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I see 'what is computation?' and 'what is information?' are not listed there. I'm curious what HN thinks of these questions. Do you think they should be on th

I see 'what is computation?' and 'what is information?' are not listed there. I'm curious what HN thinks of these questions. Do you think they should be on there or not, and why? I think they should. What makes something computation? What is it about a physical process that means it is performing computation? We do not have good answers to this question. (Turing Machines are a model of a computational device, not an account of what computation is). We often characterise computation as information processing, but precisely what does this mean? What is information? There is such a lack of clarity surrounding this notion which seems so fundamental to CS. People often think that Information Theory provides an answer, but it doesn't really enlighten us about what information is and what its nature is. I think part of the thing here is that theoretical computer science gets equated with maths, whereas these are not mathematical problems (or at least I do not think they are).

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!]
kd0amg 15y ago
What is it about a physical process that means it is performing computation? It transforms input to output -- some computation systems are just less powerful than others :-P People often think that Information Theory provides an answer, but it doesn't really enlighten us about what information is and what its nature is. Can you point to any particular problems with the notion of information as that which reduces entropy (which is itself a quantification of what is unknown about some system)?
- jamesrcole 15y ago
  Information Theory provides a measure of a quantity, not an account of what that "stuff" is. I do not think that 'that which reduces entropy' is an account of information. How is a system informed by an input that 'carries information'? What details is the system able to 'learn about' from that input/information? What's happening there is just a physical interaction of the 'inputs' interacting with the system. How is that information related to the meaning of the information - how does that work? If the brain is just computation, how does the "semantic information" in the brain work?
  - kd0amg 15y ago
    How is a system informed by an input that 'carries information'? It processes the input to determine what actions to take next. What details is the system able to 'learn about' from that input/information? Some facility for conditional execution (not just something like an "if...then...else" control structure -- the ability to compute non-constant functions). What's happening there is just a physical interaction of the 'inputs' interacting with the system. So? How is that information related to the meaning of the information - how does that work? If the brain is just computation, how does the "semantic information" in the brain work? What is "meaning of the information"? What is "semantic information"?
    - jamesrcole 15y ago
      How is a system informed by an input that 'carries information'? -> It processes the input to determine what actions to take next. So what qualifies as an input? What qualifies as an action? How do you tell if some physical system, e.g. some biological system, contains 'inputs' and 'actions'? What's happening there is just a physical interaction of the 'inputs' interacting with the system. So? See my last point. How is that information related to the meaning of the information - how does that work? If the brain is just computation, how does the "semantic information" in the brain work? -> What is "meaning of the information"? What is "semantic information"? Information informs about certain details, a system can take the information and understand its meaning. 'semantic information' - sometimes people use this notion to distinguish between 'data' and 'information' that is more meaningful, like the sort of information that humans can process.
bermanoid 15y ago
People often think that Information Theory provides an answer, but it doesn't really enlighten us about what information is and what its nature is. Information theory provides a definition. That definition turns out to be an extremely useful abstraction in a lot of mathematical theorems, and to some extent matches the intuitions we have about information. If there's a problem with the definition, and it doesn't match up with your idea of what information really is, then it's easy to come up with new definitions; if they're useful, they might even take off. But it's very hard for a field to answer questions like "what is X, and what is its nature?", because it's not clear what kind of answer would suffice, for any value of X.
- jamesrcole 15y ago
  It provides a measure of quantity, not a definition of what it is. I don't think this is a matter of definition. Here's an analogy. Back before we had an understanding of matter in terms of atomic details (or anything deeper than that), people could have disputed about what is a liquid and what is a solid and what is a gas. Different people might have given different definitions of these in terms of qualities that differentiated them from each other ("solids maintain their shape", "a gas does not weigh much" etc). But we now know that this question was not a matter of definition but a matter of understanding what was actually going on underneath the phenomenal appearances. Understanding what a liquid is not a matter of definition, it's a matter of understanding how the phenomena actually works. And in this case we have even been able to show the categories we thought existed weren't even literally different categories. Returning to the question of what information is, the idea that it's just something to be defined in one of a number of ways is an assumption.
  - jaekwon 15y ago
    I could ask you what matter is, what an atom is, or what space / time are, and I wouldn't be satisfied with your definition of matter -- no matter what. I just assume that our universe is running in a Turing machine, and that all laws are derived mathematically. I bet we could find simple emergent computational phenomena that model the laws of relativity. It's simpler than trying to work backwards like you, and it lets me sleep at night. It's programs and programmers all the way down. Or up, if you're Kardashevly inclined. The neat thing about information is that it can probably pass through boundaries of cosmological scale. The neat thing about intelligence is that it emerges, and that it wants to pass through boundaries of cosmological scale. I feel that general / special relativity has something to say about this -- that these laws permit some sort of communication across scales, and that the universe is but a bunch of astronomers and molecular physicists nerding it out. The photons that are helping you read this text is actually composed of subatomic Voyager Golden Phonograph Records with Carl Sagan's signature on each one. Billions and billions of them, into a sea of intergalactic neurons causing a glorious dawn of awakening in your head. - copyright 2012 Jae Kwon

