Action at a distance

In physics, action at a distance is the concept that an object can be affected without being physically touched (as in mechanical contact) by another object. That is, it is the non-local interaction of objects that are separated in space. Non-contact forces is action at a distance affecting specifically an object's motion. This term was used most often in the context of early theories of gravity and electromagnetism to describe how an object responds to the influence of distant objects. For example, Coulomb's law and Newton's law of universal gravitation are such early theories. More generally, "action at a distance" describes the failure of early atomistic and mechanistic theories which sought to reduce all physical interaction to collision. The exploration and resolution of this problematic phenomenon led to significant developments in physics, from the concept of a field, to descriptions of quantum entanglement and the mediator particles of the Standard Model. Stephen Gray (scientist) first made the distinction between conduction and insulation, and discovered the action-at-a-distance phenomenon of electrostatic induction. Philosopher William of Ockham discussed action at a distance to explain magnetism and the ability of the Sun to heat the Earth's atmosphere without affecting the intervening space. Efforts to account for action at a distance in the theory of electromagnetism led to the development of the concept of a 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, which can be felt by other charges as a force. Maxwell directly addressed the subject of action-at-a-distance in chapter 23 of his A Treatise on Electricity and Magnetism in 1873. He began by reviewing the explanation of Ampère's formula given by Gauss and Weber. On page 437 he indicates the physicists' disgust with action at a distance.