 Inspired by Boltzmann’s attempts in this regard, many philosophers have sought such reductions, either partial or total. Grünbaum (1973) and Smart (1967) develop entropic accounts of the knowledge asymmetry. Lewis (1979) suspects the asymmetry of traces is linked to the thermodynamic arrow but provides no specifics. Dowe (1992), like a few others, ties the direction of causation to the entropy gradient. And some have also tied the psychological arrow to this gradient (for a discussion see Kroes 1985). Perhaps the most ambitious attempts at grounding many arrows all at once can be found in Reichenbach 1956, Horwich 1987, and Albert 2000, 2015. Each of these books offers possible thermodynamic explanations for the causal and epistemic arrows, as well as many subsidiary arrows.