Newton, which states that the strength of the gravitational attraction between the two material points of mass and, separated by the distance is proportional to both masses and is inversely proportional to the square of the distance - that is:

Here is a gravitational constant, equal to about 6.6725 × 10 -11 m³ / (kg · c²).

The World of Worldwide - one of the applications of the law of reverse squares, occurring also in the study of radiation (see, for example, the pressure of light), and is a direct consequence of a quadratic increase in the area of \u200b\u200bthe sphere with an increase in the radius, which leads to a quadratic decrease in the contribution of any unit area in Area of \u200b\u200bthe entire sphere.

Gravitational field, as well as the gravity field, potentially. This means that it is possible to introduce the potential energy of the gravitational attraction of a pair of bodies, and this energy will not change after moving the bodies along a closed contour. The potential of the gravitational field involves the law of preserving the amount of kinetic and potential energy and when studying the movement of the body in the gravitational field often simplifies the solution. Within the framework of Newtonian mechanics, gravitational interaction is long-range. This means that, as it were, the massive body moves, at any point of space, the gravitational potential depends only on the position of the body at the moment.

Large space objects - planets, stars and galaxies have a huge mass and, therefore, create significant gravitational fields.

Gravity is the weakest interaction. However, since it acts at any distances, and all masses are positive, it is, nevertheless, very important power in the universe. In particular, the electromagnetic interaction between the bodies on a space scale is not enough, since the complete electrical charge of these bodies is zero (the substance is generally neutral).

Also gravity, in contrast to other interactions, is universal in action for all matter and energy. No objects were found in which there would be no gravitational interaction.

Because of the global nature, gravity is responsible for such large-scale effects as the structure of galaxies, black holes and the expansion of the universe, and for elementary astronomical phenomena - the orbits of the planets, and for the simple attraction to the surface of the Earth and falling tel.

Gravity was the first interaction described by mathematical theory. Aristotle believed that objects with different mass fall at different speeds. Only a lot later, Galileo Galilee experimentally determined that it was not so - if the resistance of the air is eliminated, all the bodies are accelerated equally. The law of universal gravity of Isaac Newton (1687) well described the general behavior of gravity. In 1915, Albert Einstein created a general theory of relativity, more precisely describing gravity in terms of the geometry of space-time.

Heavenly mechanics and some of her tasks

The easiest task of heavenly mechanics is the gravitational interaction of two point or spherical bodies in an empty space. This task within the framework of classical mechanics is solved analytically in a closed form; The result of its solutions is often formulated in the form of three laws of Kepler.

With an increase in the number of interacting bodies, the problem is sharply complicated. So, already the famous task of three bodies (that is, the movement of three bodies with non-zero masses) cannot be solved analytically in general. In the numerical solution, the instability of decisions relative to the initial conditions appear rather quickly. In applied to the solar system, this instability does not allow to predict exactly the movement of the planets on a scale exceeding a hundred million years.

In some particular cases, it is possible to find an approximate solution. The most important is the case when the mass of one body is significantly more than the mass of other bodies (examples: the solar system and the speaker of the rings of Saturn). In this case, in the first approximation, we can assume that light bodies do not interact with each other and move through the Kepler trajectories around the massive body. The interaction between them can be taken into account within the framework of the theory of perturbations and averaged in time. At the same time, non-trivial phenomena may occur, such as resonances, attractors, chaoticism, etc. The visual example of such phenomena is the complex structure of the Saturn rings.

Despite attempts to accurately describe the behavior of the system from a large number of attractive bodies of approximately the same mass, this is not possible due to the phenomenon of dynamic chaos.

Strong gravitational fields

In strong gravitational fields, as well as when driving in a gravitational field with relativistic velocities, the effects of the general theory of relativity begin to manifest themselves:

• change of space-time geometry;
  • as a result, the rejection of the law from Newtonian;
  • and in extreme cases - the emergence of black holes;
• the delay of potentials associated with the final rate of propagation of gravitational perturbations;
  • as a result, the appearance of gravitational waves;
• effects of nonlinearity: gravity has a property to interact with themselves, therefore the principle of superposition in strong fields is no longer performed.

