from “Atoms in Motion”
Each piece, or part, of the whole of nature is always merely an
approximation to the complete truth, or the complete truth so far as
we know it. In fact, everything we know is only some kind of approximation,
because we know that we do not know all the laws as yet. Therefore,
things must be learned only to be unlearned again or, more likely, to be
corrected.
The principle of science, the definition almost, is the following: the
test of all knowledge is experiment. Experiment is the sole judge
of scientific “truth.” But what is the source of knowledge? Where do the laws
that are to be tested come from? Experiment, itself, helps to produce these
laws, in the sense that it gives us hints. But also needed is imagination
to create from these hints the great generalizations– to guess at the
wonderful, simple, but very strange patterns beneath them all, and then to
experiment to check again whether we have made the right guess. This imagining
process is so difficult that there is a division of labor in physics: there are
theoeretical physicists who imagine, deduce, and guess at new laws,
but do not experiment; and then there are experimental physicists
who experiment, imagine, deduce, and guess.
We said that the laws of nature are approximate: that we first find the “wrong”
ones, and then we find the “right” ones. Now, how can an experiment be “wrong”?
First, in a trivial way: if something is wrong with the apparatus that you did
not notice. But these things are easily fixed, and checked back and forth. So
without snatching at such minor things, how can the results of an
experiment be wrong? Only by being inaccurate. For example, the mass of an
object never seems to change: a spinning top has the same weight as a still
one. So a “law” was invented: mass is constant, independent of speed. That
“law” is now found to be incorrect. Mass is found to increase with velocity, but
appreciable increases require velocities near that of light. A true
law is: if an object moves with a speed of less than one hundred miles per second
the mass is constant to within one part in a million. In some such approximate
form this is a correct law. So in practice one might think that the new law makes
no significant difference. Well, yes and no. For ordinary speeds we can certainly
forget it and use the simple constant-mass law as a good approximation. But for
high speeds we are wrong, and the higher the speed, the more wrong we are.
Finally, and most interesting, philosophically we are completely wrong
with the approximate law. Our entire picture of the world has to be altered
even though the mass changes by only a little bit. This is a very peculiar thing
about the philosophy, or the ideas, behind the laws. Even a very small effect
sometimes requires profound changes in our ideas.
Add comment July 23rd, 2004