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For author Alan Lightman, reading landmark scientific papers provides a window into the lives and intellectual adventures of the men and women behind the 20th century’s most influential ideas.

Published April 14, 2006

By Karen Hopkin

The key experiment came to him in a dream. It was 1921 and Otto Loewi, a German pharmacologist, was looking for a way to determine how nerve cells communicate. Was the signal conveyed from one neuron to the next—or from a neuron to a muscle or organ—electrical? Or was it chemical?

The scientist awoke, jotted down his musings on a slip of paper, and went back to sleep. “It occurred to me at six o’clock in the morning that during the night I had written down something most important,” he later recalled, “but I was unable to decipher the scrawl.”

From Dream to Nobel Prize

Fortunately, the idea returned the following night. That time, Loewi must have written more legibly, because he was able to carry out his Nobel Prize-winning experiment that day. He dissected the hearts from two frogs and placed them, still beating, into separate dishes of saline solution. Loewi then stimulated the vagus nerve he’d left attached to the first heart. As expected, the heart slowed its beating.

Now here’s the elegant part. Loewi took some of the solution bathing the first heart and poured it over the second heart, from which he’d stripped the vagus nerve. This heart, too, slowed, proving that the message transmitted by the vagus nerve was chemical in nature. The compound, which Loewi called “Vagusstuff,” turned out to be acetylcholine, a neurotransmitter found widely throughout the nervous system.

For Loewi, the experience suggested that “we should sometimes trust a sudden intuition without too much skepticism.” And for Alan Lightman, physicist and author of The Discoveries: Great Breakthroughs in 20th Century Science, the story illustrates how scientists think, and reminds us that science is a process of exploration carried out by human beings.

Hearing the Scientist’s Voice

Over the years, Lightman has come to realize that scientists rarely read original research papers, perhaps because they view science as being all about the bottom line. “If science is an explanation of the way that the world behaves, then you don’t need to know how you got to that understanding,” says Lightman. “You just need to know the facts, ma’am. And that’s all that matters.”

That view, although valid, is limited, Lightman told an audience at The New York Academy of Sciences (the Academy) on January 31, 2006. “You can read a textbook on the theory of relativity and you can understand relativity,” he says. “But you don’t understand the mind of Einstein. You don’t hear his voice.”

To remedy that loss, Lightman assembled The Discoveries, a handpicked collection of 22 of the greatest ideas and experiments in 20th century science. Lightman asked his scientist pals—physicists, chemists, astronomers, biologists—for recommendations and then winnowed down the resulting list to the two dozen stories he presents in the book. For each discovery—from Werner Heisenberg’s enumeration of the uncertainty principle to Barbara McClintock’s revelation that genes can jump from one chromosome to another—Lightman provides a guided tour to the original paper along with an essay on the life and times of the scientists involved.

Measuring the Distance of Stars

Among Lightman’s favorite tales is that of Henrietta Leavitt’s development of a method for measuring the distance to the stars. Leavitt was hired in the late 1800s by Edward Pickering, director of the Harvard College Observatory, to pore over photographic plates and calculate the positions and brightness of thousands of stars. As one of the cadre of women that formed Pickering’s low-paid battalion of human “computers,” Leavitt was expected to “work, not think,” says Lightman. “But some of the women disobeyed him, and Henrietta Leavitt was one of those.”

Through painstaking measurements, Leavitt uncovered a relationship between the periodicity and luminosity of the Cepheids, a group of stars that brighten and dim in predictable cycles that vary between three and 50 days. Leavitt found that the longer a star’s period, the greater its intrinsic luminosity, and that knowing how bright a star is allows one to calculate how far away from Earth it lies. Thus the Cepheids, which are scattered throughout the night sky, could serve as cosmic beacons by which astronomers could gauge distances in space.

Leavitt’s work laid the foundation for many of the astronomical discoveries that would follow, including Hubble’s determination that the universe is expanding. Yet the scientist remained uncelebrated in her lifetime. “Even today there are very few people who’ve heard of her,” notes Lightman. In 1925, a representative of the Swedish Academy of Sciences wrote to Leavitt to propose nominating her for a Nobel Prize. Unfortunately, Leavitt had been dead for three years by then, rendering her ineligible for the honor.

