 But this argument is too quick. It rests on assumptions about the nature of time which are arguably at odds with what physics tells us. (Hoefer 2003 [2016], Ismael 2016.) There is an alternative explanation for our beliefs about the “open” future as opposed to the “fixed” past—the direction of causation. Causes are always earlier than their effects. Our deliberation causes our choices, which cause our actions. But not the other way around. Our choices cause future events; they never cause past events. Why causation works this way is a deep and difficult question, but the leading view, among philosophers of science, is that the temporal asymmetry of causation is a fundamental but contingent fact about our universe. If things were different enough—if we could travel backwards in time—then we would sometimes have an ability that we don’t actually have—the ability to causally affect past persons and things (Horwich 1987; D. Lewis 1976). If this is right, then we don’t need to suppose that the past is metaphysically or absolutely necessary in order to explain the fixed past/open future contrast. The past could have been different. But, given the way things actually are, there is nothing that we are able to do that would causally affect the past.