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 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
we want to study the intenors of atoms with the aid of laboratory
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
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.
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
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*Reprinted from Physics Today 22, No. 9, 25 (1969).