Paul Erd?s in 1992
|Died||20 September 1996 (aged 83)|
|Alma mater||Royal Hungarian Pázmány Péter University|
|Known for||a very large number of results and conjectures (more than 1,500 articles) and a very large number of coauthors (more than 500)|
|Awards||Wolf Prize (1983/84)|
AMS Cole Prize (1951)
|Institutions||Victoria University of Manchester|
University of Notre Dame
Hebrew University of Jerusalem
Technion - Israel Institute of Technology
|Doctoral advisor||Lipót Fejér|
|Doctoral students||Joseph Kruskal|
George B. Purdy
Paul Erd?s (Hungarian: Erd?s Pál ['?rdø:? 'pa:l]; 26 March 1913 - 20 September 1996) was a renowned Hungarian mathematician. He was one of the most prolific mathematicians and producers of mathematical conjectures of the 20th century. He was known both for his social practice of mathematics (he engaged more than 500 collaborators) and for his eccentric lifestyle (Time magazine called him The Oddball's Oddball). He devoted his waking hours to mathematics, even into his later years--indeed, his death came only hours after he solved a geometry problem at a conference in Warsaw.
pursued and proposed problems in discrete mathematics, graph theory, number theory, mathematical analysis, approximation theory, set theory, and probability theory. Much of his work centered around discrete mathematics, cracking many previously unsolved problems in the field. He championed and contributed to Ramsey theory, which studies the conditions in which order necessarily appears. Overall, his work leaned towards solving previously open problems, rather than developing or exploring new areas of mathematics.
Erd?s published around 1,500 mathematical papers during his lifetime, a figure that remains unsurpassed. He firmly believed mathematics to be a social activity, living an itinerant lifestyle with the sole purpose of writing mathematical papers with other mathematicians. Erd?s's prolific output with co-authors prompted the creation of the Erd?s number, the number of steps in the shortest path between a mathematician and Erd?s in terms of co-authorships.
Paul Erd?s was born in Budapest, Austria-Hungary, on 26 March 1913. He was the only surviving child of Anna (née Wilhelm) and Lajos Erd?s (born as Lajos Engländer). His two sisters, aged 3 and 5, both died of scarlet fever a few days before he was born. His parents were both Jewish mathematics teachers. His fascination with mathematics developed early--he was often left home by himself because his father was held captive in Siberia as an Austro-Hungarian POW during 1914-1920, causing his mother to have to work long hours to support their household.
He taught himself to read through mathematics texts that his parents left around in their home. By the age of four, given a person's age, he could calculate in his head how many seconds they had lived. Due to his sisters' deaths, he had a close relationship with his mother, with the two of them reportedly sharing the same bed until he left for college.
Both of Erd?s's parents were high school mathematics teachers, and Erd?s received much of his early education from them. Erd?s always remembered his parents with great affection. At 16, his father introduced him to two of his lifetime favorite subjects--infinite series and set theory. During high school, Erd?s became an ardent solver of the problems proposed each month in KöMaL, the Mathematical and Physical Monthly for Secondary Schools.
Erd?s entered the University of Budapest at the age of 17. By the time he was 20, he had found a proof for Chebyshev's theorem. In 1934, at the age of 21, he was awarded a doctorate in mathematics. Erd?s's thesis advisor was Lipót Fejér, who was also the thesis advisor for John von Neumann, George Pólya, and Paul (Pál) Turán. Because he was Jewish, Erd?s decided Hungary was dangerous and relocated to the United States. Many members of Erd?s' family, including two of his aunts, two of his uncles, and his father, died in Budapest during the Holocaust. His mother survived in hiding. He was living in America and working at the Princeton Institute for Advanced Study at the time.
Described by his biographer, Paul Hoffman, as "probably the most eccentric mathematician in the world," Erd?s spent most of his adult life living out of a suitcase. Except for some years in the 1950s, when he was not allowed to enter the United States based on the pretense that he was a Communist sympathizer, his life was a continuous series of going from one meeting or seminar to another. During his visits, Erd?s expected his hosts to lodge him, feed him, and do his laundry, along with anything else he needed, as well as arrange for him to get to his next destination.
I want to be giving a lecture, finishing up an important proof on the blackboard, when someone in the audience shouts out, 'What about the general case?'. I'll turn to the audience and smile, 'I'll leave that to the next generation,' and then I'll keel over.
Erd?s never married and had no children. He is buried next to his mother and father in grave 17A-6-29 at Kozma Street Cemetery in Budapest. For his epitaph, he suggested "I've finally stopped getting dumber." (Hungarian: "Végre nem butulok tovább"). His life was documented in the film N is a Number: A Portrait of Paul Erd?s, made while he was still alive, and posthumously in the book The Man Who Loved Only Numbers (1998).
