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The Theory of Relativity

Certain theories, very few in number, have so greatly influenced scientific think­ing that they stand out above all the rest. Among them are the hypothesis of Coper­nicus concerning the motions of the plan­ets; the doctrine of universal gravitation, advanced by Sir Isaac Newton; the cell theory of Schleiden and Schwann; and Darwin's theory of organic evolution. We certainly must also include the theory of relativity, formulated by Albert Einstein and developed further by Einstein himself and several other scientists.

This theory has revolutionized our thinking. It has altered our ideas of space, time, mass, energy, motion, and gravitation. It has provided a new approach to the study of the universe. It is made up of a special theory and a general theory. Both rest on a solid mathematical foundation, and both have been confirmed by experimentation and observation.

FRAMES OF REFERENCE

The theory of relativity arose from the need for frame of reference-a standard that scientists could use in analyzing the laws of motion. The need for such a standard is obvious, for the moment we attempt ... to analyze motion, we must ask ourselves: "Motion with respect to what?"

Suppose that a pilot is flying a plane far above the Earth in a jet stream (a swift current of air) flowing at 300 kilometers per hour. The plane itself is flying at 300 kilometers per hour in the same direction as the jet stream. The pilot will be moving at a 300-kilometer-per-hour speed with respect to the jet stream, but at 600 kilometers per hour from the viewpoint of an observer stationed on the Earth. If the pilot flies against the jet stream, to the Earth-bound observer he will seem to be hovering motionless in the air.

To an observer on the planet Mars, a speed of 300 kilometers or 600 kilometers per hour would seem insignificant compared to the nearly 300kilomcter-per-second speed of the Earth as it revolves around the Sun. It is moving at many kilometers per second around the center of the Milky Way, the galaxy of which our solar system forms a very small part. The Milky Way itself is moving with respect to other galax­ies. Where, then, is our frame of reference?

At one time, men of science believed in a luminiferous, or light-bearing, Ether that might serve that purpose. The Ether was supposed to be a fluid, or a very elastic sol­id, occupying all the space between the atoms of which matter consisted. Light, it was thought, was transmitted in a series of waves through the Ether-waves at right angles to the direction of motion. Some scientists believed that the Ether itself re­mained motionless as the light waves passed through it. They compared the passage of light through the Ether to the movement of ocean waves in the sea. It is the ocean-wave form, or pattern, they said, that moves for­ward. The water particles themselves do not move to any marked extent. If scientists could show that the Ether had no motion of its own and that the heavenly bodies im­parted none to it as they passed through space, we would have a reliable starting point for a general analysis of motion.

In trying to prove that the Ether was stationary with respect to the Earth, one would have to consider that from our view­point the Earth is standing still. Therefore, the Ether would appear to be rushing past us "like the wind through a grove of trees," to quote the English physicist Thomas Young in the same way, the Sun seems to us to be moving around the Earth, while it is really the Earth that is revolving around the Sun.

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