Kalman: The Scientist Who Defined Our Field [Historical Perspectives]

Until about 1960, systems and control were identified with input/output thinking. This was the dominant, if not the unique, point of view from which control problems were approached, at least in the Western literature. In the early 1960s, new fundamental concepts introduced by Kalman precipitated what has been later dubbed "a big bang" in systems theory. Concepts such as controllability, observability [1], optimal control [2], and state estimation [3] have deeply changed the way in which scientists and engineers deal with control problems.