Scientists are refining plans to build the world’s biggest machine at a site beneath the Swiss-French border. More than $30bn (£23bn) would be spent drilling a 91km circular tunnel in which subatomic particles would be accelerated to near light speeds and smashed into each other. From the resulting nuclear debris, scientists hope they will then find clues that would help them understand the detailed makeup of the universe.
It is an extraordinarily ambitious project. However, it is also a controversial one – for many scientists fear the machine, the Future Circular Collider (FCC), could soak up funding for subatomic physics for decades and leave promising new research avenues starved of resources.
Others argue that the mega-collider is being imposed on physicists by senior officials at Cern, the European Organization for Nuclear Research, without properly consulting researchers.
“I’m amazed to see how they are lining up this concept,” particle physicist Halina Abramowicz of Tel Aviv University told the Observer. “This is not how things are supposed to work. The physics community is supposed to tell Cern what should be the next step, not the other way round.”
These arguments have led the journal Nature to warn this month that “a battle is under way for the future of particle physics”. Its analysis of the views of dozens of leading physicists revealed that many were critical of the proposed collider and warned it could trigger dangerous divisions between groups. The discontent has reached an unprecedented pitch, many researchers told the journal Nature.
For its part, Cern says that the FCC offers scientists a chance to undertake “a unique exploration of space, time and matter”. The plan is supported by many senior physicists and vigorously promoted by Cern’s current director general, Fabiola Gianotti, and also backed by Mark Thomson, who is set to take over her post in January 2026. “If approved, the FCC would become the most powerful instrument ever built to study the laws of nature at the most fundamental level,” Gianotti told Nature.
Since its formation in 1954, Cern – which is based in Geneva – has become a much-lauded example of the effectiveness of international scientific cooperation and has earned itself a reputation for generating world-leading research over the decades.
Its Large Hadron Collider (LHC) – currently the world’s biggest machine – revealed the existence, in 2012, of the Higgs particle. This was the first direct evidence that a field – known as the Higgs field – permeates the universe and is responsible for giving different fundamental particles their various masses.
However, the LHC is scheduled for closure by 2040 and many puzzles about the structure of the universe remain unsolved, despite hopes it would provide more major insights. Persisting mysteries include the nature of dark matter, whose existence is inferred from its gravitational influences on galaxies but whose exact makeup is unknown. Similarly, the fact that our universe is made up of matter – while antimatter is almost nonexistent – cannot be explained from current observations.
To get round these problems, Cern has proposed building its new mega-collider, which would be a much more powerful and much bigger version of the LHC. It would be built in two stages. The first would generate Higgs particles in vast numbers in order to understand their critical role in influencing other fundamental forces and would come online around 2040. Then it would be repurposed after a few decades so it could collide protons at vast energies and provide new data about the universe. This version would begin operations around 2070.
However, the technology to accelerate protons at the unsurpassed energies proposed for the FCC does not exist yet. It is merely assumed that, in 40 years’ time, it will have been developed. Such an assumption worries some scientists, as well as the fact that the FCC will cost so much that it will lock scientists into a device that would monopolise funds for particle physics for decades.
“What worries me most is that, by investing all this money, we will be stopping the development of other technologies because there will be no money for them. The FCC could soak up funds for years and years,” said Abramowicz, who dismissed the idea of the mega-collider as “a toy” that could certainly not be guaranteed to fix the holes that exist in current theories.
Instead, researchers have suggested that linear accelerators – which would fire particles in straight lines – might prove to be cheaper, more flexible and more likely to achieve results than a circular collider. This point was backed by Jenny List, a researcher based at the German accelerator centre Deutsches Elektronen-Synchrotron (DESY) in Hamburg.
“There are other technologies on the horizon that could be used to accelerate particles like the proton without needing huge magnets or tunnels,” she said. “Plasma wave technology is one of these. Current devices are small, but within 20 years or so we could find they are ready to use to run a big collider.”
However, if the FCC were given the go-ahead, it could lock up funds for decades and end up dictating the direction that particle physics will have to take for much of the century, List added.
“We will be telling future generations exactly what to do scientifically, and so we need to ask ourselves today: who are we to decide what our grandchildren should research and not research?”
• The headline and text of this article were amended on 30 March 2025. An earlier version mentioned a quote said to have been given to the journal Nature by Prof Ruben Saakyan. That quote had appeared in the print version of the journal but Nature added a correction to the online version of its article saying that it had “erroneously attributed the observation about the level of discontent to a specific researcher.”
