Who doesn’t know about Albert Einstein? One of the most celebrated physicists of all time, Albert Einstein, is known for his theories and observations such as, General Relativity, Special Relativity, Brownian movement, Photoelectric effect etc. This post focuses on General Relativity and space-time, one of the most important features of GR.

Albert Einstein’s General Relativity can be called as a new look towards Gravity, an upgraded and more precise version of Newton Gravitational Law. Unlike Newton’s theory, General Relativity describes gravitation as a result of curvature in the fabric of space-time. Before discussing further about General Relativity let us discuss about one of its key component, space-time.

**Space-time**

As the name suggests it is a continuum of the 3 dimensions of space along with the 4th dimension of time. It suggests that time, which was considered as an independent element in classical mechanics, is in fact dependent of factors importantly ratio of the velocity of observer and velocity of light. As this ratio increase the duration of a second with respect to an external observer, giving rise to weird paradoxes such as the twin paradox. Therefore it is realized the time is not an independent element and therefore we get a four dimensional coordinate system with time.

Similar to a point in 2-D and 3-D coordinate systems which is represented by (x,y) or (x,y,z) we have event in space-time (x,y,z,t). As time always flows in forward direction, we can say that it is not possible for anything to be stationary in an event, for example if a man is stationary in the entire 3 spatial dimension, he would be still be travelling from one event to another in the axis of time.

Now let us discuss the effect on Space-time in presence of a matter. The space-time gets curved towards the matter and this curvature results to a force which is called gravitation. The curvature is dependent on various factors such as mass, mass density. More precisely it depends on energy-momentum tensor.

**Interesting Cases**

*(i) Black hole: *

Black holes are aftermath of death of humongous stars with extremely high mass density. Black hole have extremely high gravitational field which even light cannot escape. This can be described as an extreme curvature of space-time.

*(ii) Worm holes or Einstein – Rosen Bridge:*

Wormholes can be called as a bridge between two events in a space-time. Believing that space-time is not flat it possible for there to exist a link between two different events in a space-time. This can also be described as something similar to a time machine as two different points in time can also be connected by a wormhole. However a wormhole is believed to be extremely unstable and hasn’t been observed in reality.