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Dutch-American theoretical physicist Peter Joseph Wilhelm Debye won the 1936 Nobel Prize in chemistry. He studied molecular structure, dipole movements, and X-ray and electron diffraction in gases.
Peter Joseph Wilhelm Debye (1884-1966), Dutch-American theoretical physicist, who received the 1936 Nobel Prize in chemistry for his studies in molecular structure, dipole movements, and the diffraction of X rays and electrons in gases.
Debye was born in Maastricht, March 24, 1884, and educated at the University of Munich. From 1911 to 1935 he held the post of professor of physics successively at several universities in Switzerland, the Netherlands, and Germany. He then became director of the Kaiser Wilhelm Institute for Physics in Berlin. In the U.S., he served as professor of chemistry at Cornell University from 1940 to 1952; in 1952 he became professor emeritus. He died at Ithaca, New York, on November 2, 1966.
In 1912 Debye modified the specific-heat theory put forth by Albert Einstein by calculating the probability of any frequency of molecular vibration up to a maximum frequency; the theory of specific heat constituted one of the earliest theoretical successes of the quantum theory. Debye also applied the quantum theory to explain the heat conductivity of crystals at low temperature, the variation of saturation intensity of magnetization with temperature, the theory of space quantization (with the German physicist Arnold Sommerfeld, 1868-1951), and the phenomena of scattering of X rays (with the American physicist Arthur Holly Compton). In 1923 Debye developed a theory of ionization of electrolytes (now called the Debye-Hückel theory), which is important in chemistry (see Ionization). Later he worked on the theory of quantum mechanics, including its applications to the diffraction of electrons in gases. In 1963 he was awarded the Priestley Medal by the American Chemical Society.
Among Debye's writings are Quantum Theory and Chemistry (1928), Polar Molecules (1929), and Molecule Structure (1931).

American physicist Clinton Joseph Davisson won the Nobel Prize in physics in 1937. Davisson found that electrons could be diffracted by crystals just like X rays. He also proved they can show wavelike structure.
Clinton J. Davisson (1881-1958), American physicist and Nobel laureate. Davisson made major contributions to understanding the diffraction of electrons by crystals and shared the 1937 Nobel Prize in physics with British physicist Sir George Paget Thomson for their independent proof of the wave properties of electrons.
Born in Bloomington, Illinois, Davisson entered the University of Chicago in 1902. He left to teach physics at Purdue University in 1903 and 1904. In 1905 he became a physics instructor and research assistant at Princeton University. Returning to the University of Chicago for summer sessions, Davisson finally completed his B.S. degree in physics in 1908. After earning a Ph.D. degree in physics from Princeton University in 1911, Davisson accepted an appointment as an assistant professor of physics at the Carnegie Institute of Technology.
In 1917, during World War I (1914-1918), Davisson took leave from the Carnegie Institute to work on a military telecommunications project at the engineering department of the Western Electric Company Laboratories, which later became the Bell Telephone Laboratories. After the war, he decided to remain at the laboratories, which guaranteed him freedom to do full-time research, an uncommon opportunity in commercial laboratories at that time. Davisson retired from Bell in 1946 and accepted a position as a visiting professor of physics at the University of Virginia in Charlottesville, where he remained until his retirement in 1954.
At Western Electric, Davisson pursued his interest in thermionics, the emission of electrically charged particles, or ions, from conducting materials such as metals heated to high temperatures. His experiments in thermionics revised classic theory on conduction and the thermal energy of electrons.
In 1925 an accidental explosion of a bottle of liquid air (air that has been cooled and compressed until it becomes a liquid; see Matter, States of) in Davisson's laboratory put him on the path to a great discovery. The explosion allowed a piece of nickel Davisson was using as a target for high-speed electrons to become oxidized—that is, for the outer nickel atoms to bond with oxygen atoms (see Chemical Reaction). After cleaning the target by means of prolonged heating, Davisson found that although it had originally been composed of many small crystals, it had now formed several large crystals. He continued with the experiment but found that the electrons that now bounced off the target were bouncing off at completely different angles than before. Davisson attributed the change only to the different way the target was reflecting the electrons, but a 1926 meeting of physicists convinced him to search for a further cause. There he first learned in detail about the hypothesis of French physicist Louis de Broglie that any material particle (see Matter) could behave like a wave (see Wave Motion). Joining forces in 1926 with American physicist Lester Halbert Germer, Davisson searched for evidence of interference—that is, the effects resulting from adding waves together—between the electrons as they bounced off the target; an interference pattern would be present only if the electrons were behaving like waves—purely material particles cannot produce interference patterns.
In 1927 Davisson showed that, like electromagnetic waves (see Electromagnetic Radiation), electrons can produce interference patterns and be diffracted by crystals. His experiments proved that electrons can show wavelike behavior and helped show that all matter can show wavelike behavior since electrons are one of the subatomic particles that make up all matter. For this discovery, Davisson was awarded the Comstock Prize of the National Academy of Sciences in 1928.
In the 1930s Davisson's research continued to focus on electron waves, especially in their application to crystal physics and electron microscopy (see Microscope), and helped to develop a technique for electron focusing. Davisson's later research focused on the theory and application of electron optics, the theory of electronic devices (see Electronics), and solid-state physics, also known as condensed-matter physics.

American physicist James Cronin won the 1980 Nobel Prize in physics for demonstrating the changes that occur when matter transforms into antimatter.
James W. Cronin, born in 1931, American physicist and Nobel laureate. Cronin shared the 1980 Nobel Prize for physics with American Val Logsdon Fitch for demonstrating that, unlike what was previously thought, symmetry is not always preserved when some elementary particles change in state from matter to antimatter.
Cronin was born in Chicago, Illinois, and received his bachelor's degree at Southern Methodist University in 1951. He earned both his master's and doctoral degrees in 1955 in physics from the University of Chicago. From 1955 to 1958 Cronin served as an assistant physicist at Brookhaven National Laboratory in Long Island, New York. He taught at Princeton University from 1958 to 1971 and in 1971, Cronin became professor of physics at the University of Chicago.
In 1964, Cronin, Fitch, and some of their colleagues were studying a subatomic particle called the K. meson, also known as a kaon. A meson is a particle that weighs approximately half as much as a proton. The kaon is an unstable, neutral (uncharged) meson that had been discovered in the interactions between particles from outer space and particles from the earth's atmosphere.
Physicists thought for some time that the universe followed three fundamental rules of symmetry. The first, the symmetry of charge conjugation (C), states that the result of an experiment should not change if all the particles in the experiment are switched from antimatter to matter or vice versa. The second rule of symmetry, parity (P), says that the result of an experiment should not change if the positions of all the particles in the experiment are completely reversed. The third rule, time-reversal (T), says that any reaction between elementary particles should occur equally well in either direction; that is, if two particles can come together to form one particle, the resulting particle should be able to decay to form the original two particles.
Before Cronin and Fitch started their experiment, the rules C and P had both been found to be untrue in some cases. Physicists tried to preserve the idea of symmetry by theorizing that any reaction had to be symmetric over a combination of CP; that is, if C symmetry was violated, P symmetry would have to be violated, too. Cronin and Fitch disproved this rule by showing that kaons do not preserve P, C, or CP symmetry some of the time. However, one rule of symmetry remains above suspicion: all reactions must be symmetric in the combination of charge conjugation, parity, and time (CPT).
Since every reaction has to be symmetric under CPT, Cronin and Fitch's result showed that T symmetry has to fail when CP symmetry fails. That means reactions that do not preserve CP symmetry cannot run backward. Some scientists think this explains how more matter than antimatter is created in the universe.

American physicist Leon Cooper won the Nobel Prize in physics in 1972. Cooper developed a theory of why some metals can be superconductive.
