The 100 Most Influential Scientists of All Time (38 page)

Cousteau served in World War II as a gunnery officer in France and was also a member of the French Resistance. He later was awarded the Legion of Honour for his espionage work. Cousteau's experiments with underwater filmmaking began during the war, and when the war ended, he continued this work by founding and heading the French navy's Undersea Research Group at Toulon.
To expand his work in marine exploration, he founded numerous marketing, manufacturing, engineering, and research organizations, which were incorporated (1973) as the Cousteau Group. In 1950 Cousteau converted a British minesweeper into the
Calypso
, an oceanographic research ship aboard which he and his crew carried out numerous expeditions. Cousteau eventually popularized oceanographic research and the sport of scuba diving in the book
Le Monde du silence
(1952;
The Silent World
), written with Frédéric Dumas. Two years later he adapted the book into a documentary film that won both the Palme d'Or at the 1956 Cannes International Film Festival and an Academy Award in 1957, one of three Oscars his films received.

Cousteau was the founder of the French Office of Underseas Research at Marseille, Fr. (renamed the Centre of Advanced Marine Studies in 1968), and he became director of the Oceanographic Museum of Monaco in 1957. He also led the Conshelf Saturation Dive Program, conducting experiments in which men live and work for extended periods of time at considerable depths along the continental shelves. The undersea laboratories were called Conshelf I, II, and III.

Cousteau produced and starred in many television programs, including the U.S. series “The Undersea World of Jacques Cousteau” (1968-76). In 1974 he formed the Cousteau Society, a nonprofit environmental group dedicated to marine conservation. In addition to
The Silent World
, Cousteau also wrote
Par 18 mètres de fond
(1946; “Through 18 Metres of Water”),
The Living Sea
(1963),
Three Adventures: Galápagos, Titicaca, the Blue Holes
(1973),
Dolphins
(1975), and
Jacques Cousteau: The Ocean World
(1985). His last book,
The Human, the Orchid, and the Octopus
(2007), was published posthumously.

(b. June 13, 1911, San Francisco, Calif., U.S.—d. Sept. 1, 1988, Berkeley, Calif.)

A
merican experimental physicist Luis W. Alvarez was awarded the Nobel Prize for Physics in 1968 for work that included the discovery of many resonance particles (subatomic particles having extremely short lifetimes and occurring only in high-energy nuclear collisions).

Alvarez studied physics at the University of Chicago (B.S., 1932; M.S., 1934; Ph.D., 1936). He joined the faculty of the University of California, Berkeley, in 1936, becoming professor of physics in 1945 and professor emeritus in 1978. In 1938 Alvarez discovered that some radioactive elements decay by orbital-electron capture; i.e., an orbital electron merges with its nucleus, producing an element with an atomic number smaller by one. In 1939 he and Felix Bloch made the first measurement of the magnetic moment of the neutron, a characteristic of the strength and direction of its magnetic field.

Alvarez worked on microwave radar research at the Massachusetts Institute of Technology, Cambridge (1940–43), and participated in the development of the atomic bomb at the Los Alamos Scientific Laboratory, Los Alamos, N.M., in 1944–45. He suggested the technique for detonating the implosion type of atomic bomb. He also participated in the development of microwave beacons, linear radar antennas, the ground-controlled landing approach system, and a method for aerial bombing using radar to locate targets.

After World War II Alvarez helped construct the first proton linear accelerator. In this accelerator, electric fields are set up as standing waves within a cylindrical metal
“resonant cavity,” with drift tubes suspended along the central axis. The electric field is zero inside the drift tubes, and, if their lengths are properly chosen, the protons cross the gap between adjacent drift tubes when the direction of the field produces acceleration and are shielded by the drift tubes when the field in the tank would decelerate them. The lengths of the drift tubes are proportional to the speeds of the particles that pass through them. In addition to this work, Alvarez also developed the liquid hydrogen bubble chamber in which subatomic particles and their reactions are detected.

In about 1980 Alvarez helped his son, the geologist Walter Alvarez, publicize Walter's discovery of a worldwide layer of clay that has a high iridium content and which occupies rock strata at the geochronological boundary between the Mesozoic and Cenozoic eras; i.e., about 66.4 million years ago. They postulated that the iridium had been deposited following the impact on Earth of an asteroid or comet and that the catastrophic climatic effects of this massive impact caused the extinction of the dinosaurs. Though initially controversial, this widely publicized theory gradually gained
support as the most plausible explanation of the abrupt demise of the dinosaurs.

Alvarez's autobiography,
Alvarez: Adventures of a Physicist
, was published in 1987.

(b. June 23, 1912, London, Eng.—d. June 7, 1954, Wilmslow, Cheshire)

B
ritish mathematician and logician Alan Mathison Turing made major contributions to mathematics, cryptanalysis, logic, philosophy, and biology and to the new areas later named computer science, cognitive science, artificial intelligence, and artificial life.

