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The Theory of Relativity
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ETHER CONCEPT DOUBTED

Two U.S. scientists, Albert A. Michel­son and Edward W. Morley, tried to solve the Ether problem by making delicate mea­surements of the speed of light. Let us sup­pose, they said, that the Ether is motionless as light is transmitted through it. If the Earth were also motionless in space, light would always seem to have the same veloc­ity when measured by an observer on the Earth. But the Earth moves through space. Hence the velocity of light would appear to change according to the direction in which a light beam would be flashed - that is, in the direction of the Earth's motion, or in the opposite direction, or at right angles to it.

The two scientists analyzed the dif­ferences in the arrival times of the light beams parallel to the Earth's course and at right angles to it. No matter how many measurements they made, the light ap­peared to travel just as rapidly in the direction of the Earth's motion as against it or at right angles to it. The experimenters concluded that "if there be any relative motion between the Earth and the luminiferous Ether, it must be quite small.

The man on the motorcycle sees the ball fall straight down. An observer on the side of the road, though, sees the ball fall in an arc. This illustrates the relativity of motion: Different people see the same event in different ways.

The Michelson-Morley experiments caused scientists to doubt the existence of the luminiferous Ether. What was even more important, they showed that the speed of light is independent of the motion of the observer. Remember that as we try to measure light, we are moving with the Earth through space. In other words, the velocity of light is a constant, which re­mains the same under all circumstances. This concept was to form the basis of Einstein's Special Theory of Relativity,

SPECIAL THEORY OF RELATIVITY

According to this theory, which was formulated by Einstein in 1905, it is impossible to measure or detect the absolute mo­tion of a body through space. However, we can accurately determine its relative mo­tion by using the speed of light as a basis. This speed comes to about 300,000 kilometers per second.

The special theory modified the ideas of classical physics with respect to space and time. According to these ideas, parti­cles move in a three-dimensional frame­work in space and at specific times. The three dimensions are length, breadth, and thickness, or height. This concept is a fa­miliar one. We know, for example, that a room has length, breadth, and height.

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