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Enigma of the Universe Visva-Prahelikā
THEORY OF RELATIVITY AND SPACE-TIME
O Muni Mahendra Kumar
General Theory of Relativity
In 1916, eleven years after the formulation of the special theory of relativity, Einstein extended it to interpret more general cases of non-uniform motion, i.e. where one frame of reference moves with an accelerated velocity relative to the other. This is known a general theory of relativity'. Its chief achievement is the explanation of the law of gravitation on a more refined and accurate basis than that given by Newton. Einstein has explained here the effect of the mass of the physical substances on the four dimensional continuum of space and time.
Newton's Laws
Newton, in his law of gravitation, stated that every particle in the universe attracts all other particles of the universe towards itself and the force of attraction is directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance between them. This is also known as 'inverse square law'. This concept of gravitation presupposes action at a distance and postulates the existence of a force of attraction between material bodies For instance, a mass such as the earth or the sun, is surrounded by a space in which there is a latent force ready to act upon and produce movement of a body that penetrates into the space. In consequence, the body falls towards the mass, as if attracted by it. This power of attraction exists permanently in the space near the mass even if there is no body menifesting its existence. The region of space surrounding a mass thus constitutes the gravitational field which imparts a uniform acceleration known as the acceleration due to gravity to all bodies located in that field. The mass seems to act at a distance since the attraction is exerted even through vacuum where there is no ponderable matter, as for example, in the case of the sun attracting the planets. Thus, Newton was able to explain the motion of planets in the space as well as freely falling bodies (such as apples in orchards) with the
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