IN THE SECOND “golden” decade of this century Albert Einstein unified physics and geometry and fulfilled a long cherished dream of Karl Friedrich Gauss, Bernhard Riemann and William K. Clifford. This geometrical theory of gravitation had “magnetic” types of velocity‐dependent forces and a finite velocity of gravitational interactions; it apparently predicted gravitational radiation. The equations describe gravitation in terms of the curvature of space‐time. Riemann gave the concept of the curvature of n‐dimensional space as a logical generalization of the concept of curvature of a two‐dimensional surface. Radii of curvature for such a surface are easy to visualize. There is a simple connection (given in the box on p. 39) between these radii and the sum of the angles of a small triangle made up of geodesic lines (figure 1).
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April 1968
April 01 1968
Gravitational waves
The search for gravitational radiation is snowballing with innovations in technique and technology. To measure radiation one can now use masses small enough to fit in a laboratory or large enough to be the earth or moon.
Physics Today 21 (4), 34–39 (1968);