They said about this theory that only three people in the world understood it, and when mathematicians tried to express in numbers what follows from it, the author himself, Albert Einstein, joked that now he, too, had ceased to understand it.
Special and general theory relativity is an inseparable part of the doctrine on which modern scientific views on the structure of the world are based.
"Year of Miracles"
In 1905, Germany's leading scientific publication "Annalen der Physik" ("Annals of Physics") published four articles one after another by 26-year-old Albert Einstein, who worked as an expert 3rd class - a petty clerk - at the Federal Patent Office in Bern. He had collaborated with the magazine before, but publishing so many works in one year was an extraordinary event. It became even more remarkable when the value of the ideas contained in each of them became clear.
In the first of the articles, thoughts were expressed about the quantum nature of light, the processes of absorption and release were considered electromagnetic radiation. On this basis, the photoelectric effect was first explained - the emission of electrons by a substance, knocked out by photons of light, and formulas were proposed for calculating the amount of energy released in this case. It was for the theoretical developments of the photoelectric effect, which became the beginning of quantum mechanics, and not for the postulates of the theory of relativity, that Einstein would be awarded in 1922 Nobel Prize in physics.
Another article laid the foundation for applied areas of physical statistics based on the study of the Brownian motion of tiny particles suspended in a liquid. Einstein proposed methods for searching for patterns of fluctuations - disorderly and random deviations of physical quantities from their most probable values.
And finally, in the articles “On the electrodynamics of moving bodies” and “Does the inertia of a body depend on the energy content in it?” contained the germs of what would be designated in the history of physics as Albert Einstein's theory of relativity, or rather its first part - STR - special theory of relativity.
Sources and predecessors
IN late XIX century, many physicists thought that most global problems The universe has been decided, the main discoveries have been made, and humanity only has to use the accumulated knowledge to powerfully accelerate technical progress. Only a few theoretical inconsistencies spoiled the harmonious picture of the Universe, filled with ether and living according to the immutable Newtonian laws.
The harmony was spoiled by Maxwell's theoretical research. His equations, which described the interactions of electromagnetic fields, contradicted the generally accepted laws of classical mechanics. This concerned the measurement of the speed of light in dynamic reference systems, when Galileo’s principle of relativity stopped working - the mathematical model of the interaction of such systems when moving at the speed of light led to the disappearance of electromagnetic waves.
In addition, the ether, which was supposed to reconcile the simultaneous existence of particles and waves, macrocosm and microcosm, was undetectable. The experiment, which was carried out in 1887 by Albert Michelson and Edward Morley, was aimed at detecting the “ethereal wind”, which inevitably had to be recorded by a unique device - an interferometer. The experiment lasted a whole year - the time of the Earth's complete revolution around the Sun. The planet was supposed to move against the ether flow for six months, the ether was supposed to “blow into the sails” of the Earth for six months, but the result was zero: the displacement of light waves under the influence of the ether was not detected, which cast doubt on the very fact of the existence of the ether.
Lorentz and Poincaré
Physicists tried to find an explanation for the results of experiments on the detection of ether. Hendrik Lorenz (1853-1928) proposed his mathematical model. It brought back to life the etheric filling of space, but only under a very conditional and artificial assumption that when moving through the ether, objects could contract in the direction of movement. This model was modified by the great Henri Poincaré (1854-1912).
In the works of these two scientists, concepts that largely formed the main postulates of the theory of relativity appeared for the first time, and this does not allow Einstein’s accusations of plagiarism to subside. These include the conventionality of the concept of simultaneity, the hypothesis of the constant speed of light. Poincaré admitted that at high speeds, Newton's laws of mechanics require reworking, and concluded that motion is relativity, but in application to the ether theory.
Special theory of relativity - SRT
The problems of correctly describing electromagnetic processes became the motivating reason for choosing a topic for theoretical developments, and Einstein’s papers published in 1905 contained an interpretation of a special case - uniform and rectilinear movement. By 1915, the general theory of relativity was formed, which explained gravitational interactions, but the first theory was called special.
Einstein's special theory of relativity can be briefly stated in the form of two main postulates. The first extends the action of Galileo's principle of relativity to all physical phenomena, and not just to mechanical processes. In more general form it says: All physical laws are the same for all inertial (uniformly moving in a straight line or at rest) reference frames.
The second statement, which contains the special theory of relativity: the speed of propagation of light in a vacuum is the same for all inertial frames of reference. Next, a more global conclusion is made: the speed of light is the maximum maximum value for the speed of transmission of interactions in nature.
