Although it may be true there is no absolute definition of "physical law,"
I think it is worth doing a little research to see what is in print on the
subject.
An encyclopedia that I have often found useful is the "Academic American
Encyclopedia." Our former college librarian (new retired) told me it is
clearly the best encyclopedia. That was just his opinion, but I have to say
that when I have used it to look up science stuff, I find the entries quite
well written.
The entry on "law, physical" was written by Neil Ashby and Wesley Brittin.
Neil is Professor of Physics at University of Colorada, Boulder. Wesley is
Emeritus Professor at the same institution. A quick look in the Internet
will show that Brittin has edited a ton of stuff. Note, in view of Jack
Uretsky's criticism of turning to authorities to make arguments, let me
remark that I am only partly doing that. These guys were authority enough
for the encyclopedia staff to trust their judgment. But more important,
they wrote a pretty good entry, in my opinion.
Authorities? I think so. Do we have to accept what they wrote? No. But
can any of us do better?
Here are a few excerpts from their entry in the encyclopedia. I especially
like the last paragraph.
* * * *
Physical laws give precise expression to observed regularities that occur in
nature; they are necessary for describing, explaining, or predicting the
development of natural phenomena. For example, Keplers Laws of planetary
motion, established from observation, describe how the planets move in their
orbits about the Sun. Newton's Laws of Motion and his Law of Gravitation
explain mathematically the laws of planetary motion.
<snip>
An important property of most classical physical laws is that they do not
contain statements about the initial state of a system; once the initial
conditions have been specified, however, they describe subsequent physical
behavior precisely.
<snip> <some electromagnetism and relativity stuff is included but is being
snipped at this point, also some quantum and uncertainty stuff>
The basic physical laws share two surprising properties: they are all
unproven and also unprovable. Developed from observation and
experimentation, they are assumed valid as long as no natural violations of
them can be found. The universe does not behave as we say it must; rather,
it is presumed that natural physical laws exist and have always existed. It
is the goal of scientists, mathematicians, and philosophers to discover and
define natural laws.
* * * *
Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817