In the Winter of 1953 Francis Crick interrupted the lunchtime patrons of the Eagle in Cambridge to announce he and James Watson had discovered the secret of life. In fact it wasn't far from hyperbole - they had discovered the structure of DNA and the world was forever changed.1 Something else world-changing happened later that year. Without it we wouldn't have advanced past the technologies of the 1960s. Surprisingly one of the people behind it thought it cute, but hardly worth publishing.
But first a bit of historical context
The Manhattan project began with blackboards and experiments. Individual researchers had their desk calculators, but it soon became necessary to work out how neutrons diffused when a critical mass of fissile material came together. A group of scientist's wives came together to perform the repetitive calculations. Next came IBM card reading calculators and then von Neumann became interested in developments in electronic computing at Harvard, Bell Labs and the University of Pennsylvania. There's a deep and rich history from this time on, but the important point was the meaning of "computer" was shifting from a woman with a mechanical calculator to an electronic machine.2
In 1953 electronic computers were still rare, mostly one-off machines that were expensive and temperamental. It was still a world of research and development. A few people recognized practical applications, but the machines mostly weren't ready. Except for physics.
Physicists were heavily involved in the birthing of electronic computers focusing on specific problems that tended to involve military projects or fundamental research to drive the hardware. Fundamental research was seen as the tip of the R&D effort and was often funded from military budgets which were large enough to support these efforts. Enrico Fermi had an interesting idea.
He was interested in nonlinear systems thinking they might have something fundamental to do with entropy and why time only flows in one direction. He, John Pasta and Stanislav Ulam conceived a simple toy problem - sixty four identical masses representing the atoms in a lattice connected end to end by little springs representing chemical bonds. Unfortunately calculating the restoring forces is a beast of a problem.
A linear system is one that can be described by a straight line on a graph. Consider a spring. Pull it twice as far and it exerts twice as much force. The same is true when you pluck a string on a guitar.3 Nonlinear systems have a more complex behavior. With linear systems you just add up the contributions of each element without considering the others. Nonlinear systems are nasty - you need to consider everything at once. You might be able to calculate very simple systems with a few elements, but after things become very complex.
The three physicists wrote down a mathematical description of the physics. Think of it as a strange sort of string that you pluck and then listen to as time goes on. Solving it would require a lot of computer time. The big iron at Los Alamos was called the Mathematical Analyzer, Numerical Integrator, and Computer or MANAIC-1 for short. It had been built for thermonuclear calculations, but this trio had an enormous amount of credibility and it was clearly fundamental research.
The three had no experience with programming, but Mary Tsingou was a mathematical physicist who knew how to reason with MANAIC-1. She set to work creating a program that became an experiment simulating how the lattice behaved for sixteen, thirty two and sixty four "atoms" with various spring forces.4
Imagine of the frequencies coming out of the system in terms of sound. They had expected a pure note that would shift over to more chaotic noises and finally the equivalent of just a hiss. That didn't happen.
The lattice was "plucked" and a series of overtones appeared and dissolved into each other creating a complex mixture. Then the whole process reversed and the overtones disappeared in reverse order until the original pure note reappeared and the whole process started over again.
Here's an illustration. Consider the top graph. The purple points are just the first vibration mode of a simple string - think of it as showing what would happen if it was just a simple string. The system we're talking about with equal masses and springs is in blue.
Even this simple little problem that had baffled some of the greatest minds had a beautiful and completely unexpected result and a new way of doing science had been developed - the computational experiment. The computer had become not just a bicycle, but rather a telescope for the mind.
Much of science is impenetrable without computer experiments like these. It's so common, I've done thousands, that you tend to think it's natural. But it had a beginning and without it much of what we've seen from science after the mid 1950s and the resulting technologies wouldn't have been possible. Inefficient cars and airplanes, no electronic revolution, no cellphones, no ....
Fermi thought it was cute, but not fundamentally important. That may be true for the hypothesis they tested, but how they did it changed the world.
1 There were many others who were in on this, but Crick and Watson weren't exactly the sharing kind. Most notably the x-ray diffraction work of Rosalind Franklin. But she was a women and died before the Nobel was awarded anyway.
2 George Dyson (Freeman Dyson's son) penned Turing's Cathedral. An excellent and very readable history of the efforts at Princeton. That may be the most important early thread as the computer architecture used today was developed there. Much of the slightly later development came out of Cambridge in England.
3 Sort of .. you can get it to behave non-linearly, but for now consider a spring that behaves like F = kx where x is the displacement, F is force and k is a constant that tells you about the spring's stiffness.
4 I don't know for sure, but have been told she programmed down to the iron in machine language.