-- Paul Erd?s
Possessions meant little to Erd?s; most of his belongings would fit in a suitcase, as dictated by his itinerant lifestyle. Awards and other earnings were generally donated to people in need and various worthy causes. He spent most of his life traveling between scientific conferences, universities and the homes of colleagues all over the world. He earned enough in stipends from universities as a guest lecturer, and from various mathematical awards, to fund his travels and basic needs; money left over he used to fund cash prizes for proofs of "Erd?s problems" (see below). He would typically show up at a colleague's doorstep and announce "my brain is open", staying long enough to collaborate on a few papers before moving on a few days later. In many cases, he would ask the current collaborator about whom to visit next.
His colleague Alfréd Rényi said, "a mathematician is a machine for turning coffee into theorems", and Erd?s drank copious quantities (this quotation is often attributed incorrectly to Erd?s, but Erd?s himself ascribed it to Rényi). After 1971 he also took stimulants, despite the concern of his friends, one of whom (Ron Graham) bet him $500 that he could not stop taking them for a month. Erd?s won the bet, but complained that during his abstinence, mathematics had been set back by a month: "Before, when I looked at a piece of blank paper my mind was filled with ideas. Now all I see is a blank piece of paper." After he won the bet, he promptly resumed his use of Ritalin and Benzedrine.
He had his own idiosyncratic vocabulary: although an agnostic atheist, he spoke of "The Book", a visualization of a book in which God had written down the best and most elegant proofs for mathematical theorems. Lecturing in 1985 he said, "You don't have to believe in God, but you should believe in The Book." He himself doubted the existence of God, whom he called the "Supreme Fascist" (SF). He accused SF of hiding his socks and Hungarian passports, and of keeping the most elegant mathematical proofs to Himself. When he saw a particularly beautiful mathematical proof he would exclaim, "This one's from The Book!" This later inspired a book titled Proofs from the Book.
Other idiosyncratic elements of Erd?s's vocabulary include:
In 1934, he moved to Manchester, England, to be a guest lecturer. In 1938, he accepted his first American position as a scholarship holder at Princeton University. At this time, he began to develop the habit of traveling from campus to campus. He would not stay long in one place and traveled back and forth among mathematical institutions until his death.
In 1954, the United States Citizenship and Immigration Services denied Erd?s, a Hungarian citizen, a re-entry visa into the United States, for reasons that have never been fully explained. Teaching at the University of Notre Dame at the time, Erd?s could have chosen to remain in the country. Instead, he packed up and left, albeit requesting reconsideration from the U.S. Immigration Services at periodic intervals.
Hungary at the time was under the Warsaw Pact with the Soviet Union. Although Hungary limited the freedom of its own citizens to enter and exit the country, it gave Erd?s the exclusive privilege of being allowed to enter and exit the country as he pleased in 1956.
In 1963, the U.S. Immigration Service granted Erd?s a visa, and he resumed including American universities in his teaching and travels. Ten years later, in 1973, the 60-year-old Erd?s voluntarily left Hungary.
During the last decades of his life, Erd?s received at least fifteen honorary doctorates. He became a member of the scientific academies of eight countries, including the U.S. National Academy of Sciences and the UK Royal Society. He became a foreign member of the Royal Netherlands Academy of Arts and Sciences in 1977. Shortly before his death, he renounced his honorary degree from the University of Waterloo over what he considered to be unfair treatment of colleague Adrian Bondy.
Erd?s was one of the most prolific publishers of papers in mathematical history, comparable only with Leonhard Euler; Erd?s published more papers, mostly in collaboration with other mathematicians, while Euler published more pages, mostly by himself. Erd?s wrote around 1,525 mathematical articles in his lifetime, mostly with co-authors. He strongly believed in and practiced mathematics as a social activity, having 511 different collaborators in his lifetime.
In his mathematical style, Erd?s was much more of a "problem solver" than a "theory developer" (see "The Two Cultures of Mathematics" by Timothy Gowers for an in-depth discussion of the two styles, and why problem solvers are perhaps less appreciated). Joel Spencer states that "his place in the 20th-century mathematical pantheon is a matter of some controversy because he resolutely concentrated on particular theorems and conjectures throughout his illustrious career." Erd?s never won the highest mathematical prize, the Fields Medal, nor did he coauthor a paper with anyone who did, a pattern that extends to other prizes. He did win the Wolf Prize, where his contribution is described as "for his numerous contributions to number theory, combinatorics, probability, set theory and mathematical analysis, and for personally stimulating mathematicians the world over". In contrast, the works of the three winners after were recognized as "outstanding", "classic", and "profound", and the three before as "fundamental" or "seminal".
Of his contributions, the development of Ramsey theory and the application of the probabilistic method especially stand out. Extremal combinatorics owes to him a whole approach, derived in part from the tradition of analytic number theory. Erd?s found a proof for Bertrand's postulate which proved to be far neater than Chebyshev's original one. He also discovered the first elementary proof for the prime number theorem, along with Atle Selberg. However, the circumstances leading up to the proofs, as well as publication disagreements, led to a bitter dispute between Erd?s and Selberg. Erd?s also contributed to fields in which he had little real interest, such as topology, where he is credited as the first person to give an example of a totally disconnected topological space that is not zero-dimensional, the Erd?s space.
