Immanuel Kant versus the Princes of Serendip:

Does Science Evolve through Blind Chance or Intelligent Design?

Sheldon Lee Glashow

Boston University

What's the difference between a scientist and a humanist? When humanists lecture, they usually read from a carefully prepared script. When scientists lecture, they usually project carefully prepared graphs, diagrams and equations on an overhead screen, about which they improvise explanations and elaborations. I am a scientist, but today I am wearing my humanoid UNI cap. Today, I have neither graphs, nor diagrams nor equations to show you. Today, I shall read from a carefully prepared script, whose title, once again, is Immanuel Kant versus the Princes of Serendip: Does Science Evolve through Blind Chance or by Intelligent Design? The quick answer to this question is both. There are methodical scientists who first think and then look but there are, as well, lucky scientists who first look and then think. Most successful scientists are a bit of each.

Let me begin with an extract from the writings of Immanuel Kant. Toward the close of the 18th century, he expressed this view as to the nature of the scientific endeavor:

"When Galileo caused balls, the weights of which he had previously determined, to roll down an inclined plane; when Torricelli made air carry a weight which he had calculated beforehand to be equal to that of a definite volume of water; or in more recent times, when Stahl changed metal into oxides, and oxides back into metal, by withdrawing something and then restoring it, a light broke upon all students of nature. They learned that reason has insight only into that which reason produces after a plan of its own; that reason must not allow itself to be constrained, as it were, by nature's reins, but must itself show the way... thereby constraining nature to give answer to questions of reason's own determining." Just to emphasize this point, Kant goes on: "Accidental observations, made in obedience to no previously thought-out plan, can never be made to yield a necessary law, which reason alone is concerned to discover... Reason must not approach nature in the character of a pupil who listens to everything the teacher has to say, but as an appointed judge who compels the witness to answer questions that he himself has formulated."

What Kant is saying recalls what I learned in high school: that there is a so-called scientific method. First we frame a plan (or hypothesis) about Nature. Then we compel Nature to answer certain explicit questions about the plan. That is, we devise procedures by which to test the hypothesis with experiments or through observations. Often, this is just what scientists do. But not always.

Now let us contrast Kant's view of science with a brief extract from my favorite book, the Oxford English Dictionary:

SERENDIPITY: from a former name of Sri Lanka. A word coined by Horace Walpole, who says that he had formed it upon the title of a fairy tale called "The Three Princes of Serendip," the heroes of which `were always making discoveries, by accidents and sagacity, of things they were not in quest for.'

Kant lived too soon to experience the cascade of scientific discoveries, many of them quite accidental, that were about to take place. To him, science seemed to be an entirely rational and methodological pursuit. Hypotheses that were sanctioned by experiment were adopted, and thus, in a sense, they were imposed upon Nature. Kant felt that scientists must not remain under the dominance of experience. We should neither heed the accidental observation nor listen to Nature as if we were naive pupils. Is this a proper description of the scientific enterprise, or are we better described as Princes of Serendip: prepared minds in search of unanticipated wonders? I will argue that serendipity and rationality are as much intertwined with one another as are particles and waves, that some set out to circumnavigate the globe and do just that, while others set out for China and discover the Americas instead.

I shall focus mostly on the physical science because they are what I know best. Nonetheless, I am certain that the conflict between chance and design applies just as well to the life sciences. My talk consists of an eclectic selection of historical anecdotes strung together more-or-less chronologically and interpreted in terms of what might be called Kantian and serendipitous modes of discovery. As I tell my tale, please understand that I am neither a qualified historian of science nor a philosopher. Even less am I a student Kant.

