With CERN’s Large Hadron Collider about to reopen after a two-year upgrade, any failure to uncover new physics would be a huge roadblock to progress

Will the revamped LHC make or break physics? (Image: Enrico Sacchetti)

NATURE has proven remarkably accommodating to particle physicists over the past century. Take the photon, devised by Einstein in 1905 as a theoretical convenience to help explain electromagnetism and light. Nature obliged, and the photon turned out to be real. A quarter-century later, Paul Dirac conjured up antimatter. It soon turned up in cosmic rays.

And so to 2012, when jubilant physicists at CERN’s Large Hadron Collider, near Geneva in Switzerland, announced that they had found the Higgs boson pretty much where they expected it.

The discovery of the Higgs put the finishing touch to the standard model of particle physics. Barring a few small wrinkles, everything this theory predicted has now been confirmed experimentally. But completion of the model still leaves a lot for physics to explain, with no clear indication of where to go next.


With the LHC powering up again after a two-year refit, for the first time there is no consensus on what it should find (see “It’s the faster, stronger, better Large Hadron Collider“). If the theoreticians keep their run of success going, it should turn up the first decent evidence for supersymmetry, the next-generation theory that could explain dark matter, gravity and other phenomena not covered by the standard model. But then, if you believe the theories, the LHC should already have seen many such indications. It hasn’t.

That leaves theorists and experimentalists alike in a state of excitement and trepidation. The rebooted LHC could demonstrate that supersymmetry is on the right track, albeit not quite as we expected. It could find a clutch of new particles that point in a surprising direction. Or it could find nothing. Either of the first two scenarios would be exciting. The last looms ominously.

“It would be a real sadness if the LHC discovers nothing, because then the subject I love would come to an end. But if that’s the way the universe is, that’s the way it is,” David Tong, professor of theoretical physics at the University of Cambridge, told the audience last month at a New Scientist event in London. If the upgraded LHC isn’t powerful enough to make progress, the days of smashing protons together to reveal the fundamental nature of reality are probably over. We could not be confident of finding anything new until we reached vastly greater energies – too great for any collider conceivable today.

“It would be a real sadness if the LHC discovers nothing, because then the subject I love would come to an end”

But there are alternatives. Some argue that messy collisions between protons are not the ideal way to find physics beyond the standard model. Plans already exist for more precise electron colliders – from the International Linear Collider, which might be built in Japan, to a circular collider at CERN up to 100 kilometres long – far bigger than the LHC.

Our quest to understand the nature of reality thus stands at a crossroads. Past success has bred confidence in the Big Physics approach. Government agencies, emboldened by the excitement of discovery and the emergence of spin-offs like the World Wide Web, have been happy to spend billions of dollars on particle experiments. But if the LHC comes up with nothing, will the confidence still be there to fund the next generation of machines?

Many physicists would claim that their success over the years owes more to judgement than luck. Now, without the steady hand of agreed theory to guide the way, they may need all the luck they can get.

This article appeared in print under the headline “Double or nothing”