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Biographical Memoirs: V.68 (1995)

Chapter: Walter M. Elsasser

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Suggested Citation:"Walter M. Elsasser." National Academy of Sciences. 1995. Biographical Memoirs: V.68. Washington, DC: The National Academies Press. doi: 10.17226/4990.
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WALTER M. ELSASSER March 20, ~ 904-October ~ 4, ~ 991 BY HARRY RUBIN WALTER ELSASSER WAS TRAINED as a theoretical physicist ant! macle several important contributions to funcia- mental problems of atomic physics, inclucling interpreta- tion of the experiments on electron scattering by Davisson en cl Germer as an effect of cle Broglie's electron waves and recognition of the shell structure of atomic nuclei. Circum- stances later turned his interests to geophysics, where he had important insights about the radiative transfer of heat in the atmosphere and fatherec} the generally accepted cly- namo theory of the earth's magnetism. He clevotect a major part of the last fifty years of his life to (developing a theory of organisms, concentrating on the basic features that clis- tinguish between living and inanimate matter, and he pro- clucecl four books on the subject. While his contribution to biology was not wiclely acknowlecigecI, he felt it wouIcI even- tually be seen as his major scientific achievement. BACKGROUND AND YOUTH Walter was born in Mannheim, Germany, the oIcler of two children of Maurice and Johanna Elsasser. His sister, Maria, was three years younger than him. His grandparents were prosperous Jewish merchants, but his father was a law- 103

04 BIOGRAPHICAL MEMOIRS yer who was caught up in the great wave of assimilation and both parents became nonpracticing Protestants. Walter was confirmed! in the Evangelical Church and had no iclea of his Jewish ancestry until the age of fifteen when an ac- quaintance unexpectecITy askocl him about it. His father gave evasive answers when he inquired about his ancestry, ant! it took about a year to learn the truth. Up to this time he had no notion of Jews as a separate group, but his Jewish iden- tity was to prove a crucial factor for him in the rising title or anusem~sm that culminated in the Hitler regime. One of the first manifestations of that antisemitism occurred in his last year of high school, when he applied to join a fra- ternity at the urging of his father who thought it would help turn his son from somewhat of an ociciball into an ordinary good German citizen. His application was rejectee! on the grounds of the so-called! Nurnberg articles acloptec! in 1919 by a national organization of fraternities which speci- fiec! that persons of Jewish crescent were inadmissible. Up to the age of thirteen Walter had a congenial up- bringing, although there were severe foot! shortages be- cause of WorIcl War I. His father, then in his forties, was callecl into the German army and because he was a lawyer was given a desk job at the headquarters of the Swiss bor- cler guard. Since he had earlier clevelopecI a severe ulcer, which was exacerbated by barracks foocl, he obtained per- mission to have his family join him. When headquarters were shifted from a small town to a Konstanz, the food shortage became more severe. His father's illness became so bad he was mustered out of the army and shortly after was promoter! to a judgeship at the Superior Court of Heidel- berg. Walter attendee! Gymnasium, which hac! a nine-year cur- ricuTum, roughly equivalent to the fourth through twelfth gracles in America. The emphasis was on classical subjects

WALTER M. ELSASSER 105 such as Latin, Greek, mathematics, history, and religion with only a smattering of physics and chemistry. This was in contrast to the alternative RealschuTe, which appeared in the nineteenth century en cl emphasized science, mathematics, ant! modern languages. He felt that the unpragmatic im- mersion into a past florid tended to bring out introverted] features that he already possessed. In any case, Germans preclominantly thought of science as a philosophical enter- prise, and Walter maintained a strong interest in the philo- sophical aspects of science throughout his career. THE ROAD TO SCIENCE Walter's first encounter with natural science came from a journal of popular science to which his father subscribed. The journal also issued a series of small books clearing with various subjects of scientific research, which he peruser! from the age of thirteen or fourteen. These were mono- graphs covering all branches of science by carefully chosen authors who knew their fielcis well and hac3 a knack for popular interpretation. He was particularly attracted to the books clearing with the mysteries of the discoveries of atoms and molecules, a curiosity that never left him. His math- ematics teacher around the eighth gracle took an intensive interest in him when he discovered Walter's interest in sci- ence and mathematics. They took Tong walks in the wooded hills arounc! Heidelberg ant! discussed everything concerned with science and the nature of scientific inquiry. In the ninth gracle, mathematics was chiefly concerned! with solicl geometry, which his teacher thought Walter could learn in a fraction of the time clevoted to it. He then suggested Walter get a book of calculus problems ant! do them in lieu of solid geometry. Walter worker! through these elaborate problems one by one and thereby acquired an extensive working knowlecige of calculus long before graduating from

06 BIOGRAPHICAL MEMOIRS Gymnasium. He also had a fairly good intuitive understand- ing of avant garde thought in physics from the monographs on atoms and crystals, light and X rays, and stars and galax- ies, which he read twice if not more often. Walter also found books of a philosophical character in his father's library, among them Ernst Haeckel's enormously popular The Riddles of the Universe. He already recognized the book as a statement of a very coarse rationalism or straight materialism. Although he disliked Haeckel's crude philosophy, the shock he received from it opened his eyes to genuine problems in the philosophy of science, which occupied much of his thinking in later years. Under pres- sure of antisemitism he began to identify with his forebears, the authors of the Bible. These men were unanimous about one thing that the understanding of nature, man, or God was not a wholly intellectual matter. This stood in contrast to Haeckel, whose world was nothing but Haeckel-like intel- lects trying to understand the world intellectually. Stimulated by such quasi-philosophy Walter started thinking about philosophy, in particular Hegel's dictum that, when quantitative differences in some field become pronounced, they tend to turn into differences in quality. This contrasts with the view of the great philosophers of science, that the scientist in his methods has no place for qualities: they pertain to philosophy proper, usually expressed as meta- physics. An example is the notion of heat, which first ap- pears to our perceptions as a quality but which physicists have shown is motion of molecules that can in all detail account for the properties of warm and cold bodies. Philosophical thinking eventually led Walter to the real- ization that the purpose of the scientific method, which is to structure the multifarious data of experience, is neither simple nor obvious. This is apparent in the example that for thousands of years wise men studied the motions of

WALTER M. ELSASSER 107 stars and clevelopecl complicates! mathematical descriptions for them. Arounc! 300 B.C. Aristarchos proposed that the earth rotates about itself and moves in an orbit around the sun, as did the other planets. This view was ignored as idle speculation for eighteen centuries up to Copernicus. Walter grew to realize that acceptance of scientific ideas clepencis on whether they harmonize with the prevailing icleas of society. These ideas are controlled by unconscious tenclen- cies and cannot be controlled by rational volition. He con- siclered "the current unrelieved and brutal dominance of pragmatism in science, often clothed in terms such as po- litical or other 'relevance'," a frightening development. Walter tried his hanc! briefly at the commercial enter- prise left by his grandparents. He was surprised at how much he likes! the work, primarily because it provided a frame- work for his activities. However, he had become deeply com- mittec! to scientific activity and die! not wish to abandon the sense of intellectual adventure fount! in any scientist of an inquisitive mind. He therefore returned to science with a renewed determination to become a physicist. He entered the University of Heiclelberg, where the professor of phys- ics was Phillip Lenarc3, who hacl received the Nobel Prize several years earlier. While still in high school Walter had occasionally skipped class to attend Lenard's lectures with their admirable demonstration experiments. Lenard was actively involved in right-wing politics and was later to re- tire from his professorship to devote himself entirely to the Nazi party, ending up as president of the Nazi Academy of Sciences. But in 1922 politics was far from Walter's mind when he enterer! the large lecture room for his first physics class. Every seat was taken as Lenard walked in wearing an impeccably tailorect suit bearing an enormous silver swas- tika. This was unusual as Germany was still a place of law anti order, and professors were not expected to brandish

08 BIOGRAPHICAL MEMOIRS symbols of political extremism in class. But the students gave him the longest, louclest, and most cleclicated ovation Walter ever witnessed either before or after. They had clearly voted for the swastika, ant! Walter, who knew what this meant for Jews, was cleeply disturbed. A number of people acivisecl him to leave after his first year, as he would then have to enter the laboratory where Lenarc! was as likely as not to grab him by the scruff of the neck anti throw him out bodily. He therefore clecidecI in the fall of 1923 to move to Munich, by far the best university in southern Germany. There were two kingdoms of physics in Munich, one heaclec! by the noted experimentaTist Wilhelm Wien and the other by the theoretician Arnold SommerfelcI. Walter clict consid- erable experimental work in Wien's institute and enjoyed it very much. During his third semester he worked assiclu- ously on such complicated matters as the Millikan oil drop experiment and the electrostatic quadrant electrometer. But the chief influence on him was SommerfelcI, who was as brilliant a teacher as he was a research man. Walter consict- ered Sommerfeld's classes the best he ever attended. In aciclition, he participated in Sommerfelct's weekly seminar on contemporary atomic physics attended by his assistants en c! a small number of students. The seminar stimulatecI Walter to read some scientific literature on his own. He particularly rememberer! a paper by James Franck of Gottingen on spectral lines that involved highly excited states of gaseous atoms. Calculations inclicatect orbits of the elec- trons that were incomprehensible from a simple mechani- cal point of view. This proviclec! an unexpected glimpse into a different orcler of nature in the minute dimensions of the atom that wouIcl soon be expressed in the mathematical language of quantum mechanics. In Munich Walter overIappecl for one semester with Werner Heisenberg, who then obtained his Ph.D. and went on to

WALTER M. ELSASSER 109 Gottingen. On several occasions he heard Heisenberg say that doing physics was fun. This came as a great revelation to Walter, who hac! grown up in the stolid environment of the German micictle class and who conic! think of scientific research only as a matter of duty or personal ambition or just to make money. The insight of cloing science for the fun of it left Walter exhilarates! ant! cleeply impressed. Walter became fond of traveling and hiking during his ..~ .. . years in southern Germany. While in Munich he took many weekend trips to the fore-Alps, staying in the numerous inexpensive youth hostels and hiking on the innumerable traits to the top of the mountains, often 2 kilometers high. He clecidect to become an experimental physicist, but early in his third semester in Munich an assistant professor ap- proached him with the advice that every single member of the faculty of Wien's institute asicle from the director ant! himself were card-carrying members of the Nazi party. It was, of course, in Munich in November 1923 that the abor- tive beer hall putsch by Hitler and Luclendorff, the former chief of staff of the German army cluring World War I, took place. Munich wouIc3 therefore not be a favorable place for Walter to continue to work toward his Ph.D. He suggester! that Gottingen was not only very good but "full of Jews." Walter asked Sommerfelct to write a letter of introduction to James Franck, whose work had so intrigued him, and he at once acceclec! to Walter's visit. When he arrivecl in Gottingen early in 1925, Franck accepted him almost im- mecliately as one of his Ph.D. cancliclates. THE WORLD OF GOTTINGEN Walter cleveloped a close relationship with James Franck, whom he admired greatly. Franck kept his office open, and Walter often founc! himself sitting on one end of an old battered sofa in lively discussion with Franck at the other

0 BIOGRAPHICAL MEMOIRS end. Franck's main interest was in the study of atoms and molecules by the simplest means possible, electrons and light. He hacl already shown that electrons transfer energy strictly in lumps or packages and hacI received the Nobel Prize for this achievement in 1925 along with his younger collaborator Gustav Hertz. Walter received for his thesis the subject of fluorescence, whereby one quantum of light is absorbed while another slightly different energy is emitted. While he was making technical preparations for this thesis work he would drop in now and then to Franck's office to question him about atomic physics, ant! Walter came to regard Franck as his main teacher of science. Max Born, the theoretician, was also a professor in Gottingen and the growing international reputation of Born anct Franck attracted many foreign students, among them Robert Oppenheimer, Robert Brocle, H. P. Robertson, and Patrick Blackett. Paul Dirac was a frequent visitor. Walter also hac! close interactions with German students in the institute ant! developer! close friendships with Fritz Houtermans ant! Wolfgang Harries. There were many inter- esting lectures in physics, especially theoretical physics. One course was a seminar titled "The Structure of Matter," which playecl a germinal role in the (levelopment of quantum mechanics. Although the seminar was Tong listecI under the name of Davis! Hilbert, the famous mathematician, he was no longer active en cl its conduct was left to Max Born. Walter was a regular attendant at the seminar throughout his stay · ~ ·- - ~n ~ott~ngen. One of the earliest presentations in this seminar was by Born's student, Friecirich HuncI, who later made major con- tributions to the theory of atomic spectra. The report was about an experiment of Davisson and Kunsman, two physi- cists at Bell Telephone Laboratories in New York. They shot electrons at a platinum plate and observed how they were

