Origin of Gravity and its Importance in the formation of Galaxies, Stars and Large Scale Structure in the Universe

The word 'gravity' is derived from the Latin word 'gravitas' which means 'weight'. Gravity is also referred to as gravitation and it is natural phenomenon by which all the things with mass or energy including planetary bodies like stars, galaxies and even light are attracted toward each other. As we know that Earth's gravity gives the weight to physical bodies and the Moon's gravity results the ocean tides. After big bang, due to this gravitational attraction preliminary gaseous matter present in he universe began to coalesce and form the first stars. Similarly these stars grouped together into galaxies. Therefore gravity or gravitation is responsible for so many of the large scale structure in the universe. The range of the gravitational attraction may be infinite and it becomes weaker and weaker as the distances between the bodies increase.

Gravity can be defined by the general theory of relativity with appropriate manner. This theory  is proposed by Albert Einstein in 1995 and according to this concept gravity is not a force but rather it is consequence of masses moving along geodesic lines in a curved spacetime caused by he unequal distributions of mass. One of the most central example of the curvature of spacetime is a black hole, from which nothing not even light can escape once crossed the black hole's event horizon. But for most of the applications gravity is often defined by Newton's law of gravitation, which says gravity as a force resulting any two bodies to get brought each other. This force is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

Figure: General Theory of Relativity 

Among the four fundamental interactions of physical world gravity is the weakest force. It is approximately 1038 times weaker than the strong force, 1036 times weaker than the electromagnetic force and 1029 times weaker than the weak interactions. Hence, this force has no any substantial effect at the level of subatomic particles. But at the macroscopic scale it has dominant interaction and it is the major cause of the formation of trajectories or orbit of astronomical bodies.

The modern researches and discoveries show that in the earliest universe the gravity would be in the form of quantum gravity, supergravity or gravitational singularity along with space and time. It was developed during Planck epoch (up to 10−43 seconds after the birth of the Universe). Later on, 'a theory of every thing' was proposed which is the combination of a theory of gravity, quantum mechanics and quantum gravity theory. This is based on the other three fundamental integrations of physics.