My questions in this paper are perhaps improperly analytic. Instead of trying to find new bright colors on Szilárd's portrait, I would rather think about some undercurrents of his thinking. As a historian of science, I ask about the source of his unbelievable fertility in so many fields. Is there any significance of the diversity of interests in his oevre? If the answer is positive, is there a common denominator, or, more precisely, a common basis of all his scientific, political and personal activities? I guess there is, but it is not very easy to find it.
When looking for an answer, I would shortly recall his biological papers, instead of his legendary physics or witty inventions, which sometimes appears fiction like. Some people, including William Lanouette, say that Szilárd did "botching" with ideas1, meaning that he just sat at a pleasant place and did nothing else but thinking, or as his friend, Jaques Monod put it, he "was too rich in ideas, he derived too much sheer pleasure in playing with them as a child with his toys 2." In contrast with this opinion, I think these games had a purpose, which was not the least childish.
On the occasion of their first talk, in Cold Spring Harbor, in 1947, Szilárd deeply impressed Monod, who in 1965 was awarded the Nobel-prize for his works on the genetic control of enzyme and virus synthesis. Monod wrote: "I felt that some of the more disturbing suggestion made by that strange man could not be right, I was forced to think hard to answer and convince him to his satisfaction. ...I have also recorded in my Nobel lecture, how it was Szilard who decisively convinced me with the idea...that enzyme induction reflected an antirepressive effect, rather than the reverse, as I tried, unduly, to stick to3."
This talk proved also decisive to Szilárd. They discussed Monod's observation that some bacteria when offered a mixture of glucose and lactose, two types of sugars, eat first the glucose and only when it runs out, begins to consume glucose. Szilárd suggested giving both types of sugars continuously at the speed of their consumption. This way, it could be established whether the consumption of one type excludes the consumption of the other. For this, he devised a vessel, in which the concentrations of glucose and lactose were kept constant by a steady inflow of the sugar that the bacteria have consumed. According to Aaron Novick, Szilárd' collaborator, later professor at the University of Oregon, this idea lead to the chemostat, Szilárd's principal discovery in biology. The chemostat was a device based on a feed back mechanism. In its vessel a population of bacteria could grow indefinitely if the concentration of the feeding chemicals is kept at a certain level4. This way, even the speed of growth could be controlled. With Maurice Fox, Szilárd worked out in 1955 a similar but more modern instrument, called "breeder."
Though the chemostat was probably Szilárd's major published contribution to biology, which he applied in many of his studies, it was not the first one. Among his fourteen papers published in the field of biology, and republished in his Collected Works volume, the first one concerned the lethal effect of UV rays on bacteria compared with those irradiated by visible light5.
In the same year, 1950, Szilárd and Novick published both the chemostat principle and the first results coming from the usage of the apparatus worked on this principle. The device was put together in the basement lab in Chicago. Under the conditions of the chemostat, unlimited generations of bacteria could in principle be born and die, but Szilárd and Novick observed that evolutionary factors limited the number of these generations. In their third common paper they described a new phenomenon called phenotypic mixing. In this they showed that even viruses can change their appearance, their phenotype, in the sense that they can infect a bacterium, which is normally resistant to them, but their progeny cannot do the same thing, which proves that their genotype did not change.
Later they investigated the rate of mutations and showed that surprisingly the mutations' rate was independent of the growth rate of the bacteria. When trying to influence this rate, they could prove that some substances had a significant effect on it. While some non toxic compounds increased the rate, some others decreased it, "certain nucleosides can act as anti-mutagenes" (p.425.), as Szilárd and Novick wrote, and, in general, chemical factors inside the cell exert great influence upon mutations. They observed that bacteria which had immunity to a particular virus could increase their rate in a mixture of various bacteria even in the absence of the virus, but after some generations this rate abruptly decreased and then increased again. In the chemostat they could also study the control mechanisms, particularly, the inhibitory mechanism of the formation of some enzymes, and they established that, as Novick wrote, "an amino acid could block its own syntheses by interfering with the activity of the biosynthetic enzymes."(p. 391.) Enzyme formation and its mechanism made the subject of Szilárd's two theoretical papers written in 1960, the second of which dealt with the problem of protein antibodies.
