When it comes to gravity, we involuntarily return to the memories of elementary school, where we first learned about this unusual force. We were told that it is she who keeps us on Earth, but this is not her only function.

Today we have collected 10 interesting facts about the force of gravity.

Interestingly, gravity is just a theory, not a law.

This probe has been exploring the Universe since 1977

Gravity has nothing to do with scientific laws. If you enter the word “gravity” into any search engine, you will see countless articles about the law of gravity. In fact, the concepts of "law" and "theory" in the scientific world have significant differences. The law is based on certain data from the results of actual research. A theory is an idea that explains the existence of a particular phenomenon. Understanding these concepts, it becomes clear why gravity cannot be called a law. At the moment, scientists cannot measure its impact on every celestial body. Voyager 1 (an automatic probe that explores the solar system and its environs) explored the solar system at a distance of about 21 billion km from the Earth and even briefly went beyond it. Voyager 1 has been "on a business trip" for 40 years, but the universe is too huge to explore it thoroughly.

There are gaps in the theory of gravity - and this is a fact!

Any theory is imperfect, the theory of gravity is no exception.

The theory of gravity is not perfect, but some of its gaps are invisible from Earth. For example, according to the theory, the gravitational force of the Sun should be stronger on the Moon than on the Earth, but then the Moon would revolve around the Sun, and not around the Earth. By observing the movement of the Moon in the night sky, we can absolutely determine that it revolves around the Earth. At school we were also told about Isaac Newton, who discovered gaps in the theory of gravity. He also introduced the new mathematical term "fluxion", from which he later developed the theory of gravity. The concept of "fluxion" may seem unfamiliar, today it is called "function". One way or another, we all learn functions in school, but they are not without flaws. Therefore, it is likely that in Newton's "proofs" of the theory of gravity, too, not everything is so smooth.

gravity waves

For more than half a century, scientists have been looking for confirmation of the existence of gravitational waves.

Albert Einstein's theory of relativity, also known as the theory of gravity, was introduced in 1915. Around the same time, the concept of gravity waves appeared, the existence of which was proved only in 1974. Gravity waves are vibrations in the space-time continuum resulting from the movement of masses in the universe due to the collision of black holes, the rotation of neutron stars or the occurrence of supernovae. When any of these events occur, gravitational waves form ripples, similar to circles in the water from a stone thrown on the surface of the water. These waves travel through the universe at the speed of light, which is why it took almost 60 years to prove the existence of gravitational waves. For the first 40 years, scientists observed waves from two stars that began to revolve around each other under the influence of gravity. Over time, the stars became closer and closer to each other in accordance with the miscalculations according to Einstein's theory. This was the proof of the existence of gravitational waves.

Black holes and gravity

Black holes could not exist without gravity

Black holes are one of the most mysterious phenomena in the Universe. They are formed when a star self-destructs and a new one is born, which throws parts of the old one to a fairly large distance, thus creating a place where gravity is so strong that not a single object that has fallen into it can come back. Gravity itself does not form a black hole, but helps scientists understand the essence of black holes and detect them in the universe. Since the gravitational force around the black hole is very strong, a lot of stars and gases gather around it, which helps to detect the black hole. Sometimes the gases around a black hole glow, forming a halo. If not for the super-powerful gravity in black holes, we would never have known about their existence.

Theory of dark matter and dark energy

Scientists believe that the universe consists of dark matter and is expanding due to dark energy

Approximately 68% of the Universe is made up of dark energy and 27% of dark matter. But neither dark energy nor matter have been studied in depth. However, we know that dark energy has many properties. Einstein's theory of relativity was instrumental in understanding dark energy and its ability to expand and create more space. Initially, scientists assumed that gravity was holding back the expansion of the universe, but in 1998, using the Hubble Space Telescope, it was possible to establish that the universe is expanding more and more. Thanks to this fact, it became clear that the theory of relativity cannot explain what is happening in the universe. Scientists have suggested the existence of dark matter and dark energy, thanks to which the Universe continues to grow.