WALTER M. ELSASSER 111 scattered back. They found that the intensity of the distri- bution of the electrons varied with the angle of scattering, showing maxima and minima. This was a mysterious and quite surprising result, but the source was unimpeachable. Born tried to explain the result by the variable deflection of the extraneous electrons by shells of electrons that were of different densities. Without calculations it was impos- sible to know whether this suggestion was correct. One clay in May 1925 Walter found in the library two recent papers by Einstein on the effect of quantum theory on gases. Einstein shower! that certain gases behaved like assemblies of waves rather than particles. Twenty years earlier Einstein hac! noted that light, which everyone thought to be of wave motion, also had particle properties and that light was emitted and absorbect in packets called quanta. Coming from Einstein this was highly significant news. Einstein then noted a the- sis of Louis cle Broglie, which Walter found in the univer- sity library. The thesis contained de Broglie's basic iclea that all primary components of matter have wave proper- ties ant! presented a simple formula connecting the wave length with the particle's velocity. Walter wonclerecl whether Davisson and Kunsman's maxima and minima were cliffrac- tion phenomena similar to those produced by X rays pen- etrating crystals but produced by a slight penetration and reflection of the electrons. He easily calculated the energy of the electrons required for the maxima, en cl it came out just right. Since the experiments were still crucle, his sur- mise was only a guess but an exceptionally interesting and promising one. Walter talked with Franck about the problem and was encouraged by his opinion that the idea was interesting though speculative. Franck suggested Walter think it through carefully and write to Naturwissenschaften. A few weeks later he ctic! so and, after receiving Franck's approval, sent it off.

112 BIOGRAPHICAL MEMOIRS He later learner! that the paper was reviewer! by Einstein, who incticated that he was not sure how literally the idea of waves associated with electrons should be taken but thought the paper shouIcT certainly be publishecI, which it was shortly thereafter. In print it became a note about half a page in the folio-sized volume. Heisenberg wrote to Wolfgang Pauli about the importance of Walter's note, and it was repro- cluced by Max von Laue in 1944 in a book on matter waves. In 1927 the decisive publication of Davisson and Germer appearec! which clemonstratecT the wave character of elec- trons without a doubt. The authors referrer! to Schroclinger's famous papers of 1926 but not to Walter's note. Born pub- lishecI an article in 1926 in which he treated the collision of an electron with an atom as the scattering of a cle Broglie wave and then developecl a whole mathematical machinery for wave scattering. In this article Born introduced the no- tion of probability for the first time in quantum mechanics; he proposed that the wave function was a statistical guide for the particles in the sense that the amplitude of the wave specifies a probability for the particle to travel in certain ways. At the end of the paper Born quoted Walter's note saying he hacI correctly interpreted the experimental re- sults of Davisson and Kunsman. Publication of his note turned Walter's head anc! he asked Fran ck if he could experiment with the scattering of elec- trons by metal surfaces. This was quite foolish because that type of experiment is technically very clifficult, and Walter's skill was not up to it. Franck agrees! as Tong as he wouic} do it on his own, since Franck wouIcl not allow his group to engage in highly speculative exercises. Walter tried it for three months before he realized how silly it was for an inexperienced! young man to undertake such formiciably difficult experiments on his own. Among Franck's six or eight graduate students, Walter

WALTER M. ELSASSER 113 felt he was the least successful at buiTcling apparatus, a skill that was essential to an experimental physicist of those days. He also recognized that he was the most passionately inter- estecl in ant! most knowledgeable about physical theory. This was apparently recognized by Max Born, who, in the summer of 1926, asker] Walter if he wouicI consider becom- ing a theoretical physicist en c! doing a thesis with him. Af- ter consulting with Franck he decided to accept the offer and undertook an uncomplicated study of the collision of an electron with a hydrogen atom. This involves! straight- forward mathematical techniques with a large pile of for- mulas and offered few difficulties to Walter. He had few opportunities to discuss his work with Born, who worker! at home ant! exhibited little interest in seeing students. Walter was fortunate at this stage to have the help of Robert Oppenheimer, who couIcl steer him to the proper place in a mathematical book when difficulties dicl arise. One con- versation with Born Walter rememberer! well. Born, who was a mathematical virtuoso, told Walter that he was not outstanding in mathematics but strong in conceptual thought, where Born felt less secure. A common iclea is that concep- tual thought precedes precise mathematical analysis: mod- els ant! patterns emerge out of the primal chaos of data and thoughts of human experience and often cannot be preclictecI. Walter had aIreacly recognized that his great strength lay in conceptual thought, ant! his self-confidence grew stronger with age, so he fearer! no competition in this area. Walter chose astronomy and mathematics as his required minors in the Ph.D. program. The astronomy, which was mainly astrophysics, confirmed! the icleas of the uniformity of atomic physics anc! its laws. Mathematics in Gottingen involved some of the great men of the fielcI. It had been establisher! there by Carl Friecirich Gauss, one of the most

114 BIOGRAPHICAL MEMOIRS remarkable and versatile mathematicians who ever lived. Bernard Riemann, who hac! developed Riemannian geom- etry, hac! been a professor of mathematics in Gottingen. David Hilbert was consiclerect the grand oIc! man of math- ematics while Walter was in Gottingen. The mathematician closest to the Franck-Born group of physicists was Richarc! Courant. Many mathematicians visitec! Gottingen, among them Norbert Wiener, who Walter met and occasionally en- countered after he mover! to the United States. In his 1948 book Wiener generalized the concept of feed- back, which had been cliscovered in neural circuits a cen- tury before. In the wake of the rise of computer technology the subject dealt with by Wiener is commonly caller! sys- tems theory. It is the general mathematical theory of ma- chines that operate in a causal manner. By the time Walter had react Wiener's book, quantum mechanics tract lee! to a broac! confidence in the uniformity of nature, and he felt that from there one conic! attack the central problem in the philosophy of science, the relationship of inorganic sci- ence to organic life. In the early days of science, the age of the clockwork universe, Descartes hac! clecIared that there were two substances, matter and mincI; the body pertained to matter and was a machine pure ant! simple, an automa- ton. But to clecicle whether the body was simply an automa- ton, one hac! to know just what machines can and cannot clot This is exactly what modern systems theory claims to do, ant! Wiener had given the field its greatest impetus. He thus played a major role in framing Walter's approach to the problem of the relationship of inorganic science and organic life. Another mathematician Walter met in Gottingen was John van Neumann, who later influenced his scientific thought as much as any individual. von Neumann was one of Hilbert's assistants and was charged with keeping Hilbert abreast of

WALTER M. ELSASSER 115 new clevelopments in quantum mechanics. Walter only saw von Neumann in lectures anct seminars but had regular discussions with him at Princeton between 1946 en c! 1949 on their common interest in hydroclynamics. He Earned a useful lesson from van Neumann's celebrated 1932 book The Mathematical Foundations of Quantum Mechanics, namely that any moclel of organic life based only on the existence of statistical features of physics was likely to be false. Walter studied the book carefully, and it taught him that the intro- cluction of probabilities into physics, which is the most dis- tinctive feature of quantum mechanics, clic! not "loosen up'' the framework of the theory but matle it even more (leter- ministic in the mean ant! more suitable for reducing every- thing to physics than Newtonian mechanics had ever been. Although this was a valuable lesson for Walter, it deeply clissatisfiecI him because he distrusted! reductionism, espe- cially as appliecl to organisms. He struggled with van Neumann's book for years, both to absorb its technical de- tails en cl to explore its philosophical implications. It took some twenty years of this struggle for him to escape the philosophical impasse of the mechanistic nature of quan- tum mechanics ant! his distrust of reductionism in organ- isms. The escape consisted! of comparing the infinite sets of symbols unclerlying mathematical description with the fi- nite sets of observations that experience offers. This later took the form of heterogeneity or inclivicluality among or- ganisms as a key element in setting apart organic life from the inorganic world. More will be said about this in a later section (leafing with Walter's theoretical work in biology. THE TROUBLED YEARS Shortly after receiving his Ph.D. in 1927, Walter received an unexpected invitation from Paul Ehrenfest, a well-known theoretical physicist, to be his assistant in Leiclen, Holland,

6 BIOGRAPHICAL MEMOIRS for a semester and possibly longer, and he accepted. He wonderecl who had recommenclec! him since he dice not know Ehrenfest and concluded that it must have been Oppenheimer., Shortly before leaving for Leiden, Walter re- ceived a long letter from Ehrenfest concerned not with physics but with the latter's psychological problems. Walter worried about this strange behavior of explaining the complexities of his soul to a stranger half his age, soon to be his assis- tant. Ehrenfest met him at the train station in Leiclen and immediately took him on a long walk on which he recounted his psychological problems anc! appeared to be pleacling for help. Walter offerer! to help as much as he couIcI, but as events turned out this was not to be. Walter settled clown in Leiclen, enjoying the people, the city, ant! the countryside. He loved paintings and recog- nizect scenes painter! by great Dutch artists. He came to know H. A. Lorentz, the fame c! mathematical physicist, who brought Ehrenfest to Holland to be his successor. Walter served as Lorentz's assistant at a series of lectures. The lec- tures were at first utterly strange to him, as they differed radically in style from that of the German university. Lorentz started with general propositions in a pleasantly unclulating voice that tract a hypnotic effect and after ten minutes or so shifted to a very precise description of an electron as a little charger! ball. It then became clear how it moved in an electrical field. Walter drew a parallel between this lecture style ant! the cIair-obscure style of Rembrandt's paintings with their varying shacles of brown from which there emerges an intensely illuminated face or object. This visual simile allowed Walter to understanc! Lorentz's presentation, and he thereafter enjoyed the lectures immensely. Walter later wondered how much of his own thinking originated in those lectures. This involvecl the thought that a scientist ought to imitate nature in discovering how order can be created out

WALTER M. ELSASSER 117 of chaos. He then realized that there were two forms of creation, the first being the creation of raw inorganic mat- ter in the "big bang" or other cosmic crevice. But anyone who admits that living things are not just automata has to assume that there is an ongoing creative process in organic life that is much closer at hand ant! more reactily studier! than the cosmic process. Walter developec! pleasant friendships in Holland, but his relationship with Ehrenfest deteriorated as the latter changed from aggressiveness to downright hostility, for rea- sons Walter could not unclerstancI. One day after Walter had had a haircut with the usual barber's pomade, Ehrenfest came into his office and accused him of wearing perfume. Ehrenfest said he hated perfume, grew furious, and ordered Walter out. A few days later he tolc! Walter to go back to Berlin. It is perhaps not unrelated to this behavior that a few years later Ehrenfest killed his retarded son en c! com- mittect suicide. Walter was, of course, very upset by Ehrenfest's rejection and returnee! to his parents' home then in Berlin. He real- izec! that the entire episode would greatly reduce his chances of employment abroad and that he would most likely end up as a teacher of science and mathematics in a high school. This in itself seemed a reasonable enough career, but given the ever rising title of antisemitism in Germany he felt he would be spencling much of his time defending himself against Nazi hoodlums. His growing alienation from the majority of his fellow citizens was not compensated by a strong positive feeling of being Jewish since he had never been provident with the opportunity to develop such iclenti- fication. Feeling blockocl in, he became severely clepressed anc! lackocI the initiative to formulate and carry through scientific research. Walter's parents were sympathetic and agreed to let him

18 BIOGRAPHICAL MEMOIRS spend another postcloctoral seminar away from home. He cleciclecl to study with Wolfgang PauTi in Zurich. Walter at- tended PauTi's lectures on quantum mechanics, which he found both powerful and elegant. Although he tried to work closely with Pauli, Pauli clid not seem very interested. A few years later PauTi told Walter he hac! seemed so weak and shaken up at the time that he was afraic! he would faint if he breather! on him. Many years later in 1958 Pauli read Walter's first book on "philosophical biology" ant! wrote asking questions, which Walter answered. Later that year they met in Berkeley, California, and had a pleasant visit. While in Zurich Walter also became acquainted with the famous Swiss mathematician Herman WeyI. He read Wey1's popular book on relativity that was "all the rage" among physicists at the time. At first he was very taken with the book but later realized that despite its exhibition of procti- gious mathematical skill it made only tenuous contact with reality. He began to be aware that one cannot grasp reality by a commitment to one technique or procedure. He dimly perceived that anyone who depicted nature in a manner that seemed wholly comprehensible shouIcl be approached with the greatest skepticism. Many years later he learned from experience that, as soon as one exhibits skepticism about the comprehensibility of scientific description, many otherwise sound scientists become uncomfortable en c! freeze into dogma. At the end of the semester, Walter returnee! to Berlin, where his friend Fritz Houtermans procured for him a part- time position as an auxiliary assistant in the physics labora- tory at the Polytechnic School. His parents continuer! to provide room and board at their apartment, which gave him the wherewithal to leac! at least a limiter! life of his own. He stayed on for two years in Berlin. One man who impressed him deeply was Max van Laue, the discoverer of

WALTER M. ELSASSER 119 X ray diffraction by crystals. von Laue was very favorably disposed toward Walter, partly because of Walter's paper Interpreting tne experiments of Davisson and Kunsman as demonstrating the diffraction of cle Broglie waves. It was a sign of Walter's psychological difficulties in that period that he could not utilize van Laue's good offices to start over again in theoretical physics, where he had macle a small but spectacular start. While in Leiden Walter hacl become acquainted with a Russian experimental) physicist named Obreimov, who later became director of a new physics research institute in Kharkov, a large industrial town in the Ukraine. Late in 1929 Obreimov · . . — . . ~ ~ ~ ~ ~ ~ . . , Or 1 1 , 1 _ 1 1 . aspect Walter to come lo ~narKov as a lecnnlca1 speclalls and he agreed. He was the first non-Russian to be associ- atecl with the institute, so it was a challenging undertaking. The challenge of adventure in a foreign lancI, plus the likely deterioration of the economy in Western countries follow- ing the 1929 Wall Street crash, induced Walter to accept. Russia was in the midst of a great famine, but the numer- ous engineers who hacI come from the West to work in the factories were supplied with the limitecl foocI of a special store. When he tried inviting his Russian colleagues to share in his spare meals they politely but firmly refused. He was impressed with the transformation of society from concti- tions of bare survival in peasant communities to a more technologically oriented! one. He was convinced that the revolution was primarily cultural ant! educational and only seconciarily political en cl economic. It was a desire for clean- liness, orclerliness, elementary decency, and honesty by people who hac! been confronted with a harsh environment they could not subdue and tract sunk lower and lower century after century. He met some of Russia's outstanding physi- cists en c! toured to Odessa on the Black Sea with Paul Dirac, who was attending a meeting there. Walter traveled on

20 BIOGRAPHICAL MEMOIRS through the Caucasus en c! then from Baku to Rostov before returning to Kharkov. He therefore had an opportunity to view a great clear of the countryside en c] its people. These experiences clicI his mental state much good, but he soon developed a severe case of infectious hepatitis, which re- quirect his return to Germany. Walter felt that the half-year spent in Russia was the most profound! external experience of his life. The I,600-kilome- ter displacement to the east introduced him to a new uni- verse, where almost none of the concepts he hac! grown up with were applicable. It macle him aware of the tremendous heterogeneity among people, as contrasted with the unifor- mity of the behavior of matter that allows us to predict the behavior of atoms and molecules in distant galaxies. It also convinced him that any icleas of the unification of diverse societies are just illusions. In 1931, after his recovery, he accepted an offer to be an assistant to Professor E. MacleTung in Frankfurt. An aunt who lived in Frankfurt toil him that it was an ancient mer- cantile town where Jews hac! flourisher! and that he neec! not fear discrimination. Within six months, however, Walter fount! that the racist disease hacI spread there, leaving little hope for a Jew to remain in a university position. SKETCHES FROM BERLIN In the six years between obtaining his Ph.D. and leaving Germany, Walter spent about half his time in Berlin. It hacl become a cultural capital for many groups from eastern and southwestern Europe, and many talented! people flocked! there. The most memorable was a group of Hungarians, all entirely or partly Jewish though far from the Jewish tra(li- tion. Many appear in the history of physics, such as van Neumann, Wigner, Szilard, Orowan, ant! Polanyi. They met in a weekly seminar at the Kaiser Wilhelm Institute at DahIem,

WALTER M. ELSASSER 121 and Walter frequently took the long subway trip to attend these lively and stimulating discussions. He became well acquainted with Wigner, who introduced group theory as the mathematical tool of choice for atomic physics and later, along with his student Frederick Seitz, provided the quan- tum mechanical basis for solid-state physics. On one occa- sion when Walter was "somewhat too easy with my imagina- tion," Wigner counseled him, "One should tackle a problem only when its solution seems trivially easy, it will then turn out to be just at the limits of the manageable; when it ap- pears more difficult, trying to solve it is usually a hopeless undertaking." Walter also came to know Erwin Schrodinger rather well. Schrodinger was called from his native Austria to Berlin in 1927 as the successor to Max Planck, who introduced the idea of quanta in physics a quarter-century earlier. One thing that drew Walter to Schrodinger was that both were primarily visual types in a field, theoretical physics, where most of the practitioners were passionate musicians. A sec- ond factor was Schrodinger's conception of science as a . . .. . . . . natural philosophy, that is, that science was a continuation of philosophy by other means. Still another basis for com- mon interest was the fact that Schrodinger's great papers of 1925-26 started from de Broglie's insight on the wave na- ture of matter, which Walter had recognized as the explana- tion for Davisson and Kunsman's strange results on elec- tron scattering, as later established by Davisson and Germer. Schrodinger wrote a series of thirteen small books, several of which dealt with theoretical physics and others with phi- losophy. He was a traditionalist who drew his spiritual nour- ishment from the society in which he grew up. Walter felt that it was Schrodinger's commitment to historical continu- ity that led as he grew older to doubt, along with Einstein and de Broglie, the statistical interpretation of quantum

122 BIOGRAPHICAL MEMOIRS theory and to suggest that it must ultimately be replacer! by a strictly causal theory. Walter could not unclerstand how one acquires these preclilections since he felt that "scien- tific theory consists in finding all the order that can be cletected by observations in nature, and in representing it by suitable means, mathematical, logical or other." He felt that the preference for traditional physical causality was patterned after the behavior of machines and was not an innate direction of man's minct. It probably dates from the age of Galileo and Descartes, ant! since it was born in his- tory it can disappear in history. Although Walter thought that Schroctinger's books on physics and philosophy were pearls of the art of exposition, he was highly critical of his famous little book W7iat Is Life, which influencer! many physically trainee! scientists to turn to biology. Walter thought that the book was a failer! at- tempt to reconcile Schrodinger's humanistic philosophy with biochemistry, now often called molecular biology. While he acknowledged Schro(linger's superior skill in presenting his case, he believed that the basic philosophy of strict ratio- naTism on which the book was based was a throwback to Descartes's seventeenth-century view that the worIcl is formed of two substances, matter ant! mincI-soul. The body belongs to matter and is basically a machine obeying causal laws. Walter thought that it was necessary to replace this para- ctigm with a better one before any creeper understancling of organisms was likely to occur. Basically, he believer! that the clivicting line between the inanimate and the living was much more powerful than that between man with his rational soul and brute beasts. He rejected vitalism as a flimsy sub- stitute for a real criticism of the machine nature of organ- isms. His encounter with Schroclinger, whom he clearly acI- mirecl, brought out a hitherto somewhat latent passion for natural philosophy, which inspired much of his later life.

WALTER M. ELSASSER THE CONVERSION OF A RATIONALIST 123 While Walter was still in high school, the family doctor, a distant relative, often referred to him as a "bundle of nerves." Such remarks en c! others convinced Walter that he was a high-strung individual. This appeared to him only as a defi- ciency, especially in the consiclerably brutalized environ- ment of pre-Hitler Germany. During his troubled years af- ter receiving his Ph.D., he became an aficionado of Marce! Proust, reacting in succession all twenty-two volumes that macle up the original editions of his novel. He felt Proust was an excellent introduction to depth psychology, or ex- ploration of the unconscious, which Walter hac! been con- templating for some time. He was particularly impressed that Proust hacl succeeclecI in putting his oversensitivity to work for him in creating a splenclid portrait of a whole society. He began to think of using his own perceived weak- nesses for constructive purposes and kept this idea with him for the rest of his life. When Walter moved to Frankfurt, he entered psychoanalysis with Dr. Karl I~anciauer, a man of great perception. The analysis continued every weekday for eighteen months, un- til one day in April 1933 when the Nazis actually carried out their long announced seizure of power. This act marked the cleath of the Weimar Republic ant! the beginning of the Nazi terror that was to last for twelve years. When he ar- rived that morning for his session, Dr. Lanciauer advised him to leave the country before the Nazis closed the Swiss border. Walter's immediate reaction was an indignant resis- tance to the suggestion, but when he arriver! at the univer- sity he was greeter! by a gang of brownshirts, each with a rifle stung over his shoulder. Their leacler clemandec] Walter's university identification card, which he then pocketed and told Walter to go home ant! await further orders. Seeing

124 BIOGRAPHICAL MEMOIRS the handwriting on the wall, Walter left for Zurich a few clays later while his passport was still vaTicl and the border still open. He never saw Dr. Landauer again but learned that he perished in the Holocaust. The full measure of the analytic procedure clicl not dawn on Walter until after its termination. He then hac! the phan- tom feeling that someone was cirilling on his innards, though he consciously knew the cirilling hacT stopped. Through his work with Dr. Lanciauer, Walter learner! that he was a far stronger person than he had ever perceived by self-observa- tion. Lanciauer pointed out that there was a core of aggres- siveness submerges! in Walter's unconscious that contrasted! with the timid young man c owe cl by Nazi bullying that he fancied himself. If this was correct, Walter realized he hac! the strength of cleveloping into a scientifically creative per- son by the stanciarcI psychological technique of sublima- t~on. AS a result of his analytic experience, Walter couIc3 no more question the reality of the unconscious than that of the electrons or atomic nuclei of his professional work. But the reality of psychic phenomena was of a different kind, characterizes] by elusiveness, irregularity, disorder, clishar- mony, or, in Jung's terms, irrationality. He read the litera- ture of the psychology of the unconscious ant! began to appreciate its depth and breadth. The knowledge of the human unconscious appeared to him a scientific discovery of as great a raclical novelty as the discovery of atoms, mol- ecuTes, and nuclei. Those who spoke of the unconscious before Freud were like those who spoke of gravity before Newton, correct but irrelevant. Newton click not discover gravity but the structure of its laws. Similarly, Freuc! ant! Jung did not discover the unconscious but the structure of its modes of behavior. Such musing Flee a gap in Walter's philosophical uncler-

