The man taking over the Large Hadron Collider – only to switch it off | Cern
Mr.Ark Thomson, professor of experimental particle physics at the University of Cambridge, has landed one of the most coveted jobs in global science. But it’s hard not to wonder, from one angle, if he took one for the team.
On January 1, Thomson took over as general director of Cern, the multi-Nobel prize-winning nuclear physics laboratory located in the suburbs of Geneva. It is here, deep underground, that the Large Hadron Collider (LHC), the largest scientific instrument ever built, recreates the conditions that existed just microseconds after the Big Bang.
The machine earned its place in history thanks to the discovery of the mysterious Higgs boson, whose accompanying field transforms space into a kind of cosmic glue. But one of the first things Thomson will do is shut down the machine for engineering work. He will only resume when his term is almost over.
In an office on the first floor of the Cavendish laboratory, in front of a model of the DNA double helix discovered in Cambridge by James Watson and Francis Crick more than 70 years ago, Thomson is far from inconsolable about the closure. On the contrary, he is enjoying what the next five years have in store for him.
“The machine works wonderfully and we record huge amounts of data,” he says. “There will be a lot to analyze during this period. The physics results will continue to come in.”
Thomson’s background is far from academic: he attended a comprehensive school in Worthing, West Sussex, and only took a liking to physics after reading a popular book about science at Cern in his early teens. “That kind of turned me on to management,” he says. “I wanted to understand how the universe worked.” He became the first in his family to go to university and study physics at Oxford.
The LHC accelerates protons, the nuclei of hydrogen atoms, to near the speed of light inside a 27 km-long ring beneath the French-Swiss countryside. At four points around the ring, protons shooting in one direction are directed toward others rushing toward them. The energy of the impact creates a shower of new particles which are recorded by the LHC detectors. According to Einstein’s seminal equation E=mc2more energy produces more massive particles.
Starting in June, the shutdown will make way for the High-Luminosity LHC, a major upgrade that involves installing powerful new superconducting magnets to compress the collider’s proton beams and make them brighter. This will increase the number of collisions in the machine tenfold. The detectors are also strengthened, making them better able to capture the subtle signs of new physics that collisions can reveal. “It’s an incredibly exciting project,” says Thomson. “It’s more interesting than sitting here with the machine running.”
If this upgrade works, the LHC will make more precise measurements of particles and their interactions, which could reveal flaws in today’s theories that will form the foundations of tomorrow’s. An enduring mystery surrounds the Higgs boson. Elementary particles get their mass from the Higgs, but no one knows why the masses vary like this. It’s not even clear how Higgs bosons interact with each other. “We might see something completely unexpected,” says Thomson.
Commissioning the high-luminosity LHC will dominate Thomson’s five-year mandate. But a much larger and more controversial project also requires his attention. The LHC reaches the end of its life around 2041 and CERN member states must decide what happens next. The favorite is a colossal machine called the Future Circular Collider, or FCC.
According to Cern’s feasibility report, the FCC would be more than three times larger than the LHC, which would require digging a new 91 km circular tunnel up to 400 meters underground. The machine would be built in two stages. The first, launched in the late 2040s, would cause electrons to collide with positrons, their antimatter partners. In the 2070s, this machine would be demolished to make way for a new collider capable of smashing protons at an energy seven times that of the LHC. The first phase will cost around 15 billion Swiss francs or £14 billion.
The engineering alone is ambitious, but the FCC faces broader challenges. The CERN member states, which will vote on the project in 2028, cannot pay the entire bill, hence the need to turn to other contributors. Meanwhile, a debate rages over whether it is the best machine for making new discoveries. It is not guaranteed to answer the big physics questions: what is the dark matter that clusters around galaxies; what is the dark energy that divides the universe; why is gravity so weak; and why did matter take over antimatter during the formation of the universe? Without a clear goal to aim for, Thomson’s task will be more difficult.
But Cern has always been much more than science. Thanks to this laboratory, Europe is the world leader in particle physics, attracting tens of thousands of researchers and advancing the need for new technologies. But other countries, notably the United States and China, have their own plans for advanced colliders. Whether Cern retains its pre-eminence will depend on the LHC’s successor.
“We’re not yet at the point where we’ve stopped making discoveries and FCC is the natural progression. Our goal is to understand the universe at its most fundamental level,” says Thomson. “And now is absolutely not the time to give up.”
