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The Physical Church–Turing Thesis: Modest or Bold?
The British Journal for the Philosophy of Science (2011)
  • Gualtiero Piccinini, University of Missouri-St. Louis
This article defends a modest version of the Physical Church-Turing thesis (CT). Following an established recent trend, I distinguish between what I call Mathematical CT—the thesis supported by the original arguments for CT— and Physical CT. I then distinguish between bold formulations of Physical CT, according to which any physical process—anything doable by a physical system—is computable by a Turing machine, and modest formulations, according to which any function that is computable by a physical system is computable by a Turing machine. I argue that Bold Physical CT is not relevant to the epistemological concerns that motivate CT and hence not suitable as a physical analog of Mathematical CT. The correct physical analog of Mathematical CT is Modest Physical CT. I propose to explicate the notion of physical computability in terms of a usability constraint, according to which for a process to count as relevant to Physical CT, it must be usable by a finite observer to obtain the desired values of a function. Finally, I suggest that proposed counterexamples to Physical CT are still far from falsifying it because they have not been shown to satisfy the usability constraint.
  • Computationalism,
  • Physical Church-Turing Thesis
Publication Date
December, 2011
Citation Information
Gualtiero Piccinini; The Physical Church–Turing Thesis: Modest or Bold?, The British Journal for the Philosophy of Science, Volume 62, Issue 4, 1 December 2011, Pages 733–769,