Mechanical explanations of gravitation

In the mechanical explanations of gravitation ( and kinetic theories of gravitation, or pressure theories or shock theories of gravitation) are attempts to explain the law of gravitation by the aid of basic mechanical processes, such as shocks, without recourse to the concept of action at a distance to need. These developed mainly from the 16th to the 19th century in connection with the ether theories are, however, no longer viewed as a viable explanation of gravitation. The current standard model for the description of gravity is general relativity.

Shielding

Main article: Le Sage gravitation

This most well-known mechanistic explanation model was first proposed by Nicolas Fatio de Duillier ( 1690) and later, among others by Georges -Louis Le Sage (1748 ), Lord Kelvin (1872 ) developed Hendrik Lorentz (1900), and James Clerk Maxwell ( 1875) and Henri Poincaré (1908 ) criticized.

The basic assumption of the theory is the existence of a space that is filled largely isotropic existing from one of various particles ( corpuscles ) or wave radiation field. This move with constant, very high speed in a straight line in all possible directions. Where a particle on a body, it transfers some momentum to it. If only one body A exists, it is subjected to a uniform pressure, ie he is acting in all directions due to the shocks in a balance of power and will not move. However, if a second body B exists, this acts like an umbrella, because from the direction of B A is hit by particles less than. From the other side, the same is true vice versa A and B each shade, and thereby a negative pressure is created on the sides facing each other. It will therefore have a seemingly attractive force which acts exactly in the direction of each other's body.

The distance law has been explained: If it is a body having a spherical surface ( sphere ), which must be traversed by both the reflected and the flowing particles can be seen that the size of the sphere increases in proportion to the square of the distance. However, the number of the relevant particles in these growing sections remains the same and thus their density decreases. And to achieve the proportionality to the mass, it was assumed that matter consists largely of empty space and the particles is assumed to be very small, can penetrate the body easily. That is, the particles penetrate the body, interact with all components of matter, are partially shielded or absorbed and enter weakened out again.

Criticism

This theory has been rejected primarily for thermodynamic reasons, because there shadowing occurs only when the particles or waves are at least partially absorbed, would have an enormous not observed warming occur. Just as in the ether vortex theory of resistance is also moving towards a big problem that can indeed be solved by assuming much greater than the velocities of the particles of light, but which worsens the thermal problem.

Vortex

Due to philosophical considerations explained René Descartes in 1644, that no empty space could ( = physical space delimited by the outside world, volumeninhabender part of the universe or the environment) exist and, consequently, the space must be filled with matter. The parts of this matter move in principle straightforward, but since they are close together, they can not move freely, and it includes Descartes, that all movement was basically circular or vortex- shaped. Descartes distinguishes further between different shapes and sizes of matter, with the existing parts of coarser matter of the circular movement more resists than the finer matter. By a kind of centrifugal force, the finer matter now tends to gradually move away from the center. This leads to the outer edges of the vertebrae of a compacting this matter. The coarser matter not only can not follow due to its inertia of this movement, but is forced by the pressure of the compressed, located at the outer edges of the vertebrae finer matter into the center of the vortex. This pressure at the center is none other than gravity, according to Descartes. Descartes likened this mechanism Liquid Sky matter with the fact that if you put in a water-filled vessel, the liquid in rotation, and one little pieces are easier matter ( eg wood) drops into the vessel, this in the middle of the will be collecting vessel.

The basic premises of Descartes ' following, Christiaan Huygens designed 1669-1690 a much more accurate vortex model or the first mathematically elaborated theory of gravitation at all. He assumed that the etheric substance moved smoothly in all directions, but is thrown back at the external borders of the vertebra and there occurs as in Descartes in greater concentration or density. This leads to that, even if it the finer material urges the coarser matter inwardly. Here Huygens found that the centrifugal force acting on a body is equal to the gravity ( centripetal force ). He also postulated that normal matter must consist of mostly empty space so that the etheric substance can penetrate through evenly. He concluded that the fine etheric substance moves much faster than the earth rotates. At this time, Newton developed his theory of gravitation based on attraction, which Huygens appeared insufficient due to the lack of a mechanical explanation. The realization of Newton, that gravity is governed by the law of distance, surprised Huygens, and he tried to take this into account by assuming that the velocity of the ether would always smaller at greater distances, ie basically obeys Kepler's 3rd law.

Criticism

Newton argued against the theory that here the flow resistance in the direction of movement must lead to significant deviations from the orbit, which is not observed. Also, moons often move in different directions, which argues against the vertebral opinion. After Horst toe itself also destroys the Huygens' theory itself, as a theory of gravity to explain Kepler's laws from the gravitational mechanism and should not provide.

