THEORY OF RELATIVITY

THEORY OF RELATIVITY

In 1905,Albert Einstein determined that the laws of physics are the same for all non-accelerating observers and that the speed of light in vacuum was independent of the motion of all observers. This is the theory of special relativity.
In general relativity, the effects of gravitation are ascribed to space-time curvature instead of a force. The starting point for general relativity is the equivalence principle, which equates free fall with inertial motion and describes free-falling inertial objects as being accelerated relative to non-inertial observers on the ground. In Newtonian physics, however, no such acceleration can occur unless at least one of the objects is being operated on by a force.

Einstein proposed that spacetime is curved by matter and that free-falling objects are moving along locally straight paths in curved spacetime. These straight paths are called geodesics. Like Newton's first law of motion, Einstein's theory states that if a force is applied on an object, it would deviate from a geodesic.Einstein discovered the field equations of general relativity, which relate the presence of matter and the curvature of spacetime and are named after him. The Einstein field equations are a set of 10 simultaneous, non-linear,differential equations. The solutions of the field equations are the components of the metric tensor of spacetime. A metric tensor describes a geometry of spacetime. The geodesic paths for a spacetime are calculated from the metric tensor.

WHAT IS IT?

Quite a number of experiments show that Einstein was right about this idea and a lot of others. But there are questions for which even Einstein had no answers.

For example, if gravity is a force that causes all matter to be attracted to all other matter, why are atoms mostly empty space inside? (There is really hardly any actual matter in an atom!) How are the forces that hold atoms together different from gravity? Is it possible that all the forces we see at work in nature are really different sides of the same basic force or structure?




video 1 (what is relativity)

video 2 (Time Dilation)