  Other proposals take the entropic change of a system to be mediated by an actually uneliminable “interference” into the system of random causal influences from outside the system. It is impossible, for example, to genuinely screen the system from subtle gravitational influences from the outside. The issue of the role of external interference in the apparently spontaneous behavior of what is idealized as an isolated system has been much discussed. Here the existence of special systems (such as spin echo systems encountered in nuclear magnetic resonance) plays a role in the arguments. For these systems seem to display spontaneous approach to equilibrium when isolated, yet can have their apparent entropic behavior made to “go backward” with an appropriate impulse from out side the system. This seems to show entropic increase without the kind of interference from the outside that genuinely destroys the initial order implicit in the system. In any case, it is hard to see how outside interference would do the job of introducing time asymmetry unless such asymmetry is put in “by hand” in characterizing that interference.