Gravitational radiation

One of the important predictions of OTO is gravitational radiation, the presence of which has not yet been confirmed by direct observations. However, there are significant indirect evidence in favor of its existence, namely: energy loss in close double systems containing compact gravel objects (such as neutron stars or black holes), in particular, in the famous PSR B1913 + 16 system (Pulsar Khals - Taylor) - Activate well with a model from the model in which this energy is carried out by gravitational radiation.

Gravitational radiation can generate only systems with variable quadrupole or higher multipole moments, this fact suggests that the gravitational emissions of most natural sources aimed, which significantly complicates its detection. Power gravitational n.-poly source is proportional if the multipol has an electric type, and - if the Multipol of the magnetic type, where v. - the characteristic speed of the sources in the radiating system, and c. - The speed of light. Thus, the dominant torque will be a quadrupole moment of electric type, and the power of the corresponding radiation is:

where is the tensor of the quadrupole moment of the mass distribution of the emitting system. Constant (1 / W) allows you to estimate the order of the magnitude of the radiation power.

Starting from 1969 (Weber Experiments ( english)) Attempts to directly detect gravitational radiation. In the US, Europe and Japan, there are currently several existing ground detectors (Ligo, Virgo, Tama ( english), GEO 600), as well as the Lisa Space Gravitational Detector project (Laser Interferometer Space Antenna - Laser Interferometric Space Antenna). The ground detector in Russia is being developed at the Scientific Center of Gravitational Wave Research "Dulkyn" Republic of Tatarstan.

Thin effects of gravity

Measuring the curvature of space in the orbit of the Earth (artist drawing)

In addition to the classic effects of gravitational attraction and slowing down, the overall theory of relativity predicts the existence of other manifestations of gravity, which on earthly conditions are very weak and their detection and experimental testing is therefore very difficult. Until recently, overcoming these difficulties was presented outside the possibilities of experimenters.

Among them, in particular, you can call the passion of inertial reference systems (or the lens-tyrringe effect) and the gravitomagnetic field. In 2005, the automatic apparatus of NASA GRAVITY PROBE B held an unprecedented experiment to measure these effects near the Earth. The processing of the data obtained was carried out until May 2011, and confirmed the existence and the magnitude of the effects of the geodesic precession and the hobbies of inertial reference systems, albeit with accuracy, slightly smaller initially expected.

After intensive work on the analysis and extraction of measurement interference, the final results of the mission were announced at the NASA-TV press conference on May 4, 2011 and published in Physical Review Letters. The measured magnitude of the geodetic precession was -6601.8 ± 18.3 milliseconds arcs per year, and the effect of hobbies - -37.2 ± 7.2 milliseconds Arcs per year (cf. with theoretical values \u200b\u200bof -6606.1 MAS / year and -39.2 MAS / year).

Classic gravity theories

Due to the fact that the quantum effects of gravity are extremely small even in the most extreme experimental and observational conditions, there are still no reliable observations. Theoretical estimates show that in the overwhelming majority of cases, it can be limited to a classical description of gravitational interaction.

There is a modern canonical classical theory of gravity - the overall theory of relativity, and the set of clarifying it hypotheses and theories of varying degrees of the development, competing among themselves. All these theories give very similar predictions within the framework of the approach, in which experimental tests are currently being carried out. The following describes several basic, most well-designed or known gravity theories.

General theory of relativity

In the standard approach of the overall theory of relativity (OTO), gravity is considered initially not as a power interaction, but as a manifestation of the curvature of space-time. Thus, the gravity is interpreted as a geometrical effect, and the space-time is considered within the framework of non-chloride Riemannian (more precisely pseudo-Riemannian) geometry. The gravitational field (generalization of the Newtonian gravitational potential), sometimes called the field of gravity, is identified with a tensor metric field - a metric of four-dimensional space-time, and the tension of the gravitational field - with an affine connection-time-time-defined connection.

