by David Roberson

Created on: August 01, 2007   Last Updated: September 14, 2008

To a curious mind, gravity is a curious phenomenon. The more one pays attention to it, the more fascinating and mysterious it becomes. Today, we have the advantage of having had great minds ponder the mystery and define what can be observed and inferred by studying it. Newton pondered the question "why do objects fall?" and provided us with a theory of universal gravity (along with his three laws of motion). He essentially defined the terms we now use to describe and quantify gravity, the force that attracts objects with mass to each other. A description, particularly an accurate mathematical description, of gravity is the beginning of an answer to the question "how does gravity actually work?"

Newton's theory of gravity gave us a grasp of the mechanics of motion, but until Einstein redefined our understanding of the relationship between space and time, and the relationship between mass and energy, changing our concept of gravity, we did not realize that there was a great deal more to the question. Einstein's theory of general relativity revealed an equivalence between the force of gravity and the force of acceleration, with fascinating implications for the relationship between those forces and inertia that gave us new insight into the impact of motion on time and space. Einstein's relativity introduced us to the concept of curved or warped space-time. At the same time, Einstein's revelations provide a better description of the phenomenon of gravity while subtly undermining the concept of gravity. That is, it is less clear what gravity is (or what is gravity), specifically, and that makes it more difficult to comprehend how gravity works.

One of the things that makes gravity so difficult to pin down is the fact that it is inextricably linked to matter through mass, and through mass to space, time and energy; it reveals something profound about how space, time, matter and energy truly relate to each other. We just cannot, quite, see it. We understand that gravity is defined as an inherent interaction between masses with a direct impact on the shape of space in which mass resides. Ironically, space in the form of distance dictates the strength of the force of gravity. The force of attraction between the mass of two objects is proportional to the inverse square of the distance between them. We understand that energy is equivalent to mass times the square of the speed of light (C squared). But what does that actually mean? At the moment, we are looking at the same

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