It seems that the Church-Turing thesis, that states that an universal turing machine can compute everything that is intuitively computable, has near universal acceptance among computer scientists.
I really wonder why this is so, given that there are simple cases where we can compute something that an abitrary turing machine can not compute using a notion of computation that is not extraordinary at all (and quite relevant in reality). For example, given you have a universal turing machine A that uses the alphabet {1,0} and a universal turing machine B that uses the alphabet {-1,0,1}. Now it is quite clear that the machine A cannot directly answer any questions that relates to -1. For example it cannot directly compute -1*-1=1. Machine A can only be used to use an encoded input value and encoded description of machine B, and give an output that is correct given the right decoding scheme. But for me this already makes clear that machine A is less computationally powerful than machine B. Its input and output when emulating B do only make sense with respect to what the machine B does if we already know what machine B does, and if it is known how we chose to reflect this in the input of machine A (and the interpretation of its output). Otherwise we have no way of even saying whether it emulates something, or whether it is just doing a particular computation on the alphabet {1,0}. I realize that it all comes down to the notion of computation. But why do most choose to use such a weak notion of computation? How does machine B not compute something that A doesn't by any reasonable standard? Saying that A can compute what B computes is like saying that "orange" can express the same as the word "apple", because we can encode the word "apple" as "orange". It is true in a very limited sense, but it seems mad to treat it as the foundation of what it means for words to express something (and the same goes for computation). If we use such trivial notions of computation, why not say that the program "return input" emulates all turing-machines because given the right input it gives the right output (we just give it the solution as input). I get that we can simply use the Church-turing as the definition of computation means. But why is it (mostly) treated as being the one and only correct notion of computation (especially in a computer science context)? The only explanation I have is that it is dogma. To question it would change to much and would be too "complicated" and uncomfortable. It would make computation an irreducibly complex and relative notion or - heaven forbid - even an inherently subjective notion (computation from which perspective?). -- View this message in context: http://old.nabble.com/Why-the-Church-Turing-thesis--tp34348236p34348236.html Sent from the Everything List mailing list archive at Nabble.com. -- You received this message because you are subscribed to the Google Groups "Everything List" group. To post to this group, send email to everything-list@googlegroups.com. To unsubscribe from this group, send email to everything-list+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/everything-list?hl=en.