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Einstein was convinced that Mileva was dictating the postcards, both the plaintive ones that had made him feel guilty and now the one asking him not to come for the summer hike. So he decided to go on vacation with his new love, Elsa. He explained his decision in a July 1915 letter, also recently made publicly available, to his friend Heinrich Zangger, a medical professor in Zurich who was trying to mediate between the Einsteins: My dear friend Zangger, My fine boy has been alienated from me for a few years already by my wife, who has a vengeful disposition, but also is so sly that outsiders and particularly men are always deceived by her. If you only knew what I had to live through with her, you would hold it against me that I did not find the energy for so long to separate myself from her. The postcard I received from little [Hans] Albert had been inspired, if not downright dictated, by her ... When I write to him, I get no response. Under these circumstances it appeared as if I couldn't see the children at all if I came now to Zurich in July, as I was firmly resolved to do. So at the last minute I decided, while I was at Göttingen giving talks about the general theory of relativity, to relax here in Sellin, where my cousin [Elsa] had rented lodgings with her children. A. Einstein The trip to Göttingen he referred to was to give some lectures at the invitation of the mathematical physicist David Hilbert. Einstein was particularly eager--too eager, it would turn out--to explain all the intricacies of relativity to him. The visit was a triumph, he exulted to Zangger. "I was able to convince Hilbert of the general theory of relativity."
Amid all of Einstein's personal turmoil, a new scientific anxiety was about to emerge. He was struggling to find the right equations that would describe his new concept of gravity, ones that would define how objects move through space and how space is curved by objects. By the end of the summer, he realized the mathematical approach he had been pursuing for almost three years was flawed. And now there was a competitive pressure. Einstein discovered to his horror that Hilbert had taken what he had learned from Einstein's lectures and was racing to come up with the correct equations first.
It was an enormously complex task. Although Einstein was the better physicist, Hilbert was the better mathematician. So in October 1915 Einstein threw himself into a monthlong frenzy in which he returned to an earlier mathematical strategy and wrestled with tensors, equations, proofs, corrections and updates that he rushed to give as lectures to Berlin's Prussian Academy of Sciences on four successive Thursdays--even as he was struggling to arrange a reconciliation with his sons.
His first lecture was delivered on Nov. 4, 1915, and it explained his new approach, though he admitted he did not yet have the precise mathematical formulation of it. That very afternoon, as soon as he finished his lecture, he wrote an anguished--and poignant--letter to Hans Albert: