By the way, when you hear Quantum Trajectory Theory, the “trajectory” there is not a trajectory in normal space. This misleads many, I think. This trajectory is in Hilbert Space, which is an abstract vector space. The reason that QTT requires a Hilbert Space (good lord, I am simplifying a lot here) is that calculating anything superpositioned (before decoherence) is that it evolves through an abstract vector space that does not correspond to normal Euclidean space.

This is the trajectory to which QTT refers, a trajectory through Hilbert Space.