Mark Thomson, a professor of experimental particle physics at the University of Cambridge, has landed one of the most coveted jobs in global science. But it is hard not to wonder, when looked at from a certain angle, whether he has taken one for the team.
On 1 January, Thomson takes over as the director general of Cern, the multi-Nobel prizewinning nuclear physics laboratory on the outskirts of Geneva. It is here, deep beneath the ground, that the Large Hadron Collider (LHC), the largest scientific instrument ever built, recreates conditions that existed microseconds after the big bang.
The machine won its place in history for discovering the mysterious Higgs boson, whose accompanying field turns space into a kind of cosmic glue. But one of the first things Thomson will do is turn the machine off for engineering work. It will not restart until his term is nearly over.
In an office on the first floor of the Cavendish laboratory, past 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 disconsolate about the shutdown. If anything, he is relishing what the next five years hold.
“The machine is running brilliantly and we’re recording huge amounts of data,” he says. “There’s going to be plenty to analyse over the period. The physics results will keep on coming.”
Thomson’s background is far from academic: he went to comprehensive school in Worthing, West Sussex, and got a taste for physics only after reading a popular book about science at Cern in his early teens. “It kind of set my direction,” he says. “I wanted to understand how the universe worked.” He became the first in his family to go to university, reading physics at Oxford.
The LHC accelerates protons, the nuclei of hydrogen atoms, to nearly light speed inside a 27km-long (16-mile) ring under the French-Swiss countryside. At four points around the ring, protons zipping in one direction are steered into others rushing towards them. The energy on impact creates a shower of new particles that are recorded by the LHC’s detectors. In line with Einstein’s seminal equation E=mc2, more energy yields more massive particles.
The Large Hadron Collider (LHC) nuclear particle accelerator at Cern, pictured in 2018. Photograph: EThamPhoto/Getty Images
Starting in June, the shutdown will make way for the high-luminosity LHC, a major upgrade that involves installing powerful new superconducting magnets to squeeze the collider’s proton beams and make them brighter. This will raise the number of collisions in the machine tenfold. The detectors are being strengthened too, making them better able to capture the subtle signs of new physics collisions can reveal. “It’s an incredibly exciting project,” Thomson says. “It’s more interesting than just sitting here with the machine hammering away.”
If the upgrade works, the LHC will make more precise measurements of particles and their interactions, which could find cracks in today’s theories that become the foundations for tomorrow’s. One remaining mystery surrounds the Higgs boson. Elementary particles gain their masses from the Higgs, but why the masses vary as they do is anyone’s guess. It is not even clear how Higgs bosons interact with one another. “We could see something completely unexpected,” Thomson says.
Getting the high-luminosity LHC up and running will dominate Thomson’s five-year tenure. But a much larger, and more controversial, project requires his attention, too. The LHC reaches the end of its life around 2041 and Cern’s member states must decide what comes next. The frontrunner is a colossal machine called the Future Circular Collider or FCC.
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According to Cern’s feasibility report, the FCC would be more than three times the size of the LHC, calling for a new 91km circular tunnel to be bored up to 400 metres underground. The machine would be built in two stages. The first, starting in the late 2040s, would collide electrons into positrons, their anti-matter partners. At some point in the 2070s, that machine would be ripped out to make way for a new collider that smashes protons at seven times the energy of the LHC. The first phase will cost an estimated 15bn Swiss francs or £14bn.
The engineering alone is ambitious, but the FCC faces wider challenges. Cern’s member states, who will vote on the project in 2028, cannot foot the whole bill, so other contributors are needed. Meanwhile, a debate is rumbling on over whether it is the best machine for making new discoveries. It is not guaranteed to answer any big questions in physics: what is the dark matter that clumps around galaxies; what is the dark energy that pushes the universe apart; why is gravity so weak; and why did matter win out over antimatter when the universe formed? With no clear prize to aim for, Thomson’s job will be harder.
But there has always been more to Cern than science. Because of the lab, Europe is the world leader in particle physics, attracting tens of thousands of researchers and pushing forward a need for new technologies. But other countries, notably the US and China, have their own plans for advanced colliders. Whether Cern retains its pre-eminence depends on the LHC’s successor.
“We’ve not got to the point where we have stopped making discoveries and the FCC is the natural progression. Our goal is to understand the universe at its most fundamental level,” says Thomson. “And this is absolutely not the time to give up.”
