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Pure versus Applied: John von Neumann

Writer's picture: Mishkat BhattacharyaMishkat Bhattacharya

Scientists often make a distinction between working in pure (more interesting than useful) versus applied (more useful than interesting) areas of research. A contemporary example of a pure area might be string theory; and of an applied area, nanotechnology.


But sometimes pure and applied aspects of a science can coexist and interact fruitfully. A relevant example might be quantum information science/technology where the 'purists' might be studying entanglement in black holes, while the 'appliers' might be building a quantum computer. But the two pursuits can overlap - e.g. when a quantum computer simulates black holes.


And of course there are examples from the past, of prominent researchers who contributed to both pure and applied science: Leonardo da Vinci (optics and hydraulics), Enrico Fermi (quantum physics and nuclear fission), John Bardeen (superconductivity and the transistor).


I was mulling over these matters recently when I ran into the biography of a scientist who made pioneering contributions to wide-ranging fields - John von Neumann. The book is The Man from the Future, by Ananyo Bhattacharya and recounts readably the scientific contributions of von Neumann. You can decide which are pure and which applied:


i) Quantum Physics: Von Neumann showed that the two versions of quantum mechanics, independently discovered by Heisenberg and Schrodinger were mathematically equivalent (Stone-von Neumann theorem). His book on quantum physics was very influential - Mathematical Foundations of Quantum Mechanics.

ii) Bomb-making: Von Neumann designed some of the crucial details of the atomic bomb made at Los Alamos. He was also on the committee that selected the targets for atomic bombing (Hiroshima and Nagasaki). Together with Stan Ulam, he invented the Monte Carlo method, which they used to simulate nuclear processes. This technique is used widely in many fields nowadays. Von Neumann's later work enabled the hydrogen bomb.


iii) Computing: Von Neumann is considered to be one of the pioneers of modern computing. He suggested one of the first stored-program style computer architectures, named after him, to which he converted the ENIAC. (Also see below).


iv) Game theory: Von Neumann's minimax theorem is said to have started game theory, a field with implications for economics, biology, military strategy, ethics, AI, etc. His (written along with Oskar Morgenstern) book on the subject: Theory of Games and Economic Behavior.


vi) Theory of Self-Reproducing Automata: This book by von Neumann gives a prescription for building a self-replicating machine - seems highly relevant in the age of AI! This work has elements of computation and game theory, and von Neumann talked to a lot of biologists before he wrote it.


It inspired the famous Game of Life by Conway. Von Neumann gave his prescription for machine replication before the discovery of DNA structure (that is, before the replication of animate life was understood) but had analogous units in his scheme - e.g. the idea that it was the instructions for building the machine had to be replicated.


Bhattacharya's book reveals many interesting and entertaining details about von Neumann's addiction to thinking, his prodigious feats of mental calculation, his reckless driving and totaling of cars, his wild parties in Princeton.


Before reading this book, I did not know von Neumann had authored a paper with Chandrashekhar (the astrophysicist), and filed a patent application with Klaus Fuchs (the Soviet spy). I did not know how deeply influenced he was by Godel and Turing in his thinking about the mathematics of computation. I did not know, in the later years, how central his role at the RAND corporation was.


I did know, as is mentioned on pages 130 and 138-140, that Julian Bigelow was the engineer von Neumann hired to build the first digital computer based on his eponymous architecture (at the Institute of Advanced Study in Princeton, where Einstein had spent his last years). That's because Julian Bigelow was the father of my PhD thesis advisor, Nick Bigelow.










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