Cosmogonic hypotheses are intended to explain the uniformity of motion and composition of celestial bodies. They proceed from the concept of the initial state of matter, which fills the whole space, which has inherent certain properties that cause all further evolution.
History of the emergence and development of hypotheses
Early ideas are based on Newton's law of attraction . Swedenborg's hypothesis (1732) is remarkable as the last and most developed of those built not on the law of attraction. Swedenborg proceeded from the vortex theory of Descartes and in his Principia rerum naturalium (department of de Chao Universali solis et planetarum) tells the origin of the world: due to the pressure of world matter, rather dense agglomerates ( star nuclei) appear in places, and due to the inherent particles in them matter inclination to move in spirals form vortices. These vortices capture particles of matter of a different order, and from them something like a globular dark crust forms, rotating around the already shining center - the sun. Due to centrifugal force, this crust becomes thinner, finally bursts, a ring near the sun is formed from its fragments, it, in turn, is torn into pieces, which give rise to the planets.] And on the so-called hypothesis of the primary nebula - shapeless, extremely rarefied homogeneous [Chemical composition Crookes called the Nebula the protil; from this protil, in his opinion, all chemical elements were formed.] accumulations of matter. Kant belongs in this direction the first experience ("Allgemeine Naturgeschichte und Theorie des Himmels", 1755); Laplace followed. It is completely false that the hypotheses of Kant and Laplace coincide. The properties of the primary nebula are already different in them and all its evolution radically diverge. The Laplace hypothesis, thanks to the work of Roche ("Essai sur la constitution et l'origine du système solaire", 1875), has some right to a place in astronomical treatises. Kant's hypothesis at too many points runs counter to the basic laws of mechanics and is only of historical interest. In general, all cosmogonic hypotheses cannot be considered to belong to astronomy as an exact science. In them, both initial circumstances and developmental conditions are completely arbitrary, many details contradict each other and existing phenomena. These hypotheses are just an example of how systems like the solar system could have developed without special stretches and almost without obvious contradictions to the laws of mechanics. Moving from Swedenborg and Kant to Laplace and Roche, and then to D. Darwin, the task narrows - from the whole universe to the solar system and to the formation of one satellite. At the same time, reasoning is gradually shifting to more solid ground.
Kant's hypothesis
The primary nebula is composed of individual particles. The heavier ones begin to attract relatively light ones, in some places centers of attraction are formed, the entire nebula is divided into sections, into spherical, denser clusters of matter - future stars. In each stellar nebula, a central condensation appears; particles, tending to the center, collide; while some of them fall to the center, others get lateral movement. A one-sided movement advantage accumulates accidentally, and all particles, both falling toward the center and remaining in the nebula in a suspended state, receive a rotational motion common to the entire mass. Due to rotation, the nebula is flattened, particles that have not fallen in the sun begin to cluster near local, random centers of gravity - planets are born. Depending on the position of the planet's embryo above the equator of the nebula, the orbits of the planets will be more or less inclined towards it. Carried away by the general rotation of the mass, all the planets move in one direction. The question of the rotational motion of the planets around their axes is posed by Kant very darkly, and in any case, the rotation should occur in the opposite direction to the existing one. Small clumps of the primary nebula, far from its equator, form comets. Kant has neither a gradual reduction in the volume of the entire nebula, nor the allocation of rings - these are characteristic features of the Laplace hypothesis. Kant explains the rings of Saturn as a product of the dispersion of the planet’s atmosphere.
