Dark Matter Dominates in Nearby Dwarf Galaxy

Dark matter is called "dark" for a good reason. Although they outweigh particles of regular matter by more than a factor of 5, particles of dark matter are elusive. Their existence is inferred by their gravitational influence in galaxies, but no one has ever directly observed signals from dark matter. Now, by measuring the mass of a nearby dwarf galaxy called Triangulum II, Assistant Professor of Astronomy Evan Kirby may have found the highest concentration of dark matter in any known galaxy.

Triangulum II is a small, faint galaxy at the edge of the Milky Way, made up of only about 1,000 stars. Kirby measured the mass of Triangulum II by examining the velocity of six stars whipping around the galaxy's center. "The galaxy is challenging to look at," he says. "Only six of its stars were luminous enough to see with the Keck telescope." By measuring these stars' velocity, Kirby could infer the gravitational force exerted on the stars and thereby determine the mass of the galaxy.

"The total mass I measured was much, much greater than the mass of the total number of stars—implying that there's a ton of densely packed dark matter contributing to the total mass," Kirby says. "The ratio of dark matter to luminous matter is the highest of any galaxy we know. After I had made my measurements, I was just thinking—wow."

Triangulum II could thus become a leading candidate for efforts to directly detect the signatures of dark matter. Certain particles of dark matter, called supersymmetric WIMPs (weakly interacting massive particles), will annihilate one another upon colliding and produce gamma rays that can then be detected from Earth.

While current theories predict that dark matter is producing gamma rays almost everywhere in the universe, detecting these particular signals among other galactic noises, like gamma rays emitted from pulsars, is a challenge. Triangulum II, on the other hand, is a very quiet galaxy. It lacks the gas and other material necessary to form stars, so it isn't forming new stars—astronomers call it "dead." Any gamma ray signals coming from colliding dark matter particles would theoretically be clearly visible.

It hasn't been definitively confirmed, though, that what Kirby measured is actually the total mass of the galaxy. Another group, led by researchers from the University of Strasbourg in France, measured the velocities of stars just outside Triangulum II and found that they are actually moving faster than the stars closer into the galaxy's center—the opposite of what's expected. This could suggest that the little galaxy is being pulled apart, or "tidally disrupted," by the Milky Way's gravity.

"My next steps are to make measurements to confirm that other group's findings," Kirby says. "If it turns out that those outer stars aren't actually moving faster than the inner ones, then the galaxy could be in what's called dynamic equilibrium. That would make it the most excellent candidate for detecting dark matter with gamma rays."

A paper describing this research appears in the November 17 issue of the Astrophysical Journal Letters. Judith Cohen (PhD '71), the Kate Van Nuys Page Professor of Astronomy, is a Caltech coauthor.

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Simon Receives Lifetime Achievement Award

Barry M. Simon, the International Business Machines (IBM) Professor of Mathematics and Theoretical Physics at Caltech, has been awarded the 2016 Leroy Steele Prize for Lifetime Achievement of the American Mathematical Society (AMS) for his "tremendous impact on the education and research of a whole generation of mathematical scientists through his significant research achievements, highly influential books, and mentoring of graduate students and postdocs," according to the prize citation.

In conferring the award, the AMS noted Simon's "career of exceptional achievement," which includes the publication of 333 papers and 16 books. Simon was specifically recognized for proving a number of fundamental results in statistical mechanics and for contributing to the construction of quantum fields in two space‐time dimensions—topics that, the AMS notes, have "grown into major industries"—as well as for his "definitive results" on the general theory of Schrödinger operators, work that is crucial to an understanding of quantum mechanics and that has led to diverse applications, from probability theory to theoretical physics. He has also made fundamental contributions to the theory of orthogonal polynomials and their asymptotics.

"Barry Simon is a powerhouse in mathematical physics and has had an outstanding career which this award attests to," says Vladimir Markovic, the John D. MacArthur Professor of Mathematics. "Caltech is lucky to have him."

"Barry is a driving force in mathematics at Caltech and has had enormous influence as a scholar, a teacher, and a mentor," says Fiona Harrison, the Benjamin M. Rosen Professor of Physics and holder of the Kent and Joyce Kresa Leadership Chair for the Division of Physics, Mathematics and Astronomy.

Simon spoke at the International Congress of Mathematics in 1974 and has since given almost every prestigious lecture available in mathematics and physics. He was named a fellow of the American Academy of Arts and Sciences in 2005, and was among the inaugural class of AMS fellows in 2012. In 2015, Simon was awarded the International János Bolyai Prize of Mathematics by the Hungarian Academy of Sciences, given every five years to honor internationally outstanding works in mathematics, and in 2012, he was given the Henri Poincaré Prize by the International Association of Mathematical Physics. The prize is awarded every three years in recognition of outstanding contributions in mathematical physics and accomplishments leading to novel developments in the field.

Simon received his AB from Harvard College in 1966 and his doctorate in physics from Princeton University in 1970. He held a joint appointment in the mathematics and physics departments at Princeton for the next decade. He first arrived at Caltech as a Sherman Fairchild Distinguished Visiting Scholar in 1980 and joined the faculty permanently in 1981. He became the IBM Professor in 1984.

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Two Caltech Alumni Receive Breakthrough Prize

Two Caltech alumni, Arthur McDonald (PhD '70) and Ian Agol (BS '92), have been named recipients of 2016 Breakthrough Prize awards. The prizes, which each carry a monetary award of $3 million, are given annually for achievements in mathematics and science to "encourage more pioneering research and celebrate scientists as the heroes they truly are," says Mark Zuckerberg, one of the prizes' founders.

The 2016 Breakthrough Prize in Fundamental Physics was awarded collectively to a community of more than 1,300 physicists who participated in five experiments investigating neutrinos, one of the most abundant particles in the known universe. McDonald—a 2015 Nobel laureate—was one of the seven scientists who led these experiments, heading the Sudbury Neutrino Observatory collaboration in Ontario. Neutrinos are unaffected by the two strong fundamental forces of nature—electromagnetism and the strong nuclear force—and are thus elusive, traveling through the universe essentially unimpeded and near the speed of light.

McDonald is currently Professor Emeritus at Queen's University and earlier this year shared the Nobel Prize in Physics for "the discovery of neutrino oscillations, which shows that neutrinos have mass."

Ian Agol received the 2016 Breakthrough Prize in Mathematics for his "spectacular contributions to low-dimensional topology and geometric group theory, including work on the solutions of the tameness, virtual Haken and virtual fibering conjectures." Low-dimensional topology is a field that focuses on manifolds—objects that seem flat when observed at a small scale—in four or fewer dimensions. Earth is one example of a manifold—while it is actually spherical, we humans are too small to be able to perceive Earth's curvature, and thus Earth appears flat to us.

Agol is a professor of mathematics at UC Berkeley and is currently a visiting researcher at the Institute for Advanced Study in Princeton, New Jersey.

The Breakthrough Prize was founded by Sergey Brin of Google, and Anne Wojcicki of 23andMe; Jack Ma of Alibaba, and Cathy Zhang; Yuri Milner, a venture capitalist and physicist, and Julia Milner; and Mark Zuckerberg of Facebook, and Priscilla Chan. The awards were presented at a ceremony in San Francisco on November 8.

Previous Caltech winners include Alexei Kitaev, the Ronald and Maxine Linde Professor of Theoretical Physics and Mathematics, and John H. Schwarz, the Harold Brown Professor of Theoretical Physics, Emeritus, who won the Fundamental Physics prize in 2012 and 2014 respectively. Alexander Varshavsky, the Howard and Gwen Laurie Smits Professor of Cell Biology, received the Breakthrough Prize in Life Sciences in 2014.

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Two Alumni Awarded Breakthrough Prize
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Monday, November 30, 2015

Microbial diners, drive-ins, and dives: deep-sea edition

Celebrating 50 Years of Infrared Astronomy

A Milestone in Astronomy

Fifty years ago, a group of Caltech physicists brought infrared light—then an underappreciated region of the electromagnetic spectrum—to the forefront of astrophysics. Infrared astronomy holds the keys to our cosmic origins, revealing how planets, stars, and even the earliest galaxies formed. It may even enable us to discover Earth-like planets orbiting other stars.

