On 7/27/11, Chris Warburton <[email protected]> wrote: > > Physics is certainly useful in various computing contexts, especially > statistical physics. Useful concepts include: > > Statistical mechanics: Time-evolution of averaged quantities (such as > entropy) in a system with bounded energy. This is useful for random > models such as neural networks (eg. restricted Boltzmann machines). The > concept of entropy (information) is fundamental to computing, and the > concept of reversibility can often be useful. > > Mass-and-spring simulations: These can be useful to turn a topological > model into a geometric one (eg. finding a compact layout for a graph of > nodes and edges > http://en.wikipedia.org/wiki/Force-based_algorithms_(graph_drawing) ) > > Relativity/causality: Relativity builds coherent models of space and > time (spacetime) out of partial orders on discrete events, as long as > they obey causality (an event cannot precede its cause in any partial > ordering). This is useful for studying parallel programs (eg. > http://wiki.cs.pdx.edu/rp/ ). Relativity can also be seen as the > ultimate case of locality and modularity, since it says information > cannot travel faster than the speed of light. > > Spontaneous symmetry breaking: Almost all fundamental Physics is the > study of symmetry and spontaneous symmetry breaking. Spontaneous > symmetry breaking is also important for self-organisation and emergent > behaviour, for example in distributed systems (eg. emergent networks > http://groups.csail.mit.edu/mac/projects/amorphous/Network/ ) > > Space: (Mostly Maths I know, but space is an important concept in > Physics) Geometric analogies like distance are useful for various > algorithms (eg. Kademlia uses the XOR of 2 bit strings as the distance > between them in space http://en.wikipedia.org/wiki/Kademlia ) > > Phase changes: Phase changes are useful for describing the behaviour of > a variety of systems. As well as simple phase changes like > solid<->liquid<->gas, there can be some interesting phase changes found > in derived quantities too (glass is an example of this). > > Chaos theory: Chaos theory has been studied by Physicists, but in my > opinion the neglect of chaos theory is a major problem with Physics > today and is an area where Physicists could learn from Computer > Scientists. > > Chaotic systems are those which are arbitrarily sensitive to their > initial conditions; in other words, you may be able to describe the > rules a system will obey, but you can never know the starting conditions > precisely enough to predict how it will behave. Chaotic systems are > usually avoided in Physics, unless they're being studied because of > their chaotic properties, since they're hard to model. > > Off-topic: IMHO computers are the ultimate chaotic systems, as a > universal system (eg. a universal Turing machine) can behave like > anything else, depending on its initial conditions. Seemingly every area > of Physics can be proved to allow universal systems (eg. Newtonian > mechanics http://en.wikipedia.org/wiki/Billiard-ball_computer , > thermodynamics http://lambda-the-ultimate.org/node/4120 , quantum > mechanics http://en.wikipedia.org/wiki/Quantum_computer , etc.) yet > chaos is all too often hand-waved away by such things as the Ergodic > approximation, which the universality results above prove is flawed (the > Ergodic approximation implies a solution to the halting problem). > > Locality: Mentioned in passing for relativity, but locality is a very > useful property that holds for most Physics: stuff happens because of > stuff nearby. In computing this would be the equivalent of "globals > considered harmful". The particles and fields you mentioned are an > example of this. In the STEPS example of self-organising characters in a > text editor, the interactions are all local, which makes them very easy > to reason about. In a, dare I say theological, alternative, the > all-powerful text editor seeks to position each and every character > using its ineffable algorithms, and is thus impossible to reason about > because one cannot know the mind of the text editor. > > As far as something like a type system based on Physics goes, I think > that would be a bit messy. Physics is usually a very conservative > discipline; most of its results show what definitely isn't possible > (energy cannot come from nothing, entropy cannot decrease, there is a > maximum speed, etc.), however equivalent results in a computer system > would still give such a broad envelope that it would be of little > practical value. For example, if we take the analogy of the Physical law > "information cannot be transferred faster than the speed of light", what > this translates to is that you cannot access a result before you know > the computation of it has finished. Very true, but quite useless (since > it's an obvious statement). As another example, the increase of entropy > says that your data can get corrupted, but data cannot be found in > noise. Once again true, but useless for practical purposes.
Wonderful! (Like Christmas for the mind!) Thank you. > Another reason I would argue against something like types based on > Physics is that Physics tries to work out the inconceivable ways that > the Universe actually behaves by systematically throwing away all of our > intuitions that turn out to be wrong. With a computer system, we want > the opposite; we want a system that requires as little study as > possible, and for which our intuitions are accurate. I respectfully disagree. Jef Raskin pointed out that humans have no innate intuition regarding computer systems, only familiarity. The word "intuitive" in reference to computer languages and UIs is incorrect. We want a computer system that allows us to specify our guesses (intuitions) about the world concretely and communicate them and test them, but that does so without unduly getting in our way. I think that creating computer systems that support naive or unfounded "intuitions" (whether about how computers work or about the world outside the computer system) actually does a disservice. Warm regards, ~Simon -- I live on a Pony Farm: http://fertilefuture.blogspot.com/ My blog: http://firequery.blogspot.com/ "The history of mankind for the last four centuries is rather like that of an imprisoned sleeper, stirring clumsily and uneasily while the prison that restrains and shelters him catches fire, not waking but incorporating the crackling and warmth of the fire with ancient and incongruous dreams, than like that of a man consciously awake to danger and opportunity." --H. P. Wells, "A Short History of the World" _______________________________________________ fonc mailing list [email protected] http://vpri.org/mailman/listinfo/fonc
