# The postulates of Special Relativity

1. Apr 11, 2012

### Debdutta

According to the first postulate of Special Relativity, all the laws of physics are symmetrical in all inertial frames. So that also means that Maxwell's equations are true in any such frame (experimentally verified). Now we can easily uncouple the four first-order differential equations in free space and that leads to two second order differential equations (in fact six) for the electric and magnetic fields, the wave equations, with the speed of such waves being that of light, which is precisely a constant, depending only on the permitivity and permeability of free-space. So my question is, what is the need of the second postulate if it is easily derivable from the first? It is a radical conclusion, but not an independent assumption, or is it?

2. Apr 11, 2012

### PAllen

Einstein did not want to assume Maxwell's equations. What if they were superseded? In fact, the were superseded by QED, while special relativity survives unchanged. Another way to look at it is the axiomatic framework chosen by Einstein acts to constrain any possible future theories of physics - they must be Lorentz invariant.

3. Apr 11, 2012

### Fredrik

Staff Emeritus
Another reason to not assume Maxwell's equations is that this would make SR a theory of electromagnetism. It's much prettier to define it as a model of space and time that serves as a framework in which we can define theories of particles, fields and interactions, like for example classical electrodynamics (Maxwell's equations).

4. Apr 11, 2012

### Debdutta

I see. Thank you PAllen and Fredrik. I got my answer.