Let's start with a brief biography of Sir William Herschel, whose accomplishments exemplify both modalities. Born and educated in Hanover, Germany, he emigrated to England where he became became a successful music teacher, composer and organist at the Bath Chapel. His interests, however, soon turned to astronomy. With the assistance of his siblings he set out to build a series of large telescopes, culminating in a 48" reflector-the largest telescope of his time. He was fascinated by non-stellar objects, including the fuzzy patches of light known as nebulæ. Herschel embarked upon a systematic study of the sky to identify and catalog these objects. Along the way, he discovered the seventh planet, which became known as Uranus. (He also spotted two of its moons and two additional moons of Jupiter.) For these astronomical feats, George III appointed the 43 year old musician as the King's Astronomer and awarded him a substantial lifelong pension. Herschel would eventually complete his catalog of over 5000 nebulæ, most of which he himself discovered in a thoroughly Kantian mode. Somewhat extended by Herschel's successors, it became the New General Catalog of non-stellar objects (the NCG), which remains very much in use today by astronomers. Herschel was a patient and systematic observer and was arguably the best astronomer of his day. However, he is known to physicists for an entirely serendipitous discovery: that of infrared radiation: heat rays, in common parlance.

Herschel knew (as do we all) that sunshine sheds heat as well as light. But was it any particular color of light, or a combination of colors, that conveys heat? Using a prism to separate sunlight into its constituent wavelengths, he placed thermometers at each different patch of color. Control thermometers were placed elsewhere. That was the serendipitous act! When one of the control thermometers just happened to find itself beyond the red portion of the spectrum, it registered the highest temperature of all! It was a sheer accident: in 1800, Herschel had discovered a form of light lying beyond the visible spectrum, he had discovered infrared radiation. For this great serendipitous discovery, rather than for his far more newsworthy sighting of Uranus, an ambitious European space observatory, to be launched in 2007, will be known as the Herschel Far Infrared Space Telescope.

Just one year after Herschel's discovery of the infrared, Johann Wilhelm Ritter, a devoted disciple of Immanuel Kant, "deduced" from Kant's principle of polarity, whatever that may be, that infrared light must surely have a short-wavelength complement that there must be an invisible radiation lying at the other end of the rainbow, beyond the violet. Ritter looked for it, and sure enough it was there. He had discovered ultraviolet radiation, or as Kant might have put it, he had imposed ultraviolet radiation upon Nature.

The great Danish chemist, physicist and pharmacist, Hans Christian Oersted, was a close friend of Hans Christian Andersen. More to the point, Oersted was a devoted follower of Kant. He followed his mentor's dictum that "a rational doctrine deserves the name of natural science only when the natural laws at its foundation are cognized a priori, and are not mere laws of experience." And yet, Oersted's one great discovery-that electric currents produce magnetic effects-was likely to have been wholly fortuitous. The discovery took place in 1820 during Oersted's lecture-demonstration to a class of advanced students. According to one of those students, while Oersted was performing an experiment involving an electric current, a compass needle happened by chance to lie just underneath the current-carrying wire. To everyone's astonishment, the electric current caused the needle to reorient itself. To be fair, Oersted had written seven years earlier, "that it must be tested whether electricity has any action on the magnet." However, he did not follow up on this idea until much later. A year after his famous demonstration, he wrote: "I was brought back to [this notion] by my lectures...," which is surely somewhat of an understatement.

Whether Oersted's seminal discovery was serendipitous or "cognized a priori " remains a subject of debate among philosophers who like to debate such matters. In any case, after a rather mysterious three month delay, Oersted scrupulously followed up his chance discovery with a series of careful experiments. The startling news-that electricity can make magnetism- spread rapidly throughout Europe and paved the way for others (especially Ampère, Faraday and Maxwell) to create a unified theory of electromagnetism.

Let us now turn to atoms, the supposedly indivisible constituents of all earthly matter that were first imagined to exist by some ancient Greeks. Imagined is the key word. These philospher-scientists offered little or no empirical evidence for their speculations. The modern-day atomic hypothesis was put forth and defended in the early 1800s by John Dalton, through his brilliant intuition and his rather sloppy experiments. He concluded that the atoms of each element "are perfectly alike" and "never can be metamorphosed, one into another." It could be said that Dalton had imposed his views upon Nature, which for a time, and in part, she conceded. `For a time,' because we did not yet know about isotopes and radioactive transmutation. `In part,' because, despite considerable contrary evidence, Dalton continued to insist that molecules of elemental gases, such as oxygen, consisted of single atoms, and that water molecules were made of just one atom each of oxygen and hydrogen. This confusion would plague chemists for decades. Dalton had relied too heavily on the principle of simplicity: he had cut himself with Ockham's razor.

