DOCUMENT RESUME

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AUTHOR Pollard, William G.TITLE The Mystery of Matter, World of the Atom Series.INSTITUTION Atomic Energy Commission, Oak Ridge, Tenn. Div. of

Technical Information.PUB DATE 70NOTE 64p.AVAILABLE FROM USAEC, P. O. Box 62, Oak Ridge, Tennessee 37839

(Free)

EDRS PRICE mr-s0.65 HC-$3.29DESCRIPTORS *Atomic Structure; *Atomic Theory; *Instructional

Materials; *Matter; Resource Materials; Science.History; *Secondary School Science

ABSTRACTThis booklet is one in the "World of the Atone

Series" for junior high school students and their teachers. Itdescribes the fascinating story of the search for the key to thestructure of matter. These topics are reviewed: the chemical atom ofthe 19th century, the planetary atom, the wave atam, inside theelementary particles, and the mystery of matter. Numerous photographsare Included throughout the text. (PR)

AU.S. DEPARTMENT OF HEALTH,EDUCATION & WELFAREOFFICE OF EDUCAPON

THIS DOCUMENT HAS BEEN REPRO-DUCED EXACTLY AS RECEIVED FROMTHE PERSON OR ORGANIZATION ORIG-INATING IT POINTS OF VIEW OR OPIN-IONS STATED DO NOT NECESSARILYREPRESENT OFFICIAL OFFICE OF EDUCATION POSITION OR POUCY

. on a rainy morning in the West. . . I had comeup a long gulch looking for fossils, and there, just ateye level, lurked a huge yellow-and-black orb spider,whose web was moored to the tall spears of buffalograss at the edge of te arroyo_ It was her universe,and her senses did not extend beyond the lines andspokes of the great wheel she inhabited. Her extendedclaws could feel every vibration throughout thatdelicate structure_ She knew the tug of wind, the fallof a raindrop, the flutter of a trapped moth's wing.Down one spoke of the web ran a stout ribbon ofgossamer on which she could hurry out to investigateher prey_

Curious, I took a pencil from my pocket andtouched a strand of the web. Immediately there was aresponse. The web, plucked by its menacing occu-pant, began to vibrate until it was a blur. Anythingthat had brushed claw or wing against that amazingsnare would be thoroughly entrapped_ As the vibra-tions slowed, I could see the owner fingering herguidelines for signs of struggle- A pencil point was anintrusion into this universe for which no precedentexisted. Spider was circumscribed by spider ideas; itsuniverse was spider universe- AU outside was irra-tional, extraneous, at best, raw material far spider. AsI proceeded on my way along the gully, like a vastimpossible shadow. I realized that in the world ofspider I did not exist_

_ Man, too, lies at the heart of a web, a webextending through the starry reaches of siderealspace, as well as backward into the dark realm ofprehistory_ His great eye upon Mount Palomar looksinto a distance of millions of light-years, his radio earhears the whisper of even more remote galaxies, hepeers through the elecfron microscope upon theminute particles of his own being- It is a web nocreature of earth has ever spun before_ Like the orbspider, man lies at the heart of it, listening_ Knowl-edge has given him the memory of earth's historybeyond the time of his emergence_ Like the spider'sclaw, a part of him touches a world he will neverenter in the flesh- Even now, one can see himreaching forward into time with new machines,computing, analyzing, until elements of the shadowyfuture will also compose part of the invisible web hefingers-

_ _ _ What is it we are a part of that we do not see,as the spider was not gifted to discern my face, or mylittle probe into her world?

Foreword

THE WORLD OF THE ATOM SERIES

This booklet is one in a series for junior high schoolscience students and their teachers. It describes thefascinating story of the search for the key to the structure ofmatter.

I hope you enjoy reading this booklet.

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CONTENTS

Introduction :3

The Chemical Atom of the 19th Century 11

The Planetary Atom 19

The Wave Atom

Inside the Elementary Particles

The Mystery of Matter 47

United States Atomic Energy CommissionDivision of Technical Information

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I would not like to underestimate the value of theworld view which is the result of scientific effort. Wehave been led to imagine all sorts of things infinitelymore marvelous than the imaginings of poets anddreamers of the past. It shows that the imagination ofnature is far, far greater than the imagination of man.For instance, how much more remarkable it is for usall to be stuckhalf of us upsidt- downbv amysterious attraction, to a spinning ball that has beenswinging in space for billions of years. than to becarried on the back of an elephant supported on atortoise swimming in a bottomless sea.

Richard Feynman

Introduction

Matter presents itself to our immediateexperience in a great diversity of forms. Forprimitive man there were the major divisionsbetween sea and earth and sky. Each of thesedomains contained its own diversity. The dryland had sand and soil, rocks and minerals,trees and grass. In the sky were air and rain,wind and storm, and above all the mysterioussun, moon, and stars. The sea was a vastimmensity of water populated by creaturesboth small and °Teat that served for thenourishment of man's body as well as for theterror of his soul.

Yet all of this in one way or another wasmatter. Is there some secret hidden in thehe2rt of matter that gives unity to thisbewildering diversity? Can the imaginationand the reason of man probe beneath thesurface of his immediate experience andunmask this secret? It is a fascinating questionand from time to time in the long history ofspeculative thought it has been a dominantforce.

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Epicurus

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Earty Theorie4 of Matter

At the beginnings of Greek philosophyone possible clue was seized upon. Perhaps allcould be understood in terms of four basicelements: air, fire, water, and earth. A$ abeginning this had much to commend iLAfter all, fire and earth were the ingredientsfrom which iron. copper, and bronze werederived. %. ind, water, and fire are commingledin storms. The combination of water andearth leads to Lai litv, and inan. as waswidely. believed, was made of the dust of theearth but became a living beir.g only when thebreath of life was breathed into him- Here wascertainly a fir:Ft step in the long quest tounlock the inner secret of matter.

Later in a more sophisticated vein agenuine atomic theory of matter emergedwith Leucippus and Democritus. One of thenotions that led them to this theory was thethought of dividing any piece of matter intosmaller and smaller halves. Ultimately, theyagreed, one must come to a point wherefurther division is impossible. Such a smallestor minimum piece of matter was an "atom".

Later the philosopher Epicurus elaboratedthis line of thinking into a well-developedatomic theory of matter. As the commondesignation "epicurean". reveals, he is bestknown today for his hedonism. This is chieflybecause the modern scientific atomic theoryis so recent. Prior to it, the knowledge againstwhich to evaluate his substantial achievementdid not exist.

Lucretius and the De Rerum Naturu

At the peak of the classical period, TitusLucretius Carus. a contemporary of JuliusCaesar and of Cicero. wrote the most com-plete account of the atomic theory of matterthat Gracca Roman philosophy produced.He was an ardent admirer of Epicurus. Hissole work is a long epic poem on the nature ofthings entitled De Rerum Natum.