In a most remarkable paper he studied the aging process. The population of bacteria in the chemostat consisted of a huge number of cells, therefore, it could be considered analogous to an organism. This way, the mutants that grew in it modeled the aging of an organism. According to his theory, aging is due to "aging hits," his central notion for the description of the process. An aging hit, I quote Szilárd, "destroys a chromosome of the somatic cell, in the sense that it renders all gene carried by that chromosome inactive." (p. 447.) He went on to suppose that "during the life-time of the animal, whole chromosomes, which are contained in the somatic cells, suffer a total loss of function in a single random event. ... the probability of such an event remains constant throughout life-time and it is the same for all individuals of a given species." He supposed that lifespan is genetically determined and the fact that in humans females live longer than males can be explained on the basis of females more perfect genes. Szilárd thought about the ratio of boys and girls as a function of the age of the father at a fixed age of the mother, and concluded that the ratio of boys falls with the increase of the father's age.
In his last paper, as Novick noticed, (p. 392) Szilárd closed a circle that he began to draw in his very first publication on the Maxwell demon. In this first paper, he studied the intelligence in relation to thermodynamics, while in the last he drafted a hypothetical model on the work of brain. Based on two postulates, he aimed to prove the possibility of devising a neural network model which accounts for our mental capacity, or ability to learn and to remember.
Even this very short account of his biological works might prove that Leo Szilárd achieved outstanding results in biology, even if they did not become as famous as those in physics. From biographical point of view, it is remarkable that while he became more famous of his works in the field of physics, this fourteen papers published from biology amount to half of his scientific publications consisting of not more than twenty-nine items. Consequently, when looking for the common denominator of Szilard's diverse public activities, his reasons why he turned to biology might be relevant.
At least four possible answers might be found for this exciting question. The first answer is simplistic and anecdotic. According to this, Szilárd got expelled from the paradise of nuclear physics by the head of the Manhattan-project, General Leslie Groves, whose hostility toward Szilárd came from Szilárd's unusual way of thinking and behavior that the General could not stand. In addition, after Hiroshima Szilárd also got fed up with developing arms. Because of these, Szilárd was compelled to look for an entirely new field.
The second possible answer is more biographical. It says that Szilárd wanted to change to biology already in early 1933, when in London he called on Archibald Hill, the winner of the 1922 physiology Nobel-prize, to discuss his own intention to go to biology, and Hill offered him a demonstrator position. Szilárd, however, finally decided against becoming a physiology demonstrator, because he unexpectedly came to the idea of nuclear chain reaction, which obsessed him for some decades. But after his success in exploiting nuclear energy, which only was a detour, he could return to his original goal of changing to biology6.
The third answer is related to the history of science, and is more complicated than the previous ones. This answer considers Szilárd's step something that has also been taken by some other great men of modern physics; a step that finally resulted in the formation of molecular biology, and in its most famous feat, Watson's and Crick double helix model of DNA and its role in gene replication, which was established in 1953. Where is Szilárd's place in this flow of history?
Donald Fleming wrote already in 1969 that "The men who supplied the indispensable fostering environment for Watson and Crick were four: Erwin Schrödinger, Leo Szilárd, Max Delbrück, Salvador Luria7." Only Luria was a biologist in this group, all the others were physicists.
