On the first or second Tuesday in October every year, three people walk into a room at the Royal Swedish Academy of Sciences in Stockholm, Sweden. Surrounded by oil paintings of famous scientists, the smartly dressed trio sit down at a long table facing expectant members of the international media. In the middle is the secretary-general of the academy – currently Göran Hansson – flanked on either side by the chair of the Nobel Committee for Physics and one other member of this elite group.

The three scientists are here to reveal the winners of the Nobel Prize for Physics. Currently worth about nine million Swedish kronor (about £760,000), the prize has been awarded almost every year since 1901, with the precise sum depending on the size of the academy’s coffers. It remains the most prestigious award in physics and the one that surely all physicists dream of winning, despite recent competition from newer prizes with bigger cash sums from rival organizations such as the Breakthrough and Kavli foundations.

With light filtering down from chandeliers hanging above, the secretary-general – in time-honoured tradition – reveals the winners first in Swedish, then in English. The physicists’ names and photos are flashed up on a large screen above and, from that moment on, the winners, of which there can be no more than three each year, are immortalized in history. They have joined the pantheon of great physicists of the past, from Wilhelm Röntgen, who won the first prize in 1901 for discovering X-rays, to Marie Curie, Paul Dirac, Albert Einstein, Werner Heisenberg and Erwin Schrödinger.

Part of the allure of the Nobel Prize for Physics is its mystery. The Nobel Foundation, which manages the finances and administration of the prizes, provides information about the nomination process online, but precise details of why each prize is awarded remain secret for a period of 50 years after each is awarded (though you can now do an online search of the archives of all prizes awarded more than 50 years ago at this link). It is therefore almost impossible to get an insight into the current Nobel committee’s thinking.

To tease out more information about the selection process, Physics World recently spoke to Lars Brink – a Swedish theoretical particle physicist who served on the Nobel Committee for Physics in 2001, 2004 and from 2008 to 2013. Brink was intimately involved in the awarding of those years’ prizes, especially in 2013 when he served as chair of the committee, which that year gave the Nobel prize to François Englert and Peter Higgs for developing the theory that underpinned CERN’s discovery of the Higgs boson.

Brink, who still plays a role in choosing winners of the Nobel prize as a member of the “Physics Class” of the Royal Swedish Academy of Sciences, says that awarding the prize every year is a monumental task, with no margin for error. “It took a lot of my time during those years,” he explains, referring to the eight occasions he served on the Nobel committee. “It is such a prestigious prize that we cannot make mistakes.” Indeed, he believes there have been “rather few” mistakes in the prize’s 118-year history.

All in a year’s work

Each year’s Nobel laureates are revealed in October, but the selection process actually begins the previous September. That’s when the committee, which comprises five members, two adjunct members and a secretary, sends out nomination forms to around 3000 people. Those invited to propose names include all members of the Royal Swedish Academy of Sciences, all previous physics Nobel laureates, all tenured professors of physics in the Nordic nations (Denmark, Finland, Iceland, Norway and Sweden), plus a selection of senior physicists around the world. Committee members can also make nominations themselves.

Nominations close at the end of January, by which time the committee has usually received around 400 forms. That might sound like a lot, but as Brink points out, it’s barely over 10% of the forms sent out. “You might wonder why so few people send in nominations,” he says, “but I have no good answer for that.” The committee’s secretary then compiles the nominations into a “thick book” before all committee members get to work on what Brink describes as “a very interesting time of the year”.

They scrutinize the nominations to establish whether nominees were the first people to do the cited work and if the work was high enough in quality to be worthy of the prize. Another important challenge is to ensure that the prize is awarded to no more than three people. And as they sift through the nominations, the eight members of the committee also have to decide whether to bring in external experts to help evaluate nominations in fields that lie outside their own expertise.

By the end of February, the committee will have winnowed down the nominations to a shortlist of about 20 preliminary candidates. At this point, invitations are sent out to specialists to write reports on these candidates, with the reports submitted to the committee by the end of May. This process begins afresh every year, which means that even if a physicist has been nominated previously, a new report is written each time. Indeed, Brink points out that eventual winners may have five or so past reports about their work. In a sense, these multiple reports are a “hot list”, says Brink, though he adds that each year they also see shortlisted nominations for new people.

After receiving the 20 or so reports on preliminary candidates, the committee members normally select their recommendation of the winner (or winners) in June, although Brink declines to say if this is done by majority vote or a unanimous show of hands. The committee then writes the first draft of a comprehensive report that outlines its recommendation. Although the draft report must get further approval from the Royal Swedish Academy of Sciences, in a normal year the prize will have been decided at this juncture.

While writing the report, the Nobel-committee members attend a two-to-three-day meeting, in which they meticulously go through the case for the award. As they do so, Brink says that the committee tries to ensure that information about the prize does not fall into the wrong hands. “We are extremely careful,” he says, explaining that the committee members never, for example, talk about the prize on the phone and that they always travel to have all discussions in person.

