E=mc^2 Proof: Is it OK? - Adam Aulton

[Redstart]

http://www.adamauton.com/warp/emc2.html

 

[PeterDonis]

I don't know that I would call it a "proof", exactly, but the reasoning described in the post, which is based on a well-known thought experiment of Einstein's, is valid, at least as far as establishing that the energy of radiation confined in a box must contribute to the rest mass of the box in order for energy and momentum to be conserved. But that doesn't necessarily establish $E = m c^2$ as a universally valid equation.