The clouds of dust and gas from which stars and planets form—and the newborn solar systems themselves—are too cold to be seen in visible light. However, the heat they do emit shows up in the infrared, the shortest wavelengths of which are just slightly longer than the red light we do see.  The earliest galaxies would be visible, if they were closer to us in space and time; instead, the expanding universe has stretched their light so that the wavelengths are shifted down into the infrared. However, most of this light never reaches earthbound telescopes, as Earth's atmosphere absorbs most infrared waves very efficiently.

Two next-generation space telescopes, the James Webb Space Telescope, which is slated to launch in October 2018 to replace the Hubble Space Telescope, and the Wide-Field Infrared Survey Telescope (WFIRST), which has been named a top priority for the next decade in astronomy and is being studied for launch in the mid-2020s, will be carrying forward work begun by the Infrared Astronomical Satellite (IRAS) mission in the 1980s—work in which Caltech's self-styled "Infrared Army" played a major role.

On November 2 and 3, 2015, Caltech hosted a two-day symposium in honor of the Army's three founders—the late Gerry Neugebauer (PhD '60), Caltech's Robert Andrews Millikan Professor of Physics, Emeritus; Tom Soifer (BS '68), the Harold Brown Professor of Physics and director of the Spitzer Science Center, which operates NASA's current orbiting infrared observatory, the Spitzer Space Telescope; and Keith Matthews (BS '62), chief instrument scientist for Palomar Observatory, who by his own estimation has built "scores" of instruments for the 5-meter Hale telescope at Palomar and the twin 10-meter telescopes at the W. M. Keck Observatory atop Mauna Kea, Hawaii.

Matthews' hardware output is rivaled by the rate at which Neugebauer's and Soifer's research groups have spun off infrared programs at other institutions. Says organizer Lee Armus, who arrived at Caltech as a postdoc of Soifer's in 1992, "I've got a group of grad students from the '70s and '80s, and a group from the '90s. I'm trying to sample as many epochs as I can in two days."

Neugebauer earned his doctorate in 1960 under Caltech physics professor Robert Lee Walker, who had codesigned Caltech's synchrotronthe most powerful machine of its kind in its day, capable of revving up an electron to a billion volts of energy. In those days, experimental physicists built and operated their own equipment—and thus understood it inside and out. Neugebauer brought this hands-on approach to the U.S. Army at Caltech's Jet Propulsion Lab, where he designed and operated the infrared radiometer for Mariner 2's successful flyby of Venus.

When Neugebauer returned to campus in 1962, he and fellow physics professor Robert Leighton (BS '41, PhD '47) set about making the 62-inch-diameter mirror for the world's first purpose-built infrared telescope. (It is now in the Smithsonian.) Over the next few years, they and a team of undergraduates and graduate students used the instrument to scan the entire sky—or as much as could be seen from the summit of Mount Wilson overlooking Pasadena. The Two-Micron Sky Survey's final catalog, published in 1969, inventoried some 5,000 point-like objects, many of which were previously undiscovered cool red stars or stars enshrouded in obscuring clouds of gas and dust that the stars had ejected as they entered the later stages of their life.

Other invisible objects also cropped up. In 1965, Neugebauer's first graduate student, Eric Becklin (PhD '68) discovered something in the Orion Nebula that, in the infrared, was as bright as the brightest visible star, except it had no visible counterpart. Follow-up work with the 200-inch Hale Telescope at Palomar revealed that this point of infrared light had faint "wings," about 15 times larger than its diameter, extending to its east and west—a feature unlike any ever seen before. The Orion Nebula was known to be at most a few million years old and was presumed to be a stellar nursery. The object Becklin detected was the first protostar to be caught in its shell of potentially planet-forming dust. Becklin would later pioneer high-altitude infrared astronomy aboard specially modified jet aircraft.

In the 1970s Neugebauer and Soifer became part of the science team for IRAS, a collaboration among the United States, England, and the Netherlands. Launched in 1983, IRAS surveyed more than 95 percent of the sky. The data were made available to the entire scientific community as soon as they were processed—a first for NASA—leading to the creation of Caltech's Infrared Processing and Analysis Center to curate and distribute it.


