## The Original Absent-Minded Professor

An MIT institution, Norbert Wiener did seminal work in control theory and signal processing.

From 1933, when he won the prestigious Bôcher Prize for mathematics, until 1963, when he won the National Medal of Science, Norbert Wiener was one of the most visible professors at MIT. The former child prodigy had been making headlines since he entered Tufts University at 11, and his 1948 book *Cybernetics* was a public sensation. But he was visible in a literal sense, too, because he seemed to spend hours every day wandering the Institute’s halls, appearing in his colleagues’ doorways with a jaunty “What’s new?” and launching into disquisitions on whatever topics struck his fancy, depositing the ashes of his signature cigar in the chalk tray of the nearest blackboard.

Born in Missouri in 1894, Wiener was home-schooled until the age of seven. When he entered the Peabody School in Cambridge as a somewhat underage fourth grader, he proved surprisingly inept at arithmetic, so his father, who taught Slavic languages at Harvard, pulled him out again, convinced that he would find the abstractions of algebra more congenial. His father’s teaching methods, however, were anything but. Whenever the young Norbert made an error, “the gentle and loving father was replaced by the avenger of blood,” Wiener later wrote, in the autobiography that disclosed his lifelong struggle with depression. But if his father’s methods bordered on abuse, they also got results: when Wiener went back to school at nine, it was as a high-school sophomore.

“It was just laziness from that point on,” Wiener told an interviewer in 1948, “for I knew it would take less work to specialize in math than in any other subject.” And indeed, math was the subject of both his BA from Tufts and his PhD from Harvard, which he earned at 14 and 18, respectively. Several peripatetic years followed, in which he taught, worked in industry, and even wrote features for the *Boston Herald*. But in 1919 he arrived at MIT, where he would stay for the next 45 years (the last four as an Institute Professor emeritus).

In the early 1920s, Wiener became interested in Brownian motion, the tendency of a small particle suspended on the surface of a fluid to meander about, buffeted by the vibration of the surrounding molecules. Brownian motion is the paradigm of a so-called stochastic process—one whose outcome is totally random. Wiener devised the first mathematical description that allowed it to be quantified probabilistically. You can’t predict where a particle wandering around a petri dish will wind up, but you can calculate the probability that it will end up in some region of the dish after a specified amount of time.

Wiener’s probabilistic description, known as the Wiener measure, applies to more than just specks of dust in petri dishes. It’s been used to characterize the electromagnetic noise that corrupts radio signals, the behavior of quantum particles, and the fluctuations of the stock market. “It’s a fundamental building block in stochastic models and stochastic control,” says Sanjoy Mitter, a professor of electrical engineering in MIT’s Laboratory for Information and Decision Systems. Take, for instance, the Black-Scholes equation used to value stock options. “Without the Wiener measure, there’s no Black-Scholes,” says Mitter. “That might be a slight exaggeration, but not much.”

During World War II, Wiener received a government contract to help build a system that improved the accuracy of antiaircraft guns by predicting the locations of aerial targets. He envisioned a target’s flight path as a series of discrete measurements, each correlated with the one immediately preceding it and, to a somewhat lesser degree, with the one preceding that, and so on. Previous measurements thus offer clues to future measurements; the trick is determining how much weight to give each in calculating the next one.

The same type of correlation between discrete time measurements can also be used to filter noise out of a signal, and indeed, Wiener’s wartime work (together with simultaneous but independent work by the Russian mathematician Andrey Kolmogorov) gave rise to the field of statistical filtering, which today plays a role in radio transmission, computer vision, and vehicle navigation, among other applications. The recognition that the same statistical techniques applied to problems of control (predicting how a system will respond to control signals) and communications (extracting a signal from the surrounding noise) was the foundational insight of cybernetics. “But to be honest, I don’t think Wiener had really worked it out,” says Mitter, who adds that much of his own research for the last 10 or 15 years has concentrated on making rigorous the connection that Wiener sketched.

Cybernetics sought to unify the study of biological and electromechanical systems—everything from the telephone network to the nervous system—through common principles of feedback, communication, and control. Although Wiener’s book caused a stir when it was published, cybernetics never really caught on in the United States. (Academic departments of cybernetics did, however, spring up in several Eastern Bloc states, and some of them persist today.)

But while Wiener’s book contained no new mathematics that would rival his earlier work in importance, it did offer a grand, syncretic vision that ultimately inspired a host of young scientists. His coinage—the word “cybernetics” is derived from the Greek for “steersman”—lives on in the proliferation of words with the prefix “cyber.” Indeed, Wiener himself was involved in the development of the first electromechanical prosthetic limb, which bequeathed to science fiction the notion of the “cyborg.”

“An important contribution of cybernetics was to introduce engineering principles to life-science people,” says Robert Fano ‘41, ScD ‘47, a professor emeritus of electrical engineering and computer science. It was under the aegis of a cybernetics working group, Fano says, that Wiener persuaded Jerome Wiesner, HM ‘71, director of the Research Lab of Electronics, to bring Warren Sturgis, Walter Pitts, and Jerome Lettvin ‘47 (who died in April) to MIT. All three made important early contributions to what we today call cognitive science.

Fano gives credence to some of the famous anecdotes about Wiener’s absentmindedness: the time he reported the theft of his car to the police, only to discover that he had driven it to Providence for a talk and taken the train back; the conversation in an MIT hallway that he concluded by asking his interlocutor which way he had been heading when he stopped to chat, greeting the answer with “Good! That means I’ve already had lunch.”

The MIT Museum’s website for the Institute’s 150th-anniversary celebration also sparked a good deal of Wiener reminiscence. Jay Ball ‘56, SM ‘61, recalled sitting at a Cambridge coffee shop with a Chinese friend and inviting Wiener to join their table. Wiener addressed the friend in fluent Mandarin, but the friend turned out to speak only Cantonese. So Wiener simply switched dialects. “My father spoke 17 languages fluently,” he told them, “but I’m a dope. I can only speak 12.”

Several alumni, meanwhile, remembered that during his peregrinations through the halls, Wiener typically left one hand in contact with the wall. Possible explanations abounded, but on at least one occasion, Wiener cited the mathematical theorem that an open maze can always be solved by following one wall or the other. As long as he kept his hand on the wall, he knew he would ultimately find his way back to Building 2.

Wiener died in 1964, two months after he and MIT’s Vannevar Bush, EGD ‘16, went to the White House to receive two of the first National Medals of Science ever awarded. In the MIT community today, there are only a handful of people who, like Fano, worked with him in his heyday. But as long as the Institute remains a home to professors whose eccentricities do not go unnoticed by their students, who may look somewhat rumpled as they walk the Infinite Corridor, who may even become so absorbed in theoretical speculation that they forget to wipe their eyeglasses, Norbert Wiener will remain one of its tutelary spirits.