We all know what gravity is. It is the force that holds objects on the surface of the planet. This force also causes dust particles in space to clump together. Eventually the clump is pulled into the shape that takes up the minimum amount of space, a sphere. If there is enough space dust in the neighborhood, as more and more dust is gathered up, the pressure on the stuff near the center of the sphere gets so strong that the nuclei of the atoms are forced close enough together that nuclear fusion takes place. This releases tremendous heat and light and the spherical object becomes a star. This star, built by the force of gravity, becomes the major source of energy in its neighborhood in space.

How gravity works was elegantly worked out by Albert Einstein and some of his friends. Unfortunately the explanation is incomprehensible to approximately 100% of the population of the planet. Also the interpretation of Einstein's theory, by those folks who do comprehend it, has a few loose ends even after nearly a century of study. One of those loose ends has to do the speed with which the effect of gravity travels between objects. Einstein's theory implies it is limited to the speed of light but as a practical matter it seems to be very much faster, possibly infinite. As of 2007 attempts to reconcile the theory and the evidence are inconclusive, at least in this office.