Gravitons

Scientists suggest that there is a unit of gravity

All we are taught in school is that gravity is a force of attraction, but is it? If we imagine gravity itself as a particle and call it a graviton (or a quantum of the gravitational field), then it turns out that the force of attraction is formed by gravitons. True, physicists have not been able to confirm the existence of these particles, but there are many reasons why they should exist. The first reason is that gravity is just a force (one of the four basic natural forces), and its main element cannot be determined. Even if gravitons exist, it is very difficult to determine them. Physicists purely theoretically assume that gravitational waves consist of gravitons. It is quite easy to detect gravitational waves, it is enough to create a reflection of light rays in mirrors and see their splitting. But such a method is not suitable for determining the change in the distance between gravitons.

Formation of wormholes

With the help of wormholes, travel to neighboring galaxies could become a reality

Wormholes (space-time tunnels in a hypothetical model of the universe) are truly an amazing phenomenon. What if it were possible to zip through a space tunnel at the speed of light and end up in another galaxy? If wormholes exist, then this is quite possible. To date, there is no confirmation of the existence of such tunnels, but physicists are seriously considering their creation. Using Einstein's theory of relativity, physicist Ludwig Flamm described how much gravity can warp time and space in order to create a wormhole. Of course, this is not the only theory of the emergence of such tunnels.

The planets also attract the sun

The planets also have an attractive force

Everyone knows that the force of gravity of the Sun affects the planets of our solar system, which is why they revolve around it. In the same way, the Earth pulls on the Moon. However, every celestial body that has a mass also acts on the Sun with an attractive force, the power of which depends on the mass of objects and the distance between them. And since the Sun has the strongest gravity in our Galaxy, all the planets revolve around it.

Weightlessness

It turns out that gravity also works in space.

We've all seen photos and heard stories about how there's no gravity in space, so astronauts can fly in zero gravity. Nevertheless, there is still gravity in space, but it is so small that it is even called microgravity. It is thanks to her that it seems that the astronauts are floating in the air. If there was no gravity at all in space, then the planets could not revolve around the Sun, and the Moon around the Earth, just the greater the distance, the more the gravitational force weakens.

Time travel

In space, time passes differently than on Earth.

The ability to travel in time has always been of great concern to mankind. Many theories, including the theory of gravity, can explain the possibility of time travel. The force of gravity creates a warp in time and space that causes objects to move in a spiral, causing these objects to move faster than on the surface of the Earth. For example, clocks on space artificial satellites move only 38 microseconds a day because gravity in space causes objects to move faster than on Earth. For this reason, any astronaut who returns from orbit can be considered a time traveler, just the effect is not strong enough for them to feel it. The main question remains the possibility of time travel, which we saw in the movies, but there are no answers yet.

Look today at the night sky, at this boundless and so little-studied world by man. Our Universe is huge, and who knows what other secrets it holds. Wait and see.

Gravity, also known as attraction or gravitation, is a universal property of matter that all objects and bodies in the Universe possess. The essence of gravity is that all material bodies attract to themselves all other bodies that are around.

Earth gravity

If gravity is a general concept and quality that all objects in the Universe possess, then the earth's attraction is a special case of this all-encompassing phenomenon. The earth attracts to itself all the material objects that are on it. Thanks to this, people and animals can safely move around the earth, rivers, seas and oceans can remain within their shores, and air can not fly through the vast expanses of the Cosmos, but form the atmosphere of our planet.

A fair question arises: if all objects have gravity, why does the Earth attract people and animals to itself, and not vice versa? Firstly, we also attract the Earth to ourselves, it's just that compared to its force of attraction, our gravity is negligible. Secondly, the force of gravity is directly proportional to the mass of the body: the smaller the mass of the body, the lower its gravitational forces.

The second indicator on which the force of attraction depends is the distance between objects: the greater the distance, the less the effect of gravity. Including due to this, the planets move in their orbits, and do not fall on each other.