WALTER M. ELSASSER 125 standing and even of his science. As a physical scientist it was hard for him to think about the human psyche as purely abstract functionaTities apart frown anchoring in the mate- rial substance of the brain. This led him to an encounter with the ancient philosophical problem of the dualism of belly and soul, an interest that never left him. He felt the methods of theoretical science were sufficiently advanced to rescue the central problem of philosophy, the body-sour dualism, from metaphysics in order to treat it as a specifi- cally scientific problem. This would have remained a mat- ter of speculation had it not been for his meeting with the physiologist Theophile Kahn in Paris, about a year after leaving Frankfurt. They met frequently, and Walter was im- pressed with Kahn's claim that biology was first and fore- most the realm of utter complexity. The idea appeared to him because it was simple, abstract, and general and there- fore exactly like the notions constructed and used by theo- retical physicists. He found no shortage of examples for this complexity in biology from the molecular diversity of cells to the structure of the human body. Later, when he became a leading figure in geophysics, he found that the complexity of neither the turbulence of the fluid earth or the structure of minerals and rocks in the solid earth could compare with the formidable complexity of all higher or- ganisms, nor even that of a single cell. Walter contrasted the complexity and individuality of or- ganisms with the simplicity and universality of physical sci- ence. He felt that these two pairs bring out the difference, otherwise frequently hidden, between the ways of thinking · · . · . . . . . . , . ~ needed in the biological and physical sciences. This reaTiza- tion had an overwhelming intellectual effect on him. He realized that the worlds of physics and biology could be reconciled only if one of the groups yielded and that it is the man who thinks in traditional terms of physics who

126 BIOGRAPHICAL MEMOIRS must change his ways and learn to accommodate complex- ity and individuality if he is to encounter life and under- stand its nature. In particular, the notion of creativity that arises in depth psychology, can be converted into scientific terms and applied at all levels of the living world from the cell upward. One must show that the complexity of life is broad enough to encompass the creativity of the organism. The complex structure of the organism, including that of cells, that creates the enchainment of ever-new and unpre- dictable individualities not only makes creativity possible, it is this creativity. Walter was convinced that creativity is a basic property of all life and that the transition from sim- plicity and universality toward complexity and individuality is essential to the development of a true science of life. As he became successful in his later scientific activity in the United States, he became more committed to these ideas. Their articulation in books and articles led to many clashes with the biomedical establishment. As these ideas developed, Walter began to understand Born's remark that his strength was more in conceptual thinking than mathematics. This had made no sense to him as long as he believed along extravagantly rationalistic terms that all thinking could ultimately be expressed in math- ematical form. But if the utter complexity of organisms at both the structural and logical levels impeded the applica- tion of mathematical analysis, then conceptual thought could and indeed had to have a respected role in the hierarchy of human mental endeavors. If biology is the locus of utter and perhaps irreducible complexity, it can be the locus of partial irrationality, that is, of our inability to order the phenomena exhaustively in logico-mathematical schemes. Under these conditions, organic structure serves as the ve- hicle of this irrationality, and the study of the nature of this

WALTER M. ELSASSER 127 vehicle is strictly a scientific task, which was to occupy many of Walter's later years. RUE PIERRE CURIE, PARIS Upon arriving in Zurich, Walter went directly to the physics building of the Polytechnic School, where he was heartily greeted by Pauli. Without a spoken word Pauli unclerstood that Walter was the first of many to come, escaping the grim situation in Germany. Fortunately, Pauli had just re- ceived a letter from Frederic Joliot, the son-in-law of Ma- ciame Curie, saying that the nuclear physicists in Paris needed a theoretical man, and Pauli wrote that he would propose Walter for the position. Joliot wrote back without delay ac- cepting the proposal but indicated that it woulc! take some time to set the necessary bureaucratic machinery in mo- tion. Walter waited two to three months in Zurich for an- other letter from Joliot and then cleciclecl he might as well wait in Paris. There Eliot told him that he was encounter- ing some obstacles to funcling a position for Walter, but the matter would be clearest up. Soon thereafter Walter found himself the recipient of a fellowship from the Alliance Israelite Universelle, a Jewish cultural organization. This piece of good fortune actually annoyed him since it was essentially an act of charity, although he had never had any connec- tion with Juciaism or its organizations. After a year his sup- port was transferred to the Centre National de la Recher- che Scientifique (C.N.R.S.~. He was given a small table in the library of the Tnstitut Henri Poincare from which he had to remove all his books and papers every night. The spare nature of the facilities and the restrictive working conditions were typical of the way scientists were treater! in France at that time. Walter got to know some of the remarkable men who clirectect French physical science and its instruction. Among

28 BIOGRAPHICAL MEMOIRS these was the Nobel Prize-winning experimental physicist lean Perrin, who was the first to obtain a precise value of Avogaciro's constant, the number of hydrogen atoms in a gram of hydrogen. He also met Louis cle Broglie, whose introduction of matter-waves in physics hac3 proviciecl the foundation for Walter's first publisher! paper in Gottingen. Joliot was clearly the moving spirit in the physical sciences, and since he was the one who had brought Walter to Paris, he clecicled to specialize in the structure en c! dynamics of atomic nuclei. The transition from his previous research to the application of quantum mechanics to the nucleus was not difficult. During his stay in Paris, Walter got to know Eliot en c! his wife, Irene Curie, rather well, anti he acI- mired them both. He rememberer! ioliot as a man without affectation, who couIcl (teal with every man he encountered and coulc! design experiments of formidable simplicity. In the fall of 1933 many more scientists fount] their way from Germany to Paris. Walter was the ablest of these, and since he was on excellent terms with Perrin ant! {oliot, the new arrivals, if they were physicists, were sent to him. He receiver! great support in helping these people from lean Langevin, son of the eminent physicist ant! himself a physi- cist. Langevin hac! an "excellent mincI and a heart of goicI" en cl put out great effort in trying to find a niche for the refugee physicists in the Greater Paris area. Once a poten- tial position was identified, Walter would escort the man to his destination and, if nothing was available, take him to the Alliance Israelite to keep him from starving. Walter was intensely aware that his publication recorc! was poor for one aiming to be a professional research sci- entist. He realized that he had previously hacI inhibitions about seeing his work in print. Paris provicled him with a last chance to make his mark. The two journals available for a physicist were the Comptes Rendus and the journal de

WALTER M. ELSASSER 129 Physique. There was no formal scheme for review of papers; they merely had to be submitted through a well-known per- son. The Comptes Rendus limited the length of an article to two and one-half printed pages. The pages of the journal were large and had two columns, which was space enough to clearly formulate any ordinary communication of the theoretical type that Walter would submit. There was also a limit of five of these notes per year for an individual au- thor. Walter took his first note to de Broglie, who was clos- est to his interests, and asked him to submit it. De Broglie told Walter that he had no desire to read it but might read it later at his leisure when it was in print. He advised Walter to hand his manuscripts to him at the same time each week before the start of the regular academy session. A week later the official printer had the proofs, which Walter im- mediately corrected. The next issue of the Comptes Rendus, which appeared the following week, had the article. Walter tried to publish the limit of five articles for each of the three years he remained in Paris. In addition, he published a total of seven somewhat larger articles in the journal de Physique. All of these were on the structure and dynamics of the atomic nucleus, a subject in which Walter made his second great contribution to physics. At that time Niels Bohr and his colleagues in Copenhagen had proposed the liquid drop model of the nucleus in which there was proposed to be a homogeneous agglomeration of protons and neutrons without further internal structure to the nucleus. Though there was considerable empirical sup- port for this model, Walter had certain doubts that led him to think the nucleus would have a degree of internal struc- ture. A large part of his efforts in France were devoted to following up on this idea. He discussed the problem of how the nucleus is held together with a refugee physical chem- ist, K. Guggenheimer, who had found a temporary post in a

30 BIOGRAPHICAL MEMOIRS laboratory at the College cle France. Guggenheimer had a great clear of knowledge about how molecules are held to- gether starting from atoms. There are many analogies of the molecular forces with nuclei, but the energies of nuclear binding are 100,000 times greater than those hoIcling mol- ecules together. It became clear though from a study of chemical reaction kinetics that variations in binding ener- gies of nucleons would in many cases be reflected in nuclear abundances, many of which were known. Walter proposed a joint piece of research to Guggenheimer, but they failed to agree on collaboration. Guggenheimer published two ar- ticles on binding energies of nucleons in 1935 anct then left for a position in EnglancI. Walter then found a trick to obtain at least an approximation of the bincting energies of incliviclual protons and neutrons from the directly measured disintegration energies of the very heavy, naturally raclioac- tive nuclei. He conic! then show how the bincling energy of a nucleon decreases sharply beyond the end of a nuclear shell. He was satisfied he had established the existence of nuclear shells, though these were not analogous to the elec- tron shells of atoms. Deeper physical unclerstancting of the physical forces that brought about the nuclear shell struc- tures only became available two decades later. A more de- tailecT theory of nuclear structure was then worked out by Hans Jensen and Maria G. Mayer, who hac! been a Ph.D. student of Born's just after Walter left Gottingen. Both the latter workers received the Nobel Prize in 1963, which they shared with Eugene Wigner in a Tong-clelayecl recognition of his many contributions to atomic and nuclear physics. Maria Mayer quoted Walter's earlier work in a 1964 article in Science, where she also poir;tecI out that the mathematical theory conic! not have been complete before the knowI- ecige of nuclear interactions had acivancect to the level of the 1950s. Despite the importance anct originality of this

WALTER M. ELSASSER 131 pioneering work of Walter's, it received little recognition, probably because of the impact of Bohr's liquid drop model, which made its debut a short time earlier. Walter's remarkable insight into the structure of the atomic nucleus typified other (discoveries he made in the physical sciences, some of which will be described later. He wouIc! enter a field, react exhaustively about the subject, and then through calculations and reflection develop concepts ap- propriate for structuring the publisher] observations Tong before specialists had penetrated deeply into the subject. Once he had confirmed his primary insight, he would, for various reasons, not work through the full ramifications of his ideas. The one great exception was his theory of organ- isms, which occupied much of the thinking of his last five decacles. He hac! few regrets about the limited recognition of his work in physical sciences, particularly in the matter of nuclear structure, where he wouIc] have had to remain a nuclear specialist to follow up on the insights. This ulti- mately would have involved him in developing the atomic bomb. He of course had no idea of this possibility when he was cleveloping his ideas about nuclear forces since atomic fission was not cliscovered until 193S, several years after he had left research in nuclear physics. In adclition to his work in Paris on nuclear binding, he and Frank Perrin publisher! a theoretical explanation of the exceptionally large capture cross-sections for slow neutrons that certain nuclei tract shown. Others published similar analyses at the same time, inclu(l- ing Hans Bethe, whose treatment was more extensive ant! general than those of anyone else. However, Walter was the first to explain the large capture cross-section as the square of the cle Broglie wavelength of the neutron rather than the cross-sectional area of the nucleus. The original papers of his French sojourn were hardly noticed, and he turner! to other things. He remarket to Eugene Parker that when

32 BIOGRAPHICAL MEMOIRS Shakespeare wrote Hamlet he had Walter Elsasser in mind. Parker wrote me that, "Walter had a deep aversion to as- serting himself in the generally cynical scientific arena." PASSAGE TO THE NEW WORLD By 1934 Walter's small position as investigator was fairly secure, since it was financed by the bud(ling French Sci- ence Center, ant! likely to last almost inclefinitely. He then realized that he tract to make a decision about his career. If he decided to remain in France, he would have to become a French citizen, which required two years of military ser- vice. If not a citizen, he would have to fight endlessly with a bureaucracy cleterminec] to keep him out. The alternative was to go to the Uniter! States. Since this was the time of a worIc~wide depression, it was hare! to get a job, even in sci- ence. Having a stable position in Paris macle it difficult to decide for the American option. His decision to do so was finally cletermined by his parents' situation. His father in his early sixties was ill and had retired and movecl to a small house in the Black Forest. By that time, however, the Nazi policies tract become clear: in spite of the depression, they were going to rearm, en c! the property of the non-Aryans was going to finance at least part of the rearmament. That category incluclecI not only nominal Jews but those who hac! married into the micicIle and upper classes and changed their religion. His parents wouIcI be reduced to indigents, cleprivec3 of home, income, and normal medical care. A few years later in early 1939 Walter's foresight was justified, when his parents were able to go to England for temporary resi- clence pencTing their passage to the United States. In 1940 they came to America, where they later lived with his sister in Chicago. Walter applied for an immigration visa to the United States ant! after the usual bureaucratic delays received it in 1935.