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!]

kd0amg 15y ago

What is it about a physical process that means it is performing computation? It transforms input to output -- some computation systems are just less powerful than others :-P People often think that Information Theory provides an answer, but it doesn't really enlighten us about what information is and what its nature is. Can you point to any particular problems with the notion of information as that which reduces entropy (which is itself a quantification of what is unknown about some system)?

jamesrcole 15y ago
Information Theory provides a measure of a quantity, not an account of what that "stuff" is. I do not think that 'that which reduces entropy' is an account of information. How is a system informed by an input that 'carries information'? What details is the system able to 'learn about' from that input/information? What's happening there is just a physical interaction of the 'inputs' interacting with the system. How is that information related to the meaning of the information - how does that work? If the brain is just computation, how does the "semantic information" in the brain work?
- kd0amg 15y ago
  How is a system informed by an input that 'carries information'? It processes the input to determine what actions to take next. What details is the system able to 'learn about' from that input/information? Some facility for conditional execution (not just something like an "if...then...else" control structure -- the ability to compute non-constant functions). What's happening there is just a physical interaction of the 'inputs' interacting with the system. So? How is that information related to the meaning of the information - how does that work? If the brain is just computation, how does the "semantic information" in the brain work? What is "meaning of the information"? What is "semantic information"?
  - jamesrcole 15y ago
    How is a system informed by an input that 'carries information'? -> It processes the input to determine what actions to take next. So what qualifies as an input? What qualifies as an action? How do you tell if some physical system, e.g. some biological system, contains 'inputs' and 'actions'? What's happening there is just a physical interaction of the 'inputs' interacting with the system. So? See my last point. How is that information related to the meaning of the information - how does that work? If the brain is just computation, how does the "semantic information" in the brain work? -> What is "meaning of the information"? What is "semantic information"? Information informs about certain details, a system can take the information and understand its meaning. 'semantic information' - sometimes people use this notion to distinguish between 'data' and 'information' that is more meaningful, like the sort of information that humans can process.

bermanoid 15y ago

People often think that Information Theory provides an answer, but it doesn't really enlighten us about what information is and what its nature is. Information theory provides a definition. That definition turns out to be an extremely useful abstraction in a lot of mathematical theorems, and to some extent matches the intuitions we have about information. If there's a problem with the definition, and it doesn't match up with your idea of what information really is, then it's easy to come up with new definitions; if they're useful, they might even take off. But it's very hard for a field to answer questions like "what is X, and what is its nature?", because it's not clear what kind of answer would suffice, for any value of X.

jamesrcole 15y ago
It provides a measure of quantity, not a definition of what it is. I don't think this is a matter of definition. Here's an analogy. Back before we had an understanding of matter in terms of atomic details (or anything deeper than that), people could have disputed about what is a liquid and what is a solid and what is a gas. Different people might have given different definitions of these in terms of qualities that differentiated them from each other ("solids maintain their shape", "a gas does not weigh much" etc). But we now know that this question was not a matter of definition but a matter of understanding what was actually going on underneath the phenomenal appearances. Understanding what a liquid is not a matter of definition, it's a matter of understanding how the phenomena actually works. And in this case we have even been able to show the categories we thought existed weren't even literally different categories. Returning to the question of what information is, the idea that it's just something to be defined in one of a number of ways is an assumption.
- jaekwon 15y ago
  I could ask you what matter is, what an atom is, or what space / time are, and I wouldn't be satisfied with your definition of matter -- no matter what. I just assume that our universe is running in a Turing machine, and that all laws are derived mathematically. I bet we could find simple emergent computational phenomena that model the laws of relativity. It's simpler than trying to work backwards like you, and it lets me sleep at night. It's programs and programmers all the way down. Or up, if you're Kardashevly inclined. The neat thing about information is that it can probably pass through boundaries of cosmological scale. The neat thing about intelligence is that it emerges, and that it wants to pass through boundaries of cosmological scale. I feel that general / special relativity has something to say about this -- that these laws permit some sort of communication across scales, and that the universe is but a bunch of astronomers and molecular physicists nerding it out. The photons that are helping you read this text is actually composed of subatomic Voyager Golden Phonograph Records with Carl Sagan's signature on each one. Billions and billions of them, into a sea of intergalactic neurons causing a glorious dawn of awakening in your head. - copyright 2012 Jae Kwon