68. Proximity and action at a distance

Proximity action.

The law of interaction of stationary electric charges was established experimentally. But the question of how the action of force is transferred from one charge to another remained unsolved.

If we observe the action of one body on another at some distance from it, then before assuming that the action is direct, we tend first to examine whether there is any material connection between the bodies: threads, cords, etc. If there is such a connection, we explain the action of one body on another through these intermediate links. Thus, when the bus driver turns the handle that opens the door (fig. 1), the consecutive parts of the connecting rod are compressed, then they move until the door opens. In modern buses, the driver opens the door by forcing the compressed air in the cylinder to control the door mechanism. It is also not difficult to adapt an electromagnet for this purpose by conducting electric current through the wires. All three ways of opening the door have one thing in common: there is a continuous connecting line between the driver and the door, at each point of which some physical process is performed. Through this process, which runs from point to point, the action is transferred. And not instantly, but with this or that final speed.

So, the action between the bodies at a distance in many cases can be explained by the presence of the transmitting action intermediate links. Isn't it reasonable, even in cases where there is no links, no proxies between the interacting bodies, to allow the existence of some intermediate links? Otherwise, according to Maxwell's observation, we would have to assume that the body acts where it does not exist.
(Here and in the future, we will use Maxwell's article "Action at a distance".)

Who is not familiar with the properties of air, it may think that the mouth or vocal cords of a companion directly affect his ears, and consider the transmission of sound invisible environment, something completely incomprehensible. However, you can trace the entire process of sound wave transmission in detail and calculate their speed.

The assumption that the interaction between bodies distant from each other is always carried out with the help of intermediate links (or environment), transmitting the interaction from point to point, is the essence of the theory of Proximity action.

Many minds, according to Maxwell, have plunged into reflections about invisible currents surrounding planets and magnets, about invisible atmospheres around electrified bodies. These reflections were sometimes quite witty, but had an important disadvantage: they did not give anything to science.

Action at a distance.

This continued until Newton established the law of universal gravitation, however, without offering any explanation for its action. The following successes in the study of the solar system so captured the imagination of scientists that they generally began to tend to the idea that the search for any intermediaries, transmitting the interaction from one body to another, is not necessary at all.

The theory of direct action at a distance directly through the free space (void) appeared. According to this theory, the action is transmitted instantly at any great distance. The bodies are able to "feel" each other's presence without any environment between them. Supporters of action at a distance were not confused by the idea of the body's action where it was not there. "Don't we see," they reasoned, "how a magnet or an electrified comb right through the free space attracts bodies?" And the force of attraction, like a magnet, doesn't change noticeably if you wrap it in paper or put it in a wooden box. Moreover, even if it seems to us that the interaction of bodies is caused by direct contact, in reality it is not. At the closest contact, there is a small gap between the bodies. After all, a weight, for example, hanging on a string, does not break this string, even though there is a free space between the individual atoms of which it consists. Action at a distance is the only way of action that is found everywhere.

Objections to the theory of proximity action, as you can see, were quite strong, especially since they were supported by the remarkable success achieved by such convinced supporters of action at a distance, such as Coulomb and Amper, who discovered the laws of the interaction of electric charges and electric currents.

If the development of science was straightforward, it would seem that the victory of the theory of action at a distance is ensured. But in reality, development is more like a screw line. Having passed one turn, they return to approximately the same ideas, but already on a higher level. This is exactly what happened in the development of the theory of proximity action.

Success in the discovery of the laws of interaction of electric charges and currents were not closely related to the idea of action at a distance. After all, the experimental study of the forces themselves does not presuppose certain ideas about how these forces are transmitted. First of all, it was necessary to find mathematical expression of forces, and to find out their nature was possible later.