Why the world needs more Leo Szilards

The body of men and women who built the atomic bomb was vast, diverse, talented and multitudinous. Every conceivable kind of professional - from theoretical physics to plumber - worked on the Manhattan Project for three years over an enterprise that spread across the country and equaled the US automobile industry in its marshaling of resources like metals and electricity.

The project may have been the product of this sprawling hive mind, but one man saw both the essence and the implications of the bomb, in both science and politics, long before anyone else. Stepping off the curb at a traffic light across from the British Museum in London in 1933, Leo Szilard saw the true nature and the consequences of the chain reaction six years before reality breathed heft and energy into its abstract soul. In one sense though, this remarkable propensity for seeing into the future was business as usual for the Hungarian scientist. Born into a Europe that was rapidly crumbling in the face of onslaughts of fascism even as it was being elevated by revolutionary discoveries in science, Szilard grasped early in his youth both a world split apart by totalitarian regimes and the necessity of international cooperation engendered by the rapidly developing abilities of humankind to destroy itself with science. During his later years Szilard once told an audience, "Physics and politics were my two great interests". Throughout his life he would try to forge the essential partnership between the two which he thought was necessary to save the human species from annihilation.

A few years ago, physicist and author William Lanouette brought out a new, revised edition of his definitive, sensitive and sparkling biography of Szilard. It is essential reading for those who want to understand the nature of science, both as an abstract flight into the deep secrets of nature and a practical tool that can be wielded for humanity's salvation and destruction. As I read the book and pondered Szilard's life I realized that the twentieth century Hungarian would have been right at home in the twenty-first. More than anything else, what makes Szilard remarkable is how prophetically his visions have played out since his death in 1962, all the way to the year 2014. But Szilard was also the quintessential example of a multifaceted individual. If you look at the essential events of the man's life you can see several Szilards, each of whom holds great relevance for the modern world.

There's of course Leo Szilard the brilliant physicist. Where he came from precocious ability was commonplace. Szilard belonged to the crop of men known as the "Martians" - scientists whose intellectual powers were off scale - who played key roles in European and American science during the mid-twentieth century. On a strict scientific basis Szilard was perhaps not as accomplished as his fellow Martians John von Neumann and Eugene Wigner but that is probably because he found a higher calling in his life. However he certainly did not lack originality. As a graduate student in Berlin - where he hobnobbed with the likes of Einstein and von Laue - Szilard came up with a novel way to consolidate the two microscopic and macroscopic aspects of the science of heat, now called statistical mechanics and thermodynamics. He also wrote a paper connecting entropy and energy to information, predating Claude Shannon's seminal creation of information theory by three decades. In another prescient paper he set forth the principle of the cyclotron, a device which was to secure a Nobel Prize for its recognized inventor - physicist Ernest Lawrence - more than a decade later.

Later during the 1930s, after he was done campaigning on behalf of expelled Jewish scientists and saw visions of neutrons branching out and releasing prodigious amounts of energy, Szilard performed some of the earliest experiments in the United States demonstrating fission. And while he famously disdained getting his hands dirty, he played a key role in helping Enrico Fermi set up the world's first nuclear reactor.

Szilard as scientist also drives home the importance of interdisciplinary research, a fact which hardly deserves explication in today's scientific world where researchers from one discipline routinely team up with those from others and cross interdisciplinary boundaries with impunity. After the war Szilard became truly interdisciplinary when he left physics for biology and inspired some of the earliest founders of molecular biology, including Jacques Monod, James Watson and Max Delbruck. His reason for leaving physics for biology should be taken to heart by young researchers - he said that while physics was a relatively mature science, biology was a young science where even low hanging fruits were ripe for the picking.

Szilard was not only a notable theoretical scientist but he also had another strong streak, one which has helped so many scientists put their supposedly rarefied knowledge to practical use - that of scientific entrepreneur. His early training had been in chemical engineering, and during his days in Berlin he famously patented an electromagnetic refrigerator with his friend and colleague Albert Einstein; by alerting Einstein to the tragic accidents caused by leakage in mechanical refrigerators, he helped the former technically savvy patent clerk put his knowledge of engineering to good use (as another indication of how underappreciated Szilard remains, the Wikipedia entry on the device is called the "Einstein refrigerator"). Szilard was also finely attuned to the patent system, filing a patent for the nuclear chain reaction with the British Admiralty in 1934 before anyone had an inkling what element would make it work, as well as a later patent for a nuclear reactor with Fermi.

