On 05-Sep-01, Russell Standish wrote: > Brent Meeker wrote: >> >> Hello Marchal >> >> On 05-Sep-01, Marchal wrote: >> >> Even if we are "more than" a universal computing machine, it is easy >> to explain there is a sense in which we are *at least* universal >> computing machines (even the kind which can know that(°)), and that >> is enough for making the world possibly very complex. >> >> We are certainly *less* than universal turing machines - since a >> universal turing machine requires infinite storage to work with. >> >> Brent Meeker > > The storage issue is completely bogus. UTMs require unbounded storage, > but only a finite amount of storage at any finite time in their > computation. A human being working with a pile of pebbles will die > before exhausting the world of its pebbles. Hence, homo sapiens, with > its extra-somatic storage devices can implement any possible Turing > machine, limited only by lifespan.
Yet that is a limit. Similarly the number of pebbles, or iron oxide magnetic domains, is also finite. You are of course correct that these limits are unlikely to restrict any computation a human might actually undertake - but on this list assertions are often drawn, such as the world is our computation, which really need storage greater than the number of particles in the universe, to say nothing of pebbles and neurons. Even if they don't need unbounded storage, the conclusion that we are UTM's sufficient for making (computing) a very complex world in not warranted. Brent Meeker 2 + 2 = 5 (for extremely large values of 2) --- Marcin Orlowsky