  We establish correspondence between macroscopic thermodynamical quantities
and complementarity in wave interference. The well known visibility and
predictability in a double slit--like experiment are shown to be connected to
magnetic susceptibility and magnetization of a general interacting spin chain.
This gives us the ability to analyze the tradeoff between thermodynamical
quantities in the same information--theoretic way that is used in analyzing the
wave--particle duality. We thus obtain new physical insights into usually
complicated thermodynamical models, such as viewing a phase transition simply
as a change from an effective single slit diffraction to a double slit
interference.
