# How the equivalence principle was discovered and what it assumes

The provisions of this principle apply to the field ofthe study of the forces 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 the most general form, the equivalence principleEinstein 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, EinsteinI 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 force of inertia 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 are alsowill have weight, and this 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 thatthe equivalence principle can be considered as the main one in the whole theory of relativity, and therefore the gravitational field is also a noninertial reference frame. However, such a statement can be considered reliable only in part. The fact is that each non-inertial 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 andstrong variants of the manifestation of the principle of equivalence, the difference of which is that, for small distances between objects, there will be no special discrepancies in the actions of the laws of nature, regardless of which of these reference systems these objects are in.

The fundamental foundations of this theory are A. Einstein formulated in 1907. When considering the significance of this principle on the scale of all physics, it should be said that the discovery of Einstein 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 principleequivalence on 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.