Much later, James Clerk Maxwell (he who proved light to be an avatar of electromagnetism) would use the atomic hypothesis to prove the existence of a Creator. Maxwell wrote that "a number of exactly similar things cannot each of them be eternal and self existent; they must therefore have been made." By what or by whom Maxwell does not say.

Atoms come in many different forms. Way back in the late 18th century Lavoisier listed twenty-one of what he regarded as unmixed substances or what we call chemical elements. Apart from the inclusion of heat and light, his list was a good one. However, the number of known chemical elements was to grow rapidly. Indeed, it is still growing. A few scientists came to believe that there were simply too many different kinds of atoms for all of them to be elementary. Among these scientists was William Prout, to whose work we will have several occasions to allude. In the early 19th century, the relative masses of different kinds of atoms, or what we call the atomic weights of the chemical elements, began to be measured. Curiously, they all seemed to be integer multiples of the atomic weight of hydrogen. In a series of articles published anonymously, Prout argued that this unlikely to be coincidental. He explained the integer values of atomic weights with the conjecture that all atoms were somehow made up of hydrogen atoms. Although we now know that atomic weights satisfy no such exact rule, there is a profound element of truth in Prout's hypothesis... and it was profoundly accidental that the elements then studied did have approximately integer atomic weights: chlorine, whose mean atomic weight lies midway between integers at about 37.5, fortunately had not yet been discovered!

One of Prout's less well-known endeavors, and one to which he did put his name, had to do with the age-old search for a cheap and effective purple dye. Unfortunately for him, the product he came up with in 1828, ammonium purpurate, was not much of a commercial success.

Prout's new dye was made from uric acid, which itself was extracted from kidney stones or urine. Thus it was an `organic compound' and not one that anyone knew how to make from scratch. Why do I say this? ...because, until the middle of the 19th century, the doctrine of `vitalism' placed a seemingly impenetrable barrier between organic and inorganic chemistry. Organic compounds, such as urea and acetic acid, could not be synthesized from inorganic materials, or so it was believed, because they contained within them the `vital force' of life which lay beyond the scope of the physical sciences. Organic chemicals had to be extracted from blood, urine or other life-related materials. In 1828, Frederich Wöhler was astonished when he found, quite by accident, that a compound he had synthesized, ammonium cyanate, was identical to urea. He wrote to one of his vitalist colleagues: "I must tell you that I have prepared urea without requiring a kidney or an animal, neither dog nor man." Wöhler's serendipitous discovery, and quite soon afterward, the rather more Kantian synthesis of acetic acid from its constituent elements by Wöhler's student, were the first cracks in the organic-inorganic barrier. Unfortunately, the discredited notion of vitalism continues to affect the credulous and lives on as various bizarre pseudo-medical perversions: Qi Gong, Ayurveda, Reflexology, Fen Shui, ad infinitum.

Our next short and happy tale deals with the discovery of the first really useful artificial dye. In 1856, William Henry Perkin, an aspiring 17-year-old student of chemistry, set out on his first scientific research project. His mentor was the German chemist August von Hofmann, who was then visiting England. Perkin was instructed to attempt to synthesize quinine from coal tar. Perkin did not succeed in this quest: the task was far more difficult than von Hoffman thought. Instead of producing the pure white crystals of quinine, Perkin ended up with a dark, sticky and foul-smelling sludge. Indeed, Perkin's assignment would not be completed until the urgencies of WWII intervened. In 1944, the first total synthesis of quinine was accomplished, in a fully Kantian mode, by Robert Woodward and my friend and Harvard colleague Bill Doering.

But Perkin was a true Prince of Serendip. Noticing that his noxious coal-tar derivative had a purplish tint, he forgot about quinine and abandoned his academic career. The enterprising lad set up a factory to manufacture the first aniline dye, to which enthusiastic French designers gave the name mauve. When Queen Victoria and Empress Eugénie publically flaunted mauve dresses, his new dye became so popular that the period became known as the Mauve Decade. As a rich man of 36, Perkin sold his business and returned to academic science, having laid the foundations to synthetic organic chemistry.

