When Isaac Newton published his theory of universal gravitation in 1686, he knew he'd have to confront a few critics. Like a ghost stretching its arms across empty space, Newton's theory described the gravitational attraction between two masses, say, the Sun and the Earth, as a mysterious force that acted instantaneously between them.
How could the Sun influence the Earth, and the Earth the Sun, without direct contact?
This is the challenge of instantaneous "action-at-a-distance," unexplained in Newton's theory. Newton tried to preempt his enemies' attacks by adding a disclaimer to his work. He argued that his theory was so good at explaining so many things that to ask where the force of gravity comes from, or how it acts across space was, irrelevant. Rather, he would "feign no hypotheses" as these could not be part of "experimental philosophy."
To read more, click here.