# Forever Is a Day: Supertasks in Pitowsky and Malament-Hogarth Spacetimes

@article{Earman1993ForeverIA, title={Forever Is a Day: Supertasks in Pitowsky and Malament-Hogarth Spacetimes}, author={John Earman and John D. Norton}, journal={Philosophy of Science}, year={1993}, volume={60}, pages={22 - 42} }

The standard theory of computation excludes computations whose completion requires an infinite number of steps. Malament-Hogarth spacetimes admit observers whose pasts contain entire future-directed, timelike half-curves of infinite proper length. We investigate the physical properties of these spacetimes and ask whether they and other spacetimes allow the observer to know the outcome of a computation with infinitely many steps.

## 130 Citations

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A physical device in relativistic spacetime which can compute a non-Turing computable task, e.g. which can decide the halting problem of Turing machines or whether ZF set theory is consistent or not is described.

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