At a speech on April 27, 1900 at the Royal Institution of Great Britain, Lord Kelvin said: “Theoretical physics is a harmonious and complete edifice. In the clear sky of physics there are only two small clouds - the constancy of the speed of light and the curve of radiation intensity depending on the wavelength. I think that these two particular questions will soon be resolved and the physicists of the 20th century will have nothing left to do.” Lord Kelvin turned out to be absolutely right in indicating the key areas of research in physics, but did not correctly assess their importance: the theory of relativity and quantum theory that emerged from them turned out to be endless fields of research that have occupied scientific minds for more than a hundred years.
Since it did not describe gravitational interaction, Einstein, soon after its completion, began to develop a general version of this theory, the creation of which he spent 1907-1915. The theory was beautiful in its simplicity and consistency with natural phenomena with the exception of one point: at the time Einstein compiled the theory, it was not yet known about the expansion of the Universe and even about the existence of other galaxies, therefore scientists of that time believed that the Universe existed for an infinitely long time and was stationary. At the same time, it followed from Newton’s law of universal gravitation that the fixed stars should at some point simply be pulled together to one point.
Not finding a better explanation for this phenomenon, Einstein introduced into his equations , which compensated numerically and thus allowed the stationary Universe to exist without violating the laws of physics. Subsequently, Einstein began to consider the introduction of the cosmological constant into his equations as his biggest mistake, since it was not necessary for the theory and was not confirmed by anything other than the seemingly stationary Universe at that time. And in 1965, cosmic microwave background radiation was discovered, which meant that the Universe had a beginning and the constant in Einstein’s equations turned out to be completely unnecessary. Nevertheless, the cosmological constant was nevertheless found in 1998: according to data obtained by the Hubble telescope, distant galaxies did not slow down their expansion as a result of gravitational attraction, but even accelerated their expansion.
Basic theory
In addition to the basic postulates of the special theory of relativity, something new was added here: Newtonian mechanics gave a numerical estimate of the gravitational interaction of material bodies, but did not explain the physics of this process. Einstein managed to describe this through the curvature of 4-dimensional space-time by a massive body: the body creates a disturbance around itself, as a result of which surrounding bodies begin to move along geodesic lines (examples of such lines are the lines of the earth's latitude and longitude, which to an internal observer seem to be straight lines , but in reality they are slightly curved). In the same way, the rays of light bow out, which distorts visible picture behind a massive object. With a successful coincidence of the positions and masses of objects, this leads to (when the curvature of space-time acts as a huge lens, making the source of distant light much brighter). If the parameters do not match perfectly, this can lead to the formation of an “Einstein cross” or “Einstein circle” in astronomical images of distant objects.
Among the predictions of the theory there was also gravitational time dilation (which, when approaching a massive object, acted on the body in the same way as time dilation due to acceleration), gravitational (when a beam of light emitted by a massive body goes into the red part of the spectrum as a result of its loss energy for the work function of exiting the “gravity well”), as well as gravitational waves (perturbation of space-time that is produced by any body with mass during its movement).
Status of the theory
The first confirmation of the general theory of relativity was obtained by Einstein himself in the same 1915, when it was published: the theory described with absolute accuracy the displacement of the perihelion of Mercury, which previously could not be explained using Newtonian mechanics. Since then, many other phenomena have been discovered that were predicted by the theory, but at the time of its publication were too weak to be detected. The latest such discovery on at the moment was the discovery of gravitational waves on September 14, 2015.
At the beginning of the 20th century, the theory of relativity was formulated. What it is and who its creator is, every schoolchild knows today. It is so fascinating that even people far from science are interested in it. This article describes the theory of relativity in accessible language: what it is, what are its postulates and application.
They say that Albert Einstein, its creator, had an epiphany in an instant. The scientist allegedly rode a tram in Bern, Switzerland. He looked at the street clock and suddenly realized that this clock would stop if the tram accelerated to the speed of light. In this case, there would be no time. Time plays a very important role in the theory of relativity. One of the postulates formulated by Einstein is that different observers perceive reality in different ways. This applies particularly to time and distance.