In the mathematical calculations of STR, the formula E=mc² is given, which had previously appeared in physical publications, but it was thanks to Einstein that it became the most famous and popular in the history of science. The conclusion about the equivalence of mass and energy is the most revolutionary formula of the theory of relativity. The concept that any object with mass contains huge amount energy became the basis for developments in the use of nuclear energy and, above all, led to the appearance of the atomic bomb.
Effects of special relativity
Several consequences follow from STR, called relativistic effects. Time dilation is one of the most striking. Its essence is that in a moving frame of reference time goes by slower. Calculations show that on a spacecraft making a hypothetical flight to the Alpha Centauri star system and back at a speed of 0.95 c (c is the speed of light) 7.3 years will pass, and on Earth - 12 years. Such examples are often cited when explaining the theory of relativity for dummies, as well as the related twin paradox.
Another effect is a reduction in linear dimensions, that is, from the point of view of an observer, objects moving relative to him at a speed close to c will have smaller linear dimensions in the direction of movement than their own length. This effect, predicted by relativistic physics, is called Lorentz contraction.
According to the laws of relativistic kinematics, the mass of a moving object is greater than its rest mass. This effect becomes especially significant when developing instruments for studying elementary particles - without taking it into account, it is difficult to imagine the operation of the LHC (Large Hadron Collider).
Spacetime
One of essential components SRT is a graphical representation of relativistic kinematics, a special concept of a unified space-time, which was proposed by the German mathematician Hermann Minkowski, who was at one time a mathematics teacher for a student of Albert Einstein.
The essence of the Minkowski model is a completely new approach to determining the position of interacting objects. The special theory of relativity focuses on time special attention. Time becomes not just the fourth coordinate of the classical three-dimensional coordinate system; time is not an absolute value, but an inseparable characteristic of space, which takes the form of a space-time continuum, graphically expressed in the form of a cone, in which all interactions occur.
Such space in the theory of relativity, with its development to a more general nature, was later subjected to curvature, which made such a model suitable for describing gravitational interactions.
Further development of the theory
SRT did not immediately find understanding among physicists, but gradually it became the main tool for describing the world, especially the world of elementary particles, which became the main subject of study of physical science. But the task of supplementing SRT with an explanation of gravitational forces was very urgent, and Einstein did not stop working, honing the principles of the general theory of relativity - GTR. The mathematical processing of these principles took quite a long time - about 11 years, and specialists from areas of the exact sciences related to physics took part in it.
Thus, a huge contribution was made by the leading mathematician of that time, David Hilbert (1862-1943), who became one of the co-authors of the gravitational field equations. They were the last stone in the construction of a wonderful building, which received the name - the general theory of relativity, or GTR.
General Theory of Relativity - General Relativity
The modern theory of the gravitational field, the theory of the “space-time” structure, the geometry of “space-time”, the law of physical interactions in non-inertial reporting systems - all this various names, which are endowed with Albert Einstein's general theory of relativity.
The theory of universal gravitation, which for a long time determined the views of physical science on gravity, on the interactions of objects and fields of various sizes. Paradoxically, its main drawback was the intangibility, illusory, and mathematical nature of its essence. Between the stars and planets there was a void, an attraction between celestial bodies was explained by the long-range action of certain forces, and instantaneous ones at that. Albert Einstein's general theory of relativity filled gravity with physical content and presented it as direct contact of various material objects.
Geometry of gravity
The main idea with which Einstein explained gravitational interactions is very simple. He declares space-time to be a physical expression of gravitational forces, endowed with quite tangible signs - metrics and deformations, which are influenced by the mass of the object around which such curvatures are formed. At one time, Einstein was even credited with calls to return to the theory of the universe the concept of ether, as an elastic material medium that fills space. He explained that it is difficult for him to call a substance that has many qualities that can be described as vauum.
Thus, gravity is a manifestation of the geometric properties of four-dimensional space-time, which was designated in STR as uncurved, but in more general cases it is endowed with curvature, which determines the movement of material objects, which are given the same acceleration in accordance with the principle of equivalence declared by Einstein.
This fundamental principle of the theory of relativity explains many of the “bottlenecks” of Newton’s theory of universal gravitation: the bending of light observed when passing near massive cosmic objects during some astronomical phenomena and, noted by the ancients, the same acceleration of the fall of bodies, regardless of their mass.
Modeling the curvature of space
A common example used to explain the general theory of relativity for dummies is the representation of space-time in the form of a trampoline - an elastic thin membrane on which objects (most often balls) are laid out, simulating interacting objects. Heavy balls bend the membrane, forming a funnel around themselves. A smaller ball launched across the surface moves in full accordance with the laws of gravity, gradually rolling into depressions formed by more massive objects.