And what ever happened to Perkin's mentor? He was no slouch. Inspired by the success of his young protegé, he proceeded to synthesize the second synthetic aniline dye in 1859. Von Hoffman valled it magenta. Only the historically literate among you will understand why it was that a patriotic German scientist would name his discovery after a battle of that same year at which the French army defeated the Austrians. Subsequently, von Hofmann returned to Germany where he systematically developed a whole panoply of purple dyes and contributed mightily to his country's primacy in the new industry that emerged from his student's moment of serendipity.

As organic chemistry flourished, so did its inorganic sibling. With the development of spectroscopy, the pace of discovery quickened. Some newly discovered elements were named after the colors of their most prominent spectral lines: Rubidium for red, Cesium for blue, and Thallium for bud-green. Mendeleev found a predictive pattern among the elements that was confirmed by the discoveries of Scandium, Germanium and Gallium. These new elements fit neatly into blank spaces that Mendeleev had wisely reserved in his table. The newfound elements displayed just the chemical and physical properties that he had foreseen. To Mendeleev, the success of his periodic table of the chemical elements was yet another hint - beyond Prout's Law and the revelations of spectroscopy - of the structured nature of atoms. "Does not order imply structure?" his argument could be put. Mendeleev's great triumph resulted from a wholly Kantian approach and was not in the least serendipitous.

As Mendeleev was puzzling out his table, the French philosopher Auguste Comte declared that we could never learn the chemical composition of the stars. A few years later, astronomers, using the new technologies of spectroscopy and photography, managed to do just that. They found that the spectral lines of sunlight and starlight coincided in wavelength with the lines produced by earthly elements. It followed that the sun and the stars are made of the same stuff as we are. Will philosophers ever learn never to say never? However, a few lines were seen that had no earthly counterpart. Norman Lockyer, in 1868, interpreted certain otherwise unseen solar lines as those of a new element which he called helium. The -ium suffix indicated Lockyer's suspicion that the solar element would turn out to be a metal. Several decades would pass before his error would be corrected.

In 1882, Lord Rayleigh returned to the nagging issue of Prout's Law. The then-measured density of oxygen gas was 15.96 times that of hydrogen. "The deviation of this number from the integer 16," he wrote, "seemed not to be outside the limits of experimental error." Rayleigh's precise experiments revealed the density to be 15.88. He proved that it was most certainly not an integer. So much for Prout's Law! Rayleigh then turned his attention to nitrogen. Using two quite different approaches, he was surprised and perturbed to obtain two quite different results. The density of nitrogen in air seemed to be greater than its density when extracted from ammonia. He later wrote: "On the supposition that the air-derived gas was heavier than the `chemical' nitrogen [from ammonia] on account of the existence in the atmosphere of an unknown ingredient, the next step was the isolation of this ingredient..." With the assistance of the chemist William Ramsay, he succeeded in isolating and studying the not-so-rare gas that makes up fully 1% of our atmosphere. In the most serendipitous discovery of their careers, Rayleigh and Ramsay discovered the surprisingly nonreactive element Argon (the lazy one). In a last ironic twist, the measured density of pure nitrogen showed that its atomic weight was almost exactly 14 times that of hydrogen. But by this time Rayleigh had lost interest in Prout's law.

The adventure continued as Ramsay and his coworkers went on to find several other inert gases in air: Neon (the new one), Krypton (the secret one) and Xenon (the foreign one). Finally, they discovered earthly helium within certain minerals. Helium turned out not to be a metal after all. It is the lightest of the seemingly inert gases. (They did not know at the time that one more inert gas remained to be discovered: Radon, the radioactive one. And even less could they know that most of the helium on Earth had been produced by the radioactive decay of uranium and thorium. Radioactivity had not yet been discovered.)

Oh how embarassing these discoveries must have been to chemists! The work of Rayleigh and Ramsay forced a reluctant Mendeleev to add a whole new column to his periodic table, one to account for the newly found family of elements with zero valence. (Incidentally, Perkin's mentor von Hofmann, Mr. Magenta, was largely responsible for the notion of valence and had coined an earlier version of the word.) For their work, Sir William Ramsay won the 1904 Nobel Prize in Chemistry, and Lord Rayleigh the Physics Prize of the same year. Never before and never again would the chemistry and physics prizes in a given year be so intimately related.