Accounting for the observer's position
That day, Albert realized that, speaking in the language of science, the description of any physical phenomenon or event depends on the frame of reference in which the observer is located. For example, if a tram passenger drops her glasses, they will fall vertically down in relation to her. If you look from the position of a pedestrian standing on the street, then the trajectory of their fall will correspond to a parabola, since the tram is moving and the glasses are falling at the same time. Thus, everyone has their own frame of reference. We propose to consider in more detail the main postulates of the theory of relativity.
The Law of Distributed Motion and the Principle of Relativity
Despite the fact that when reference systems change, the descriptions of events change, there are also universal things that remain unchanged. To understand this, we need to ask ourselves not the drop in glasses, but the law of nature that causes the drop. For any observer, regardless of whether he is in a moving or stationary coordinate system, the answer remains the same. This law is called the law of distributed motion. It works the same both on the tram 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 is usually expressed in scientific language, invariant. This is the principle of relativity.
Einstein's two theories
This principle, like any other hypothesis, had to be first tested by correlating it with natural phenomena operating in our reality. Einstein derived 2 theories from the principle of relativity. Although related, they are considered separate.
Particular, or special, theory of relativity (SRT) is based on the proposition that for all kinds of reference systems, the speed of which is constant, the laws of nature remain the same. The general theory of relativity (GTR) extends this principle to any frame of reference, including those that move with acceleration. In 1905, A. Einstein published the first theory. The second, more complex in terms of mathematical apparatus, was completed by 1916. The creation of the theory of relativity, both STR and GTR, became an important stage in the development of physics. Let's take a closer look at 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 ideas about how the world works. We are talking about those effects that are observed when the speed of movement approaches the speed of light. The most famous among them is the effect of time dilation (clock movement). A clock that moves relative to the observer goes slower for him than the one that is 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. Scientists call this effect the Lorentz-Fitzgerald contraction. Back in 1889, it was described by George Fitzgerald, an Italian physicist. And in 1892, Hendrik Lorenz, a Dutchman, expanded it. This effect explains the negative result given by the Michelson-Morley experiment, in which the speed of our planet in outer space is determined by measuring the “ethereal wind”. These are the basic postulates of the theory of relativity (special). Einstein supplemented these mass transformations by analogy. According to it, as the speed of a body approaches the speed of light, the mass of the body increases. For example, if the speed is 260 thousand km/s, that is, 87% of the speed of light, from the point of view of an observer who is in a resting frame of reference, the mass of the object will double.
Service station confirmations
All these provisions, no matter how contrary to common sense they may be, have been directly and completely confirmed in many experiments since the time of Einstein. One of them was conducted by scientists at the University of Michigan. This curious experiment confirms the theory of relativity in physics. Researchers placed ultra-accurate watches on board an airliner that regularly made transatlantic flights. Each time after it returned to the airport, the readings of these watches were checked against the control ones. It turned out that the clock on the plane was falling further and further behind the control clock each time. Of course, we were talking only about insignificant numbers, fractions of a second, but the fact itself is very indicative.
For the last half century, researchers have been studying elementary particles using accelerators - huge hardware complexes. In them, beams of electrons or protons, that is, charged ones, are accelerated until their speeds approach the speed of light. After this, they fire at nuclear targets. In these experiments, it is necessary to take into account that the mass of particles increases, otherwise the results of the experiment cannot be interpreted. In this regard, SRT is no longer just a hypothetical theory. It has become one of the tools used in applied engineering, along with Newton's laws of mechanics. The principles of the theory of relativity have found great practical application today.
SRT and Newton's laws
By the way, speaking of (the portrait of this scientist is presented above), it should be said that the special theory of relativity, which seems to contradict them, actually reproduces the equations of Newton’s laws almost exactly if it is used to describe bodies whose speed of motion is much less speed of light. In other words, if special relativity is applied, Newtonian physics is not abandoned at all. This theory, on the contrary, complements and expands it.
The speed of light is a universal constant
Using the principle of relativity, one can understand why in this model of the structure of the world it is the speed of light that plays a very important role, and not anything else. This question is asked by those who are just starting to get acquainted with physics. The speed of light is a universal constant due to the fact that it is defined as such by the law of natural science (you can learn more about this by studying Maxwell's equations). The speed of light in a vacuum, due to the principle of relativity, is the same in any frame of reference. You might think this is counterintuitive. It turns out that the observer simultaneously receives light from both a stationary source and a moving one (regardless of how fast it is moving). However, this is not true. The speed of light, due to its special role, is given a central place not only in special relativity, but also in general relativity. Let's talk about her too.
