What is Albert Einstein's general theory of relativity?
Einstein field equations The Einstein field equations (EFE; also known as Einstein's equations) is the set of 10 equations in Albert Einstein's general theory of relativity that describes the fundamental interaction of gravitation as a result of spacetime being curved by mass and energy. First published by Einstein in 1915 as a tensor equation, the EFE equate local "" (expressed by the Einstein tensor) with the local energy and momentum within that spacetime (expressed by the stress–energy tensor).
Synchronous frame In the special theory of relativity, choice of coordinates is limited by the requirement for a special kind of spacetime metric: the Minkowski metric. In the general theory of relativity, there is no such requirement so that the choice of reference frame is not limited: the three space coordinates "x", "x", "x" can take any values that define the positions of bodies in space while the time coordinate "x" can be measured by clocks with any possible adjustment. The problem thus arises how one can determine the real distances and time intervals by the values of "x", "x", "x", "x".