## Saturday, 20 July 2013

### Gravity and Orbits explained by General Relativity

Explanation of Gravity

You would recall the explanation of Gravity by Newtonian Universe which said that Gravity is a Natural force of attraction between any two bodies. Particle physics however explains gravity as a result of attraction force caused by a bosonic (force carrier) particle called Graviton. But Einstein's Theory of General Relativity has a completely different explanation of Gravity.

According to General theory, Gravity is the distortion of Space and Time which causes a force or acceleration in the path of an object in motion. Whenever an object changes its direction, it is said to be accelerated. Newton's first law states that an object moving in a straight line continues to do so unless it is accelerated by an external force. Thus an object (particle or boson or light) continues to travel in a straight line but due to distortion in Space Time it is forced to change its direction towards the mass offering the distortion in Space Time. For example The sun causes distortion in Space Time due to which all celestial bodies who should have moved in a straight path are forced to move around the sun.

 A satellite moves around earth due to Space time distortion

A white dwarf star is a star which is very dense, planet sized like the Sun. A white star creates a very huge distortion in Space Time that a normal Celestial body cannot. A neutron star is exceedingly dense stellar remnant that makes a very deep distortion in space time even deeper than white dwarf star. Light passing in its distortion is significantly effected but not completely. A black hole is a concentration of huge mass which is infinitely dense at its center which is called singularity. Its Space Time distortion is completely funnel shaped with closed end. Light entering its Space Time distortion cannot exit as it creates the maximum possible distortion in Space Time.

 Space Time distortion by a black hole

Free fall

Free fall is any motion of a body where its weight is the only force acting upon it. Classical Physics explains Free fall as an effect of Gravity. But General Relativity says that it is a kind of acceleration towards the mass which created a distortion in the Space Time forcing any body moving in a straight path to move towards the mass. In fact you are not able to escape any planet not because of its gravitational pull but due to local Space Time distortion. Space Time is forcing you to stay on or around the planet.

Explanation of Orbits

The orbits of the celestial bodies is governed by Kepler's law. However General Relativity has a different explanation for this. General Relativity states that it is the distortion in Space Time which is responsible for Orbits if Celestial bodies. Take for example the distortion of Space Time of Solar System by Sun. Due to huge distortion in Space Time Mercury is forced to follow a small circular path around the sun to be in motion. The Space Time distortion is huge in the inner part of Solar system and less in the outer part. Thus the outer planet mainly Neptune and Pluto has to follow a elliptical path around the Sun, i.e they follow a Circular path in the outer area but forced to bend in the inner areas. Newtonian Gravity couldn't account for such explanation to Gravity.

The following video explains Einstein's gravity :

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