It is noteworthy that the Earth, the Moon, the Sun and other planets owe their spherical shape precisely to the force of gravity. It acts in the direction of the center, pulling towards it the substance that makes up the "body" of the planet.

Earth's gravitational field

The gravitational field of the Earth is a force energy field that is formed around our planet due to the action of two forces:

• gravity;
• centrifugal force, which owes its appearance to the rotation of the Earth around its axis (daily rotation).

Since both gravity and centrifugal force act constantly, the gravitational field is also a constant phenomenon.

The gravitational forces of the Sun, the Moon and some other celestial bodies, as well as the atmospheric masses of the Earth, have an insignificant effect on the field.

Law of gravity and Sir Isaac Newton

The English physicist, Sir Isaac Newton, according to a well-known legend, once walking in the garden during the day, saw the moon in the sky. At the same time, an apple fell from the branch. Newton was then studying the law of motion and knew that an apple falls under the influence of a gravitational field, and the Moon revolves in an orbit around the Earth.

And then the idea came to the mind of a brilliant scientist, illuminated by insight, that perhaps the apple falls to the earth, obeying the same force due to which the Moon is in its orbit, and does not rush randomly throughout the galaxy. This is how the law of universal gravitation, also known as Newton's Third Law, was discovered.

In the language of mathematical formulas, this law looks like this:

F=GMm/D2 ,

where F- force of mutual gravitation between two bodies;

M- mass of the first body;

m- mass of the second body;

D2- distance between two bodies;

G- gravitational constant, equal to 6.67x10 -11.

Obi-Wan Kenobi said that strength holds the galaxy together. The same can be said about gravity. The fact is that gravity allows us to walk on the Earth, the Earth to revolve around the Sun, and the Sun to revolve around the supermassive black hole at the center of our galaxy. How to understand gravity? About this - in our article.

Let's say right away that you will not find here an unambiguously correct answer to the question "What is gravity." Because it just doesn't exist! Gravity is one of the most mysterious phenomena that scientists puzzle over and still cannot fully explain its nature.

There are many hypotheses and opinions. There are more than a dozen theories of gravity, alternative and classical. We will consider the most interesting, relevant and modern.

Want more useful information and fresh news every day? Join us on telegram.

Gravity is a physical fundamental interaction

There are 4 fundamental interactions in physics. Thanks to them, the world is exactly the way it is. Gravity is one of these forces.

Fundamental Interactions:

• gravity;
• electromagnetism;
• strong interaction;
• weak interaction.

At the moment, the current theory describing gravity is GR (general relativity). It was proposed by Albert Einstein in 1915-1916.

However, we know that it is too early to talk about the ultimate truth. After all, several centuries before the advent of general relativity in physics, Newtonian theory, which was significantly expanded, dominated to describe gravity.

At the moment, it is impossible to explain and describe all issues related to gravity within the framework of general relativity.

Before Newton, it was widely believed that gravity on earth and celestial gravity were different things. It was believed that the planets move according to their own, different from earthly, ideal laws.

Newton discovered the law of universal gravitation in 1667. Of course, this law existed even during the dinosaurs and much earlier.

Ancient philosophers thought about the existence of gravity. Galileo experimentally calculated the acceleration of free fall on Earth, discovering that it is the same for bodies of any mass. Kepler studied the laws of motion of celestial bodies.

Newton was able to formulate and generalize the results of observations. Here's what he got:

Two bodies are attracted to each other with a force called gravitational force or gravitational force.

The formula for the force of attraction between bodies is:

G is the gravitational constant, m is the mass of the bodies, r is the distance between the centers of mass of the bodies.

What is the physical meaning of the gravitational constant? It is equal to the force with which bodies with masses of 1 kilogram each act on each other, being at a distance of 1 meter from each other.

According to Newton's theory, every object creates a gravitational field. The accuracy of Newton's law has been tested at distances of less than one centimeter. Of course, for small masses these forces are insignificant and can be neglected.

