What does the Church-Turing thesis actually mean?

ANNOUNCEMENT: [Venue change] SQ Collective has generously offered to host the venue for this session for free. It is only appropriate that we allocate some capacity to them (via a Luma event). This is a chance for folks in the AI builder community to participate in our group’s philosophy practice, and for us to broaden our audience within that community. If you have already signed up via Meetup, there is no need to double-register through Luma, should the Luma event be made public.

“You insist that there is something that a machine can't do. If you will tell me precisely what it is that a machine cannot do, then I can always make a machine which will do just that.”
—John von Neumann, in a talk at the Institute for Advanced Study at Princeton, 1948

“Everything is computer!”
– Donald J. Trump, sometime in 2025

What is computation? These days, it seems more provocative to stipulate what isn’t computation. For instance, to suggest that the brain can be functionally anything other than a kind of computer is suspect in the current technological zeitgeist. It seems self-evident that any system of information processing to achieve some output can be explicated in terms of computation. At the foundation of this conviction is the Church-Turing thesis, which both gave a logical definition to and circumscribed the bounds of computation in the form of the Universal Turing Machine, “a most general formulation of machine” (Alan Newell 1980). The idea that the Universal Turing Machine is an abstract design template that can encompass any kind of information-processing system has led some to extend the scope of the thesis to physics itself: “any finite physical system can be simulated by Universal Turing Machines” (David Deutsch 1985).

What do we make of such ideas? Instead of fumbling in the accreted fog of the present, a quiet philosophical dialectic was already underway at the time Alan Turing demonstrated Universal Turing Machines in his seminal paper *On Computable Nu