Gravity and general theory of relativity

 Gravity and General theory of relativity:                                                        Gravity:                                                                 what is gravity? It is an illusion extract by two objects with non-zero mass. Not only, gravity means the Apple  falls on the earth. You may consider two objects in the space an astronaut and an apple, in this case both two objects pulling other object towards each other. The astronaut pulling the Apple towards him and the Apple pulling the astronaut towards it. This attractive force between any two  masses is called the gravitational force . Gravitational force is an attractive force between any two object with non -zero mass  separated by a distance. Now , you  may  have a question  , if two objects attract each other . Why don't two humans get attach? It is because, consider two person with masses m1  and m2 standing between a distance d extract a force  F1 and F2 towards them . 

       According to Newton's universal law of gravitation : 

     

                    Force F ~to m1×m2

                                     F ~to 1/ d²

                         F = G m1× m2                                                              ____________                                                                     d²                        

     G is universal gravitational constant It's value is 6.674 ×10-¹¹Nm² kg- ²

                    The two persons with masses m1 and m2 did not attract because the earth's gravitational force is much bigger than their masses . Although, they attract to the earth first and did not to each other. 

General theory of relativity:

                                Albert Einstein, said that gravity is not a force. It is a space time curvature. He discovered it with his imagination and thoughts. First thought , he saw a man cleaning a window on the top of the building and suddenly falls, he was under free fall condition. He feels weightlessness during that time.  

                             The same thing when a person on rocket was an under free fall condition feels weightlessness. 

                           Second thought, a person in the rocket as an ball and the rocket movin g upwards with acceleration 9.8 ms -². The ball suddenly touches the ground. But actually   ball doesn't touch the ground the rocket moved upwards with acceleration touched the  ball  . Exactly what we can do on the earth the same thing we can do in the rocket. 

                            Third thought, in earth with gravity if we throw a ball from 1m after 90cm the ball became bend and reaches the ground. The same thing if we throw a ball in rocket and suddenly accelerate the ball bends. He said that gravity on earth = acceleration g = a  . 

                                Then, the thought if we torch a light and accelerate ,the light bends  and he also said light bends in gravity also. 

                                To check this, if a rocket moves with acceleration 980 ms-² the light bends into an photon. To check it with gravity the sun 's G value is 28 times greater than earth's gravity. From mathematical Albert Einstein , said  that light bends from this gravity is 1.75 arc second ( arc second means 60 seconds in that 1.75 arc second) . 

                            To test this royal science academy conducted a experiment. To research the light bends from sun . We need  a light source, bending acceleration should be at the center ( the sun ) . And to measure this we need to look back from sun. So scientists selected a star on the backside of the sun and pin point it took pictures. Waited for solar eclipse and took 16 photos the stars direction was changed. It is because the sun 's gravity bends the light from the star to earth. 

                                   The light goes on straight line but the space time was curved  . So, the light also curved. Space time means the space is not empty it is curved. For example : imagine a sheet and place a object with 10 kg and later 100 kg object the 10kg object comes closer to 100 kg object because it has large mass.  The space time is curved due to its mass. 

                           The same thing happen in space the sun with 3 lakhs 30 thousands more mass than earth makes space time curved and earth rounds the sun. Finally gravity it is not a force . It is due to space time curved.