3D Movie of Stellar Orbits in the Central Parsec
Tracking the stars in close orbit around the center of our galaxy reveals the existence of a black hole containing four million times the mass of our sun. This 3-D orbital reconstruction begins in the year 1893 at the galactic center, about 0.05 light years from the supermassive black hole, and pulls back to end at a distance of 0.65 light years in the year 2013. Young stars are shown in teal green, old stars are shown in orange, and those of unknown spectral type are shown in magenta.

IRAS got the field of infrared astronomy off the ground. "Astronomers could trust our catalogs," Soifer says. "Every source was real. We gained the respect of the astronomical community because they could take some other telescope and point it at our coordinates, and they'd find really interesting objects to explore with millimeter telescopes, radio telescopes, optical telescopes."

Matthews "started working in cosmic rays in 1959 with Professor of Physics [Eugene] 'Bud' Cowan [PhD '48]," and still sees himself as a physicist. "I do anything that has technique to it," he says. In addition to helping design the infrared aspects of the Keck 10-meter telescopes, he built the observatory's Near-Infrared Camera, the first instrument to be mounted on the telescope.

In the early 1990s Andrea Ghez (MS '89, PhD '93), one of Neugebauer's last graduate students, used this instrument and a technique called "speckle interferometry" to measure the positions of stars close to the galactic center. Ghez now uses the telescopes as the founder and director of UCLA's Galactic Center Group. Nearly two decades' worth of measurements, mostly using the second- generation Near-Infrared Camera for the Keck II telescope built by Matthews, have allowed her to derive radial velocities of stars as they orbit that still-elusive black hole. Thanks to her work, however, the mass of our galaxy's black hole is now precisely known, making it a little less mysterious.

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Celebrating 50 Years of Infrared Astronomy
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Fifty years ago, Caltech and its self-styled Infrared Army of experimental physicists and astronomers helped to found the discipline of infrared astronomy

Elachi to Retire as JPL Director

Charles Elachi (MS '69, PhD '71) has announced his intention to retire as director of the Jet Propulsion Laboratory on June 30, 2016, and move to campus as professor emeritus. A national search is underway to identify his successor.

"A frequently consulted national and international expert on space science, Charles is known for his broad expertise, boundless energy, conceptual acuity, and deep devotion to JPL, campus, and NASA," said Caltech president Thomas F. Rosenbaum in a statement to the Caltech community. "Over the course of his 45-year career at JPL, Charles has tirelessly pursued new opportunities, enhanced the Laboratory, and demonstrated expert and nimble leadership. Under Charles' leadership over the last 15 years, JPL has become a prized performer in the NASA system and is widely regarded as a model for conceiving and implementing robotic space science missions."

With Elachi at JPL's helm, an array of missions has provided new understanding of our planet, our moon, our sun, our solar system, and the larger universe. The GRAIL mission mapped the moon's gravity; the Genesis space probe returned to Earth samples of the solar wind; Deep Impact intentionally collided with a comet; Dawn pioneered the use of ion propulsion to visit the asteroids Ceres and Vesta; and Voyager became the first human-made object to reach interstellar space. A suite of missions to Mars, from orbiters to the rovers Spirit, Opportunity, and Curiosity, has provided exquisite detail of the red planet; Cassini continues its exploration of Saturn and its moons; and the Juno spacecraft, en route to a July 2016 rendezvous, promises to provide new insights about Jupiter. Missions such as the Galaxy Evolution Explorer, the Spitzer Space Telescope, Kepler, WISE, and NuSTAR have revolutionized our understanding of our place in the universe.

Future JPL missions developed under Elachi's guidance include Mars 2020, Europa Clipper, the Asteroid Redirect Mission, Jason 3, Aquarius, OCO-2, SWOT, and NISAR.

Elachi joined JPL in 1970 as a student intern and was appointed director and Caltech vice president in 2001. During his more than four decades at JPL, he led a team that pioneered the use of space-based radar imaging of the Earth and the planets, served as principal investigator on a number of NASA-sponsored studies and flight projects, authored more than 230 publications in the fields of active microwave remote sensing and electromagnetic theory, received several patents, and became the director for space and earth science missions and instruments. At Caltech, he taught a course on the physics of remote sensing for nearly 20 years

Born in Lebanon, Elachi received his B.Sc. ('68) in physics from University of Grenoble, France and the Dipl. Ing. ('68) in engineering from the Polytechnic Institute, Grenoble. In addition to his MS and PhD degrees in electrical science from Caltech, he also holds an MBA from the University of Southern California and a master's degree in geology from UCLA.