After the quantum revolution in the 1920s and in the midst of the fast development of nuclear physics, some most eminent physicists, including Niels Bohr, came to the conclusion that biology, the so-called secret of life, should be the next big leap in scientific progress. In possession of an apparently all powerful scientific methodology, they started to study living organisms. Schrödinger, in his popular book, "What is life?" wrote about the possible transfer of genetic information between the cells, and supported Delbrück's suggestion to use quantum mechanics, namely, the Heitler-London approach in biology8. Max Delbrück, awarded the medical Nobel-prize in 1969, initiated the usage of quantum mechanics in actual biological research. He chose as an elementary living particle to be studied the bacteriophage, and set up a research group in the USA which exercised an enormous influence upon almost everybody in the field, including Watson, who played a significant role in the formation of molecular biology.
But what did Szilárd do? From the citations of his papers, it might have become clear that with chromosomes, genes, mutations, immun systems, enzyme formations, bacteria and viruses, his subjects were about the same as those of the phage peoples'. His first talk to Monod occurred in a phage group seminar, in Delbrück's phage church, as Szilárd called it. According to David Grandy, "Szilárd straddled the ideological divide that separated physics and evolutionary biology9," (p. 116.) which means that he was brave enough to attack biological problems on the basis of his training as a physicist. Fleming suggested a more general explanation when cited an interview conducted with Szilárd. He said his influence in biology did come from "not any skills acquired in physics, but rather an attitude: the conviction which few biologists had at that time, that mysteries can be solved." (p.161) Besides this attitude and the hottest research subjects and his original thinking, Lanouette emphasized Szilárd's extreme fertility in creating ideas that he passed to anybody he met. "Most of his ideas" according to Lanouette "were carried away and tested by others." Einstein said with resentment that Szilárd only laid the golden eggs.
The fourth answer to the question why Szilárd made this career change is philosophical. This answer may also solve the problem of the common denominator of his diverse activities. When recounting Szilárd's publications, his most important patents, research report and newspaper articles were omitted. But a more detailed account of his biology would throw light on his pioneering thoughts about fertility, about birth control, including his specific calendar of the most fertile days, about his thinking on the harms of smoking etc. All these subjects were entirely new at that time and very close to everyday life, which he wanted to improve with all his efforts.
For this attitude, I would say Szilárd was not a specialist. A biographer called him the "elusive Szilárd," because it was impossible to put his thinking into one well-defined category10. I would say that the common denominator of all his activities was his philosophy. Indeed, Szilárd did not publish explicit philosophical essays, but this is not unusual as many of his most important ideas remained unpublished. His philosophy should be read from his scientific papers, from his political activities and from his strategies in everyday life.
What kind of philosophy did he develop and follow? Besides his extreme rationalism, which prevented him from writing "great" literature, besides his hedonism that took him to many pleasant restaurants, besides his unbelievable unselfishness, as Karl Polányi characterized him, or for all these, I think he was Platonic.
His Platonic thinking can perhaps most vividly be seen in his paper on an elite group called "der Bund," which Szilárd drafted around 193011. The Bund could be considered an anticipation and prototype of later organizations conceived and set up by him, like Pugwash or the Council for a Livable World. The Bund would have been a group of young people selected on the basis of their high intelligence and high standard of moral. They would have been educated and trained so that they should be able to lead the society in various fields. Their role would be to complete the parliamentary system and if this system collapses, as Szilárd thought, it could collapse any time, the Bund would have been able to take over. Without considering his famous predictive gift, which let him guess the coming collapse of the Weimar Republic, the Platonic way of solution could be pointed out. The Bund appears equal to Plato's philosophers in his Republic. The roles of the philosophers however are played by scientists or, in more general terms, experts. Szilárd mixed Platonism with scientism and with this he always followed the line of his favorite writer H. G. Wells.
In conclusion, I would say that Szilárd was a philosopher with a strong conviction to rationalism, scientism and Platonism. But what intention can be shown behind all this? What was the common element in discovering the nuclear chain reaction, in initiating the Manhattan-project, setting up organizations like the Council for a Livable World, in thinking about the secret of biological life, or inventing refrigerators or birth control clocks? Szilárd could reply in one sentence: to save the world.
Created: 23. November 1998 by Pluhár Emese