All that remains to be done is to dot the ‘i’s and cross the ‘t’s: that’s a recurring refrain in physics, and one that’s invariably wrong. At the dawn of the 20thcentury, there were those who were saying that physics was complete. Fortunately, there were others who chose to focus on the apparently innocuous clouds obscuring the contemporary theory’s horizon. Thanks to them, we now have quantum mechanics and relativity, concepts that underpin today’s physics, not to mention a raft of industries that would be impossible without them, even though quantum mechanics and relativity were literally unimaginable within the paradigm of 19thcentury physics. 

We’re in a similar situation today, although the clouds are somewhat bigger. After decades notching up success after success, the Standard Model rules supreme over the world of fundamental particles. Discoveries such as that of the top quark in 1995 fit precisely into the theory like pieces in a jig-saw puzzle.

The discovery of the Higgs boson was different. Paradoxically, it was both the crowning achievement of the Standard Model, and the biggest cloud to rain on its parade. We know the Standard Model is incomplete; the discovery of the Higgs introduced us to a range of fundamental forces hitherto unprobed. It’s for this reason that we need to plan for a future collider to pick up the reins when the LHC reaches the end of its lifetime in the second half of the 2030s. The discovery of the Higgs is simultaneously the end of one journey, and the start of another. Just as Galileo could not have anticipated where his innovation would lead when he perfected the telescope, we cannot predict where future colliders will take us in terms of bringing new knowledge. Then as now, one thing is certain: such innovations lead to great rewards. 

The telescope is a fitting comparison, since today the fields of particle physics and cosmology are inextricably intertwined. They increasingly address the same questions from opposite ends of the distance scale. If we are to ensure that humankind’s centuries-old voyage of scientific discovery in fundamental physics does not come to an end, we need a globally coordinated effort with a diversified experimental programme ranging from particle physics to observational cosmology, astroparticle physics and beyond. In this mix, high-energy particle colliders will remain an indispensable ingredient. CERN, and European physics have always been in the vanguard of accelerator science, and have much to offer to the field as we move beyond the LHC era. The future of fundamental physics needs colliders as much as ever, and that’s why this update of the European strategy for particle physics is so important.

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