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In the pantheon of 20th-century genius, there are a few stand-out figures: Albert Einstein, Alan Turing, Steven Hawking, and, without question, John von Neumann belongs in their company, even if many have no idea who he is.

John von Neumann was one of the most influential figures of the 20th century. He is someone who has likely impacted your life more directly than just about any of the great minds of the past 150 years, touching on everything from quantum mechanics to climate science.

Von Neumann’s biggest contribution is the modern computer, taking the brilliant theoretical framework laid down by Turing and actually constructing the architecture that would eventually power just about every digital computer ever made.

More controversially, von Neumann made significant contributions to the Manhattan Project during World War II, including refining the design of the atomic bomb itself and the mechanism critical to its functioning.

Unlike some other Manhattan Project veterans, von Neumann never expressed regret over his role in the project and even promoted the policy of Mutually Assured Destruction during the Cold War.

John von Neumann is a complicated figure — to say the least — but he has few equals in the 20th century, and he is arguably more responsible for the modern world than just about any of his contemporaries.

## A Child Prodigy

John von Neumann was born Neumann János Lajos on December 28, 1903, in Budapest, Kingdom of Hungary. The son of wealthy and respected parents, von Neumann’s father was a banker and his mother was the daughter of Austro-Hungarian aristocrats.

In 1913, the Austro-Hungarian Emperor Franz Joseph made von Neumann’s father a member of the nobility, granting the family a hereditary title of *Margittai, *or “of Margitta”, now Marghita, Romania. The title was purely honorific, as the family had no connection to the place, but it was one that von Neumann would hold onto throughout his life.

The young von Neumann was immediately singled out among his peers as a true child prodigy, especially in mathematics. He is believed to have had a photographic memory, which helped him absorb considerable knowledge from a very early age. By age six, he was dividing two, eight-digit numbers in his head, and by age eight he had mastered calculus.

His father believed that all his children needed to speak the major languages of Europe beyond their native Hungarian, so von Neumann was taught English, French, Italian, and German.

As a boy, he also had a deep interest in history, and read the entire 46-volume *General History in Monographs* by the German historian Wilhelm Oncken.

Encouraged by his teachers, von Neumann excelled in his studies, but his father did not believe that a career as a mathematician would be financially lucrative. Instead, von Neumann and his father agreed that he would take up chemical engineering, and he went to study in Berlin at age 17, and later in Zurich.

Chemistry was one of the few fields that seemed to hold no interest for von Neumann, though he did receive a Zurich diploma in chemical engineering, while also earning a Ph.D. in Mathematics at the same time.

## Early career

John von Neumann published early, starting at the age of 20 when he wrote a paper defining the ordinal numbers, which is still the definition we use today. He wrote his Ph.D. dissertation on set theory and made several contributions to the field in the course of his life.

By 1927, von Neumann had already published 12 papers of note in Mathematics. By 1929, he was up to 32 published works, grinding out major contributions at a rate of roughly one academic paper a month.

He became a Privatdozent at the University of Berlin in 1928, becoming the youngest person ever given the position in any subject in the University’s history. The position allowed him to lecture at the university, which he did until 1929 when he became a Privatdozent at the University of Hamburg.

Von Neumann also converted to Catholicism that same year, following the death of his father in 1929. On New Year’s Day in 1930, John von Neumann married Marietta Kövesi, an economics student at Budapest University, with whom he would have his only child, Marina, in 1935.

While von Neumann might have seemed destined for a promising career in the German academy, in October 1929, he was offered a position at Princeton University in New Jersey, which he fatefully accepted, traveling to the US with his wife in 1930.

## Emigration to the United States

By 1933, John von Neumann became one of the original six mathematics professors at the newly founded Institute for Advanced Study in Princeton, a post he would remain in for the rest of his life.

When he moved to New Jersey, like many American immigrants before him, von Neumann anglicized his Hungarian name (Margittai Neumann János became John von Neumann, using the German-style of hereditary honorific).

In 1937, he and his wife divorced, and the following year von Neumann remarried, this time to Klara Dan, whom he first met in Budapest during his final visits to Hungary in the lead up to the Second World War.

In 1937, von Neumann became a naturalized US citizen and in 1939, his mother, siblings, and in-laws all emigrated to the US as well (his father had died earlier).

## The War Years

One of John von Neumann’s most significant contributions to history was his work on the Manhattan Project during the Second World War.

True to form, von Neumann couldn’t let a mathematical challenge go unresolved, and one of the more difficult problems was how to model the effects of explosions.

Von Neumann threw himself at these problems in the 1930s and became something of an expert in the field. If he had a specialty, it would have been on the mathematics of shaped charges, which are used to control and direct the force of their explosive energy.

This put him in fairly regular consultation with the US military, particularly the US Navy. When the Manhattan Project began its work in the early 1940s, von Neumann was recruited for his expertise.