Newton's formula is applicable both for calculating the force of attraction of planets to the sun, and for small objects. We simply do not notice the force with which, say, the balls on the billiard table are attracted. Nevertheless, this force exists and can be calculated.

The force of attraction acts between any bodies in the universe. Its effect extends to any distance.

Newton's law of universal gravitation does not explain the nature of the force of attraction, but establishes quantitative patterns. Newton's theory does not contradict general relativity. It is quite sufficient for solving practical problems on the scale of the Earth and for calculating the motion of celestial bodies.

Gravity in General Relativity

Despite the fact that Newton's theory is quite applicable in practice, it has a number of shortcomings. The law of universal gravitation is a mathematical description, but does not give an idea of ​​the fundamental physical nature of things.

According to Newton, the force of attraction acts at any distance. And it works instantly. Considering that the fastest speed in the world is the speed of light, there is a discrepancy. How can gravity act instantaneously at any distance, when light needs not an instant, but several seconds or even years to overcome them?

Within the framework of general relativity, gravity is considered not as a force that acts on bodies, but as a curvature of space and time under the influence of mass. Thus, gravity is not a force interaction.

What is the effect of gravity? Let's try to describe it using an analogy.

Imagine space as an elastic sheet. If you put a light tennis ball on it, the surface will remain flat. But if you put a heavy weight next to the ball, it will push a hole in the surface, and the ball will begin to roll towards the large and heavy weight. This is "gravity".

By the way! For our readers there is now a 10% discount on

Discovery of gravitational waves

Gravitational waves were predicted by Albert Einstein back in 1916, but they were only discovered a hundred years later, in 2015.

What are gravitational waves? Let's draw an analogy again. If you throw a stone into calm water, circles will go on the surface of the water from the place of its fall. Gravitational waves are the same ripples, perturbations. Only not on the water, but in the world space-time.

Instead of water - space-time, and instead of stone, say, a black hole. Any accelerated movement of mass generates a gravitational wave. If the bodies are in a state of free fall, the distance between them will change when a gravitational wave passes.

Since gravity is a very weak force, the detection of gravitational waves has been associated with great technical difficulties. Modern technologies have made it possible to detect a burst of gravitational waves only from supermassive sources.

A suitable event for registering a gravitational wave is the merger of black holes. Unfortunately or fortunately, this happens quite rarely. Nevertheless, scientists managed to register a wave that literally rolled through the space of the Universe.

To register gravitational waves, a detector with a diameter of 4 kilometers was built. During the passage of the wave, oscillations of mirrors on suspensions in vacuum and the interference of light reflected from them were recorded.

Gravitational waves confirmed the validity of general relativity.

Gravity and elementary particles

In the standard model, certain elementary particles are responsible for each interaction. We can say that particles are carriers of interactions.

The graviton is responsible for gravity - a hypothetical massless particle with energy. By the way, in our separate material, read more about the Higgs boson and other elementary particles that made a lot of noise.

Finally, here are some interesting facts about gravity.

10 facts about gravity

1. To overcome the force of gravity of the Earth, the body must have a speed equal to 7.91 km / s. This is the first cosmic speed. It is enough for a body (for example, a space probe) to move in orbit around the planet.
2. To escape the Earth's gravitational field, a spacecraft must have a speed of at least 11.2 km/s. This is the second space velocity.
3. Objects with the strongest gravity are black holes. Their gravity is so strong that they even attract light (photons).
4. You will not find the force of gravity in any equation of quantum mechanics. The fact is that when you try to include gravity in the equations, they lose their relevance. This is one of the most important problems in modern physics.
5. The word gravity comes from the Latin “gravis”, which means “heavy”.
6. The more massive the object, the stronger the gravity. If a person who weighs 60 kilograms on Earth weighs on Jupiter, the scales will show 142 kilograms.
7. NASA scientists are trying to develop a gravitational beam that will allow objects to be moved contactlessly, overcoming the force of gravity.
8. Astronauts in orbit also experience gravity. More specifically, microgravity. They seem to fall endlessly along with the ship in which they are.
9. Gravity always attracts and never repels.
10. A tennis ball-sized black hole pulls objects with the same force as our planet.