He also excelled at what we today called networking; his networking skills were on full display for instance when he secured rare, impurity-free graphite from a commercial supplier as a moderator in Fermi's nuclear reactor; in fact the failure of German scientists to secure such pure graphite and the subsequent inability of the contaminated graphite to sustain fission damaged their belief in the viability of a chain reaction and held them back. Szilard's networking abilities were also evident in his connections with prominent financiers and bankers who he constantly tried to conscript in supporting his scientific and political adventures; in attaining his goals he would not hesitate to write any letter, ring any doorbell, ask for any amount of money, travel to any land and generally try to use all means at his disposal to secure support from the right authorities. In his case the "right authorities" ranged, at various times in his life, from top scientists to bankers to a Secretary of State (James Byrnes), a President of the United States (FDR) and a Premier of the Soviet Union (Nikita Khrushchev).

I am convinced that had Szilard been alive today, his abilities to jump across disciplinary boundaries, his taste for exploiting the practical benefits of his knowledge and his savvy public relations skills would have made him feel as much at home in the world of Boston or San Francisco venture capitalism as in the ivory tower.

If Szilard had accomplished his scientific milestones and nothing more he would already have been a notable name in twentieth century science. But more than almost any other scientist of his time Szilard was also imbued with an intense desire to engage himself politically - "save the world" as he put it - from an early age. Among other scientists of his time, only Niels Bohr probably came closest to exhibiting the same kind of genuine and passionate concern for the social consequences of science that Szilard did. This was Leo Szilard the political activist. Even in his teens, when the Great War had not even broken out, he could see how the geopolitical landscape of Europe would change, how Russia would "lose" even if it won the war. When Hitler came to power in 1933 and others were not yet taking him seriously Szilard was one of the few scientists who foresaw the horrific legacy that this madman would bequeath Europe. This realization was what prompted him to help Jewish scientists find jobs in the UK, at about the same time that he also had his prophetic vision at the traffic light.

It was during the war that Szilard's striking role as conscientious political advocate became clear. He famously alerted Einstein to the implications of fission - at this point in time (July 1939) Szilard and his fellow Hungarian expatriates were probably the only scientists who clearly saw the danger - and helped Einstein draft the now iconic letter to President Roosevelt. Einstein's name remains attached to the letter, Szilard's is often sidelined; a recent article about the letter from the Institute for Advanced study on my Facebook mentioned the former but not the latter. Without Szilard the bomb would have certainly been built, but the letter may never have been written and the beginnings of fission research in the US may have been delayed. When he was invited to join the Manhattan Project Szilard snubbed the invitation, declaring that anyone who went to Los Alamos would go crazy. He did remain connected to the project through the Met Lab in Chicago, however. In the process he drove Manhattan Project security up the wall through his rejection of compartmentalization; throughout his life Szilard had been - in the words of the biologist Jacques Monod - "as generous with his ideas as a Maori chief with his wives" and he favored open and honest scientific inquiry. At one point General Groves who was the head of the project even wrote a letter to Secretary of War Henry Stimson asking the secretary to consider incarcerating Szilard; Stimson who was a wise and humane man - he later took ancient and sacred Kyoto off Groves's atomic bomb target list - refused.

Szilard's day in the sun came when he circulated a petition directed toward the president and signed by 70 scientists advocating a demonstration of the bomb to the Japanese and an attempt at cooperation in the field of atomic energy with the Soviets. This was activist Leo Szilard at his best. Groves was livid, Oppenheimer - who by now had tasted power and was an establishment man - was deeply hesitant and the petition was stashed away in a safe until after the war. Szilard's disappointment that his advice was not heeded turned to even bigger concern after the war when he witnessed the arms race between the two superpowers. In 1949 he wrote a remarkable fictitious story titled 'My Trial As A War Criminal' in which he imagined what would have happened had the United States lost the war to the Soviets; Szilard's point was that in participating in the creation of nuclear weapons, American scientists were no less or more complicit than their Russian counterparts. Szilard's take on the matter raised valuable questions about the moral responsibility of scientists, an issue that we are grappling with even today. The story played a small part in inspiring Soviet physicist Andrei Sakharov in his campaign for nuclear disarmament. Szilard also helped organize the Pugwash Conferences for disarmament, gave talks around the world on nuclear weapons, and met with Nikita Khrushchev in Manhattan in 1960; the result of this amiable meeting was both the gift of a Schick razor to Khrushchev and, more importantly, Khrushchev agreeing with Szilard's suggestion that a telephone hot-line be installed between Moscow and Washington for emergencies. The significance of this hotline was acutely highlighted by the 1962 Cuban missile crisis. Sadly Szilard's later two attempts at meeting with Khrushchev failed.

After playing a key role in the founding of the Salk Institute in California, Szilard died peacefully in his sleep in 1964, hoping that the genie whose face he had seen at the traffic light in 1933 would treat human beings with kindness.

Since Szilard the common and deep roots that underlie the tree of science and politics have become far clearer. Today, when science and facts seem under attack and where truth constantly threatens to become a casualty, we need scientists like Szilard to stand up for science every time a scientific issue political ideology. When Szilard pushed scientists to get involved in politics it may have looked like an anomaly, but today it's not simply optional. All of us need to be involved in small and big ways. At the same time, it's worth noting that Szilard's motto for the interaction of science with politics was often one of accommodation. He was always an ardent believer in the common goals that human beings seek, irrespective of the divergent beliefs that they may hold. He was also an exemplar of combining thought with action, projecting an ideal meld of the idealist and the realist. Whether he was balancing thermodynamic thoughts with refrigeration concerns or following up political idealism with letters to prominent politicians, he taught us all how to both think and do. As interdisciplinary scientist, as astute technological inventor, as conscientious political activist, as a troublemaker of the best kind, Leo Szilard leaves us with an outstanding role model and an enduring legacy. It is up to us to fill his shoes.

Born on this day: Physicist Emilio Segrè, who changed the direction of the Manhattan Project

The road to mutually assured destruction unintentionally started in 1944, at the end of a mountain trail with flowers and snakes, with a man called The Basilisk. But he didn't know it then. In the fall of 1944, the sprawling, top secret atomic bomb project at Los Alamos faced a huge crisis. Ever since the laboratory had been set up in 1943, it had been working on two kinds of bombs. One would work on uranium which was being separated using cyclotrons at Oak Ridge, Tennessee. The other would work on plutonium which was being created in nuclear reactors in Hanford, Washington. The basic design for nuclear weapons had been worked out in 1942 and was simple in principle: slam together two lumps of uranium and plutonium using a "gun" so that they come together to create a critical mass, and the ensuing exponential chain reaction would guarantee a tremendous explosion. In 1944 it seemed like that design was well underway for both uranium and plutonium. 

Then in the fall of 1944 came news that this design would be useless for plutonium. Millions of 1944 dollars and the resources of thousands of workers and scientists were at stake. The laboratory's director, Robert Oppenheimer, felt so embattled that he briefly considered resigning. The man who delivered this bad news to Oppenheimer and the others was Emilio Segrè.

Emilio Segrè who was born today in 1905 was a member of the small band of brilliant physicists led by Enrico Fermi in Rome in the 1930s. Each member of the team had a nickname. Fermi was "The Pope" because of his infallible knowledge of physics. Segrè's sharp tongue and quick mind made others name him "The Basilisk". Segrè was part of all of Fermi's key experiments, including the ones leading up to his Nobel Prize. Segrè himself won a Nobel Prize later for his discovery of the antiproton. But in 1944, he must have been seen as the bearer of bad news. This news, however, galvanized the lab and forced it to explore a novel idea that became the basis of nuclear arsenals around the world.

At Los Alamos Segrè was assigned the task of measuring the neutron properties of uranium and plutonium and their byproducts. Because his work involved large quantities of potentially dangerous neutrons, he was put in a cabin several miles removed from the main laboratory. The cabin was at the end of a trail populated by rattlesnakes and beautiful flowers. What Segrè discovered in that cabin was that the plutonium bomb would fizzle out prematurely if it were assembled by the gun technique. Premature explosion had been considered by the Los Alamos scientists and was not thought to be a serious issue. The probability of premature explosion depended on the rate of neutrons spontaneously generated by the fissile mass. Left to themselves, uranium and plutonium have a small but fixed background rate of spontaneous neutron emission. During critical assembly, a high rate of neutron emission meant that the fission would start occurring before the critical mass was reached, and the result would at best be a small, inefficient explosion. It was thus essentially a contest between this rate and the speed with which the two pieces were brought together that would decide the fate of the bomb.

Physicists were not ignorant of the rate of spontaneous fission in uranium and plutonium and in fact had measured it to reassure themselves that it would not matter. However, they had reached this conclusion based on experiments on small quantities of uranium-238 and plutonium-239 produced in cyclotrons built by Ernest Lawrence's team at Berkeley. However cyclotrons cannot be used to make plutonium in any measurable quantity. By the time the Manhattan project picked up steam, Pu-239 was being produced in gram quantities in the nuclear reactors at Hanford.

What the physicists had not realized was the role that a rogue isotope of plutonium would play in thwarting their plans for a gun type bomb. It turns out that the spontaneous fission depends on the precise isotope under consideration. Plutonium-239 is produced by bombarding uranium-238 by neutrons. However there is another isotope of plutonium that is produced in the process: Pu-240. Pu-240 has a much greater spontaneous fission rate than Pu-239. The net rate depends on the ratio of the two isotopes.