Committee members never talk about the prize on the phone and they have all discussions in person

The committee’s draft report is also made available to members of the Physics Class, which consists of about 50 senior physicists, mostly from Sweden. “The class can decide to make another recommendation,” says Brink, who serves as a member of the current Physics Class, despite no longer being on the prize committee itself. “I’m very active in those discussions,” he explains, drawing on his experience as a committee member and the time spent working on and thinking about prize proposals. Brink admits, though, that the class recommends an alternative candidate only “rarely”.

In September, with the official announcement barely a month away, the committee writes a comprehensive scientific report about the imminent winner(s) of that year’s Nobel Prize for Physics. This report is released to the public and the media on the day the prize is announced, along with a much simpler description of the research for non-scientists. All that remains now is final approval from the Royal Swedish Academy of Sciences, which selects the winner(s) through a majority vote. This approval occurs surprisingly late in the process – on the very same morning that the prize is announced.

Given that it’s taken over a year to get to this stage, leaving the final decision to the very last minute might seem precarious. Indeed, very occasionally, it is possible for the committee’s recommendation to be rejected at the final hurdle. Brink says that this happened in 1956 when the committee had initially intended to award that year’s prize to William Shockley, John Bardeen and Walter Brattain for their invention of the transistor in 1947. But during its deliberations, the committee changed its mind, later deciding that it was too early to award a prize for that work and recommending to the academy that no prize should be given that year. However, the academy overruled the committee and the trio were duly recognized after all.

Once the prize has been announced – this year it is due to be revealed at 11.45 a.m. Swedish time on Tuesday 8 October 2019 – Brink says it is “usually a relief because then there is nothing happening until the ceremonies during ‘Nobel week’, as we call it”. The centrepiece of these festivities, which occur in Stockholm in December, is a lavish and elaborate white-tie and ballgown banquet attended by the Swedish royal family. (There’s also a bizarre event at Stockholm University where students force newly minted Nobel laureates to jump around like a frog.)

Selection difficulties

In his time on the committee, Brink mostly covered particle physics and gravitational physics. Indeed, three awards were given during that period to work by particle theorists. In 2004 the prize went to David Gross, David Politzer and Frank Wilczek for discovering asymptotic freedom, which essentially explains why quarks behave almost as free particles at high energies. Four years later, one half of the prize went to Yoichiro Nambu for discovering the mechanism of spontaneous symmetry breaking in particle physics, with the other half shared by Makoto Kobayashi and Toshihide Maskawa for working out how the broken symmetry predicts the existence of quarks.

The 2013 prize, which went to Higgs and Englert, was perhaps the most notorious, with several other physicists having played crucial roles in the theory that led to the discovery of the Higgs boson. “Those years I had to work very hard, really trying to master those subjects,” Brink says. “I had to know exactly what people had done.” It was particularly challenging for these three particle-physics prizes, which were given for theoretical work done decades earlier.

“I had to understand what was happening back then,” Brink says. It involved lots of reading, commissioning confidential reports from experts and discussing the matter with Nobel laureates, he recalls. Indeed, he believes that the reports that the committee prepares and publishes when the prizes are announced are important contributions to the history of physics. “You learn a lot and expose yourself to criticism, but it is important to share the  knowledge.”

Choosing Nobel winners is a heavy responsibility and Brink does have some regrets. One is that only three people can share the prize, and Brink says there have been cases in which deserving candidates were left out. Despite admitting that the three person “rule” – as he describes it – is harsh, Brink says that the academy is hesitant to open the Nobel Prize for Physics up to organizations or collaborations such as CERN. “We don’t want 5000 people calling themselves Nobel laureates,” he says.

But he says limiting the prize to three people is difficult, citing the 2011 award, which went to Saul Perlmutter, Brian Schmidt and Adam Riess “for the discovery of the accelerating expansion of the universe through observations of distant supernovae”. For this prize, Brink did much of the work on scrutinizing the theoretical aspects of the research. It had been carried out by two collaborations: the Supernova Cosmology Project (which included Perlmutter, who was awarded half the prize); and the High-Z Supernova Search Team (which included Schmidt and Riess, who shared the other half of the prize). “We worked for a long time to try to select one or two people from each of the collaborations,” says Brink.

To acknowledge the collaborative aspect of the work, Brink says that the formal prize citation was written so that the winners were described as members of their respective collaborations. Furthermore, the public materials describing the laureates’ work emphasized that it was carried out by two teams, with the 2011 press release, for example, stating that “in 1998, cosmology was shaken at its foundations as two research teams presented their findings”.

In the 2011 prize, a way was found to pick no more than three winners in a field where hundreds, if not thousands, of people had contributed. But Brink admits that the no-more-than-three “rule” is a recurring problem. “If there are four people, what do you do? I don’t have a solution for that,” he says. Fortunately for Brink, the heavy weight of choosing Nobel winners has been lifted now that he is no longer on the committee. “It’s really nice to be free in the summer,” he quips.

Brink says that, after a while, writing and updating reports on candidates became a bit of a burden. He says he did it because he was interested in the fields of physics he covered for the committee – sometimes fields in which there are not currently hot candidates – but he does not miss doing it and that he has full confidence in his successors. “It was difficult the year after [I left] being so involved in it for many years. In some sense, I miss it and on the other hand, as I say, I trust them.”