What physics wants

A flood, twice told

This history of physics begins with a story nearly every Chinese child knows. Gonggong, the god of water, went to war with Zhuanxu for rule of the world and lost. In his fury he rammed his head against Mount Buzhou, the pillar that held up the sky. The pillar broke. The sky tilted toward the northwest, which is why the sun, moon, and stars still slide that way, and the earth sank toward the southeast, which is why China’s great rivers flow east to the sea. Another story in the same collection tells how the goddess Nüwa melted stones of five colors to patch the broken sky, and cut the legs off a giant turtle to prop up its four corners.

Western readers know a similar tale: Noah and the flood. Nearly every ancient culture remembers a catastrophe of water. The question is how to read such stories, and one answer comes from an article in the journal Science.

In 2016, a team led by the Chinese geologist Wu Qinglong reported strange sediments in Jishi Gorge on the upper Yellow River. Their reading was that an earthquake had set off a landslide at a hairpin bend, where the river runs narrow. The rubble dammed the river, and a lake filled behind it. The dam rose roughly as high as the Hoover Dam. When it burst, it released one of the largest floods of the last ten thousand years, and the water surged some two thousand kilometers downstream. The team dated it to about 1920 BCE and linked it to damage at human settlements along the river. They also tied it to China’s own flood legend. Yu the Great, founder of the Xia, China’s first dynasty, is remembered for taming a great flood, and the ancient texts say he began guiding the Yellow River at a place called Jishi, the gorge’s name today. If this was Yu’s flood, the team argued, the Xia began around 1900 BCE, a few centuries later than its traditional date.

Now turn back to the myth. Perhaps, this course suggests, Gonggong’s people really were in charge of controlling floods. When a catastrophe came, the rival tribe blamed them, and the story remembered the blame as a god’s rage. A myth and a scientific finding describe the same event. One gives it a meaning, the other gives it a cause.

Explain, repeat, predict

Human beings do two basic things with the world: they try to understand it, and they try to change it. Myth, religion, philosophy, and science are all ways of understanding. Why has science won so much of our attention and support? This course offers a three-part test. A scientific account must be able to explain, it must be repeatable, and it must predict.

Myth passes the first test. Rain? The Dragon King sneezed. A flood? The water god lost his temper. Science can explain the same things. The difference shows in the other two tests. You can’t make Gonggong ram the mountain again to see what happens. A scientific cause, by contrast, can be checked by experiment, or by watching nature repeat itself under the same conditions.

Prediction, this course argues, is the most important test, and the reason myth never raised anyone’s harvest. If rain is a sneeze, when will it rain next? Whenever the Dragon King sneezes again. Nobody can say when that will be. Modern weather forecasting, by contrast, feeds humidity, temperature, wind, and airborne particles into supercomputers. For a small area, it can forecast almost minute by minute.

Physics offers a classic example. The Moon shows phases as it waxes and wanes. The sun-centered theory of the planets predicted that Venus should show phases too, a full set from thin crescent to nearly full. Nobody had ever seen them, because Venus stays close to the sun in our sky. In 1610 Galileo turned a telescope on it and saw exactly that.

Why physics?

Among the sciences, physics is arguably the one philosophers study most, because it is the oldest and the most complete. Its laws, experiments, mathematics, and logic support one another. When one part wobbles, the others usually show where the problem lies. That is why a subject with a history of two or three thousand years still feels new.

What does physics value? The answer here is that physicists are never satisfied with a list of laws. It isn’t enough to have Newton’s three laws of motion, a law of gravity, and the laws of heat. Mechanics has its principles, and electromagnetism, heat, and optics each have theirs. Physicists want to know what those branches share underneath. One joke puts it this way. God, surely, didn’t create the world by following a stack of textbooks a foot thick. More likely it was a single sheet of paper with a few simple rules on it. What those rules are, nobody yet knows. Einstein stated the goal more formally:

The supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender the adequate representation of a single datum of experience.

Albert Einstein, “On the Method of Theoretical Physics,” 1933

A paradigm you can borrow

A useful word comes from the American historian Thomas Kuhn: paradigm. A paradigm is what a community shares, whether physicists, investors, or insurers: its beliefs, its values, and its techniques. In shorthand, a paradigm is a philosophy plus a method. In this reading, physics has the purest paradigm of all. It uses only objective conditions and the tools of mathematics, which has a complete logic of its own.

That suggests a bargain for readers in business, or in any other field. Borrow the physicist’s paradigm and add what your own field knows about people and society. Physics knowledge can be the flesh of your thinking, and the physicist’s way of thinking can be its skeleton.

Simple is beautiful

Physics has an aesthetic too, though that may be hard to believe. Aren’t physicists the people who fill blackboards with scrawls? But if an equation looks like a mess to you, it probably isn’t the beautiful kind. The beautiful kind is simple. The best example is E = mc², which links mass and energy through one universal constant, the speed of light.

This isn’t just a matter of taste. Three witnesses from three eras of physics agree. Aristotle, the great figure of ancient physics, held that nature does nothing in vain. Newton, the founder of modern mechanics, made the idea the first of his rules of reasoning:

Nature does nothing in vain, and more is in vain when less will serve; for Nature is pleased with simplicity, and affects not the pomp of superfluous causes.

Isaac Newton, Principia, Rule I of Reasoning (1729 translation)

And Max Planck, who started quantum physics in 1900, wrote that physics’ most urgent aim is to gather every natural phenomenon, observed or yet to be observed, under a single simple principle, one that can calculate the past and, above all, the future. The same hope runs from Aristotle to Newton to Planck: a few simple laws beneath everything. The rest of this course follows the first great attempt to find them.