But such an example is quite conventional. Real space-time is multidimensional, its curvature also does not look so elementary, but the principle of the formation of gravitational interaction and the essence of the theory of relativity become clear. In any case, a hypothesis that would more logically and coherently explain the theory of gravity does not yet exist.
Evidence of truth
General Relativity quickly began to be perceived as a powerful foundation on which modern physics could be built. From the very beginning, the theory of relativity amazed not only specialists with its harmony and harmony, and soon after its appearance it began to be confirmed by observations.
The point closest to the Sun - perihelion - Mercury's orbit gradually shifts relative to the orbits of other planets solar system, which was discovered in the middle of the 19th century. This movement - precession - did not find a reasonable explanation within the framework of Newton's theory of universal gravitation, but was accurately calculated on the basis of the general theory of relativity.
The solar eclipse that occurred in 1919 provided an opportunity for yet another proof of general relativity. Arthur Eddington, who jokingly called himself the second person out of three who understand the basics of the theory of relativity, confirmed the deviations predicted by Einstein when photons of light passed near the star: at the moment of the eclipse, a shift in the apparent position of some stars became noticeable.
An experiment to detect clock slowdown or gravitational redshift was proposed by Einstein himself, among other evidence of general relativity. Only later for many years It was possible to prepare the necessary experimental equipment and conduct this experiment. The gravitational shift of radiation frequencies from the emitter and receiver, separated in height, turned out to be within the limits predicted by General Relativity, and the Harvard physicists Robert Pound and Glen Rebka, who conducted this experiment, subsequently only increased the accuracy of the measurements, and the formula of the theory of relativity again turned out to be correct.
Einstein's theory of relativity is always present in the justification of the most significant space exploration projects. Briefly, we can say that it has become an engineering tool for specialists, in particular those who work with satellite navigation systems - GPS, GLONASS, etc. It is impossible to calculate the coordinates of an object with the required accuracy, even in a relatively small space, without taking into account the signal slowdowns predicted by general relativity. Especially when we are talking about objects separated by cosmic distances, where the error in navigation can be enormous.
Creator of the theory of relativity
Albert Einstein was still a young man when he published the principles of the theory of relativity. Subsequently, its shortcomings and inconsistencies became clear to him. In particular, the most main problem GTR has become impossible for it to grow into quantum mechanics, since the description of gravitational interactions uses principles that are radically different from each other. Quantum mechanics considers the interaction of objects in a single space-time, and for Einstein this space itself forms gravity.
Writing the "formula of all things" - unified theory a field that would eliminate the contradictions of general relativity and quantum physics was Einstein’s goal for many years, he worked on this theory until the last hour, but did not achieve success. The problems of general relativity have become an incentive for many theorists to search for more perfect models peace. This is how string theories, loop quantum gravity, and many others appeared.
The personality of the author of General Relativity left a mark on history comparable to the significance for science of the theory of relativity itself. She still does not leave anyone indifferent. Einstein himself wondered why so much attention was paid to him and his work by people who had nothing to do with physics. Thanks to his personal qualities, famous wit, active political position and even expressive appearance, Einstein became the most famous physicist on Earth, the hero of many books, films and computer games.
The end of his life is described dramatically by many: he was lonely, considered himself responsible for the appearance of terrible weapon, which became a threat to all life on the planet, his unified field theory remained unrealistic dream, but the best result can be considered the words of Einstein, spoken shortly before his death, that he had completed his task on Earth. It's hard to argue with that.
One of the pearls of scientific thought in the tiara of human knowledge with which we entered the 21st century is the General Theory of Relativity (hereinafter referred to as GTR). This theory has been confirmed by countless experiments; I will say more, there is not a single experiment where our observations would differ even a little bit, even a tiny bit, from the predictions of the General Theory of Relativity. Within the limits of its applicability, of course.
Today I want to tell you what kind of beast this General Theory of Relativity is. Why is it so difficult and why In fact she's so simple. As you already understand, the explanation will go on your fingers™, therefore, I ask you not to judge too harshly for very free interpretations and not entirely correct allegories. I want anyone to read this explanation humanitarian, without any knowledge of differential calculus and surface integration, was able to understand the basics of general relativity. After all, historically this is one of the first scientific theories, beginning to move away from the usual everyday human experience. With Newtonian mechanics everything is simple, three fingers are enough to explain it - here is the force, here is the mass, here is the acceleration. Here is an apple falling on your head (has everyone seen how apples fall?), here is the acceleration of its free fall, here are the forces acting on it.