Passion and Obsession

The most satisfying stories, Lightman says, are the ones in which the researchers’ personalities drive the discovery. Take, for example, Arno Penzias and Robert Wilson’s detection of the cosmic background radiation—the persistent hum left over from the Big Bang. “Both men were incredibly meticulous experimentalists,” says Lightman. “If they hadn’t been so anal compulsive about the details then they wouldn’t have been so certain that this residual hiss in their antenna was something worth investigating.”

But, he adds, “they were so fastidious, so picky, and so careful” that they methodically chased after the source of the noise. And after they eliminated every possible thing they could think of, Penzias and Wilson concluded “this was something worth writing about,” says Lightman. Indeed, their almost comically understated paper, entitled “A measurement of excess antenna temperature at 4080 Mc/s,” formed the basis of their 1978 Nobel Prize.

In the end, Lightman himself discovered a thing or two in putting together the book. Although he did not uncover any particular scientific temperament—scientists’ personalities run the regular human gamut—Lightman did find that, regardless of the field in which they worked or how they came to their discoveries, all the scientists he profiled “were really passionate about what they do. All loved to solve puzzles. They all loved to challenge authority. All were independent thinkers. And all were really obsessed with science.”

And though all didn’t necessarily dream about their work, they did labor tirelessly to solve their favorite puzzles, leaving behind them tales that are certainly worth telling.

About the Speaker

Alan Lightman, PhD, is adjunct professor of humanities at the Massachusetts Institute of Technology. As a novelist, essayist, physicist, and lecturer, Lightman is committed to making science accessible and understandable to a wide audience. His writings cover a range of topics dealing with science and the humanities, particularly the relationship between science, art, and literature. Lightman’s short fiction, essays, and reviews have appeared in numerous popular magazines and publications, including Discover, Harper’s, Nature, and The New Yorker.

He is the author of four novels, including the international bestseller Einstein’s Dreams, which was runner-up for the 1994 PEN New England/Boston Globe Winship Award, has been translated into 30 languages, and is the basis for more than two dozen independent theatrical and musical productions. In addition to his novels, Lightman is the author of several science books, drawing on his research in the areas of gravitational theory, accretion disks, stellar dynamics, radiative processes, and relativistic plasmas.

Lightman holds a PhD in theoretical physics from the California Institute of Technology, and an Honorary Doctorate of Letters from Bowdoin College. He served a postdoctoral fellowship at Cornell University before becoming assistant professor of astronomy at Harvard University and research scientist at the Harvard-Smithsonian Center for Astrophysics. In 1989 Lightman joined the faculty of MIT, and in 1995 was appointed John E. Burchard Professor of Humanities, a position he resigned in 2001 to allow more time for his writing.

For his contributions to physics, Lightman was elected fellow of the American Physical Society and the American Association for the Advancement of Science, both in 1989. In 1996 he was elected fellow of the American Academy of Arts and Sciences, and that same year, was recipient of the American Institute of Physics Andrew Gemant Award for linking science to the humanities.

Missives from Feynman in Perfectly Reasonable Deviations from the Beaten Track, a book of his letters edited by daughter Michelle Feynman, reveal his genius and wit. What was his contribution to the canon of 20th-century quantum physics?

Published February 3, 2006

By Chris H. Greene

“Science alone of all the subjects contains within itself the lesson of the danger of belief in the infallibility of the greatest teachers in the preceding generation … Learn from science that you must doubt the experts. As a matter of fact, I can also define science another way: Science is the belief in the ignorance of experts.”
— Richard Feynman, 1981

We all know the stories of Richard Feynman. He was at times a showman and a clown. He expressed irreverence toward prestigious, hoary organizations like the National Academy of Sciences and the Royal Swedish Academy of Sciences. The tragic death of his young wife during the time of the Manhattan Project became familiar to millions through the touching Matthew Broderick film, Infinity. But behind his public persona lay one of the truly independent and innovative minds of the 20th century. Richard Feynman felt an intense, personal need to see physical phenomena in his own terms, and from his own perspectives, using theories that he generated himself.

At the same time, Feynman’s theoretical constructs did not arrive on the planet like a bolt from nowhere. His most important contributions were ideas that were in some sense already “in the wind,” but his way of developing them into consistent theoretical descriptions of nature differed dramatically from methods popular at the time.

Paradoxical Infinities

It may seem surprising, but the theoretical program that resulted in Feynman’s 1965 Nobel Prize (also awarded that year to Julian Schwinger and Sin-Itiro Tomonaga) was not aimed so much at explaining the result of any particular experiment, as it was an attempt to resolve some of the apparently self-contradictory aspects of both classical and quantum electrodynamics theory. If you shake an electron, it radiates light waves, whose electric fields must in turn act back on the electron to lower its energy. But attempts to calculate this “radiative reaction force” led to infinities which were paradoxical and in clear contradiction with experience.

In Feynman’s doctoral thesis work with John Wheeler at Princeton, the two entertained fantastic possibilities in a desperate attempt to solve these paradoxical infinities. One peculiar notion that emerged was that if, in a certain sense, the classical fields are allowed to propagate backward in time, the paradoxes and the infinities appeared to be magically removed.

A variant of this idea survived when Feynman wrote down his quantum mechanical formulation of this problem, which he credits to Wheeler for originally tossing out: that the positron, the antiparticle of an electron, can be regarded as an ordinary electron moving backward in time. Surely you’re joking, Mr. Feynman! As fantastic and unbelievable as this idea seems when stated in words, when formulated mathematically it was found that a consistent theoretical framework emerged, without the troubling infinities.

Moreover, Feynman created a simple way for these complicated calculations to be carried out, which is still used today: first, draw lines that represent electrons, positrons, and photons moving forward and backward in time in different ways that can contribute to the process of interest. Then apply Feynman’s rules for translating each such Feynman diagram into a precise mathematical formula.

Quantum Electrodynamics

One of the most famous applications of Feynman’s quantum electrodynamics was his calculation of a tiny frequency difference between two nearly identical energy levels (2S1/2 and 2P1/2) of the simplest atom, hydrogen. Willis Lamb and Robert C. Retherford had caused a stir in 1947 when they measured this frequency difference to be 1057 million cycles per second (MHz), because the then-accepted theory of Paul Dirac suggested that this difference should be identically zero. The methods for calculating this interaction between an atomic electron and the “vacuum-fluctuating electric fields of free space” gave infinity, a useless result entirely irrelevant to the experiment.

Using the Feynman calculus, however, a result very close to the experimental frequency splitting (the so-called “Lamb shift”) was obtained. In the intervening decades, both experiment and theory have improved, and we now know this Lamb shift experimentally to be 1057.8447 (plus or minus 0.0034) MHz, while theory based on Feynman’s work predicts 1057.839 (plus or minus 0.006) MHz.

Within experimental uncertainties, and within theoretical uncertainties associated with our imperfect understanding of the proton’s nuclear structure, these agree. Nature thus confirms the remarkable synthesis of theoretical ideas into working quantum electrodynamics, achieved by Feynman, as well as by Schwinger and by Tomonaga.

Advancing the World of Theoretical Physics

And what are we to take from these strange notions? Are positrons really just electrons moving backward in time? Feynman tended to dismiss such queries as having no more relevance to physics than debates about how many angels fit on the head of a pin. Here is one more example where the equations developed by theoretical physicists, after extensive testing, are the bottom line. Seemingly bizarre philosophical implications, when those equations are stated in words (such as “particles moving backward in time”), do not matter a whit. What matters from the physicist’s perspective is the explanatory and predictive power of the resulting theory.

In the end, Feynman’s work parallels eerily the way the “luminiferous aether” was abandoned as irrelevant, once physicists accepted around the beginning of the 20th century that Maxwell’s equations by themselves adequately describe all classical phenomena of electricity and magnetism. And it is similar to the way Einstein’s equations of relativity, and the peculiar quantum theory, were accepted despite their troubling, almost nonsensical implications for how we think about time, space, and reality. As Niels Bohr wrote and was quoted in Wheeler and Feynman’s 1945 Reviews of Modern Physics article:

We must, therefore, be prepared to find that further advance…will require a still more extensive renunciation of features which we are accustomed to demand of the space time mode of description.

The world of theoretical physics is better today because Richard Feynman was brave enough to contemplate and develop ideas that required such a renunciation.

Also read: The Challenge of Quantum Error Correction