In 1943, von Neumann made his most significant and lasting impact on the Manhattan Project. The Los Alamos Laboratory where the atomic bomb was being designed, discovered that the plutonium-239 — one of the fissile materials used by the project — was incompatible with the laboratory’s working bomb design.

A physicist at the lab, Seth Neddermeyer, had been working on a separate, implosion-type bomb design that showed promise but many considered it to be unworkable.

To detonate a nuclear explosion, you need to trigger a runaway fission chain reaction in the bomb’s reactant. The rate of the chain reaction is exponential, so controlling the explosion long enough for sufficient fissile material to undergo the required reaction is a significant challenge.

The implosion-type bomb required even more sophisticated controls to generate the reaction, but it also would not require nearly as much material as the prevailing gun-type bomb design being developed at Los Alamos.

An implosion-type device uses a series of controlled conventional explosions to compress the fissile reactant in its core. Under this pressure, the fissile material quickly starts a nuclear fission chain reaction that is held in place by the force of the implosion, allowing more fissile material to release its energy.

Controlling these explosions to create the exact right implosive force to produce the desired reaction was a challenge that von Neumann took on with considerable passion. He believed that using less material shaped into a sphere and properly compressed by an implosive force could generate a more efficient and effective explosion that used as much of the available fissile material as possible.

He was often one of the few voices arguing for the implosive method and eventually worked out the math that showed how it could be done if the implosion managed to maintain a spherical geometry with at least 95% accuracy.

Von Neumann also worked out that the effectiveness of the blast would be increased if it was detonated above the target by some significant distance rather than having it detonate on hitting the ground.

This greatly increased the lethality of the atomic bomb and also reduced the amount of fallout produced by the explosion.

Von Neumann was selected as part of the team of science advisors who would consult the military on possible targets for the bombs. Von Neumann suggested the cultural capital of Kyoto, Japan, whose destruction might be enough to force a quick end to the war. He wasn’t alone in this suggestion, but the Secretary of War Henry Stimson vetoed targeting Kyoto, with its many historic buildings and important religious shrines, and Hiroshima and Nagasaki were chosen instead.

Von Neumann was present during the Trinity Test on July 16, 1945, where the first atomic weapon was detonated. After the bombing of Hiroshima and Nagasaki, Japan surrendered and World War Two came to an end.

Unlike some of his contemporaries in the Manhattan Project, von Neumann did not seem to have any of the reflective anguish, regret, or even a passing doubt about his work on the atom bomb. In fact, von Neumann became one of the most vocal proponents of nuclear weapons development and the doctrine of Mutually Assured Destruction (MAD) as the only way to prevent another catastrophic world war.

## Post-War Work on Nuclear Weapons

Like a lot of Americans in the early Post-War era, John von Neumann was concerned about America falling behind the Soviet Union in nuclear weapon development. By the late 1940s to early 1950s, it was becoming evident that the idea of strategic bombers dropping more Fat Men on the enemy was falling away to new rocket technology.

Missiles, von Neumann believed, were the future of nuclear weapons, and due to his contact with German scientists working on the Soviet Weapons program, he knew that the USSR saw it the same way he did.

The race was on to build small enough H bombs that could fit into a warhead on the top of an intercontinental ballistic missile and von Neumann aggressively pushed to close the “missile gap” with the Soviets.

Von Neumann served on the Atomic Energy Commission after the war, advising government and military leaders on technological development and strategy, and is widely credited as the architect of MAD, which would go on to be adopted as de facto US policy during the Cold War.

## Building the First True Computers

John von Neumann met Alan Turing in the early 1930s while Turing was working on his Ph.D. at Princeton, but he had known of him even before then. In 1937, Turing had published his landmark paper “On Computable Numbers” which casually laid the theoretical foundation for modern computing.

Von Neumann recognized the significance of Turing’s discovery and furthered the development of computer science in the 1930s, including long discussions with Turing at Princeton around the idea of artificial intelligence.

As a mathematician, von Neumann approached computer science from a more abstract perspective, especially since there weren’t really any working computers in the 1930s, but that would change soon after World War II.

Von Neuman was deeply involved in the development of the ENIAC, the first programmable, electronic computer that was “Turing-complete”, meaning that it was able to recognize and decide on other data-manipulation rule sets than the one it started with. It was von Neumann who modified ENIAC to run as a stored-program machine.

This latter fact made modern programs as we understand them today possible. Von Neumann himself wrote several of the first programs to run on the ENIAC, and used it extensively to run simulations on his nuclear weapons research as part of the Atomic Energy Commission.

Without question, von Neumann’s most lasting contributions to the field of computer science are with two foundational concepts used in every computer running today: von Neumann architecture and the stored-program concept.

Von Neumann architecture involves the way the physical electronic circuits that make up a computer are organized. His design for the computer consists of an Arithmetic and Logic Unit (ALU), a Control Unit, and Temporary Memory Registers that together make up a Central Processing Unit (CPU).

