Yes, but Einstein[/i'] still had to postulate it. It already had to hold in E&M applications in order for Maxwell's equations to work, so it wasn't too much of a stretch. But it has some bizarre implications for the uninitiated.

 

Yeah it was a postulate of special relativity wasn't it. Well the point stands, its not a "theoretical" thing, its something that was measured, not deduced by the theory itself. I really is wierd when you think about it.

its a set law represented by a mathematical equation. the one thing with the 'theory' of special relatively and many other 'theories' is that they are not theoretical at all, they are true tested facts.

would that not make them a theorem then ?

well yes... i would assume, a theorem is:

a general proposition or statement, not self-evident but demonstrable by argument or a chain of reasoning on the basis of given assumptions

 

where as a theory is:

a hypothesis that has been confirmed or established by observation or experiment and is accepted as accounting for known facts.

 

therefore the theory of relativety is a theory, where as pythagoras's theorem is a theorem!

 

the definition of 'a theory' is often placed parallel to theoretical, which it isnt.

 

definitions supplied by shorter oxford english dictionary (5th edition) on CD-ROM v2.0

To explain a bit more quickly: theories are based on evidence, theorems are based entirely on logical progression.