CERN’s next giant leap is a machine that could unlock the universe

Still full of mystery: the universe, its origins and building blocks are what CERN wants to get to the bottom of. NSF NOIRLab / Keystone

CERN’s Large Hadron Collider transformed our understanding of the universe. Now the European Organization for Nuclear Research wants to build something far bigger, and scientists are united behind it. 

For over 70 years, the CERN research laboratory on the outskirts of Geneva has been the world’s foremost temple of particle physics. It is built on collaboration among 25 member states, ten associate member states as well as observers like the US and the European Union (EU). It is also built on the premise that some questions are too big for any one country to answer alone – questions like: what is the universe made of? Why does matter exist at all? What happened in the first instant after the Big Bang?

In 2012, that premise paid off. Scientists working at CERN’s Large Hadron Collider (LHC) announced the discovery of the Higgs boson – the so-called God particle, which gives mass to fundamental particles, the smallest building blocks of the universe. “Without the Higgs boson, we wouldn’t be here,” says Fabiola Gianotti, who led CERN as director-general for ten years until January this year.  

The future of CERN: a series

The stories in this series look at where the world’s largest particle physics laboratory stands in its scientific ambitions and its efforts to remain an international crossroads for understanding our universe. 

But the discovery raised as many questions as it answered. And now, with the LHC approaching the limits of what it can reveal, CERN is planning its boldest move yet: a new particle collider nearly four times the size of the LHC, buried 200 metres underground, threading beneath Lake Geneva and the Rhône River. Called the Future Circular Collider, or FCC, it should begin operations in the 2040s and would become the largest scientific instrument ever built – and, its proponents argue, the most important. It is also slated to cost CHF15 billion ($19 billion) to build, and CERN’s next big challenge is raising those funds amid challenging geopolitical circumstances. 

“The FCC is extremely important for the field, and if anyone can do it, it is CERN,” says Maria Spiropulu, a CERN collaborator who works at the California Institute of Technology.

What the Higgs left behind

“When I give public lectures, I always pick out eight big open questions in particle physics, and always, half of them have something to do with the Higgs boson,” says Mark Thomson, a British physicist who became CERN’s new director-general in January. Thomson wants to understand why the 12 known fundamental particles have different masses, and whether the Higgs boson itself should be considered a fundamental particle. These are not questions the current LHC can answer with sufficient precision.

Other physicists are drawn to even more fundamental mysteries. Ben Kilminster, a particle physicist at the University of Zurich, is preoccupied with dark matter. “It’s a little bit embarrassing to say that you have a model of all the particles in the universe but you don’t know what the remaining 80–85% of the universe is made of,” he says. Then there is the puzzle of why the Big Bang produced more matter than antimatter.

“The FCC can tackle the biggest number of open questions through independent tests,” says Kilminster.

>>“The most extraordinary instrument ever built”? Watch our video about the FCC:

A machine for the next century

The FCC would be, in its first phase, what physicists call a “Higgs factory”: a machine designed to produce many Higgs bosons under precisely controlled conditions. Electrons and positrons would circulate in a new ring 90.7 kilometres in circumference –  more than three times the length of the LHC – buried up to 200 metres underground.

“The prime motivation for the FCC is really to explore the Higgs in detail and use it to explore the universe in areas we don’t understand,” says Thomson.

In a second phase, potentially operational in the 2070s, the same tunnel would house a proton collider capable of smashing particles together with ten times the energy of the current LHC. This new machine would push current theoretical assumptions to their limits and possibly find new, heavier particles. “You could make particles that have about ten times the mass of current ones,” says Kilminster.

A feasibility study by 1,500 experts and approved by the CERN Council confirmed the scientific case. It reviewed the lab’s scientific objectives, the area’s geology, and the costs and environmental impacts of a new collider. The European Strategy Group, which is appointed by CERN and gathers some of the continent’s most prominent particle physicists, described the FCC as delivering “the world’s broadest high-precision particle physics programme, with an outstanding discovery potential.” There is, says Thomson, “an absolute, clear consensus within the particle physics community that FCC is the right way to go.”

“We looked at all the options, and FCC is clearly the scientifically preferred machine to build,” he says.

>>How the financial side of the FCC is proving to be even trickier than the science:

Beyond physics

While the scientific consensus behind the FCC is firm, the political and social case for the machine is still being negotiated. The necessary CHF15 billion in funding is far from secured, and local opposition is rising. A network of Swiss and French associations, led by the Geneva-based NGO Noé21, has mounted a sustained campaign against the project. CERN’s electricity consumption already amounts to roughly one-third of the power used by the entire canton of Geneva, and construction would generate around 8 million cubic metres of excavation material. “I understand their needs, but it doesn’t mean we must accept something that will cost tens of billions and poison the region for years to come,” says Jean-Bernard Billeter of Noé21.

Thomson acknowledges that the case has yet to be fully made. “We have to demonstrate that we can build this machine in an environmentally responsible way,” he says.

Scientists also point out that the dividends from discoveries made at CERN extend far beyond the lab. CERN is where the World Wide Web was invented. Particle accelerators gave rise to radiotherapy machines used in cancer treatment. High-energy synchrotron light sources, developed at CERN, are today critical tools for analysing new materials and developing new drugs.

The FCC’s second stage would drive advances in high-temperature superconductors for high-field magnets – technology with direct applications in medical imaging and fusion energy. “In particle physics, we try to do the near impossible, and then we develop our technologies to the near impossible, and downstream, something will inevitably come out,” says Thomson.

Phase 1: Rebuilding the LHC

Before any work on the FCC begins, CERN’s existing machine is getting a major overhaul. On June 30, the Large Hadron Collider will shut down for four years. The upgraded machine – known as the High Luminosity LHC, or HiLumi – aims to produce roughly ten times more proton collisions than the LHC’s original design, enabling far more detailed measurements of the Higgs boson, including how it interacts with itself for the first time.

Physicists will install new magnets made of novel superconducting materials, generating magnetic fields of 11.3 tesla – up from the current 8.6. Maria Spiropulu of CalTech has helped develop a new timing detector for the CMS experiment, able to distinguish collisions that occur just 30 picoseconds apart.

The HiLumi upgrade is, in Thomson’s words, “a new era for the LHC” – and a scientific bridge to whatever comes next.

Edited by Gabe Bullard and Veronica DeVore/dos