  The quantum deformation of the Hopf algebra describes the skeleton of quantum
field theory, namely its characterizing feature consisting in the existence of
infinitely many unitarily inequivalent representations of the canonical
commutation relations. From this we derive the thermal properties of quantum
field theory, with the entropy playing the role of the generator of the
non-unitary time evolution. The entanglement of the quantum vacuum appears to
be robust against interaction with the environment: on cannot ``unknot the
knots" in the infinite volume limit.