Elachi was elected to the National Academy of Engineering in 1989 and is the recipient of numerous other awards including an honorary doctorate from the American University of Beirut (2013), the National Academy of Engineering Arthur M. Bueche Award (2011), the Chevalier de la Légion d'Honneur from the French Republic (2011), the American Institute of Aeronautics and Astronautics Carl Sagan Award (2011), the Royal Society of London Massey Award (2006), the Lebanon Order of Cedars (2006 and 2012), the International von Kármán Wings Award (2007), the American Astronautical Society Space Flight Award (2005), the NASA Outstanding Leadership Medal (2004, 2002, 1994), and the NASA Distinguished Service Medal (1999).

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He will move to campus as professor emeritus. A national search is underway to identify his successor.

JPL News: Black Hole Has Major Flare

The baffling and strange behaviors of black holes have become somewhat less mysterious recently, with new observations from NASA's Explorer missions Swift and the Nuclear Spectroscopic Telescope Array, or NuSTAR. The two space telescopes caught a supermassive black hole in the midst of a giant eruption of X-ray light, helping astronomers address an ongoing puzzle: How do supermassive black holes flare?

Read more at JPL News

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Two space telescopes have caught a supermassive black hole in the midst of a giant eruption of X-ray light.

Caltech Physicists Uncover Novel Phase of Matter

Finding could have implications for high-temperature superconductivity

A team of physicists led by Caltech's David Hsieh has discovered an unusual form of matter—not a conventional metal, insulator, or magnet, for example, but something entirely different. This phase, characterized by an unusual ordering of electrons, offers possibilities for new electronic device functionalities and could hold the solution to a long-standing mystery in condensed matter physics having to do with high-temperature superconductivity—the ability for some materials to conduct electricity without resistance, even at "high" temperatures approaching  –100 degrees Celsius.

"The discovery of this phase was completely unexpected and not based on any prior theoretical prediction," says Hsieh, an assistant professor of physics, who previously was on a team that discovered another form of matter called a topological insulator. "The whole field of electronic materials is driven by the discovery of new phases, which provide the playgrounds in which to search for new macroscopic physical properties."

Hsieh and his colleagues describe their findings in the November issue of Nature Physics, and the paper is now available online. Liuyan Zhao, a postdoctoral scholar in Hsieh's group, is lead author on the paper.

The physicists made the discovery while testing a laser-based measurement technique that they recently developed to look for what is called multipolar order. To understand multipolar order, first consider a crystal with electrons moving around throughout its interior. Under certain conditions, it can be energetically favorable for these electrical charges to pile up in a regular, repeating fashion inside the crystal, forming what is called a charge-ordered phase. The building block of this type of order, namely charge, is simply a scalar quantity—that is, it can be described by just a numerical value, or magnitude.

In addition to charge, electrons also have a degree of freedom known as spin. When spins line up parallel to each other (in a crystal, for example), they form a ferromagnet—the type of magnet you might use on your refrigerator and that is used in the strip on your credit card. Because spin has both a magnitude and a direction, a spin-ordered phase is described by a vector.

Over the last several decades, physicists have developed sophisticated techniques to look for both of these types of phases. But what if the electrons in a material are not ordered in one of those ways? In other words, what if the order were described not by a scalar or vector but by something with more dimensionality, like a matrix? This could happen, for example, if the building block of the ordered phase was a pair of oppositely pointing spins—one pointing north and one pointing south—described by what is known as a magnetic quadrupole. Such examples of multipolar-ordered phases of matter are difficult to detect using traditional experimental probes.

As it turns out, the new phase that the Hsieh group identified is precisely this type of multipolar order.  

To detect multipolar order, Hsieh's group utilized an effect called optical harmonic generation, which is exhibited by all solids but is usually extremely weak. Typically, when you look at an object illuminated by a single frequency of light, all of the light that you see reflected from the object is at that frequency. When you shine a red laser pointer at a wall, for example, your eye detects red light. However, for all materials, there is a tiny amount of light bouncing off at integer multiples of the incoming frequency. So with the red laser pointer, there will also be some blue light bouncing off of the wall. You just do not see it because it is such a small percentage of the total light. These multiples are called optical harmonics.

