There exists a growing literature on the so-called physical Church-Turing
thesis in a relativistic spacetime setting. The physical Church-Turing thesis
is the conjecture that no computing device that is physically realizable (even
in principle) can exceed the computational barriers of a Turing machine. By
suggesting a concrete implementation of a beyond-Turing computer in a spacetime
setting, Istv\'an N\'emeti and Gyula D\'avid (2006) have shown how an
appreciation of the physical Church-Turing thesis necessitates the confluence
of mathematical, computational, physical, and indeed cosmological ideas. In
this essay, I will honour Istv\'an's seventieth birthday, as well as his
longstanding interest in, and his seminal contributions to, this field going
back to as early as 1987 by modestly proposing how the concrete implementation
in N\'emeti and D\'avid (2006) might be complemented by a
quantum-information-theoretic communication protocol between the computing
device and the logician who sets the beyond-Turing computer a task such as
determining the consistency of Zermelo-Fraenkel set theory. This suggests that
even the foundations of quantum theory and, ultimately, quantum gravity may
play an important role in determining the validity of the physical
Church-Turing thesis.Comment: 27 pages, 5 figures. Forthcoming in Synthese. Matches published
versio
