Reverse Turing test to a human) a response along the lines of "is this really a human?". Describing such a situation as a "reverse Turing test" typically occurs retroactively. There are also cases of accidental reverse Turing tests, occurring when a programmer is in a sufficiently non-human mood that his conversation unintentionally resembles that of a computer. In these cases the description is invariably retroactive and humorously intended. The subject may be described as having passed or failed a reverse Turing test or as having failed a Turing test. The latter description is arguably more accurate in these cases; see also the next
Church–Turing thesis three formally-defined classes of computable functions coincide with the "informal" notion of an effectively calculable function. Since, as an informal notion, the concept of effective calculability does not have a formal definition, the thesis, although it has near-universal acceptance, cannot be formally proven. Since its inception, variations on the original thesis have arisen, including statements about what can physically be realized by a computer in our universe (physical Church-Turing thesis) and what can be efficiently computed (Church–Turing thesis (complexity theory)). These variations are not due to Church or Turing, but arise from later work in complexity theory and digital physics.