General theory of relativity
It is used, as we have already said, for all reference systems, not necessarily those whose speed 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 passed between their publications. General relativity includes special as a special case. Therefore, Newton's laws are also included in it. However, general relativity goes much further than its predecessors. For example, it explains gravity in a new way.
Fourth dimension
Thanks to general relativity, the world becomes four-dimensional: time is added to three spatial dimensions. All of them are inseparable, therefore, we no longer need to talk about the spatial distance that exists in the three-dimensional world between two objects. We are now talking about spatial-temporal intervals between various events, combining both their spatial and temporal distance 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 whether one of them preceded the other. However, the cause-and-effect relationships are not violated. In other words, even general relativity does not allow the existence of such a coordinate system, where two events occur in different sequences and not simultaneously.
General relativity 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. The Earth from this position rotates around the Sun, since there are forces of mutual attraction between them. Nevertheless, general relativity forces us to look at this phenomenon from a different perspective. Gravity, according to this theory, is a consequence of the “curvature” (deformation) of space-time, which is observed under the influence of mass. The heavier the body (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 General Relativity, rotates around the Sun like a small ball that rolls around the cone of a funnel created as a result of the Sun “pushing through space-time.” And what we are accustomed to consider the force of gravity is actually an external manifestation of this curvature, and not a force, in Newton’s understanding. To date, no better explanation of the phenomenon of gravity than that proposed in General Relativity has been found.
Methods for checking GTR
Note that general relativity is not easy to verify, 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. GR also helps explain various phenomena observed in space. These are, for example, small deviations of Mercury from its stationary orbit. From the point of view of Newtonian classical mechanics they cannot be explained. This is also why electromagnetic radiation coming from distant stars is bent when passing close to the Sun.
The results predicted by general relativity actually differ significantly from those given by Newton's laws (his portrait is presented above) only when superstrong gravitational fields are present. Therefore, for a full verification of general relativity, either very accurate measurements of objects of enormous mass or black holes are necessary, since our usual concepts are not applicable to them. 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 from science, are occupied by the theory of relativity created by Einstein. We briefly explained what it is. This theory overturns our usual ideas about the world, which is why interest in it still does not fade.
The special theory of relativity (STR) or partial theory of relativity is a theory of Albert Einstein, published in 1905 in the work “On the Electrodynamics of Moving Bodies” (Albert Einstein - Zur Elektrodynamik bewegter Körper. Annalen der Physik, IV. Folge 17. Seite 891-921 Juni 1905).
It explained the motion between different inertial frames of reference or the motion of bodies moving in relation to each other with constant speed. In this case, none of the objects should be taken as a reference system, but they should be considered relative to each other. SRT provides only 1 case when 2 bodies do not change the direction of movement and move uniformly.
The laws of SRT cease to apply when one of the bodies changes its trajectory or increases speed. Here the general theory of relativity (GTR) takes place, giving a general interpretation of the movement of objects.
Two postulates on which the theory of relativity is built:
- The principle of relativity- According to him, in all existing reference systems, which move in relation to each other at a constant speed and do not change direction, the same laws apply.
- The Speed of Light Principle- The speed of light is the same for all observers and does not depend on the speed of their movement. This is the highest speed, and nothing in nature has higher speed. The speed of light is 3*10^8 m/s.
Albert Einstein used experimental rather than theoretical data as a basis. This was one of the components of his success. New experimental data served as the basis for the creation of a new theory.
Physicists with mid-19th centuries have been searching for a new mysterious medium called ether. It was believed that the ether can pass through all objects, but does not participate in their movement. According to beliefs about the aether, by changing the speed of the viewer in relation to the aether, the speed of light also changes.
Einstein, trusting experiments, rejected the concept of a new ether medium and assumed that the speed of light is always constant and does not depend on any circumstances, such as the speed of a person himself.
Time intervals, distances, and their uniformity
The special theory of relativity links time and space. In the Material Universe there are 3 known in space: right and left, forward and backward, up and down. If we add to them another dimension, called time, then this will form the basis of the space-time continuum.
If you are moving at a slow speed, your observations will not converge with people who are moving faster.
Later experiments confirmed that space, like time, cannot be perceived in the same way: our perception depends on the speed of movement of objects.