WALTER M. ELSASSER 133 He then took a large German steamer from Le Havre to New York. The ambiance on boarcl was his last closeup of the subdued nazification he encountered. On board, how- ever, he met Margaret Trahey, an American girl of Scotch- Trish extraction, who was later to be his wife. She was reacI- ing C. P. Snow's The Search, about the rise of a young man from modest circumstances to academic research as a physi- cist. Since Walter was the first of that strange breect she hac! met, it helpec! smooth the way to a further understanding of each other. Walter always remembered vividly his first sighting of the Statue of Liberty when the steamer enterer! New York har- bor. He felt that no one who had not undergone years of persecution couicl fully appreciate what this means to an immigrant the chance to begin life over again without the impediments that Europe throws in the way of anyone not born of a privileged social class. Although free immigration tract stopped when he arrived in the United States, the country still accommodated itself to the reception of persecuted minorities. In his mine! it was the spirit that counted com- parable conditions for entry existent in South America but little that correspondecl to the reception of the clowntrod- clen masses at the feet of the Statue of Liberty. Two days after disembarkation Walter met I. T. Rabi of Columbia University, whom he knew from the latter's stay in Europe. Rabi set him up in a dormitory room on the Columbia campus en c! introcluced him to HaroIc! Urey. He also visited Davisson at the oIc] Bell Telephone Laborato- ries, where the latter hac! first clemonstrated electron clif- fraction. Walter was alert to the possibility of obtaining a position in all his meetings, but there was none to be had. He traveled on to Ann Arbor to attend a summer course by Enrico Fermi whom he came to know personally to some degree. Although Fermi was perhaps the most scientifically

34 BIOGRAPHICAL MEMOIRS gifted of all the physicists Walter hac} encountered, he was simple ant! modest in his personal contacts. During his month-Ion" stay in Ann Arbor, Walter frequently visited with a young theoretical physicist, Davic! Inglis, whom he had first known in Pauli's institute in Zurich. Inglis ant! his wife Betty introduced him to many of the nuances of American life that are not explained in guidebooks. If in France he was impressed by the sensitivity of the residents, he was impressed by the generosity of Americans. Unlike Europeans, the prospect of an uncertain economic future does not breec! cynicism or despair among Americans. Walter went on to Chicago, where he met Arthur Compton, discoverer of the Compton effect, the most spectacular clem- onstration that light exhibits corpuscular in addition to the well-known wave properties of light. Compton was most un- sympathetic to Walter's quest for a position because he thought it unethical to give positions to Europeans when many American scientists were out of work. He hacl in fact sent back to Germany a young German physicist, although the latter hacI married an American and wished to stay in the Uniter! States. Walter knew this young man from his Frankfurt days. He was of frail constitution and ctied soon after being ciraftecI into the German army from the exer- tions of a forced march. Thereafter Compton was always the first and most vociferous among those who helpec! clis- placect scholars from Europe. After Chicago Walter returned to New York to take the boat back to Europe for another year in Paris. His trip hac! shown him that the prospects for nuclear research in the Uniter! States were slim, ant! he began to think seriously about another specialty. Since many of the ideas described above uncler "Conversion of a Rationalist" hac! aireacly cle- velopect in embryonic form, he began to think that much of the science of the future would be concerned with com-

WALTER M. ELSASSER 135 plex systems. Although the ideal place for such study would be biology, Walter was reluctant to commit himself to that field because it involved too much chemistry, to say noth- ing about the details of biology. He was later to approach biology by way of the semiphilosophical ideas described ear- lier. it occurred to him that in geophysics he could indulge the study of complex systems, using the tools of the theo- retical physicist and some knowledge of astronomy, which had been a minor subject along with mathematics in his Ph.D. examination. He decided to cut loose from his moor- ings in Paris and on his next trip to the United States try his luck in California, specifically at CalTech. He wrote to Oppenheimer about his intention to go to Pasadena, where Oppenheimer spent a few months in the spring of every year as a part-time professor of physics. Oppenheimer an- swered promptly, suggesting that Walter first visit his wealthy father on his way through New York and then stop off at his ranch in New Mexico. Walter followed up on both invita- tions in 1936 after he arrived in the United States for the second time. in a long, friendly conversation with Oppenheimer's fa- ther in New York, Walter found the man to be warm and generous. After a few days exploring the "marvelous and complex city" of New York, Walter moved on to Chicago, where he visited Margaret and they announced their en- gagement to her family. They also decided they could man- age between their two small incomes. A year later they mar- ried and had a girl and five years later a boy. He derived the deepest happiness of his life from the seventeen years of their marriage, which ended with the loss of Margaret under extremely tragic circumstances. He did not remarry until ten years after the tragedy. After several weeks in Chicago, Walter took the westward train headed for Albuquerque and Los Angeles and stoppe`l

36 BIOGRAPHICAL MEMOIRS off at a small station some distance from Santa Fe. He was picket! up by Oppenheimer ant! driven to his ranch in the Sangre cle Cristo mountains, where he couIc3 see through the trees the mountain range in which the loos Alamos IJabo- ratory was later to rise. Includes! in his stay on the ranch was a daylong horseback trip with Oppenheimer into the surrounding mountains, which was exhilarating but tiring to one unaccustomed to riding. On their return Oppenheimer offered him a Chili drink he hac! prepared according to an oil recipe. A mouthful of the vermilion fluid tasted like what Walter imagined sulfuric acid wouIc! taste, and he immecliately spit it out. Oppenheimer told him he hac! passed the first but failecI the second part of the initiation ceremony at the ranch. After a few days of relaxation on the ranch, Walter took the train to Los Angeles and then on to Pasadena. There he met a physicist, Jesse DuMoncI, who introduced him to several people at CalTech, including Linus Pauling, who, though a young man, was already head of the chemistry department. Pauling almost at once offerer] him a position in his laboratory, but feeling he hacl no background! in chem- istry Walter refused. He considered this one of the wiser decisions he macle in his life. In 1936 DuMoncl ma(le an appointment for Walter to see _ _ __ _ , ~ ~ ~ r rat ~~ ~ ~ ~ Robert Millikan, tne neact or Bat ~ ecn, wnom ne was to see many times thereafter. He told Millikan that he was a theo- retician who had worker! in atomic and nuclear physics but was mIling to work in other areas such as geophysics. Millikan toil him, "If you want to clo geophysics we can use you. If you want a place in nuclear physics or in astrophysics ~ can Ho ~hsol~elv nothing for vain 1 J ~~ All $~5 ^~$ 7~.... If you are serious about geophysics I can promise you that I will find some salary for you.'' Walter considered Millikan one of the most extraordi- nary men he had ever met. He was, of course, famous for

WALTER M. ELSASSER 137 the oil-drop experiment of his younger years, which estab- lished the unit charge of the electron. His forte was not original thought but subtle and controlled strength in ev- erything he clict a human powerhouse. Among his many accomplishments was to build CalTech into a major scien- tific institution. He once toIct Walter, "You are a producer; if you were put on the top of a mountain you would still produce." Considering the eminence of the source, Walter thought of this as the highest compliment he ever receiver! about his qualifications as a scientist. Margaret came west in the spring of 1937 to find a job. She die! find a tolerable but rather Tow-paying job, ant! they got married. Walter decided to make his break with nuclear physics gradually, so he macle the acquaintance of Charles taur~tsen and his capable group of research students who represented nuclear physics at CalTech. Their work was at the forefront of studies on nuclear structure and dynamics then going on in the florid. Oppenheimer was the official theoretician for the group, but he only spent two or three months each spring in Pasadena. Since Walter knew quite a bit about the subject, it was easy for him to converse with the group, which he dice in the summer and fall of 1936. In return, men of the Lauritsen group alternated in teaching him one skill that was essential for a full life in the western Uniter! States, namely driving a car. Early in 1938 he and Margaret bought their first automobile, a somewhat aged ForcI, in which they macle many excursions. By the time Oppenheimer arrived in the spring of ~ 937, Walter tract herome cleeply engrossed in the physics of the atmosphere WhICh seemed a weird subject to nuclear physicists, includ- ing Oppenheimer. As Walter had stopped reacting the bur- geoning literature of nuclear physics, he eventually lost touch with the congenial crowd of Lauritsen's laboratory. ~ · ~ ~ · ~ ~ · 1 J

38 BIOGRAPHICAL MEMOIRS EARTH SCIENCE In 1937 Walter joined the fairly new Meteorology Depart- ment at CalTech at Millikan's suggestion. Millikan hat1 got- ten a contract from the Department of Agriculture to be administered! by the Weather Bureau, which was then part of Agriculture. Walter knew nothing about meteorology, but he react a few textbooks anct came up with some unsolvecl problems in which he conic use his accumulated knowI- ecige of atomic physics. He then began to receive a small salary to supplant the loans on which he had been existing up to that point. He undertook the study of the effect of infrared radia- tion on the atmosphere. The American Meteorological So- ciety had for years been urging the American Physical Soci- ety to do research on infrared racliation in view of its importance for the atmosphere, but nothing was clone. The far infrared spectra of the atmosphere have a very compli- catecT structure that required an understancling of quantum mechanics for its full eTuciciation. The basic material on infrared spectroscopy hac! been gathered and presented by the physicist Gerhard Herzberg, another refugee from Ger- many then living in Canada. Walter spent the years 1937-41 analyzing the properties of far-infrared atmospheric raclia- tion from first principles. After lengthy calculations, he envier! up with tables and graphs that a practitioner conic] use to fincI the heating ant! cooling of the atmosphere when he knew the (distribution of temperature and moisture. This was a time of rest and recovery for Walter, despite the pinched material circumstances under which he livecI. The hot breath of Hitler was off his neck for the first time in twenty years. Extreme brutalities clic! not exist in the California environment, and he had a congenial wife. He hac! plenty of time to think, which allowed him to develop

WALTER M. ELSASSER 139 the two basic icleas that clominated the scientific icleas of his later life: those that lecl to the theory of the earth's magnetic field] and the relation between quantum mechan- ics and organic life on the background sketched out above under "Conversion of a Rationalist." After he had clone the atmospheric research for a few years with emphasis on calculations and cirafting, Walter felt frustrated at his previous inability to do experiments. To correct this deficiency, he befrienclecT John Strong, a very successful experimentaTist. Strong taught him the pro- ceclures user! by a successful experimenter, including care- ful advance planning and breaking clown the procedure into a number of little steps, mastering each before pro- ceeding to the next. Walter then set out to measure the far- infrared transmission of the atmosphere along paths up to 300 meters in length. This was clone on an athletic field next to CalTech with equipment he built with his own hands. He monitored the temperature ant! moisture continuously and wrote up the results. Although he realized he would never be a first-rate experimentalist, the experience restorer! his self-conficlence and macle him realize that the American ambiance had a relaxing ant! stabilizing influence on him. In 1936, before he was officially employecI, Walter de- cided to take a meteorology course. Almost all of the twenty some students in the course were career military officers sent to Pasadena for training as weather officers. They were well aware that in a few years their new skills might be required for a war against Hitler. Much of the course was practical plotting of weather characteristics and upper-air ciata. Walter learner! much about the peculiarities and va- garies of the earth's atmosphere, which proved useful in his later work on the earth's magnetism. He learner! that the earth's atmosphere is full of unpreclictable contingencies on every level of its scale, which gives the meteorologist a

