The theory of relativity - what is it? The postulates of the theory of relativity. Time and space in the theory of relativity

At the beginning of the 20th century, the theory of relativity was formulated. What is this and who is its creator, knows today every schoolboy. It is so fascinating that even people who are far from science are interested in it. In this article, the available language describes the theory of relativity: what is it, what are its postulates and application.

They say that epiphany came to Albert Einstein, its creator, in a moment. The scientist allegedly rode a tram in the Swiss Bern. He looked at the street clock and suddenly realized that this clock would stop if the tram was accelerating to the speed of light. In this case, time would not be. Time in the theory of relativity plays a very important role. One of the postulates formulated by Einstein is that different observers perceive reality in different ways. This applies in particular to time and distance.

Accounting for the position of the observer

On that day, Albert realized that, in the language of science, the description of any physical phenomenon or event depends on which frame the observer is in. For example, if some tram passenger drops their glasses, they will fall vertically down towards her. If you look from the standpoint of a pedestrian standing on the street, then the trajectory of their fall will correspond to the parabola, as the tram moves and simultaneously the glasses fall. Thus, each has its own reference frame. We propose to consider in more detail the basic postulates of the theory of relativity.

The law of distributed motion and the principle of relativity

Despite the fact that when changing the reference systems the descriptions of events change, there are also universal things that remain unchanged. In order to understand this, we must ask ourselves not the fall of the glasses, but the law of nature that causes this fall. For any observer, regardless of whether it is in a moving or fixed coordinate system, the answer to it remains unchanged. This law is called the law of distributed motion. It acts equally in the streetcar and on the street. In other words, if the description of events always depends on who observes them, then this does not apply to the laws of nature. They are, as they say in the scientific language, invariant. This is the principle of relativity.

Two theories of Einstein

This principle, like any other hypothesis, was first to be verified by correlating it with the natural phenomena operating in our reality. Einstein deduced 2 theories from the principle of relativity. Although they are related, they are considered separate.

Private, or special, theory of relativity (SRT) is based on the proposition that for all possible reference systems whose velocity of movement is constant, the laws of nature remain the same. The general theory of relativity (GTR) extends this principle to any reference frame, including those that move with acceleration. In 1905, A. Einstein published the first theory. The second, more complex in terms of mathematical apparatus, completed by 1916. The creation of the theory of relativity, both SRT and GRT, has become an important stage in the development of physics. Let us dwell in more detail on each of them.

Special theory of relativity

What is it, what is its essence? Let's answer this question. It is this theory that predicts many paradoxical effects that contradict our intuitive notions of how the world works. These are effects that are observed when the speed of motion approaches the speed of light. The most famous among them is the effect of slowing down time (the course of hours). Hours that move relative to the observer, for him are slower than those that are in his hands.

In the coordinate system, when moving at a speed close to the speed of light, time is stretched relative to the observer, and the length of objects (spatial extent), on the contrary, is compressed along the axis of the direction of this movement. This effect is called the Lorentz-Fitzgerald contraction. Back in 1889, he was described by George Fitzgerald, an Italian physicist. And in 1892 Hendrik Lorentz, a Dutchman, supplemented him. This effect explains the negative result given by the Michelson-Morley experiment, in which the speed of our planet's motion in outer space is determined by the measurement of the "ether wind". These are the basic postulates of the theory of relativity (special). Einstein supplemented these equations with the formula for the transformation of mass, made by analogy. According to her, as the speed of the body approaches the speed of light, the body weight increases. For example, if the speed is 260 thousand km / s, that is 87% of the speed of light, from the observer's point of view, which is in the stationary frame of reference, the mass of the object will double.

Confirmations of SRT

All these provisions, no matter how they contradict common sense, since the time of Einstein have found direct and full confirmation in a variety of experiments. One of them was conducted by scientists at the University of Michigan. This curious experience confirms the theory of relativity in physics. The researchers placed on board an airliner, which regularly made transatlantic flights, an ultra-precise atomic clock. Each time he returned to the airport, the testimony of these hours was checked against the control. It turned out that the clock on the plane each time more and more lagged behind the control. Of course, it was only about minor figures, fractions of a second, but the very fact is very revealing.

