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Shvoong Home>Science>Physics>The theory of Relativity: A Simplified Exposition Summary

# The theory of Relativity: A Simplified Exposition

Article Summary   by:shovanadhikary     Original Author: Shovan

THE THEORY OF RELATIVITY: A SIMPLIFIED EXPLANATION One of the most spectacular things to have ever happened in the world of science is the scholarly exposition of the theory of relativity by one of the greatest scientists of all times, nay the greatest physicist of the century known to the world as Albert Einstein. This gave an entirely new dimension to the world of physics and brought to light certain aspects hitherto unknown. The theory of relativity has been a topic of much discussion and debate since its exposition. But very few people actually understand the real meaning of the theory of relativity. Here is a humble attempt to explain the theory of relativity in as lucid and simple language as possible. The theory of relativity was propounded by Einstein in two parts: 1) The Special Theory & 2) The General Theory. Therefore a complete picture of the theory of relativity would emerge only if we separately understand each part of the theory of relativity. The Special Theory: The special theory put forward in 1905 considers only bodies moving at a constant velocity relative to each other. This sub-part of the theory of relativity is in turn based on two basic postulates: a) The speed of light in vacuum is constant and it does not depend on the source or the observer. b) Laws of physics remain unchanged in all inertial frames (i.e. matter at rest or in uniform motion) The first postulate was a negation of the early 19th century premise that light needed a medium for propogation and that it travelled through stationary medium called ether which is evenly spread throughout the space. Similarly it also rejected the notion that all movements should be measured with respect to ether which filled space. Further, the notion that the speed of light is relative and can be measured relative to a moving observer was also put to rest. Einstein put forward the notion that the speed of light always remains constant no matter how fast or slow is the observer moving. The speed of light is absolute and no material body can travel faster than light. It was only on the basis of his scientifically arrived at conclusions as discussed above that Einstein went on to put forward the first part of his theory of relativity:- The Special Theory of Relativity. The special theory says that the physical quantities like mass, length and time are not absolute. They change as the bodies move. If a body moves with large velocities its mass increases and its length becomes shorter. This change in mass and length is not noticeable when bodies move with ordinary speeds. Such changes become evident only when bodies move at a very high speed approaching the speed of light.
Cars on the high speed freeways do become heavier and shorter as they travel faster, but the effect is very small. On the other hand an electron travelling at 99% of the speed of light becomes seven times heavier than its original mass when it was at rest. However according to Einstein nobody can actually attain the speed of light and if it does, it would be infinitely heavy and have zero length. Here it is important to remember that the weight changes because of the change in mass which increases (weight = Mass x acceleration due to gravity). This increase in mass and decrease in length of a body as its speed increases prompted Einstein to conclude that mass(denoted by m) and energy(denoted by E) are different aspects of the same thing, but are intimately related to each other. These relationships made Einstein derive the famous mass- energy equation: (E=mc2), where E denotes energy, m mass and c stands for the speed of light. Nuclear energy is a direct consequence of this equation.
The second part of Einstein’s theory of relativity is called the General Theory (published in 1915). While the special theory of relativity applies only to bodies moving with constant speeds, the general theory deals with the accelerated motions of bodies i.e. with the way the force of gravity acts on the mass. Gravity as per Einstein is a property of space and time. Space becomes curved by the presence of mass and this provides the inward pull (gravity) in the same way as a sinking ship would create an inward pull towards all objects in the surrounding water where the ship is sinking. Thus, the motion of stars and planets are controlled by this curvature of space which provides the inward pull or the gravitational pull keeping the planets in their path. In the same vein it can also be said that the light rays too are bent by the curvature of the space around a body that has mass.
Thus, the Theory of Relativity is one of the most valuable contributions of all times which has revolutionized modern day physics by throwing light on those physical phenomenon hitherto unexplored and hence unknown.
Published: April 05, 2008
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