Aside from the isolation and identification of the inert gases, another two spectacular and unexpected scientific discoveries would take place in Mauve Decade. In 1895, William Conrad Röntgen had his moment of serendipity when he found something so entirely unexpected that he said to his wife, "People will say that Röntgen has probably gone crazy." He was far from crazy. Röntgen had stumbled upon X rays, and he followed up his serendipitous discovery with the care and alacrity one expects of a great scientist.

A few years later, Henri Becquerel entered-and in my view won- the serendipity sweepstakes. He had devoted himself to the study of luminescence and phosphorescence - the production of light by means other than heat - as had his father and grandfather before him and as would his only son. Soon after Röntgen found X rays, Becquerel suspected a possible linkage between the new radiation and his beloved phenomenon of cold light. As he later reminisced, "I thought immediately of investigating whether [X rays] could not... give rise to [luminescence] and whether all [luminescent] bodies could not emit similar rays. The very next day I began a series of experiments along this line of thought." Kant would have approved!

Most of us know what happened next. Certain chemicals are phosphorescent. After being placed in sunlight for a few hours and taken to a dark room, they continue to glow. Becquerel chose his favorite phosphorescent chemical from his laboratory shelf. Through a quirk of fate, the particular material he chose was a compound containing uranium. Becquerel proceeded as follows:

One wraps a photographic plate in thick black paper. A piece of phosphorescent material is laid upon the paper and the whole is exposed to the sun for a few hours. When the photographic plate is developed, one observes the silhouette of the phosphorescent substance... If a coin is placed between the phosphorescent substance and the paper, then its image can be seen to appear on the negative. The phosphorescent material emits radiations which traverse the opaque paper.

Becquerel thought he had confirmed that phosphorescent substances produce X rays as well as light after being exposed to sunlight. A week later, to his amazement, he realized that the image on his film had nothing to do with sunlight, nothing to do with X rays, and not even anything to do with phosphorescence!

The sky was overcast when Becquerel attempted to repeat his experiment. He put his wrapped photographic plate along with his phosphorescent uranium salt in a dark desk drawer to await a winter sun that never came. A few days later (who knows why?) he developed the plate. His son Jean, who had collaborated with his father, wrote that "Becquerel was stupified when he found that his silhouette picture was even more intense than the ones he had obtained the week before." Becquerel had discovered radioactivity! I've described Becquerel's work at some length because his initial discovery (which he followed up scrupulously in a more Kantian mode) was a rare instance of triple serendipity:

i.: What if the Paris sun had come out on that fatefully dark December day?
ii.: What if Becquerel had not developed the plate from the dark desk drawer?
iii.: And what if he had used a phosphorescent material that did not contain uranium?

In the late 19th century, several arguments, quite aside from Prout's law and the periodic table, suggested that atoms have internal structure. Decades earlier Faraday showed how neutral atoms in solution behave as if they were electrically-charged ions bearing charges that were integer multiples of a fundamental unit of electric charge. If atoms did have electrically-charged constituents, as Faraday's work suggested, then perhaps their vibrations could generate the characteristic spectral lines of each chemical element. In 1891, the Irish physicist G. Johnstone Stoney wrote that "these charges, which it will be convenient to call electrons, cannot be removed from the atom." His name for the then-hypothetical particle stuck. Just a few years later, J.J. Thompson discovered the electron by means of the careful and systematic study of cathode rays. It was the first of the so-called elementary particles. Contrary to Stoney's assertion, electrons could quite easily be removed from atoms, but its tiny mass posed a weighty problem: What were the positively-charged constituents of atoms?

