Wolfgang Pauli is one of the most fascinating physics giants of the 20th century, although he is not well known outside of this science, as was the case with other colleagues in his profession.
That he was brilliant is hard to deny. Just look at the reason he received the 1945 Nobel Prize: nothing less than the discovery of a new law of nature — the exclusion principle.
He was nicknamed “the conscience of physics” because of the scathing criticisms he made of the studies and theories of his colleagues, who adored and feared him in equal measure.
Furthermore, Pauli was able to predict the existence of the neutrino particle decades before it was confirmed. He himself was dismissive of his discovery: “I did something terrible. I postulated a particle that was impossible to detect.”
The particle was detected, but only 25 years later. And these particles are like “ghosts” — notoriously difficult to detect, despite being incredibly abundant in the universe.
The physicist is also remembered for a superstition that his colleagues called the “Pauli effect”: apparently, when he was around, some disaster happened.
For years, anecdotes have circulated about failures in experimental equipment supposedly caused by their presence.
But while most of his colleagues viewed this with humor, some even banned him from entering their laboratories.
Wolfgang Pauli himself thought there was truth in this “curse”. Even more so after the prank played by a friend when he participated in an international conference in Brussels in 1948.
Italian physicist Beppo Occhialini created a mechanism so that a ceiling lamp would fall when Pauli entered his laboratory. But when Pauli entered, the mechanism failed.
Pauli also engaged in a long exploration of the nature of reality with the influential Swiss psychiatrist Carl Jung and left a long legacy of correspondence with scientists that serves as a source of knowledge to this day.
His parents were secular Jews who converted to Catholicism due to rising anti-Semitism in Europe.
Later, this would force him to go into exile in the United States, due to the risk of the Nazis ignoring his family’s religious conversion.
In addition to his natural aptitudes, everything around him fed his intellect: his father was a respected university professor of chemical medicine and his mother, Bertha Camilla Schütz, a prominent writer, pacifist, socialist and feminist.
His social circle included personalities such as the physicist and philosopher Ernst Mach, whom Albert Einstein himself recognized as being the precursor of his theory of relativity.
Mach was Pauli’s godfather. Particle physicist Frank Close, professor emeritus at the University of Oxford, told the BBC that the godfather’s influence was such that Pauli spent his life following Mach’s anti-metaphysical school of reasoning.
At school, Pauli stood out for his excellence in mathematics and physics, and at the age of 18 he entered the University of Munich to study with theoretical physicist Arnold Sommerfeld, his dream mentor: among his students were six Nobel Prize winners.
Sommerfeld was so impressed with Pauli’s mathematical ability that when Einstein turned down an invitation to write an article on the theory of relativity for the prestigious Encyclopedia of Mathematical Sciences, Sommerfeld asked Pauli to do so.
At that time, the theory of relativity was not only revolutionary, but still very new, and not even most physicists knew it very well.
Entrusting a student fresh out of high school with the task of writing such an important text was not wise, as emphasizes physicist Hans von Baeyer from the Metanexus Institute.
But Sommerfeld’s bet was right.
Pauli’s more than 200-page review was praised by the great mathematicians of the time.
“In addition to writing a simple study of the theory, he pointed out problems that were open in it,” Michela Massimi, professor of philosophy of science at the University of Edinburgh, told the BBC.
“This impressed everyone and put him on the international stage once and for all,” he added.
Einstein himself praised Pauli’s text.
“No one who studies this mature and grandly conceived work would believe that its author is a 21-year-old man,” commented the author of the theory of relativity.
Pauli’s review became an instant classic and continues to be a reference work.
Physics experts saw the young student as very promising.
And he didn’t disappoint.
Exclusivity at 24 years old
After receiving his doctorate, Pauli worked as an assistant to the German mathematician and physicist Max Born (1954 Nobel Prize winner) at the University of Göttingen.
The following year, Niels Bohr (Nobel 1922), the Danish physicist who revolutionized the understanding of the atom, invited him to work with him in Copenhagen, Denmark.
But it was when he moved to Germany, to teach at the University of Hamburg, that Pauli proposed two radical ideas that solved fundamental problems in the structure of the atom.
One of them was the one that would win him the Nobel Prize: the exclusion principle or Pauli principle.
Understanding it well is complicated, but it’s worth trying with the help of physicist Frank Close, who explained to the BBC why this principle is so fundamental.
At that time it was already known that atoms had a nucleus, with a positive charge, and that electrons revolved around them in elliptical orbits, separated like the steps of a ladder.
In each step, or quantum state, there can be a specific number of electrons: at the lowest, there can only be two at most.
And this defines what the elements are: hydrogen has a single electron in the lowest step; if there are two electrons, it is helium.
