Great Idea 2

Idea 2: Action at a distance

Action at a distance is the concept that an object can be affected or influenced without being physically in contact by another object. It is the nonlocal interaction of objects that are separated in space. Some forces can act between two objects without physical contact. We call these non-contact forces. Action at a distance explains the operation of non contact forces.

                 Aristotelian physics holds that every motion requires a conjoined mover. Thus according to Aristotle, action can  never occur at a distance, but needs a medium enveloping the body. Although natural motions like free fall and magnetic attraction were recognized in the post-Aristotelian period, the rise of the corpuscularian philosophy again banned  unmediated actions at a distance. Cartesian physical theory  postulated a ‘subtle matter’ to fill space and provide the medium for force and motion. Its successor, the aether, was postulated in order to provide a medium for transmitting forces and causal influences between objects that are not in direct contact. 
                “Action at a distance” was introduced in the context of early theories of gravity and electromagnetism. Coulomb's law and Newton's law of universal gravitation describe non cntact forces acting at a distance without an intervening medium. The gravitational force of earth acts on moon at a distance, a bar magnet can  pick up a steel paperclip from a distance. Efforts to account for action at a distance in the theory of electromagnetism led to the development of the concept of an electric field which mediated interactions between currents and charges across empty space. According to field theory, we account for the Coulomb (electrostatic) interaction between charged particles through the fact that charges produce around themselves an electric field, whose influence can be felt by other charges as a force.