Mainz University

**This theme involves a context of discovery, from 1905-1915, as well as a context of
justification that unfolded afterward. In 1907, when he first began to contemplate a theory of
gravitation and inertia based on a generalized theory of relativity, Einstein was guided by two
physical ideas: his equivalence principle and the notion that inertial effects were related to
fields generated by moving bodies. He later added a third, mathematical demand: the principle
of general covariance. The latter was inspired by the Ricci calculus, which Einstein first
learned about from his friend Marcel Grossmann in 1912. He quickly attached deep physical
meaning to this principle, seeing it as a royal road to a general theory of relativity. When he
made his momentous breakthrough to a generally covariant theory of gravitation in November
1915, however, the foundations of general relativity were by no means secure. After tracing
Einstein's journey up through November 1915, we turn to the context of justification in the
early history of GRT. During the period 1916-1920 several key contributions to GRT were
made by leading mathematicians and astronomers, including Karl Schwarzschild, David
Hilbert, Willem de Sitter, Hermann Weyl, and Felix Klein. However, the physical,
mathematical, and conceptual foundations of GRT continued to arouse passionate debates,
few of which helped to clarify any fundamental issues.
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