After proving the special relativity which we discussed previously Albert Einstein began thinking of gravity. Isaac Newton said that when two bodies of masses m1 and m2 are placed near each other at a distance r from each other, a force F will be formed between them which is F=(m1*m2)/r^2.This force was the force which caused the apple to fall on Newton's head, the force causing us to orbit the sun and holding us on the surface of our home (the Earth). The explanation of gravity which Newton explained was completely true till Albert Einstein explained it. From the point of view of Newton if we were orbiting the sun and it was suddenly removed we will escape from our orbit at the same moment in the tangential direction. But Albert Einstein proved that Earth won't leave its orbit at the same moment by GENERAL RELATIVITY. Albert Einstein wanted to prove why a gravitational force is formed when two bodies are placed near each other. Einstein proved that when a massive body is placed in space it warps the space around it so the other body falls in its field and field particles are produced. Let's imagine what is going on, If you have a very big paper and you put in the center of it an apple the paper will have a small curvature but if you put a watermelon this curvature will be very big and deep. If you placed at the corner of this paper a an apple and in the center of this paper you placed a watermelon the apple will fall in this curvature. This what really happens in our universe When a big massive object like the Earth warps the space around it to make the moon fall in its field so gravitational force is created between them to let gravitational field particles be exchanged between the two massive bodies. Field particles are the particles which are responsible for any force to be formed. When the exchanging of these field particles increase the force increases. There are four field particles in our universe: Gravitons which are the field particles of gravitational force, photons which are the field particles of the electromagnetic force, Gluons which are the field particles of the strong force(a strong force is the force responsible for holding the nucleus components together) and the weak force which is responsible for the nuclear decay. Then what will happen to Earth if the sun disappeared suddenly?? According to General Relativity a giant wave will happen in space that will make us escape from our orbit but when this wave reaches our planet. Let's imagine what will happen, Imagine you have a very very big stretched elastic planar surface. put a watermelon at the center of this surface and an apple at the ends of this surface. What will happen when you suddenly take away the watermelon?? A strong wave will occur that will cause the apple to fly away from its position but when this wave reaches the apple. This what will really happen if the sun vanished suddenly and this is the general relativities explanation for Gravity.