Leon N. Cooper, born in 1930, American physicist, professor, and Nobel Prize winner. Cooper contributed significantly to the development of a theory of superconductivity by discovering what are now called “Cooper pairs”—that is, two electrons that, when situated a certain way among positive ions, no longer repel each other but instead develop an attraction for each other. These pairs then accumulate and move in the same direction; the result is a superconducting metal because there is no resistance to the flow of electricity through the metal. For his work in superconductivity, Cooper shared the 1972 Nobel Prize in physics with fellow American scientists John Bardeen and J. Robert Schrieffer.
Cooper was born in New York City. As a high school senior, he entered the Westinghouse Science Talent Search competition with a research project that analyzed how certain bacteria can become penicillin resistant. For his efforts, he was selected as one of 40 national winners. In 1954 Cooper received a Ph.D. degree in physics from Columbia University. His dissertation was supervised by American physicist J. Robert Oppenheimer, who had directed the development of the atomic bomb.
In 1955 Cooper was working on quantum field theory at the Institute for Advanced Study in Princeton, New Jersey, when John Bardeen, a scientist at the University of Illinois, invited Cooper to study superconductivity with him. First discovered in 1911, superconductivity is a phenomenon in which certain metals, when cooled to a temperature that is near absolute zero, no longer resist a flow of electricity running through them. The resulting free flow of electrons in the metal results in increased conductivity—an important discovery, particularly for the electronics industry. Electrical devices can waste large amounts of energy simply in trying to overcome electrical resistance, a problem that could be virtually eliminated if superconducting materials were used instead.
But for years after the discovery of superconductivity, scientists encountered difficulty when trying to apply the phenomenon in practical ways because of the extremely low temperature to which the metals must be cooled in order to overcome the electrical resistance. From 1955 to 1957 Bardeen, Cooper, and another physicist, J. Robert Schrieffer, developed what would later become known as the BCS theory of superconductivity, which explains why certain materials can be superconductive.
In 1957 Cooper left the University of Illinois to become an assistant professor of physics at Ohio State University. Since 1958 he has taught physics at Brown University in Providence, Rhode Island. Cooper holds honorary degrees from several United States universities and has received many awards for his work. In recent years, he has devoted his efforts toward a better understanding of memory and other brain functions.

Edward U. Condon (1902-1974), American physicist, noted for his work in quantum theory, nuclear reactions, and the spectra of atoms and molecules. He was born in Alamagordo, New Mexico, and educated at the University of California at Berkeley. From 1928 to 1937 he taught physics at Princeton University. He was one of the early supporters of the atomic bomb program. Between 1943 and 1945 he worked at the University of California on the electromagnetic separation of uranium-235. He became professor of physics and fellow of the Joint Institute for Laboratory Astrophysics at the University of Colorado in 1963. Between 1966 and 1969 he was also a scientific director of the government-financed investigation of unidentified flying objects.

American physicist Arthur Holly Compton won the Nobel Prize in physics in 1927. Compton confirmed that radiation has both particle and wave characteristics
Arthur Compton (1892-1962), American physicist and Nobel laureate whose studies of X rays led to his discovery in 1922 of the so-called Compton effect. The Compton effect is the change in wavelength of high energy electromagnetic radiation when it scatters off electrons. The discovery of the Compton effect confirmed that electromagnetic radiation has both wave and particle properties, a central principle of quantum theory.
Arthur Holly Compton was born in Wooster, Ohio, and educated at Wooster College and Princeton University. In 1923 he became professor of physics at the University of Chicago. While at the University of Chicago, Compton directed the laboratory where the first sustainable nuclear chain-reaction was performed. (see Nuclear Energy). Compton also played a role in the development of the atomic bomb (see Nuclear Weapons). From 1945 to 1953 Compton was chancellor of Washington University, and after 1954 he was professor of natural philosophy there. For his discovery of the Compton effect and for his investigation of cosmic rays and of the reflection, polarization, and spectra of X rays, he shared the 1927 Nobel Prize in physics with the British physicist Charles Wilson.