It is a unique contribution to the litera-ture of mankind in that, unlike other epics ofsimilar length, it is not devoted to great humanexploits and deeds, but rather attempts todevelop a complete and comprehensive scien-tific d-Icription of the whole universe. Itcovers the infinity of space, cosmology, thestructure of matterz other worlds with theirown earth, sun, and moon; the evolution oflife and genetics; the origin of man and hisdevelopment from primitive wild states tocivilized societies. Nothing quite like it hasever been attempted before or since.

Lucretius repeats the earlier argumentsagainst the indefinite divisthility of matter asthe most basic argument for atoms, but heuses a number of others that are remarkablyperceptive. One of these is based on trans-formations of matter. Veins, blood, bones,and sinews are formed out of :In- food we eat.Flowers, shrubs, and trees are formed fromthe earth and water in which they Prow.Wood is converted through burnint, intoflame, smoke, and ashes.

9 5

In all these cases the atoms are eternal andunchangeable. Different combinations withdifferent motions and with varying amountsof void betwkten them account for thesetransformations from one kind of substanceinto another.

Another argument comes very close to theBrownian motion as evidence of the atomiccharacter of matter. Here Lucretius notes thatwhen a ray of sunlight passes through thedark hall of a house, one sees in it manyspecks or mites in incessant motion, tumblingand jerking as from invisible blows. He con-cludes that the invisible atoms are in a similarincessant motion and make collisions withnext larger objects, with the result that theprimeval motions ascend stage by stage to apoint where we can observe such motionsdirectly.

Just as the letters of the alphabet can beused in different combinations to produce agreat variety of words and these in turn canexpress a vast range of ideas, so all things inexistence come into being through particularcombinations of atoms and then disintegrateinto the same atoms again. The atoms them-selves never change, but their associations,motions, and proportions are in a continualstate of flux. As he puts it at one point in hispoem:*

". . for theseSame germs do put together sky, sea, lands,Rivers, and sun, grains, trees, and breathing things,But yet commixed they are in divers modesWith divers things, forever as they move."

*Lucretius, Of the Nature of Things, translated byWilliam Ellery Leonard, Everyman's Library edition,Book I, p. 31-

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From our vantage point 2000 years later,Lucretius shows many amazing flashes ofinsight. Yet in spite of these striking parallelsto a modern scientific view of the nature ofthings, his entire poem is pure speculationbased on general experience, and untouchedby the discipline of the slow and painstakingverification of ideas that has gradually builtour view. Indeed, we gain an impression of hisexceptional insight largely by selecting in-stances of his thought that agree with ourview of things.

There are, however, numerous instances inhis poem of notions that are ludicrous from amodern vantage point. For example, he sug-gests that honey or syrup is made of smooth,round atoms, while bitter or acid foods aremade of sharp-edged or barbed atoms. He usesthe same idea in explaining the differencebetween freshwater and seawater. The hard-ness and strength of rocks and iron areattributed to a tortuous and irregular con-

ration of their atoms that causes them tointertangle and form a rigid structure. Themind and soul he considers formed fromextremely small atoms in a very dilute state.

Lucretius had little effect on his contem-poraries, although Cicero admired his poemand was probably responsible for its preserva-tion. But he was not widely read and had nodiscernible influence on subsequent thought.Indeed, the whole of Greek atomism hadsurprisingly little influence and seemed to beof little interest in the classical period.

Only in the Renaissance was Lucretiusrediscovered and in the 15th and 16th cen-turies numerous editions of his poem were

11

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produced. It was then that the idea of asystematic and unified view of nature, whichwas Lucretius' passionate vision, began toattract and excite the minds of men, boththose who admired Lucretius and those whoopposed him. He formed the link between theclassical quest for the seci-et of matter and thenew scientific quest that began in the 17thcentury. We now turn to this quest and thestrange depths of reality to which it has ledus.

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The Chemical Atom of the 1 gth Century

The idea of atoms as the elementaryconstituent of matter blossomed in the Re-naissance from the thin line it had followedthrough the centuries from ancient Greece. Atthe dawn of modern science in the beginningof the 17th century, it was popularized by thephilosopher Pierre Gassendi and accepted byGalileo Galilei, Isaac Newton, and RobertBoyle. But with all of them it remained arather vague general idea, unattached to anyspecific facts or processes.

John Dalton and the Atomic Theory

It was left to a Cumberland, England,handloom weaver named John Dalton tobegin the process by which atoms becameconcrete and identifiable. This he did, in thefirst decade of the 19th century, through theidea that atoms come in classes with all atomsin each class being identical, and each classconstituting a chemical element. AlthoughLucretius had thought of atoms running inclasses, his classes were based on shape andgeometrical form. The idea of chemical ele-ments was distinctly new and of course John Daltonturned out to be immensely fruitfuL

As with all great ideas, this one had itshistory. In 1783 Henry Cavendish sparkedhydrogen and oxygen in a closed volume andnoticed that only water was produced andthat the initial and fmal volumes were in thesimple ratio of three to two. This was the firstinstance of what gradually came to be recog-nized as a general factthe "law of simplemultiple proportions".

In time each chemical element could beassigned an "atomic weight". Careful experi-ments by Dalton and others showed thatwhenever two or more elements combinedchemically to make a compound, the relativeamounts had to fit a clef-mite proportion ifnone of the elements was left over after thereaction was complete.

Thus emerged the picture of all mattermade up of a relatively small number ofchemical elements, each of which consisted ofsmall, indivisible, and identical atoms. Theseelementary atoms combined in definite pro-portions to form molecules, which were thesmallest units of compounds formed fromtwo or more elements.

Dmitri Mendeleev and the Periodic Table of Elements

Throughout the 19th century this ideawas elaborated into a complete theory of thenature of matter far grander and more unifiedin scope, and much more concrete in applica-tion than Lucretius ever dreamed of. DmitriMendeleev, a Russian chemist, perfected theperiodic arrangement of elements thatbrought out the similarities of groups, such aschlorine, bromine, and iodine, and showedgaps indicating undiscovered elements. This

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arrangement also gave order to the idea ofvalence, which pointed the way to systematiz-ing the kinds of compounds that any elementcould form.

The Chemical Nature of Matter

In the last half of the century a greatflowering of organic chemistry occurred, andthe structures of a great variety of biologicallyimportant compounds were worked out. Thevast variety of nature, both inanimate andanimate, was surely and steadily yielding tothe discovery of what seemed to be herinnermost secret..

That secret was the underlying simplicityof some 90 elements whose atoms formed theirreducible and eternal constituents of allmatter. With these atoms the almost infinitevariety of molecules could, in principle, andincreasingly in fact, be built in precise ways,which were described by chemical formulaethat revealed their exact structures. Not onlycould the I.9t.h century confidently supportLucretius that "sky, sea, lands, rivers, andsun, grains, trees, and breathing things" areput together out of these 90 elements, but itcould go further and show precisely whichatoms were involved in each case and howthey were combined.

