  The zero temperature effective equation of motion is derived for a scalar
field interacting with other fields. For a broad range of cases, involving
interaction with as few as one or two fields, dissipative regimes are found for
the scalar field system. The zero temperature limit constitutes a baseline
effect that will be prevalent in any general statistical state. Thus, the
results found here provide strong evidence that dissipation is the norm not
exception for an interacting scalar field system. For application to
inflationary cosmology, this provides convincing evidence that warm inflation
could be a natural dynamics once proper treatment of interactions is done. The
results found here also may have applicability to entropy production during the
chiral phase transition in heavy ion collision.
