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I don't think you can answer these questions with theorems or experiments about models of computation (which is how TCS answers questions), so I don't think the

by alextp 15y ago

I don't think you can answer these questions with theorems or experiments about models of computation (which is how TCS answers questions), so I don't think they are TCS questions. They are, however, central questions in the philosophy of computing.

jamesrcole 15y ago
I'm know most people think this, but to me it seems narrow to construe TCS that way. There may be theoretical questions you can only answer once you understand clearly what computation is, especially by having a more physical notion of it. Those questions may be considered philosophical now, while they are not understood, but what happens once they become understood (presuming that happens)? Say we had a precise understanding of what computation was - wouldn't that become a central theoretical part of computer science?
- arethuza 15y ago
  I'm not sure there is much utility in trying to define "computation" as an intrinsic property of anything in the real world, rather it is a useful property that we can ascribe to particular systems if that proves to be useful. For example, I once worked for a distinguished engineering professor who told me about he started his career building simulation models of fluid flow using hydraulic analogue computers. Note that they constructed mathematical models of the fluid flow and then solved these using hydraulics - it wasn't an attempt to simply copy the "real" systems being modelled into an idealised experiment. In this case the fluid in the simulation was arguably "computing" in the sense you mean - but there was nothing that looked like a digital computer or a program or even an algorithm.
  - jamesrcole 15y ago
    In my opinion it's not a matter of definition, it's a matter of understanding a real type of phenomenon. In this case the fluid in the simulation was arguably "computing" in the sense you mean - but there was nothing that looked like a digital computer or a program or even an algorithm. I would suggest that you need a solid understanding of what computation is in order to properly answer the question of whether that case really is the same, in a fundamental sense, as more familiar computation, despite these (perhaps) superficial differences.
    - arethuza 15y ago
      Not really - all that anyone is bothered about is whether the predicted results are as useful from the digital computer with it's program than from a bunch of pipes, tanks and pumps. I can see at a philosophical level the question is of interest - but arguably at a practical or theoretical level the question is either irrelevant or can't really be stated.
      - jamesrcole 15y ago
        What about if a clearer understanding of what made something computation suggested new ways of implementing computation? Ways that were more efficient or had other useful properties? What it a better understanding of what computation is helped you analyse what was going on in biological information processing? The thing is, we can't predict what benefit might come from some new theoretical understanding. Take Quantum Mechanics for an example. All sorts of practical things have come from it, but there was no way to predict what these would be before fact.
        arethuza 15y ago
        Quantum Mechanics is a theory that makes testable predictions about the world. Asking about "what is computation?" is asking a question about our definition of an abstraction, not about anything concrete. So yes, it's an interesting philosphical question - but it's meta to the level that most people are actually interested in. [NB - I am not a physicist, so take any of my statements about what QM is or isn't with a pinch of salt!]
        jamesrcole 15y ago
        ...an answer to the question "what is computation" would be a theory that makes testable predictions about the world.
    - bermanoid 15y ago
      In my opinion it's not a matter of definition, it's a matter of understanding a real type of phenomenon. That's fine, and there very well may be some issues here that are worth investigating that don't just involve figuring out a definition. But your specific questions, "What makes something computation", and "What is it about a physical process that means it is performing computation?", both hinge on a blurry notion of "computation" that needs to be pinned down before they can even be taken on. Because if we take the first definition of the word from Google, "The action of mathematical calculation", then the answer is pretty trivial: a physical process is performing a computation if the states of the physical system reliably map to the result of a known mathematical operation, no more, no less. Now, we may quibble over what is a useful computation, whether a computation is happening if we don't observe it, etc., and that's the kind of tightening of focus that's necessary to get any answers in these situations. Those tightenings are not implicit in the word "computation". This is a typical philosophical problem - questions like "what is consciousness?" and "what about a physical process makes it conscious?" may be answered in a straightforward manner by going to the dictionary (google (Define consciousness) -> "The state of being awake and aware of one's surroundings"), but answers along those lines reliably fail to satisfy philosophers because they don't actually mean "The state of being awake and aware of one's surroundings" when they use the word "consciousness", they're using some personal tightening of the term that carries a lot of unspecified baggage (or perhaps they'll hide this baggage in "awake" or "aware", which just shifts the issue). Arguments then ensue about the right definition of the word, the one that matches the "know it when I see it" feeling that each person involved has about it, and little progress is made because nothing is pinned down concretely enough to actually discuss.

