Fundamental Forces in Nature

We all carry an intuitive sense of "force" from everyday experience — the push needed to move an object, the impact felt when something hits us, the pull we feel on a merry-go-round. Turning that intuition into a precise scientific concept took a long time; even Aristotle got it wrong. It was Newton, in his laws of motion (and his explicit form for the gravitational force between two bodies), who finally got it right.

At the macroscopic level we encounter what feels like a great variety of different forces: muscular force, contact force, friction, the tension in a stretched spring or a taut rope, buoyancy and viscous drag when a solid meets a fluid, pressure forces, surface tension, and — at the microscopic level — electric and magnetic forces, nuclear forces between protons and neutrons, and interatomic and intermolecular forces.

One of the great insights of twentieth-century physics is that this apparent variety collapses down to just a handful of fundamental forces. The spring force, for instance, feels like its own separate thing, but it actually arises from the net electric attraction and repulsion between neighbouring atoms as the spring is stretched or compressed — an "unbalanced sum" of far more fundamental electric forces between charged particles. So the laws governing these familiar derived forces (spring force, friction, and so on) are not independent laws at all; they are consequences — often very complicated ones — of the laws of the fundamental forces.

At our present level of understanding there are exactly four fundamental forces in nature: