stern@bnl.UUCP (Eric Stern) (04/04/85)
With the reappearence of the old debate on whether
all those who question scientific theory should be heard out
or not, I thought I would clarify the situation of how
theories get to become accepted, and why the current system
acts to prevent the acceptance of false opinion and dogma.
Along the way, I will discuss the related issues of experi-
mentation and theories, and peer review of scientific work.
In general, theories do not develop in a vacuum.
There is usually a body of knowledge that requires explana-
tion. This body of knowledge is acquired through experimen-
tation. What experimenters do is to measure parameters of
phenomena. Sometimes, they are verifying existing theories,
or searching for deviations from theories, but sometimes
they also perform searches for new phenomena independent of
any theories. This provides the grist for the mill of new
theories.
When they perform experiments and make measurements,
the answer they come up with is subject to independent
verification. An experiment that nobody can reproduce is
not considered to be valid. This is happening all the time.
For instance, an experiment has been done at Stanford that
seems to observe fractional charge, by a method based on the
Millikan oil drop experiment, only this one uses charged
niobium spheres. The result would seem to indicate the
existence of free quarks, which have not been seen else-
where. In fact, the Stanford experiment has been repeated
at other institutions, with a null result. Because the
Stanford result is not reproducible, free quarks are con-
sidered to be unobservable.
The result of an experiment is expected to include an
experimental error. The experimenter estimates the magni-
tude of deviation from the quoted value that he or she con-
siders possible, given the nature of the measuring apparatus
and procedure. The experimenter cannot cheat and quote a
error that is too small, lest a future experiment make a
measurement which does not agree within the error limits.
If the error quoted is too large, to insure that future
experiments will agree, the experiment is considered to be
worthless in the eyes of the scientific community. After
all, if there is such a large error on the measurement, they
think, it is no better than no measurement at all. Once
several experiments agree on a phenomenon, those measure-
ments enter the general body of knowledge and become candi-
dates for theoretical explanation.
So, Joe Experimentalist discovers a new phenomenon and
gets a Nobel Prize. There is still this matter of an unex-
plained observation to deal with. How does one go about
cooking up a theory? One cannot make up an arbitrary
theory, there are guidelines that should be observed. A new
theory can't directly invalidate an old theory. The old
theory did perfectly well at explaining its set of
phenomena. The new theory must include the old theory as a
special case; it must reduce to the old theory in the limit
of a regime where the old theory held. This point must be
stressed. Old theories don't die, they just become incor-
porated into new ones. The two great new theories of this
century, special relativity and quantum mechanics, conform
to this principle. Classical Newtonian Mechanics is the
limit of special relativity considered at velocities small
compared to the speed of light. Quantum mechanics reduces
to classical mechanics in the limit of large quantum
numbers.
The two examples above illustrate something in physics,
that, while is not a fixed law, is a general principle of
operation. That is, new phenomena occur when new regimes
are looked at for the first time. Quantum effects become
noticable on the microscopic scale, and special relativity
becomes apparent at high velocities.
Another good thing to have in a new theory is general-
ity or universality. Physicists hate special cases, and
find the idea of a theory that just applies to one thing, to
be morally repugnant. Good theories should explain many
different kinds of effects without making special assump-
tions about each one. Proliferation of theories and of
assumptions is something to avoid. The best clue a physi-
cist has, that a theory is not fundamental, or just not
working, is when new assumptions, new principles, and new
laws have to be continually added to a theory to make it fit
the data.
Let us look at this in practice. The geocentric views
of planetary motion were very complicated indeed. The
planets moved around the sky, but periodically, they would
reverse their motion. Furthermore, each planet had a dif-
ferent manner of behavior that varied with the time of year.
Then Kepler came along. Kepler showed that from a heliocen-
tric point of view, the sky is very simple. The apparent
oddities of planetary motion arise from the motion of our
own viewpoint. All objects orbiting the sun share a common
pattern, a relationship between the orbit period, and the
orbit distance that holds for all planets.
