Introduction: The Ruler, the Clock, and the Thermometer
MOST OF US are likely to start our day with a series of questions: Where do I have to go? What time is it? How cold is it? In going to sleep, we anticipate tomorrow's answers to those same questions. The measurements of length, time, and temperature, implicit or explicit, set our life's rhythms. I'm particularly fascinated by temperature, the subtlest of the three. While new ideas expand our horizons, the everyday understanding of length and time has not changed appreciably in millennia. We've had rulers and clocks for a long time. This is not the case with temperature. Even though we can agree that a baby immediately knows hot from cold, our ability to measure temperature is only a few hundred years old. Our scientific understanding of even a gas's temperature—the average kinetic energy of molecules in thermal equilibrium—is much more recent.
Traditionally, science books intended for the general public describe a specific discipline or a particular problem. Books on cosmology or genetics or neuroscience are useful and often wonderful. I'm taking a different path, using the measurement of temperature as a guide in exploring many aspects of science. Such a wide sweep inevitably entails selection; the ensuing choices reflect my own background and taste, as well as my ignorance and knowledge. As a caveat, I should first tell you who I am and where this story is heading.
I'm a physicist. When people ask what I do for a living, I tell them I'm in the family business. My brother is a physicist, my nephew is one, lots of cousins are, my uncle received the Nobel Prize in physics, my wife's father was a well-known German physicist, and her sister is married to an even more famous Viennese physicist. Physics, my professional life, also has a familial side for me.
Two generations ago, the family business was paper. My Jewish grandfather Giuseppe moved, as a young man, from Mantova in northern Italy to Tivoli, a city about fifteen miles west of Rome. He built there a small paper mill that grew with the increased demands of the prospering capital of a newly unified Italy. The new and yet old country, once barely tolerant of Jewish enterprise, now encouraged it. Giuseppe was rewarded for his efforts when the new Italy awarded him the honorific title of commendatore.
Tivoli had thrived in Roman times. Known then as Tibur, it is nestled in the foothills of the Apennines, surrounded by poplar forests and cooled by the Aniene River with its numerous waterfalls. Tibur was an agreeable place to spend the hot summer months. Villas and temples sprung up as the wealth of the Roman Empire grew. In the second century A.D., Hadrian built his magnificent residence at the point where the Tibur hills met the Roman countryside. As described in Marguerite Yourcenar's Memoirs of Hadrian, it was more than just a villa. With its theater, reflecting pool, and other outlying buildings, it was probably the single largest residence of the classical world and yet it exuded quiet and tranquility. Yourcenar imagines the emperor thinking:
Once more I have gone back to the Villa, to its garden pavilions built for privacy and for repose, to the vestiges of a luxury free of pomp, and as little imperial as possible, conceived of rather for the wealthy connoisseur who tries to combine the pleasures of art with the charms of rural life.
This jewel had been long abandoned, but excavations began in 1870 at Villa Adriana, as it was now called, just as Rome became the capital of a reborn Italy.
In the Renaissance, Tivoli, the new name for Tibur, was, as before, a fabled retreat from the heat of the nearby metropolis. In 1550 Cardinal Ippolito d'Este began the transformation of an old monastery into Villa d'Este, a sumptuous residence with Italy's finest display of Renaissance fountains. He built it on the hillside to heighten the effect of the cascading waters and also to allow the cardinals and the nobles, promenading along its cool paths, to glimpse the dome of Saint Peter's Basilica in the distance. Tivoli became a byword for elegance and charm. Such far-flung establishments as the amusement park in Copenhagen still carry its name.
The nineteenth century saw the arrival of industry. Paper
mills require trees for wood pulp, plentiful water, power, and,
hopefully, a nearby market. Tivoli had all of that, and so my
grandfather built his mill just below Villa d'Este, on the site of
the old Roman Temple of Hercules. The ruins of the temple
provided the backbone of the factory, in what to present sen
sibility is an unthinkable sacrilege. But in those days, the
growing demands of the new Rome made the rocks of old
Rome seem an appropriate foundation. Late in his own life
my father joked that the only trace of the Segre family in
Tivoli would be a plaque saying `Here is the Temple of Her
cules, desecrated by the Segre family, but restored to its for
mer grandeur in-------- `
My grandparents had three children, all boys. They grew up in a world dramatically poised between the old and the new. The oldest, Angelo, my father, wandered as a child through the ruins of Villa Adriana, collected Roman coins, and studied the past. He eventually became a professor of ancient history, but he wanted to do more than just chronicle the past. He wanted to understand how people paid their bills, what they traded, the way their economy worked, how the currencies in the Mediterranean were valued, what Romans did in times of fiscal crisis. His most significant work was a two-volume treatise, Metrology and Monetary Circulation in the Ancient World, metrology being the study of measurement. I still remember him describing to me his excitement when, told of the discovery of an ancient storeroom full of broken pots, he realized he could predict the size each pot would have when reassembled. He knew what had been in the room, what was stored in the pots, who sold them, who bought them, and for how much. He knew all the measurements.
A charming, lovable, idiosyncratic man, impractical but immensely learned, my father increasingly came to regard the study of the ancient world as a kind of luxury. Fascinated by the emergence of quantum mechanics, relativity, genetics, and the idea of an expanding universe, he urged his children to study science, possibly regretting his own early decision not to do so. Perhaps another way of viewing my father's feelings is that historical awareness was so ingrained in him that he urged others to explore what to him was foreign.
The middle son, Marco, took the conventional route, staying in the old family business and running the paper mill. The measurements he studied were the prosaic but certainly important ones of balance sheets, cash flows, and growth curves.
