The clockwork universe

Two industrial revolutions

Newton’s physics didn’t stay in books. This course traces two industrial revolutions to it, and the relationship between science and technology flipped between them.

The first industrial revolution, roughly 1760 to 1840, ran on steam. James Watt didn’t invent the steam engine; Thomas Newcomen’s engine had pumped water from mines since 1712. But Watt’s improvements, above all his separate condenser of 1769, made steam efficient enough to drive factories. Machines replaced muscle in spinning and weaving, mining, metalworking, and shipping, and then came the railway. Early railroads staged races between locomotives and horses to win over the public. They were, in effect, advertising, and in the most famous American one, in Maryland in 1830, the horse actually won after the engine’s belt slipped. In this first revolution, technology led and science followed. The engines worked before anyone fully understood why, and engineers pressed science to explain the physics of heat.

China hardly noticed. This was the reign of the Qianlong Emperor. When a British embassy under Lord Macartney arrived in 1793 bearing samples of British manufactures, the emperor wrote to King George III:

We possess all things. I set no value on objects strange or ingenious, and have no use for your country’s manufactures.

The Qianlong Emperor, letter to George III, 1793 (translation of 1914)

The second industrial revolution, from about 1870, ran on electricity: generators, motors, electric light, the telephone. This time science led. Once electricity was understood, through Coulomb, Faraday, Ampère, and Maxwell, and approached with Newton’s methods, the technology followed quickly. Physics could now work with fields and energy, not just pushes and pulls. By then China had lost the two Opium Wars, of 1839–42 and 1856–60, and its officials were scrambling to adopt Western technology in what was called the Self-Strengthening Movement. The lesson: science accelerates.

Idea, experiment, mathematics

Course 3 summed up ancient physics as observation plus speculation. Classical physics, by the same measure, is ideas plus experiment plus mathematics. The change from observation to experiment is huge. Observation is waiting for nature to happen to show you something. In an experiment, you create new phenomena yourself, stripping away the clutter until the core of the matter is left, so you can explain it and predict it correctly.

The Nobel laureate C. N. Yang (杨振宁), whom you met in Course 1, sketched how physics grows:

Experiments reveal new phenomena. A phenomenological theory, a first guess at the pattern, describes them. Joined with mathematics, it becomes a theoretical framework. New experiments test the framework. If they don’t fit, you look for a new phenomenological theory to repair it. And if it can’t be repaired, you tear it down and build again.

Newton even wrote down rules for this kind of reasoning. The first, which you met in Course 3, is to admit no more causes than are true and sufficient. The second is to assign the same causes to natural effects of the same kind, as far as possible. The shared inverse-square law of gravity and electricity, which led to the idea of the field, is that rule at work. In this reading, these rules express the values physics has held all along: simplicity, and laws that hold everywhere.

The world as a machine

Newton’s ideas quickly spread through society, this course argues, because people wanted a scientific explanation of the world, and this one was right and reassuring. Just follow the rules. The organic, purposeful cosmos of Aristotle gave way to a mechanical one with three ingredients: matter, motion, and space. Space is an infinite, uniform void. Particles, and the bodies they make up, move through it without resistance, either at rest, or in steady straight-line motion, or changing speed under a force. And one simple mathematical law, gravitation, connects every body to every other. The historian Alexandre Koyré called this the passage “from the closed world to the infinite universe.” It is a single world, not a chaos of isolated particles.

Two features of this picture matter for what comes next. First, humans are separate from nature. The stars ran by mathematics before people existed, and they would run the same without us. Second, the picture is reductionist. If a system is too complicated, take it apart. The solar system is complex, so study the sun and the earth, then the sun and Mars, then put the pieces together. To predict any body’s motion, you only need its position, speed, and the forces on it at one instant. From that instant follows the next, and from the next the whole.

Cracks in the clockwork

It worked brilliantly. Still, something seemed wrong. Stephen Hawking put it this way:

I have noticed even people who claim everything is predestined, and that we can do nothing to change it, look before they cross the road.

Stephen Hawking, Black Holes and Baby Universes, 1993

If Laplace’s demon is right and everything was fixed from the start, why look both ways? Nobody really lives as if they believed it. Three problems stand out.

Chaos. Even when every law is fixed, some systems are exquisitely sensitive to where they start. Change the starting conditions by a tiny fraction, run the system for a while, and the results differ completely, with no way back. In 1963 the MIT meteorologist Edward Lorenz found this in a simple model of the weather, and a later talk of his gave it a famous name: the butterfly effect. The novel The Three-Body Problem takes its name from a classic case: three bodies pulling on one another by Newton’s own law of gravity can move in ways no one can forecast for long.

People. The physicist David Bohm objected that the mechanical picture makes a human being no different from a machine, a collection of point masses. Surely, Bohm argued, something about people is special.

The first push. A question was raised as soon as Newton’s physics appeared: if the planets keep moving by inertia, who set them moving in the first place? Newton himself answered that “this most beautiful system of the sun, planets, and comets could only proceed from the counsel and dominion of an intelligent and powerful Being.”

Newton’s mechanical worldview describes our world remarkably well. But something seems to be missing, and the rest of this series, in Courses 5 and 6, goes looking for it.