Brian Blais raises the question of introducing the concept of reality
into physics teaching. I think students should be told that reality
is a deep concept, and that we won't treat it in a physics class. It
is a good topic for bull sessions, of course, as are sex, politics,
and religion. Since the latter three classical topics are now
considered to be improper for teacher-student intercourse, perhaps
discussion of reality has some merit.
I have spent a great deal of time trying to define what I mean by
reality, a subjective approach to the question. I have read what many
others have had to say on that topic, and I conclude that it is a
task that will ultimately prove fruitless. On rereading I have been
unsatisfied with anything I have written on the topic. Many
philosophers have written extensively on reality, which doesn't help,
since I am seeking concision. Descartes's contribution, while
concise, doesn't help, since I have never doubted my own reality.
Nonetheless, reality seems to be the philosophers' game rather than
the physicists'. Metaphysics, I have decided, is either not in the
physicist's job description, or else is above his pay grade. I will
note that no Physics Nobel Prize has ever been awarded for a
description of reality *per se*. On the other hand, many Nobel Prizes
have been awarded for proving the existence of an entity that
previously had been realized only as the product of a theory.
Physics is the quantitative description of Nature. The description
relates natural entities to one another in what seem to be elegant
mathematical constructs we call "theories" and even "laws". These
theories are mutually consistent, and they have predictive value.
There are many candidates for true theories*, and there is agreement
that a theory may be invalidated by demonstration that it fails to
predict the result of an experiment correctly*. Thus physicists now
consider mesons, antiparticles, and neutrinos to be real, and as I
noted before, they have earned their discoverers many Nobel Prizes.
(I think the neutrino epitomizes the tenuous nature of the
physicist's hold on the nature of reality.)
Leigh
* "Truth" is another concept beyond the physicist's ken.
Metaphysicians worry about truth, too. My own view is that, like
reality, truth has no practical importance. I would substitute
"valid" for "true", in the sense that a valid theory has not (perhaps
"not yet") been invalidated in Nature.
** Note that this is a weaker requirement than Popper's requirement
that a theory must be falsifiable. We now accept theories in
astrophysics that cannot be falsified by observation or experiment
because results of these are forever inaccessible. "Inflation" is one
such theory.