  For a quantum field in a thermal equilibrium state we discuss the group
generated by time translations and the modular action associated with an
algebra invariant under half-sided translations. The modular flows associated
with the algebras of the forward light cone and a space-like wedge admit a
simple geometric description in two dimensional models that factorize in
light-cone coordinates. At large distances from the domain boundary compared to
the inverse temperature the flow pattern is essentially the same as time
translations, whereas the zero temperature results are approximately reproduced
close to the edge of the wedge and the apex of the cone. Associated with each
domain there is also a one parameter group with a positive generator, for which
the thermal state is a ground state. Formally, this may be regarded as a
certain converse of the Unruh-effect.
