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Newton
Isaac Newton was the first physicist to explain, accurately, the force of gravity. In his laws he introduced the idea that any object will continue to move at a constant speed in a straight line unless another force acts upon it. From this theory, much can be learned about gravity. Gravity is a major force affecting objects throughout the universe. Newton described gravity's force to be pulling objects toward one another throughout space. He explained that the gravitational force between any two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them. This translates to mean that both mass and distance affect the gravitational pull between two objects. It is important to understand that the distance is the distance between the centers of gravity. This means that no matter how compact a given object is, an object at a certain distance from it will not be less attracted to it although the distance to the surface is greater. Black Holes are extremely dense bodies. A common misconception is explained through Newton's theory. Objects at a great enough distance will not be any more affected than if the Black Hole were less dense (retaining its mass).
Like Newton, Einstein revolutionized the field of physics. Using the idea of four-dimensional space-time, Einstein redefined the laws of gravity to a more accurate level. Einstein suggested that gravity is not a force acting on objects, but rather it is the shape of space-time curvature. According to Einstein in his General Theory of Relativity, space-time is curved around any mass or energy. In his famous equation E=mc2 he states that there is a direct corrolation between mass and energy. Mass and energy are proportional. Some scientists believe that one can even think of energy and mass as part of the same 'thing.' E is energy, m is mass, and c is the speed of light (a constant 300,000 kilometers or 186,000 miles per second). An analogy to Einstein's concept of space-time curvature is to imagine a bowling ball sitting on a trampoline. The bowling ball makes an indentation on the trampoline. If you roll a golf ball past the bowling ball, the path of the golf ball will curve around the bowling ball. A black hole creates a large amount space-time curvature, greatly affecting the surrounding space.
Read more about space-time curvature and its reactions with light.