40 BIOGRAPHICAL MEMOIRS feeling for reality that is radically different from that of the laboratory scientist who can minimize contingencies. The Meteorology Department at CalTech was part of Aero- nautical Engineering header! by an outstanding man, Theodore van Karman, who hac! come to Pasadena from Europe in 1930 after a brilliant academic career. He tried to induce Walter to leave his meteorological studies and turn to hydroclynamic problems such as turbulence and thereby become an aeronautical theorist. As a result of Walter's refusal, he never got closer to von Karman. He also began to see that von Karman hack only accepted me- teorology into his laboratory as an accommodation to Millikan, who believecl it was his patriotic cluty to foster that subject. Walter saw that the smallness of his position was .. .. ~ . . . .... . . .. ~ the result ot a protracted political accommodation between two powerful men, en c] he began looking for other employ- ment. His efforts were unsuccessful because positions were still rare in the wake of the great depression, en c! he hac] no money to travel around looking for opportunities. He asker! Oppenheimer about a job on one of the campuses of the University of California, particularly the Los Angeles campus, but was told, "We do not wish to encourage gradu- ate teaching outside of Berkeley." Walter's position at CalTech came to a rather luclicrous end in 1941. He had gone to Washington on some business connected with his research. While there he encounterer! Carl Rossby, who was heat! of research for the Weather Bu- reau. Walter had gotten to know him well in the summer of 1938 when Rossby was head of the Department of Meteo- rology at MIT and hacl invited him to lecture there. Rossby controllecl scientific meteorology in the United States, a task he found overwhelming, and clecicled to clele~ate con- trol of the western part of the country to a deputy, that deputy being Walter. Walter thought this was some sort of

r WALTER M. ELSASSER 141 fantasy that would never work out when confronted with reality but saic] nothing. However, von Karman got wincl of this plan from Rossby, who toIcl him that the Meteorology Department at CaTTech was inadequate, since its heacI, a young assistant professor, was more commercially than sci- entifically incTinecI. He said that there was already an excel- lent man on the spot, Elsasser, ant! that he hacI already discussed with Elsasser his future functions. To emphasize his point, he decIarect that the contract with the Meteorol- ogy Department would not be renewed. Von Karman re- portec3 to Millikan that Elsasser hac! used the fecleral gov- ernment to pressure CalTech into an appointment for himself. When von Karman informed Walter of the situation, he saw no sense in asserting his innocence. He walkout out of van Karman's office and consiclerec} himself fired. It oc- curred to him that the logical course of action was to move east, where, with the war coming on, there were greater opportunities. He wrote to Charles Brooks, professor of meteorology at Harvard, who was in charge of the Blue Hill An. . . ~ ,. ~ observatory In South Boston. Brooks agreed to give Walter a position compiling tables of various data with spare remu- neration. He and Margaret packed their few belongings in ~ ~ Ire . _% the car anct ctrove Ott to Boston. While there he wrote a monograph on atmospheric racliation, which Brooks pub- lishecl in a series he eclited. Rossby, who by then was suffer- ing from a bac! conscience, hac! most of the edition bought up and clistributec! to meteorology students. Walter started thinking seriously about the source of the earth's magnetism arounc! 1940. Three months after the Japanese attacker] Pearl Harbor, he receiver! a telegram from the U.S. Signal Corps Laboratories at Fort Monmouth, New Jersey, telling him to promptly report there for duty. He spent the first part of the wartime years there ant! the sec- onc! part working in the Empire State Building in New York

42 BIOGRAPHICAL MEMOIRS for the Radio Propagation Committee of the National De- fense Research Council. The chief part of his theoretical work on the earth's magnetism was clone cluring the war. He had plenty of time on the weekends to work on this problem, especially towarc] the end of the war. He used this time to do calculations en cl write articles that appeared in a series of three papers in the Physical Review in 1946-47. The first systematic summary of the physics of the earth's inte- rior was given in an article in the Reviews of Modern Physics in 1950. Full exploration of the earth's hotly had begun in the IS9Os, when the first seismological stations were set up. In the clecacles following, the main features of the earth's inte- rior came into view. The most important of these was the sharp boundary about halfway between the surface and the center of the earth separating the core from the mantle. The core is made of molten iron, the mantle of conven- tional rock. There is by now a thorough quantitative knowI- ecige of all the mechanical properties of the earth's inte- rior. The one characteristic of the earth as a whole that was not included in this scheme was magnetism, a property stu(l- iecl scientifically since :1600. Early thinking was that the earth behaves like a bar magnet, magnetized along the earth's axis. But mysterious deviations were later cliscoverec3 in the regularity of the earth's magnetic fielcI. These irregularities occurred! not only from place to place but from time to time, leaching physicists to speak of the secular variation in the earth's magnetic field. In the first half of the nine- teenth century, the famous Gottingen mathematician, Gauss, showed that if one knows the magnetic field over all of the earth's surface the field can be mathematically diviclect into a part whose sources are inside the earth anct a part whose sources are outside. The overwhelming part of the fielcI arises from sources within the earth. Toward the end of the

WALTER M. ELSASSER 143 century, it became clear that the internal source conic! not be of the bar magnet type, since the temperatures inside the earth are too high for this sort of magnetism to occur. Two competing theories arose to replace the idea of a bar magnet. The first, espoused by a prominent group of theoretical physicists with Albert Einstein at the head, be- lieved that a theory must be creates! in which large bodies such as the earth are magnetic by the very fact of their rotation. This involved fincling a new term in Maxwell's equations to provide a connection between gravity fielcis and electromagnetic fielcis. The alternative theory was that electric currents flow in the conducting molten iron of the outer core. This iclea hacI its origin in the observation in 1908 by the astronomer George Hale, founder of the Mount Wilson Observatory in Pasadena, that all sunspots have large magnetic fielcis. The British physicist I. I. Larmor attributed the sun's magnetism to a dynamo effect in analogy to the engineering term for power station machines that convert mechanical motion to electrical currents, the conventional rotating generators. Although Larmor vaguely suggested in 1919 that the earth's magnetism might be explainecl along these lines, not a single article appeared about it in the intervening years. The likely explanation for the total ab- sence of papers on the subject is that the limited number of those qualified to handle the solution of problems of theoretical physics was absorbed by the two main streams of inquiry then existing in physics, namely relativity and quan- tum mechanics. Walter's work was truly pioneering because there was no theoretical literature in the field. The main problem was to fins! a mechanism to sustain the electric currents for bil- lions of years. The decisive step was the discovery that there conic! en cl should be a toroicial field inside the earth. Walter spent a lengthy period making calculations on the basis of

44 BIOGRAPHICAL MEMOIRS different moclels and fount] that only the dynamo moclel gave an adequate numerical magnitude. Reassuringly for the dynamo model, the calculations came out just right. He then adapted a two-step strategy to resolve the problem. The first step was to assume a constant main magnetic fielc! and calculate how it wouIc3 be mollified by ecIdy-type mo- tions in the core. Then he constructed the mathematical machinery that could describe the field as it was generates! by currents insicle the core. Using his meteorological knowI- ecige about the dynamics of the atmosphere, he clerivect rules about the character of the Quill motions needecl to produce the fielcI. He thus showed how a metallic fluicI dynamo can be self-sustaining indefinitely as a result of or- tinary electromagnetic induction. This involvecl mathematical demonstration of how the kinetic energy of fluid motion in the earth's core can be converted to electromagnetic en- ergy. The key element is a feedback process in which en- ergy is exchanged between two components of the mag- netic fielcI, that extending to the earth's surface and beyonc! (the poloicial field) and that containec~within the core (the toroidal field). The convective motion of the fluid! is the agent in the exchange process. Walter was greatly aiclecI in this work by magnetic maps consisting of lines of constant rates of secular or long-term variation, prepares! under the direction of E. H. Vestine. These closely resembled ordinary weather maps. From these maps Walter calculatecl the average speec! of fluicI iron in the core, which was 0.03 cm/seconcI. He also clerivecl an important formula for predicting the strength of magnetic fields in celestial objects. By balancing Coriolis and Lorentz forces acting on the conducting fluid, he concluclecI that the earth's dynamo is characterized by a particular value of a cTimensionIess parameter that includes the magnetic field strength, the electrical conductivity of the core, and the

WALTER M. ELSASSER 145 rotation rate of the earth. This parameter is now caller! the Elsasser number en c! is the critical parameter in modern dynamo theories. After the war, Walter renewed his acquaintance with John von Neumann, then at the Institute for Advanced Study in Princeton, who tract gotten interested in the problems of magnetohydroclynamics during his work at Los Alamos. Von Neumann listened with interest but, like everyone else, re- fusec! to believe that magnetic fields could be created by fluid! motions alone. Over many visits in the course of a year Walter convinced him that his arguments were math- ematically unassailable. Stimulated by remarks of von Neumann, a distinguished British hydro(lynamicist, K. G. Batchelor, carried out calculations showing that when an electrically conducting fluid is in random turbulent mo- tion, a random stray magnetic field that happens to exist in the field! will always be amplif~ecl by random shears engen- clered by the turbulence. When Batchelor's work appeared] in 1950, the objections to dynamo moclels disappeared, and in a few years the dynamo iclea was fully accepted, as incti- catec! by Walter's election to membership in the National Academy of Sciences in 1957. This gave him a strong sense of personal achievement since his was mainly an indiviclual accomplishment. It is perhaps of more than passing inter- est that this work was done in his spare time en c] had no direct connection to his war work. A similar pattern will be seen in his later biological work. When the concept of plate tectonics revolutionized the geological sciences in the 1960s, Elsasser turner] his atten- tion to the question of the striving force for plate motions. One of his prime contributions cluring this period was an analysis of how stress diffuses across tectonic plates. This work explained the phenomenon of postseismic cleforma- tion observer! in seismically active plate boundary regions

146 BIOGRAPHICAL MEMOIRS such as the San Ancireas fault zone following large earth- quakes. As in other areas of physical science, Walter's cen- tral contributions to plate tectonics continue to influence moclern thinking to this clay. WORLD WAR II AND THE POSTWAR YEARS While Walter was working at the Blue Hill Observatory en cl before he was ordered to Fort Monmouth, he com- pletec! his monograph on infrared atmospheric radiation. When he received the orders to move, Charles Brooks, cli- rector of the observatory, offerer! to read the proofs, so Walter, his wife, and six-month-oic] daughter conic! depart for Fort Monmouth. There he was given a civil service cias- sif~cation as a meteorologist ancl a salary corresponding to his age, education, and experience, which lifted him to a comfortable level considerably higher than the marginal one he hacl before. He soon found, however, that the Sig- nal Corps no longer hac! much interest in meteorology, since the subject hacl been taken over by the Air Corps. He was toIc! he was to become an electronics specialist, thus ending his career as a meteorologist. Walter protested, mainly against the military way of doing things, but was toicl this was war and he hacI to obey orders. He was assigned to the quartz crystal (livision, one of the largest and busiest branches of the Signal Corps Laborato- ries. He found himself in charge of a small group of younger people. Incliviclualist that he was he did not relish the bu- reaucratic functions the job entailed. This resulted! in an awkward situation one day when he was surprised while hoicling a soldering iron in his hand by an inspector from the Civil Service who severely rebuked him for stooping to such manual efforts, when the government could hire people to clo it for half what he was being paid. Nonetheless, he rapicITy learned electronics in this work and carried out

WALTER M. ELSASSER 147 technical supervision and inspection of industries that built quartz crystals into radio transmitters. About a year later, an emergency arose that requires! the help of men versed in meteorology. There had been trouble with anomalous propagation, in which radio waves are bent by moisture in the air. This interferes with the ability of radar to measure distances of targets and causes artillery that is guiclect by racier to be directed! to a wrong distance. Walter wrestIecl with the problem for some time without success, when he was told it was to be transferred to the Radio Wave Propagation Committee of the National De- fense Research Committee. He was then released to serve with the committee, which had set up an office in one of the upper floors of the Empire State BuiTcling in New York City. He spent the rest of the war there with a half dozen other technical people. During this time he wrote a simply worclecl pamphlet for technical personnel explaining the meteorological origins of anomalous propagation, how to recognize it, and how to make the best use of radar sets that one could uncler such conditions. It was illustrated by a very capable artist, was printed in tens of thousands of copies, and was ctistributec! to the technical branches of the Allies! armed services. This constituted Walter's basic con- tribution to the war effort. After the end of the war, his office was disbanded. He had lost his connections with atomic physicists many years before en c] hac] no desire to return to meteorology. Through a contact he tract maple on the Raclio Wave Propagation Committee, Walter obtained a position in the RCA labora- tories at Princeton testing antennas of new design. Since this clic! not appeal to him, he managed to get himself trans- ferred to a section supervises! by Dwight 0. North, a theo- retical physicist. The group was studying the properties of solicis user! in electronic solid-state devices. Walter found a

