Dr. Neville Thomas Jones, Ph.D.
The 'Law of Universal Gravitation' is well-known now, but there was a time when it did not exist. Prior to its formulation, by Sir Isaac Newton, the night sky was described by various combinations of circular motions, with the World positioned immovable at the centre of the universe. The motions that we could perceive were physically produced by circular orbits, themselves considered to be a consequence of the object in question being affixed to a rigid, transparent shell that rotated about the World. These shells could be somehow fixed to other shells, etc. Physics was uncomfortable with this not because there was any serious error in the predicted trajectories of celestial bodies, but because of the necessary reliance upon unknown mechanisms.
Instead of maintaining a central, non-moving World, and looking for alternative explanations of heavenly motion, the World was demoted to being a 'planet' orbiting the Sun, with the stars being pushed enormous distances away. This allowed for a theoretical framework to be developed, essentially by Kepler and Newton, in a freer and easier philosophical atmosphere.
Newton's gravity law is empirical; which means that it was simply an educated guess. Newton's intellect is extremely impressive, but a guess is still a guess, no matter who makes it, and it may be wrong or ill-founded.
Specifically, the assumption was made that the force of attraction between two physical bodies is directly proportional to the product of their masses, and inversely proportional to the square of the separation between their centres of mass. Once this guess was made, the constant of proportionality (as such a thing is termed in physics) was subsequently determined by experiment.
This constant of proportionality, G, is called the gravitational constant and is nothing deep or fundamental, as many claim. It simply ties the guess to the observational data. Notice also that there is no attempt to describe why this supposed relationship holds true. Newtonian physics has no conception of what gravity actually is.
That changed to some extent with the completion of Dr. Albert Einstein's General Theory of Relativity. Gravity was suddenly 'explained' by the warping of four-dimensional space-time (a concept due to Minkowski). We are told to believe that this is analogous to a ball-bearing sitting on a rubber sheet. Despite the illustration, which may or may not have merit, the cause of gravity remains very much a mystery.
That there exists gravity on the World is evident enough, as Newton allegedly discovered whilst sat under the apple tree, but why should other objects in God's universe require gravitational fields? If these objects are set in the firmament, then why does gravity need to be 'universal' at all? - And God made two great lights; the greater light to rule the day, and the lesser light to rule the night: he made the stars also. And God set them in the firmament of the heaven to give light upon the earth, and to rule over the day and over the night, and to divide the light from the darkness: and God saw that it was good. And the evening and the morning were the fourth day. (Gen. 1:16-19, KJV.) One alternative is that gravity is local to the World, with the World's gravitational field perhaps extending throughout the universe, but without any other fields to interact with.
It then consequentially follows that all of modern cosmology collapses (as demonstrated in the scientific paper, "The size of the physical universe"). Or, to put it another way, all of our current ideas and hypotheses regarding the universe are based upon Newton's initial guess!
Newton's law of universal gravitation, taught to us when we were children, is more accurately termed, Newton's guess regarding gravitation. Modern astronomy and cosmology are based, in their entirety, upon this guesswork.