The General Theory of Relativity was published by Albert Einstein in 1915.This theory gives the current description of gravitation in modern physics.It unifies special relativity and Newton's law of universal gravitation.the development of this theory began with the Equivalence Principle,under which the states of accelerated motion and being at rest in a gravitational field are physically identical.The main concept is that free fall is inertial motion;that is, it says that an object in free fall is falling because that is how objects move when there is no force exerted on them.and not due to the force of gravity , as given in Classical Mechanics.
After publishing the theory of Special Relativity in 1905 , Albert Einstein began to think on how to incorporate gravity into his relativistic framework.In 1907,he embarked on what would be an eight-year journey in the search for a relativistic theory of gravity.His work culminated in the November 1915 presentation to the Prussian Academy of Sciences of what are now known as Einstein's Field Equations.
General relativity is best understood by examining its similarities with and departures from Classical physics.The first step is the realization that classical mechanics and Newton's law of gravity admit of a geometric description.The combination of this description and the laws of Special Relativity results in a derivation of General Relativity.
At the base of classical mechanics,is the notion that a body's motion can be described as a combination of free motion ,and deviations from this free motion.However ,Einstein's theory goes much beyond this.General Theory is a metric theory of gravitation.At its core are Einstein's equations ,which describe the relation between the geometry of a four-dimensional model representing space-time on one hand ,and the energy -momentum contained in that space-time in the other.
CONSEQUENCES OF EINSTEIN'S GENERAL RELATIVITY
General Relativity has a number of physical consequences. A few of these are given below ;
1.Gravitational time dilation and Frequency shift.
2.Light deflection and Gravitational time delay.
3.Gravitational waves.
4.Orbital effects and the Relativity of direction.
Here,I will give some of the Astrophysical Applications of General Relativity:
1. Gravitational Lensing
The deflection of light by gravity is responsible for a class of astronomical phenomena .If a massive object is situated between the observer and a distant target object with appropriate mass and relative distances,the observer will see multiple distorted images of the target.Such effects are known as Gravitational Lensing.
2.Black Holes and other Compact Objects
Whenever the ratio of an object's mass to its radius becomes sufficiently large , General Relativity predicts the formation of a Black Hole,a region of space from which nothing, not even light, can escape.They are thought to be the final stage in the evolution of stars.Usually , galaxies have a super massive Black Hole with a few million to a few billion solar masses at its centre.Their presence played a significant role in the formation of galaxies and larger cosmic structures.
CURRENT STATUS
General Theory of Relativity has emerged as a highly successful model of gravitation and cosmology.It has so far passed every unambiguous observational and experimental test.However, there are strong indications that the theory is incomplete.Even now ,it is still an open question as to how the concepts of Quantum Theory can be reconciled with those of General Relativity.The evidence of Dark Energy and Dark Matter indicates the need for new physics.In spite of all this ,General Relativity is rich with possibilities for further exploration ,and even today,more than ninety years after its publication, remains an active area of research.
REFERENCES:
www.wikipedia.org
www.physics.fsu.edu
www.archive.ncsa.illinois.edu
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