Editing Loschmidt's paradox (section)

==Information theory==

A more recent proposal concentrates on the step of the paradox in which velocities are reversed. At that moment the gas becomes an open system, and in order to reverse the velocities, position and velocity measurements have to be made.<ref>{{cite journal|title=The reversibility paradox: Role of the velocity reversal step|author-last=Binder|author-first=P.M.|author-link=P.M. Binder|journal=[[International Journal of Theoretical Physics]]|date=2023|volume=62|issue=9 | page=200|doi=10.1007/s10773-023-05458-x |bibcode=2023IJTP...62..200B |url= https://rdcu.be/dmmuZ |doi-access=free}}</ref> Without this, no reversal is possible. These measurements are themselves either irreversible, or reversible. In the first case, they require an increase of entropy in the measuring device that will at least offset the decrease during the reversed evolution of the gas. In the second case, [[Landauer's principle]] can be evoked to reach the same conclusion. Hence, the gas+measuring device system obeys the Second Law of Thermodynamics. It is not a coincidence that this argument mirrors closely another one given by Bennett to explain away [[Maxwell’s demon]]. The difference is that the role of measurement is obvious in Maxwell’s demon, but not in Loschmidt’s paradox, which may explain the 40-year gap between both explanations. In the case of the single-trajectory paradox, this argument preempts the need for any other explanation, although some of them make valid points. The broader paradox, “an irreversible process cannot be deduced from reversible dynamics,” is not covered by the argument given in this section.