According to Einstein's theory of relativity, the universe is like a giant grid made up of space, time and particles of matter. The presence of a planet, or other large mass, causes spacetime in the grid to curve. Gravity is created by this distortion and makes distortions of its own by warping the curvature even more, obligating particles to respond. These accelerating particles create energy as waves of gravity, much like radio waves create a distortion as they move through space.
Distortions in spacetime curvature produce energy that acts on particles. All matter is made up of particles that are influenced by the four fundamental forces: electromagnetism, gravity, strong nuclear force and weak nuclear force. Gravity attracts particles toward itself by distorting the spacetime curvature. But gravity is a relatively weak force and can be easily overcome. Throwing a ball in the air, for example, is rebelling against gravity.
Gravity is not a constant. A good example is a black hole, which distorts both time and space. This event is called "frame-dragging," and scientists theorize it happens because the center of the black hole was once a massive planet. The energy released after the destruction of the planet creates such a strong gravitational pull that it drags space with it.
As of 2011, studies continue on the science of string theory. In 1984 the theory changed to include a different take on gravity. This is after anomalies in the mathematical equations supporting the theory were found to cancel each other out when gravity became the focus. The theory expands upon relativity by asserting that particles have a more active part to play in gravity. This is because they are vibrating strings that move through multiple dimensions responding to, and comprising, the fundamental forces of physics.