Throughout his career, Erd?s would offer payments for solutions to unresolved problems. These ranged from $25 for problems that he felt were just out of the reach of the current mathematical thinking (both his and others), to several thousand dollars for problems that were both difficult to attack and mathematically significant.
There are thought to be at least a thousand remaining unsolved problems, though there is no official or comprehensive list. The offers remained active despite Erd?s's death; Ronald Graham was the (informal) administrator of solutions, and a solver could receive either an original check signed by Erd?s before his death (for memento only, cannot be cashed) or a cashable check from Graham.
Perhaps the most mathematically notable of these problems is the Erd?s conjecture on arithmetic progressions:
If the sum of the reciprocals of a sequence of integers diverges, then the sequence contains arithmetic progressions of arbitrary length.
If true, it would solve several other open problems in number theory (although one main implication of the conjecture, that the prime numbers contain arbitrarily long arithmetic progressions, has since been proved independently as the Green-Tao theorem). The payment for the solution of the problem is currently worth US$5,000.
The most familiar problem with an Erd?s prize is likely the Collatz conjecture, also called the 3N + 1 problem. Erd?s offered $500 for a solution.
His most frequent collaborators include Hungarian mathematicians András Sárközy (62 papers) and András Hajnal (56 papers), and American mathematician Ralph Faudree (50 papers). Other frequent collaborators were the following:
For other co-authors of Erd?s, see the list of people with Erd?s number 1 in List of people by Erd?s number.
Because of his prolific output, friends created the Erd?s number as a tribute. An Erd?s number describes a person's degree of separation from Erd?s himself, based on their collaboration with him, or with another who has their own Erd?s number. Erd?s alone was assigned the Erd?s number of 0 (for being himself), while his immediate collaborators could claim an Erd?s number of 1, their collaborators have Erd?s number at most 2, and so on. Approximately 200,000 mathematicians have an assigned Erd?s number, and some have estimated that 90 percent of the world's active mathematicians have an Erd?s number smaller than 8 (not surprising in light of the small world phenomenon). Due to collaborations with mathematicians, many scientists in fields such as physics, engineering, biology, and economics have Erd?s numbers as well.
Several studies have shown that leading mathematicians tend to have particularly low Erd?s numbers. For example, the roughly 268,000 mathematicians with a known Erd?s number have a median value of 5. In contrast, the median Erd?s number of Fields Medalists is 3. As of 2015, approximately 11,000 mathematicians have an Erd?s number of 2 or less. Collaboration distances will necessarily increase over long time scales, as mathematicians with low Erd?s numbers die and become unavailable for collaboration. The American Mathematical Society provides a free online tool to determine the Erd?s number of every mathematical author listed in the Mathematical Reviews catalogue.
The Erd?s number was most likely first defined by Casper Goffman, an analyst whose own Erd?s number is 2. Goffman published his observations about Erd?s's prolific collaboration in a 1969 article titled "And what is your Erd?s number?"
Jerry Grossman has written that it could be argued that Baseball Hall of Famer Hank Aaron can be considered to have an Erd?s number of 1 because they both autographed the same baseball (for Carl Pomerance) when Emory University awarded them honorary degrees on the same day. Erd?s numbers have also been proposed for an infant, a horse, and several actors.
Erd?s signed his name "Paul Erdos P.G.O.M." When he became 60, he added "L.D.", at 65 "A.D.", at 70 "L.D." (again), and at 75 "C.D."
Erd?s is the subject of at least three books: two biographies (Hoffman's The Man Who Loved Only Numbers and Schechter's My Brain is Open, both published in 1998) and a 2013 children's picture book by Deborah Heiligman (The Boy Who Loved Math: The Improbable Life of Paul Erd?s).
In his own words, "I'm not qualified to say whether or not God exists. I kind of doubt He does. Nevertheless, I'm always saying that the SF has this transfinite Book that contains the best proofs of all mathematical theorems, proofs that are elegant and perfect...You don't have to believe in God, but you should believe in the Book.".
I kind of doubt He [exists]. Nevertheless, I'm always saying that the SF has this transfinite Book ... that contains the best proofs of all theorems, proofs that are elegant and perfect.... You don't have to believe in God, but you should believe in the Book.
Erdös, an atheist, named 'the Book' the place where God keeps aesthetically perfect proofs.
With a heavy heart I feel that I have to sever my connections with the University of Waterloo, including resigning my honorary degree which I received from the University in 1981 (which caused me great pleasure). I was very upset by the treatment of Professor Adrian Bondy. I do not maintain that Professor Bondy was innocent, but in view of his accomplishments and distinguished services to the University I feel that 'justice should be tempered with mercy.'