The standard task is from the determination of the metric tensor component, in the aggregate of the geometric properties of space-time, according to the known distribution of power sources in the system of four-dimensional coordinates under consideration. In turn, knowledge of the metric allows you to calculate the movement of test particles, which is equivalent to knowledge of the properties of the field of gravity in this system. Due to the tensor character of the equations from the OTO, as well as with a standard fundamental substantiation of its wording, it is believed that gravity is also tensor. One of the consequences is that gravitational radiation should be no lower than quadrupole order.

It is known that there are difficulties in connection with the non-invariance of the energy of the gravitational field, since this energy is not described by the tensor and can be theoretically determined in different ways. The classic alone also arises the problem of describing the spin-orbit interaction (since the spin of the extended object also does not have a unambiguous definition). It is believed that there are certain problems with the uniqueness of the results and the substantiation of consistency (the problem of gravitational singularities).

However, experimentally confirmed until recently (2012). In addition, many alternative Einsteinovsky, but standard for modern physics approaches to the formulation of the theory of gravity lead to the result that coincides with the OTO in the low-energy approximation, which is now available to experimental verification.

Einstein theory - Cartan

Such a disintegration of equations into two classes takes place in the RTG, where the second tensor equation is introduced to taking into account the relationship between the non-smoke space and the Minkowski space. Due to the presence of a dimensionless parameter in the theory of Jordan - Brons - Dickka, it is possible to choose it so that the results of the theory coincide with the results of gravitational experiments. At the same time, with the desire of the parameter to infinity, the prediction of theory are becoming increasingly close to OTO, so it is impossible to refute the theory of Jordan - Brons - Dickka is impossible by any experiment confirming the general theory of relativity.

Quantum theory of gravity

Despite the more than half a century, the history of attempts, gravity is the only fundamental interaction, for which the generally accepted consistent quantum theory has not yet been built. At low energies, in the spirit of quantum field theory, gravitational interaction can be represented as the exchange of graviton - calibration bosons with spin 2. However, the resulting theory is intolerable, and therefore is considered unsatisfactory.

In recent decades, three promising approach to solving the task of quantization of gravity are developed: string theory, loop quantum gravity and causal dynamic triangulation.

String theory

Instead of particles and background space, strings and their multidimensional analogs perform in it. For multidimensional problems, breasts are multidimensional particles, but from the point of view of particles moving inside These Bran, they are spatial-temporal structures. An embodiment of the theory of strings is a M-theory.

Loop quantum gravity

It makes an attempt to formulate a quantum field theory without binding to a space-time background, space and time on this theory consist of discrete parts. These small quantum cells of the space in a certain way are connected to each other, so that on a small scale and length they create a pedigree, the discrete structure of the space, and on a large scale smoothly go into continuous smooth space-time. Although many cosmological models can describe the behavior of the universe only from the plank time after a large explosion, loop quantum gravity can describe the explosion process itself, and even look earlier. The loop quantum gravity allows you to describe all the particles of the standard model, without requiring to explain their masses of the introduction of the Higgs boson.

Main article: Causal dynamic triangulation

In it, the spatial-temporal manifold is built from elementary Euclidean simplides (triangle, tetrahedron, pentahor) sizes of the order of plank taking into account the principle of causality. The four-dimensions and pseudo-chylidity of space-time in a macroscopic scale are not postulated in it, but are a consequence of theory.

see also

Notes

Literature

• Vizin V. P. Relativistic theory of gravity (origins and formation, 1900-1915). - M.: Science, 1981. - 352C.
• Vizin V. P. Unified theories in the 1st third of the twentieth century. - M.: Science, 1985. - 304c.
• Ivanhenko D. D., Sardanashvili G. A. Gravity. 3rd ed. - M.: URSS, 2008. - 200С.
• Mizner C., Thorn K., Wheeler J. Gravity. - M.: Mir, 1977.
• Thorn K. Black holes and time folds. Bold heritage Einstein. - M.: State Publishing House of Physics and Mathematics Literature, 2009.

Links

• The law of global gravity or "Why doesn't the moon fall on earth?" - Just about the difficult
• Gravity problems (Doc. BBC film, video)
• Earth and gravity; Relativish theory of gravity (TV shows Gordon "Dialogues", video)