[Doctor Stochastic]

NB: e = mc² is not only not a theory (it's a law), it's only approximate.

[Virginia-American]

Dr. S said: NB: e = mc² is not only not a theory (it's a law), it's only approximate.

Could you please expand on this?

In particular, how is it approximate?

I was under the impression that SR was based on the fact that Maxwell's equations aren't invariant under Newtonian (Galilean) transformations of the inertial frame of reference, but are invariant under Lorentzian transformations.

Einstein basically said that this should be true of physical laws in general, and using this and the invariance of the speed of light (which I believe is a consequence of Maxwell's equations being invariant under Lorentz transformations), came up with SR and introduced the spacetime interval, energy-momentum 4-vector, and so forth, and deduced E=mc² from this theory.

So I'm curious why you said it's a "law", which I understand to mean an unexplained observational regularity (eg Charles' Law, Boyle's Law, the Law of Faunal Succession, etc), rather than a prediction of a theory, which could be used to falsify the theory.

[Elsie]

e = mc2 is not only not a theory (it's a law), it's only approximate.

The BigBang 'theory' re-arranges it:

M=E/C²

Then the question becomes:

"Where did the Energy come from?