Describing Gravity

      from the time when pre- humans were still being bruised from falling out of trees we have been acutely aware of the force that tugs on us from below. Probably regarded as a spirit that pulled everything down to a lowest level it, along with other natural spirits living on mountains and in the clouds, was described by its effects. The gravitational spirit pulled rain from the clouds and pulled rocks and mud from the sides of mountains in an attempt to bring them down from a presumptive position of elevated self importance.  Mayan myths include an anti gravity below the Earth's surface where other people walked upside down and where the sun went when it set and, during the upright people's darkness, lighted the world below. Many other ancient myths describe gravity and it's effects in ways we may find naïve but linger on in our own experiences as a strange but familiar force.
     Modern science allows us to measure and describe gravitational effects in more detail but does not explain it. Newton, on a sabbatical from his studies at Oxford to escape the plague, developed a formalized description of gravity, a new mathematical concept, (the calculus), to calculate it's effects. He also solidified the concept of mass as a measure of the amount and density of material needed to produce a gravitational field of a certain strength. This mass/gravity equivalency is still at the core of the physical sciences, orbital calculations and cosmology even after being called into question by Einstein and the recent discovery of gravity without any apparent causal mass, (dark matter).
     The Mayans had the upside down people on the other side of a thin flat plane but were getting close to the truth. The persistent and unavoidable observations of a curved horizon hinted at a sphere and the Greeks, using shadow lengths taken at different latitudes, were able to calculate the size of the ball implied by the curved horizon. But persistent popular common sense opinions clung to a flat earth image with an edge which you could fall off if you sailed too far. Until astronomy advanced, and adventurers sailed beyond the horizon and returned did the full realization that we were stuck to a giant ball by a mysterious force called gravity become widespread and accepted.
     Newton's new math established the mass of the earth and it's gravitational field as a measure of acceleration as objects are pulled to earth from a height, and used this 32 feet per second/per second standard as a yardstick for measuring other massive objects in space by observing their orbits, but we still don't have an explanation, we only have a description and sometimes the description results in some very strange concepts.
     Newton's math describes why we can accelerate a satellite to 18,000 miles per hour and have it continually fall around the Earth instead of directly to the ground. It also allows us to calculate a speed, 25,000 miles per hour needed for the accumulated potential energy of a space probe's acceleration to exceed gravities potential to pull it back and escape into space beyond the Earths influence.
Strangely, Newton's math also describes a point of zero gravity at the center of the Earth and, if the world could be hollowed out, leaving only a thick crust, the surface people would still feel the effects of, (a reduced gravity), but people inside the hollow Earth would always be weightless, even when near the inside of the crust.
     With the advent of quantum theory gravity's description gets even more strange and as we smash the basic particles of matter together looking for clues inside cloud chambers we still don't have an explanation, only a more complicated and confusing description. Is the proton the source of gravity? It has mass but so do other sub atomic particles. Is gravity a by product of the strong force? Is it created by the gluons buzzing around and holding the quarks together inside the proton, and what about the Higgs particle. We are surrounded by and made up of mostly empty space. Empty space inside atoms and their constituents and between stars and galaxies, but gravity from dark matter and luminous matter continues to tug on itself at a distance and continues to shape the Universe and control how things move within it.
     We can describe gravity but still have no idea what it is. Maybe it is a spirit like our ancestors thought.