Tilman Sauer

Field equations in teleparallel space–time: Einstein's Fernparallelismus approach toward unified field theory

Abstract A historical account of Einsteins Fernparallelismus approach toward a unified field theory of gravitation and electromagnetism is given. In this theory, a space–time characterized by a curvature-free connection in conjunction with a metric tensor field, both defined in terms of a dynamical tetrad field, is investigated. The approach was pursued by Einstein in a number of publications that appeared in the period from summer 1928 until spring 1931. In the historical analysis special attention is given to the question of how Einstein tried to find field equations for the tetrads. We claim that it was the failure to find and justify a uniquely determined set of acceptable field equations that eventually led to Einsteins abandoning this approach. We comment on some historical and systematic similarities between the Fernparallelismus episode and the Entwurf theory, i.e., the precursor theory of general relativity pursued by Einstein in the years 1912–1915.

Marcel Grossmann and his contribution to the general theory of relativity

This article reviews the biography of the Swiss mathematician Marcel Grossmann (1878-1936) and his contributions to the emergence of the general theory of relativity. The first part is his biography, while the second part reviews his collaboration with Einstein in Zurich which resulted in the Einstein-Grossmann theory of 1913. This theory is a precursor version of the final theory of general relativity with all the ingredients of that theory except for the correct gravitational field equations. Their collaboration is analyzed in some detail with a focus on the question of exactly what role Grossmann played in it.

REMARKS ON THE ORIGIN OF PATH INTEGRATION: EINSTEIN AND FEYNMAN

I offer some historical comments about the origins of Feynmans path integral approach, as an alternative approach to standard quantum mechanics. Looking at the interaction between Einstein and Feynman, which was mediated by Feynmans thesis supervisor John Wheeler, it is argued that, contrary to what one might expect, the significance of the interaction between Einstein and Feynman pertained to a critique of classical field theory, rather than to a direct critique of quantum mechanics itself. Nevertheless, the critical perspective on classical field theory became a motivation and point of departure for Feynmans space-time approach to non-relativistic quantum mechanics.

Nova Geminorum 1912 and the origin of the idea of gravitational lensing

Einstein’s early calculations of gravitational lensing, contained in a scratch notebook and dated to the spring of 1912, are reexamined. A hitherto unknown letter by Einstein suggests that he entertained the idea of explaining the phenomenon of new stars by gravitational lensing in the fall of 1915 much more seriously than was previously assumed. A reexamination of the relevant calculations by Einstein shows that, indeed, at least some of them most likely date from early October 1915. But in support of earlier historical interpretation of Einstein’s notes, it is argued that the appearance of Nova Geminorum 1912 (DN Gem) in March 1912 may, in fact, provide a relevant context and motivation for Einstein’s lensing calculations on the occasion of his first meeting with Erwin Freundlich during a visit in Berlin in April 1912. We also comment on the significance of Einstein’s consideration of gravitational lensing in the fall of 1915 for the reconstruction of Einstein’s final steps in his path towards general relativity.

THE EINSTEIN-VARIĆAK CORRESPONDENCE ON RELATIVISTIC RIGID ROTATION

The historical significance of the problem of relativistic rigid rotation is reviewed in light of recently published correspondence between Einstein and the mathematician Vladimir Varicak from the years 1909 to 1913.