Gravitation

Gravity is a force that holds together the hundred billion stars of the Milky Way. It makes the Earth revolve around the Sun and the Moon around the Earth. There are three great names in the history of man's understanding of gravity: Galileo who was the first to study in detail the process of free and accelerated fall; Newton, the first to have the idea of gravity as a universal force. However, Newton admitted that he did not know its ultimate cause ("I will not feign hypothesis") but he offered many a keen guess at the nature and mechanism of gravitation; and Einstein, who said that gravity is nothing but the curvature of the four-dimensional space-time continuum.

In specifying gravitation on the new geometrical view Einstein did not prove "Newton's law of gravitation" wrong but offered a refining modification – though this involved a radical change in viewpoint. We must not think of either law as right (or wrong) because it is suggested by a great man or because it is embodied by beautiful maths; we are offered it as a brilliant guess from the real universe. The changes from Newton's predictions to Einstein's, though fundamental in nature, are usually too small in effect to make any difference in laboratory experiments or even in most astronomical measurements. By reducing gravity to geometrical properties of a space-time continuum, Einstein concluded that the electromagnetic field must also have some purely geometrical interpretation. The unified field theory, which grew from this conclusion had rough going and Einstein died without completing it. Some scientists claim that it is very odd indeed that the theory of gravitation originated by Newton and developed further by Einstein should stand now in majestic isolation, having nothing to do with the rapid development of other branches of science. This is not the case, however. The progress in quantum mechanics, modern cosmology and astrophysics makes this claim unjustified.

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