How did he ever derive the fact that the speed of light is a constant and time is variable? And did he ever calculate the speed of light and how in the hell did he do it? I have tried that standing on the train platform stunt and don’t believe it.
Hi jartz - welcome to the SDMB!
Someone else here can probably answer your question about Einstein’s ideas…but here is a good link with info on the history of determining the speed of light.
http://math.ucr.edu/home/baez/physics/measure_c.html
A nice speculative book on ‘how Einstein came up with it’ is Einstein’s Dreams, by Alan Lightman. It doesn’t really answer the question, since it is fiction, but it’s intriguing nonetheless.
I haven’t followed the link, but it was known that the speed of light was staying constant and that there was no ‘ether’ to which it could move relative to (unless the ether behaved wierdly) from previous experiments (Michelson & Morley were the ones who measure the speed of light using timed reflections. Einstein’s experiments were theoretical, but were the best way to explain the phenomena.
I’m not going to go into it too deep, but I can give you the short answers.
Einstein’s big idea came straight out of Maxwell’s equations for electromagnetism. Sweet Al noticed that the equations had no corrections built in for the motion of the source or the observer, and decided to see where that would take him. Most theoreticians would probably have tried to work out a mathematical treatment that would show the slightly different results you could expect in a moving reference frame, but Einstein looked at it the other way. He assumed that Maxwell was correct to ignore motion.
That would mean that the speed of light was not dependant on the motion of the source or the observer. Starting from this idea, the only consistant result is that time is dependant on motion.
In the end, that led to such profound results that it seemed that the assumptions were true. As it turned out, Maxwell’s equations don’t need any fudge factors based on motion.
As far as measuring the speed of light, Einstein didn’t do that. As far as he was concerned, it was just one of the constants in his equations, and its exact value was not needed to do the math. Experimenters have used many different methods to measure the value of c, both before and after Einstein published Special Relativity.