Claude Shannon
Claude Elwood Shannon was an American polymath who was a mathematician, electrical engineer, computer scientist, cryptographer and inventor known as the "father of information theory" and the man who laid the foundations of the Information Age.
Shannon was the first to describe the use of Boolean algebra—essential to all digital electronic circuits—and helped found the field of artificial intelligence. The roboticist Rodney Brooks declared Shannon the 20th century engineer who contributed the most to 21st century technologies, and the mathematician Solomon W. Golomb described his intellectual achievement as "one of the greatest of the twentieth century".
At the University of Michigan, Shannon dual-degreed, graduating with a Bachelor of Science in electrical engineering and another in mathematics, both in 1936. As a 21-year-old master's degree student in electrical engineering at MIT, his 1937 thesis, "A Symbolic Analysis of Relay and Switching Circuits", demonstrated that electrical applications of Boolean algebra could construct any logical numerical relationship, thereby establishing the theory behind digital computing and digital circuits. Called by some the most important master's thesis of all time, it is the "birth certificate of the digital revolution", and started him in a lifetime of work that led him to win a Kyoto Prize in 1985. He graduated from MIT in 1940 with a PhD in mathematics; his thesis focusing on genetics contained important results, while initially going unpublished.
Shannon contributed to the field of cryptanalysis for national defense of the United States during World War II, including his fundamental work on codebreaking and secure telecommunications, writing a paper which is considered one of the foundational pieces of modern cryptography, with his work described as "a turning point, and marked the closure of classical cryptography and the beginning of modern cryptography". His work was foundational for symmetric-key cryptography, including the work of Horst Feistel, the Data Encryption Standard, and the Advanced Encryption Standard. As a result, Shannon has been called the "founding father of modern cryptography".
His 1948 paper "A Mathematical Theory of Communication" laid the foundations for the field of information theory, referred to as a "blueprint for the digital era" by electrical engineer Robert G. Gallager and "the Magna Carta of the Information Age" by Scientific American. Golomb compared Shannon's influence on the digital age to that which "the inventor of the alphabet has had on literature". Shannon is also regarded as the most important post-1948 contributor to the theory. Advancements across multiple scientific disciplines utilized Shannon's theory—including the invention of the compact disc, the development of the Internet, the commercialization of mobile telephony, and the understanding of black holes. He formally introduced the term "bit", and was a co-inventor of both pulse-code modulation and the first wearable computer. He also invented the signal-flow graph.
Shannon joined the Central Intelligence Agency's Special Cryptologic Advisory Group in 1951. From 1956 to 1978, he was a professor at MIT. He also made numerous contributions to the field of artificial intelligence, including co-organizing the 1956 Dartmouth workshop, considered to be the discipline's founding event, and papers on the programming of chess computers. His Theseus machine was the first electrical device to learn by trial and error, being one of the first examples of artificial intelligence.
Biography
Childhood
The Shannon family lived in Gaylord, Michigan, and Claude was born in a hospital in nearby Petoskey. His father, Claude Sr., was a businessman and, for a while, a judge of probate in Gaylord. His mother, Mabel Wolf Shannon, was a language teacher, who also served as the principal of Gaylord High School. Claude Sr. was a descendant of New Jersey settlers, while Mabel was a child of German immigrants. Shannon's family was active in their Methodist Church during his youth.Most of the first 16 years of Shannon's life were spent in Gaylord, where he attended public school, graduating from Gaylord High School in 1932. Shannon showed an inclination towards mechanical and electrical things. His best subjects were science and mathematics. At home, he constructed such devices as models of planes, a radio-controlled model boat and a barbed-wire telegraph system to a friend's house a half-mile away. While growing up, he also worked as a messenger for the Western Union company.
Shannon's childhood hero was Thomas Edison, whom he later learned was a distant cousin. Both Shannon and Edison were descendants of John Ogden, a colonial leader and an ancestor of many distinguished people.
Logic circuits
In 1932, Shannon entered the University of Michigan, where he was introduced to the work of George Boole. He graduated in 1936 with two bachelor's degrees: one in electrical engineering and the other in mathematics.In 1936, Shannon began his graduate studies in electrical engineering at the Massachusetts Institute of Technology, where he worked on Vannevar Bush's differential analyzer, which was an early analog computer that was composed of electromechanical parts and could solve differential equations. While studying the complicated ad hoc circuits of this analyzer, Shannon designed switching circuits based on Boole's concepts. In 1937, he wrote his master's degree thesis, A Symbolic Analysis of Relay and Switching Circuits, with a paper from this thesis published in 1938. A revolutionary work for switching circuit theory, in it Shannon diagramed switching circuits that could implement the essential operators of Boolean algebra. Then he proved that his switching circuits could be used to simplify the arrangement of the electromechanical relays that were used during that time in telephone call routing switches. Next, he expanded this concept, proving that these circuits could solve all problems that Boolean algebra could solve. In the last chapter, he presented diagrams of several circuits, including a digital 4-bit full adder. His work differed significantly from the work of previous engineers such as Akira Nakashima, who still relied on the existent circuit theory of the time and took a grounded approach. Shannon's ideas were more abstract and relied on mathematics, thereby breaking new ground with his work, with his approach dominating modern-day electrical engineering.
