【不断更新】利用空闲时间读一篇文章吧：‘It’s a Mess’: A Brain-Bending Trip to Quantum Theory’s 100th Birthday Party

‘It’s a Mess’: A Brain-Bending Trip to Quantum Theory’s 100th Birthday Party¹

—— Hundreds of physicists (and a few journalists) journeyed to Helgoland, the birthplace of quantum mechanics, and grappled with（原意为扭打，搏斗，这里引申为努力解决，竭力应对） what they have and haven’t learned about reality.

TOPICS: history of science; physics; QBism ;Quanta Podcast
quantum interpretations; quantum physics; The Quanta Podcast

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In the summer of 1925, a young Werner Heisenberg retreated to （撤退到） Helgoland in the North Sea and reemerged with the first full-fledged version of quantum mechanics. A century later, the theory’s meaning remains unsettled.
—— Señor Salme for Quanta Magazine

“Happy 100th birthday, quantum mechanics!” a physicist bellowed into a microphone（对着麦克风高喊） one evening in June, and the cavernous banquet hall（代表宴会厅宏大） of Hamburg’s Hotel Atlantic erupted into cheers and applause. Some 300 quantum physicists had traveled from around the world to attend the opening reception（接待） of a six-day conference marking （标志着）the centennial（百年纪念 ） of the most successful theory in physics. The crowd included well-known pioneers of quantum computing and quantum cryptography（量子密码学）, and four Nobel Prize winners.

“I feel like I’m at Woodstock（1969年的伍德斯托克音乐节，是20世纪最著名的摇滚音乐节之一）,” Daniel Burgarth² of the University of Erlangen-Nuremberg in Germany told me. “It’s my only chance to see them all in one place.”

One hundred years to the month had passed since a 23-year-old postdoc named Werner Heisenberg was driven by a case of hay fever （花粉过敏）to Helgoland, a barren, windswept island（一个荒凉多风的小岛） in the North Sea. There, Heisenberg completed a calculation that would become the heart of quantum mechanics, a radical new theory （全新的激进的理论）of the atomic and subatomic world（原子和亚原子世界）.

The theory remains radical.

Before quantum mechanics hit the scene（走上历史舞台）, “classical” physics theories dealt （deal的过去式，应对，处理）directly with the stuff of the world and its properties: the orbits of planets（行星的轨道）, say, and the speeds of pendulums（钟摆的速度）. Quantum mechanics deals in something more abstract: possibilities. It predicts the chances that we’ll observe an atom doing this or that, or being here or there. It gives the impression that particles can engage in （表现出）multiple possible behaviors at once, that they have no fixed reality. So physicists have spent the last century grappling with questions like: What is real? And where does our reality come from?

The morning after the banquet （宴会）in Hamburg, the gathered physicists (and a handful of journalists（少数的记者） traveled by ferry（渡轮） to Helgoland to discuss where things stand a century after the theory’s birth.

Discussion began almost as soon as we boarded the boat. By the time I reached my seat, Časlav Brukner and Markus Arndt, both of the University of Vienna, were deep in conversation about whether the fabric of space and time（时空结构） follows the same quantum rules that particles do. Adán Cabello of the University of Seville soon joined in. I saw a passionate finger pointing into the air, and someone exclaimed, “What do you mean, what do I mean?”

As the ferry left the shelter of the Elbe River and entered the rough waves of the North Sea, Cabello threw up his hands（摊开双手）. “We are here happily celebrating 100 years,” he said, “but actually it’s a mess. We were given this theory, and we still don’t understand what it means.”

Suddenly feeling a wave of nausea（恶心）, I excused（中断） myself from the philosophizing and sought fresh air on the ship’s second-floor deck.

Heisenberg in Helgoland

I clenched the railing with both hands and stared into a thick fog, vainly seeking the steady sensory input of a horizon as we pitched up and down in the swell. (The ferry operators canceled later crossings that day.) Eventually, to the relief of the many passengers with less-than-perfectly-steeled stomachs, the ferry pulled into the port of Helgoland.

We had reached a world apart. The German island has nearly 1,400 residents, whose modest homes are split between an Unterland at sea level and an Oberland perched on the rim of a grassy plateau, dotted with sheep and free-wheeling seabirds. It was in this divided land that the seed of quantum mechanics sprouted in Heisenberg’s mind.

For decades, clues had been mounting that matter and light defied common logic. In classical physics, locations, speeds and other properties of objects had always been free to take on any value, and consequently, changes always took place in a smooth, continuous way. But in 1900, measurements of light shining from hot objects led Max Planck to argue that matter must gain and lose energy only in discrete amounts, with the energy rising and falling in tiny hops. It was the first hint that the world was “quantized,” the namesake of quantum mechanics. Five years later, Albert Einstein made the case that light — which had always acted steadfastly like a continuous wave — also came in particle-like chunks of energy. And in 1913 Niels Bohr proposed that electrons orbit the atom only at certain fixed distances; when they gain or lose energy, they instantaneously “jump” between orbits. But nobody had yet managed to gather these curious facts into a coherent description.

Heisenberg, a protégé of Bohr, took daily walks and long swims on Helgoland as he mulled things over. Bohr’s model of the atom, he knew, wasn’t quite right. It predicted the correct frequencies of light emitted by hydrogen atoms but didn’t work for bigger, more complicated atoms.

So Heisenberg took a conceptual leap that still boggles minds today. At the conference, Bill Unruh (opens a new tab), a renowned physicist with a beard that would make Santa Claus jealous, told me he simply cannot see how Heisenberg arrived at the calculation that he did, calling his route “a mystery.” One night over drinks, the astrophysicist Matt O’Dowd (opens a new tab), host of the PBS Space Time YouTube channel, joked that perhaps the wilds of Helgoland hide some mushrooms with mind-opening effects. Nathalie de Leon (opens a new tab) of Princeton University noted in her talk that Heisenberg had reportedly used cocaine to alleviate his allergies.

Whatever sparked it, his insight triggered a seismic shift in physics. He relinquished the mental image of the atom as a little solar system with electrons orbiting on fixed paths. Such fine microscopic clockwork lay beyond the reach of direct experiment, he reasoned, so the theory shouldn’t refer to it directly either. In his new description, Heisenberg restricted himself only to properties measurable by machines far away from an atom — namely, the color and intensity of the light that it emits. After a long night of calculations, he found a way to remix arrays of numbers describing measurable attributes of light in a way that reproduced Bohr’s prediction of hydrogen’s glow. He did it without referencing the hydrogen atom or the movement of its putative parts. His observation-based framework was more abstract, and therefore more likely to work for other atoms too.

Decades later, Heisenberg wrote about how his eureka moment on Helgoland inspired a sunrise climb by the sea near the Unterland. I “felt almost giddy at the thought that I now had to probe this wealth of mathematical structures nature had so generously spread out before me,” he recalled.

By the fall, his colleagues had discerned something wonderful in his math. That October, Heisenberg’s fellow wunderkind and sometime rival, the 25-year-old Wolfgang Pauli, wrote that the work gave him “a new hope and a new enjoyment of life.” Max Born, a more senior physicist, realized that Heisenberg had unwittingly hit on the rules for multiplying grids of numbers called matrices — high mathematics in the 1920s. With matrices, the order in which you multiply