48 BIOGRAPHICAL MEMOIRS very congenial group among his collaborators but decided it was too late in life for him to switch to industry. After two years at RCA, he found a position as associate professor of physics at the University of Pennsylvania in Philadelphia. He taught a graduate course in mechanics that later became his mainstay in teaching. He wrote a re- view for physicists, "The Interior of the Earth and Geomag- netism," in 1950 that made him known to his American colleagues. He had been warned by friends that there was an ingrained political constellation in Philadelphia that would make an extended stay unpleasant. He found this to be true, so when he received an offer from the University of Utah's physics department to join the faculty and develop a graduate program he was definitely interested. Oppenheimer, who was then director of the Institute for Advanced Study in Princeton, told him that the University of Utah had a very high scholastic level judging from the excellent stu- dents he got from there when he was still in Berkeley. Con- sidering Oppenheimer's critical acumen, this seemed a very high recommendation and Walter accepted the offer in 1950. At Utah he gradually wound up teaching a comprehensive set of courses in theoretical physics, with the exception of quantum mechanics, which was taught by the most distin- guished member of the faculty, the theoretical chemist Henry Eyring. In an earlier discussion with John von Neumann, Walter had expressed the desire for a small inexpensive computer. He was told that the first such machine had just come out. The Air Force wanted such machines tested by competent academic people, so they bought one and loaned it to him in 1951, indifferent about the scientific problem he pro- posed to solve. Walter became intimately familiar with the design of the machine since it had been hastily constructed and the diodes frequently burned out and had to be re-

WALTER M. ELSASSER 149 placed. As a result he was unable to carry out any lengthy calculation, but he clic3 teach himself Boolean algebra, the formal logic of computing machines. This experience with early electronic computers gave Walter a sense of their ca- pacities anct limits, which was to prove useful in comparing them with living organisms. He gained first-hanc3 knowl- ecige of what was called cybernetics, now called systems theory, and he gave some thought to using the computer as a model of the brain. He cleciclecI to write a book in which the first two chapters were a survey of the basic ideas and tech- niques of cybernetics, followed by more philosophical no- tions. This book, The Physical Foundation of Biology ~ ~ 958), was the first of four books he wrote in biology. In 1955 after he wrote the first draft of the book, Walter clecidect to get an opinion about it from the university's biomedical community. When he asker! several members of that community whom they recommended to react the book, they all named a young professor of biophysics who had an interest in theory. This man took it home and brought it back a few days later. He said, "l have react this. It is thought provoking, in fact extremely thought provoking but so far as ~ am concerned, T clo not think, ~ observe." This was Walter's first encounter with a kinc! of mentality he founcI widespreacl among biologists who, living among the most gigantic accumulation of ciata the world hacl ever seen, proclaimer! that salvation lay in more data. This was, so to speak, a shattering incident for Walter since it cleniec! science as a creative activity. He hack always considered! sci- entific research in which observation was related by a recip- rocal interaction with thought; observational results tended to mollify thought, which in turn engenclerecl suggestions for more observations until significant knowledge tract come close to its boundaries. This dynamic process embocTiecT the advance in un(lerstancling in physical science, but it seemed

50 BIOGRAPHICAL MEMOIRS that in the life sciences the prevailing approach, the phi- losophy as it were, had assumed a quite different form. This discrepancy became increasingly clear in Walter's later years and sharpened his desire to pursue the philosophical interpretation of biological matters. Walter decided early cluring his tenure in Salt Lake City that he had risen as high as he could in an academic career short of moving to a more prestigious university. To do so would require that he specialize in only one of the several scientific fields in which he had become competent, in or- cler to remain on top in one of the fields. Instead, he de- ciclec3 to remain a generalist or, as he preferred to call it, a "natural philosopher." This decision was reinforced by the tragic loss in 1954 of his beloved wife Margaret. Since he clid not want to become a purely speculative philosopher, he invented a technique in which he ctiviclect his time into periods of several weeks to several months in which he con- centratec! on only one of the subjects in which he was inter- ested. He found periods of this size long enough to permit strong concentration and continued the scheme for the rest of his life. The loss of his wife left Walter alone with their children. He hac3 clevelopecl cordial relations with his neighbors, who were mainly Mormons, and his children felt at home in the neighborhood. He had become fond of the Mormons with their simple way of life combined with their appreciation of higher education, but he dicI not want to see himself or his children dissolved in the Mormon collectivity. Therefore, he accepted an offer from Roger Revelle to become the first professor at the newly developing University of Califor- nia at San Diego, which was actually locater! in La Jolla. Not long after he arriver! in 1956 at La lolls, the univer- sity committed itself to develop the San Diego branch into a major center of graduate study equivalent to that of the

WALTER M. ELSASSER 151 Berkeley anct Laos Angeles campuses. A building to accom- modate the nascent physics department was completed, and ~ n',mher of highly competent vaunt nhvsicists were re- . . . ~ J - - O 1- J cruitecI. Walter felt that these men were completely steeped in technology and clid not share his philosophical interests. He decidecl he click not fit into such a department, and Revelle created a niche for him at the Scripps Institution of Oceanography to (lo research in geophysics. However, about this time Walter hearct from Harry Hess, chairman of the Geology Department at Princeton, with an offer of a professorship in geophysics. Hess was the in(li- vidual among geologists who above all took Alfred Wegener's theory of continental drift seriously. Walter's interest in geoclynamics therefore fit with Hess's interest. The Geology nen~rtment was in one wine >if a building built earIv in the . c, ~ , century when evolution excited the academic world, with much of the research centered on paleontology. The Geol- ogy Department was in one wing of the building and biol- ogy in the other, en cl the libraries for both were in one large common room in the center. These seemed ideal con- clitions for Walter to continue his dual existence in geo- physics and the philosophy of biology, and he accepted the offer in 1962. Moving to Princeton was relatively easy for Walter since his chiTclren were now grown. Two years after his arrival he married again, this time to a cousin, Susanne, whom he hacT known from childhood. Although he met several clis- tinguishecl biologists during his five years at Princeton, he fount! that his philosophical probings into the foundations of biology macle them uncomfortable, as might be expecter! for one who aims to solve a specific question ant! does not want to be distractec! from it. He concludec! that biology hac! always been like what physics had become only late in its existence, (luring his lifetime. It was only by stripping off

52 BIOGRAPHICAL MEMOIRS the practical implications and complexities that physicists as natural philosophers could develop the methods that led to the major experimental discoveries en cl the great unify- ing mathematical schemes that constitute the grancI evince of modern physical science. The situation in biology was far more difficult. There was no grand edifice, but there was evidence of a general unity of pattern in organic nature. Walter felt that the situation in our age is uniquely propi- tious for developing a basic theory of organisms because there was, for the first time, an altogether coherent ab- stract scheme, quantum mechanics, for representing the physical basis of life. It needed only the assumption that biology is the realm of the utterly complex to realize that the simple black and white world of mathematics might no longer apply, en c! the whole conceptual system of scientific analysis might have to be reconstructed. This task was to occupy most of the rest of Walter's life. In 1967 he left Princeton for a research professorship at the University of Marylancl, which reliever! him of all teaching obligations. While he lost the prestige of Princeton, he gainer! the free- dom to clo whatever research he pleased. In the summer of 1974, having reached his seventieth birthday, he was duly retired from the University of Maryland. A few months later he received an offer of a suitable postretirement affiliation as adjunct professor in the Department of Earth and Plan- etary Sciences at Johns Hopkins University, which entailed no formal obligations. There he wrote the memoirs that form the backbone of this article up to this point. BIOLOGICAL WORK Walter's specific interest in biology as a scientific clisci- pline began in Paris in the early 1930s as a result of his discussions with Theophile Kahn, but his particular approach to the problems of biology grew out of his earlier experi-

WALTER M. ELSASSER 153 ence with (lepth psychology in Frankfurt. He felt there was a fundamental distinction between the living anct nonliving states, but it hack to be one that did not violate quantum mechanics. Van Neumann's 1932 book Mathematical Foun- dations of Quantum Mechanics demonstrated that all ensemble averages of physical quantities obey clifferential equations of a simple kincI; that is, their change in time is causally determined. Since Walter was convinced that a clistinguish- ing characteristic of organisms was that their long-term be- havior was not causally cleterminecI, he set himself the task of finding a way around von Neumann's completeness proof ant] founcl it in the concept that the members of any bio- Togical class are heterogeneous; that is, they share some but not all characteristics, while the members within any physi- cal class such as electrons, photons, atoms, and molecules are rigorously identical to one another. The heterogeneity of biological classes arises from the unfathomable complex- ity of living things. His aim was to construct a formal scien- tific logic that is suitable for organisms. His first publica- tion explicitly in biology was in 1951, although he lists a ~ 937 paper on quantum measurements and generalized complementarily among his biological publications. Alto- gether there were about thirty published papers in biology through 1984 plus at least as many ctrafts of papers extencI- ing through 1989, which did not get publishecl but are in the Elsasser collection in the Milton Eisenhower Library at Johns Hopkins. Seven of the latter were written in 1988 and 1989, indicative of his continued interest and activity in the area. Walter also wrote four books on theoretical biology, the first appearing in 1958 and the last in 1987. r first became aware of Walter's biological thought in the early 1960s through his first book en cl his articles in the fournal of Theoretical Biology. The book, The Physical Founda- tion of Biology, was heavy going for an experimental biolo-

54 BIOGRAPHICAL MEMOIRS gist, for the first half clealt with unfamiliar physical feecI- back control systems and information theory while the sec- onct half was more abstract ant! philosophical than most biologists are accustomed to. Some twenty years went by cluring which ~ became increasingly aware from my daily work that conventional ideas of causality were inacloquate to deal with the often unpreclictable behavior of cells in culture. One day in 1981 upon reading Volume ~ of Leslie FouIcts's classic book on cancer, Neoplastic Development, ~ came upon a brief account of Walter's biological thought that seemed to anticipate the types of problem ~ was encounter- ing. Rather than go back to his earlier papers, ~ wrote a letter to Walter asking about further clevelopment of his concepts, half expecting my request to be consigne(1 to the wastebasket. To my clelight he answered promptly in a friendly manner that seemed to invite further correspondence. That began an intense intellectual exchange that lastecl through the 1980s ant! grew to some 500 pages. As it began, Walter was writing a draft of his last book, Reflections on a Theory of Organisms (1987), which he sent me in stages. The manu- script went through many revisions and several privately printer! editions, paid for out of Walter's pocket before he found a one-woman publishing company in Canada to bring the book out. Through all this time he was unbelievably generous with his time, writing extensive expositions of his biological thought and general philosophy, often in response to naive questions of a pragmatically trainee! biologist. While at Princeton Walter wrote a seconc! book, Atom and Organism (1965~. After it appeared, he cleciclecl he had fallen uncler the sway of the establishment. This made him fee! as though he tract been flying with clipped wings, a situation he was determined to correct. The third book, The Chief Abstractions of Biology (1975), was written while he was at the University of MarylancI, where he was free to clo whatever

WALTER M. ELSASSER 155 research he chose. It formalizes many of the thoughts of the earlier books in a few abstract concepts. The fourth and final book is a distillation and refinement of the con- cepts formulatecl in the previous books. The following sum- marizes some of the main ideas expressed in his biological oeuvre. All of Walter's biological writings refer to the immense complexity of the organism based on the number and types of atoms in a cell and the number of possible bonds con- necting the atoms in organic molecules. Complexity is taken as an intrinsic aspect of the living state. Another important consideration is the near reversibility of most biochemical reactions as expressed in a well-known textbook by Conant anti Blatt.~ "Biochemical reactions liberate or absorb small amounts of energy. ... Apparently the necessity for revers- ible reactions with relatively small energy changes is charac- teristic of biochemical reactions." Walter recognizes! that the heat of biochemical reactions is close to that of thermal noise and therefore almost the direct opposite in its prop- erties for maintaining and transmitting information from those of computing machinery, which maximizes the differ- ence between signal and noise. The input by noise in biol- ogy is therefore removed from empirical control, en cl acI- equate results can no longer be obtained by a purely mechanistic model. The closeness of energy exchange in biochemical reactions to thermal noise is necessary for the clecision-making ability of the organism, allowing it to choose between available states without need for more than a mini- mal supply of energy. This condition contributes to what Walter called the fragility of the living state, defined as the capacity of the system to respond with large-amplitucle changes to small perturbations. In that sense fragility may also be characteristic of the processes involves! in clevelop- ment and differentiation of the organism. At the same time,

