The doctrine of relativity. So was Einstein right? Checking the theory of relativity. General relativity and the law of universal gravitation

By this point in Einstein's life, his poorly disguised contempt for German roots, authoritarian teaching methods in Germany had already played a role and he was kicked out of high school, so he moved to Zurich in hopes of enrolling in the Swiss Federal Institute of Technology (ETH).

But first, Einstein decided to spend a year preparing at a school in the nearby town of Aarau. At this point, he soon found himself wondering what it was like to run next to a beam of light.

Einstein had already learned in physics class what a ray of light is: a multitude of vibrating electric and magnetic fields moving at a speed of 300,000 kilometers per second, the measured speed of light. If he ran alongside this speed, Einstein realized, he could see many vibrating electric and magnetic fields next to him, as if frozen in space.

But that was impossible. First, stationary fields would violate Maxwell's equations, mathematical laws, in which everything that physicists knew about electricity, magnetism and light was laid. These laws were (and still are) quite strict: any waves in these fields must move at the speed of light and cannot stand still, no exceptions.

Worse, the stationary fields did not fit with the principle of relativity, which has been known to physicists since the days of Galileo and Newton in the 17th century. Basically, the principle of relativity says that the laws of physics cannot depend on how fast you move: you can only measure the speed of one object relative to another.

But when Einstein applied this principle to his thought experiment, a contradiction arose: relativity dictated that everything he could see moving alongside a beam of light, including stationary fields, must be something mundane that physicists could create in a laboratory. But no one has ever seen such a thing.

This problem will worry Einstein for another 10 years, all the way through his studies and work at ETH and his journey to the Swiss capital Bern, where he will become an examiner at the Swiss Patent Office. It is there that he will resolve the paradox once and for all.

1904: measuring light from a moving train

It wasn't easy. Einstein tried every solution that came to his mind, but nothing worked. Almost desperate, he began to ponder a simple yet radical solution. Maxwell's equations might work for everything, he thought, but the speed of light has always been constant.

In other words, when you see a beam of light passing by, it doesn't matter if its source is moving towards you, away from you, to the side or somewhere else, and it doesn't matter how fast its source is moving. The speed of light that you measure will always be 300,000 kilometers per second. Among other things, this meant that Einstein would never see stationary oscillating fields, since he would never be able to catch a beam of light.

It was the only way which Einstein saw to reconcile Maxwell's equations with the principle of relativity. At first glance, however, this decision had its own fatal flaw. He later explained it with another thought experiment: Imagine a beam that is launched along a railroad embankment while a train passes by in the same direction at a speed of, say, 3000 kilometers per second.

Someone standing near the embankment would have to measure the speed of the light beam and get the standard number of 300,000 kilometers per second. But someone on the train will see light traveling at 297,000 kilometers per second. If the speed of light is not constant, Maxwell's equation inside the car should look different, Einstein concluded, and then the principle of relativity would be violated.

This seeming contradiction made Einstein pause for almost a year. But then, one fine morning in May 1905, he went to work with his best friend Michel Besso, an engineer he had known from his student days in Zurich. The two men talked about Einstein's dilemma, as they always did. And suddenly Einstein saw a solution. He worked on it all night, and when they met the next morning, Einstein told Besso, “Thank you. I completely solved the problem. "

May 1905: Lightning strikes a moving train

Einstein's revelation was that observers in relative motion perceive time differently: it is quite possible that two events will occur simultaneously from the point of view of one observer, but in different time from the point of view of the other. And both observers will be right.

Einstein later illustrated his point with another thought experiment. Imagine that an observer is again standing next to the railway and a train rushes past him. The moment the central point of the train passes by the observer, lightning strikes at each end of the train. Since lightning strikes at the same distance from the observer, their light hits his eyes at the same time. It is fair to say that lightning strikes at the same time.

