  The present work is an attempt to investigate whether the evolutionary
history of the Universe from the offset of inflation can be described by
assuming the cosmic fluid to be an ideal gas with a specific gas constant but a
varying negative absolute temperature (NAT). The motivation of this work is to
search for an alternative to the "exotic" and "supernatural" dark energy (DE).
In fact, the NAT works as an "effective quintessence" and there is need to deal
neither with exotic matter like DE nor with modified gravity theories. For the
sake of completeness, we release some clarifications on NATs in Section 3 of
the paper.