French physicist Claude Cohen-Tannoudji shared the 1997 Nobel Prize in physics with two other physicists. All three physicists were recognized for their individual work in cooling and trapping atoms
Claude Cohen-Tannoudji, born in 1933, French physicist and Nobel laureate. Cohen-Tannoudji pioneered research into cooling, slowing, and trapping atoms—one of the basic building blocks of matter—with special beams of light called lasers (see Particle Trap). The techniques Cohen-Tannoudji and others developed led to significant advancements in the study and manipulation of atoms, resulting in many applications. These applications include more accurate atomic clocks and more precise devices for measuring gravity. He shared the 1997 Nobel Prize for physics with two American scientists who were also successful in slowing atoms, Steven Chu and William D. Philips. The three didn’t work side by side; yet each contributed to and built upon the work of the other two.
Born in Constantine, Algeria, Cohen-Tannoudji earned his undergraduate degree in 1957 and his Ph.D. degree in 1962 in physics from École Normale Supérieure (ENS) in Paris, France. As a student at ENS he worked under the direction of French physicist Alfred Kastler, who won the Nobel Prize in physics in 1966, and Jean Brossel, another noted French physicist. Cohen-Tannoudji remained a researcher at ENS throughout his career. He was instrumental in the creation of a research center devoted to atomic physics and optics. The center is named the Kastler-Brossel Laboratory, after his two professors.
Cohen-Tannoudji joined the Centre National de la Recherche Scientifique (CNRS) in 1960. In 1973, while still associated with CNRS, he began a lengthy stint as chair of atomic and molecular physics at the Collége de France in Paris.
As a student, researcher, and professor, Cohen-Tannoudji became an expert in the field of slowing atoms. At room temperature, atoms move at speeds of about 4000 km/h (about 2500 mph), too fast for scientists to study them thoroughly. Heat results from atomic motion, so slowing atoms down lowers their temperature. Cohen-Tannoudji was among the first to propose using lasers to slow down atoms. The concept involves bombarding the atoms with laser light. Packets of light wave energy called photons strike the atoms in a way that is roughly the same as raindrops hitting a beach ball. Even though the photons have no mass, they move fast enough (at the speed of light) to produce enough momentum to slow the atoms with their impacts.
In 1985 Steven Chu and his team cooled atoms to 240 millionths of a Celsius degree (430 millionths of a Fahrenheit degree) above absolute zero (-273.15° C, or -459.67° F), which slowed atoms to about 0.5 km/h (0.3 mph). By 1988 William D. Philips and his research team had cooled atoms to 40 millionths of a Celsius degree (70 millionths of a Fahrenheit degree) above absolute zero, which was below the temperature that was believed to be theoretically possible at the time. In 1995 Cohen-Tannoudji and his team achieved a temperature of 0.2 millionths of a Celsius degree (0.4 millionths of a Fahrenheit degree) above absolute zero. Through his career Cohen-Tannoudji developed several cooling mechanisms used to trap atoms.
Manipulating atoms and studying them more closely allows scientists to improve many areas of technology. In an atomic clock, the more control the mechanism has over the atoms that it uses to keep track of time, the more accurate it can be. Increasingly accurate atomic clocks improve space navigation and global positioning systems that rely on the clocks. Trapped atoms are also useful in measuring the force of gravity of a particular spot on the earth. Changes in the gravitational field of the earth from place to place indicate changes in the density of the earth, which can lead scientists to oil and other valuable deposits within the earth. The ability to control atoms also raises the possibility of using atoms to etch electronic circuits. This would increase the circuits’ capabilities by making the circuits finer, and each area of circuit board would be able to hold more circuits.
In 1996 Cohen-Tannoudji won CNRS’s gold medal. In 1997, along with former students Jacques Dupont-Roc and Gilbert Grynberg, he wrote the book Introduction to Quantum Electrodynamics.

American physicist Steven Chu shared the 1997 Nobel Prize in physics with two other researchers. Chu was honored for his work in cooling and trapping atoms and other small particles.