Meanwhile, exactly in the center of the train, another observer sits. From his point of view, light from two lightning strikes travels the same distance and the speed of light will be the same in any direction. But since the train is moving, the light coming from the back lightning must travel a greater distance, so it hits the observer a few moments later than the light from the beginning. Since light pulses arrive at different times, it can be concluded that lightning strikes are not simultaneous - one is faster.

Einstein realized that it is precisely this simultaneity that is relative. And once you recognize that, the strange effects we now associate with relativity are resolved with simple algebra.

Einstein frantically wrote down his thoughts and submitted his work for publication. The title was "On the electrodynamics of moving bodies", and it reflected Einstein's attempt to link Maxwell's equations with the principle of relativity. Special thanks were given to Besso.

September 1905: mass and energy

This first work, however, did not become the last. Einstein was obsessed with relativity until the summer of 1905, and in September he sent a second article for publication, already in hindsight.

It was based on another thought experiment. Imagine an object at rest, he said. Now imagine that he simultaneously emits two identical pulses of light in opposite directions. The object will remain in place, but as each pulse carries away a certain amount of energy, the energy contained in the object will decrease.

Now, Einstein wrote, what would this process look like for a moving observer? From his point of view, the object will simply continue to move in a straight line, while the two impulses will fly away. But even if the speed of the two impulses remains the same - the speed of light - their energies will be different. A pulse that moves forward in the direction of travel will have a higher energy than one that moves in the opposite direction.

With a bit of algebra, Einstein showed that in order for all of this to be consistent, an object must not only lose energy when sending out pulses of light, but also mass. Or mass and energy should be interchangeable. Einstein wrote down the equation that connects them. And it became the most famous equation in the history of science: E = mc 2.

A hundred years ago, in 1915, a young Swiss scientist, who at that time had already made revolutionary discoveries in physics, proposed a fundamentally new understanding of gravity.

In 1915, Einstein published general relativity, which characterizes gravity as a fundamental property of spacetime. He presented a series of equations describing the influence of the curvature of space-time on the energy and motion of the matter and radiation present in it.

One hundred years later, general theory of relativity (GR) became the basis for constructing modern science, she passed all the tests with which scientists pounced on her.

But until recently it was impossible to carry out experiments under extreme conditions to test the robustness of the theory.

It's amazing how strong the theory of relativity has proven itself over 100 years. We're still using what Einstein wrote!

Clifford Will, theoretical physicist, University of Florida

Scientists now have the technology to search for physics outside of general relativity.

A new look at gravity

General relativity describes gravity not as a force (as it appears in Newtonian physics), but as the curvature of space-time due to the mass of objects. The Earth revolves around the Sun, not because the star attracts it, but because the Sun deforms space-time. If you put a heavy bowling ball on a stretched blanket, it will change its shape - gravity affects space in much the same way.

Einstein's theory predicted some crazy discoveries. For example, the possibility of the existence of black holes that bend space-time to such an extent that nothing can escape from the inside, not even light. Based on the theory, evidence was found for the generally accepted opinion today that the universe is expanding and accelerating.

General relativity has been confirmed by numerous observations. Einstein himself used general relativity to calculate the orbit of Mercury, whose motion cannot be described by Newton's laws. Einstein predicted the existence of objects so massive that they bend light. This is a gravitational lensing phenomenon that astronomers often encounter. For example, the search for exoplanets is based on the effect of subtle changes in radiation curved gravitational field the star around which the planet revolves.

Testing Einstein's theory

General relativity works well for gravity of ordinary force, as shown by experiments on Earth and observations of planets. Solar system... But it has never been tested under conditions of extremely strong fields in spaces lying on the boundaries of physics.

The most promising way to test a theory under these conditions is to observe changes in space-time called gravitational waves. They appear as a result of major events, when two massive bodies, such as black holes, merge, or especially dense objects - neutron stars.

