Bingo the Einsteiniano (aka Leonard Susskind) is a famous professor and deduces the constancy of the speed of light (Einstein's 1905 second postulate) from the principle of relativity (Einstein's 1905 first postulate). Here is the essence of his argument:
Premise 1: The laws of physics are the same in every inertial frame (principle of relativity).
Premise 2: Einstein said that the speed of light is a law of physics.
Conclusion: The speed of light is the same in every inertial frame.
Leonard Susskind: "The principle of relativity is that the laws of physics are the same in every reference frame. That principle existed before Einstein. Einstein added one law of physics - the law of physics is that the speed of light is the speed of
light, c. If you combine the two things together - that the laws of physics are the same in every reference frame, and that it's a law of physics that light moves with certain velocity, you come to the conclusion that light must move with the same
velocity in every reference frame. Why? Because the principle of relativity says that the laws of physics are the same in every reference frame, and Einstein announced that it is a law of physics that light moves with a certain velocity."
https://youtu.
be/toGH5BdgRZ4?t=626
Needless to say, the original deduction belongs to Einstein. The speed of light is constant, c, because, if it is variable ("comes out smaller than c"), then "this result comes into conflict with the principle of relativity":
Albert Einstein: "If a ray of light be sent along the embankment, we see from the above that the tip of the ray will be transmitted with the velocity c relative to the embankment. Now let us suppose that our railway carriage is again travelling along the
railway lines with the velocity v, and that its direction is the same as that of the ray of light, but its velocity of course much less. Let us inquire about the velocity of propagation of the ray of light relative to the carriage. It is obvious that we
can here apply the consideration of the previous section, since the ray of light plays the part of the man walking along relatively to the carriage. The velocity W of the man relative to the embankment is here replaced by the velocity of light relative
to the embankment. w is the required velocity of light with respect to the carriage, and we have w = c - v. The velocity of propagation of a ray of light relative to the carriage thus comes out smaller than c. But this result comes into conflict with the
principle of relativity set forth in Section 5."
http://www.bartleby.com/173/7.html
More here:
https://twitter.com/pentcho_valev
Pentcho Valev
--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)
