was not requested, but was shared by a friend of a friend a while back, and I have things to say about it.
Recently, the YouTube Channel Veritasium posted a video “Why the Speed of Light* Can’t be Measured”. The video argues that all measurements of the speed of light involve sending light in one direction, and waiting for it to come back. However, the light could theoretically be traveling faster in one direction than the other. It seems we are not directly measuring the speed of light, but rather the average speed of light in both directions. The constant speed of light in all directions is a matter of theoretical convention rather than empirical fact.
In the Facebook thread where I first saw the video shared, many people were incredulous. As for myself, I immediately understood the argument from the title, and immediately agreed that it was correct. However, I feel the video is misleading, as it does not explain why there is a theoretical convention that the speed of light is constant. And by doing so, I feel it misses the point of relativity theory.