Quite a number of scientists attempted to impose their views on the structure of atoms: Thompson had his `plum-pudding' model and Nagaoka his `saturnian' model. But Nature had something very different in mind. The surprising answer emerged from a series of experiments carried out by Ernest Rutherford. First, he showed that radioactivity produces three distinct kinds of radiation, which he called alpha rays, beta rays and gamma rays, with a deplorable lack of poetic sensibility. Rutherford showed alpha rays to consist of rapidly moving charged particles, and that "the alpha particle, after it has lost its positive charge, is a helium atom." (Nowadays we would say it differently: the helium atom, after it has lost its electrons, is an alpha particle.) Rutherford also identified beta rays as energetic electrons and gamma rays as energetic electromagnetic radiation. It was quite a tour de force. And I haven't even mentioned his earlier and epochal discovery (along with Frederick Soddy) of the law of radioactive transformation, which they dared not call by its old alchemical name of transmutation. It was this discovery that put a full stop to the ancient notion of the immutability of atoms. But I digress.

Of all the forms of radioactivity, alpha particles were Rutherford's pets. In 1909, he and his collaborators, Geiger (of the Geiger counter) and Marsden, directed a beam of them spewing from a radioactive source toward a thin gold foil target. "It seems surprising," they understated, "that some of the alpha particles can be turned by 90 degrees, and even more." Two years later, Rutherford formulated the notion of an atomic nucleus. Later he would describe his moment of serendipity:

"It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you. On consideration... I saw that it was impossible unless you took a system in which the greatest part of the mass of an atom was concentrated in a tiny nucleus."

So much for plum puddings! Rutherford's discovery of the atomic nucleus and the planetary structure of atoms marks a great divide between the studies of atomic phenomena (and the development of quantum mechanics) and those of the sub-nuclear world and radioactivity. For want of time, I shall focus the latter. Systematic (i.e., Kantian) studies of radioactive transformations and X-ray spectroscopy showed that the electric charge of an atomic nucleus is always an integer multiple of the electronic charge. It is called the atomic number, and its value (1 for hydrogen and 92 for uranium) determines the number of electrons in the neutral atom as well as the chemical properties of the element and its place in the periodic table. Henry Moseley, the promising young physicist who is largely responsible for this great discovery, enlisted soon afterward in the British army and was killed at the Battle of Gallipoli.

Just a few years later, the discovery of isotopes taught us that Prout was right, if only in an approximate sense. Atoms of a given element may come in several forms or isotopes. Their nuclei have the same electric charge, but they differ in mass. If we adopt today's convention wherein the atomic weight of the most common isotope of carbon is defined to be exactly 12, it turns out that the atomic weight of every other isotope is very nearly (but not precisely) an integer. Thus each and every atomic nucleus is uniquely characterized by two integers: Z (its electric charge in units of the electron's charge, and A (the nearest integer to its atomic weight). These systematic properties, along with the fact that there were far too many different nuclear species for them all to be elementary, strongly suggested that atomic nuclei were composite systems. But of what simpler things were they made?

Rutherford, again using alpha particles, succeeded in knocking particles out of nitrogen that seemed (and were) identical to hydrogen nuclei. He concluded that the hydrogen nucleus is a constituent of all atomic nuclei, that it is an elementary particle (the second one!) which he sometimes called the prouton (in honor of William Prout), and at other times, the proton (from Greek protos, meaning first). Only the latter name stuck. And so it was that Prout's hypothesis was reborn in a nuclear context. A nucleus with atomic number Z and mass number A was supposed to consist of A protons and A-Z internal electrons. This quite erroneoud proton-electron model of nuclear structure would persist until the year of my birth.

If two electrons bind four protons into a helium nucleus, Rutherford wondered whether one electron could form an intimate union with one proton to form a tiny electrically neutral nucleus, a conjectured composite particle to which he gave the name neutron. The story of its discovery would be a heady mix of serendipity and reasoned experimental analysis. In 1930, Bothe and Becker made the accidental discovery that alpha particles (once again!), impinging on beryllium, produce an electrically neutral radiation which they assumed to consist of gamma rays. Then Irene Joliot-Curie and her husband Frederick Joliot showed that these beryllium rays would liberate energetic protons from paraffin. But they clung to the incorrect electromagetic interpretation and missed their greatest research opportunity.