Laplace-Roche Conjecture
This hypothesis does not apply to stellar worlds, but only to the solar system. The primary nebula is the gaseous red-hot atmosphere of the Sun, which extended far beyond the current planetary system. The sun was already looming as a rather dense condensation in the center. The entire planetary system is like foggy stars or planetary nebulae with a central condensation. Uniform rotation is inherent in the sun and its atmosphere from eternity. The atmosphere is bounded by a surface where centrifugal force is balanced by the attraction of the central core and the entire atmosphere. Under the influence of attraction, partly due to external cooling, the atmosphere contracts. Then the rotation is accelerated; centrifugal force increases; the equilibrium surface of both forces recedes into the entire mass, and the layer of foggy matter should separate under the equator in the form of a foggy rotating ring. In this case, particles that were located outside the equator flow down to it; but, possessing insufficient speeds to break away from the total mass, they are absorbed back into the nebula and form elliptical currents near the sun inside the atmosphere itself, form inner fog rings. Some of them fall in the sun and increase its mass. The alternating increase in the central condensation, giving way to an external reduction in volume due to cooling and compression, causes the equilibrium surface to recede irregularly, and the separation of the foggy rings occurs rhythmically - matter is not released non-stop at the equator. Each ring sank into one lump - the future planet, the formation of one planet from the ring is the weakest point of the hypothesis; the ring should break up into many small bodies (like asteroids). The rotation of the planets around the axes was originally back to the movement of the planets around the sun, but a new factor came forward - tides caused by the sun in the planetary mass. Their friction gradually slows down this reverse rotation, there comes a moment when the rotation disappears, then, in favorable cases, a direct rotation can occur. The tides on Uranus and Neptune are too small to destroy their initial reverse rotation. The period of revolution of the planet near the sun is equal to the time of rotation of the atmosphere of the sun at the time the ring is allocated. The inner rings explain the rapid circulation of the moons of Mars and the rings of Saturn. The formation of satellites occurs in each planetary mass in exactly the same way as the formation of the planets themselves. Tides prevent the formation of second-order satellites. The inclinations and eccentricities of the orbits of the planets are caused by subsequent mutual disturbances of the planets. - Helmholtz introduced the law of conservation of energy into the Laplace-Roche hypothesis, and indicated compression as the only sufficient source of radiant energy of the sun.
The disadvantages of the Laplace-Roche theory:
- The density of the primary nebula should be so small that it could not rotate like a solid (uniformly);
- The separation of matter cannot occur abruptly and only in the equatorial plane, but must occur either quasicontinuously or centrally symmetrically, like a shell discharge during the formation of a planetary nebula ;
- Rings with a mass equal to the mass of the planets could not thicken, but would disperse in space;
- The source of solar energy is not compression, but thermonuclear fusion in the solar interior.
Fay's hypothesis
It allows the eternal existence of "chaos" as a dark and cold nebula. Due to the begun compression caused by the attraction, the matter warmed up and began to glow weakly, quite like nebulae, by open photography. In various directions, chaos plow the "streams" of matter. In some places, due to the meeting of opposite flows, vortices are obtained - the ancestors of spiral nebulae, and after them various star systems. The main type of these systems are close binary and multiple stars, where the masses are distributed fairly evenly, and the constituent stars rotate around a common center of gravity. To create a system like our solar system, extremely favorable conditions were required. Fi insisted that planetary systems were a rare exception among the stellar worlds. Where there was no meeting of movements in chaos, it was not vortices that formed but slowly thickening clouds of small hot bodies (an example of this is in the constellation of Hercules, Centaurus). In such a system, the resultant force of the Newtonian mutual attraction of individual particles is always directed toward the center of the system and is directly proportional to the distance of the particle to it. The same law of forces prevailed in our system before the addition of the sun. As a result of this, the rings formed inside the nebula give rise to planets with direct rotation around the axes. Meanwhile, a central condensation is forming - the sun, whose mass finally far exceeds the mass of the remaining nebula, and the law of forces changes: the central attraction begins to prevail, inversely proportional to the square of the distance. All particles of a nebula move already according to Kepler’s laws. Planets that have not yet formed from the rings receive the opposite rotation. Thus, according to the hypothesis of Fay, the earth and internal planets are older than the sun, and it is older than Uranus and Neptune. Despite the successful observation of a change in the law of forces, Fay's hypothesis explains some points (e.g. ring formation) less satisfactorily than the Laplace-Roche hypothesis. Even its main goal - to explain the anomalous rotation of Uranus and Neptune - has not been fully achieved.
Jeans hypothesis
In 1919, the English astrophysicist J. Jeans put forward a hypothesis according to which all objects of the solar system were formed from the substance of the Sun , which was torn out of it as a result of the close passage of a star near it. The torn matter initially moved along a very elongated path, but, over time, as a result of the resistance of the medium, consisting of small droplets of the same solar matter, the orbits of large clots became almost circular. Based on this hypothesis, it followed that the formation of planetary systems around stars is an extremely rare event, since most stars in the galaxy do not experience such proximity even once during their entire existence.
