  When gas molecules collide, they accelerate, and therefore encounter the
Fulling-Davies-Unruh and Moore-DeWitt effects. The size of these effects is
sufficient to randomize the motion of the gas molecules after about 1
nanosecond at standard temperature and pressure. Such observations show that
quantum field theory modifies what is required to isolate a physical system
sufficiently for its behaviour to be unitary. In practice the requirements are
never satisfied exactly. Therefore the evolution of the observable universe is
non-unitary and thermodynamically irreversible.