Now you know the definition of gravity and you can say what formula is used to calculate the force of attraction. If the granite of science is holding you down harder than gravity, contact our student service. We will help you learn easily under the heaviest workloads!

Gravity is a seemingly simple concept known to every person since the school days. We all remember the story of how an apple fell on Newton's head and he discovered the law of universal gravitation. However, everything is not as simple as it seems. In that article we will try to give a clear and exhaustive answer to the question: what is gravity? And also consider the main myths and misconceptions about this interesting phenomenon.

In simple terms, gravity is the attraction between any two objects in the universe. Gravity can be determined by knowing the mass of bodies and the distance from one to the other. The stronger the gravitational field, the greater will be the weight of the body and the higher its acceleration. For example, on the Moon, the weight of an astronaut will be six times less than on Earth. The strength of a gravitational field depends on the size of the object it surrounds. So, the lunar force of gravity is six times lower than the earth. Isaac Newton first substantiated this scientifically and proved it with the help of mathematical calculations back in the 17th century.

What fell on Newton's head

Despite the fact that the great English scientist himself partially confirmed the well-known legend about an apple and a head injury, nevertheless, now we can say with confidence that when the law of universal gravitation was discovered, there were no injuries or insights. The basis that laid a new era in the natural sciences was the work "Mathematical Principles of Natural Philosophy". In it, Newton describes the law of gravity and the important laws of mechanics that he discovered over many years of hard work. The famous physicist was a leisurely and reasonable nature, as befits a brilliant scientist. And therefore, more than 20 years have passed from the beginning of reflections on the nature of gravity to the publication of a scientific work on it. However, the legend of the fallen fruit could have had some real basis, but the physicist's head definitely remained intact.

The laws of attraction were studied even before Isaac Newton by a wide variety of scientists. But only he was the first to mathematically prove the direct relationship between gravity and the motion of the planets. That is, an apple falling from a branch and the rotation of the moon around the earth are controlled by the same force - gravity. And it acts on any two bodies in the universe. These discoveries laid the foundation for the so-called celestial mechanics, as well as the science of dynamics. The Newtonian model dominated science for more than two centuries until the advent of the theory of relativity and quantum mechanics.

What modern scientists think about gravity

Gravity is the weakest of the four currently known fundamental interactions that all particles and bodies composed of them obey. In addition to the gravitational interaction, this also includes the electromagnetic, strong and weak. They are studied on the basis of different theories, for example, in the approximate velocities of small gravity, Newton's theory of gravitation is used. And in the general case, Einstein's general theory of relativity is used. In addition, the description of gravity in the quantum limit will have to be carried out with the help of quantum theory that has not yet appeared.

Of course, today physics is complex and goes far beyond the ideas about the world around the ordinary person. But it is necessary to be interested in it at least at the level of basic concepts, because it is quite possible that in the near future we can witness amazing discoveries in this area that will radically change the life of mankind. It will be embarrassing if you don't understand what's going on at all.

Myths about gravity

Not only ignorance, but also constant new discoveries in this scientific field give rise to various nonsense and myths about gravity. So, a few common misconceptions about this unique phenomenon:

• Artificial satellites will never leave the Earth's orbit and will forever revolve around it. It is not true. The fact is that in addition to the earth's gravity in space, there are various other factors that affect the orbit of bodies. This is the deceleration of the atmosphere for low orbits and the gravitational fields of the Moon and other planets. Most likely, if the satellite is allowed to spin without control for a long time, its orbit will change, and eventually it will either fly away into space or fall on the surface of the nearest body.
• There is no gravity in space. Even at stations where astronauts stay in weightlessness, there is a fairly strong gravity, slightly less than on Earth. Why don't they fall then? It can be said that the station employees are in a state of constant fall, but they will not fall.
• An object approaching a black hole will be torn apart. Pretty well known myth. The gravity of a black hole will indeed increase as you approach it, but it is not at all necessary that the tidal forces will be so powerful. Most likely they have a finite value at the event horizon, since the distance is considered from the center of the hole.

