Science in Christian Perspective
Physics inthe Future
Where Do We Go From Here?*
ARTHUR E. RUARK
7952 Orchid St. N. W. Washington, 13. C. 20012
From: JASA 22 (March 1970): 4-7.
Because all science feeds on unsolved problems, it is our privilege, from time
to time, to make some forecast of the future. Naturally, the forecaster can do
nothing about some great surprise that may come, with sudden force, to change
the course of a whole science. Nevertheless, in a well developed science such
as physics, one can see some invariant driving forces. There are tides in the
affairs of physics that drive us onward without cease. The greatest tide of all
appears to be explicit faith in the unity and consistency of natural behavior.
This faith implies that parts of our subject that develop in relative isolation
will come together to form a broader, more perfect structure.
A very striking feature of our times has been the extension of
physical and chemical
and biological studies to very small sixes and time intervals. I am
talking about
our ability to deal with atoms, nuclei and elementary particles. Again, there
has been extension of our ability to learn about the large-scale
features of this
universe-this "bourne of space and time," as Tennyson said. These are
intellectual and moral endeavors, in the sense that we have to deal with great
uniformities in nature; with creation, evolution and final fate.
Here, my unifying thread of thought will be the increasing interaction between
subatomic physics and the physics of the heavens. I shall consider some
solved problems in these fields. The list is highly selective. I have excluded
nearly all the things in the mainstream of current effort, in order to include
others that now receive little attention but may be in the mainstream in years
to come. Let us proceed, beginning with a few topics in fundamental
physics.
THE VERY, VERY SMALL
We all know of the close relation between the relativity theory and the quantum
theory. However, there are curiosities connected with this matter. Partly they
arise because the field on which the game of quantum theory is played
is a classical
manifold, the field of space and time, or better spoken,
"space-time."
Let me indicate how these two theories are connected at their very roots.
"After taking bachelor's, master's and doctor's degrees at Johns Hopkins
University, Arthur E. bark taught at Yale, Pittsburgh, North Carolina
and Alabama
universities. tIc joined the Atomic Energy Commission in 1956 as chief of the
controlled thermonuclear program and recently retired as senior
associate director
of the division of research as the AbC.
Quantum theory is a relativistic theory. The basic papers of Louis de
Brogue and
of Erwin Schrodinger already showed that the waves belonging to a particle of
speed v have a phase speed c2/e, where c is the speed of light. This
formula arises
from special relativity; if one uses Newtonian mechanics, a wrong
result is obtained.
Special relativity deals with space and time enördinatesx and t, so that
it is usually considered to he a classical theory; that is to say, a nonquantum
theory. This seems to be correct when one considers it as a
mathematical scheme;
for there is no mention of Planck's constant is in the axioms set up by Albert
Einstein. On the other hand, I do not think it is generally
understood that this
point of view has to be modified a hit when we take a hard look at
the interpretation
of the theory.
There are tides in the affairs of physics that drive us onward without cease. The greatest tide of all appears to be explicit faith in the unity and consistency of natural behavior.
In order to use the theory in physics, we have to say what the quantities x and
f stand for, and Einstein made the choice that is really useful. When lie said
x, he meant a length measured with a real meter stick. He did not
mean a hypothetical
nonexistent "rigid ruler," the kind talked about in geometry classes.
When he said t, he meant a time measured with a laboratory clock. Now, this has
consequences. The object to he measured is a dynamic thing, and so is
the standard.
The meter stick is a group of crystals, a vibrating body held
together by quantum
forces, and so is the clock. It looks as though we are caught in a
vicious circle;
we want to study the intenors of atoms with the aid of laboratory
standards, and
Lo! The standards are made out of the very things we want to study.
True enough, we do not actually thrust a meter stick down into the
atom. We have
none with divisions fine enough, and we know that such a disturbance
of the atom
would not he pertinent if we could do so. Actually, we have to study
the wavelengths
of light emitted (and other useful quantities), recording them always with the aid of gross apparatus-a favorite topic of Niels Bohr.
Always there are experimental troubles. Always, we are making use of a chain of
experimental results and interpretation, concerned with the whole
coupled apparatus
and based on special relativity and quanturn theory together. A
central question
is whether we wish to use our ordinary ideas about lengths and distances when
we get into the domain of the very, very small; is this practice
really bad? Not
at all. The physicist is always trying to extend the scope of his
laws or to find
their limitations. He is a great fellow for cutting Gordian knots; so
he says:
"I shall continue to use special relativity and quanturn theory
as a strange
pair of partners, to interpret results of my experiments on collisions between
elementary particles; and I shall find out whether I run into
discrepancies."
Breakdown?
Nowadays, one kind of search for such discrepancies is called experimentation
on the breakdown of quantum electrodynamics. It is carried on by studying, for
example, collisions between two electrons; one looks at the
distribution of scattered
electrons to see whether it agrees with predictions from electrodynamics. As of
1968, there was no clear evidence of trouble,1 down to inferred
distances between
the collision partners as small as about 1.8 x 10-14 cm.
The question now arises: Could particle theory continue to make use
of the customary
spacetime concept if a breakdown of electrodynamics were found? Let us see. A
failure of present-day theory would simply lead to construction of
some new formulation,
not to a modification of the space-time picture. People would keep
that picture.
What they want is consistency in theoretical talk over the whole
range of space-time
dimensions, "from zero to infinity." It will be extremely
bard to eject
the space-time picture from any part of physics. Curvature may he introduced;
broader geometries may be invoked, but the continuous manifold will
still be there
because of the flexibility with which new physical fields can be
introduced when
experiments appear to suggest their presence.
Weak and Infrequent Things
The success of Fred Reincs and Clyde Cowan2 in starting up the
subject of experimental
neutrino physics showed us that studies involving miniscule cross sections can
he worth a great deal of effort. There is also the search for
gravitational waves,
it is heartening to know that Joseph Weber3 has really excellent apparatus to
look for these waves; his laboratory is full of seismographs and the like, for
throwing out spurious effects from tides and earthquakes. It is still
more heartening
to know that he has some events that are difficult to explain by
means of terrestrial
disturbances.
We should not forget that there may he very weak forces in nature,
still undiscovered,
aside from the gravitational ones. I do not know of any current search for such
forces.
The whole trend in physics has been to assume that particles are extremely well
standardized. Nevertheless a few people4 have been looking for
anomalous or nonstandard
particles; here I am talking about aberrant electrons, protons, or
what-have-you?
The resources of modem technique (and in particular, the capabilities
of optical
spectrographs) are not now
being fully used to make some progress with this matter. The trouble
is that when
one starts to speculate about such particles, the possibilities are very wide;
so one must look very selectively for good opportunities to do an interesting
experiment.
The Search for Underlying Levels
In recent years we have seen rather extensive searches for an underlying level
of simpler things from which a horde of elementary particles might be
made. There
was the quark search and the search for Dirac magnetic poles; now there is the
interest in so-called "W particles." The quark idea, as a
mathematical
scheme, is indeed ingenious arid interesting. The quarks are sometimes thought
of as the ultimate particles, but there is a trouble with such ideas. If we had
quarks, people would just say, "What are they made of?"
This is an example
of the infinite Regression-a question such that if you answer it you
come up against
another question of the same kind.
Astrophysics and Cosmology
We are all aware of the highly fruitful relations betweets advances in atomic
and nuclear physics and those in astrophysics and nebular physics. Furthermore,
the fruits of cosmic-ray work, radio astronomy and x-ray astronomy show us that
high-energy physics is one essential key to the understanding of very violent
astrophysical events." But there is mounting evidence that, in a broader
sense, particle physics and cosmology are closely related. Let us
turn our attention
to a few aspects of this fascinating realm of ideas.
Space-time and Matter
It is frequently said that the material content of space and the motion of that
material determine the curvature of the space-time manifold. This is
often called
Mach's principle. Indeed, Einstein's gravitational equations say that a tensor
built from curvature quantities is equal to the matter-energy tensor TiK . If
TiK is treated as an arbitrary source term, the above statement is justified, but we
are left with an incomplete story on our hands. Thus, if TiK comes
from electromagnetic
sources, the fields appearing in it should be taken from Maxwell's equations,
written out for curved space-time. Then the curvature and the
matter-energy tensor
are determined together, from these coupled equations. Einstein
proceeded in this
way, arriving at his first combined theory of gravitation and electromagnetism.
True enough, he abandoned it later for reasons of personal taste, but
others have
carried on, and this first unified theory is a lively field of
research even today,
50 years after it was created. However, a salient question still confronts us.
When we proceed to a specific case, that of a single electron for example, do
we simply put in the electronic charge as an unexplained parameter?
Or do we look
for underlying relations whereby the electron can be represented as a curlicue
of particular dimensions in space-time? To speak more generally-do we
want a completely
unified theory of space-ttme and matter, or a dualistic theory? There
is a literature
on this subject, too extensive for discussion here.' An idea of the Mach type
runs through it all. If I were asked for a comprehensive generalization of the
Mach idea, I would say, "There is just one manifold. The
equations describing
physical phenomena contain not only fields defined on that manifold
but also quantities
characterizing the geometry of the manifold. The connections are such that the fields and the
geometrical
quantities are determined together, consistently." And I recommend to the
reader some interesting studies of a generalized Mach principle, by
Mendel Sachs.7
This is a good place to ask, "How is it that space
has three dimensions?" This question is at least 70
years old. I have seen nothing on the subject that is more than a plausibility
argument, but I have a small suggestion as to a fresh approach. Suppose we use
the methods of tensor and spinor calculus to examine physical
equations in space-time
of several dimensions, from two up to six, for example. Let us cover
both classical
theory and quantum theory, remembering to look closely at the
properties of simple
solutions that represent point particles; we search for features that
appear particularly
desirable or unique (or both), in the case of fourdimensional
space-time. If such
features emerge, we may understand a little better the preference for
three space
dimensions in this universe. The results would still be plausibility arguments,
but if they looked attractive, we would promote them to the status of
assumptions;
and that would be that.
Consistency: A Desirable Feature
Perhaps the most significant fact that has emerged
from exploration of the distant galaxies is the general consistency of physical
law over very large spaces and long time intervals. Apparently we are
not dealing
with different bodies of law, linked together only by very weak connections. We
appear to be living in a Universe-not in some sort of Diverse, or Polyverse. A
cardinal piece of support for this welcome notion is the red shift of
Vesto Slipher,
Edwin Hubble and Milton Ilumason. To an approximation, the light from distant
galaxies is shifted toward the red, by amounts that can he explained
by assuming
that they move outward with speeds c, proportional to their distances
R from us;
the relation is
v = 75R,
with c in kilometers per second and R in megaparsecs; one megaparsec
is 3.09 X 1024 cm.
Allowing for this red shift, we see the same spectral series, the same atomic
behavior, that is found here on earth. Of course, this probing out to
great distances
means that one is looking back a long way in time. What is the inner meaning of
this consistency? The distant atoms would not show the spectral series properly
if they did not obey the Pauli principle. Those atoms are testifying
to identity
of the electrons and identity of the nuclei in the whole region available for
observation. They are revealing a most extraordinary degree of quality control
in the creation and maintenance of these particles. Why, not even
RollsRoyce...!
Is this uniformity of particle properties due to a uniformity in the properties
of space-time itself? Or are these two ideas just the same idea
clothed in different
words? I leave the answer to you-or your grandchildren.
Long Ago and Far Away
There is another important fact that bears on the question of
universal consistency.
Suppose an atom in a galaxy 10 light years away emits a parcel of
energy characterized
by a far-ultraviolet wavelength. Looking aside from experimental difficulties,
we can
set up a suitable bull) containing sodium vapor, here in our solar system, to
receive the light. After 109 years an electron may he kicked out of a
single atom
in that vapor. If we believe that an electromagnetic field traveled
all that time
through empty, darksome space, then we have to say that the field
causes a definite
amount of energy to appear at a target only 10-s cm in diameter, after running
through a distance of about 1027 centimeters. Also; from the observed
conservation
of energy in such processes, we have to conclude that the field does
nothing elsewhere.
What shall we say about this result? An orthodox quantum theorist
might say, "It
is all a matter of chance; this matter was explained in 1927." A
thoroughgoing
determinist might say, "This astounding accuracy of aim is
evidence of extraordinary
quality control." A classical relativist might say, "All point events
that are connected by light rays are at the same spot in space-time.
We are dealing
with a sort of contact action. From the standpoint of a being who
perceives point
events directly and intuitively, there is no problem." We
possess considerable
flexibility in contemplation of these answers or others like them;
for each answer
is based on some set of axioms, and axioms are arbitrary indeed. The orthodox
quantum theorist will say, "Yes, but look at the fruits of my
axioms."
And we shall reply "The fruits of your axioms are very great indeed, but
a large number of very respectable people are not satisfied with the
foundations
of your theory."
Perhaps the most significant fact that has emerged from exploration of the distant galaxies is the general consistency of physical law over very large spaces and long time intervals... We appear to be living in a Universe-not in some sort of Diverse, or Polyverse.
Permanence: A Desirable Feature
Let us consider the permanence of gross matter. The customary
estimates of universe
duration lie a little above 1010 years. It happens that Reines and his students
have found lower limits for the lifetimes of electrons and nucleons by looking
for their decay.0 There are some nuances, but roughly the half-life
figures are:
for the electron, more than 2x 1021 years; for nucleons, more than 1027 years.
Thus we are confronted with a terrific factor of safety, 1011 at
least, relative
to the universe duration mentioned above. This looks like very good
engineering.
The stuff is made so it will last.