Atomic and Molecular Motion

Striking as this achievement was, theatomic theory of the 19th century wentconsiderably beyond it by explaining a varietyof other phenomena with its atoms. The firststep was the recognition that heat is mechan-ical energy at the atomic level. This was

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verified quantitatively in a series of beautifulexperiments during the first half of thecentury. In a gas, like air, the molecules are incontinual motion. The temperature of the gaswas a measure of the average energy of anygiven mode of motion (rotation, vibration,etc.) of which the molecules are capable.

When the gas is heated, the total amountof energy put into it distributes itself over allmodes of motion of all its molecules. From aknowledge of these modes of motion and thenumber of molecules in the gas, the tempera-ture rise for a given input of energy can beco mpute d.

Moreover, the pressure exerted by the gason the walls of its container is the result ofthe continual bombardment of moleculesstriking the walls and reflecting from them. Insolids, the atoms and molecules can onlyvibrate about fixed positions. When a solid isheated, the energy goes into increased vibra-tion of the atoms, and the temperature isincreased in proportion as the average energyof each mode of vibration is increased.

This line of development led to theformulation of thermodynamics as a generaldescription of the behavior of heat in allphysical or chemical systems. By the end ofthe century the properties of gases were welldescribed in the kinetic theory. James ClerkMaxwell and Ludwig Boltzmann had devel-oped statistical mechanics so that it gave adetailed picture of the distribution of veloci-ties throughout the molecules of a gas, themanner in which atoms or molecules shareenergy among themselves, and the differentways in which they are free to move- The

19 15

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solid, liquid, and gaseous phases of matterwere well understood m a general way.

This atomic theory of the 19th centurywas an immense achievement of human un-derstanding. When the century began, the ideaof atoms had scarcely changed since Lucretiusand his Greek atomist predecessors. As itcame to a close, most of the elementaryatoms of nature had been identified and theirrelative weights determined.

A tremendous number of substancesmetals, minerals, salts, fluids, gases, and numer-ous organic materials found in living sys-temshad been precisely defined as specificcombinations of these elements. The motionsexecuted by these atoms or molecules had alsobeen meticulously defined. The several statesin which matter is found were rather wellunderstood in terms of forces between mole-cules and the motions of the molecules.

Much insight had been achieved into themechanical and thermal properties of dif-ferent substances in their solid or gaseousphases. The nature of matter was understoodin a beautifully structured system of greatinternal consistency and elegance. such aseven Lucretius in his most fanciful momentscould never have imagined possible. Not onlywas this synthesis conceptually elegant, but itfurther authenticated itseff by leading tomany practical applications in syntheticchemicals, steam and internal combustionengines, and the like.

In the first flush of enthusiasm over suchan achievement in a bare hundred years ofhuman history, the universal tendency was tothink of nature as more or less transparent.

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The secret of matter seemed to lie not farbelow the surface. The achievement was theresult of many investigators working in dif-.ferent fields oi a variety of seemingly unre-lated problems. Yet the results of their laborsoften converged to bring out some new andunexpected facet of the total picture.

It was as though nature were like a vastmaze with many openings on its perimeterthrough which scientists entered in search ofher secrets. Yet as successive hurdles to under-standing were overcome, the separate chan-nels of the maze seemed to be leading to theone great secret at the center. Wherever onestarted at the surface, one would ultimatelywind inward to this central principle at theheart of reality.

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From the oscillating universe, beating like a giganticheart, to the puzzling existence of antimatter, order,in a human sense, is at least partially an illusion. Ours,in reality, is the order of a time, and of aninsignificant fraction of the cosmos, seen by thelimited senses of a finite creature.

Loren Eiseley

The Planetary Atom

The quest for the central secret of thenature of matter in the 20th century has hadmany surprises. Not the least of thesc is therealization that there seem to be limitlessdepths in nature. The feeling at the end of the19th centurythat the explanation of naturelay just below the surface and that its majoroutlines had already been mapped outhasprcwed to be quite deceptive.

We have been plunged successively intothree deeper levels below that reached by thebeginning of the century. Each of these levelsis something like a whole world undergirdingand explaining the one above it. Yet at eachstage of exploration of one level the veryexistence of the level below was unrecognizeduntil most of the exploration in the precedinglevel had been carried out.

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Michael Faraday

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Throughout this century the quest for the

secret of matter has been an exciting one

filled with amazement and many surprises

along the way. As a result we no longer think

of nature as shallow and of matter as basically

simple and rather obvious when its secret is

revealed. On the contrary nature seems to

have apparently inexhaustible depths and

matter to have inner symmetries and struc-

tures of great beauty, which are neither

simple nor obvious but rather intricate and

strange.The 19th century atoms were hard elastic

spheres with no inner structure of their own

and possessing mass as the sole basic property

of the matter of which they were constituted.

Yet parallel with the development of the

atomic synthesis, which the chemists and

thermodynamicists were achieving, a number

of physicists had been investigating an ap-

parently unrelated phenomenonelectricity.When dissolved in water a number of atoms

became electrically charged. Such charged

atoms were called "ions".

Michael Faraday and Electrolysis

Michael Faraday had studied the process

of electrolysis (familiar in electroplating and

in storage batteries) of such ions in solution.

The most important result of his investiga-tions was that the amount of electricity onions of all kinds was always a simple integral

multiple of a fundamental amount, either

positive or negative; this unit is called the

faraday.

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This was the minimum amount of elec-tricity carried by a sufficient number of ionsto make a mass in grams numerically equal tothe atomic weight of their atoms. How manyatoms were required to do this was unknownthen, so that the amount of mass and electriccharge on each ion could not be determined.

Electricity and Magnetism

In other studies it was also found thatmetals and some other substances had theproperty of conducting electricity. A currentof electric charge could be made to flowthrough them continuously under certainconditions. Different metals were character-ized by offering different amounts of resis-tance to the flow of such a current.

Yet for most of the century the relation-ship between these electrical properties ofmetals and of ions in solution and thedeveloping atomic theory was not suspected.Electricity and magnetism were simply in-teresting auxiliary phenomena to be studiedin their own right, but not apparently signifi-cant in the quest for the secret of matter andthe atoms of which it is made.

The Electron

Then at the very end of the Century,Wilhelm Roentgen discovered the mysteriousX rays and Joseph J. Thomson discovered.theelectron. Suddenly with these discoveries elec-tricity came to play a fundamental role inatoms. The new electrons were over a thou-sand times less massive than even the lightest

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Wilhelm Roentgen

J. J. Thomson

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atom and yet they were clearly a constituentof matter. In the first quarter of this centurya series of brilliant experiments led to thedevelopment of the solar system model ofatoms, which is still the popular picture in thenonscientific world.

Other Atomic Particles

Far from being pictured as the simpleelementary spheres of the last century, atomswere now seen to be complex structures ofmore elementary particles. These particles arethe neutron, proton, and electron. Each atomconsists of a small central body called thenucleus, which is made up of neutrons andprotons and contains almost all the atom'smass. A number of negatively charged elec-trons equal to the number of positivelycharged protons move around the centralmassive nucleus in planet-like orbits.

This picture of the nature of matterdramatically reduced the number of elementsfrom the 90 or so atoms of the chemists tojust three basic elementary particles. Protonsand neutrons could be combined in a varietyof ways so as to obtain a rich assortment ofnuclei.

In these combinations the number ofprotons determined which of the chemicalelements that nucleus would form when itcollected itS full complement of electrons.Tills is because the chemical properties of theatom, such as the kinds of molecular com-pounds it would form, its position in theperiodic table, etc., depend only on the

electrons circulating around the nucleus, andnot on the properties of the central nucleusitself.

By analogy we might suppose that thedifferences between our solar system andother similar ones would depend on thenumber of planets in them, their size andmass, and the kinds of orbits they executearound their central sun. The stars at theircenter would be very much like our sun. Inthe case of atoms, those with one electron arehydrogen, those with six are carbon, thosewith twenty-six are iron, and those withninety-two are uranium.

Nuclei with the same number of protonsbut different numbers of neutrons are called"isotopes" of the same chemical elements.Thus the simplest element, hydrogen, withonly one proton and one electron has threeisotopes. The lightest and most common hasno neutrons at all and its nucleus consists of asingle isolated proton. Heavy hydrogen ordeuterium has a nucleus with one proton andone neutron, and a radioactive form ofhydrogen called tritium has one proton andtwo neutrons in its nucleus.

Electricity and the Structure of Matter

With this picture of the atom, electricitycame to be seen as an integral part of thestructure of matter. Faraday's ions in solutionwith their special properties in electrolysiswere seen to be atoms of their chemicalelement with one or more electrons removedfrom or added to them.

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A metal such as copper could conductelectricity by having electrons move ratherfreely from atom to atom.. But perhapsthe most striking result of this model ofan atom was its application to theemission of light by atoms.. Toward theend of the preceding century the brilliantwork of Heinrich Hertz and Maxwell haddemonstrated that light is a wave motion ofelectric and magnetic fields, and that theseelectromagnetic waves can be generated withsuitable equipment so that radio and radarbecame possible.

It was quickly seen that the characteristiclight emitted by various atoms in a flame oran electrical discharge, such as a neon tube,came from changes in the motions of theelectrons in orbit in the individual atoms. Ineffect each atom could be regarded as aminiature radio or radar sending and receivingstation_ Thus the phenomenon of light be-came intimately involved with atoms. Atomsas electrical systems are the universal emittersand absorbers of light.

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Ruz Lhuihier

The Wave Atom

At this stage of our understanding ofmatter, it did seem that the progress ofscience involved the clearing up of onemystery after another so as to reveal a verysimple and unmysterious mechanical structureas the universal base of all things.

But from this point on, the furtherdevelopment of our scientific understandingof matter has taken a very different turn. Thisturn was forced on us by a number of severedifficulties encountered by the end of thefirst quarter of this century with the solarsystem model of atoms. The chemical atomsof the 19th century were hard elastic spheresthat could collide with each other and re-bound like billiard balls. Miniature planetarysystems are neither hard nor elastic. Collisionsbetween them should simply scatter the elec-trons like chaff. This is only one of severaldifficulties that the planetary atom en-countered_

3127

The second quarter of the century wasdevoted to the development of a new andvery strange picture that resolved all thedifficulties of the planetary atom with re-markable success. But this success has beenachieved at the cost of giving up 19th centuryexpectations that the secret of matter wouldbe simple and easily understood in terms ofordinary human experience.

The Electron as a Wave

In the new picture the electron is nolonger a particle occupying a definite place.but has become a wave centered on thenucleus and filling the whole atom. Freeelectrons in space are like waves on the ocean:they have a wide expanse and travel in thedirection in which the electron as a particlewould be moving. The positive charge in thenucleus of an atom attracts the negativelycharged electron wave to it and constrains itto vibrate in a fixed pattern centered aroundthe nucleus. These wave patterns are ratherlike those formed by a vibrating membrane ordrumhead. There is a fundamental mode ofvibration and a sequence of overtone modesas in the case of a violin string or a drumhead.

There is a strange relationship betweenthe frequency of the wave and the energy ofthe particle. When two atoms or moleculescollide, thc wave frequency rises sharply astheir elecil-on waves begin to overlap. Thecorresponding increase in energy results in apowerful force pushing them apart. The effectis exactly the same as a collision of two hard

28 3 2

eiastic spheres. Yet the electron waves are thevery opposite of our normal ideas of "hard-ness" or "solidity". Moreover the waves arenot motions of anything in our ordinary spacebut are rather waves of chance or probabilityin a shadow space called "configurationspace".

These electron waves account beautifullyfor the identity of all atoms of the sameelement. The wave patterns formed by vibrat-ing electron waves are determined solely bythe electrical force exerted on the wave bythe nucleus, and so produce identical patternsin all atoms with the same charge. In thesimplest atom, hydrogen, the electron vibratesin the lowest frequency or fundamental modein every hydrogen atom in the universe that isin its normal or undisturbed state. Thushydrogen always has the same physical andchemical properties and its atoms always areidentical in size and spherical shape.

If energy is added to the electron in ahydrogen atom by a collision with anotheratom, by electrical means, or by the absorp-tion of light, the electron wave may beexcited to vibrate in one of its higher fre-quency overtone modes, lt then drops to alower frequency mode by emitting a particleof light called a "photon" whose wave fre-quency is equal to the difference between thefrequencies of the electron wave's two modesof vibration between which it was produced.

Thus the light emitted by hydrogen atomsforms a spectrum of discrete frequenciescorresponding to the spectrum of overtonemodes of electron wave vibration in the atom.

33 29

One hundred and fiftyfoot spectrographic ab-mrption tube used tostudy the atmospheresof planets.

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Spiral galaxy photographed edge on.

The Spectrum of an Element

Each element has a characteristic spec-trum that can be used to identify it even in thelight from distant stars. lf the electrons wereparticles moving in orbits, they should radiatelight continuously with steadily increasingfrequency as the electron spiraled into thenucleus. There would be no discrete spectrumand no normal or undisturbed state at whichfurther radiation of light would stop. Butwhen the electron wave reaches its funda-mental mode of vibration there is no lowerfrequency overtone mode to which it can goand so no possibility of further radiation.

For example, a tuning fork can be forcedto vibrate in any one of its overtone modes,but there is no way for it to produce a lowerpitch than its fundamental tor.e. It is the samewith atoms.

Another feature of the chemical elementsfor which the planetary atom could notaccount was their arrangement in the periodictable and the associated valence forces be-tween atoms by which they form molecules.This the wave atom accomplishes with re-markable precision and faithfulness to all thelaws of chemistry.

The number and characteristics of variouspatterns of electron waves just match theperiodic arrangement of atoms. Resonancesbetween wave vibrations in different atomsresult in a decreasing frequency of wavemotion as the atoms move closer together.This gives rise to attractive forces between theatoms corresponding to their decreasing en-ergy, and these forces are of exactly the samestrength and direction as those observed inmolecules built of these atoms.

Indeed, the beautiful symmetries of snowcrrstaL are a direct reflection on a macro-scopic scale of the interlocking hydrogen andoxygen wave patterns responsible for formingthe water molecule. With the planetary elec-tron atom, none of this could be understood,and there was no explanation for the kindsand forms of molecules created out of atoms.The figure on the next page shows someelectron wave patterns in the hydrogen atom.

Photographsflakes.

of snow-

31

Third overtone mode

First overtone mode

Fundamental mode

The patterns of vibration of the electron waves in a hydrogen atom are

shown above for the lowest frequency fundamental mode and for

several higher frequency overtone modes. The fundamental mode has

the lowest energy and is the one occupied in all hydrogen atoms in their

normal state. In an electrical discharge tube filled with hydrogen, the

atoms are excited into various overtone modes. As they make

transitions back, they emit the light spectrum characteristic of

hydrogen.

32 36

These are only a few of the ways in whichthe wave atom has succeeded where theplanetary atom simply would not work.Within the nucleus itself, where neutron andproton waves vibrating in discrete patternswith fundamental and overtone modes areinvolved, it has been very successful too. Theextent to which this wave theory of matter,called "quantum mechanics", mirrors every-thing we have been able to observe aboutmolecules, atoms, and nuclei is so broad andso precise that its reality can scarcely bequestioned.

Yet in our search for the secret of matterit has forced on us a very strange pictureindeed. These matter waves are some-times called "probability waves" because theiramplitude at a given point is connected withthe probability of finding the particle at thatpoint. They are just about as insubstantial asanything that can be imagined. Yet they giveatoms their shape, size, hardness, and elas-ticity, and they determine the forces thatatoms exert on each other in forming mole-cules.

33

e

Looking upward and outward into the heavens hasalways held a special appeal for the inquiring humanspirit. But much of the knowledge achieved in ourcentury about what happens in the astronomicalreaches of space has been learned by peering down-ward and inward into the innermost recesses ofmatter. Particle research has given new objectives andnew impetus to cosmology, the science whose prov-ince is the universe as whole, its origins, its develop-ment and its ultimate destiny.

Victor Guillernin

Inside the Elementary Particles

At the outbreak of the second world war,it seemed that a rather complete and fullunderstanding of matter was within reach.The triumphs of quantum mechanics werenumerous and remarkable. They explainedthe wave atom and molecules and had made amost promising start on the structure ofatomic nuclei. Just four elementary particleswere required to account for the wholeuniverse.

One could see how the nuclei of allatoms were what they were because of thelaws governing the combinations of neutronsand protons out of which they were consti-tuted. Given these nuclei, electrons wouldthen assemble in well-defmed states of vibra-tion with predictable wave patterns to formall known atoms. These in turn could com-bine to form the molecules, crystalline solids,or liquids needed to account for all themanifold diversity of nature as we experienceit.

39

36

Added to this was the particle of light orradiation, the photon, which accounts for theexchange of energy between atoms and mole-cules. We had almost in hand with these fourelementary constituents of matterneutrons, protons, electrons, and photonsanearly complete and universal picture of thestructure of matter. It was and still is abeautifully coherent and all-embracing pictureof the world. We seemed close to grasping thesecret of the nature of things that Lucretiushad so ardently longed to unlock.

But there were a few isolated phenomenathat did not fit this otherwise universalpicture. At the end of the 19th century thephenomena of electricity and magnetism andthe existence of electrically charged atoms orions did not agree with the atomic theory.They seemed to be minor exceptions, butthey provided the key that led to the nextstep in depth by revealing the nuclear atomwith electrons. So at this stage what seemedto be unimportant exceptions to the generalpicture now appear to be leading us toanother deeper level beneath or inside theneutron, proton, and electron.

Antimatter

These exceptions were the phenomena ofradioactivity and the discovery of antimatter.

A radioactive nucleus transforms itselfinto the nucleus of an atom one step higher inthe periodic table of elements by emitting anelectron and another particle called a "neu-trino". The neutrino is an uncharged electron,which, like the photon, is massless.

4 0

The other exception was the discovery ofthe antielectron or positron. This was the firstinstance of what we now know to be a generalproperty of matter, namely, that for everyparticle of matter there is a kind of mirrorimage of it made of antimatter. A photon ofsufficient energy can disappear and in itsplace an electronpositron pair can materi-alize. Part of the energy of the photon is usedto create the masses of the particle and theantiparticle, and what is left over is sharedbetween them as kinetic energy.

When a negatively charged electron andpositively charged antielectron come together,they annihilate each other, and the energy oftheir masses is shared between two photonsradiating away from the point at which theelectrons disappeared. All the properties of anantielectron except for its mass, are theopposites of those of an electron. The anti-electron did not fit the otherwise uniformscheme of things ,any mere than did theuncharged electron 6: neutrino.

Strange Particles

The period since 1950 has seen a profuseelaboration of other strange particles that donot conform with the theory that prevailed inthe second quarter of the -century.

Leptons

They divide themselves into two classes.The first class, is called "leptons", meaninglightweight or tiny particles. Two of these areuncharged electrically and are neutrinos. Aneutrino has zero mass and therefore always

41 37

38

travels with the speed of light At the speed oflight a rotating or spinning object must spinusing the direction of its motion as an axis.Both neutrinos spin counterclockwise asviewed along their direction of motion and soadvance like a left-handed screw.

The neutrinos can be electrically chargedbut will take only a negative, never a positive,charge. When charged, one of them becomesan electron and the other a heavy electron or"rntion". It is as though one of the neutrinoswere very small and the other some 200 timeslarger. (The work required to concentrate thesame amount of electric charge on the smallneutrino would then be 200 times greaterthan that required to put it on the largeneutrino.) Since the rest mass of a particlemeasures the work required to produce it, theelectron would then be a charged large neu-trino, and the heavy electron or muon wouldbe a charged small neutrino with a rest massmore than 200 times that of the largeneutrino.

These four particles of matter have fourmirror images of antimatter in which theirspin and electric charge are reversed. The twoantineutrinos both spin clockwise aroundtheir direction of motion and so advance likeright-handed screws. The antineutrinos canonly be charged positively. The charged largeantineutrino is the antielectron or positron,and the charged small antineutrino is theheavy aittielectron or positively chargedmuon.

In addition to these eight, there are twoother leptons, which are radiation particles (asopposed to matter parttcles). One is the

42

quantum of electromagnetic radiation or lightcalled the photon. It has zero rest mass and aspin double that of an electron or neutrino.The other is the quantum of the gravitationalfield called the "graviton". It also .has zerorest mass but a spin twice that of the photon.

These ten leptons form a group by them-selves. We have some idea why photons andgravitons exist or at least where they fit in the

Neutrino interactions in a spark chamber.

scheme of things. But so far we have no hintas to why neutrinos and electrons exist. Theneutrino is as near nothing as anything can beand still be something. It is a point ofspinning nothingness traveling at the velocityof light. Why there are two of :.hem and whatdistinguishes these two we do not know. (Itwas really simpleminded of me to call them"large" and "small" neutrinos. This distinc-tion does not really stand up as a physicalexplanation and should not be taken seri-ously.) We do not know why they will only

39

take a negative electric charge, nor do weknow why electric charge always comes innature in the units characteristic of theelectron or positron. These arc "mysteries" inthe detective story sense, however, whichsomeone may some day explain.

Given the two neutrinos and the fact thatthey will take only one unit of nativecharge, we can see, however, why there areonly two electrorts or charged neutrinos. Alsogiven these four particles, we can also see therelationship to them of their four mirrorimages or antiparticles. At the moment we seesome patterns and symmetries in nature andsome hints of their interrelationship but it isvery much like seeing "through a glassdarkly". There are fascinating hints here ofsome hidden principle of order beneath theobserved reality, which we ought to be able todiscover if we only knew how to get at it.This is one of the really great challenges forthe next generation of physicists.

Baryons

The I.;ptons play a very important role innature, but they are overthadowed by a muchmore complicated class of particles that makeup most of the mass and substance of matterin the universe. These are the "baryons",meaning heavy or massive particles, and the'mesons'', meaning intermediate particles.There are 18 basic baryons, which, with their18 mirror images or antibaryons, make agroup of 36. Eight of these have the sameamount of spin as the neutrinos and electrons,and the other 10 have a spin three times asgreat. The neutron and proton belong to the

first group and all 18 baryons make up"matter" in its primary form in the universe.

Mesons

The mesons form a different class ofparticles comparable to the radiation par-ticles, the photon and graviton. among theleptons. There are 17 basic mesons in all. Onegroup of eight has zero spin and the othergroup of nine has one unit of spin like thephoton. The mesons are related to the nuclearforce that holds neutrons and protons to-gether in the nuclei of atoms in much thesame way that photons are related to theelectromagnetic force and gravitons to thecrravitational force.

'This complicated array of what were firstreferred to as "strange particles" is a far cryfrom the neat scheme of building the wholeuniverse out of just four elementary constit-uentsneutrons, protons, electrons, andphotrmswhich largely characterized thefirst half of this century. Just as the firstquarter of the century was largely devoted tothe planetary atom and the second quarter tothe wave atom, so it seems that this thirdquarter is largely cerk..-erned with the quest forunderstanding this subatomic strata of strangeparticles on which the wave atom that makesup our familiar world rests.

Quarks

Quite recently a fascinating breakthroughhas been made that brings a geat deal oforder into this be, -ildering assortment ofstrange particles. It has been found that all 18particles of matter called baryons, including

4 5 41

the familiar neutron and proton, can beexplained by supposing that each one is acomplex system of three elementary particlescalled "quarks".* The corresponding 18 anti-particles are then made up of three anti-quarks. The 17 mesons are each a systemconsisting of a quark and antiquark in inti-mate association.

The quarks themselves are very strangeobjects indeed. Two of them make a pair of"common" quarks viith a positive electriccharge two-thirds that of an electron and anegative electric charge one-third that of anelectron. The third or "strange" quark hasone unit of a property called "strangeness"and a negative electric charge one-third thatof an electron. The neutron and proton andfour other baryons, called "delta" particles,are made up of only the first two or commonkinds of quarks and so have zero strangeness.The remaining particles have one or more ofthe third kind of quark in them and so one ormore (up to three) units of strangeness. Themost common meson, a triplet of threeparticles called "pions", and a single particlecalled the "eta , are quarkantiquark combi-nations involving only the common quarks.Others contain either a strange quark or astrange antiquark.

A few examples will show how all theseparticles can be constructed of quarks. De-note the two common quarks by P with an

-*Murray Gell-Mann, an American physicist, for-mulated the quark theory. He took the name from"Three quarks for Muster Mark", a line that H. C.Earwicker, a bartender, repeats in James Joyce'sFinnegan's Wake_

42

-"`""..1.4^^,T"." -,,Vvx.r.rnsps

electric charge of +2/3 and R with an electriccharge of 1/3, and the s:range quark by Swith a charge of 1/3 and one unit ofstrangeness. There are only four ways ofcombining the two common quarks intothree-quark particles. These are PPP, PPR,PRR, and RRR_ These constitute the fourdelta parqcles with electric charges +2, +1, 0,and 1 respectively. There are three combina-tions with one S quark, two combinationswith two S quarks and, of course, only onewith three S quarks. This last, SSS, is calledthe Omega Minus, but it had not beendiscovered at the time the quark theory wasdeveloped. It was predicted with all its physi-cal properties including its three units ofstrangeness and then was discovered sometimelater. This discovery was a great triumph forthe quark theory. All ten of these particleshave spins three times that of the neutron andproton.

The neutron and proton belong toanother group of eight baryons with smallspin. The neutron consists of two R quarksand one P quark and so has zero electriccharge since the R's have -1/3 each and the Phas +2/3 charge. The proton is two P quarksand one R quark and so has an electric chargeof +1 unit. Four others in this group have oneS quark and the remaining two have two Squarks each and so two units of strangeness.

The quark model is remarkably successfulin accounting for the whole complicated arrayof baryons and mesons with all their proper-ties of spin, electric charge, strangeness, andmass. This success rather persuasively estab-lishes the reality of quarks as the inner

43

structural element of all these particles. Yet

so far every effort to observe them has been

unsuccessful. It may be that they are somassive that none . of our present high-energy

particle accelerators provides sufficient energy

to dislodge one from a neutron or proton. A

major motive for building an ii_imense 200

billion electron volt (Bev) accelerator* is to

determine whether this will be sufficient to

produce individuai quarks.On the other hand, it may well prove to

be the case that quarks can only occur in

combinations of three or in pairs of quarks

and antiquarks. If this were really a law of

nature, then quarks could never be observed

singly or in pairs, but only in the combina-

tions already observed. In that case they

would remain an interesting and successful

mathematical device for explaining what we

do observe, but their reality and existence

would remain questionable. Mv own opinion

is that this latter alternative is the probable

one, and that individual quarks will never be

observed. This, however, is only an opinion or

hunch, and other physicists deeply involved in

this question do not share it.

'This is now being built at the National Accelera-

tor Laboratory near Batavia, Illinois.