Connecting energy with mass
Einstein came up with a formula that combined energy with mass. This formula is widely used in physics, and it is familiar to every student: E=m*c², in which E-energy; m - body mass, c - speed propagation of light.
The mass of a body increases in proportion to the increase in the speed of light. If you reach the speed of light, the mass and energy of a body become dimensionless.
By increasing the mass of an object, it becomes more difficult to achieve an increase in its speed, i.e., for a body with an infinitely huge material mass, infinite energy is required. But in reality this is impossible to achieve.
Einstein's theory combined two separate provisions: the position of mass and the position of energy into one general law. This made it possible to convert energy into material mass and vice versa.
Back in late XIX century, most scientists were inclined to the point of view that the physical picture of the world was basically built and would remain unshakable in the future - only the details remained to be clarified. But in the first decades of the twentieth century, physical views changed radically. This was the consequence of a "cascade" of scientific discoveries made during an extremely short historical period spanning recent years The nineteenth century and the first decades of the twentieth, many of which did not fit into the understanding of ordinary human experience. A striking example is the theory of relativity created by Albert Einstein (1879-1955).
Theory of relativity- physical theory of space-time, that is, a theory that describes the universal space-time properties of physical processes. The term was introduced in 1906 by Max Planck to emphasize the role of the principle of relativity
in special relativity (and, later, general relativity).
In a narrow sense, the theory of relativity includes special and general relativity. Special theory of relativity(hereinafter - SRT) refers to processes in the study of which gravitational fields can be neglected; general theory of relativity(hereinafter referred to as GTR) is a theory of gravitation that generalizes Newton’s.
Special, or special theory of relativity
is a theory of the structure of space-time. It was first introduced in 1905 by Albert Einstein in his work “On the Electrodynamics of Moving Bodies.” The theory describes movement, the laws of mechanics, as well as the space-time relationships that determine them, at any speed of movement,
including those close to the speed of light. Classical Newtonian mechanics
within the framework of SRT, it is an approximation for low speeds.
One of the reasons for Albert Einstein's success is that he valued experimental data over theoretical data. When a number of experiments revealed results that contradicted the generally accepted theory, many physicists decided that these experiments were wrong.
Albert Einstein was one of the first who decided to build a new theory based on new experimental data.
At the end of the 19th century, physicists were in search of the mysterious ether - a medium in which, according to generally accepted assumptions, light waves should propagate, like acoustic waves, the propagation of which requires air, or another medium - solid, liquid or gaseous. Belief in the existence of the ether led to the belief that the speed of light should vary depending on the speed of the observer in relation to the ether. Albert Einstein abandoned the concept of the ether and assumed that all physical laws, including the speed of light, remain unchanged regardless of the speed of the observer - as experiments showed.
SRT explained how to interpret motions between different inertial frames of reference - simply put, objects that move with constant speed in relation to each other. Einstein explained that when two objects are moving at a constant speed, one should consider their motion relative to each other, rather than taking one of them as an absolute frame of reference. So if two astronauts are flying on two spacecraft and want to compare their observations, the only thing they need to know is the speed relative to each other.
The special theory of relativity considers only one special case (hence the name), when the motion is rectilinear and uniform.
Based on the impossibility of detecting absolute motion, Albert Einstein concluded that all inertial reference systems are equal. He formulated two most important postulates that formed the basis of a new theory of space and time, called the Special Theory of Relativity (STR):
1. Einstein's principle of relativity - this principle was a generalization of Galileo’s principle of relativity (states the same thing, but not for all laws of nature, but only for the laws of classical mechanics, leaving open the question of the applicability of the principle of relativity to optics and electrodynamics) to any physical ones. It reads: all physical processes under the same conditions in inertial reference systems (IRS) proceed in the same way. This means that no physical experiments carried out inside a closed ISO can establish whether it is at rest or moving uniformly and rectilinearly. Thus, all IFRs are completely equal, and the physical laws are invariant with respect to the choice of IFRs (i.e., the equations expressing these laws have the same form in all inertial reference systems).
2. The principle of the constancy of the speed of light- the speed of light in a vacuum is constant and does not depend on the movement of the source and receiver of light. It is the same in all directions and in all inertial frames of reference. The speed of light in a vacuum is the limiting speed in nature - this is one of the most important physical constants, the so-called world constants.
