"Patrick Reany" wrote in message
om...
Taken from:

FOUNDATIONS OF PHYSICS

BY ROBERT BRUCE LINDSAY, Ph.D.
Associate Professor of Theoretical Physics, Brown University

AND

HENRY MARGENAU, Ph.D.
Assistant Professor of Physics Yale University

NEW YORK
JOHN WILEY & SONS, Inc.
LONDON: CHAPMAN & HALL, LIMITED, 1936




From the poster: Note the role that conventionalism and agreement play
in the founding of a science by these authors. Why do the authors
define physics as they do: the "task of physics as of all science is
found in the coherent description of experience"? Do you hgave a
better definition or characterization of physics? Is the notion of the
"material world" really problematic? What would the realist say? What
would the instrumentalist say?


------------------------------------------------------

--- p. 1 ---


THE MEANING OF A PHYSICAL THEORY

1.1. The Data of Physics. Physics is concerned with a certain portion
of human experience. From this experience the physicist constructs
what he terms the physical world, a concept which arises from a
peculiar combination of certain observed facts and the reasoning
provoked by their perception. While most textbooks of physics set
themselves the task of presenting to the student in the most adequate
pedagogical manner the features of the physical world as they have
been historically developed, it is the principal purpose of the
present volume to conduct an inquiry into the logical constituents of
these features, analyzing them into such elements as observed facts,
definitions, postulates, and deductions.

What, then, is experience, and how much of it concerns the physicist?
A detailed answer to the first part of this question would lead us
into the depths of philosophy, to which this book is not primarily
devoted. Nevertheless, a few remarks on this point are necessary to
avoid possible misconceptions. We shall at once assume the possibility
of experience and knowledge as the metaphysical basis upon which any
science fundamentally rests. Moreover, we shall accept the genuineness
of the sense-perceptions of normal people and abstain from quarreling
about the meaning of normality in this connection. Naturally, the
physicist like all scientists must be forever on his guard against
abnormal perceptions, but he has, we assume, objective criteria for
detecting them. We must also grant the possibility of the exchange of
knowledge, that is, the understanding of another's sense-perceptions
and reflections in terms of one's own.

A further assumption, however, must be made about experience before
science as we know it becomes possible. Not only must there be
agreement about it among normal people, but also it must exhibit a
certain uniformity. That is, many sense-perceptions do not occur
completely at random, but certain more or less well-defined groups of
perceptions repeat themselves over and over again with only slight



--- p. 2 ---

2 THE MEANING OF A PHYSICAL THEORY

and often insignificant variations. The alternation of day and night
with their attendant phenomena illustrates this point, and the reader
will be able to supply other examples from all branches of science.
There thus appears to be a kind of order in natural phenomena which is
often expressed as the law of cause and effect: if a certain group of
sense-perceptions appears a number of times associated with a second
group, we expect that a repetition of the first group will always be
associated with that of the second. This is not the place for a
detailed discussion of the significance for physics of the assumption
of uniformity in its various forms. We shall have occasion later
(Chapter X) to investigate these matters more closely and are here
introducing them merely as a means of initiating our discussion.

Now, clearly, physics is not concerned with the whole body of human
experience. How, then, are the data of physics selected? Before we
come to this question, however, let us make quite plain that the task
of physics as of all science is found in the coherent description of
experience. Physics has nothing to say about a possible real world
lying behind experience. It is extremely important to realize that,
although physics rests upon the assumptions of the possibility of
knowledge and the uniformity of experience, the other philosophical
problems connected with realism and idealism have no significance for
it. One often hears the statement that the task of physics is to
describe or explain the behavior of the material world. We cannot help
feeling that this is meant to imply the existence of such a world,
though what the adjective "material" here means is by no means clear.
The physicist has been striving for years to attach a clear meaning to
the term matter, and undoubtedly we have reason to believe that the
concept means much more to us today than to the physicists of fifty
years ago. However, to have a clear understanding of a physical
concept like matter is not at all equivalent to the assumption that
there is a "real" world behind our sense-perceptions which is
responsible for the existence of matter. There is perhaps no harm in
such an assumption---in fact, certain minds may find that it enables
them more firmly to grasp and feel confidence in physical theories;
yet it must be stressed that the assumption is no necessary part of
physics, and that in a logical development of the subject the safest
course is to omit it entirely. It is possible, indeed, to take the
view that adopting such an assumption as part of the physicist's
stock-in trade involves a handicap. There is scarcely any use in
believing in a real material world behind physical phenomena unless it
is a permanent, unchanging affair toward the knowledge of which we
progress with slow but certain steps. But our knowledge of it is based
naturally


--- p. 3 ---

1.1 THE DATA OF PHYSICS 3

on the prevailing physical theories. It seems as if the belief in such
a world may tend to encourage too close adherence to reasonably
successful physical theories with too small allowance for their
necessary revision to meet the demands of new experience. Thus, the
term "physical world" used in the introductory paragraph is not to be
construed as being identical with real world.

-----------------------------------

My definition of physics:

Physics is the search for the smallest set of rules by
which we can completely describe the behavior of
inanimate matter under natural circumstances.


Back when mechanics was thought to be the correct program to found all
of physics, it made sense to think of matter as fundamental and
irreducible, but since the advent of field theories this is not so
meaningful, as the material particle itself can be modeled as a
"localization" or accumulization of field, like the bunching up of a
tablecloth.

Patrick
Since this post has appeared in sci.physics.relativity as well as
sci.physics, I would like to endorse the emphasis the author has placed on
assumption, and where it show up in Einstein's "On the Electrodynamics of
Moving Bodies".
quote
In agreement with experience we further assume the quantity
2AB/(t'A-tA) = c,
to be a universal constant...
unquote
If I toss a ball to you and run away, you toss it back and I catch it, then
my experience is that it will take longer for you to return the ball to me
than it did for me to send the ball to you. It is my further experience that
the speed of the ball, relative to me, will be different to the speed of the
ball relative to you in neither direction. Only if I remain at rest with
respect to you can we agree on the velocities and the times of transit in
each direction. Why would anyone make an assumption that the times and
speeds were equal when the same situation is applied to light, since it is
not in agreement with experience?
It is at this juncture that a turning point is made in the history of
physics. We've departed from experience, gone into the realms of assumption,
and live in a mathematical world that has no correlation with Nature.
If you want to *find* the smallest set of rules, it's probably best not to
create them out of assumption. Human imagination knows no bounds, but Nature
is there to be studied, not created from our minds. Ptolemy's epicycles
worked well for 2000 years, and were hopelessly wrong, becuase he assumed
the Earth was the centre of the universe. We've been making a similar
mistake, based on asumption, for the last 98 years.
Androcles