On 05 Jun 2015, at 07:33, John Clark wrote:

Bruno Marchal <marc...@ulb.ac.be> wrote:

>> The physical device is far more complex than the algorithm, astronomically more complex, so you tell me which is a simplified approximation of which.

> The physical device is no more relevant to the algorithm than any other universal system. Yes, an algorithm is a simplified approximation of the way a real computer works, and in general good simplified approximations work with a large number of real world situations.

And so can be indeopendent of them, and belong to another realm, like logic and arithmetic. But, actually, you are wrong. Computations have been discovered by mathematicians (who were unaware of Babbage), and computer have been constructed after.



> You can implement the factorial in fortran, and you can implement fortran in lisp, and you can implement lisp Correct again, but whatever language you implement your algorithm in it must be implemented in matter that obeys the laws of physics because you can't make a calculation with software alone.


But the goal of making real-life computations is not our goal. Your remark remains non relevant. Eventually we will have to explain "real-life appearances" by an internal statistics on the computations existing in arithmetic.




> The level of complexity is not relevant here.

It's very relevant if you want to know what is a simplified approximation of what. And we both agree that a electronic computer is vastly more complex than it's logical schematic, so why can we make a working model of the complex thing but not make a working model of the simple thing when usually it's easier to make a simple thing than a complex thing? The only answer that comes to mind is that particular simplified approximation is just too simplified and just too approximate to actually do anything. That simplification must be missing something important, matter that obeys the laws of physics.

If you agree that the math notion of computation miss something (matter), then you agree that they are mathematical. Now, when a the Milky Way is emulated by arithmetic below our substitution level, explain me how the simulated humans can guess that matter is missing. Do you agree that the simulated "john Clark" will still complain that matter is missing in computation, despite we know that he refers to number relations, without knowing it?

Bruno




  John K Clark

  John K Clark




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