The Large Hadron Collider (LHC), run by CERN (the European Organisation for Nuclear Research), is one of the largest, most expensive, and most ambitious science experiments in history. The particle accelerator, and the 17-mile tunnel under France and Switzerland that houses it, took ten years to build. Since its opening in 2008, it has closed twice for upgrades – first between 2013 and 2015, and then in 2018 until now (with resumption of operations planned for 2021). Estimates vary, but it seems to have cost $5 billion to build and $1 billion each year to run.

In 2012, the LHC achieved its most significant discovery – the Higgs boson. This particle, whose existence was first predicted in the 1960s, is responsible for giving other particles mass. Now CERN has even grander plans. They have proposed constructing a new particle accelerator, the so-called Future Circular Collider (FCC), which would be four times larger in diameter and six times more powerful than the LHC.

“They have proposed constructing a new particle accelerator, the so-called Future Circular Collider (FCC), which would be four times larger in diameter and six times more powerful than the LHC.”

The FCC would be a so-called “Higgs factory”, allowing the still-mysterious particle to be studied in much greater detail. Supporters of the project argue that it could lead to new discoveries that would transform our understanding of physics. But others – including some experts in the field – have questioned whether the FCC would be a good use of money at all.

The LHC itself was controversial. Construction started not long after the Superconducting Super Collider, an American project that would have been more powerful than the LHC, was cancelled due to budgetary concerns; billions has been spent on it already. The LHC first functioned in 2009, soon after the global financial crisis; this was a year later than planned, due to a helium leak in September 2008 that required extensive repairs. Other minor issues have also caused problems; in 2016, the accelerator was switched off for several days when a weasel made its way into the electrical equipment.

Whilst the discovery of the Higgs boson was a huge achievement, and led to a Nobel Prize for its predictors in 2013, it did not come as a surprise. The Higgs boson is part of the standard model of physics, which is an extremely successful theory, but also one we know to be incomplete – it fails to explain phenomena such as dark matter.

“Particle physicists had hoped that the LHC would be able to discover fundamentally new physics; more than a decade since it was switched on, it hasn’t.”

Others argue that the accelerator has been a success; the Higgs boson could have turned out not to exist, after all, and there have been other discoveries, such as new exotic particles like tetraquarks and pentaquarks. It has also generated huge amounts of data in support of the standard model – again, something that was far from certain. Unlike the LHC, the FCC would not be looking for a specific particle – it would be “much more exploratory”, as Professor John Butterworth says. We could discover almost anything.

Or almost nothing.

The German physicist Sabine Hossenfelder contends that there is no reason to believe that the FCC would lead to a breakthrough in physics. The tens of billions of pounds it would cost could well be at best a huge gamble, and at worst a huge waste. In a blog post in 2018, she went further, arguing that some physicists “fabricate arguments for why a next larger collider should see new particles”, and that people have been too drawn to “beautiful” mathematical theories of physics, such as supersymmetry, despite a lack of evidence.

Other scientists agree that the FCC may not be worth the money. Jared Kaplan, another physicist, has said that “[t]he scientific case is weaker than it has been for past colliders”, and disputes the claim that the FCC would lead to useful technological improvements. Many also argue that the billions invested in colliders could be better spent on cheaper experiments, or on other areas of science altogether.

It is uncertain if the FCC will ever be constructed. CERN is funded by European countries, including the United Kingdom (whose membership is unaffected by Brexit), and they may well prove unwilling to pay the billions required – particularly after the economic problems caused by the coronavirus pandemic. What will happen to particle physics if it is not built? A Chinese proposal for a similar-sized collider, the Circular Electron–Positron Collider, is one possibility, but whether it is ever built is far from certain. Without a new, larger collider, the field would need to reconsider its plans for the coming decades.

Would the FCC have practical benefits to our lives? Probably not. Would it transform our understanding of physics? Again, probably not. It would teach us something about the universe we live in, even if that just involves refining the standard model or disproving a few hypotheses. Basic, theoretical research in the sciences has always been seen as important, and rightly so, irrespective of whether it leads to practical benefits or not. The question ultimately is: how much are we willing to pay to learn a little more about the world we live in?