: Historically, the constant speed of light was an empirical observation, and not just an assumption. Maxwell's theory predicted that electromagnetic waves traveled at the speed of light, and that was observed. It was one of the big reasons for concluding that light was an electromagnetic wave. Experiments like Michelson-Morley (1887) found a constant speed of light. Also, there were astronomical reasons for believing in a constant speed of light. Distances were measured in light-minutes or light-years, and that only makes sense if the speed is constant. Yes, Einstein declared the constant speed of light to be postulate in 1905, but by then it was a well-accepted empirical fact. Going faster than ''c'' or finding a variable ''c'' would now violate so much physics that it would be like finding a perpetual motion machine. [[User:RSchlafly|RSchlafly]] 10:27, 25 August 2011 (EDT) | : Historically, the constant speed of light was an empirical observation, and not just an assumption. Maxwell's theory predicted that electromagnetic waves traveled at the speed of light, and that was observed. It was one of the big reasons for concluding that light was an electromagnetic wave. Experiments like Michelson-Morley (1887) found a constant speed of light. Also, there were astronomical reasons for believing in a constant speed of light. Distances were measured in light-minutes or light-years, and that only makes sense if the speed is constant. Yes, Einstein declared the constant speed of light to be postulate in 1905, but by then it was a well-accepted empirical fact. Going faster than ''c'' or finding a variable ''c'' would now violate so much physics that it would be like finding a perpetual motion machine. [[User:RSchlafly|RSchlafly]] 10:27, 25 August 2011 (EDT) |