In a famous passage drawing implications from determinism, Laplace introduced the image an intelligence who knew the positions and momenta of all of the particles of which the universe is composed, and asserted that in a deterministic universe such an intelligence would be able to predict everything that happens over its entire history. It is not, however, difficult to establish the physical possibility of a counterpredictive device, i.e., a device designed to act counter to any revealed prediction of its behavior. (...) What would happen if a Laplacean intelligence were put into communication with such a device and forced to reveal its prediction of what the device would do on some occasion? On the one hand, it seems that the Laplacean Intelligence should be able to predict the device's behavior. On the other hand, it seems like that device should be able to act counter to the prediction. An examination of the puzzle leads to clarification of what determinism does entail, with some insights about various other things along the way. (shrink)

The inference from determinism to predictability, though intuitively plausible, needs to be qualified in an important respect. We need to distinguish between two different kinds of predictability. On the one hand, determinism implies external predictability , that is, the possibility for an external observer, not part of the universe, to predict, in principle, all future states of the universe. Yet, on the other hand, embedded predictability as the possibility for an embedded subsystem in the universe to make such predictions, does (...) not obtain in a deterministic universe. By revitalizing an older result—the paradox of predictability —we demonstrate that, even in a deterministic universe, there are fundamental, non-epistemic limitations on the ability of one subsystem embedded in the universe to predict the future behaviour of other subsystems embedded in the same universe. As an explanation, we put forward the hypothesis that these limitations arise because the predictions themselves are physical events which are part of the law-like causal chain of events in the deterministic universe. While the limitations on embedded predictability cannot in any direct way show evidence of free human agency, we conjecture that, even in a deterministic universe, human agents have a take-it-or-leave-it control over revealed predictions of their future behaviour. (shrink)