On the origin of (statistical) temperature in quantum Universe

In my talk we will argue that within a non-relativistic quantum-mechanical model of a Universe (the q-Universe) the statistical temperature emerges as a consequence of quantum entanglement. In particular, I will model the q-Universe as a system of interacting spin-1/2 particles described by a specific Hamiltonian (e.g. the Ising Hamiltonian). The q-Universe is assumed to be in a pure state of its Hamiltonian. I will show that any (almost) sub-system of the q-Universe is in a mixed state described by a density operator such that probabilities of outcomes of measurements in the energy eigenbasis of the sub-system can be very well approximated by the Boltzmann distribution