The crucial discovery which Segrè made was that reactor-produced plutonium had a much higher percentage of Pu-240 than cyclotron-produced plutonium and therefore a much higher spontaneous fission rate. All the spontaneous fission rate measurements done by the physicists on cyclotron-produced plutonium were therefore useless for reactor-produced plutonium. The high spontaneous fission rate in reactor-produced plutonium would doom a gun type plutonium weapon to a premature fizzle. Chemical separation of the Pu-240 from the Pu-239 was also out of the question: chemically separating uranium 235 (the fissile isotope of uranium) from the more abundant uranium 238 was already a mammoth undertaking that strained the country's resources. Separating Pu-240 from Pu-239 would be almost impossible.

Segrè's bad news plunged the laboratory in a big crisis. Fortunately there was a physicist named Seth Neddermeyer who had proposed a backup alternative for assembling a plutonium bomb. This alternative was implosion and consisted of rapidly squeezing a sphere of plutonium inwards to criticality. Implosion would be much faster than a gun type assembly and the spontaneous fission rate would not be a problem. The laboratory was rapidly reorganized by Oppenheimer and Leslie Groves to make implosion a high priority.

Implosion was still a risky endeavor, so the first atomic bomb test that the world saw on July 16, 1945 was of the implosion bomb. Less than a month later, Nagasaki was destroyed by the same kind of bomb. And ten years later the United States and other countries were building terrible hydrogen bombs in which plutonium implosion was an essential mechanism. Since then thousands of hydrogen bombs have been added to the world's nuclear arsenals, placing humanity at the risk of instant obliteration. What Segre thought about this is lost to history.

Irving Langmuir and pathological science: A warning for our times

It's American chemist Irving Langmuir's birthday today, so it's a good time to remind ourselves of his very illuminating and timeless warning about "pathological science". Langmuir was the first industrial scientist to win the Nobel Prize. The prize was awarded to him for pioneering contributions to surface chemistry, although he also did important research in electronics and solution chemistry. He did most of his work during the early part of the 20th century when science - especially physics and chemistry - was advancing at breakneck speed. Not surprisingly, when science advances at breakneck speed, so do its quacks. 

Langmuir took note of the many cases of fraudulent science published during the previous decades and in 1953 gave a talk about the misuses of science which he titled "pathological science". His basic definition of pathological science was "science" which tricked people into believing false results by "subjective effects, wishful thinking and threshold interactions." Not all pathological science is willfully fraudulent, but all of it suffers from a common set of pitfalls that distinguish it from solid science. One can recognize how prescient Langmuir's talk was by the fact that many of the criteria we use today for evaluating scientific results or progress and identifying scientific misconduct are elaborations of his theses.

Among the cases of pathological science that Langmuir cited were N-rays, Martian canals, UFOs and extrasensory phenomena. The list has only grown since then, and to it we can today add homeopathy, polywater, cold fusion, "arsenic bacteria", faster-than-light neutrinos and evidence of cosmic inflation. There are many causes of pathological science. Some of them are simply the result of working at the frontier of science where little is known and mistakes are easy to make, others are the result of cognitive, social and emotional biases which scientists suffer from as much as anyone else, and yet others can be the result of active fabrication.

Langmuir listed many tell-tale signs for identifying pathological science. Among these were the following:

1. The maximum effect that is observed is produced by a causative agent of barely detectable intensity, and the magnitude of the effect is substantially independent of the intensity of the cause.

Homeopathy is a classic manifestation of this particular feature of pathological science. It rests on the potent medical effects of barely detectable (and in many cases non-existent) substances dissolved in water. However, the example of "arsenic" bacteria looks at this feature from a different vantage point. In that case what the authors (who claimed that they had discovered bacteria growing on arsenic instead of phosphorus) failed to test for was traces of phosphorus that could have actually invalidated their hypothesis. 

Sometimes a causative agent of "barely detectable intensity" could in fact be valid, but even in that case its effects need to be consistent and reproducible, and there also needs to be a good theory which can support its causal connection to the phenomenon under investigation; that connection can validate the dependence of the effect on the intensity of the cause. The arsenic bacteria case failed on both counts.

1. The effect is of a magnitude that remains close to the limit of detectability; or, many measurements are necessary because of the very low statistical significance of the results.

This is a straightforward caveat against statistical insignificance. When Langmuir was lecturing the science of statistics was just coming into its own. Since then and especially in the last decade or so, mountains of material have been published on key statistical concepts and pitfalls like p-hacking, effect size, sampling bias and cherry-picking. Pioneering psychologists like Daniel Kahneman and Amos Tversky have showed how humans can be fundamentally incapable of thinking statistically. Failure to pay attention to any one of the myriad important statistical measures can deceive scientists into seeing a result where none exists. In my own field of molecular modeling, due attention to statistics has become a rallying cry for many scientists. The reproducibility crisis has turned into one of the biggest challenges to contemporary science.

