Pierre-Louis Moreau de Maupertuis (1698-1759) was the first to formally state the principle of least action in 1744. The principle says that the path a physical system takes between two states is the one that minimizes (or makes stationary) a quantity called the action. Euler and Lagrange later gave it rigorous mathematical form. In modern notation, the action S is defined as:
S = ∫ L dt
where L is the Lagrangian (kinetic energy minus potential energy). The principle states that the physical path makes S stationary: δS = 0. This one equation underlies classical mechanics, general relativity, and quantum field theory. Feynman's path integral formulation of quantum mechanics is built directly on it.
Pierre-Louis Moreau de Maupertuis (1698-1759) was the first to formally state the principle of least action in 1744. The principle says that the path a physical system takes between two states is the one that minimizes (or makes stationary) a quantity called the action. Euler and Lagrange later gave it rigorous mathematical form. In modern notation, the action S is defined as:
where L is the Lagrangian (kinetic energy minus potential energy). The principle states that the physical path makes S stationary: δS = 0. This one equation underlies classical mechanics, general relativity, and quantum field theory. Feynman's path integral formulation of quantum mechanics is built directly on it.