What do I mean by the term "model?" I mean an abstract
picture which explains an observation that was made. This might be a physical
(scale) model, a computer simulation, a set of equations, or anything else
which allows us to use it effectively. In this sense, a road map is a
model of the key features of a geographic area. Like all models, a road
map leaves out much, but we hope that it is adequate to permit us to find
our way. To be accepted, a model must "save the data," and predict new
data. If it can do so quantitatively, so much the better. Usually, simpler
models are preferred, although simplicity is not easily defined. Newton's
idea of "force" is a model used to explain acceleration.
One of the things we look for in a model, beyond its capacity
to explain the data, is that it be testable. There should be a way to check
it out. If it fails to explain the data provided by the test, it must be
modified or discarded or the data must be replaced by "better" data.
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