That being said, one has to appreciate that scientists in some areas like particle physics are working at the very edges of statistical meaning; particles like the Higgs boson are discovered by looking at three or four sigma levels of statistical significance. In that case Langmuir's second caveat is important; you have to make many more measurements than what would be ordinarily necessary - or feasible for that matter - to confirm the effect. That is why data at the LHC comes from billions or even trillions of collisions between particles. The same goes for testing subtle effects of drugs across diverse populations.

1. Claims of great accuracy.

Solid science never tries to make claims that are bigger than what its edifice would sustain. I would think that most pathological science actually tries to keep away from proclamations of great accuracy, instead trying to skirt falsification by keeping its claims as vague and generic as possible. Astrology is a notorious example, keeping its "predictions" so vague that almost any event will "confirm" them. And yet I can also imagine practitioners of pathological science trying to dazzle credulous believers with the false veneer of accuracy. In this category I would probably place any number of health fads that allow you to lose 20 pounds in exactly 13 days, or guarantee immunity against a remarkably accurate and comprehensive list of maladies. So Langmuir is right in this regard; if it sounds too accurate, it probably is.

1. Fantastic theories contrary to experience.

This particular caveat was Langmuir's way of saying that "extraordinary claims require extraordinary evidence", about twenty five years before Carl Sagan said it. Any number of pseudoscientific phenomena will fall into this category: alien abduction, psychokinesis, the afterlife, reincarnation...the list goes on. More challenging claims are those like the ones about "arsenic" bacteria. These are at least plausible enough in principle and don't seem to violate any known laws of physics and chemistry, but given the number of conditions that need to be simultaneously satisfied in order for them to be true, they are extremely unlikely except in the face of convincing evidence.

At this point it's worth pointing out that there have been a number of theories in science, most notably in physics, that are in fact quite fantastic. Time dilation, spacetime curvature and quantum entanglement are only three of them. Yet what made these amazing creations of the mind plausible was the mathematical rigor behind them and their agreement with previous theories (relativity for instance arose from a desire to make Newton's laws of motion and Maxwell's laws of electromagnetism consistent with each other). And even then, they were regarded as hypotheses before experiment overwhelmingly confirmed them; that is why even today, in spite of the fact that they run completely "contrary to experience", we still believe these theories.

1. Criticisms are met by ad hoc excuses thought up on the spur of the moment.

I can think of no better example of this feature of pathological science than creationism and intelligent design. Come up with an objection to a creationist idea and the creationist will have an answer for it. In almost every case the answer will be non-falsifiable and so general that it will either be impossible to disprove it or it would be possible to always "prove" it because of its hollow generality. At some point your theory then becomes so wide as to accommodate every single objection and fact, and a theory that explains everything then ends up explaining nothing.

1. Ratio of supporters to critics rises up to somewhere near 50% and then falls gradually to oblivion.

This is an especially amusing and true aspect of pathological science. Usually when an improbable discovery is announced there's always enough number of believers to push hard for its plausibility and significance. Part of the reason is psychological; we actually want new, groundbreaking discoveries in science. The discovery of cosmic inflation and that of arsenic bacteria both fall in this category. I don't know how many of those who read about these believed in them, but Langmuir's estimate sounds rather reasonable. It did not take much longer then for this number to rapidly dwindle and fall to oblivion.

The political environment in the near future is almost certainly going to push its own brand of "science" on the public, even as it revels in its own version of "facts". In addition, the deluge of big data has already made it hard to separate the wheat from the chaff. All this has lowered the bar for deception and outright fraud. Only scientists can police each other and make sure that chicanery, both willful and accidental, don't become part of established scientific fact. Irving Langmuir's warning about pathological science shines as brightly as ever.

Einstein's wonderful letter to David Hilbert: A message for our times

David Hilbert (born today in 1862) was one of the greatest mathematicians of the 20th century. He made incisive contributions to a remarkable range of mathematical fields, published a best selling textbook on mathematical methods in physics, laid out a famous list of twenty-three unsolved problems which still challenge the field's practitioners and was a kind of philosophical godfather to at least two generations of mathematicians. Under his influence German mathematics reached its zenith before it was scattered apart by the rise of totalitarianism.

Perhaps less known is Hilbert's friendly and sometimes not-so-friendly rivalry with Einstein. Einstein's two most serious mathematical competitors were Hilbert and Henri Poincare. Poincare came close to discovering special relativity. Hilbert came close to discovering the equations of general relativity. Unlike Einstein, both were men of prodigious mathematical talent. Einstein's own mathematical shortcomings are well known; he had to learn most of the mathematics he needed for cracking open general relativity from friends and colleagues, most notably Marcel Grossmann.