The 2-mile electron accelerator at Stanford Uni-

versity.

44

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41111116

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....1."Ilik.

The same thrill, the same awe and mystery, comeagain and again when we look at any problem deeplyenough. With more knowledge comes deeper, morewonderful mystery, luring one on to penetrate deeperstill. Never concerned that the answer may prcvedisappointing. but with pleasure and contVence weturn over each new stone to find unimagined strange-ness leading on to more wonderful questions andmysteriescertainly a grand adventure!

Richard Feynman

The Mystery of Matter

We have come a long way since the earlyGreeks in our search for the secret of matter,and there have been many surprises along theway. Let us pause and reflect on what e

have learned from the quest so far.One thing we have learned is an apprecia-

tio:i for the depth, openness, and strangenessof nature. For the 19th century and the firstpart of the 20th, mture seemed shallow andmore or less transparent The secrets of natureseemed to lie just below the surface of things.The word "mystery" was never used inscientific writing, because it was widely be-lieved that science was rapidly dispelling all

tz 47

J. Robert Oppenheirner

mysteries. Everything seemed to be fittinginto an intelligible and rather simple pattern.Soon one could anticipate a single greatformula that would explain everything.

The actual course, as we have seen, hasproved quite different. Nature has shownunexpected and amazing depths. The questfor the secret of matter has led us down intoone depth after another. At each plunge theworld that has been revealed to us has:-Jssessed strange new wonders and sym-metries. At each stage it has proved amazinglyintelligible to the human mind, but never-theless in terms increasingly far removed fromthe obvious or familiar world of our everydayexperience.

J.Robert Oppenheimer* has likened all ofscience to a vast underground palace with anunending series of interconnecting rooms. Atfirst as we began to explore the antechambersnear the entrance, it seemed a familiar build-ing of limited size much like other buildingswe were familiar with. But as this century hasadvanced unsuspected rooms have been en-tered and surprising interconnecting passage-ways discovered. Each new room or suite ofrooms has been full of surprises, strange newbeauties, and unsuspected wonders. Yet eachtime we began to think that we had reachedthe palace boundary and were in the inner-most rooms, hidden doorways have beenstumbled upon, which have led us into stilldeeper and more amazing sections of thepalace.

*Science and the Common Understanding, Simonand Schuster, Inc., New York, 1954, pp. 83-85.

Others have likened science to a crystalgrowing in solution and revealing neu sym-metries and beauties as the fmgers and facetsof the crystal multiply. The crystal has aunity of its own, but it is unbounded in itspossibilities for new growth. As science hasdeveloped, each mystery that has been clearedup, each question that has been answered hasonly posed several new questions.

This quality of reality in which eachquestion opens up several more questions in adivergent rather than coavergent series repre-sents genuine unfathomable mystery. It is nota question of individual mysteries that can hesolved one at a time. Instead it is an overallstate of affairs characteristic of the wholequest for understanding reality itself. Thissituation alone has introduced a sense ofmystery and wonder into modern science,which is quite the opposite of the spirit ofscience in the 19th century.

There are many ways in which the questfor the inner secret of matter has developedthis sense of mystery. For the 19th century,matter possessed the one simple property ofmass. By now we recogri:ze several inde-pendent properties in complex admIxtures indifferent samples of matter. It is by virtue ofmass that the gravitational attraction of ob-jects takes place. Electric charge determinesthe electromagnetic forces on matter and iswholly independent of mass. A third prop-erty, possessed by neutrons and protons butnot by electrons (ordinary or heavy), mightbe called "nuclearity" and determines thevery strong force that holds neutrons andprotons together in nuclei. Another property

Polyhedral salt crystalsgrowing from solution.

49

determines tb ability of matter to emit orabsorb unchargt:d electrons or neutrinos.

If quarks exist, they possess a fifth prop-erty indeF .trident of these others by virtue ofwhich they exert immensely powerful attrac-tive forces on each other- The three commonconstituents of matter possess these proper-ties in varying combinations- The electron hasmass and electric charge but no nuclearity;the neutron has mass and nuclearity but noelectric charge; while the proton has all three.

Even more amazing than this variety inthe basic composition of matrtr is the exis-tence for every form of matter of its mirrorimage in antimatter_ Because of this, matterand antimatter can be materialized in equalquantities and then later be annihilated. Thislends an impression of insubstantiality andtransitoriness to matter, which is quite atvariance with earlier convictions about it. Thischaracter of matter is further emphasized bythe universal applicability of quantum me-chanics whereby all particles of matter dis-solve and smear out into probability waves inconfiguration space.

The old materialism that reduced every-thing to simple masses in motion has certainlybeen swept away_ The contemporary materi-alist must visualize material reality in terms ofmatter and antimatter waves in a kind ofshadow world, and consider them to be madeup of mass, charge, nuclearity, and other basicconstituents according to various recipes. It isa strange and shadowy kind of materialismwith none of the simple, substanlial, andsturdy obviousness or the old establishedkind_

50 5 4

00-Y

In preparation for Conp-essional hearingsbefore the Joint Committee on Atomic En-ergy on the national program in high-energyphysics, a collection of papers by leadinghigh-energy physicists was prepared for thepurpose of asking for the appropriation oflarge funds for constructir the 200-11evaccelerator. Something of the new spirit ofscience with its aura of mystery about thequest for the secret of matter is conveyed inthe concluding paragraph of the paper bySteven Weinberg in this collection:*

Instead of feuding with one another forpublic favor, it would be fitting for scientists tothink of themselves as members of an expeditionseat to explore an unfamiliar but civilized com-monwealth whose laws and customs are dimlyunderstood. However exciting and profitable itmay Ee to -..-stablish themselves in the rich coastalcities of biochemistry and solid state physics, itwould he tragic to cut off support to the partiesalready working their way up river, past theportages of particle physics and cosmology,toward the mysterious inland capital where thelaws are made.

Earlier generations of scientists wouldnever have spoken of what they consideredthey were up to in such terms or with such animage. Yet passages such as this appear withincreasing frequency in contemporary scien-tific literature. The whole atmosphere todayis in sharp contrast to that of the last century.Yet the notions about science that character-ize the attitudes of the general public todayare still largely derived from the convictions

*Nature and Matter: Purposes of High EnergyPhysics, L. C. L. Yuan, (Ed.), Brookhaven NationalLaboratory, Upton, Long Island, N. Y.

55 51

52

about it that scientists held early in thiscentury.

It is interesting to speculate on where thequest for the secret of matter may ultimatelylead. If quarks exist and individual ones are intime observed, a persistent question aboutthem will remain. _ re they the ultimateelementary particles of nature, or is there astill deeper level that describes what quarksare made of? On the other hand, if quarkshave no individual existence, perhaps thebasic reality of matter is to be found in themathematical operation that defines them_This operation is a rotation in a special kindof space called "Hilbert Space", which Isknown as a special unitary transformation inthree dimensions and designated as SU(3).

