Synge, John Lighton (1897–1995)

J. L. Synge, an Irish physicist and mathematician, made important contributions to science, especially with respect to the theory of relativity. During his career he worked in various universities and scientific institutions in Canada, the United States, and Ireland. In theperiod 1948–1972 he was professor in the School of Theoretical Physics at the Institute for Advanced Studies in Dublin, which would grow, thanks to him, into one of the most prominent centers for the study of relativistic physics.

Synge was the author of numerous books and papers marked by a noteworthy originality in thinking. For example, he was the first physicist to seriously consider the interior of black holes. In 1950, he showed that the surrounding of the central singularity in the Schwarzschild solution (the centrally symmetric gravitational field with a “point” source) represents two separated regions, the black hole and the white hole, the first of them denoting the end and the second denoting the beginning of the time for all objects occurring there. Synge's books Relativity: The Special Theory (1956) and Relativity: The General Theory (1960) are counted among the best monographs on the subject in question. They are distinguished by their original approach, philosophical depth, and brilliant literary style.

In his books and articles, Synge presented an important contribution to the understanding of the meaning of time and its measurement. According to him, chronometry presents an essential part of the theory of relativity. The determination of the geometry of spacetime consists in the measurement of lengths of sections of world-lines performed by ideal clocks and in the measurement of intervals between the emission and the reception of light signals, which allows the synchronization of clocks in different places and the measurement of spatial distances. In this way, ideal clocks and light signals are sufficient for the determination of the metrics of spacetime and there is no need for measuring rods. Synge believed that many physical and geometric notions (e.g., mutual orthogonality of spacetime vectors) could be expressed chronometrically.

[Page 1214]It was Synge's special distinction to have devised and popularized the use of spacetime diagrams (in, e.g., his Relativity of Time), which helped to make the explanation of many relativistic subjects more vivid and understandable.

He also showed the effectiveness of the use of the world function in relativistic calculations. This function assigns to every pair of events half the square of the length of the section of geodesic joining of these events. Thus, in the case of causally connected events, the world function is equal to the half of the square of the maximal time elapsed between them.