A cosmic fireworks display of this magnitude will be reflected in space-time only in the smallest ripples. For example, if two black holes collided and merged somewhere in our Galaxy, gravitational waves could stretch and contract the distance between objects on Earth, a meter apart, by one thousandth the diameter of an atomic nucleus.

Experiments have appeared that can record changes in space-time due to such events.

There is a good chance of detecting gravitational waves in the next two years.

Clifford Will

The Laser Interferometric Gravitational Wave Observatory (LIGO), with observatories in the vicinity of Richland, Washington, and Livingston, Louisiana, uses a laser to detect minute distortions in twin L-shaped detectors. When ripples of space-time pass through the detectors, they stretch and contract the space, causing the detector to resize. And LIGO can measure them.

LIGO began a series of launches in 2002, but has not achieved results. Improvement work was carried out in 2010, and the organization's successor, the Advanced LIGO Observatory, should be operational again this year. Many of the planned experiments are aimed at finding gravitational waves.

Another way to test the theory of relativity is to look at the properties of gravitational waves. For example, they can be polarized, like light passing through polarizing glasses. The theory of relativity predicts the features of such an effect, and any deviations from the calculations may cause doubts in the theory.

Unified theory

Clifford Will believes that the discovery of gravitational waves will only strengthen Einstein's theory:

I think we should continue to search for evidence of general relativity to be sure that it is correct.

Why are these experiments needed at all?

One of the most important and elusive tasks of modern physics is the search for a theory that will link together Einstein's research, that is, the science of the macrocosm, and quantum mechanics, the reality of the smallest objects.

Advances in this direction, quantum gravity, may require changes in general relativity. It is possible that experiments in the field of quantum gravity will require so much energy that they will be impossible to carry out. "But who knows," says Will, "maybe there is an effect in the quantum universe that is subtle but searchable."

The special theory of relativity, which at the beginning of the last century overturned generally accepted ideas about the world, still continues to excite the minds and hearts of people. Today we will try to figure out together what it is.

In 1905, Albert Einstein published special theory relativity (SRT), which explained how to interpret movements between different inertial reference frames - simply put, objects that move with constant speed in relation to each other.

Einstein explained that when two objects move at a constant speed, one should consider their motion relative to each other, instead of accepting one of them as an absolute frame of reference.

So if two astronauts, you and, say, Herman, are flying on two spaceships and want to compare your observations, the only thing you need to know is your speed relative to each other.

Special relativity considers only one special case (hence the name), when the motion is rectilinear and uniform. If a material body accelerates or turns to the side, the SRT laws no longer apply. Then comes into force general theory relativity (GR), which explains the movements of material bodies in the general case.

Einstein's theory is based on two basic principles:

1. The principle of relativity: physical laws are preserved even for bodies that are inertial reference frames, that is, moving at a constant speed relative to each other.

2. The principle of the speed of light: the speed of light remains unchanged for all observers, regardless of their speed in relation to the light source. (Physicists use the letter c for the speed of light.)

One of the reasons for Albert Einstein's success is that he put experimental data above theoretical ones. 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 new theory based on new experimental data.

At the end of the 19th century, physicists were in search of a mysterious ether - an environment in which, according to generally accepted assumptions, should have spread light waves, like acoustic ones, for the propagation of which air is needed, or another medium - solid, liquid or gaseous. The belief in the existence of the ether led to the belief that the speed of light should change depending on the speed of the observer in relation to the ether.

Albert Einstein abandoned the concept of ether and suggested that all physical laws, including the speed of light, remain unchanged regardless of the speed of the observer - as experiments have shown.

Homogeneity of space and time

Einstein's SRT postulates a fundamental relationship between space and time. The material Universe, as you know, has three spatial dimensions: up and down, right and left, and forward and backward. One more dimension is added to it - the temporal one. Together, these four dimensions make up the space-time continuum.

If you are moving at a high speed, your observations in relation to space and time will differ from those of other people moving at a slower speed.

