I imagine that the quantum physicist’s response to my last post would be to suggest that the probabilistic nature of a quantum physics is “hard”, or ontological, or objective, while the probabilistic nature of a cat is “soft”, or epistemic, or subjective. Quantum physics really is probabilistic, while cats only seem probabilistic because our knowledge is limited. Suppose we assume that this is correct. I still think it worth noticing that our knowledge is in fact probabilistic in both cases, and that the prediction problem with regard to cats is not likely to be simpler, should we ever be in a position to seriously attempt it, than the prediction problem with regard radioactive decay. We might look at the gulf between the two rather differently than our hypothetical physicist. The radioactive decay of an atom is extremely simple event, while the future state of a cat is an extremely complicated event. The attention we have devoted to the former is sufficiently large in relation to the difficulty of the problem that we might reasonably expect to have arrived at a complete understanding if it is possible for us to do so. The attention we have devoted to the latter is sufficiently minute in relation to the difficulty of the problem that we can be certain our understanding is incomplete and will remain so for the foreseeable future. It is easier to imagine that a complete understanding of a cat’s future state is theoretically possible because we are so far from it that the possible realm of understanding is quite unconstrained, while we are close enough to a complete understanding of a radioactive atom that we can see some boundaries to our possible realm of understanding. This leads us to an odd inversion. The more difficult a problem is, and the further we are from solving it, the more willing we are to believe that solving it is theoretically possible.

There’s also an odd inversion in the narrative we tell about quantum physics. The traditional narrative is something like: macroscopic objects follow definite rules that make sense. We can know the location and velocity of a ball precisely, and we can predict how its location and velocity will change based on any force exerted on it. Quantum physics is a bizarre world in which none of this really seems to apply. The rules don’t make sense and violate our understanding of reality, We can’t know locations and velocities precisely, things often seem to be in multiple places at once or to affect each other even when there is no identifiable force connecting them, future states are probabilistic rather than deterministic. However, all the ways in which quantum physics differs from classical physics are also ways in which our experience of the world also differs from classical physics. The world we interact with may well follow very definite, coherent, deterministic rules, but phenomena in the actual world–and especially the social world, which occupies a great deal of our attention and interest–are so complicated that our experience of it is so full of uncertainty, confusion, and context-dependence that the world of quantum physics is really quite orderly and well-behaved in comparison. We might as well have a narrative about how bizarre classical physics is. The simplest situations we know of share some of the same uncertainties and ambiguities as the most complex situations we know of, while there is this funny realm in between where certainty and precision make an appearance.