In 1915 Hilbert came very close to publishing the equations of general relativity before Einstein did. Einstein had given a lecture in Berlin on his tentative attempts at formulating the equations. Hilbert was in the audience and doubled his efforts to find the right formulas. In the end Einstein ended up finding the correct form of the equations just a few days before Hilbert. It's quite likely that Hilbert would have gotten there first had Einstein gotten stalled for some reason.

However this story may paint a false picture of why it was Einstein and not Hilbert who ended up inventing general relativity. The short answer is that it was not mathematics but physics that was at the heart of relativity theory. Hilbert was the greater mathematician among the two, but Einstein's physical insights and visualization of thought experiments were unparalleled in the history of physics. Like a select few scientists - Feynman, Faraday and Fermi come to mind - he saw the physics first and then dragged the math behind him later. He had already viewed gravity as a field of spacetime which could be deformed and pulled by the time he started thinking about the equations. Hilbert, like more traditional physicists, tried to solve the equations first and get to the physical picture later. 

Generally speaking, truly great and successful physicists are ones who see the physical picture first, and Einstein was in the front rank of this group. Thus even if Hilbert had gotten to the equations first, Einstein would still have won the day. His 1915 paper on relativity contains not only the equations but all kinds of amazing physical insights that would lead to observations on the bending of spacetime and the expansion of the universe.

The last word belongs to Einstein, not because he was a great scientist but because he was a great human being. After the whole nail-biting race was over, he wrote a sensitive letter to Hilbert that exuded generosity, acknowledged his own flaws and sought reconciliation and friendship. 

The letter is a role model for competition and disagreement, and should be a must read in this era of political disagreement and conflict. Ultimately Einstein showed that while physics is important, being good human beings is even more important.

Gertrude Elion: Nobel Laureate, inventor of lifesaving drugs, woman in science

It's Gertrude Elion's birthday today. Below is one of hundreds of typical letters of gratitude that she received when she was awarded the Nobel Prize for Physiology or Medicine in 1988.

The prize - one of a select few recognizing drug discovery - was awarded to her, George Hitchings and James Black for the discovery of life-saving medicines for cancer, organ transplantation, viral diseases and stomach ulcers. She was only the fifth women to get it.

Elion repeatedly used to say that such letters and the saved lives of their recipients had long since made up for any formal honors or degrees that she might have lacked. One such degree was the PhD. When Elion applied to PhD programs after graduating with high honors from Hunter College in New York City in 1938, in the middle of the Great Depression, fifteen colleges refused her scholarships or fellowships because she was a woman. Until then Elion, who had been raised in a strongly egalitarian household by a generous-minded father, never thought that her being a woman would make a difference. But in 1938 in did, and Elion persisted and succeeded against such odds.

If some men held her back, others like her father, her fiancé and George Hitchings pushed her ahead. Her fiancé was a young man with a promising career in statistics whom she fell in love with as a student at Hunter College. His death due to a bacterial infection that could be completely cured just a few years later by penicillin cemented two desires in Elion: to stay married to her work and to devote her life to curing human disease and misery. Throughout her life, when she was approached by men either with proposals of marriage or bewilderment that she was a female scientist, she cheerfully dismissed such overtures and simply moved on without holding grudges; her work would speak for itself.

Elion found a job at the company Burroughs Welcome (which later became Glaxo Smithkline) by sheer chance, when her father who had seen an ad in the paper asked her to reach out to them. She asked if she could interview there on a Saturday since she was attending classes for graduate school on weekdays. Fortunately the company said yes, and fortunately George Hitchings was also working there on a Saturday.

Hitchings was interested in the application of chemistry to medicine. At that point in history, all medicines had been discovered by trial and error, with the latest example being sulfa drugs. Scientists typically sifted through thousands of molecules like dyes and petrochemicals with the hope that one of them would show interesting activity against diseased cells. Antibiotics hadn't been invented yet. Hitchings wanted to make drug discovery more rational, and his hypothesis was that one should do this by looking at the difference between normal cells and abnormal cells such as cancer cells. He had worked on nucleic acids before and he knew that cancer cells used much more nucleic acid for growth and metabolism. Why not try to look at the structures of nucleotides and modify their chemical structures in order to "trick" cancer cells into using the wrong material?

Hitchings's idea gripped Elion and she spent the rest of her life exploring its manifestations in a spectacular manner. Hitchings never held her back from going out on her own and made sure she was always listed as an author on all the important papers. There was another woman in the lab named Elvira Falcon; she was both Elion's scientific partner and opera partner, and the two enjoyed regularly watching leading operas at the Met. For some time Elion kept on working part time on her PhD, but she finally decided to forgo an official degree because the dean would no longer let her work part time; he dismissed her by saying that surely she must not be serious about becoming a scientist if she was interested in only working on her degree part time. Elion's lack of a PhD shows both the burdens of the PhD system as well as the prejudice against scientists without PhDs.

