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when you have good reason to believe something about model-entities, you don't thereby have good reason to believe it about actual-entities, unless you also hav
by lg 16y ago
when you have good reason to believe something about model-entities, you don't thereby have good reason to believe it about actual-entities, unless you also have good reason to believe that model-entities are relevantly similar to actual-entities. So the model itself is just a piece of a theory.
- jshen 16y agoisn't a model a functional representation of a theory? I don't see how it is only a piece of a theory if the whole theory is represented in the model and is functional.
- lg 16y agoCan you represent the whole theory in the model? The model would need to represent evidence that its representations of the world are accurate. If that evidence is a mathematical proof, a program could probably encode it. But if it's experimental evidence, I don't know how it could.
- barrkel 16y agoThat seems backwards to me. Theories don't "represent" evidence, experimental or otherwise (I'm not even sure what that's supposed to mean, it doesn't make sense to me). You formulate your theory - which is a model of cause and effect - from one set of observations, and test it with another set of observations. The model - the theory - may include facts from experimental evidence, eg G the gravitational constant, but that doesn't seem problematic for theory representation in program form. Theories make predictions about the world. I'd argue they're useless without this. As such, they are function of a prior state, returning the new state. Certainly you can't validate your theory without doing physical experiments, or at least having lots of data that the theory was not based on, to check it. But validation of a theory is distinct from its representation.
- whimsy 16y ago"Theories should pay rent in anticipated experimental data."
- lg 16y agosay i have a theory that says, changes in temperature depend on changes in pressure in some specified way. And you say, oh I have a similar theory, it's a computational model. In my model of the universe, when my model of temperature changes, then so does my model of pressure, and it changes in exactly the same way your theory describes. I'd say ok, that's a great theory about your model of pressure and your model of temperature in your model of the universe. And you say, no no, this is a theory about actual pressure and temperature in the actual universe, just like your theory. In that case your model is not enough. I also need reason to believe that your models of temperature and pressure are relevantly similar to actual temperature and pressure such that relational properties that hold of the entities of your model also hold of the entities they're supposed to represent. If it turns out you modeled temperature as a jpeg representing a picture of a cat, then how is that a theory about the temperature? Whereas my theory is a theory about temperature simply because my theory says: temperature, that real thing in the world, will do such-and-such.
- barrkel 16y agoBoth the theory and the model depend on the definitions of their constituents. If you don't have a theory of temperature or pressure, your theory is similarly useless, because you will have no way to interpret the words "temperature" and "pressure". Your theory assumes these things, but you want to say that the model is invalid because it also assumes these things. But the more important misconception you appear to have is that you are not considering the human element; no representation of the theory has meaning unless a human interprets it. Programs manipulate symbols; but it is the human who chooses what the symbols mean, and that includes incorporating theories / models implied or assumed about those meanings. It's no different for a theory written down in a book.
- barrkel 16y agoI don't think there is any difference between believing something about "model-entities" and believing something that a theory predicts will be the case. You haven't justified your implied assertion that predictions according to theories are not only different, but more trustworthy, than predictions according to models (theories in computational form).
- JoeAltmaier 16y agoUnless we believe that the universe is actually made of math, then Maxwell's Equations are also just a model.
- shasta 16y agoI think the argument being made isn't that "theories in computational form" are inferior, but rather something more pedantic - that there's no such thing as a "theory in computational form". Theories are about nature. A computer program that performs some simulation isn't itself a theory. The theory is "such and such natural phenomenon behaves like this here computer program."
- barrkel 16y agoWell, theories must be stored in some representation, whether it's a configuration of neuron state, ink markings in a book, verbal descriptions in sound, etc. My position is that programs are just another representation.
- shasta 16y agoProgramming languages generally don't have semantics that include claims about the physical world.
- barrkel 16y agoInk scratches on wood pulp don't have semantics either; it's the interpreter - i.e. the reader - that imbues them with semantics. Similarly, programs manipulate symbols. It's up to the person who runs the program to imbue those symbols with meaning. F=ma; that's some coloured pixels on your screen. It's also an expression of one of the laws of Newtonian mechanics. It can be used to calculate the approximate acceleration of a mass after a particular force has been applied to it. But the coloured pixels on your screen isn't doing that; you need to apply your mind. Similarly, here's a function: function calc_a(m, F) { return F / m; } That might be part of a program which calculates the acceleration due to a force. It's also just a series of bytes, which, when interpreted by a translator, will ultimately shuffle bits of electrical state around a very complex circuit. You still need to apply your mind to give it meaning.