Re: special relativity

[John Mallinckrodt <ajmallinckro@CSUPOMONA.EDU>]

On Mon, 20 May 2002, Justin Parke wrote:

> Most textbooks and teachers (at least all that I have seen or
> known) introduce special relativity by introducing two
> postulates:
>
> 1)  The laws of physics are the same in all reference frames
>
> 2)  The speed of light is independent of the speed of the
> source and the observer.
>
> I have always thought that these are redundant.  Isn't 2)
> implied in 1)?

This is certainly a fair enough question from our current
perspective.  Statement 2 *is* implied by statement 1 if you
consider it to be a law of physics.  (Note that the speed of sound
is NOT independent of the speed of the source and the observer,
nor is it implied to be so by statement 1.)  At the time Einstein
proposed the second postulate, it had not been accepted as a law
of physics.

Perhaps it would be clearer today to write:

1)  The laws of physics are the same in all reference frames

2)  One of the laws of physics is that the speed of light is a
    universal constant.

John Mallinckrodt      mailto:ajm@csupomona.edu
Cal Poly Pomona          http://www.csupomona.edu/~ajm