The picture below shows a thought experiment to help you understand this idea. Imagine that you are on spaceship, you have a laser in your hands, with which you send beams of light to the ceiling on which the mirror is fixed. The light, reflected, falls on the detector, which registers them.

Above - you sent a beam of light into the ceiling, it reflected and fell vertically on the detector. Below - for Herman, your light beam moves diagonally to the ceiling, and then diagonally to the detector

Let's say your ship is moving at a constant speed equal to half the speed of light (0.5c). According to Einstein's SRT, it doesn't matter to you, you don't even notice your movement.

However, Herman, watching you from a resting starship, will see a completely different picture. From his point of view, the beam of light will travel diagonally to the mirror on the ceiling, reflect from it and fall diagonally onto the detector.

In other words, the trajectory of the light beam will look different for you and for Herman, and its length will be different. Therefore, the length of time it takes for the laser beam to travel the distance to the mirror and to the detector will seem different to you.

This phenomenon is called time dilation: time on a starship moving at high speed, from the point of view of an observer on Earth, flows much slower.

This example, like many others, clearly demonstrates the inextricable connection between space and time. This connection is clearly manifested for the observer only when it comes to high speeds close to the speed of light.

Experiments since Einstein published his great theory have confirmed that space and time are actually perceived differently depending on the speed of movement of objects.

Combining mass and energy

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 the object moves, the heavier it becomes. In the case of reaching the speed of light, 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; to accelerate a body with an infinite mass, an infinite amount of energy is required, therefore it is impossible for material objects to reach the speed of light.

Before Einstein, the concepts of mass and energy in physics were considered separately. The brilliant scientist proved that the law of conservation of mass, like the law of conservation of energy, are parts of a more general law of mass-energy.

Due to the fundamental connection between these two concepts, matter can be turned into energy, and vice versa - energy into matter.

The article describes Einstein's theory of relativity without any formulas and abstruse words

Many of us have heard about Albert Einstein's theory of relativity, but some cannot understand the meaning of this theory. By the way, this is the first theory in history that takes us away from the usual worldview. Let's talk about her in simple words... We are all accustomed to three-dimensional perception: vertical plane, horizontal and depth. If we add time here and consider it as the fourth quantity, then we get a four-dimensional space. This is due to the fact that time is also a relative value. So, everything in our world is relative. What does it mean? For example, let's take two twin brothers, one of them will be sent into space at the speed of light for 20 years, and the other will be left on Earth. When the first twin returns from space, he will be 20 years younger than the one who remained on Earth. This is due to the fact that even time is relative in our world, like everything else. As an object approaches the speed of light, time slows down. When it reaches a speed equal to the speed of light, time stops altogether. From this we can conclude that if you exceed the speed of light, then time will go back, that is, into the past.

This is all in theory, but what about in practice? It is impossible to approach the speed of light, let alone exceed it. With respect to the speed of light, it always remains constant. For example, one person is standing on the platform of the station, and the second is traveling by train in his direction. If the one standing on the platform shines with a flashlight, then the light from it will travel at a speed of 300,000 kilometers per second. If the person who rides on the train also shines with a flashlight, then the speed of his light will not increase due to the speed of the train, it is always 300,000 kilometers per second.

Why is it still impossible to exceed the speed of light? The fact is that when approaching a speed equal to the speed of light, the mass of the object increases, and accordingly the energy required for the movement of the object also increases. If you reach the speed of light, then the mass of the object will be infinite, as, in principle, and energy, but this is impossible. Only objects that do not have their own mass can move with the speed of light, and this object is just light.

In addition, gravity is involved in this matter, it can change time. According to the theory, the higher the gravity, the slower time flows. But this is all in theory, but what about in practice? Today's navigation systems connected to satellites are so accurate because of this. If they did not take into account the theory of relativity, then the difference in measurements could be on the order of several kilometers.

"What is the theory of relativity?" - a short popular science film directed by Semyon Reitburt on Vtoroi creative association film studio "Mosnauchfilm" in 1964.