Another example of universality relates to chemistry.
In the 1700's and 1800's, many new chemical elements were
discovered. They all seemed to have different chemical pro-
perties. Mendeleev arranged the elements in a table,
ordered by atomic weight, and found a repeating pattern.
Elements separated by a certain amount in the table had
similar chemical properties. Later on, it was determined
that atoms consist of smaller particles, and it was the con-
figuration of these constituent particles that determined
the chemical behavior of the atom. But, the clue that
something funny was going on was the proliferation of the
number of elements, and the discovery of a pattern made it
obvious that there was an underlying principle.
The story is not over when a successful theory is
found. The new theory continues to undergo tests to deter-
mine its applicability in new situations. Even well esta-
blished theories are tested anew, when improvements in
experimental technology allow more sensitive measurements of
a theory's validity. The Coloumb inverse square law for
electric and magnetic fields, which was discovered about
1770 are tested as better techniques become available. A.
S. Goldhaber wrote a Scientific American article in 1979
describing experiments which verify the inverse square law
by observing the Earth's magnetic field. An observed devia-
tion from the inverse law would imply a non-zero photon
mass, which would have many consequences.
An established theory is used as the basis to build
more theories. Physics advances by building new structures
on top of old ones. Conversely, new theories depend on the
validity of previous theories. Every new theory verified
acts to confirm the theories upon which it is built.
With that preface out of the way, we can ask the real
question that prompted this article: what are the odds that
someone working independently of the "scientific establish-
ment" discovers something wrong in a basic theory, such as
classical electrodynamics? Well, it has to be pretty small
odds. The "scientific establishment" has been working for
over 100 years testing its own basic premises. If something
was wrong with a basic theory, we would be seeing incon-
sistencies in later work based on those same basic theories.
In fact, something wrong *was* discovered in about 1890.
Classical mechanics seemed to be inconsistent with electro-
dynamics. That was just one problem. Radiation calcula-
tions based on electrodynamics indicated that all the elec-
trons orbiting nuclei would radiate all their energy and
crash into the nucleus. This was the great "Ultraviolet
Catastrophe", so named because the radiation given off would
be high frequency, low wavelength, hence ultraviolet. The
resolution of these two problems eventually led to the
development of special relativity, quantum mechanics, and
finally quantum electrodynamics. As it happens, the most
precisely verified quantity known is the gyromagnetic ratio
of the electron. This property of the electron has been
measured to over eight significant figures and found to
agree with the value predicted by quantum electrodynamics.
The correctness of quantum electrodynamics implies the vali-
dity of almost every previous theory including classical
mechanics, classical electrodynamics, quantum mechanics and
special relativity. So it seems, if past experience is any
guide, physics is quite capable of recognizing its own prob-
lems and dealing with them.
Current physical theory is the result of several hun-
dreds of years of work by people who didn't necessarily like
each other, and includes results of thousands of experiments
verifying the theories. Because of all this work, a physi-
cist feels confident in rejecting the assertions of someone
who gets the idea that physics is wrong. The views of those
who feel that rejecting such notions is equivalent to the
treatment given Gallileo and Capernicus may be answered by
noting that prior to these visionaries, there was no esta-
blished science. At that time, ideas of the physical world
were dictated by preconceived notions having no basis in
observation.
Physics, in the final analysis is totally based upon
experimental observations. There is no accepted physical
theory which can't be demonstrated to be correct in the
laboratory. Given the large body of knowledge that has been
collected about the laws of the universe, and the demonstra-
tion by several independent experimenters of the validity of
the procedures used to accumulate this knowledge, the ines-
capable conclusion is that the theories which have been
developed to explain the observations must reflect the true
behavior of the universe.
Eric G. Stern
Dept. of Physics
SUNY StonyBrook
StonyBrook, NY 11794
stern@bnl.arpa
stern@bnl.bitnet
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