exists no free choice for the direction of the arrow of time.

Because the wave equations for fields (including the electromagnetic fields) do not have an asymmetrical sense of the direction of time built into them, we can entertain at the quantum mechanical level the possibility that the arrow of time is reversed for a short duration during a measurement of the properties of a particle, due to the reduction of the wave function $\psi$ describing an entangled system of particles including the particle being measured. The choice of the advanced Green function is then subject only to boundary conditions [*chosen on the basis of observations*]{}. We shall argue that [*nonlocal*]{} quantum theory observations do select the advanced Green function boundary conditions during the collapse of the wave function.

We shall adopt the usual approach to QM theory that the Schrödinger equation $$i\hbar \frac{\partial\psi}{\partial t}=H\psi$$ describes a purely deterministic, unitary evolution of the wave function $\psi$. This also holds true for the fields in a relativistic quantum field theory. However, this abruptly ceases to be true when we perform a measurement of the wave function $\psi$, which destroys the coherence of the state vector by triggering a reduction of the 