The Hsieh group's experiment exploited the fact that changes in the symmetry of a crystal will affect the strength of each harmonic differently. Since the emergence of multipolar ordering changes the symmetry of the crystal in a very specific way—a way that can be largely invisible to conventional probes—their idea was that the optical harmonic response of a crystal could serve as a fingerprint of multipolar order.   

"We found that light reflected at the second harmonic frequency revealed a set of symmetries completely different from those of the known crystal structure, whereas this effect was completely absent for light reflected at the fundamental frequency," says Hsieh. "This is a very clear fingerprint of a specific type of multipolar order."

The specific compound that the researchers studied was strontium-iridium oxide (Sr2IrO4), a member of the class of synthetic compounds broadly known as iridates. Over the past few years, there has been a lot of interest in Sr2IrO4 owing to certain features it shares with copper-oxide-based compounds, or cuprates. Cuprates are the only family of materials known to exhibit superconductivity at high temperatures—exceeding 100 Kelvin (–173 degrees Celsius). Structurally, iridates and cuprates are very similar. And like the cuprates, iridates are electrically insulating antiferromagnets that become increasingly metallic as electrons are added to or removed from them through a process called chemical doping. A high enough level of doping will transform cuprates into high-temperature superconductors, and as cuprates evolve from being insulators to superconductors, they first transition through a mysterious phase known as the pseudogap, where an additional amount of energy is required to strip electrons out of the material. For decades, scientists have debated the origin of the pseudogap and its relationship to superconductivity—whether it is a necessary precursor to superconductivity or a competing phase with a distinct set of symmetry properties. If that relationship were better understood, scientists believe, it might be possible to develop materials that superconduct at temperatures approaching room temperature.

Recently, a pseudogap phase also has been observed in Sr2IrO4—and Hsieh's group has found that the multipolar order they have identified exists over a doping and temperature window where the pseudogap is present. The researchers are still investigating whether the two overlap exactly, but Hsieh says the work suggests a connection between multipolar order and pseudogap phenomena.

"There is also very recent work by other groups showing signatures of superconductivity in Sr2IrO4 of the same variety as that found in cuprates," he says. "Given the highly similar phenomenology of the iridates and cuprates, perhaps iridates will help us resolve some of the longstanding debates about the relationship between the pseudogap and high-temperature superconductivity."

Hsieh says the finding emphasizes the importance of developing new tools to try to uncover new phenomena. "This was really enabled by a simultaneous technique advancement," he says.

Furthermore, he adds, these multipolar orders might exist in many more materials. "Sr2IrO4 is the first thing we looked at, so these orders could very well be lurking in other materials as well, and that's exactly what we are pursuing next."

Additional Caltech authors on the paper, "Evidence of an odd-parity hidden order in a spin–orbit coupled correlated iridate," are Darius H. Torchinsky, Hao Chu, and Vsevolod Ivanov. Ron Lifshitz of Tel Aviv University, Rebecca Flint of Iowa State University, and Tongfei Qi and Gang Cao of the University of Kentucky are also coauthors. The work was supported by funding from the Army Research Office, the National Science Foundation (NSF), and the Institute for Quantum Information and Matter, an NSF Physics Frontiers Center with support from the Gordon and Betty Moore Foundation.

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Physicists Uncover Novel Phase of Matter
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Not a conventional metal, insulator, or magnet, it could hold the solution to a long-standing mystery related to high-temperature superconductivity.
Friday, October 30, 2015
Beckman Institute Auditorium – Beckman Institute

Teaching Statement Workshop

Feynman's Nobel Year

A Milestone in Physics

Fifty years ago on October 21, 1965, Caltech's Richard Feynman shared the Nobel Prize in Physics with Julian Schwinger and Sin-Itiro Tomonaga. The three independently brokered workable marriages between 20th-century quantum mechanics and 19th-century electromagnetic field theory.