The most important consequence of SRT was the famous Einstein's formula about the relationship between mass and energy E=mc 2 (where C is the speed of light), which showed the unity of space and time, expressed in a joint change in their characteristics depending on the concentration of masses and their movement and confirmed by the data of modern physics. Time and space ceased to be considered independently of each other and the idea of a space-time four-dimensional continuum arose.
According to the theory of the great physicist, when the speed of a material body increases, approaching the speed of light, its mass also increases. Those. The faster an object moves, the heavier it becomes. If the speed of light is reached, the mass of the body, as well as its energy, become infinite. The heavier the body, the more difficult it is to increase its speed; Accelerating a body with infinite mass requires an infinite amount of energy, so it is impossible for material objects to reach the speed of light.
In the theory of relativity, “two laws - the law of conservation of mass and conservation of energy - lost their validity independent of each other and turned out to be combined into a single law, which can be called the law of conservation of energy or mass." Thanks to the fundamental connection between these two concepts, matter can be turned into energy, and vice versa - energy into matter.
General theory of relativity- a theory of gravity published by Einstein in 1916, which he worked on for 10 years. Is further development special theory of relativity. If a material body accelerates or turns to the side, the laws of STR no longer apply. Then GTR comes into force, which explains the movements of material bodies in the general case.
The general theory of relativity postulates that gravitational effects are caused not by the force interaction of bodies and fields, but by the deformation of the space-time itself in which they are located. This deformation is related, in part, to the presence of mass-energy.
General relativity is currently the most successful theory of gravity, well supported by observations. GR generalized SR to accelerated ones, i.e. non-inertial systems. The basic principles of general relativity boil down to the following:
- limitation of the applicability of the principle of constancy of the speed of light to regions where gravitational forces can be neglected(where gravity is high, the speed of light slows down);
- extension of the principle of relativity to all moving systems(and not just inertial ones).
In general relativity, or the theory of gravity, it also proceeds from the experimental fact of the equivalence of inertial and gravitational masses, or the equivalence of inertial and gravitational fields.
The principle of equivalence plays an important role in science. We can always directly calculate the effect of inertial forces on any physical system, and this gives us the opportunity to know the effect of the gravitational field, abstracting from its heterogeneity, which is often very insignificant.
A number of important conclusions were obtained from general relativity:
1. The properties of space-time depend on moving matter.
2. A ray of light, which has an inertial and, therefore, gravitational mass, must bend in the gravitational field.
3. The frequency of light under the influence of the gravitational field should shift towards lower values.
For a long time, there was little experimental evidence of general relativity. The agreement between theory and experiment is quite good, but the purity of experiments is violated by various complex side effects. However, the effects of spacetime curvature can be detected even in moderate gravitational fields. Very sensitive clocks, for example, can detect time dilation on the Earth's surface. To expand the experimental base of general relativity, in the second half of the 20th century new experiments were carried out: the equivalence of inertial and gravitational masses was tested (including by laser ranging of the Moon);
using radar, the movement of Mercury's perihelion was clarified; the gravitational deflection of radio waves by the Sun was measured, planetary radar was carried out solar system; the influence of the gravitational field of the Sun on radio communications with spaceships that were sent to the distant planets of the solar system was assessed, etc. All of them, one way or another, confirmed the predictions obtained on the basis of general relativity.
So, the special theory of relativity is based on the postulates of the constancy of the speed of light and the same laws of nature in all physical systems, and the main results to which it comes are as follows: the relativity of the properties of space-time; relativity of mass and energy; equivalence of heavy and inert masses.
The most significant result of the general theory of relativity from a philosophical point of view is the establishment of the dependence of the space-time properties of the surrounding world on the location and movement of gravitating masses. It is thanks to the influence of bodies
With large masses, the paths of light rays are bent. Consequently, the gravitational field created by such bodies ultimately determines the space-time properties of the world.
The special theory of relativity abstracts from the action of gravitational fields and therefore its conclusions are applicable only to small areas of space-time. The cardinal difference between the general theory of relativity and the fundamental physical theories that preceded it is the rejection of a number of old concepts and the formulation of new ones. It is worth saying that the general theory of relativity has made a real revolution in cosmology. On its basis, various models of the Universe emerged.