Gravitational theory by Einstein

Gravitation is commonly understood as the force of attraction between objects by virtue of their mass. In 1687, Newton published The Philosophiae Naturalist Principia Mathematica in which he prop0soed his law of gravitation.

Richer Cassini and Piccard had found evidence in 1672 that the earth had an equatorial bulge. Newton was able to use his new gravitational theory to calculate a theoretical value for this oblateness of 1/230. He then considered the gravitation attraction of the moon and sun on the oblate earth and calculated that the earth’s spin axis should process at baa rate do about 50’’.0 per annum.

According to this law the gravitational force of attraction between two bodies is always proportional to their masses and inversely proportional to the square of their distance apart, and it acts instantaneously through infinite distance.

A more widely applicable theory of gravitation is Albert Einstein’s general theory of relativity. According to Einstein’s general theory of relativity published in 1913, gravitation is not a forced of attraction but rather the force required to prevent the natural motion of matter, which is to follow a geodesic in space time.

Einstein introduced into gravitational theory a type of mathematics that was then unfamiliar to most physicists thus presenting an initial impression of incomprehension. In his theory Einstein used the space-time continuum introduced by Hermann Minskowski in 1907, the non-Eucladian geometry developed by Bernhard Riemann in 1854 and the tensor calculus published by Gregorio Ricci in 1887.

The first indirect experimental proof of gravitational waves was provided in 1984 by Weisberg and Taylor. By studying the pulsar 1913+16, they showed that the period of the pulsar around its companion star decreased exactly as predicted by the Einstein equation.

In 1969, Joseph Weber, a physicist at the University of Maryland, claimed to have detected gravitational waves using a six-foot-long aluminum cylinder as an antenna. In Feb 2016, a team of scientists at the Laser Interferometer Gravitational Wave Observatory (LIGO) announced they had detected agravitational waves resulting from the collision of two black holes some 1.3 billion years ago.

Scientists say that some 1.4 billion years ago two black holes - one the size of 36 suns and the other the size of 29- circled each other in a distant galaxy before finally colliding.

The collision of the two black holes—about 29 and 36 times more massive than the sun, respectively—produced a gigantic amount of energy in a fraction of a second, the equivalent of about 50 times the power of the entire visible universe. This energy, in the form of gravitational waves, is still spreading outwards today.
Gravitational theory by Einstein