  It can be argued that the ordinary description of the reversible quantum
process between two one-to-one correlated measurement outcomes is incomplete
because, by not specifying the direction of causality, it allows causal
structures that violate the time symmetry that is required of a reversible
process. This also means that it can be completed simply by time-symmetrizing
it, namely by requiring that the initial and final measurements evenly
contribute to the selection of their correlated pair of outcomes. This leaves
the description unaltered but shows that it is the quantum superposition of
unobservable time-symmetrized instances whose causal structure is completely
defined. Each instance consists of a causal loop: the final measurement that
changes backwards in time the input state of the unitary transformation that
leads to the state immediately before it. In former works, we have shown that
such loops exactly explain the quantum computational speedup and quantum
nonlocality. In this work we show that they lead to a completion of the
anthropic principle that allows a universe evolution with quantum speedup.
