 Trouble looms over this explanation of time asymmetry (see Brown, Myrvold, &amp; Uffink 2009). Before Boltzmann explained entropy increase as described above, he proposed a now notorious “proof” known as the “\(H\)-theorem” to the effect that entropy must always increase. Loschmidt 1876/1877 and Zermelo 1896 launched objections to the \(H\)-theorem. If we take as premises classical mechanical dynamics, they pointed out, it’s impossible to get any function of the classical state to monotonically increase. Loschmidt focused on the time reversal invariance of the classical dynamics and Zermelo on its recurrence property (roughly, that a bounded system, left to itself, will eventually return arbitrarily close to its initial state, for any given initial state). They were right: time reversal means that for every entropy-increasing solution to the classical equations there is a mirror entropy-decreasing solution; and recurrence means that every solution will at some point have its entropy decrease if we wait long enough. Some time asymmetric ingredient that had not been properly announced had been smuggled into the theorem.