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Re: special relativity



Hi all,

Untill some one logically derives (2) from (1), or gives us a reference
where this is done/argued, I find such arguments a bit misleading: I found
always confusing the word "same" in sentence (1).
I always understood (1) as having more an heuristical value: "To be
correct, any law of physics should be covariant". It is more like a
meta-law. When one adds then (2), Lorenz rule of transformations are
obtained. In this sense they seem to me to be two independent postulates.
How did Einstein wrote his first postulate?

Regards,
Miguel A. Santos



On Mon, 20 May 2002, John S. Denker wrote:

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)?

More or less, yes, it is implied.

Proposition (1) is quite sweeping, because it makes reference
to "the laws of physics" which means !!all!! the laws of physics.
In particular, it brings in Maxwell's equations, which predict
a definite frame-independent speed for electromagnetic waves.

I would preface proposition (2) with "in particular" to clarify
its logical status relative to proposition (1).

I'm not sure "redundant" is the right word to describe proposition
(2). The latter serves a useful purpose, as a first step in
removing some of the vagueness of proposition (1).