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Does the solar system compute the laws of motion?

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The counterfactual account of physical computation is simple and, for the most part, very attractive. However, it is usually thought to trivialize the notion of physical computation insofar as it implies ‘limited pancomputationalism’, this being the doctrine that every deterministic physical system computes some function. Should we bite the bullet and accept limited pancomputationalism, or reject the counterfactual account as untenable? Jack Copeland would have us do neither of the above. He attempts to thread a path between the two horns of the dilemma by buttressing the counterfactual account with extra conditions intended to block certain classes of deterministic physical systems from qualifying as physical computers. His theory is called the ‘algorithm execution account’. Here we show that the algorithm execution account entails limited pancomputationalism, despite Copeland’s argument to the contrary. We suggest, partly on this basis, that the counterfactual account should be accepted as it stands, pancomputationalist warts and all.

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  1. The CTM is a broad church which leaves room for different views as regards which particular types of mental states—intentional, or phenomenal, or both—are computational. These divisions within the CTM will not concern us here.

  2. Limited pancomputationalism is to be contrasted with unlimited pancomputationalism, which says that every physical system computes every function (perhaps modulo certain complexity constraints) (Piccinini 2017). Arguments due to Putnam (1988) and Searle (1990) show that the so-called ‘simple mapping account’ (Godfrey-Smith 2009) of physical computation implies unlimited pancomputationalism. The counterfactual account greatly improves on the simple mapping account in being invulnerable to Putnam’s and Searle’s arguments—see Chalmers (1996a), Fresco (2014, pp. 86–94) and Piccinini (2015, pp. 16–22). Putnam’s and Searle’s arguments for unlimited pancomputationalism will not concern us here.

  3. The solar system is too big for us puny human beings to manipulate its parameters. Hence the necessity of bringing ‘God’s hand’ into the discussion in order to access the relevant counterfactuals. But, by the same token, a laptop computer would have the counterfactual dispositions it has even if it was on a planet whose only intelligent inhabitants were tiny ants too small and weak to press its keys.

  4. This trivialization result doesn’t extend to indeterministic physical systems for the simple reason that the inputs to such systems underdetermine their outputs.

  5. Piccinini is alive to these difficulties and has developed a theory of teleological functions to address them (Piccinini 2015, pp. 100–117). We are dubious of his theory’s adequacy, but explaining why is a task for another occasion.

  6. Here we use the terminology of Copeland (2017).

  7. See Wolfram (2002) for a compendious discussion of ECAs.

  8. It is called the ‘110 rule’ because the binary sequence ‘01101110’ represents the number one-hundred-and-ten, or, in decimal, 110.

  9. These six rules merely tell the MECA what to do if it is in State 1. They are silent as to what the MECA will do if it is any other state. A complete set of state-transition rules, capable of fully determining the MECA’s behaviour, would therefore need to include numerous other rules in addition to these six.

  10. The solar system will doubtlessly have other computational architectures and algorithms too, there surely existing an endless variety of other abstract isomorphs of the solar system, in addition to SSS. But it suffices for our purpose of refuting Copeland to describe just one abstract computing device that the solar system physically implements.


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Correspondence to Douglas Ian Campbell.

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Campbell, D.I., Yang, Y. Does the solar system compute the laws of motion?. Synthese 198, 3203–3220 (2021).

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