“If the human observer is envisaged as one of the spherical spaceships, and time is seen as the other, then the same possible explanations still apply. The observer could be stationary while time flows past. Time could be stationary while the observer and his experiential concatenation of observed events flow past. Or both time and the observer could be progressing at different velocities along the same track. The nature, velocity, and direction of time-flow ought to be susceptible to scientific analysis in due course — even if it can’t be done definitively at our present level of scientific knowledge and technological skill.”