Steven Chu, born in 1948, American physicist and Nobel laureate. Chu led a team of physicists in the mid-1980s who were the first to trap atoms (one of the basic units of matter) with special beams of light called lasers. These laser traps (see Particle Trap: Neutral Particle Traps) allow scientists to study atoms more closely and use atoms more efficiently in devices such as atomic clocks. Chu’s research helped pave the way for important discoveries in atomic physics. It also led to the development of many new practical applications, including more accurate atomic clocks and more precise devices for measuring the pull of gravity. He shared the 1997 Nobel Prize for physics with two other researchers who made separate and complementary advancements in the field, French physicist Claude Cohen-Tannoudji and American physicist William D. Philips.
Chu was born in St. Louis, Missouri, and grew up on Long Island, New York. He earned dual undergraduate degrees in physics and mathematics at the University of Rochester in New York in 1970. In 1976 he received his doctoral degree in physics from the University of California, Berkeley. Chu spent two years conducting post-doctoral research at Berkeley, then served as a member of the technical staff of American Telephone and Telegraph (AT&T) from 1978 to 1983.
In 1983 Chu was named head of the quantum electronics research department at AT&T’s Bell Laboratories and moved to the lab’s complex in Holmdel, New Jersey. That year he began discussing the possibility of trapping atoms with American physicist Arthur Ashkin. Over the next few years, Chu, Ashkin, and fellow American physicists John Bjorkholm and Alex Cable conducted experiments in which six lasers bombarded atoms from six sides in a vacuum chamber at Chu’s lab.
At room temperature, atoms move at speeds of about 4000 km/h (2500 mph), much too fast for scientists to easily study them. The speed of atoms is related to their temperature—atoms at a higher temperature move faster than cooler atoms. Slowing a sample of atoms will therefore make the atoms cooler. Chu pioneered a technique for slowing and cooling atoms that uses lasers to immerse the atoms in photons (packets of light wave energy). The photons strike the atoms in a way that is roughly analogous to raindrops hitting a beach ball. The photons have no mass, but because they move at the speed of light, they carry momentum and can affect a small mass, such as an atom. In Chu’s trap, the impact of enough photons hitting atoms slowed the atoms down. The atoms moved so slowly that they seemed to be stuck, so Chu’s team named the process “optical molasses.”
In 1985 Chu and his team cooled atoms to 240 millionths of a Celsius degree (430 millionths of a Fahrenheit degree) above absolute zero, the point at which all matter stops moving (–273.15° C, or -459.67° F). By 1988 William D. Philips and his research team had cooled atoms to 40 millionths of a Celsius degree (70 millionths of a Fahrenheit degree) above absolute zero, which was lower than scientists believed to be theoretically possible at the time. Claude Cohen-Tannoudji and his team achieved a temperature of 0.2 millionths of a Celsius degree (0.4 millionths of a Fahrenheit degree) above absolute zero in 1995.
The ability to manipulate atoms and study them more closely led to many real and potential applications, including increased accuracy in atomic clocks, which improved their use in space navigation and global positioning systems. Atomic clocks keep track of time by counting waves of radiation emitted by special atoms in traps inside the clock. If the traps can hold the atoms at lower temperatures, the traps and mechanisms inside the clock can exercise more control over the atom, reducing the possibility of error. Atom manipulation also contributes to increased accuracy of the measurement of gravitational force, which is useful in, among other things, oil exploration. This is because a deposit of oil or other substance beneath the earth’s crust has a different density from the areas around it. Changes in density produce changes in the local gravitational field, because the gravitational force of an area is related to the mass of that area. Advances in the manipulation of atoms have also raised the possibility of using atoms to etch electronic circuits, thereby increasing the circuits’ capabilities.
In 1987 Chu joined the faculty at Stanford University as a professor of physics and applied physics. While at Stanford, he and his colleagues continued the study of cooled atoms. In 1992 Chu was named a fellow of the American Academy of Arts and Sciences and a year later a member of the National Academy of Sciences.

Indian-born American theoretical astrophysicist Subrahmanyan Chandrasekhar won the 1983 Nobel Prize in physics. He studied the process by which stars evolve.
Subrahmanyan Chandrasekhar (1910-1995), American theoretical astrophysicist and Nobel laureate, who contributed greatly to the current understanding of stellar evolution. He was born in Lahore, India (now Pakistan), and was educated in India and at Trinity College and the University of Cambridge, earning a Ph.D. in 1933. In 1953 he became a U.S. citizen.