The son of a British member of the Indian civil service, Turing entered King's College, University of Cambridge, to study mathematics in 1931. After graduating in 1934, Turing was elected to a fellowship at King's College in recognition of his research in probability theory. In 1936 Turing's seminal paper
On Computable Numbers, with an Application to the Entscheidungsproblem [Decision Problem]
was recommended for publication by the American mathematician-logician Alonzo Church, who had himself just published a paper that reached the same conclusion as Turing's. Later that year, Turing moved to Princeton University to study for a Ph.D. in mathematical logic under Church's direction (completed in 1938).

The
Entscheidungsproblem
seeks an effective method for deciding which mathematical statements are provable within a given formal mathematical system and which are not. In 1936 Turing and Church independently showed that in general this problem has no solution, proving that no consistent formal system of arithmetic is decidable.
This result and others—notably the mathematician-logician Kurt Gödel's incompleteness theorems—ended the dream of a system that could banish ignorance from mathematics forever. (In fact, Turing and Church showed that even some purely logical systems, considerably weaker than arithmetic, are undecidable.)

An important argument of Turing's and Church's was that the class of lambda-definable functions (functions on the positive integers whose values can be calculated by a process of repeated substitution) coincides with the class of all functions that are effectively calculable—or computable. This claim is now known as Church's thesis—or as the Church-Turing thesis when stated in the form that any effectively calculable function can be calculated by a universal Turing machine, a type of abstract computer that Turing had introduced in the course of his proof. (Turing showed in 1936 that the two formulations of the thesis are equivalent by proving that the lambda-definable functions and the functions that can be calculated by a universal Turing machine are identical.) In a review of Turing's work, Church acknowledged the superiority of Turing's formulation of the thesis over his own, saying that the concept of computability by a Turing machine “has the advantage of making the identification with effectiveness… evident immediately.”

In the summer of 1938 Turing returned from the United States to his fellowship at King's College. At the outbreak of hostilities with Germany in September 1939, he joined the wartime headquarters of the Government Code and Cypher School at Bletchley Park, Buckinghamshire. The British government had just been given the details of efforts by the Poles, assisted by the French, to break the
Enigma code, used by the German military for their radio communications. As early as 1932, a small team of Polish mathematician-cryptanalysts, led by Marian Rejewski, had succeeded in reconstructing the internal wiring of the type of Enigma machine used by the Germans, and by 1938 they had devised a code-breaking machine, code-named
Bomba
(the Polish word for a type of ice cream). The
Bomba
depended for its success on German operating procedures, and a change in procedures in May 1940 rendered the
Bomba
virtually useless.

During 1939 and the spring of 1940, Turing and others designed a radically different code-breaking machine known as the Bombe. Turing's ingenious Bombes kept the Allies supplied with intelligence for the remainder of the war. By early 1942 the Bletchley Park cryptanalysts were decoding about 39,000 intercepted messages each month, which rose subsequently to more than 84,000 per month. At the end of the war, Turing was made an officer of the Order of the British Empire for his code-breaking work.

In 1945, the war being over, Turing was recruited to the National Physical Laboratory (NPL) in London to design and develop an electronic computer. His design for the Automatic Computing Engine (ACE) was the first relatively complete specification of an electronic stored-program general-purpose digital computer. Had Turing's ACE been built as planned, it would have had considerably more memory than any of the other early computers, as well as being faster. However, his colleagues at NPL thought the engineering too difficult to attempt, and a much simpler machine was built, the Pilot Model ACE.

In the end, NPL lost the race to build the world's first working electronic stored-program digital computer—an
honour that went to the Royal Society Computing Machine Laboratory at the University of Manchester in June 1948. Discouraged by the delays at NPL, Turing took up the deputy directorship of the Computing Machine Laboratory in that year (there was no director). His earlier theoretical concept of a universal Turing machine had been a fundamental influence on the Manchester computer project from its inception. Turing's principal practical contribution after his arrival at Manchester was to design the programming system of the Ferranti Mark I, the world's first commercially available electronic digital computer.

Turing was a founding father of modern cognitive science and a leading early exponent of the hypothesis that the human brain is in large part a digital computing machine. He theorized that the cortex at birth is an “unorganised machine” that through “training” becomes organized “into a universal machine or something like it.” A pioneer of artificial intelligence, Turing proposed (1950) what subsequently became known as the Turing test as a criterion for whether a machine thinks.

Though he was elected a fellow of the Royal Society in March 1951, Turing's life was about to suffer a major reversal. In March 1952 he was prosecuted for homosexuality, then a crime in Britain, and sentenced to 12 months of hormone “therapy”—a treatment that he seems to have borne with amused fortitude. Judged a security risk by the British government, Turing lost his security clearance and his access to ongoing government work with codes and computers. He spent the rest of his short career at the University of Manchester, where he was appointed to a specially created readership in the theory of computing in May 1953.