For the past half-century, researchers have been studying elementary particles on accelerators - huge hardware complexes. In them, beams of electrons or protons, that is, charged subatomic particles, are accelerated until their velocities approach the speed of light. After that, they are firing nuclear targets. In these experiments, one must take into account the fact that the mass of particles increases, otherwise the experimental results are not amenable to interpretation. In this respect SRT has long been a mere hypothetical theory. It has become one of the tools used in applied engineering, along with the Newtonian laws of mechanics. The principles of the theory of relativity have found great practical application in our day.

SRT and Newton's laws

By the way, speaking of Newton's laws (the portrait of this scientist is presented above), one should say that the special theory of relativity, which, it would seem, contradicts, actually reproduces the equations of Newton's laws almost exactly if it is used to describe bodies whose velocity Much less than the speed of light. In other words, if a special theory of relativity is applied, Newtonian physics is not at all abolished. This theory, on the contrary, supplements and expands it.

The speed of light is a universal constant

Using the principle of relativity, one can understand why in the given model of the structure of the world a very important role is played by the speed of light, rather than something else. This question is asked by those who are just beginning to get acquainted with physics. The speed of light is a universal constant due to the fact that it is defined as such by a natural-science law (for more details, see the Maxwell equations). The speed of light in a vacuum, due to the action of the principle of relativity, is the same in any reference frame. You might think that this contradicts common sense. It turns out that both the stationary source and the moving light reach the observer simultaneously (regardless of how fast they move). However, it is not. The speed of light, due to its special role, is given a central place not only in special, but also in general relativity. We will also talk about it.

General theory of relativity

It is used, as we have already said, for all frames of reference, not necessarily those whose velocity of movement relative to each other is constant. Mathematically, this theory looks much more complicated than the special one. This explains the fact that 11 years have passed between their publications. GTR includes a special one as a special case. Consequently, Newton's laws also enter into it. However, the UTO goes much further than its predecessors. For example, it explains the gravity in a new way.

Fourth dimension

Thanks to OTO, the world becomes four-dimensional: time is added to three spatial dimensions. All of them are inseparable, therefore, we need to speak no longer of the spatial distance existing in a three-dimensional world between two objects. It is now a matter of time-space intervals between various events that unite both the spatial and temporal remoteness of them from each other. In other words, time and space in the theory of relativity are considered as a kind of four-dimensional continuum. It can be defined as space-time. In this continuum, those observers who move relative to each other will have different opinions even about whether two events occurred simultaneously, or one of them preceded another. However, the causal relationship is not violated. In other words, the existence of a coordinate system in which two events occur in different sequences and not simultaneously does not even allow GRT.

OTO and the law of universal gravitation

According to the law of universal gravitation discovered by Newton, the force of mutual attraction exists in the Universe between any two bodies. Earth from this position rotates around the Sun, because between them there are forces of mutual attraction. Nevertheless, GR forces one to look at this phenomenon from the other side. Gravitation, according to this theory, is a consequence of the "curvature" (deformation) of space-time, which is observed under the influence of mass. The body is heavier (in our example, the Sun), the more space-time "bends" under it. Accordingly, its gravitational field is stronger.

In order to better understand the essence of the theory of relativity, let us turn to a comparison. The earth, according to GR, rotates around the Sun, like a small ball that rolls around the cone of the funnel, created as a result of "squeezing" space-time by the Sun. And what we used to think of as gravity is in fact an outward manifestation of this curvature, not force, in Newton's understanding. A better explanation of the phenomenon of gravity than that proposed in the UTO has not been found to date.

Methods for testing GRT

We note that it is not easy to check the GRT, since its results in laboratory conditions almost correspond to the law of universal gravitation. However, scientists still conducted a number of important experiments. Their results allow us to conclude that Einstein's theory is confirmed. GTR, in addition, helps to explain the various phenomena observed in space. This, for example, small deviations of Mercury from its stationary orbit. From the point of view of Newtonian classical mechanics they can not be explained. This is also why electromagnetic radiation emanating from distant stars is warped when it passes near the Sun.

The results predicted by GRT are in fact significantly different from those that give Newton's laws (his portrait is presented above), only when superstrong gravitational fields are present. Consequently, for a complete verification of general relativity, either very precise measurements of objects of enormous mass or black holes are necessary, since our usual notions with respect to them are inapplicable. Therefore, the development of experimental methods for testing this theory is one of the main tasks of modern experimental physics.

The minds of many scientists, and even people far removed from science, are occupied by Einstein's theory of relativity. What is it, we briefly told. This theory turns our usual notions about the world, so the interest to it is still not quenched.