Although Chandrasekhar worked on theories of radiative transfer and convective transport of heat in stellar atmospheres, his most important studies concerned the small, dim, hot, dense stars known as white dwarfs (see Star). He determined that a star with a mass more than 1.44 times that of the mass of the Sun cannot directly become a white dwarf, a limit now called the Chandrasekhar limit. He shared the Nobel Prize in physics in 1983 with U.S. physicist William Fowler for his work on stars. His books include An Introduction to the Study of Stellar Structure (1939) and Principles of Steller Dynamics (1942). The Chandra X-ray Observatory, a powerful X-ray telescope named after Chandrasekhar, was launched by the United States into Earth’s orbit from a space shuttle in 1999.

American physicist Owen Chamberlain won the Nobel Prize in physics in 1992. Chamberlain confirmed the existence of the antiproton, a form of antimatter
Owen Chamberlain (1920-2006), American physicist and Nobel laureate. For their collaborative discovery of the antiproton (see Proton), Chamberlain and Italian-born American physicist Emilio Gino Segrè shared the 1959 Nobel Prize in physics.
Born in San Francisco, California, Chamberlain completed his undergraduate studies at Dartmouth College, receiving a B.S. degree in physics in 1941. From 1942 to 1946 he served as a researcher on the Manhattan Project, which developed the atomic bomb (see Nuclear Weapons) during World War II (1939-1945). From 1947 to 1949 he worked at the Argonne National Laboratory near Chicago, Illinois, obtaining a Ph.D. degree in physics at the University of Chicago in 1949. He then joined the faculty of the University of California at Berkeley, becoming a professor of physics in 1958, a position he held until his retirement in 1989.
Chamberlain's work in nuclear physics began with close investigation of subatomic particles, or particles that make up atoms (see Elementary Particles). His part in the atomic-bomb project led him to study alpha-particle decay, neutron diffraction, and high-energy nuclear reactions (see Nuclear Chemistry; Nuclear Energy). In 1955 Chamberlain, with Emilio Segrè, discovered the antiproton, a form of antimatter. Later Chamberlain also confirmed the existence of the antineutron.

Chester Carlson (1906-1968), American physicist, patent attorney, and inventor of xerography, an electronic dry-copying process for the reproduction of images or documents, commonly known now as photocopying.
Born in Seattle, Washington, Chester Floyd Carlson worked for a printer before studying physics at the California Institute of Technology. After graduating in 1930, he worked for a short time for the Bell Telephone Company, earned a law degree, and took a position in the patent department of an electronics firm in New York City. Carlson found it difficult to get copies of patent drawings, so in his spare time he searched for a cheap, dry method of copying documents, specifically printed or drawn matter. He developed a process that used electrostatic attraction to cause powder to adhere to plain paper, making his first successful copy on October 22, 1938. Because the process used no ink, Carlson called the technique xerography, from the Greek words meaning “dry writing.” This process is now known as photocopying.
In this process a plate coated with a light-sensitive material, such as selenium, is given a positive electric charge, and a powder, called toner, is given a negative electric charge. The toner and plate are therefore attracted to each other. Light is reflected from the original document through a lens onto the plate, and when the toner is applied to the plate, it clings to those places where light has not penetrated and destroyed the charge. In other words, the toner clings to the shadows cast by the opaque printing of the object copied. Paper is applied to the plate, and the image is transferred. Heat then fixes the toner on the paper, completing the copy. Photocopying is quick and involves no moisture—and thus it produces little mess. A variation of the process, known as xeroradiography, is used in the production of X-ray images.
Although his invention would eventually become the worldwide standard for copying, Carlson spent years securing a patent. He also had trouble finding a company willing to market the process. Finally, in 1947, the Haloid Company of Rochester, New York, obtained the rights to his invention. Working with the company, which changed its name to the Xerox Corporation, Carlson significantly refined copying for office use. In 1959 the Xerox Corporation introduced the first automatic copier.