Among half a dozen others, Elion discovered at least three breakthrough drugs which were the first of their kind and which are still used in diverse areas of medicine. She was a pioneer in both chemotherapy and antiviral therapy. In 1950 she made 6-mercaptopurine which cut the rate of death from acute childhood leukemia in half. Although it brought temporary remission, it could be combined with other drugs to increase lifespan. Elion was only thirty two when she discovered 6-mercaptopurine. Much more important than the specific drug was the new paradigm she unveiled; cancer could now be attacked by looking at chemical differences between molecules used by normal and cancerous cells. It's an approach that is at the heart of cancer drug discovery even today.

Another compound made by Elion was azathioprine. Azathioprine dramatically reduced the immune response and became the first immunosuppressant. Until then organ transplantation had been a nightmare, with violent rejection of kidneys, livers and other organs dooming patients to early deaths. Azathioprine made organ transplantation possible. Doctors who used it were heralded as miracle workers and received Nobel Prizes. The icing on the cake for Elion and Hitchings was being able to see and talk to patients whose lives they had played a direct role in saving, a rewarding experience that organizations really should confer on their scientists. The third important drug which Elion discovered was acyclovir, used against the herpes virus. This drug was discovered on the same basis as the anticancer drugs, by assuming that a compound similar to that used by the virus in its own metabolism would thwart its growth. Acyclovir is still used at the frontline when it comes to fighting viral diseases, not just for herpes but also against chickenpox, shingles and other infections. I quickly benefited from it myself when I came down with chickenpox.

Elion kept on working until the end of her life and died in 1999. It is difficult to overestimate how many lives she saved with her discoveries, and the steady stream of letters of gratitude she received were the best testaments to her work. She was working in a golden age of drug discovery where relatively cheap research would yield important medicines, FDA regulations were slim and drugs could be easily tested on patients. But the powerful paradigm she unearthed will always be a model for drug discovery. Today the pharmaceutical industry has largely supplanted the logic used by Elion with random screening of synthetic and natural molecules. Perhaps it's time to again refocus on Elion's paradigm and look for molecules that are similar to those used by diseased cells and tissues. Fortunately the field of cancer metabolism and cancer immunology are partly based on such thinking. The flame that Elion and Hitchings lit is still alive and seems to be aglow with new hopes and promises.

Physics Nobel Prize winners and second acts: A rare pairing

Luis Alvarez made a major contribution to geology and biology
with his son after winning a Nobel Prize in physics

A while ago I had a discussion with a friend about physicists who did significant work even after winning an honor such as the Nobel Prize. The examples are few but noteworthy; accomplishing one significant piece of scientific work is hard enough, so if you manage more than one it’s quite something. I decided to dig a bit deeper and looked at the list of all Nobel Prizes in physics starting from 1900 and found interesting examples and trends.

Let's start with the two physicists who are considered the most important ones of the twentieth century in terms of their scientific accomplishments and philosophical influence - Albert Einstein and Niels Bohr. Einstein got a Nobel Prize in 1921 after he had already done work for which he would go down in history; this included the five groundbreaking papers published in the "annus mirabilis" of 1905, his collaboration on Bose-Einstein statistics with Satyendranath Bose and his work on the foundations of the laser. After 1921 Einstein did not accomplish anything of similar stature but he became famous for one enduring controversy, his battle with Niels Bohr about the interpretation of quantum theory that started at the Solvay conference in 1927 and continued until the end of his life. This led to the famous paper on the EPR paradox in 1935 that set the stage for all further discussions of the weird phenomenon known as quantum entanglement.

Bohr himself was on the cusp of greatness when he received his prize in 1922. He was already famous for his atomic model of 1913, but he was not yet known as the great teacher of physics - perhaps the greatest of the century - who was to guide not just the philosophical development of quantum theory but the careers of some of the century's foremost theoretical physicists, including Heisenberg, Gamow, Pauli and Wheeler. Apart from the rejoinders to Einstein's objections to quantum mechanics that Bohr published in the 30s, he contributed one other idea of overwhelming importance, both for physics and for world affairs. In 1939, while tramping across the snow from Princeton University to the Institute for Advanced Study, Bohr realized that it was uranium-235 which was responsible for nuclear fission. This paved the path toward the separation of U-235 from its heavier brother U-238 and led directly to the atomic bomb. Along the same lines, Bohr collaborated with his young protégé John Wheeler to formulate the so-called liquid drop model of fission that likened the nucleus to a drop of water; shoot an appropriately energetic neutron into this assembly and it wobbles and finally breaks apart. Otto Hahn who was the chief discoverer of nuclear fission later won the Nobel Prize and it seems to me that along with Fritz Strassman, Lise Meitner and Otto Frisch, Bohr also deserved a share of this award.

