Poincare and Einstein on Mass-Energy Equivalence: A Modern Perspective on their 1900 and 1905 Papers

TL;DR

This paper revisits Poincaré's and Einstein's 1900 and 1905 derivations of mass-energy equivalence, highlighting the importance of momentum considerations often overlooked in Einstein's original analysis.

Contribution

It demonstrates that Einstein's derivation omits momentum considerations, clarifying historical criticisms and providing a modern perspective on their foundational work.

Findings

Einstein's derivation relies solely on energy conservation and relativity.

Objections to Einstein's approach stem from neglecting momentum considerations.

Revisiting Poincaré's approach offers a more complete understanding of mass-energy equivalence.

Abstract

Both Poincar\'e in his 1900 Festschrift paper \cite{Poincare} and Einstein in his 1905 \textsl{Annalen der Physik} article \cite{Einstein} were led to $E=mc^2$ by considering electromagnetic processes taking place in vacuo. Poincar\'e's treatment is based on a generalization of the law of conservation of momentum to include radiation. Einstein's analysis relies solely on energy conservation and the relativity principle together with certain assumptions, which have served as the source of criticism of the paper beginning with Max Planck in 1907. We show that these objections raised by Planck and others can be traced back to Einstein's failure to make use of momentum considerations. Relevance of our findings to a proper understanding of Ives' criticism of Einstein's paper is pointed out.