To the question "What is power?" physics answers as follows: "Force is a measure of the interaction of material bodies with each other or between bodies and other material objects - physical fields." All forces in nature can be attributed to four fundamental types of interactions: strong, weak, electromagnetic and gravitational. Our article talks about what gravitational forces are - a measure of the last and, perhaps, the most widespread type of these interactions in nature.

Let's start with the attraction of the earth

Everyone living knows that there is a force that pulls objects to the ground. It is commonly referred to as gravity, gravity, or terrestrial attraction. Thanks to its presence, a person has the concepts of "up" and "down", which determine the direction of movement or location of something relative to the earth's surface. So in a particular case, on the surface of the earth or near it, gravitational forces manifest themselves, which attract objects with mass to each other, manifesting their action at any, both the smallest and very large, even by cosmic standards, distances.

Gravity and Newton's third law

As you know, any force, if it is considered as a measure of the interaction of physical bodies, is always applied to one of them. So in the gravitational interaction of bodies with each other, each of them experiences such types of gravitational forces that are caused by the influence of each of them. If there are only two bodies (it is assumed that the action of all others can be neglected), then each of them, according to Newton's third law, will attract another body with the same force. Thus, the Moon and the Earth attract each other, resulting in the ebb and flow of the earth's seas.

Each planet in the solar system experiences several forces of attraction from the Sun and other planets at once. Of course, it is the gravitational force of the Sun that determines the shape and size of its orbit, but astronomers also take into account the influence of other celestial bodies in their calculations of their trajectories.

What will fall to the ground faster from a height?

The main feature of this force is that all objects fall to the ground at the same speed, regardless of their mass. Once, until the 16th century, it was believed that the opposite was true - heavier bodies should fall faster than light ones. To dispel this misconception, Galileo Galilei had to perform his famous experiment of simultaneously dropping two cannonballs of different weights from the inclined Leaning Tower of Pisa. Contrary to the expectations of the witnesses of the experiment, both nuclei reached the surface at the same time. Today, every schoolchild knows that this happened due to the fact that gravity gives any body the same free fall acceleration g = 9.81 m / s 2, regardless of the mass m of this body, and its value, according to Newton's second law, is F = mg.

The gravitational forces on the Moon and on other planets have different values ​​of this acceleration. However, the nature of the action of gravity on them is the same.

Gravity and body weight

If the first force is applied directly to the body itself, then the second to its support or suspension. In this situation, elastic forces always act on the bodies from the side of supports and suspensions. Gravitational forces applied to the same bodies act towards them.

Imagine a weight suspended above the ground on a spring. Two forces are applied to it: the elastic force of a stretched spring and the force of gravity. According to Newton's third law, the load acts on the spring with a force equal and opposite to the elastic force. This strength will be its weight. For a load weighing 1 kg, the weight is P \u003d 1 kg ∙ 9.81 m / s 2 \u003d 9.81 N (newton).

Gravitational forces: definition

The first quantitative theory of gravity, based on observations of the motion of the planets, was formulated by Isaac Newton in 1687 in his famous Principia of Natural Philosophy. He wrote that the attractive forces that act on the Sun and the planets depend on the amount of matter they contain. They propagate over long distances and always decrease as the reciprocal of the square of the distance. How can these gravitational forces be calculated? The formula for the force F between two objects with masses m 1 and m 2 located at a distance r is:

• F \u003d Gm 1 m 2 / r 2,
  where G is the constant of proportionality, the gravitational constant.

