The Field Equations of Gravitation
On November 25, 1915, Einstein presented to the physics-mathematics section of the Prussian Academy of Sciences a paper in which 'finally the general theory of relativity is closed as a logical structure' [E1]. The title of that paper is identical with the heading of the present chapter, in which it is described how his field equations reached their final form.
Einstein was still a professor at the ETH when he presented his report to the Vienna meeting discussed in Chapter 13. However, by then he had already decided to leave Zürich.
In the spring of 1913, Planck and Nernst had come to Zürich for the purpose of sounding out Einstein about his possible interest in moving to Berlin. A combination of positions was held out to him: membership in the Prussian Academy with a special salary to be paid, half by the Prussian government and half by the physics-mathematics section of the Academy from a fund maintained with outside help, a professorship at the University of Berlin with the right but not the obligation to teach, and the directorship of a physics institute to be established. The new institute was to be under the auspices of the Kaiser Wilhelm Gesellschaft, an organization founded in 1911 to support basic research with the aid of funds from private sources.*
Much later, Einstein recalled an interesting exchange between himself and Planck during this Zürich visit. ' Planck had asked him what he was working on, and Einstein described general relativity as it was then. Planck said, "As an older friend I must advise you against it for in the first place you will not succeed; and even if you succeed, no one will believe you."' [S1].
Einstein reacted rapidly and positively to the approach from Berlin. His correspondence from that period makes abundantly clear the principal reason for his interest in this offer. Neither then nor later was he averse to discussing physics issues with younger colleagues and students; but he had had enough of teaching classes. All he wanted to do was think. The catalogue of PhD theses awarded at____________________