General Relativity

General relativity is a theory about space-time and gravity proposed by Albert Einstein in 1915. It is an extension of special relativity and mainly deals with the effects of gravity, providing a theoretical description of how gravity influences the structure of space-time. In general relativity, gravity is regarded as the curvature of space-time, and matter and energy produce gravitational fields by curving space-time. Mass and energy cause space-time to curve, and other objects move along the curved paths of space-time, which is what we call gravity.

The basic assumptions of general relativity include the equivalence principle and the principle of general covariance. The equivalence principle states that the inertial mass of an object is equal to its gravitational mass and that gravity is equivalent to the inertial force in an accelerating frame of reference. The principle of general covariance holds that all differential equations reflecting physical laws should maintain the same form in all reference frames, meaning that all reference frames are equivalent.

After its establishment in 1915, Einstein proposed three experimental tests to verify the correctness of general relativity: the deflection of light near the sun, the precession of Mercury’s perihelion, and the gravitational redshift of spectral lines. These experimental observations quickly confirmed the correctness of general relativity. Additionally, general relativity has significant applications in astrophysics, such as predicting the existence of black holes, gravitational lensing, and gravitational waves. Gravitational waves have been indirectly observed and direct observation is the goal of current projects like the Laser Interferometer Gravitational-Wave Observatory (LIGO).