Quantum electrodynamics, as this previously reluctant partnership is known, treats the behavior of electromagnetic fields in the same manner as it treats the behavior of the electrons producing them—as particles, whose interactions can be described using probability theory. (In this case, the particles are little packages of electromagnetic energy called photons, which we usually think of as particles of light.) The so-called probability amplitude for anything more elaborate than an isolated hydrogen atom is far too complex to solve directly, so the standard quantum-mechanics approach is to start with a solvable, relatively simple equation and keep adding smaller and smaller corrections to it according to well-defined rules. The solution gets closer and closer to the actual answer as the corrections diminish in size, so you simply decide how accurate you need to be for the task at hand. However, describing an electromagnetic field in such a manner means allowing the photons to carry infinite momentum, and it had become clear by the late 1930s that such equations did not converge on the correct answer—adding corrections merely piled infinities upon infinities.

While Schwinger and Tomonaga used highly mathematical approaches to the problem, Feynman characteristically took a different point of view. He drew pictures of every possible interaction between photons and electrons, including those involving "virtual" particles undetectable by the outside world. For example, an electron can spontaneously emit and reabsorb a photon—a self-interaction that contributes appreciably to the electron's mass. And a photon can transmute into an electron and its antimatter twin, the positron, with the two immediately annihilating each another to produce a new photon and helping to create the so-called vacuum energy that pervades empty space. Far more complex pictures are possible—and usually necessary. These iconic doodles, now called Feynman diagrams, allowed him to calculate each scenario's probability amplitude independently and add them all up to get the correct answer.

Back in the 1960s, Nobel laureates got a congratulatory 9:00 a.m. telegram from Stockholm rather than a 3:00 a.m. phone call. Even so, Feynman was awakened at 3:45 a.m. by a reporter who broke the news to him, then asked, "Aren't you pleased to hear that you've won the prize?" "I could have found out later this morning," the groggy Feynman replied. "Well, how do you feel, now that you've won it?" the reporter persisted.

At the customary press conference held at a more reasonable hour at Caltech's faculty club, the Athenaeum, a reporter asked, "Is there any way your work can be explained in layman's terms?" "There certainly must be," Feynman replied. "But I don't know what it is."

Feynman was a master teacher with a flair for showmanship, and for him to be at a loss for words—even in jest—may have been a first. The final installment of his textbook The Feynman Lectures on Physics had come out that June. Distilled from the Physics 1 and 2 course sequence he had taught to 180 Caltech freshmen in 1961–62 and to the same group as sophomores the following year, the work's three volumes appeared in 1963, 1964, and 1965. The lectures, a complete reimagining of introductory physics, had been motivated by the rapid pace of discoveries in the field in the 1950s and by the improvements in high-school mathematics instruction brought on by the space race—which the Soviets were winning in 1961 by a score of three to nothing, having successively put the first satellite, the first animal (Laika the dog), and the first human (Yuri Gagarin) into orbit.

"A substantial number" of Caltech's physics faculty had proffered outlines of topics the two-year course should cover, wrote professor Robert Leighton (BS '41, MS '44, PhD '47) in the foreword to the series. He noted that the hundred-plus lectures were envisioned as "a cooperative effort by N staff members who would share the total burden symmetrically and equally: each man would take responsibility for 1/N of the material, deliver the lectures, and write text material for his part." This unworkable scheme was quickly abandoned after physics professor Matthew Sands volunteered Feynman for the entire job. Feynman agreed—on the condition that he did not have to write anything. Instead, each lecture was audiotaped and transcribed, and every diagram was photographed. "It was expected that the necessary editing would be minor . . . to be done by one or two graduate students on a part-time basis. Unfortunately, this expectation was short-lived," Leighton wrote. In fact, it "required the close attention of a professional physicist for from ten to twenty hours per lecture!" Leighton and Sands worked on it by turn, with Feynman doing the final edit himself.

In the end, however, it was all worth the effort. More than 1.5 million sets of the iconic, bright red volumes have been sold in English alone, and at least a dozen translations into other languages exist. The book has gone through three editions and remains in print to this day; on September 13, 2013 Caltech posted a freely available electronic version whose equations and graphics scale automatically to the reader's device. In the 25 months since then, the site has been accessed more than eight million times by nearly 1.7 million individuals.

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Feynman's Nobel Year
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Richard Feynman had a banner year in 1965, sharing the Nobel Prize in Physics and seeing the final volume of "The Feynman Lectures on Physics" published.

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