  In this paper we shall derive the thermal properties of the relativistic
quantum vacuum from a more primordial underlying structure which shares some
properties with the old Dirac-sea picture. We show in particular how the
Tomita-KMS structure in RQFT is a consequence of the structure and dynamics of
the underlying pattern of vacuum fluctuations. We explain the origin of the
doubling phenomenon in thermofield theory and the duality symmetry between a
local algebra of fields or observables and its commutant in RQFT and give an
interpretation of the notion of thermal time.