This CPU is connected to a Memory Unit that contains all of the data that is going to be processed and manipulated by the CPU. The CPU is also connected to input and output devices to alter data as needed and retrieve the results of a running program.

This is essentially how most general-purpose computers in existence operate today, and very little has changed since von Neumann introduced it in 1945.

The other major innovation is related to von Neumann architecture, and the two are usually taken together as a whole. This is the stored-program concept, which means that both the data being manipulated or processed as well as the program that describes how to manipulate and process that data are both stored in the computer’s memory.

These two intertwined innovations took the theoretical framework of Turing machines and actually turned them into machines we could use to compute everything from payroll data and artillery trajectories to modern computer games and the internet.

## Contributions to Fields as Diverse as Quantum Mechanics to Climate Science

John von Neumann’s contributed to several other fields beyond mathematics and computer science throughout his life, though many of them are in some way related or similar.

In his early career, von Neumann made major contributions to the burgeoning field of quantum mechanics. In 1932, he and Paul Dirac published the Dirac-von Neumann axioms, the first thorough mathematical framework for the field in his book *Mathematical Foundations of Quantum Mechanics*. In this book, he also proposed a formal system of quantum logic, the first of its kind.

Von Neumann also established Game Theory as a rigorous mathematical discipline, something that undoubtedly influenced his later geopolitical strategic work on MAD. His game theory included the idea that, in a broad category of games, it is always possible to find an equilibrium from which neither player should deviate unilaterally.

In the life sciences, von Neumann conducted a thorough mathematical analysis of the self-replication of cellular automata, principally the relationships between a constructor, the thing that is being built, and the blueprint the constructor follows to construct the thing in question. This analysis described a self-replicating machine and was designed in the 1940s, without the use of a computer.

Von Neumann applied his mathematical acumen to climate science as well. He wrote the first climate modeling program and used the ENIAC to make the world’s first forecast with numerical data on an electronic computer in 1950.

Von Neumann anticipated global warming as a consequence of human activity, writing in 1955 that “the Carbon dioxide released into the atmosphere by industry’s burning of coal and oil — more than half of it during the last generation – may have changed the atmosphere’s composition sufficiently to account for a general warming of the world by about one degree Fahrenheit.”

Von Neumann is also credited with being the first to describe the Technological Singularity. Von Neumann’s friend Stan Ulam later described conversations he had with von Neumann that sounds eerily prescient today.

“One conversation centered on the ever-accelerating progress of technology and changes in the mode of human life,” Ulam said, “which gives the appearance of approaching some essential singularity in the history of the race beyond which human affairs, as we know them, could not continue.”

There are far too many examples of von Neumann’s contributions across so many various fields that one really can’t do them justice.

## The Death and Legacy of John Von Neumann

In 1955, John von Neumann was diagnosed with cancer after a growth was found on his collarbone during a doctor’s visit, and he didn’t take the revelation well.

By all accounts, von Neumann was terrified of the coming end. Eugene Wigner, a lifelong friend of von Neumann’s, wrote of this period:

When von Neumann realized he was incurably ill, his logic forced him to realize that he would cease to exist, and hence cease to have thoughts…It was heartbreaking to watch the frustration of his mind, when all hope was gone, in its struggle with the fate which appeared to him unavoidable but unacceptable.

His disease progressed throughout 1956, and he was eventually admitted into Walter Reed Army Medical Center in Washington, DC. He had a constant security detail to guard against his divulging classified information due to his condition.

Von Neumann invited a Catholic priest to consult with him on his deathbed and was given his last rites, though the priest, Anselm Strittmatter, said that von Neumann didn’t appear to be comforted by them.

On February 8, 1957, von Neumann succumbed to cancer at the age of 53 and was buried at Princeton Cemetery in Princeton, New Jersey.

Whether John von Neumann’s cancer was a result of radiation exposure he suffered during his time with the Manhattan Project has been long debated, but there’s no question that humanity lost one of its greatest scientific minds well before his time.

Von Neumann’s assistant, P.R. Halmos, wrote of him in 1973:

The heroes of humanity are of two kinds: the ones who are just like all of us, but very much more so, and the ones who, apparently, have an extra-human spark. We can all run, and some of us can run the mile in less than 4 minutes; but there is nothing that most of us can do that compares with the creation of the Great G-minor Fugue. Von Neuman’s greatness was the human kind. We can all think clearly, more or less, some of the time, but von Neumann’s clarity of thought was orders of magnitude greater than that of most of us, all the time.

John von Neumann’s brilliance is unquestionable, though his legacy, — especially his work on nuclear weapons — is more complicated than his friends and admirers would probably want to admit. It takes a different kind of mind indeed to look at an atomic bomb and innovate ways to make them even more deadly to take even more lives. No matter where we land on John von Neumann in the end, all we can say for sure is we aren’t likely to see a mind of his caliber for another generation or more.