Indeed, there is an alternative to quarkscalled the "bootstrap" model in which all ofthe many baryons and mesons are sirr plycombinations of each other. In this Tut delthere are no elementary constituents of mat-ter but instead a democracy of particles eachof which is a combination of two or moreother particles. Matter then materializesthrough a mathematical operation that pro-ducef, it out of nothing in much the same wayas a man lifting himself by pulling on hisbootstraps- At the moment we do not knowwhich of these possibilities, if either, willprove to be the case.

i'his situation suggests a parallel to afamous passage in the Chandogya Upanishadin which a father instructs his son about thenature of reality through various actions likepeeling an onion, or dissolving a grain of saltin water_ As layer after layt is removed, the

boy finally reaches a point at which he findsnothing at all. There is a void at the heart ofthe onion, and the salt grain disappears as thelast layer dissolves. Yet the father explainsthat the invisible central point is the ultimateessence, not only of the phenon.cnal universe.but of the boy himself: "That which is thesubtil essense, in it all that exists has its self.It is the True. It is the Self, and thou, 0Svetaketu. art it.-*

The 19th century belief that the mazethrough which it was threading toward theone geat formulathe essence of all ma-terial existence at its certeris being re-placed by another possibility that suggestsitself more and more insistently: In theinnermost chamber we will find simply noth-ing. The end of the quest for the secret of

*A Short Comparative History of Religions, T. H.Robinson, Gf-ruld Duckworth, London, 1951, p. 80.

":53

matter mav be no "thing" existing in spaceand time at all, but rather a hypotheticalquark that doesn't exist or: a three-dimensional mathematical bootst ap opera-tion in Hilbert Space.

Like Plato's famous cave, it may turn ontthat the whole material universe in three-dimensional space and time with all its seem-ing substantiality is at heart made up of mereshadows of realities that transcend space andtim:7 and so are inaccessible to our directobservation. The mysterious probabilitywaves in configuration space that describe allthe components of atoms so completely aresuggestive of just such an outcome. So too isthe complementary relationship between mat-ter and antimatter. In any event, however, theaura of mystery that surrounds the wholequestion of the secret of matter seems now tobe a permanent characteristic that no con-ceivable future research is likely to dispel.

It should be evident from all this thatwhen we speak of "mystery" in science we nolonger mean unknown areas or puzzles whichresearch in the future may be expected toclear up. We are not speaking of a mystery ofanything unknown at all. Rather we arespeaking of the mysteriously amazing charac-ter of the known. There is a true mystery ofthe known and our modern knowledge inscience confronts us with that mystery verystrongly. A very important element of thismystery of the known is the way in which ourknowledge of matter keeps beckoning ustoward transcendent realities beyond spaceand time. The more deeply we probe into the

54

secret of matter the more our knowledgeseems to point us beyond spacetime.

The hints grow stronger that the under-lying reality of things in nature is to be foundbeyond nature in a kind of super-nature orhyper-nature in which all space and time isimmersed. But in all human experience theessence of mystery has resided in the sense ofan invisible and unseen reality enveloping thevisible and seen world of direct experience.Throughout the whole of man's life on earthexcept for just the last two centuries of hishistory this has been an essential element ofall human experience of external reality. It istoward a return to this primordial mysterythat the modern quest for the secret of matterseems surely to be leading us.

Mobile that is shown in motion on page 18.

The Museum of K.Idern Art, New Yk, Mary Canary Collection

55

Quotations

Fag

Inside cover Copyright ©1964 and 1969 by Loren Eiseley. e-and 19 printed from his volume The Unexpected Universe by

permission of Harcourt Brace Jovanovich, Inc.,New York.

3 and 47 From Frontiers in Science, Edward Hutchings, Jr., Ed.).Copyright C) by Basic Books, Inc., New York. Re-printed by permission.

56

Photo Credits

Cover courtesy Vincent J. SchaeferAuthor's photo courtesy Oak Ridcre Associa

Universities.Contents page c

England.urtesy Seiene

Top,Iiek Observatory; bottom Jan Hahn.Metropolitan.'Mnioum- f Art",'Ne* York,

Rogers Fund, 1911.Top, 1J,.S. Dellartment of Agriculture; bot-

, , _

tom, CyrilStanley Smith.,- Hale Observatories,-From

,

PSSC Physics D. C. Heath ari

om Discovery of the Elements,E;Weeks, Cherrucal-EdUcation:

any.

0

11

97

35

From Elementary Particles and Their Currents -eremyBenistein, 1969. Copyright © by W. H. Freeman Com-pany, San Francisco, California. Reprinted by permission.From The Buried Past: A Survey of Great ArcheologicalDiscoveries, Henri-Paul Eydoux, Frederick A. Praeger,Publishers, New York, 1966. Copyright © by GeorgeWeidenfeld and Nicolson, Ltd., London, England. Re-printed by permission.From The Story of Quanutri Mechanics, Victor Guillem1968. Copyright 0 by Charles Scribner's Sons,New York. Reprinted hy permission.

21 Top, Library of CongrThomson.

25 Hale ObservatoriesCurrent", Bridget Riley, 1964. The Museumof Modern Art Collection, New York,Philip Johnson Fund.

Top, Hale Observatories; bottom, NationalCenter for Atmospheric Research.

Vincent J. Schaefer34 "Color Motion", Edna Andrade, 1965.

Philadelphia Museum of Modern Art Col-lection, Photograph by A. J. Wyatt.

Nevis Laboratories, Columbia University andBrookhaven National Laborato

StanfOrd UniverlityWilliam -ThonsonAlan,W. Richards

LI

George Brazili-x,:Ine., New York=Twelfth century Chinese painting-after a 4t11

, to 5th century design attributed to 1Cu Wai-f the,ChirifdYnast}7..The Sr;iithsohian

_

on,- reer'Gallerk_ of Art, Washington,

rAlexandir _Calder, 1936.,

Modern' YOrk,-_

57

The Author

William G. Pollard, an articulate and well-known lecturer and author, isan Episcopal priest and a physicist. He has been executive director ofOak Ridge Associated Universities (ORAU) since 1947_ ORAU sponsorsnuclear-related research -and conducts a variety of programs for theeducation and training of professional people and the general public innuclear fields. Dr. Pollard received his BA, from the University ofTennessee, his M.A. and Ph.D. from Rice Institute, and his D.D. fromHobart College. He is the author of numerous articles and booksincluding Chance and Providence, Charles Scribner's Sons, 1958;Atomic Energy and Southern Science, ORAU, 1966; Man on aSpaceship, Claremont Graduate School and University Center, 1967.The Mystery of Matter is adapted from a chapter in his most recentbook Science and Faith: Twin Mysteries, Thomas Nelson and Sons,

1970.

The Cover

Photograph of a snowflake.

58

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Nature's Invisible RaysCurrent research involving the radiation that

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