2 Physics has never existed
Yang Dong was a physicist. A string theorist. And she killed herself.
Her note was only one line long:
Physics has never existed, and will never exist.
A sentence like that does not belong in a suicide note. It belongs in the opening line of a metaphysics textbook. But Yang knew it was not philosophy. It was despair.
For Wang Miao, a nano-material scientist, the note was incomprehensible. How could physics never have existed, when it is the skeleton of modern life? Lasers, satellites, GPS, semiconductors—all monuments to physical laws. What did Yang see that broke her faith so completely?
When asked, Yang’s partner, the physicist Ding Yi, did not answer with words. He answered with a demonstration.
2.1 The Pool Table
Science has always loved metaphors of colliding spheres. Newton used them to explain light, Descartes sketched them to describe celestial orbits, and Einstein invoked them in discussions of Brownian motions. Ding Yi continued the tradition—since the 19th century, billiards have been routinely used in physics textbooks for illustration.
He placed the ball at one end of the table, struck it with the cue at a fixed angle and force, and watched it collide with the side cushions. The rebound was predictable. Then he placed the ball elsewhere, struck again with the same angle and force. The collisions traced out an identical pattern. He did it again. And again.
Five times. Five experiments.
Each yielded the same result.
“Aren’t you shocked by the results?” Ding asked rhetorically. Wang did not know how to respond.
“Come on, let’s celebrate. We’ve discovered a great principle of nature: The laws of physics are invariant across space and time.”
This was no trivial statement. It is one of the great articles of faith in science: that laws are not local customs, but universal decrees. Strike a ball here, or there, today or tomorrow—it doesn’t matter. The physical laws remain the same.
Try it yourself. Ding Yi’s pool table has been reconstructed here. (Widget 2.2).
Drag the ball anywhere you like. Release it. A cue will strike with the same direction and force each time. Watch the numbers: position, velocity, acceleration. Try it again, and again.
Notice how the experiment becomes boring. That boredom is the signature of a law.
2.2 The Seduction of Invariance
Science seduces us with boredom. That is its secret charm. We want the universe to behave, not to surprise. Every replication, every repeated experiment that yields the same result, feels like a reassurance that we live in an orderly cosmos.
Philosophers gave this reassurance a name: the Principle of the Uniformity of Nature. David Hume, the great skeptic, articulated it in the 18th century: the assumption that the future will resemble the past; that nature tomorrow will behave like nature today; that “the course of nature continues always uniformly the same.”
Across cultures and centuries, thinkers embraced the principle without hesitation. Thales sought a single element to ground the flux of the world. Aristotle believed nature’s motions could be classified because they followed regular causes. Xunzi wrote 天行有常 — “the heavens move with constancy.” The Stoics saw the cosmos ordered by logos. Aquinas and medieval scholastics argued that God’s creation was rational and therefore reliable. Galileo, Kepler, and Newton assumed their laws applied everywhere. Bacon made nature a system governed by its own laws and the very source of knowledge. And knowledge is power.
This conviction — that the rhythm of nature is reliable, and thus knowable — is what keeps us from superstition. However framed — through omen or through reason — the majority have trusted that the world follows patterns so that we are not at the mercy of whimsical gods.
That trust is what makes science possible. Once we believed in order rather than caprice, knowledge could accumulate. Experiments became expected to repeat, results communicable, and science emerged as a shared project. This conviction, more than any single discovery, is what allowed the modern worldview to take root.
Without the Principle of Uniformity of Nature, replication collapses, prediction is impossible, and “law” becomes an empty word. With it, the modern scientific worldview takes shape: not pleasing the gods, but trusting that the world itself is knowable, and that what we learned here and now will apply tomorrow and elsewhere.
Ding Yi concluded forcefully,
… a great principle of nature: The laws of physics are invariant across space and time. All the physical laws of human history, from Archimedes’ principle to string theory, and all the scientific discoveries and intellectual fruits of our species are the by-products of this great law.
But here is the scandal: Hume could never prove it. No one has. The uniformity of nature is not a discovery. It is a bet. A metaphysical faith disguised as an empirical law. Even in the twentieth century, Einstein marveled that “the most incomprehensible thing about the universe is that it is comprehensible.”
Yang Dong’s suicide note was an act of apostasy.
2.3 The Lawful Table
Now, physicists don’t spend their lives rolling pool balls the same way over and over again. They juggle a zoo of variables—spin, friction, imperfections, air currents, hidden quirks of the felt—each one a potential troublemaker, each one an invitation for variance and disorder.
And yet, beneath the clutter, the pursuit is the same: change the knobs, keep the laws. Find that invariance that stands like granite.
Set the ball, pick an angle, choose a force, slide the friction. Watch the ball run like a wild child across the felt. Then, look to the right: the number that refuses to panic: total energy. The surface changes, the invariant doesn’t. Complexity multiplies, but the promise of invariance holds. That’s what a law feels like from the inside.
Physics hides its treasures in invariants. They are its balance sheets. No matter how wild the day’s trading—balls ricocheting, particles colliding—the books close clean. Energy in, energy out. Momentum tallied to the last decimal.