•  150
    Hypercomputation and the Physical Church‐Turing Thesis
    British Journal for the Philosophy of Science 54 (2): 181-223. 2003.
    A version of the Church-Turing Thesis states that every effectively realizable physical system can be simulated by Turing Machines (‘Thesis P’). In this formulation the Thesis appears to be an empirical hypothesis, subject to physical falsification. We review the main approaches to computation beyond Turing definability (‘hypercomputation’): supertask, non-well-founded, analog, quantum, and retrocausal computation. The conclusions are that these models reduce to supertasks, i.e. infinite computa…Read more
  •  115
    A brief critique of pure hypercomputation
    Minds and Machines 19 (3): 391-405. 2009.
    Hypercomputation—the hypothesis that Turing-incomputable objects can be computed through infinitary means—is ineffective, as the unsolvability of the halting problem for Turing machines depends just on the absence of a definite value for some paradoxical construction; nature and quantity of computing resources are immaterial. The assumption that the halting problem is solved by oracles of higher Turing degree amounts just to postulation; infinite-time oracles are not actually solving paradoxes, …Read more
  •  21
    Buttresses of the Turing Barrier
    Acta Analytica 30 (3): 275-282. 2015.
    The ‘Turing barrier’ is an evocative image for 0′, the degree of the unsolvability of the halting problem for Turing machines—equivalently, of the undecidability of Peano Arithmetic. The ‘barrier’ metaphor conveys the idea that effective computability is impaired by restrictions that could be removed by infinite methods. Assuming that the undecidability of PA is essentially depending on the finite nature of its computational means, decidability would be restored by the ω-rule. Hypercomputation, …Read more
  • On the Interpretation of Church's Thesis
    Epistemologia 15 (2): 315-350. 1992.
    Church's Thesis states the equivalence of computable functions and recursive functions. This can be interpreted as a definition, as an explanation, as an axiom, and as a proposition of mechanistic philosophy. A number of arguments and objections, including a pair of counterexamples based on Gödel's Incompleteness Theorem, allow to conclude that Church's Thesis can be reasonably taken both as a definition and as an axiom, somewhat less convincingly as an explanation, but hardly as a mechanis…Read more