Claude Shannon

Claude Shannon the American mathematician and engineer (1916-2001) who founded information theory and is widely regarded as the father of the digital age. His 1948 paper defined the fundamental unit of information, established the conditions under which data can be transmitted reliably, and showed that computing could be built on the logic of switching circuits.

Early Life and Education

Claude Elwood Shannon was born on 30 April 1916 in Petoskey, Michigan, and grew up in the town of Gaylord, where his father was a judge and businessman and his mother a teacher. He was a bright and curious boy who enjoyed building model planes and a radio-controlled boat, and he did chores for the inventor Thomas Edison, a distant relative. He studied at the University of Michigan, graduating in 1936 with degrees in mathematics and electrical engineering.

He then entered the Massachusetts Institute of Technology, where he worked on the differential analyser, an analogue computer, and wrote a master's thesis that applied the algebra of logic to the design of relay switching circuits. This thesis, published in 1938, showed that Boolean algebra could describe and simplify the networks used in telephone exchanges, and it is often called one of the most consequential master's theses ever written. He completed a doctorate in mathematics at MIT in 1940.

Information Theory

In 1948 Shannon published a paper entitled A Mathematical Theory of Communication that founded the field of information theory. He defined information in terms of the reduction of uncertainty, introduced the bit as the basic unit, and formulated a measure of uncertainty now known as entropy. He proved the surprising result that any source of messages has a limit to how much it can be compressed, determined by its statistical structure.

He then showed that a noisy channel has a definite capacity, and that if the rate of transmission is below that capacity, messages can be sent with arbitrarily small probability of error by means of suitable encoding. This noisy-channel coding theorem was remarkable because it separated the problem of reliable communication from the physics of the channel. It underlies the error-correcting codes, compression methods and digital communication systems on which modern technology depends.

Switching Circuits and the Digital Age

The insight of his master's thesis, that electrical switches could implement the operations of symbolic logic, gave engineers a systematic way to design digital circuits. It established a direct link between abstract reasoning and physical hardware and made it possible to build complex machines out of simple on-off elements. This conception of the two-state device as the embodiment of a logical proposition is fundamental to all digital computers.

He extended these ideas in later work on the design of switching networks and on the theory of reliable machines, including a study of how logical circuits could be made dependable by redundancy. His interest in the boundaries of the possible led him also to design chess-playing programs, a mechanical mouse that could learn to find its way through a maze, and other experimental machines that anticipated later work in artificial intelligence.

Wartime Work and Applied Research

During the Second World War Shannon worked at the Bell Telephone Laboratories on problems of fire control and cryptography. He designed a gun-directing computer and also studied the mathematics of secrecy, work that contributed to the theory of cryptography and to the coding of secure messages. He was associated with the fire-control research that produced systems for directing anti-aircraft fire, applying mathematical analysis to a pressing military problem.

After the war he returned to Bell Labs, where he continued to work on communication and computing and where he wrote the papers that established information theory. He also held an appointment at MIT, where he was a professor of mathematics and of electrical engineering, and he guided students in the emerging fields of information and computing. His combination of abstract theory and practical invention was characteristic of his career.

Influence and Legacy

Shannon received many honours, including the National Medal of Science and the Kyoto Prize, and he was elected to the National Academy of Sciences. His information theory gave a mathematical language to communication, cryptography, computing, linguistics and biology, and the bit became one of the most useful concepts of the twentieth century. His papers on the subject remain among the most cited and most translated in the history of technology.

He was in private life a playful inventor, unicyclist, juggler and maker of gadgets, and he retired from teaching in 1978 while continuing to tinker and lecture occasionally. He died on 24 February 2001. He is remembered as the thinker who showed that information is a quantifiable substance and who thereby laid the conceptual foundation for the digital revolution, from compact discs to deep-space communication.

See also

• Information theory
• Bit
• Entropy
• Noisy-channel coding theorem