Gravitational interaction, definition and study. A-Z index of Cognitio.

Gravitational interaction is one of the four fundamental interactions known in physics. The more complete theory, the general relativity, interprets gravitational interaction as a consequence of the bend of the space-time created by the presence of bodies with mass or energy. The gravitational field resulting from it is a tensorial field, mathematically represented by a metric tensor tied to the bend of space-time through the Riemann tensor. Plato believed that matter was pervaded by a dynamis, that is, an intrinsic energy, which drives the like to attract the like; a conception drawn from Aristotle, for which the whole universe hastens to the perfection of the first motionless engine (God).

Only in this area, therefore, some bodies, those which Plato and Aristotle called serious, are subject to gravity: they were compounds of the four fundamental elements (fire, air, water, earth), while the ether fluctuated above of them. According to Aristotelian theory of natural places, all that is earth tends to return to where the earth resides, or at the center of the universe; Above there is the sphere of water that attracts all that is liquid; likewise the air and fire circles behave. Newton’s theory of gravitation has allowed us to accurately describe the great majority of gravitational phenomena in the Solar System.

Solar system, definition and study. A-Z Index of Cognitio.

Solar system

Einstein subsequently developed a new theory of gravitation, called General Relativity, published in 1915. In Einstein’s theory, gravity is not a force, like all others, but is the property of matter to deform space-time. The presence of mass determines geometric curvature (more precisely, the metric structure) of space-time: since bodies moving in “free fall” follow geodetic trajectory space-time, and the latter are not straight if the space – the time is curved, so the motion of the other bodies undergoes the accelerations that are classically attributed to the “force of gravity”.

Cosmic space, definition and study. A-Z index of Cognitio.

Cosmic space

The planets of the Solar System therefore have elliptical orbits not because of an attraction force exerted directly by the Sun, but because the mass of the Sun spans space-time. A further observational evidence, found for the first time during the solar eclipse of 1919, consists in the effect of the said gravitational lens: the image of a celestial body seen from Earth appears to be shifted from the actual position of the body due to deflection that light undergoes when stretching a space region with high mass density.

This confirms that gravitation deforms space-time, and that such deformation is also sensed by mass-free particles (photons). A different mechanical approach to gravity is given by Loop Quantum Gravity theory and, within the strings theory, by the existence of gravitons.

Gravitational interaction, definition and study. A-Z index of Cognitio.

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Gravitational interaction, definition and study. A-Z index of Cognitio.

Gravitational interaction