How the principle of equivalence was discovered and what it assumes

The provisions of this principle apply to the field of gravity and inertia. The equivalence principle we are considering is the heuristic principle that was applied by the great Albert Einstein when he was engaged in the development of his greatest scientific discovery - the general theory of relativity.

In its most general form, Einstein's equivalence principle says that the forces of gravitational interaction between objects are directly proportional to the gravitational mass of the body, and the inertia forces of this body, in this case, are proportional to the inertial mass of the body. And in the case when both of the body masses are equal, it is not possible to determine which of the forces acts on this body.

To prove these conclusions, Einstein used this experiment. It is necessary to imagine that two bodies are in an elevator. This elevator is infinitely far from the gravitating bodies acting on it and moves with acceleration. In this case, the inertia force will act on all the bodies that are in the elevator , and they will have a certain weight.

If the elevator is stationary, then the bodies inside it will also have weight, which means that all mechanical transformations in both elevators will occur in the same way. This effect Einstein extended to all phenomena of mechanics, and even all physics, then the scientist's conclusions supplemented the fundamental principles of equivalence.

Today, some researchers believe that the principle of equivalence can be considered as the main in the whole theory of relativity, and therefore, and the gravitational field is a noninertial reference frame. However, such a statement can be considered reliable only in part. The point is that each noninertial system in the special theory of relativity of A. Einstein has as its basis the usual linear space-time. In the general theory, which includes the metric concept of gravity, space-time is curved. This discrepancy is explained by the fact that metric concepts do not contain global inertial systems at all. Here the principle of equivalence can manifest itself only if the curvature itself is neglected.

It is also advisable to differentiate the weak and strong variants of the manifestation of the equivalence principle, the difference of which lies in the fact that for small distances between objects there are no special discrepancies in the actions of the laws of nature, irrespective of which of these reference systems these objects are in.

The fundamental foundations of this theory were formulated by A. Einstein in 1907. When considering the significance of this principle on the scale of all physics, it should be said that Einstein's discovery continues and develops Galileo's claim that all bodies, regardless of their mass, acquire accelerations in the gravitational field. This provision led to the conclusion that the inertial mass is equivalent. Later this equivalence was measured and metrically, with accuracy up to the 12th sign.

It is important to note that the use of Einstein's discovery is effective only for small spatial volumes, because only under such conditions can gravity be assumed to be a constant value.

Einstein extended his principle of equivalence to all reference frames in a state of free fall, and also developed in more detail the concept of a local system. It was necessary to do this because in the Universe the gravitational field is present everywhere, and the gravitation is variable - it differs from point to point, because each point has its own parametric characteristics. Therefore, these systems, according to Einstein, should not be identified with inertial ones, which violates Newton's first law.