Dave Slaven: "Einstein's first postulate seems perfectly reasonable. And his second postulate follows very reasonably from his first. How strange that the consequences will seem so unreasonable." http://webs.morningside.edu/slaven/P...lativity3.html

Does Einstein's second, constant-speed-of-light postulate follow "very reasonably" from the first, the principle of relativity? If it does, the constancy of the speed of light is as true as the principle of relativity, in accordance with one of the principles of deduction, and Einstein's relativity is invincible. Here is the syllogism:

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

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