Irreversibility and Mechanics

Abstract

PROF. K. R. POPPER has recently pointed out the error in the belief that “ ‘classical’ mechanics … can describe physical processes only in so far as they are reversible in time”¹. He cites the spreading of water waves resulting from a dropped stone as an example of a ‘classical’ process which is irreversible. This example is, however, not altogether convincing, since it is not obvious that a reversed set of water waves cannot be set up by a system of generators, coherently operating on the periphery of the water wave system; also, the propagation of water waves is in any event irreversible by virtue of being a dissipative process, while Popper's argument was for irreversibility of the waves on other grounds.