The next element is lithium, but since it has three electrons, the electrons occupy the next step and so on.
The principle, Close noted, says that “if you already have an electron occupying one of these quantum states, you can’t put another electron there: it’s excluded.”
To illustrate, he gave an example: “If I hit the table, my hand doesn’t pass through the table because the electrons on the outer edge of my finger are trying to occupy a state that is already occupied by an electron in the wood of the table.”
“The fact that electrons cannot go anywhere, that they are placed in special places because occupied states are already excluded, gives rise to the different chemical natures of atoms,” says Frank Close.
The consequence of this, according to him, is that you and I, the Universe and everything else exist.
If the exclusion principle didn’t force electrons to stay in different places in the puzzle and build structures, they would be floating and wouldn’t form atoms, solids, crystals… nothing.
“Even in the cosmos, the death of stars is related to the exclusion principle. As the star collapses, its constituents try to compress themselves more and more until they cannot, because they are excluded.”
Other physicists were quick to recognize the importance of the discovery.
“The news spread very quickly,” says Michela Massimi of the University of Edinburgh.
“Pauli announced the exclusion rule — and I emphasize that he called it a rule, not a principle, because at the time it was just a humble rule of thumb — in a letter to Alfred Landé, a prominent experimental physicist, in late 1924.”
“A month later, Niels Bohr wrote to Pauli from Copenhagen saying: ‘We are all very excited about the many beautiful things you have discovered and I need not hide any criticism because you yourself described it all as madness’.”
“The reality is they were trying to understand the exclusionary rule,” Massimi says.
“And Pauli introduced in 1924, before the foundations of quantum mechanics had really been laid, a rule that finally provided a solution to a problem that had plagued physicists for decades,” says Massimi.
Later the rule would be confirmed as a principle and, as Professor I. Waller, member of the Nobel Physics Committee said when awarding him the prize, it came to be characterized as a fundamental law of nature.
“The principle, first discovered for electrons, has been shown to be valid for hydrogen nuclei, called protons, and also for neutrons that are formed in many nuclear reactions,” he said.
This is despite the fact that, as Hans Von Baeyer says, he introduced this rule by decree.
“He proposed no new force between electrons, no mechanism, not even logic, to support this idea.”
“It was simply a rule, imperative in its peremptory nature and unlike anything else in the entire domain of modern physics.”
“Electrons avoid each other’s private quantum numbers for no other reason than ‘out of fear of Pauli,’ as one physicist put it (Paul Ehrenfest, 1931).”
It wasn’t fake
Pauli made all his discoveries and deductions by deeply analyzing the experimental and theoretical knowledge of atomic physics at the time and using his incredible mathematical skills.
This also made him an imposing critic of the work of others.
His opinion on new ideas was so important to his acceptance or rejection by the physics community that they nicknamed him the “conscience of physics.”
“No form of approval could be more valuable to physicists, including Bohr, than a benevolent gesture from Pauli,” noted Belgian physicist Leon Rosenfeld.
He left a curious legacy of phrases that continue to be quoted.
The most famous of them is devastating.
As physicist Rudolph Peierls wrote in his biographical memoir of Pauli, “a friend showed him a paper by a young physicist whom he suspected was not of great value, but about whom he wanted to know Pauli’s opinion.”
“Pauli commented sadly: ‘It’s not even fake'”.
Other sources report that his response was: “Not only is it not correct, it is not even false”, but the fact is that the phrase was adopted to dismiss arguments so speculative that they do not qualify for philosopher Karl Popper’s principle of falsifiability.
When you test a flawed hypothesis, Popper said, you learn something in the process, and that feeds science; but if it’s not false, you’re just wasting time.
Thus, several of his criticisms remained in the memory because, although scathing, they were witty and generally welcome.
However, some were offended and some wondered if this was the reason why the Nobel Prize Committee took so long to award him the prize, despite him being nominated 20 times by great scientists between 1933 and 1944.
No one really knows why he was awarded in 1945, 20 years after he formulated his principle of exclusivity.
That year, one of the three who nominated him was Einstein, who was present at the ceremony organized to honor the new Nobel Prize winner at Princeton University, in the United States, where Pauli had worked since leaving Europe in 1940 because of of the Second War.
As the CERN website (French acronym for the European Organization for Nuclear Research) reports, after several distinguished guests spoke, Einstein stood up and gave an impromptu speech, referring to Pauli as his intellectual successor.
Pauli was deeply moved, he recalled this in a letter to Max Born ten years later, days after Einstein’s death, and regretted that, as the speech had been spontaneous, there was no record of it.
He did not have time to establish himself as his intellectual successor: Pauli died three years later in Zurich, the city where he had moved in 1946.