From a physical point of view, the Jeans hypothesis was untenable. Experimental data show that the specific moment of momentum enclosed in the Sun is an order of magnitude smaller than that for planets. Calculations N.N. Pariysky confirmed that the substance torn from the Sun should either fall back on him or be carried away by the star that vomited it.
Fesenkov hypotheses
Academician V.G. Fesenkov , being an opponent of the cosmogonic theory of O. Yu. Schmidt , himself created several hypotheses of the formation of the solar system, none of which, however, was worked out in detail.
So in one of the early hypotheses, V. G. Fesenkov suggested that the planets were formed from gas masses that separated from the Sun during its rotation. This assumption was made possible by the fact that at that time it was assumed that all stars are born hot, but, over time, they dump part of their substance, reduce temperature, moving along the main sequence of the Hertzsprung-Russell diagram .
By the mid-50s, the position of Schmidt's theory that the planets were formed from a cold gas-dust medium became widely recognized. Based on this, V. G. Fesenkov suggested that the planets were formed from a cold gas-dust cloud surrounding the cloud from which the Sun was formed, which already had an excess reserve of rotation. The outflow of matter in the equatorial plane of the emerging Sun increased the density of the gas-dust medium in this plane, which allowed the formation of planetary nuclei with a density of about 10 −5 g / cm 3 . The formation of planets was supposed to begin from the periphery of the solar system.
Hypothesis of the shape of the planets
In the time of Laplace, it was believed that a rotating liquid mass must take the form of a body of revolution for balance. Hence the hypothetical division of the mass into parts inevitably occurred in the form of circular rings. Jacobi (1856) was the first to indicate a triaxial ellipsoid as a form of equilibrium of a rotating fluid, and thus laid the foundation for a new study. Poincare (1890) found that as the rotation speed increases, the Jacobi ellipsoid goes into a different, “pear-shaped” (apioid) form of equilibrium; a further increase in speed should cause a rupture of the entire mass into two unequal parts. D. Darwin arrived at the same results in the opposite way. Investigating the tidal interaction of two close masses, he deduced that such masses should have been one before, the figure of which is close to the Poincare apioid. None of the above hypotheses explains the formation of a planet from a ring; the more likely a new conclusion is that the formation of the ring is a completely anomalous phenomenon and took place in the solar system only once (for asteroids), yet planets and satellites occurred by separating the club of matter. If the torn club was too small, it did not have time to move away from the larger mass and was torn apart by its tidal action. An example of this is the rings of Saturn, the true genesis of which, as a scattered satellite, was discovered by Roche (1848). For the moon-earth system, Darwin's research can be called very successful; they have less significance for the evolution of other planets. Only for the system of satellites of Mars do they give new explanations. Seee attached D. Darwin's conclusion to stellar systems. He pointed out (1893) the similarity of the figures found by Poincare and Darwin with double nebulae and explained by tidal action the significant eccentricities of the orbits of most binary stars. Xi confirms Fay's view that planetary systems are an exception in the universe, while the type of binary stars devoid of planets dominates. All the cosmogonic theories presented have common weak points, which, perhaps, should be attributed to the very hypothesis of the primary nebula. The beginnings of this hypothesis are seen in the explanation of the new stars of 1572 and 1606 by Tycho Brahe and Kepler. Halley in 1714 speaks of the widespread and eternal existence of matter in a rarefied state. In parallel with the speculations of Kant and Laplace, V. Herschel came from the observations to the hypothesis of foggy matter. He thought to trace in various nebulae all stages of the development of stars. Some time later, Lord Ross showed that many of these nebulae decay into individual stars, and thus confidence in the hypothesis was shaken. However, spectral analysis confirmed that there are luminous gaseous masses with a very weak continuous spectrum, on which brilliant lines stand out. But we must admit that the hypothesis of the evolution of all celestial bodies from the primary nebula is completely empirical and has no actual evidence.
See also
- Cosmological paradoxes
Notes
Links
- V. Serafimov , World Systems // Encyclopedic Dictionary of Brockhaus and Efron : 86 volumes (82 volumes and 4 additional). - SPb. , 1890-1907.