What is "relativity"?

Relativity is the basic theory about space-time and gravity, which was mainly founded by Einstein and divided into special relativity (special relativity) and general relativity (general relativity). The basic assumptions of relativity are the principle of invariance of light speed, the principle of relativity and the principle of equivalence. Relativity and quantum mechanics are two basic pillars of modern physics. Classical mechanics, which laid the foundation of classical physics, is not suitable for high-speed moving objects and objects under microscopic conditions. Relativity solves the problem of high-speed motion; Quantum mechanics solves problems under microscopic subatomic conditions. Relativity has greatly changed the common sense concepts of the universe and nature, and put forward new concepts such as simultaneous relativity, four-dimensional space-time and curved space.

restricted theory of relativity

Principal term: special relativity

Special relativity is a kind of relativity that is limited to the discussion of inertial system. Newton's view of time and space holds that space is a flat, isotropic and isotropic three-dimensional space, and time is a single dimension independent of space (so it is absolute). Special relativity holds that space and time are not independent of each other, but a unified four-dimensional space-time whole, and there is no absolute space and time. In the special theory of relativity, the whole space-time is still flat, isotropic and isotropic, which is an ideal situation corresponding to the "global inertial system". Special relativity assumes that the speed of light in vacuum is constant, and Lorentz transformation can be deduced by combining the principle of special relativity and the above-mentioned space-time properties.

Theory of relativity

Main project: general relativity

General relativity is a theory published by Albert Einstein in 19 15. Einstein put forward the "equivalence principle", that is, gravity and inertia force are equivalent. This principle is based on the equivalence between gravitational mass and inertial mass (currently confirmed by experiments to be between 10? Within the precision range of 12, there is still no difference between gravitational mass and inertial mass). According to the principle of equivalence, Einstein extended the principle of relativity in a narrow sense to the principle of relativity in a broad sense, that is, the form of physical laws is unchanged in all reference systems. The motion equation of an object is the geodesic equation in the reference system. Geodesic equation has nothing to do with the inherent properties of the object itself, but only depends on the local geometric properties of time and space. And gravity is the expression of local geometric properties of time and space. The existence of material mass will cause the bending of time and space. In curved space-time, objects still move along the shortest distance (that is, along the geodesic-in Euclidean space). For example, the geodesic movement of the earth in curved space-time caused by the sun actually revolves around the sun, resulting in a gravitational effect. Just like on the surface of the earth, if you move in a straight line, you actually walk around the great circle on the surface of the earth.