Counterfactuals and the “Past Hypothesis”
In my book and on this blog, I emphasize that determinism, when paired with standard physics, undermines many of the counterfactual conditionals that we ordinarily assert. Some philosophers, including David Albert (pictured), seem to agree. But Albert claims that we can rescue ordinary counterfactuals by adding to standard physics something he calls the “Past Hypothesis” (PH), which says that at (or near) the big bang the universe was in “whatever particular low-entropy highly condensed…macrocondition it is that the normal inferential procedures of cosmology will eventually present to us” (Albert 2000: 96).
My book concedes that, without PH, standard physics makes probability-claims about the past that don’t fit well with our experience, such as the claim that the partly melted ice cube now in your drink was almost certainly more melted five minutes ago. But if we add PH as a postulate, then those awkward probability-claims don’t follow from the physics.
The problem, however, is that standard physics gives PH itself a probability of virtually zero: 1 chance in roughly 10^10^122. That’s why I argue in my book that PH, even if actually true, would almost certainly not be true in any counterfactual circumstance that we might imagine. As I wrote, “Winning the lottery against all odds does not justify the belief that you also would have won, against all odds, if you had chosen a different ticket, much less the particular different ticket that you now have in mind” (p. 133).
Albert is aware of this problem. In answer to it, he claims that PH is not just luckily true. Rather, PH is a law of nature! If PH is a law of nature, he notes, then PH will continue to be true in the nonactual circumstances that we imagine when we assert ordinary counterfactual conditionals. He’s right, but that’s a big “If”! Many philosophers who know this area much better than I do deny that PH even could be a law of nature. They note that PH is unlike standard laws of nature in being vague, hand-waving, and restricted to a particular event. Instead, they say, PH is at best a “boundary condition” for the laws of nature, not a law of nature in its own right.
A recent article by Eddy Keming Chen tries to answer these objections. I found myself unconvinced, not least because Chen asserts that PH is a brute, “fundamental” law of nature that has no explanation, in violation of PSR.