Using electrical switches to implement logic is the fundamental concept that underlies all electronic digital computers. Shannon's work became the foundation of digital circuit design, as it became widely known in the electrical engineering community during and after World War II. The theoretical rigor of Shannon's work superseded the ad hoc methods that had prevailed previously. In 1987, Howard Gardner hailed Shannon's thesis "possibly the most important, and also the most famous, master's thesis of the century." Herman Goldstine described it in 1972 as "surely... one of the most important master's theses ever written... It helped to change digital circuit design from an art to a science." One of the reviewers of his work commented that "To the best of my knowledge, this is the first application of the methods of symbolic logic to so practical an engineering problem. From the point of view of originality I rate the paper as outstanding." Shannon's master's thesis won the 1939 Alfred Noble Prize.
Shannon received his PhD in mathematics from MIT in 1940. Vannevar Bush had suggested that Shannon should work on his dissertation at the Cold Spring Harbor Laboratory, in order to develop a mathematical formulation for Mendelian genetics. This research resulted in Shannon's PhD thesis, called An Algebra for Theoretical Genetics. However, the thesis went unpublished after Shannon lost interest, but it did contain important results. Notably, he was one of the first to apply an algebraic framework to study theoretical population genetics. In addition, Shannon devised a general expression for the distribution of several linked traits in a population after multiple generations under a random mating system, which was original at the time, with the new theorem unworked out by other population geneticists of the time.
In 1940, Shannon became a National Research Fellow at the Institute for Advanced Study in Princeton, New Jersey. In Princeton, Shannon had the opportunity to discuss his ideas with influential scientists and mathematicians such as Hermann Weyl and John von Neumann, and he also had occasional encounters with Albert Einstein and Kurt Gödel. Shannon worked freely across disciplines, and this ability may have contributed to his later development of mathematical information theory.
Wartime research
Shannon had worked at Bell Labs for a few months in the summer of 1937, and returned there to work on fire-control systems and cryptography during World War II, under a contract with section D-2 of the National Defense Research Committee.Shannon is credited with the invention of signal-flow graphs, in 1942. He discovered the topological gain formula while investigating the functional operation of an analog computer.
For two months early in 1943, Shannon came into contact with the leading British mathematician Alan Turing. Turing had been posted to Washington to share with the U.S. Navy's cryptanalytic service the methods used by the Government Code and Cypher School at Bletchley Park to break the cyphers used by the Kriegsmarine U-boats in the north Atlantic Ocean. He was also interested in the encipherment of speech and to this end spent time at Bell Labs. Shannon and Turing met at teatime in the cafeteria. Turing showed Shannon his 1936 paper that defined what is now known as the "universal Turing machine". This impressed Shannon, as many of its ideas complemented his own.
Shannon and his team developed anti-aircraft systems that tracked enemy missiles and planes, while also determining the paths for intercepting missiles.
In 1945, as the war was coming to an end, the NDRC was issuing a summary of technical reports as a last step prior to its eventual closing down. Inside the volume on fire control, a special essay titled Data Smoothing and Prediction in Fire-Control Systems, coauthored by Shannon, Ralph Beebe Blackman, and Hendrik Wade Bode, formally treated the problem of smoothing the data in fire-control by analogy with "the problem of separating a signal from interfering noise in communications systems." In other words, it modeled the problem in terms of data and signal processing and thus heralded the coming of the Information Age.
Shannon's work on cryptography was even more closely related to his later publications on communication theory. At the close of the war, he prepared a classified memorandum for Bell Telephone Labs entitled "A Mathematical Theory of Cryptography", dated September 1945. A declassified version of this paper was published in 1949 as "Communication Theory of Secrecy Systems" in the Bell System Technical Journal. This paper incorporated many of the concepts and mathematical formulations that also appeared in his A Mathematical Theory of Communication. Shannon said that his wartime insights into communication theory and cryptography developed simultaneously, and that "they were so close together you couldn't separate them". In a footnote near the beginning of the classified report, Shannon announced his intention to "develop these results … in a forthcoming memorandum on the transmission of information."
While he was at Bell Labs, Shannon proved that the cryptographic one-time pad is unbreakable in his classified research that was later published in 1949. The same article also proved that any unbreakable system must have essentially the same characteristics as the one-time pad: the key must be truly random, as large as the plaintext, never reused in whole or part, and kept secret.