# Explain briefly about the theory of relatively.

## Question:

Explain briefly about the theory of relatively.

## The Special Theory Of Relativity

Pre- relativistic classical physics had two eminently successful theories. One was Newtonian mechanics which dealt with matter and the other was Maxwell's theory of the electromagnetic field. Newtonian mechanics gives the correct particle dynamics in any inertial frame of reference. To translate the data obtained in one frame of reference to the variables used in the other frame the Galilean transformation equations are used. The Newtonian theory is Galilean invariant. That is, Newton's law has the same mathematical structure in all inertial frames. Next, consider maxwell's equations. The entire gamut of known electromagnetic phenomena falls within its ambit. But there is one problem. Maxwell's equations are not Galilean invariant. The mathematical structure changes from one inertial frame to another when Galilean transformation equations are applied. The humongous success of the Newtonian theory and the relative newness of maxwell's equations prompted a modification of the Maxwellian theory in order to make it Galilean invariant. New terms were appended to maxwell's equations. But this predicted new electromagnetic phenomena which failed to show up under rigorous experimental conditions. In the meantime, out of sheer curiosity, Lorentz worked out the transformation equations that rendered Maxwell's equations invariant under translation from one inertial frame to another. Thus at the turn of the 19th century, classical physics had to face the conundrum of having to deal with two eminently successful theories each with its own transformation relation but apparently not in conformity with each other.

Enter Albert Einstein. This patent clerk had no qualms in summarily dismissing the Newtonian theory as incomplete and suggesting that Maxwell's equations with its attendant Lorentz transformations should be given primacy over the Newtonian theory and the related Galilean transformations. Thus it is the Newtonian theory that is in need of modification. The basic conceptions of mechanics namely mass, length and time all undergo drastic changes once they are made Lorentz compliant. The first casualty is the concept of simultaneity. Two events which are simultaneous in one frame of reference need not be simultaneous in other frames. Next comes the concept of length. The length of an object measured in its rest frame is always greater than the length as determined in a frame in which the object is moving. Similarly the lifetime of a particle in its own rest frame is less than the lifetime as determined in a frame in which it is moving. The mass of a particle in its own rest frame is less than the mass it would have in a frame in which it is moving.

These counter-intuitive phenomena follow from the postulates of relativity as stated by Einstein. There are two postulates. The postulate of relativity states that the laws of physics should have the same mathematical structure in all inertial frames. The correct transformation equations from one Frame to the other are the Lorentz transformations. The second postulate is called the postulate of the constancy of the speed of light. It states that the speed of light is the same in all inertial frames. The results of the Michelson- Morley experiment and Fizeau's experiment can easily be explained with the special theory of relativity. With the advent of elementary particle experiments, the theory of relativity has been borne out innumerable times. 