Diluteness: A Convenient Feature
People are generally impressed with the vast spaces between the stars
of our galaxy,
and also the spaces between galaxies, which, on the average, are somewhat like
tennis balls 8 meters apart. This diluteness is much to be prized,
because violent
things happen when big pieces of matter get too close together. I invite your
attention to the famous case of the galaxy M 82. A photograph of this
galaxy can
be found in
reference 9. More or less perpendicular to the disk of the galaxy
there are great
masses of ejected matter, believed to be mostly hydrogen. There was a
big explosion
in the middle of this galaxy. The products are pouring out at a speed
of the order 108 cm: sec. It is estimated that this explosion involved disruption
of a million
stars in the dense core of the galaxy.
Information From Far Away
How much can we hope in learn about very distant objects? In
general, the farther
away an object is, the less we can find out about it. Details fuss out; light
signals from the object are fainter; spectra move out to the
infrared. It is only
in recent times that attention has been paid to the quantitative side of this
common observation. Kenneth Metxner and Philip Morrison10 have calculated the
amount of information carried to us by the photons from a distant galaxy in any
experiment of limited duration. They consider simple expanding
universes of several
types. This is a matter worthy of further research, because it can show us the
boundary between verifiable physics and unverifiable speculation.
Beyond the domains
where individual galaxies can be identified-and there are hundreds of millions
within sight-there may be others that show up as a faint general
background. Astronomers
know that they must increase their studies of this faint background light, when
more big telescopes come on stream, a few years hence.
If and when they reach the limit of their resources, we shall be
confronted with
an interesting situation. For a long time philosophers have been
saying that physicists
continually work on the soluble problems, so that metaphysics is
necessarily the
bin of unsolved ones. Now I shall leave it to the reader to ponder
the situation
of an experimental science that reaches a limit because the objects
under investigation
cannot provide sufficient amounts of information to our detectors to give the
answers we should like to know.
EPILOGUE
I have pointed out some lines of endeavor that lie at or beyond the
present limits
of our capabilities, and I have only two hints for those who may choose to attack these matters. The first is that one should pay close attention to a
method used by Rene Descartes. I call it the "Method of Complete
Skepticism."
He adopted a systematic policy of denying any statement he was considering and
of looking at the consequences. The second hint is connected with economy and
simplicity of thought. I quote the famous dictum of William of Occam:
"Entia
non multiplicanda stint, praeter necessitatem." Entities are
not to be multiplied
except for reasons of necessity.
In closing, I mention once more the consistency, the connectivity, revealed by
physical studies up to the present. Though each of us usually thinks of himself
as a part of the universe, this is a one-sided view, for great portions of our
surroundings are always exerting their influence upon us. As an overstatement,
one might say that the universe is apart of every man. Sir George Thomson11 says
in his book, The Foreseeable Future:
"The universe that includes our perceptions and our feelings is one, and no single part can be put into a ring-fence completely isolated from all the rest."
Therefore I end this story with the thought: The universe is the proper study
of mankind.
REFERENCES
1W. C. Barber, B. Cittelnian, C. K. O'Neill, B. Richter, Phys. Rev.
Lets. 16, 1127
(1966),
2F. Reines, C. L. Cowan Jr, Physics Today 10, no. 8, 12
(1957).
3J. Weber, Phys. Rev. Lett. 20, 1307 (1968).
4C. M. Kukavadzc, L. Ya. Memelova, L. Ya. Suvorov, Soy.
Phys.-JETP 22, 272 (1965); E. Fisehbach, T. Kirsten, C. A. Schaeffer,
Phys. Rev. Lett. 20, 1012 (1965).
5S. Colgate, Physics Today 22, no. 1, 27 (1969).
6J. A. Wheeler, Geometrodynanics, Academic Press, New
York (1962). D. K. Sen, Fields and/or Particles, Academic Press, New
York (1968).
7M. Sachs, Physics Today 22, no. 2, 51 (1969).
8M. K. Moe, F. Rcioes, Phys, Rev. 140, B992 (1965);
XV. R. Kropp Jr. F. Reines, Phys. Rev. 137, B740 (1965); C. C.
Ciansati, F. Reines,
Phys. Rev. 126, 2178 (1962).
9C. F. Burhidgc, E. RI. Rurbidge, A. M. Sandage,
Rev.Mod. Phys. 35, 947 (1963).
10A. W. K. Metzner, P.Morrison, Mon. Not. Roy. Astron, Soc. 119, 657 (1959).
11P. Thomson, The Foreseeable Future, 2nd ed., Viking Press,
N.Y. (1960)
*Reprinted from Physics Today 22, No. 9, 25 (1969).