Tychomancy: Inferring Probability from Causal Structure
Michael Strevens
Language: English
Pages: 280
ISBN: 0674073118
Format: PDF / Kindle (mobi) / ePub
Tychomancy―meaning “the divination of chances”―presents a set of rules for inferring the physical probabilities of outcomes from the causal or dynamic properties of the systems that produce them. Probabilities revealed by the rules are wide-ranging: they include the probability of getting a 5 on a die roll, the probability distributions found in statistical physics, and the probabilities that underlie many prima facie judgments about fitness in evolutionary biology.
Michael Strevens makes three claims about the rules. First, they are reliable. Second, they are known, though not fully consciously, to all human beings: they constitute a key part of the physical intuition that allows us to navigate around the world safely in the absence of formal scientific knowledge. Third, they have played a crucial but unrecognized role in several major scientific innovations.
A large part of Tychomancy is devoted to this historical role for probability inference rules. Strevens first analyzes James Clerk Maxwell’s extraordinary, apparently a priori, deduction of the molecular velocity distribution in gases, which launched statistical physics. Maxwell did not derive his distribution from logic alone, Strevens proposes, but rather from probabilistic knowledge common to all human beings, even infants as young as six months old. Strevens then turns to Darwin’s theory of natural selection, the statistics of measurement, and the creation of models of complex systems, contending in each case that these elements of science could not have emerged when or how they did without the ability to “eyeball” the values of physical probabilities.
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probability, the kind of probability that scientific theories ascribe to events or processes in the world, independently of our epistemic state. Physical probabilities predict and explain frequencies and other statistical patterns. They are usually understood to include the probabilities attached to gambling setups such as tossed dice and roulette wheels, the probabilities found in stochastic population genetics—and the probabilities of statistical physics. On the other hand is epistemic
coin at the moment that it lands. Consider the lower half of the strip, corresponding to landings in which heads is facing upward (or at least, closer to facing upward than tails). If there were no bouncing phase—if the coin had been snatched out of the air at this point rather than allowed to bounce—then the result of the toss would have been heads. But the coin bounces. For some landing orientations the bounce will reverse the outcome, producing tails, while for others it will preserve the
contours of diatomic gas molecules such as oxygen and nitrogen, or more complex molecules such as carbon dioxide, methane, or ammonia (figure 7.1). The key questions here are, first, whether the microdynamic rule applies to collisions between objects with these geometries, and second, whether the uniformity rule applies to their position and direction of travel. The answers in both cases are affirmative. The microdynamic rule applies because the collisions will be sensitive to the pre-collision
points along the way, but it may be worth pausing to face this niggling question squarely, gathering together in one place some of the more important excuses for the aggregate level of intricacy so far attained. To that end, consider several ways in which the equilibrium rule package complicates itself. First, the package provides rules for inferring both short-term and long-term probability distributions over the parameters of the system to which it is applied: a microequiprobabilistic
initial conditions at least roughly track the ratio of probabilistically weighted initial conditions? Two conditions sufficient for rough tracking are 1. The initial conditions—such as the distance of predator and prey when the predator is first detected, the angle of one to the other, the ambient light, and so on—are smoothly (that is, microequiprobabilistically) distributed.12 2. The outcomes are sensitively dependent on initial conditions, so that the advantageous and disadvantageous sets of