It was James Chadwick, by means of a series of carefully designed experiments, who proved that the beryllium rays could not possibly be photons. Instead, he showed them to consist of neutral particles with about the same mass as the proton. Thus Chadwick discovered the neutron in 1932, but it was not at all the particle that Rutherford had envisaged. The neutron is not a proton stuck to an electron. It is a particle in its own right, an electrically neutral sibling of the proton. There are no electrons in atomic nuclei after all, just neutrons and protons. (Of course, we now know that neither of these particles is truly elementary. Each of them is made up of three quarks, but that is quite another matter.)

Today's discovery becomes tomorrow's research tool. As we have seen, alpha particles, soon after they were found, were put to good use to discover atomic nuclei and neutrons. They were also used to induce nuclear reactions that normally never take place on Earth. The same applies to neutrons. Because they are electrically neutral, neutrons can far more readily enter large nuclei than charged particles. Immediately upon Chadwick's discovery, the Italian physicist Enrico Fermi set out to see what happens when different elements were bombarded with neutrons. He found that a neutron striking a large nucleus is often absorbed. The heavier and unstable isotope thus formed would rapidly transmute itself into an element one step higher in the periodic table.

What would happen, Fermi wondered, if neutrons impinged on uranium, which lay at the very end of the periodic table? In 1934, he concluded that by this means he had synthesized elements number 93 and 94, to which he gave the names Ausenium and Hesperium. He was awarded 1938 Nobel Prize in Physics "for his demonstration of the existence of new radioactive elements" and for his investgations of slow neutrons. Now I would not for a moment question whether Fermi deserved his Nobel prize, but in fact he had not discovered any transuranic elements at all.

Ida Noddack was an accomplished chemist who had discovered, along with her husband-to-be, the last of the stable chemical elements: Rhenium. (This suggests that there may have been a marital resolution to a potential priority dispute.) In 1934, responding to Fermi's claims, she published a paper entitled "Uber das Element 93" in which she wrote, "It is conceivable that in the bombardment of heavy nuclei with neutrons, these nuclei break up into several large fragments which are actually isotopes of known elements, not neighbors of the irradiated element." She pointed out that all the known elements must be excluded to draw the conclusion that element number 93 had been produced from uranium. Otto Hahn later claimed that Noddack's argument "was not taken seriously as it appeared to be in opposition to all physical views of nuclear structure." And, after all, he was aware that Dr. Noddack was a woman... but she was certainly the first person to foresee the possibility of nuclear fission.

And that portentous process, nuclear fission, will be last of the discoveries I will discuss today. It was not so much a serendipitous discovery as it was anti-Kantian. Nature was trying to tell Fermi something when he found that uranium and thorium behave rather differently from other elements when irradiated with neutrons. But Fermi listened neither to nature nor Noddack. In December of 1938, just as Fermi was accepting his award from the hands of the Swedish king, the astonishing discovery of Hahn, Meitner and Strassman was announced. Working in collaboration, until Meitner was compelled to flee from the Nazis, they identified barium as a product of neutron absorbtion by uranium. The conclusion was inescapable: the uranium nucleus had been induced to split. "Oh what idiots we have been!" said Niels Bohr, "this is just as it must be." The word describing this process, nuclear fission or Kernspalung in German, was coined by Lisa Meitner and her nephew whilst they were in Swedish exile. The 1944 Nobel Prize in Chemistry was awarded to Otto Hahn for its discovery. Meanwhile, elements number 93 and 94 (now called neptunium and plutonium) as well as numbers 95 and 96, had been synthesized and isolated in Berkeley, California.

So what should you conclude from these disjointed incidents of travel through the history of science? Perhaps you may begin to understand why modern scientists rarely consult the classical philosophers. Whereas Kant believed that "reason must not approach Nature in the character of a pupil who listens to everything the teacher has to say, but must act as an appointed judge who compels the witness to answer questions that he himself has formulated," we would put it somwhat differently: "Although reason may sometimes act as an appointed judge and compel Nature to answer well-posed questions, reason must always listen carefully to everything Nature has to say."

This research was partially supported by the National Science Foundation under grant number NSF-PHY-0099529.

File translated from T_EX by T_TH, version 3.33.
On 3 Mar 2003, 11:58.