With general relativity, not everything is so simple - curvatures of space, gravitational time dilation, black holes - all this should cause (and does!) a lot of vague suspicions in an unprepared person - are you messing with my ears, dude? What are the curvatures of space? Who saw these distortions, where do they come from, how can something like this even be imagined?
Let's try to figure it out.
As can be understood from the name of the General Theory of Relativity, its essence is that in general, everything in the world is relative. Joke. Not really though.
The speed of light is the quantity relative to which all other things in the world are relative. Any frame of reference is equal, no matter where they move, no matter what they do, even spin in place, even move with acceleration (which is serious blow to the guts of Newton and Galileo, who thought that only uniformly and rectilinearly moving reference systems could be relative and equal, and even then only within the framework of elementary mechanics) - anyway, you can always find clever trick(scientifically this is called coordinate transformation), with the help of which it will be possible to painlessly move from one frame of reference to another, practically without losing anything along the way.
A postulate helped Einstein reach such a conclusion (let me remind you - a logical statement taken on faith without proof due to its obviousness) "on the equality of gravity and acceleration". (Attention, there is a strong simplification of the wording here, but in general outline That's right - the equivalence of the effects of uniformly accelerated motion and gravity is at the very heart of General Relativity).
Prove this postulate, or at least mentally taste it quite simple. Welcome to the Einstein Elevator.
The idea of this thought experiment is that if you were locked in an elevator without windows and doors, then there is not the slightest, absolutely not a single way to know what situation you are in: either the elevator continues to stand as it stood at the ground floor level, and you (and all other contents of the elevator) the usual force of attraction acts, i.e. the force of gravity of the Earth, or the entire planet Earth was removed from under your feet, and the elevator began to rise upward, with an acceleration equal to the acceleration of free fall g=9.8m/s 2 .
No matter what you do, no matter what experiments you carry out, no matter what measurements of surrounding objects and phenomena you make, it is impossible to distinguish between these two situations, and in the first and second cases, all processes in the elevator will take place exactly the same.
The reader with an asterisk (*) probably knows one tricky way out of this difficulty. Tidal forces. If the elevator is very (very, very) large, 300 kilometers across, it is theoretically possible to distinguish gravity from acceleration by measuring the force of gravity (or the magnitude of acceleration, we don’t yet know which is which) at different ends of the elevator. Such a huge elevator will be slightly compressed by tidal forces in the cross section and slightly stretched by them in the longitudinal plane. But these are already tricks. If the elevator is small enough, you won't be able to detect any tidal forces. So let's not talk about sad things.
In total, in a fairly small elevator we can assume that gravity and acceleration are the same thing. It would seem that the idea is obvious, and even trivial. What’s so new or complicated here, you might say, even a child should understand it! Yes, in principle, nothing complicated. It was not Einstein who invented this; such things were known much earlier.
Einstein decided to find out how a beam of light would behave in such an elevator. But this idea had very far-reaching consequences, which no one seriously thought about until 1907. I mean, to be honest, many people thought about it, but only one decided to get so deeply involved.
Let's imagine that we shine a flashlight on Einstein in our mental elevator. A ray of light flew out of one wall of the elevator, from point 0) and flew parallel to the floor towards the opposite wall. While the elevator is standing still, it is logical to assume that the light beam will hit the opposite wall exactly opposite the starting point 0), i.e. will arrive at point 1). The rays of light travel in a straight line, everyone went to school, they all learned this at school, and so did young Albertik.
It’s easy to guess that if the elevator went up, then during the time the beam was flying across the cabin, it would have time to move a little upward.
And if the elevator moves with uniform acceleration, then the beam will hit the wall at point 2), that is when viewed from the side it will seem that the light moved as if in a parabola.
Well, it's clear that In fact there is no parabola. The beam flew straight and still does. It’s just that while it was flying in its straight line, the elevator managed to go up a little, so here we are Seems that the beam moved in a parabola.
Everything is exaggerated and exaggerated, of course. A thought experiment, why our light flies slowly, and elevators move quickly. There is still nothing particularly cool here, all this should also be understandable to any schoolchild. You can conduct a similar experiment at home. You just need to find “very slow beams” and good, fast elevators.
But Einstein was truly a genius. Today many people scold him, like he’s a nobody and nothing at all, he sat in his patent office, weaved his Jewish conspiracies and stole ideas from real physicists. Most of those who say this do not understand at all who Einstein is and what he did for science and humanity.
