Claude Elwood Shannon (April 30, 1916 – February 24, 2001) was an American polymath who was a mathematician, electrical engineer, computer scientist, cryptographer, and inventor known as the "father of information theory" and is generally credited with laying the foundations of the Information Age.
Shannon was among 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 graduated with Bachelor of Science degrees in electrical engineering and mathematics, both in 1936. The following year, in his MIT electrical engineering master's thesis "A Symbolic Analysis of Relay and Switching Circuits", he 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1940 with a PhD in mathematics; his thesis, which focused on genetics, contained important results though it remained unpublished and relatively unknown until recently.
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 (DES), and the Advanced Encryption Standard (AES). 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 concept of a signal-flow graph and evaluation of the graph determinant.
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.
The Shannon family lived in Gaylord, Michigan. Claude was born in a hospital in nearby Petoskey. His father, Claude Sr. (1862–1934), was a businessman and, for a while, a judge of probate in Gaylord. His mother, Mabel Wolf Shannon (1880–1945), 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 subjects. 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, who he later learned was a distant cousin: the two were descendants of John Ogden (1609–1682), a colonial leader and an ancestor of many distinguished people.
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 (MIT), 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.