Information-theoretic limits of control

Fundamental limits on the controllability of physical systems are discussed in the light of information theory. It is shown that the second law of the rmodynamics, when generalized to include information, sets absolute limits to the minimum amount of dissipation required by open-loop control. In addi tion. an information-theoretic analysis of control systems shows feedback c ontrol to be aero sum game: each bit of information gathered from a dynamic al system by a control device can serve to decrease the entropy of that sys tem by at most one bit additional to the reduction of entropy attainable wi thout such information. Consequences for the control of discrete state syst ems and chaotic maps are discussed.