The physical mechanism of gravity

Newton was not completely satisfied with his theory, since it involved interaction between gravitating bodies at a distance. The great Englishman himself was convinced that there must be some physical agent responsible for transferring the action of one body to another, about which he spoke quite clearly in one of his letters. But the time when the concept of a gravitational field was introduced, which permeates all space, came only after four centuries. Today, speaking of gravity, we can talk about the interaction of any (cosmic) body with the gravitational field of other bodies, the measure of which is the gravitational forces arising between each pair of bodies. The law of universal gravitation, formulated by Newton in the above form, remains true and is confirmed by many facts.

Gravity theory and astronomy

It was very successfully applied to solving problems in celestial mechanics during the 18th and early 19th centuries. For example, mathematicians D. Adams and W. Le Verrier, analyzing the violations of the orbit of Uranus, suggested that it is affected by gravitational forces of interaction with a still unknown planet. They indicated its supposed position, and soon the astronomer I. Galle discovered Neptune there.

There was one problem though. Le Verrier calculated in 1845 that Mercury's orbit precesses 35"" per century, in contrast to Newton's zero precession. Subsequent measurements gave a more accurate value of 43"". (The observed precession is indeed 570""/century, but a painstaking calculation to subtract influence from all other planets yields a value of 43"".)

It was not until 1915 that Albert Einstein was able to explain this inconsistency in terms of his theory of gravity. It turned out that the massive Sun, like any other massive body, bends space-time in its vicinity. These effects cause deviations in the orbits of the planets, but Mercury, as the smallest and closest planet to our star, they manifest themselves most strongly.

Inertial and gravitational masses

As noted above, Galileo was the first to observe that objects fall to the ground at the same speed, regardless of their mass. In Newton's formulas, the concept of mass comes from two different equations. His second law says that the force F applied to a body with mass m gives an acceleration according to the equation F = ma.

However, the force of gravity F applied to a body satisfies the formula F = mg, where g depends on the other body interacting with the one under consideration (of the earth, usually when we talk about gravity). In both equations, m is a proportionality factor, but in the first case it is inertial mass, and in the second it is gravitational, and there is no obvious reason that they should be the same for any physical object.

However, all experiments show that this is indeed the case.

Einstein's theory of gravity

He took the fact of equality of inertial and gravitational masses as a starting point for his theory. He was able to construct the equations of the gravitational field, the famous equations of Einstein, and with their help calculate the correct value for the precession of the orbit of Mercury. They also give a measured value for the deflection of light rays that pass near the Sun, and there is no doubt that the correct results for macroscopic gravity follow from them. Einstein's theory of gravity, or general relativity (GR) as he called it, is one of the greatest triumphs of modern science.

Gravitational forces are acceleration?

If you cannot distinguish between inertial mass and gravitational mass, then you cannot distinguish between gravity and acceleration. An experiment in a gravitational field can instead be performed in a rapidly moving elevator in the absence of gravity. When an astronaut in a rocket accelerates, moving away from the earth, he experiences a force of gravity that is several times greater than that of the earth, and the vast majority of it comes from acceleration.

If no one can distinguish gravity from acceleration, then the former can always be reproduced by acceleration. A system in which acceleration replaces gravity is called inertial. Therefore, the Moon in near-Earth orbit can also be considered as an inertial system. However, this system will differ from point to point as the gravitational field changes. (In the Moon example, the gravitational field changes direction from one point to another.) The principle that one can always find an inertial frame at any point in space and time in which physics obeys the laws in the absence of gravity is called the principle of equivalence.

Gravity as a manifestation of the geometric properties of space-time

The fact that gravitational forces can be viewed as accelerations in inertial coordinate systems that differ from point to point means that gravity is a geometric concept.

We say that space-time is curved. Consider a ball on a flat surface. It will rest or, if there is no friction, move uniformly in the absence of any forces acting on it. If the surface is curved, the ball will accelerate and move to the lowest point, taking the shortest path. Similarly, Einstein's theory states that four-dimensional space-time is curved, and the body moves in this curved space along a geodesic line, which corresponds to the shortest path. Therefore, the gravitational field and the gravitational forces acting in it on physical bodies are geometric quantities that depend on the properties of space-time, which change most strongly near massive bodies.