Currents

Isaac Newton participated in 1675 that gravity arises because the gravitational ether of a liquid is comparable to that condenses on the surface of normal matter. This creates a flow which entrains the surrounding mass is proportional to 1 / r ².

Similar to Newton, but worked out mathematically detailed, Bernhard Riemann was in 1853 on the assumption that the gravitational aether is an incompressible fluid and normal matter are to be construed as "sinks " in this ether. That Etheric matter is destroyed by the bodies in proportion to their masses or absorbed and thus transferred into another world or dimension, so to every body a stream that entrains all the surrounding body towards the center of mass.

Ivan Ossipowitsch Jarkowski adopted in 1888, that the absorbed ether is neither destroyed nor liquefied, but transformed into new chemical elements, which should cause an expansion of the earth.

Criticism

As with the Le Sage gravity of the disappearance of energy in the bodies violates the conservation of energy, as would have a resistance to flow in the direction of movement may be present. Also, a creation of new matter is not observed.

Static ether

In contrast to his first statement struck Newton later ( 1717) a static ether before, in the vicinity of the heavenly bodies is getting thinner, and the result is analogous to the buoyancy in liquids acting in the direction of the earth force. ( However, Newton gave no reason why you should remove the density with the inverse square law ). The usual resistance in liquids in motion direction for moving bodies, he minimized the fact by assuming an extremely low density of gravitational ether. Newton has then, at all distances with the Note to want to put any hypotheses of all mechanical explanations and possibly went to witness some of his friends like Nicolas Fatio de Duillier or David Gregory on the assumption that the gravitational based directly on the will of God.

As Newton put Leonhard Euler in 1760 requires that the gravitational aether loses density in accordance with the law of distance near the body, but he also gave no reason for this decrease in density. As Huygens, Fatio and Le Sage, he assumed that the matter possessed very fine pores through which the ether can penetrate easily to maintain the Massenproportionalität.

Criticism

As added by Newton and Euler himself missing here an explanation of why the density of the ether should change at all. James Clerk Maxwell, furthermore, pointed out that in this " hydrostatic " model an enormous burden of being defined as rigid ether occurs which is about 3000 times stronger than the most resistant then known steel could withstand.

Waves

Robert Hooke speculated in 1671 that gravity may be caused when the body produce waves that rush through the ether in all directions. Other bodies that interact with these waves, then move toward the source of the wave. Hooke saw it as an analogy to the fact that the movement of small objects on a disturbed water surface at the center of the disturbance down.

Was mathematically developed a similar theory by James Challis of 1859 until 1876. He calculated that the case attraction occurs when the wavelength is large compared to the distance between the gravitating bodies. If the wavelength is small, the body repel. Through a combination of these effects, he tried to explain all the other forces.

Criticism

Maxwell argued that this continuous re-generation of waves must be accompanied by an infinite consumption of energy, which is not compatible with the conservation of energy. Challis himself admitted to be unable to reach a final result due to the complexity of the processes.

Pulsation

Here the ether is, for example, by Kelvin (1871 ) and Carl Anton Bjerknes ( 1871-1880 ) regarded as a liquid, with normal matter to pulsate within this liquid. As was found in experiments in liquids, there are 2 body don, when their pulsations are in phase, and it results in a repulsive force when their pulsations are not in phase. This hypothesis is, inter alia, also been studied by George Gabriel Stokes and Woldemar Voigt.

Criticism

To the universal gravitation must be assumed to explain that all the pulsations of the universe are in phase, which seems very artificial. And the ether should be substantially incompressible, to ensure the attraction over a greater distance away. And it would have, as Maxwell said, the constant re-creation as well as destruction of ether are explained.

Other historical speculation

Pierre Varignon declared in 1690 that all bodies are exposed from all directions by a shock etheric substance. At a certain distance from the Earth is now to be located a limit on the do not get off the ether particles. Body it then fall to the ground, when the distance between the surface and the body is less than the distance between the body and limitation. Because this implies in his opinion, that on top of the body more and more collisions take place than at the bottom.

The inside Russia very influential physicist Mikhail Vasilyevich Lomonosov took in 1748 that the effect of etheric substance is proportional to the total surface of the elementary components from which matter is composed (as well as Huygens and Fatio before him). He also takes this as an enormous penetrability of matter. However, he no details have been given, how exactly the ether particles act on the matter, so that the result is the law of gravity.

John tried Herapath 1821 he helped develop the model of the kinetic theory of gases applied to gravitation. He assumed that the ether is a gas comparable, which is heated by heat radiation of matter and loses its density, so that the other bodies are forced into these regions of lower density. How Taylor showed this assumption was wrong: The density of this ether gas decreases at higher temperature due to the thermal expansion from, but the speed of the ether particles increases in the same proportion, so no attraction effect.