Traces of particle collision and decay in LHC

Interview with Guido Tonelli, particle physicist at CERN

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Guido Tonelli is an Italian particle physicist best recognised for his role in the discovery of the Higgs Boson at the Large Hadron Collider (LHC). He is a professor at the University of Pisa and his third book translated into English, Genesis, charts billions of years of cosmological evolution using the metaphor of the seven days of creation.

Tonelli is one of the few particle physicists to have been visible to the public. Involved for decades with work on the Compact Muon Solenoid (CMS) experiment at the LHC at CERN, he was one of two spokespeople – the other being Fabiola Gianotti of ATLAS – who presented the first evidence of the presence of the Higgs Boson in a seminar in December 2011.

Genesis: The Story of How Everything Began emerged from conservations with non-scientists: friends, people he was called on to debate, students, and members of the public. During these discussions, he became certain that it is possible to explain his work in ordinary, accessible language rather than the scientific syntax that takes years to learn to use. Tonelli told E&T that he wanted to use that language to share science; not only for practical purposes, but because it is exciting and informs our perceptions of ourselves.

“With some effort it is possible to write, to express the beauty of these ideas such that the general public can share this beauty. It felt like a duty, let’s say a sort of moral need [to share the science],” he said. “The importance of science in society – not just for technology, not only for the tools that science is able to develop which change the lives of millions of people – but how it changes the shape of our thinking, the way we look at ourselves and the universe.”

“I can remove this barrier, I can give the flavour – the basic concept – without losing rigour and accuracy, while using the language which is understood by everybody. This is why, in my book, the connection with culture is important – the connection with music, painting, art, philosophy – because this will make the reader feel at home. We are not in discussion with a scientist who uses language which is completely impossible to understand, you are discussing it with a friend who is trying to explain to you the beauty of this idea.”

Genesis perhaps presented a greater challenge than popular science books usually do. The concepts covered in the book seem to contract not only common sense but logic, such as the idea that there was no “before” the Big Bang and other “things that cannot be imagined”. This presented Tonelli with the question of whether ordinary human language can fail us when it comes to talking about the fundamental nature of the universe, which is described by physicists using mathematics.

“Our mind, our brain, and our language were developed as a tool to survive in the environment in which matter, ordinary matter, behaves in a certain way – completely different to the way matter behaves when it is very small objects, elementary particles, or really huge objects like a galaxy,” Tonelli explained.

“Our way of looking at things has been a powerful tool to allow humankind to expand all over the planet earth but as soon as you move away from this thin surface and go deeply to the small distances to explore with a particle accelerator or the very long distances explored by huge telescopes – matter in these worlds behave in a way that is completely unusual for us.”

He adds that scientists struggle to get their heads around this just as much as non-scientists. After all, scientists are human too, and no more rational by temperament than anyone else (“scientific research is one of the hottest environments in terms of emotion!”).

Genesis uses the analogy of the Biblical seven days of creation to describe the development of the universe, with the “days” varying in length from 10-35 seconds to 13.8 billion years. Tonelli has filled his book with original metaphor and analogy, having a real distaste for simple school-physics analogies which compare cosmological objects to mundane objects such as fruit and footballs.

“If I need to use metaphors and analogies, why should I use something which is childish? I’d think Oh my god this is too naïve. When I could give the same flavour using art or history or personal experience? […] I decided to use these to transmit the basic concept at a certain high level, having confidence in the reader,” he said. “Maybe you don’t understand all of what I say in terms of science but if you read this book, you are curious and you are curious not only in science but in general in culture, in music, in art, history.”

His use of metaphor extends to animating particles and astronomical objects and infusing them with character; quasars are like cosmic dragons, he writes, while neutrinos are shy. One often gets the impression that Tonelli is creating a cosmological mythos. This is deliberate, Tonelli said; he wanted to create the sense of engagement children experience when told fantastic stories by their parents.

Tonelli came from a working-class family; his father was a railway worker and amateur painter. He credits his father’s artistic perspective with helping him see the beauty in nature with “an eye that was somehow trained to look for beauty in small details”. This, in turn, led him to becoming a scientist.

Many scientists before him have spoken eloquently about the beauty in science, but Tonelli is also frank about the realities of the life scientific: the up-and-down emotions while working on such a huge project as the search for the Higgs Boson, the particle which – in the very simplest terms – gives things mass. He describes it as painful, frustrating, full of crises but culminating an outpouring of exhilaration in the CERN community which he compared with football fans seeing their team win a major tournament (“a collective explosion of joy”). Even now, more than a decade later, he sometimes wakes and wonders if it can be true that he and his colleagues made this historic discovery.

“It’s difficult to explain the emotion that we felt in the weeks in which we were close to the major discovery of the Higgs Boson, it was like being in a roller coaster because everything seemed to be converging towards the announcement […] there is nothing you can compare with the feeling you have, once you realise you are among the first human beings looking at a state of matter that has never been seen before.”

In Tonelli’s view, the search for the Higgs attracted so much attention due to scare stories that circulated around the switching-on of the LHC, stories about it creating a black hole that would swallow Earth. This may sound amusing now, but he recollects people being sincerely afraid and the LHC sticking in the public conscience. This meant that the search was followed by more press attention than he could have possibly expected, as a particle physicist. A press conference had been called in December 2011 with the expectation that 10-20 journalists would attend, but 250 attended. The “official” announcement that followed was unprecedented, becoming a highlight in world news.

As a spokesperson for CERN – especially for an experiment that had been associated with public panic – there was unbelievable pressure on Tonelli and Gionnati. He recalls journalists doing their best to encourage them to admit that they had found the Higgs Boson when they said that they were only at three sigma certainty: “They knew, they saw it in our eyes! But in the end they were very accurate in their reporting”.

He said that he felt a great responsibility to represent a huge community of people, including junior colleagues whose careers could be jeopardised if he misspoke. “If we announce a fake discovery, the people that announce the discovery might lose some credibility but they are still a professor, in a tenure track position, while the young students or people planning to get a contract? Their life could be destroyed by a word you use, so you are protecting their credibility”.

Looking ahead, Tonelli is filled with excitement about the potential discoveries that could occur in his lifetime.

“Let’s say 10 years, assuming everything goes well and there’s no other pandemic, [I would like to see] mankind to make progress in two issues. Dark matter is something that really disturbs me, it disturbs many other scientists. We need to grasp this component that accounts for a quarter of the universe; it is embarrassing to continue to say we have no idea what it is made of!”

“The other one is the inflation – the real mechanism – that transforms this microscopic fluctuation of the vacuum. We may have an identity – we know many characteristics of this particle – but we have not yet discovered it. I think we could have surprises coming both from particle accelerators and gravitational wave detectors; they look for signs of gravitational waves coming from the inflationary stage which could give us additional information,” he said. “Having two tools that could be used to limit the corner in which we might find the particle responsible for inflation.”

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