Since we are talking about Nobel Prizes, what better second act than one that actually results in another Nobel Prize. As everyone knows, this singular achievement belongs to John Bardeen who remains the only person to win two physics Nobels, one for the invention of the transistor and another for the theory of superconductivity. Both of these developments were singularly important, not just for the physics of the 20^th century but for the engineering of the 21^st. And like his chemistry counterpart Fred Sanger who also won two prizes in the same discipline, Bardeen may be the most unassuming physicist of the twentieth century. Along similar lines, Marie Curie won another prize in chemistry after her pathbreaking work on radioactivity with Pierre Curie.

Let's consider other noteworthy second acts. When Hans Bethe won the prize for his explanation of the fusion reactions that fuel the sun, the Nobel committee told him that they had trouble deciding which one of his accomplishments they should reward. Perhaps no other physicist of the twentieth century contributed to physics so persistently over such a long time. The sheer magnitude of Bethe's body of work is staggering and he kept on working productively well into his nineties. After making several important contributions to nuclear, quantum and solid-state physics in the 1930s and serving as the head of the theoretical division at Los Alamos during the war, Bethe opened the door to the crowning jewel of quantum electrodynamics by making the first decisive calculation of the so-called Lamb shift that was challenging the minds of the best physicists. This work culminated in the Nobel Prize being awarded to Feynman, Schwinger and Tomonaga in 1965. If the rules of the prize did not limit it to three people, Bethe and Freeman Dyson would almost certainly have received a share of it. Later, at an age when most physicists are just lucky to be alive, Bethe provided an important solution to the solar neutrino puzzle in which neutrinos change from one type to another as they travel to the earth from the sun. There's no doubt that Bethe was a supreme example of a second act.

Another outstanding example is Enrico Fermi, perhaps the most versatile physicist of the twentieth century, equally accomplished in both theory and experiment. After winning a prize in 1938 for his research on neutron-induced reactions, Fermi was the key force behind the construction of the world's first nuclear reactor. That the same man who designed the first nuclear reactor also formulated Fermi-Dirac statistics and the theory of beta decay is a fact that still beggars belief. The sheer number of concepts, laws and theories (not to mention schools, buildings and labs) named after him is a testament to his mind. And he achieved all this before his life was cut short at the young age of 53.

Speaking of diversity, no discussion of second acts can ignore Philip Anderson. Anderson spent his entire career at Bell Labs before moving to Princeton. The extent of Anderson's influence on physics becomes clear when we realize that most people today talk about his non-Nobel Prize winning ideas. These include one of the first descriptions of the Higgs mechanism (Anderson is still regarded by some as a possible contender for a Higgs Nobel) and his firing of the first salvo into the "reductionism wars"; this came in the form of a 1972 Science article called "More is Different" which has since turned into a classic critique of reductionism. Now in his nineties, Anderson continues to write papers and has written a book that nicely showcases his wide-ranging interests and his incisive, acerbic and humorous style.

There's other interesting candidates who show up in the list. Luis Alvarez was an outstanding experimental physicist who made important contributions to particle and nuclear physics. He also designed the detonators for the bomb dropped over Nagasaki. But after his Nobel Prize in 1968 he re-invented himself and contributed to a very different set of fields; planetary science and evolutionary biology. In 1980, along with his son Walter, Alvarez wrote a seminal paper proposing a giant asteroid as the cause for the extinction of the dinosaurs. This discovery about the "K-Pg boundary" really changed our understanding of the earth's history and is also one of the most exemplary examples of a father-son collaboration.

There's a few more scientists to consider including Murray Gell-Mann, Steven Weinberg, Werner Heisenberg, Charles Townes and Patrick Blackett who continued to make important contributions after winning a Nobel Prize. It's worth noting that this list focuses on achievements after winning the prize; a "lifetime achievement" list would include many more scientists like Lev Landau, Subrahmanyan Chandrasekhar and Max Born.

Neither is research necessarily the epitome of a scientist’s career. It's also important to focus on non-research activities that are still science-related and in which many physicists excelled with zeal. A list of these achievements would include teaching (Feynman, Fermi, Bohr, Born), writing (Blackett, Feynman, Bridgman, Weinberg), science and government policy (Bethe, Compton, Millikan, Rabi) and administration (Bragg, Thomson, de Gennes, Rubia). Bonafide research is not the only thing at which great scientists excel; they do not rest on their laurels and keep on exploring multiple aspects of their chosen path until their last breath.