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TULASI-PRAJNA, June, 1990
vided for distinguishing the absolute motion from relative motion. He based his theory on the two fundamental assumptions:
1. The velocity of light is the same constant to all observers. 2. The laws of natural phenomens are the same for all observers.
Michelson-Morley experiment had already shown that the velocity of light is not affected by the motion of the earth. Einstein took this as a revealation of a natural law and assumed that if the velocity of light is constant and remains unaffected by the motion of the earth, it should not be affected also by the motion of sun, moon, stars, planets or any other moving system. He generalised this law and assuined that all laws of nature should remain the same for all the uniformly moving systems.
Einstein's argument was that though the earth is in motion (revolving round the sun at a speed of 20 miles per second) we cannot feel our motion through space, nor has any physical experiment ever proved that the earth actually is in motion. In the same way, the whole universe is a restless place : stars, nebulae, galaxies, and all the vast gravitational systems of outer space are incessantly in motion. But their movements can be described only with respect to each other, for in space there are no directions and no boundaries. If only a single system were allowed to move and the rest of the systems were removed from the universe, nobody would be able to say whether the system is at rest or moving with a speed of 100000 miles per second. For motion is a relative state ; unless there is another system to compare with, it is futile to make any statement about the motion of a system.
Thus, Einstein showed that it is futile for the scientists to try to discover the "true" velocity of any system by using light as a measuring rod, for the velocity of light is constant throughout the universe and is unaffected either by the motion of its source or the motion of the receiver. 12
It also follows that there is no such substance as ether, to which Maxwell's equations referred. For, if there were such ether, light which keeps its velocity constant, would not be able to do so on account of ether's effect on its velocity. Actually. Einstein found ether quite useless, and therefore, he abandoned it. Since, according to him, all systems of reference that are in uniform translation motion with respect to each other are equivalent for the description of nature, there is no meaning in the statement that there is a substance, the ether, which is at rest in only one of these systems. Such a substance is in fact not needed and it is much simpler to say that light waves are
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