Journey Through Relativity 1912–1916: From Covariance to Entwurf and Back Again

This chapter offers a fresh perspective on Einstein’s complex and iterative journey toward general relativity between 1912 and 1916. In 1912, Einstein was on the verge of formulating the correct field equations based on the Ricci tensor, which he ultimately presented in 1915. However, he temporarily abandoned this approach, favoring field equations derived from invariants that he explored and struggled within his Zurich notebook. This chapter challenges the conventional narrative that Einstein completely rejected the November tensor during this period. During the “Entwurf” phase, Einstein developed a novel framework, although his field equations lacked general covariance. By 1916, Einstein revisited his 1915 general relativity and integrated it with David Hilbert’s equations from Hilbert’s 1915 paper, “Foundations of Physics”. While it might appear that Einstein’s 1916 work repackaged the 1914 “Entwurf” theory in a generally covariant guise, he demonstrated ingenuity and originality by deriving equations akin to the 1914 formulations from a fundamentally different framework-a generally covariant theory. This methodology reflects Einstein’s creative approach to reinterpreting earlier work. Notably, in his 1918 gravitational waves paper, he recast the third type of gravitational wave he had identified in 1916 into a transverse gravitational wave (see discussion in Chap. 3). This chapter underscores Einstein’s ability to navigate and reconcile different theoretical approaches, offering new insights into his path to general relativity.