incompressibility enables dual views of measurement evolution vs state evolution

#learning

Two ways to view how a measurement changes as the phase space evolves with time:

1. We stay in the old, pre-evolution, coordinate system, so the measurement operator doesn't change, but the state (distribution) has changed
2. We move to a new coordinate system defined by the phase space evolution, so the measurement operator has now changed, while the state has not (this is the part that relies on incompressibility!)