Poincare and Einstein on Mass-Energy Equivalence: A Modern Perspective on their 1900 and 1905 PapersPlanck criticized Einstein's derivation in 1907. Various Einstein biographers and idolizers have attempted to support Einstein, but his 1905 work was inferior to what Poincare did in 1900.
Patrick MoylanBoth Poincaré 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. Poincaré'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.
Einstein never believed that an atomic bomb was possible, until Szilard and others convinced him around 1940.
Einstein never cites the Poincare 1900 paper, or the Hasenoehrl 1904 and 1905 papers on the subject. For Einstein's derivation to work, he needs radiation to have momentum, but never mentions it.
So how did Einstein do it? The obvious possibilities are: (1) he made a blunder, and just happened to get the right answer; (2) he read the Poincare and Hasenoerhl papers, and learned about radiation momentum from them; or (3) he rediscovered radiation momentum on his own, but did not think it was important enough to mention.
Considering that Einstein spent his whole life concealing and lying about his sources, the obvious conclusion is (2). His most famous relativity papers do not cite any sources, even though they directly build on the work of others. He spent his whole life pretending that he did not know about Poincare's work.
There is a myth that Einstein worked in isolation and obscurity, but that is not true. He was very well read on current Physics, and often wrote reviews of current research papers. The above paper says:
After all, it is hard to imagine that Einstein, at the time he wrote his paper, was not aware of Poincar ́e’s Festchrift article, which was one of the most important and widely read physics papers of that time [41], and it seems almost certain he would have been aware of Hasen ̈ohrl’s papers published some months before in the same journal to which he submitted his first two relativity papers [28].Before his death, someone finally confronted Einstein with the fact that Poincare had published all of his relativity ideas beforehand, and Einstein had no response.
The above paper does a good job of explaining the mental gymnastics that the Einstein idolizers have done to defend him.