Einstein's Theory of General Relativity
Added on 20190920
3 Pages1058 Words123 Views



According to newtonian theory, gravitational effects propagate from place toplace instantaneously. With the advent of Einstein's special theory of relativity in 1905, a theory uniting the concepts of space and time into that of four dimensional flat spacetime (named Minkowski spacetime after the mathematician Hermann Minkowski), a problem became discernible with newtonian theory. According to special relativity, which is the current guideline to the form of all physical theory, the speed of light,c= 3 × 1010cm s1, is the top speed allowed to physical particles or forces: There can be no instantaneous propagation. After a decade of search for new concepts to make gravitational theory compatible with the spirit of special relativity, Einstein came up with the theory of general relativity (1915), the prototype of all modern gravitational theories. Its crucial ingredient, involving a colossal intellectual jump, is the concept of gravitation, not as a force, but as a manifestation of the curvature of spacetime, an idea first mentioned in rudimentary form by the mathematician Ceorg Bernhard Riemann in 1854. In Einstein's hands gravitation theory was thus transformed from a theory of forces into the first dynamical theory of geometry, the geometry of four dimensional curved spacetime.Why talk of curvature? One of Einstein's first predictions was the gravitational redshift: As any wave, such as light, propagates away from a gravitating mass, all frequencies in it are reduced by an amount proportionalto the change in gravitational potential experienced by the wave. This redshift has been measured in the laboratory, in solar observations, and by means of high precision clocks flown in airplanes. However, imagine for a moment that general relativity had not yet been invented, but the redshift hasalready been measured. According to a simple argument owing to Alfred Schild, wave propagation under stationary circumstances can display a redshift only if the usual geometric relations implicit in Minkowski spacetime are violated: The spacetime must be curved. The observations of the redshift thus show that spacetime must be curved in the vicinity of masses, regardless of the precise form of the gravitational theory.Einstein provided 10 equations relating the metric (a tensor with 10 independent components describing the geometry of spacetime) to the material energy momentum tensor (also composed of 10 components, one ofwhich corresponds to our previous). These Einstein field equations, in which both of the previously mentioned constantsGandcfigure as parameters, replace Poisson's equation. Einstein also replaced the newtonianlaw of motion by the statement that free test particles move along geodesics,the shortest curves in the spacetime geometry. The influential gravitation theorist John Archibald Wheeler has encapsulated general relativity in the aphorism "curvature tells matter how to move, and matter tells spacetime how to curve." The EotvosDickeBraginsky experiments demonstrate with high precision that free test particles all travel along the same trajectories in
End of preview
Want to access all the pages? Upload your documents or become a member.
Related Documents