Relativistic mechanics, Problems in the search for harmony of...

Relativistic mechanics

The main purpose of this chapter is to ensure that the student understands the conceptual design of relativistic mechanics. As a result of studying the material in this chapter, the student must:


• the main concepts of relativistic mechanics and ways to manage them;

• Principles of invariance and maximum speed of communication, concepts of simultaneity, interval, space-time;

be able to

• determine the place of any concept in the structure of relativistic mechanics;

• Give any phenomenon a conceptual interpretation;

• give a dynamic explanation of the phenomena occurring;


• conceptual interpretation of actual problem situations related to the interpretation of the concepts of relativistic mechanics;

• a critical attitude to the views of various authors;

• a philosophical apparatus necessary for the interpretation of relativistic mechanics.

Keywords: the principle of invariance of the maximum transfer rate of interactions, the concept of relative simultaneity, space-time and interval.

Problem in the search for harmony of electrodynamics

Newton's mechanics uses the concepts of power and energy. But the mechanism of interactions does not receive a detailed explanation. The interaction of bodies is for the most part regarded as their collision. Newton himself was genuinely interested in gravitational phenomena. But he was also unable to explain the mechanism of gravitational interaction. In his time, the gravitational field was discussed mainly in purely hypothetical terms. It was not clear, for example, how the Earth and the Moon attract each other. In the XVIII-XIX centuries. clearly increased the need to understand the mechanism of physical interactions, taking into account their not only macro, but also micro-nature. In this case, the main impulses did not come so much from the theory of gravitation as from the theory of electromagnetic phenomena, so productively studied by Michael Faraday and James Maxwell.

They both used the concept of the field, i.e. The environment that acts on physical bodies, for example, on charged objects. Both the field and the body were recognized as physical objects, but of a fundamentally different nature. Bodies by definition have pronounced angular dimensions, lengths and durations. The field is omnipresent, it is everywhere. Often expressed in this way: there is substance and field. This distinction can not be called clear. If the materiality is understood as the presence of mass, then it is not alien to the field. The author prefers to compare with the field of the body. Unlike fields, bodies are physical objects with distinct condensation. The field has more volatile character, which is in front of a big conversation.

In 1865 Maxwell managed to present the basic laws of the electromagnetic field in the form of four equations. Their physical meaning was as follows:

1) electric charges generate an electric field;

2) there are no magnetic charges;

3) the currents and changes in the electric field in time cause a magnetic field;

4) the change in the magnetic field causes an electric field.

The new theory, as a rule, leads to unexpected results. So it happened with Maxwell's electrodynamics. One of them was that the speed of light (c) as an electromagnetic process was associated with two constants:

where - electrical; and is the magnetic constant.

When physicists manage to discover the law of interrelation of some parameters, they rightfully celebrate success. But in this case, he was marred by the impossibility of his consistent interpretation. It turned out that the speed of light in a medium characterized by electrical and magnetic permeability does not depend on the speed of its source. But this contradicts the classical idea of ​​the addition of velocities.

Another trouble was that Maxwell's equations turned out to be noninvariant for those systems that were considered equivalent in classical mechanics. In classical mechanics, the invariance principle assumes the recognition of the Galilean transformations. Consider them in the simplest form, however, trying not to lose sight of the physical essence of the processes.

If the system S moves relative to the system S 'with a constant speed and along the axis x, and the systems start coincide at the initial time in both systems, then the Galileo transformations have the form:


These transformations are followed by the relationship between the speed of the point and its accelerations in both frames:



Maxwell's equations are not invariant with respect to the Galilean transformations. Of course, physicists could not but excite the rejection of the Galilean transformations and, consequently, the principle of invariance (the principle of relativity).

Special unrest caused confusion with the nature of electromagnetic waves, including light. Physicists were sure that waves propagate in some elastic medium. No environment - no waves. The medium of electromagnetic waves was an ether. He had to be found. Of course, physicists have tried to do this.

Typically, the environment is detected by the resistance it has to the processes occurring in it. It was this idea that guided Albert Michelson, who in 1881 conducted a unique experiment that he repeated six years later with Henry Morley. Scientists believed that the passage of the Earth through the ether should cause the ether wind. It was this fact that the scientists intended to discover.

Scientific experiment

According to the Michelson-Morley experiment, a monochromatic beam of light was split into two beams that were directed to the mirrors, and after reflection from them they got into the interferometer. One beam of light moved in parallel, and the other was perpendicular to the imaginary ether wind. The experimenters turned the interferometer 90 ° and waited for changes in the interference pattern. A predictable change in the interference pattern was not detected. Scientists have recorded uttermost ethereal calm. But in this case, the existence of the ether itself was questioned.

So, on the eve of the 20th century, physicists faced a set of problems that awaited their resolution. It was necessary to achieve the desired harmony in the theory of electromagnetic phenomena.


1. Despite the abundance of experimental results, physicists have had difficulty in reconciling the conceptual foundations of Newtonian mechanics and Maxwell's electrodynamics.

2. Maxwell's equations confirmed the thesis of the equality of all inertial reference frames, but they were not invariant with respect to the Galilean transformations.

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