In a recent opinion piece for Scientific American, physicists Grigoris Panoutsopoulos and Frank Zimmermann advocate spending billions of dollars on what would be the largest particle collider yet—the Future Circular Collider (FCC), currently planned at CERN, near Geneva. Their argument, in a nutshell, is that we should stop asking particle physicists to justify large investments into their research area and just give them money. I strongly disagree.
In the past decades, particle physicists have made headlines claiming their colliders would probe the creation of the universe, find new “supersymmetric” particles or tell us what constitutes dark matter. This narrative was already spun for the (canceled) Superconducting Super Collider in the 1990s, but it has been particularly pervasive for CERN’s current particle collider, the Large Hadron Collider (LHC). Indeed, the essay by Panoutsopoulos and Zimmermann also starts with an appeal to these big questions—unsurprisingly so, because these are particle physicists’ best sales points, as the authors know full well.
Unfortunately, the LHC has not shed light on the big questions it was sold with the promise of answering. Instead, the mega experiment has made it painfully clear that particle physicists have greatly exaggerated the promise of their research. Rather than being a long-awaited triumph, the LHC has demonstrated that particle physicists’ arguments that their colliders would help answer the big questions were wrong. Consequently, now such physicists do not have plausible arguments for why a bigger collider should make a fundamentally new discovery.
A bigger machine would measure more precisely the properties of the already known particles. And of course, one cannot exclude that it would make a new discovery. But we currently have no reason to think a new discovery is plausible. And spending billions just to put a next digit on some constants is a tough sell.
Absent compelling scientific arguments for why the new particle collider is a good investment, Panoutsopoulos and Zimmermann try to convince their readers no reason is necessary. Instead they advocate that experimentation should “assume the leading role, so that it can help get the stuck wagon of particle physics moving and out of the mire.”
Their assertion is an improvement over earlier arguments that rested on concocting theoretical reasons for building a collider. But Panoutsopoulos and Zimmermann’s reasoning isn’t any more convincing, because the current stagnation in particle physics was not caused by a lack of experiments.
Following the stunning success in the first half of the 20th century, the foundations of physics have been showered with generous funding. Until the 1970s, theory and experiment progressed hand in hand, and physicists completed the theoretical underpinnings of the Standard Model of particle physics. A “theory of everything” seemed within close reach.
But after the 1970s, further experiments merely confirmed the already known theories. The particles of the Standard Model that were still missing in the 1970s have since been detected. The last missing particle, the Higgs boson, was found at the LHC in 2012. The theory for the Higgs boson, as well as those for other new measurements—such as neutrino masses or the cosmological constant—date to before the 1970s.
Today, at half a century of age, the Standard Model is still particle physicists’ best take on the structure of matter. A theory of everything is nowhere in sight. Searches for further particles with ever larger particle colliders and an artillery or medium- and small-scale experiments have consistently returned nothing new.
So, no, it is not a lack of experimentation that has given rise to this phase of stagnation. The reason progress in the foundations of physics has stalled is simply that physicists have been careless when deciding what experiments to make. Much expense and effort has been wasted this way already. Mindlessly throwing money at bigger experiments in the desperate hope to recover some of particle physics’ lost relevance is not the way forward. The lesson particles physicists should have learned from 40 years of stagnation is to think more before investing money, not to ask for a free pass to unthinkingly spend billions.
Panoutsopoulos and Zimmermann’s declared hope to make particle physics come unstuck therefore merely returns us to the question of which experiment we should finance to make that hope a reality. And to answer the question posed by their essay’s title—“Which Should Come First in Physics: Theory or Experiment?”—we should obviously draw on all available information when we have to decide what experiment to do next. We need to know what is feasible and we need realistic expectations for the turnout.
Let us therefore recap what we know: A larger particle collider is presently extremely costly as compared with other planned but unfunded large-scale experiments into the foundations of physics, such as telescopes, satellite missions, gravitational–wave interferometers or high-precision measurements. At the same time, we have no reason to think that this larger collider would help us solve any of the open problems in the foundations of physics, while many of the other experiments stand a better chance of doing so.
This means a large collider presently has a high cost and little expected benefit. Existing alternatives have a lower cost and higher benefits. We should thus do the other experiments first and reconsider building larger colliders when their costs come down or when new evidence emerges that makes building them more scientifically promising.
In their essay, Panoutsopoulos and Zimmermann seek support in a quote from Victor Weisskopf, former director-general of CERN, according to whom “machine builders are the most important [kind of physicists].” This quote dates to 1977, the time when the stagnation in particle physics began.
We do not live in the 1970s anymore. It’s about time particle physicists wake up and show some respect for the taxpayers who finance their research. “Just do it” is not reason enough to spend billions of dollars.