  We consider an alternative approach to the foundations of statistical
mechanics, in which subjective randomness, ensemble-averaging or time-averaging
are not required. Instead, the universe (i.e. the system together with a
sufficiently large environment) is in a quantum pure state subject to a global
constraint, and thermalisation results from entanglement between system and
environment. We formulate and prove a "General Canonical Principle", which
states that the system will be thermalised for almost all pure states of the
universe, and provide rigorous quantitative bounds using Levy's Lemma.
