Time evolution in string field theory and T-duality

The time evolution operator (Schrodinger functional) of quantum field theory can be expressed in terms of first quantised particles moving on S-1/Z(2). We give a graphical derivation of this that generalises to second quantised string theory. T-duality then relates evolution through time t with evolution through 1/t and an interchange of string fields and backgrounds. (C) 2004 Elsevier B.V. All rights reserved.