Is There a Rigorous Proof That E_0 = mc^2?

[quZz]

Hello everyone
Can some one please provide (a link to) the most rigorous proof of E_0 = mc^2?
Actually, I got stuck on this question: why doesn't E_0 = mc^2 + \rm{const}? How to prove that \rm{const} = 0?

 

[DrStupid]

Can some one please provide (a link to) the most rigorous proof of E_0 = mc^2?

I can provide you with the original:

http://www.fourmilab.ch/etexts/einstein/E_mc2/e_mc2.pdf

 

[quZz]

Hi, thanks for a quick reply.
In this paper it only proves that if energy of a body at rest is changed by dE, its mass also changes by dm=dE/c^2. It doesn't prove, however, a much stronger statement that all its energy equals its mass times c squared...