CERN's Future Circular Collider: The Next Giant Leap in Particle Physics

Three Times the LHC

In early 2025, CERN’s governing council took a historic decision: to move forward with the feasibility study for the Future Circular Collider, the most ambitious particle physics project ever conceived. If built, the FCC would be a 91-kilometre underground ring beneath the French and Swiss countryside — more than three times the circumference of the Large Hadron Collider.

The goal is nothing less than to crack the mysteries the LHC has exposed but cannot solve on its own.

Why the LHC Is Not Enough

The LHC’s discovery of the Higgs boson in 2012 completed the Standard Model — but also deepened its puzzles. The Higgs mass is unnaturally light according to theoretical calculations, suggesting unknown physics is stabilising it. The Standard Model cannot explain dark matter, the matter-antimatter asymmetry, or why gravity is so much weaker than the other forces.

The LHC has searched extensively for new particles but found none beyond the Standard Model. This does not mean they do not exist — it may simply mean they are too heavy or too weakly interacting for the LHC’s energy and precision to reach. The FCC would extend both frontiers dramatically.

Two Machines in One Tunnel

The FCC programme is planned in two phases:

Phase 1: FCC-ee (Electron-Positron Collider)

The first machine would collide electrons with positrons at energies between 90 and 365 GeV. Electron-positron collisions are far cleaner than proton-proton collisions — there is no debris from composite particles, making precision measurements exquisitely accurate.

FCC-ee would operate as a “Higgs factory,” producing millions of Higgs bosons and measuring their properties to sub-percent precision. It would also precisely measure the W and Z bosons, the top quark, and search for exotic particles with very weak couplings — including potential dark matter mediators.

Phase 2: FCC-hh (Proton-Proton Collider)

After FCC-ee completes its programme, the same tunnel would house a proton-proton collider reaching 100 TeV — seven times the LHC’s current energy. At this scale, entirely new particles could be produced directly. FCC-hh could discover heavy partners of known particles, probe the Higgs self-coupling (revealing whether our universe’s vacuum is truly stable), and potentially produce dark matter particles.

The Engineering Challenge

Building a 91-kilometre tunnel at depths of 100–400 metres through the geological complexity of the Geneva basin is a colossal engineering undertaking. The tunnel would pass beneath Lake Geneva and through multiple rock types, requiring advanced tunnel-boring technology.

The magnets for FCC-hh would need to generate fields of 16 Tesla — nearly double the LHC’s current magnets — requiring advances in high-temperature superconductor technology. This magnet R&D is already underway and could have spin-off applications in fusion energy, medical MRI, and industrial processes.

The energy consumption of such a machine is a legitimate concern. CERN is investigating powering the FCC with renewable energy and using waste heat for district heating in nearby communities.

The Scientific Stakes

Several fundamental questions motivate the FCC:

The Higgs sector — Is the Higgs boson truly elementary, or is it composite? Does it couple to itself as the Standard Model predicts? Are there additional Higgs bosons? Precision Higgs measurements are the most promising route to answering these questions.

Dark matter — If dark matter particles interact with ordinary matter through any force other than gravity, the FCC’s energy reach and precision could detect them. Many theoretical models predict dark matter candidates in the mass range accessible to FCC-hh.

Matter-antimatter asymmetry — The universe is made almost entirely of matter, but the Standard Model cannot explain why. New sources of CP violation (the asymmetry between matter and antimatter processes) might be visible at FCC energies.

Unification — Some theories predict that the four fundamental forces merge into one at extremely high energies. While the FCC cannot reach unification energies directly, it could find the new particles that mediate this merging.

Beyond Pure Science

Historically, every generation of particle accelerator has produced transformative technologies. The World Wide Web was invented at CERN to share LHC data. Proton therapy for cancer grew from accelerator expertise. Superconducting magnet technology developed for colliders is now used in MRI scanners, maglev trains, and fusion reactors.

The FCC’s R&D programme is expected to advance high-temperature superconductors, cryogenics, vacuum technology, data science, and energy-efficient computing — technologies with applications far beyond physics.

The Debate

Not everyone agrees the FCC is the right investment. Critics argue the money could be better spent on smaller, more targeted experiments, or on pressing societal challenges. Supporters counter that fundamental research has an unmatched track record of generating unexpected breakthroughs and that the international collaboration model spreads costs across dozens of countries over decades.

What is not in dispute is the ambition: the FCC represents humanity’s determination to understand the deepest laws of nature, pushing the boundaries of both scientific knowledge and engineering capability into the second half of the 21st century.