56 BIOGRAPHICAL EMOIRS the maintenance of information is so powerful that many species do not change their species-specific characteristics for millions of generations. These thoughts lee! Walter to formulate a holistic set of principles to represent the living state. These principles are not scientific laws in the usual sense since they are not clerivable from the mathematics of quantum mechanics. They define that which is in the form of regularities but not determined by atomic en cl molecular physics. The basic as- sumption in his holistic interpretation is that "an organism , ~ Lor a cell] is a source (or sometimes a sink) of causal chains which cannot be traced beyond a terminal point because they are lost in the unfathomable complexity of the organ- ism for cells." The basic principles of organisms as listed in his 1987 book are the following: 1. The first principle is orclerec! heterogeneity. Combina- torial analysis shows that the number of structural arrange- ments of atoms in a cell is immense; that is, much greater that 10~°°, a number that is itself much larger than the number of elementary particles in the universe (108°~. But biology shows us there is regularity in the large where there is heterogeneity in the small, hence artier above heteroge- neity. This concept of ordered heterogeneity was first intro- cluced by the molecular biologist Rollin Hotchkiss, system- atized by the embryologist Paul Weiss, but given quantitative definition and set in a general theory by Walter. 2. The second principle is creative selection. A choice is macle in nature among the immense number of possible patterns inferred in the first principle. The availability of such a choice is consi(lered the basic and irreplaceable cri- terion of holistic or nonmechanistic biology. The term "cre- ative" refers to phenomena that, like everything in biology, are compatible with the laws of physics but are not uniquely

WALTER M. ELSASSER 157 determined by them. No mechanism can be specified by whose operation those selected differ from those not se- lectecI. He points out that the number of different patterns is also immense in the physical science of statistical me- chanics, but in that case the variation of structure from pattern to pattern averages out. The patterns of inorganic systems repeat themselves over and over again ace infinitum, while those of each organism are unique. The selection of a relatively small number of organisms from the immense number of possibilities allowed by quantum mechanics is a primary expression of biological order and is the scientific counterpart of the term "creativity" used in ordinary lan- guage. 3. The third! principle is holistic memory. It provides the criterion for choice not expressed in the second principle. That criterion is information stability. The term "memory" in a generalized sense indicates stability of information in time or, as in the case of heredity, the reproduction of information in an emplrlca sense, that IS, Wit rout our ~now- ing the full mechanism of reproduction. The creative selec- tion of the second principle means the organism has many more states to choose from than are actually neeclecI. The thirc! principle says the organism uses this freedom to cre- ate a pattern that resembles earlier patterns. Walter bor- rowec! the term "memory without storage" from the phi- losopher Henri Bergson, who was considering the memory function of the brain in his book Matter and Memory. Walter consiclere(1 holistic memory an epistemological innovation that was the touchstone of his theoretical scheme but real- izect that it might seem like black magic to many of his readers. However, he noted that the concept is free from internal contradiction while it obviously runs counter to habitual thought. In that formal sense it is no different from the concept of the antipodes, which wouicl have been

58 BIOGRAPHICAL MEMOIRS inconceivable before Newton since the people in Australia should have fallen off the earth. Memory without storage is consiclerecl as transmission of morphological features through time without a material memory crevice, just as relativity is based on the transmission of signals through space without a materia carrier. 4. Holistic memory requires a fourth principle, operative symbolism, to indicate that a material carrier of informa- tion is needled, namely DNA, but this acts as a releaser or operative symbol for the capacity of the whole organism to reconstruct a complete message that characterizes the aclult of the next generation. Walter was sketchy and superficial about the fourth principle and consiclerec! it in the nature of a specific cletail. In other words, operative symbolism is not necessary to the clevelopment of the postulational sys- tem of the first three principles that can c30 away with the conceptual clifficulties and internal contradictions that al- ways appear in any purely mechanistic interpretation of or- ganic life. The informational system of organisms is there- fore postulated to be clualistic; on one level it is mechanistic in the operation of the genetic code; on the other level it is holistic, involving the entire cell or organism. Walter's epistemological revision for the life sciences has been ignores] by most biologists and attacked by some. The coo} en cl sometimes downright hostile response of the bi- ologists is probably relater! to the challenge presenter! to the basic preconceptions, often subconscious, that underlie their present moclus operancli. The most pervasive of these preconceptions is that biology is ultimately an extension of physics and chemistry and can be stuclied in an analogous manner. Walter's theoretical innovations require a novel experimental approach that is just beginning to take shape to clear with the holistic aspects of cell ancl organismic be-

WALTER M. ELSASSER 159 havior. Despite the difficulties, his thought has found strong support from a few outstanding biologists such as Leslie Foulds and Paul Weiss. It has also met with approval from some notables among theoretical physicists, including Pauli and Wigner, and from the information theorist L. Brillouin. Perhaps his strongest support has come from Frederick Seitz, a student of Wigner's in the early 1930s and a founder of modern solid-state physics. Seitz spent a decade as presi- dent of the Rockefeller University, where he was in continu- ous contact with many of the most creatively active indi- viduals in molecular and cell biology and was impressed with their ingenuity. However, he was struck by the com- parative rigidity of their molecular concepts and their enor- mous confidence (or overconfidence) that reductionism To would lead to an understanding of all aspects of living sys- tems. Flying in the face of these attitudes was the fact that the picture of such systems that was evolving at the molecu- lar level was becoming ever more complex with each new major phase of development. Seitz felt that the outlook of the molecular biologists was somewhat reminiscent of the attitude of some nineteenth-century physicists who believed that the universe was a gigantic clockwork governed by the laws of classical physics. Ironically, Seitz's own work pro- vides the theoretical foundation for the currently fashion- able field of structural biology. While musing on the situa- tion in biology he came upon Walter's work, which he considered a "profound analysis of the status of biological systems in the physical world." He felt that the biological community had "to a substantial degree lost sight of the forest for the trees and presumably will continue to do so until it is forced to reexamine its own foundations either through the appearance of obvious paradoxes or because it becomes enmeshed in unresolvable complexity or both." When that time comes, he is "certain that the profoundness

60 BIOGRAPHICAL MEMOIRS of Walter's work will be appreciated and will form a signif~- cant part of the cornerstone of unclerstancling of living sys- tems by the biological community." Walter's work has aIreacly formed the cornerstone of my own unclerstancting of living systems through its effect on my clay-to-day work with cells in culture. A major feature of the behavior of cells dissociatecl from the organism and from one another is their radical heterogeneity in a large variety of behavioral anc! physico-chemical properties. This was anticipate<] in Walter's principle of ordered heteroge- neity but appeared experimentally at the cellular level rather than the molecular level which most concerned him. An- other feature of these cells in Walter's terms is their fragil- ity, so they change their growth behavior in a striking ant! encluring fashion in response to small physiological cliffer- ences in their environment. These responses are foreshac3- owe(1 in Walter's principle of creative selection, which ~ moclif~ed to progressive state selection to image cellular be- havior. Paracloxically, the behavior of some cells, clepend- ing on their initial state, is extremely stable, so that both fragility and stability are subsumed in the same system, as full consideration of Walter's theory would suggest. This goes along with his insight that there are no "yes/no" or purely arithmetic answers in the behavior of living systems. All clepends on the initial state of the cells and the pertur- bations to which they are subjected. On a personal note, his philosophical analysis liberated me from the recluction- ist strictures that clominate biological thought anc! allowecl me to acknowlecige and organize the actual behavior of cells as seen every clay before my own eyes rather than sweep the frequently inconvenient behavior under the rug. There is no doubt in my mind that Walter was correct in the evaluation he left with his own collected papers in the Johns Hopkins library that, although he was best known for

WALTER M. ELSASSER 161 his work in geophysics, his controversial ideas in theoretical biology were what historians would want to study. ~ believe his ideas will play a central role in the future clevelopment of biology. WALTER ELSASSER S Memoirs of a Physicist in the Atomic Age was the ma- jor source of information used here in describing his life up to 1974. His sister, Maria Lindberg, and Eugene Parker of the Univer- sity of Chicago provided some personal insights. Peter Olson of Johns Hopkins provided a description of Walter's work on geomag- netism and plate tectonics. Frederick Seitz, formerly president of Rockefeller University, contributed his thoughts on Walter's bio- logical work. Most of the section on that work was derived from Walter's published biological writings and from his extensive corre- spondence with me between 1981 and 1991. My wife, Dorothy Rubin, helped in every phase of preparing this memoir. NOTE 1. The Chemistry of Organic Compounds, 2nd ea., Ch. 20. New York: MacMillan, 1947.

62 BIOGRAPHICAL MEMOIRS HONORS 1932 Research Prize of the German Physical Society 1957 Member, National Academy of Sciences 1971 John A. Fleming Medal, American Geophysical Union 1972 Fellow, American Academy of Arts and Sciences 1977 Gauss Medal, Braunschweig, Germany, (200th Anniversary of Gauss's birth) 1979 Penrose Medal (USA) 1987 National Medal of Science

WALTER M. ELSASSER SELECTED BIBLIOGRAPHY ATOMIC AND NUCLEAR PHYSICS 1925 Bemerkungen zur Quantenmechanik Naturwissenschaften 13:711. 1928 163 frier Elektronen. Interfernzerscheinungen an Korpuskularstrahlen. Natunvissenschaften 16:720. 1933 A possible property of the positive electron. Nature 131:674. 1935 Energies de laison des noyaux lourdes. [. Phys. (Paris) 6:473. Theorie de la capture selective des neutrons rents par certains noyaux. J. Phys. (Paris) 6:194. 1937 The self-consistent field and Bohr's nuclear model. Phys. Rev. 51:55. GEOPHYSICS 1938 New values for the infrared absorption coefficients of atmospheric water vapor. Mon. Weather Rev. 68:175. 1942 Heat Transfer by Infrared Radiation in the Atmosphere. A Monograph. Cambridge, Mass.: Harvard University Press. 1947 Induction effects in terrestrial magnetism, III. Phys. Rev. 72:821. 1950 The earth's interior and geomagnetism. Rev. Mod. Phys. 22:1.

164 BIOGRAPHICAL MEMOIRS 1955 With H. Takeuchi. Non-uniform rotation of the earth and geomag- netic drift. Trans. Am. Geophys. Union 36:584. 1956 Hydromagnetism, II. A Review. Am. J. Phys. 24:85. 1959 With H. C. Urey and M. G. Rochester. Note on the internal struc- ture of the moon. Astrophys. jr. 129:842. 1968 The mechanics of continental drift. Proc. Am. Philos. Soc. 112:344. THEORETICAL BIOLOGY 1958 The Physical Foundation of Biology, An Analytical Study. New York: Pergamon Press. 1966 Atom and Organism, A New Approach to Theoretical Biology. Princeton, Nisi.: Princeton University Press. 1969 Acausal phenomena in physics and biology; a case for reconstruc- tion. Am. Sci. 57:502-16. 1970 The role of individuality in biological theory. In Towards a Theoreti- cal Biology, vol. III, ed. C. H. Waddington. Edinburgh: Edinburgh University Press. 1975 The Chief Abstractions of Biology. New York: Elsevier.

WALTER M. ELSASSER 165 1981 Principles of a new biological theory: a summary. {. Theor. Biol. 89:131-50. A form of logic suited for biology. Prog. Theor. Biol. 6:23-62. 1982 The other side of molecular biology. [. Theor. Biol. 96:67-76. 1984 Outline of a theory of cellular heterogeneity. Proc. Natl. Acad. Sci. U.S.A. 81:5126-29. 1987 ReQections on a Theory of Organisms. Frelighsburg, Quebec: Orbis Pub- lishing. AUTOBIOGRAPHICAL 1978 Memoirs of a Physicist in the Atomic Age. New York: Neale Watson Academic Publications, Inc.

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Biographic Memoirs Volume 68 contains the biographies of deceased members of the National Academy of Sciences and bibliographies of their published works. Each biographical essay was written by a member of the Academy familiar with the professional career of the deceased. For historical and bibliographical purposes, these volumes are worth returning to time and again.

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