In the mid-1920s, my grandfather's third son, Emiiio, still an undergraduate at the University of Rome, began doing research with Enrico Fermi. Fermi, newly arrived in Rome, was only four years older than Emilio, but he was already a professor and beginning his rise to fame. In collaboration with Fermi and others, Emilio went on to a very successful career in physics, both in Europe and later in the United States.
Emilio is best known for his work with Fermi on neutrons and for the discovery of the antiproton, which led to his receiving the 1959 Nobel Prize in physics with Owen Chamberlain. I like to remember him for a less well known discovery: that of the element technetium and, in particular, the measurement of its half-life. The story goes as follows: Emilio became acquainted during a visit to Berkeley in 1937 with the great American experimentalist Ernest Lawrence, the builder of the first cyclotron. They corresponded regularly after that, since they had similar interests. At one point, Lawrence sent to Emilio, still in Italy, a molybdenum foil that had been placed in Lawrence's California cyclotron. Emilio suspected the cyclotron bombardment might have in fact led to the production of the forty-third element of the periodic table, an element that had never before been detected. After a careful set of chemical separations done with the help of his colleague Carlo Perrier, Emilio found he was right; they named the new element technetium. One of the reasons it had been missed in earlier chemical analyses was that technetium has several chemically identical forms, none of them stable.
I know the discovery had a special meaning for my uncle because, when World War II was over and Emilio could finally visit his father's grave, he brought some technetium with him. As he says,
I scattered a small sample of technetium on my father's tomb at the Verano Cemetery in Rome, my tribute of love and respect as a son and as a physicist. The radioactivity was minuscule, but its half-life of hundreds of thousands of years will last longer than any monument I could offer.
Emilio turned to history as he grew old. His first nonsci-entific venture was a biography of his mentor, Enrico Fermi. Later, trying to frame what he had seen in his life, he wrote a history of twentieth-century physics and finally a book on the history of classical or prequantum physics. These books are an attempt by Emilio to uncover, as he admitted, the meaning of Dante's phrase `Chi furono li maggiori tuoi?` (Literally, this means, `Who were your greaters?` but in an intellectual sense, `Who were your ancestors?`)
My uncle's involvement and my father's guidance surely pushed me to participate in physics, the new family business. My father went a step further—he announced I should become a theoretical physicist. When I pressed him on how he reached this decision, he replied that theoretical physics seemed to be a profession with two cardinal virtues: you can tell right from wrong and you don't have to talk to anyone you don't want to talk to. Although both assertions are arguable, I became one anyway and certainly proved I was an obedient son. Over the past thirty years I have mainly worked on problems in elementary particles, occasionally branching out to condensed matter physics and astrophysics.
As 1 look back at my own pursuits and at the lives of my father and his brothers, I see us all drawn to the three types of measurement that rule our lives: length, time, and temperature. The volume of an amphora, the half-life of technetium, and the temperature in a neutron star are measured with sophisticated instruments. Simpler appraisals are made with the ruler, the clock, and the thermometer.
I knew at the outset that I wanted to incorporate in this book a discussion of some of the big questions science has addressed in the past century, many of which remain unanswered. In endeavoring to do this, I was pleased to discover that temperature was necessarily part of the narrative, not a peripheral marker. Consider three examples.
Our Earth was formed about 4.5 billion years ago from a protoplanetary disc, but when did life first appear? Although it was certainly present 3.7 billion years ago, was the intervening period, 800 million years, long enough for primordial organic molecules to assemble into genetic material? Was the necessary aquatic environment present? The answers depend on early Earth's temperature—how long a favorable climate existed and how resistant life was to thermal jumps. If conditions were such that life could not have formed that quickly on Earth, we must search for its origins elsewhere in the solar system. If life came from elsewhere, where did favorable conditions exist four billion years ago and how did life make the journey to Earth?
Next, consider the universe's birth in the cosmic explosion known as the Big Bang. Unimaginably hot in the beginning, the universe cooled over the course of 300,000 years to 3300 degrees (3000 degrees Kelvin is the way this is usually presented). Experimental evidence says the temperature in that 3300-degree universe was almost completely uniform, the same at one point as at another. Yet it cannot have been completely uniform, or galaxies, stars, and planets would not have evolved. The signals from temperature fluctuations of less than a degree, present at that early time, are now studied with the tools of modern astronomy.
As a third example, consider the rather strange concept of a lowest possible temperature, an absolute zero. The notion of approaching that limit, first glimpsed less than 200 years ago, has turned into the exploration of a new world in which rules of quantum mechanics dictate behavior, wires have no electrical resistance, and flowing fluids experience no friction. This world, so remote from our own experience, has its counterpart in stellar interiors. Beyond that, it may yield important new technologies that can serve our everyday lives.
Some of temperature's most interesting puzzles, perhaps not as sweeping as the three just mentioned, are no less important. There is no simple answer to why our bodies maintain a constant temperature whether we live in the Arctic or the Sahara, why that temperature is 37 degrees, or why most mammals and birds have approximately the same temperature. The demand for unvarying brain readiness and response is clearly an important factor. But more is involved, as we see from the myriad adaptive mechanisms our animal brethren have adopted. Nor is there a complete answer to what advantages are offered us by the evolution of fever as a response to infection.
This book raises many puzzles. Some of the contents may seem paradoxical: for instance, it's surprising that we know the temperature at the center of the Sun with greater precision than that at the center of the Earth. However, many of the problems addressed have explanations that seem almost obvious upon reflection. While I don't claim to offer an overarching view of science, I stress the connections of the approaches as well as of the solutions. Temperature is the thread.