On 01 Aug 2011, at 01:12, Craig Weinberg wrote:

What machine attributes are not Turing emulable? I thought Church says
that all real computations are Turing emulable.


But for Church the "real computations" are what can do a finite mind with a finite set of transparent instructions, in a finite time, but with as much memory and time he needs. It is the "intuitively computable functions". There is no reference at all with any idea of "real" in the sense of physically real, which is something never defined. David Deutsch has introduced a "physical" version of Church thesis, but this has no bearing at all with Church thesis. Actually I do think that Church thesis makes Deutsch thesis false, but I am not sure (yet I am sure that Church thesis + "yes doctor" leads to the existence of random oracle and local violation of Church thesis by some physical phenomena (akin to iterated self-multiplication).

Bruno


http://iridia.ulb.ac.be/~marchal/



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