Sticky bead argument: Encyclopedia II - Sticky bead argument - The Bern and Chapel Hill conferences

Sticky bead argument - The Bern and Chapel Hill conferences

In 1955, an important conference honoring the semi-centennial of special relativity was held in Bern, the Swiss town where Einstein was working the famous patent office during the Annus mirabilis. Rosen attended and gave a talk in which he computed the Einstein pseudotensor and Landau-Lifschitz pseudotensor (two alternative, non-covariant, descriptions of the energy carried by a gravitational field, a notion which is notoriously difficult to pin down in general relativity). These turn out to be zero for the Einstein-Rosen waves, and Rosen argued that this reaffirmed the negative conclusion he had reached with Einstein in 1936.

However, by this time a few physicists, such as Felix A. E. Pirani and Ivor Robinson, had come to appreciate the role played by curvature in producing tidal accelerations, and were able to convince many peers that gravitational radiation would indeed to produced, at least in cases such as a vibrating spring where different pieces of the system were clearly not in inertial motion. Nonetheless, some physicists continued to doubt whether radiation would be produced by a binary star system, where the world lines of the centers of mass of the two stars should, according to EIH approximation (dating from 1938 and due to Einstein, Infeld, and Banesh Hoffmann), follow timelike geodesics.

Inspired by conversations by Felix Pirani, Hermann Bondi took up the study of gravitational radiation, in particular the question of quantifying the energy and momentum carried off 'to infinity' by a radiating system. During the next few years, Bondi developed the Bondi radiating chart and the notion of Bondi energy to rigorously study this question in maximal generality.

In 1957, at a conference at Chapel Hill, North Carolina, appealing to various mathematical tools developed by John Lighton Synge, A. Z. Petrov and André Lichnerowicz, Pirani explained more clearly than had previously been possible the central role played by the Riemann tensor and in particular the tidal tensor in general relativity. He gave the first correct description of the relative (tidal) acceleration of initially mutually static test particles which encounter a sinusoidal gravitational plane wave.

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