Einstein said - since “gravity and acceleration are equivalent” (I repeat once again, he didn’t say exactly that, I’m deliberately exaggerating and simplifying), it means that in the presence of a gravitational field (for example, near the planet Earth), light will also fly not in a straight line, but along a curve . Gravity will bend the light beam.
Which in itself was an absolute heresy for that time. Any peasant should know that photons are massless particles. This means that light “doesn’t weigh” anything. Therefore, light should not care about gravity; it should not be “attracted” by the Earth, as stones, balls and mountains are attracted. If anyone remembers Newton's formula, gravity is inversely proportional to the square of the distance between bodies and directly proportional to their masses. If a ray of light has no mass (and light really has none), then there should be no attraction! Here contemporaries began to look sideways at Einstein with suspicion.
And he, the infection, went even further. He says we won’t break the peasants’ heads. Let's believe the ancient Greeks (hello, ancient Greeks!), let the light spread as before strictly in a straight line. Let's better assume that the space itself around the Earth (and any body with mass) bends. And not just three-dimensional space, but four-dimensional space-time.
Those. The light flew in a straight line and still does. Only this straight line is now drawn not on a plane, but lies on a sort of crumpled towel. And in 3D too. And it is the close presence of the mass that crumples this towel. Well, more precisely the presence of energy-momentum, to be absolutely precise.
All to him - “Albertik, you are driving, stop with opium as soon as possible! Because LSD has not yet been invented, and you definitely wouldn’t think of such a thing on a sober head! What a bent space, what are you talking about?”
And Einstein was like, “I’ll show you again!”
Locked yourself in your white tower (in the patent office, that is) and let’s adjust the mathematics to the ideas. I pushed for 10 years until I gave birth to this:
More precisely, this is the quintessence of what he gave birth to. In the more detailed version there are 10 independent formulas, and in the full version there are two pages of mathematical symbols in small print.
If you decide to take a real General Relativity course, here introductory part ends and then two semesters of studying harsh language must follow. And to prepare to study this math, you need at least three more years of higher mathematics, considering that you have completed high school and are already familiar with differential and integral calculus.
Hand on heart, the matan there is not so much complicated as tedious. Tensor calculus in pseudo-Riemannian space is not a very confusing topic to understand. This is not quantum chromodynamics, or, God forbid, not string theory. Everything is clear here, everything is logical. Here's a Riemann space, here's a manifold without breaks or folds, here's a metric tensor, here's a non-degenerate matrix, write out formulas for yourself, and balance the indices, making sure that covariant and contravariant representations of vectors on both sides of the equation correspond to each other. It's not difficult. It's long and tedious.
But let's not go to such lengths and return to to our fingers™. In our opinion, in a simple way, Einstein’s formula means approximately the following. To the left of the equal sign in the formula are the Einstein tensor plus the covariant metric tensor and the cosmological constant (Λ). This lambda is essentially dark energy which we still have today we don't know anything, but we love and respect. And Einstein doesn’t even know about it yet. There's one here interesting story worthy of a whole separate post.
In a nutshell, everything to the left of the equal sign shows how the geometry of space changes, i.e. how it bends and twists under the influence of gravity.
And on the right, in addition to the usual constants like π , speed of light c and gravitational constant G there is a letter T- energy-momentum tensor. In Lammer terms, we can consider that this is the configuration of how mass is distributed in space (more precisely, energy, because what mass or energy is the same emtse square) in order to create gravity and bend space with it in order to correspond to the left side of the equation.
That, in principle, is the whole General Theory of Relativity on your fingers™.
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, except for one thing: at the time Einstein compiled the theory, the expansion of the Universe and even the existence of other galaxies were not yet known, therefore scientists of that time believed that the Universe existed indefinitely 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 phenomenon for this best explanation, 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.
Even at the end of the 19th century, most scientists were inclined to the point of view that the physical picture of the world was basically constructed 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 a consequence of the "cascade" scientific discoveries made in an extremely short time historical period, covering the last years of the 19th century and the first decades of the 20th century, many of which completely did not fit into the understanding of ordinary human experience. A striking example may serve as 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 question on the applicability of the principle of relativity to optics and electrodynamics) to any physical. 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, and radar was carried out on the planets of the Solar System; the influence of the gravitational field of the Sun on radio communications with spaceships, which went to the distant planets of the solar system, 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 with philosophical point vision is to establish the dependence of the spatio-temporal 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 ones that preceded it physical theories in 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.
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 general interpretation 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.