Description

General Relativity (GR) is arguably considered as the most elegant theory in

physics. GR pronounces gravitation as the manifestation of space-time geometry.

GR has been extremely successful at describing observations and passed all

experimental tests conducted so far. GR based cosmology is the cornerstone of

the current hot Big Bang description of our Universe. However, some unexpected

components turn out to make up most of the Universe's mass-energy budget in

the GR description of the observations at large scales.

Recent cosmological observations suggest that the Universe is undergoing a phase

of accelerated expansion. The explanation of such accelerated expansion in the

purview of general relativity requires the presence of a large amount of some

exotic form of energy density with negative pressure, the so-called dark energy.

On the other hand, the amount of luminous matter in galaxies is found insufficient

to explain the observed galactic rotation curves and thereby the existence of

non-luminous or dark matter, that neither interacts with radiation nor with the

conventional matter except through the gravitational field or through some feeble

interaction, has to be assumed. This dark matter component is also required to

be non-relativistic (i.e. cold) in view of structure formation. It appears from a

wide variety of astrophysical observations that ordinary baryonic matter constitutes

just 4.9% of the energy density in the Universe while dark matter composes

about 26.8% and the dark energy contributes most - about 68.3% of the energy

density in the Universe.

The journey of exploring the laws of nature had crossed a milestone when Nicolus

Copernicus predicted the actual planetary motion and his student Galileo Galilei

proved his teacher's prediction by his revolutionary discovery of Telescope. The

laws of planetary motion by Johannes Kepler, created a perception about motion

inside the solar system which was given a proper and generalized dimension by

Isac Newton with his revolutionary Theory of Gravitation 2]. The invention of the

telescope and the theory of Gravitation explored the gateway of gathering knowledge

about the phenomena not only beyond the Earth but beyond the solar system

also.