Author: Peter Galison

Both Poincaré and Einstein possessed the most extensive scientific correspondences of the 19th and 20th centuries, respectively, including thousands of exchanged letters with various individuals. However, in the intersection of their lives, these two never exchanged a single postcard. In the final stages of Poincaré's life, they met once when Poincaré chaired a highly significant physics conference, during which Einstein presented his new ideas regarding light quanta.

At the conclusion of the meeting, Poincaré remarked that Einstein's presentation was so different from what physics should entail — that is, being describable by causal interactions, reasonable differential equations, and clear articulation of principles and conclusions — that he found it utterly intolerable. In his concluding remarks, Poincaré explicitly stated that what Einstein had said was so self-contradictory that anything could be derived from it. He considered it a disaster for science.

After returning home, Einstein hastily wrote a note to a friend, describing the remarkable work their colleagues were doing and expressing his admiration, even reverence, for Lorentz. Yet, he disparaged Poincaré, suggesting that Poincaré seemed to understand nothing. They brushed past each other like ships in the night, unable to acknowledge each other's existence due to relativity.

However, a few weeks after their unpleasant encounter, Poincaré wrote a recommendation letter for Einstein, who was applying for a highly important position. The letter was remarkable, essentially stating that this young man might accomplish some of the greatest things. Even if only a few of his wild ideas were proven correct, he would still be an immensely significant figure. The letter was remarkably gracious and generous. They never directly communicated again, nor did they meet thereafter.