Conclusion
A. Einstein's theory of relativity is a physical theory that considers the space-time properties of physical processes. Since the laws established by the theory of relativity are common to all physical processes, they are usually referred to simply as properties of space-time. These properties depend on the gravitational fields in a given space-time region. A theory that describes the properties of space-time in an approximation, when the fields of gravity can be neglected, is called a special or private theory of relativity, or simply a theory of relativity. The properties of space-time in the presence of gravitational fields are investigated in the general theory of relativity, also called Einstein's gravitational theory. Physical phenomena described by the theory of relativity are called relativistic and are found at velocities v of motion of bodies close to the velocity of light in vacuum c.
The basis of the theory of relativity are two provisions: the principle of relativity, which means the equality of all inertial frames of reference, and the constancy of the speed of light in vacuum, its independence from the speed of movement of the light source. These two postulates determine the formulas for the transition from one inertial frame of reference to another - the Lorentz transformation, which is characterized by the fact that such transitions change not only the spatial coordinates but also the moments of time (relativity of time). The main effects of the special theory of relativity are derived from the Lorentz transformations: the existence of a limiting rate of transmission of any interactions - the maximum speed to which the body can be accelerated, which coincides with the speed of light in vacuum; relativity of simultaneity (events simultaneous in one inertial frame of reference, generally not simultaneous in another); slowing down the flow of time in a fast moving body and reducing the longitudinal - in the direction of motion - the size of bodies, etc. All these regularities of the theory of relativity are firmly confirmed by experience.
The theory of relativity revealed the limited ideas of classical physics about "absolute" space and time, the illegality of their separation from moving matter: it gives a more accurate, in comparison with classical mechanics, the reflection of objective processes of reality.
A number of conclusions of the general theory of relativity differ qualitatively from the conclusions of the Newtonian theory of gravity. The most important of them are related to the appearance of black holes, singularities of space-time, the existence of gravitational waves (gravitational radiation).
Perceptions of space and time form the basis of the physical worldview, which in itself determines the value of the theory of relativity. Particularly important is its role in the physics of the nucleus and elementary particles, including the calculations of gigantic installations, which are intended for the flows of very fast particles necessary for experiments that allow us to advance in the study of the structure of matter.