This is an interpretation of the Space-Gravity Theory which was mostly conceived by Einstein. In 1915, Albert Einstein developed the theory of general relativity in which he considered that objects accelerated with respect to each another. He developed an entirely new approach to the concept of gravity, based on the principle of equivalence, which states that gravity pulling in one direction is completely equivalent to an acceleration in the opposite direction, so that it is theoretically impossible to distinguish between gravitational and acceleration forces. He said that acceleration and gravity were actually the same phenomenon and that the gravity you feel is actually the force of acceleration acting on you as you move through space-time. Gravity could be considered an effect of space itself and not a force.
Acceleration is defined as the rate of change of velocity.
If a person were standing in a stationary rocket on earth, his feet would be pressing against the floor of the rocket with a force equal to his weight. If he had no frame of reference, the astronaut could not tell whether the rocket was at rest on the earth or accelerating somewhere in space. Thus, Einstein concluded that the force of acceleration is not distinguishable from the force due to gravity. In particular, the gravity of any mass, such as our sun, has the effect of warping the space and time around it. For example, the angles of a triangle no longer add up to 180 degrees and clocks tick more slowly the closer they are to a gravitational mass like the sun.