  We conjecture chronology is protected in string theory due to the
condensation of light winding strings near closed null curves. This
condensation triggers a Hagedorn phase transition, whose end-point target space
geometry should be chronological. Contrary to conventional arguments,
chronology is protected by an infrared effect. We support this conjecture by
studying strings in the O-plane orbifold, where we show that some winding
string states are unstable and condense in the non-causal region of spacetime.
The one-loop string partition function has infrared divergences associated to
the condensation of these states.