by alextp 15y ago

jamesrcole 15y ago

I'm know most people think this, but to me it seems narrow to construe TCS that way. There may be theoretical questions you can only answer once you understand clearly what computation is, especially by having a more physical notion of it. Those questions may be considered philosophical now, while they are not understood, but what happens once they become understood (presuming that happens)? Say we had a precise understanding of what computation was - wouldn't that become a central theoretical part of computer science?

arethuza 15y ago
I'm not sure there is much utility in trying to define "computation" as an intrinsic property of anything in the real world, rather it is a useful property that we can ascribe to particular systems if that proves to be useful. For example, I once worked for a distinguished engineering professor who told me about he started his career building simulation models of fluid flow using hydraulic analogue computers. Note that they constructed mathematical models of the fluid flow and then solved these using hydraulics - it wasn't an attempt to simply copy the "real" systems being modelled into an idealised experiment. In this case the fluid in the simulation was arguably "computing" in the sense you mean - but there was nothing that looked like a digital computer or a program or even an algorithm.
- jamesrcole 15y ago
  In my opinion it's not a matter of definition, it's a matter of understanding a real type of phenomenon. In this case the fluid in the simulation was arguably "computing" in the sense you mean - but there was nothing that looked like a digital computer or a program or even an algorithm. I would suggest that you need a solid understanding of what computation is in order to properly answer the question of whether that case really is the same, in a fundamental sense, as more familiar computation, despite these (perhaps) superficial differences.
  - arethuza 15y ago
    Not really - all that anyone is bothered about is whether the predicted results are as useful from the digital computer with it's program than from a bunch of pipes, tanks and pumps. I can see at a philosophical level the question is of interest - but arguably at a practical or theoretical level the question is either irrelevant or can't really be stated.
    - jamesrcole 15y ago
      What about if a clearer understanding of what made something computation suggested new ways of implementing computation? Ways that were more efficient or had other useful properties? What it a better understanding of what computation is helped you analyse what was going on in biological information processing? The thing is, we can't predict what benefit might come from some new theoretical understanding. Take Quantum Mechanics for an example. All sorts of practical things have come from it, but there was no way to predict what these would be before fact.
      - arethuza 15y ago
        Quantum Mechanics is a theory that makes testable predictions about the world. Asking about "what is computation?" is asking a question about our definition of an abstraction, not about anything concrete. So yes, it's an interesting philosphical question - but it's meta to the level that most people are actually interested in. [NB - I am not a physicist, so take any of my statements about what QM is or isn't with a pinch of salt!]
        jamesrcole 15y ago
        ...an answer to the question "what is computation" would be a theory that makes testable predictions about the world.
  - bermanoid 15y ago
    In my opinion it's not a matter of definition, it's a matter of understanding a real type of phenomenon. That's fine, and there very well may be some issues here that are worth investigating that don't just involve figuring out a definition. But your specific questions, "What makes something computation", and "What is it about a physical process that means it is performing computation?", both hinge on a blurry notion of "computation" that needs to be pinned down before they can even be taken on. Because if we take the first definition of the word from Google, "The action of mathematical calculation", then the answer is pretty trivial: a physical process is performing a computation if the states of the physical system reliably map to the result of a known mathematical operation, no more, no less. Now, we may quibble over what is a useful computation, whether a computation is happening if we don't observe it, etc., and that's the kind of tightening of focus that's necessary to get any answers in these situations. Those tightenings are not implicit in the word "computation". This is a typical philosophical problem - questions like "what is consciousness?" and "what about a physical process makes it conscious?" may be answered in a straightforward manner by going to the dictionary (google (Define consciousness) -> "The state of being awake and aware of one's surroundings"), but answers along those lines reliably fail to satisfy philosophers because they don't actually mean "The state of being awake and aware of one's surroundings" when they use the word "consciousness", they're using some personal tightening of the term that carries a lot of unspecified baggage (or perhaps they'll hide this baggage in "awake" or "aware", which just shifts the issue). Arguments then ensue about the right definition of the word, the one that matches the "know it when I see it" feeling that each person involved has about it, and little progress is made because nothing is pinned down concretely enough to actually discuss.