CERN’s new chief on the gamble that could fix our picture of reality

Mark Thomson assumed leadership of CERN on January 1, 2024, inheriting the world's largest particle physics laboratory at a pivotal moment in the discipline's evolution. The physicist, who previously led particle physics research at the University of Cambridge, now directs an organisation employing roughly 2,500 staff across its Geneva-based headquarters and sprawling facilities, including the Large Hadron Collider buried beneath the Franco-Swiss border. Thomson's appointment arrives as CERN confronts fundamental questions about which scientific puzzles deserve priority funding and research focus during a period when the organisation's flagship experiments have generated perplexing results that challenge prevailing theoretical frameworks in physics. His tenure begins with the institution at a crossroads, requiring strategic decisions that will shape particle physics research for decades and influence how human understanding of reality itself evolves.

The significance of Thomson's timing cannot be overstated within the contemporary scientific landscape. CERN has operated the Large Hadron Collider since 2008, achieving its historic discovery of the Higgs boson in 2012, a watershed moment that vindicated the Standard Model of particle physics. Yet the intervening years have revealed that this theoretical framework, despite its successes, remains fundamentally incomplete. Dark matter comprises approximately 85 percent of the matter in the universe, yet its nature remains unknown. Dark energy drives the accelerating expansion of the cosmos, yet physicists cannot adequately explain it. The Standard Model contains no mechanism for gravity's integration with quantum mechanics, representing a profound theoretical gap that haunts contemporary physics. Thomson inherits an organisation grappling with whether its existing infrastructure can probe these mysteries or whether entirely new experimental apparatus demands construction. The stakes extend beyond academic advancement; understanding fundamental physics underpins technological innovation ranging from medical imaging to quantum computing, making CERN's strategic choices consequential for innovation ecosystems globally.

Thomson faces concrete challenges defined by specific measurements and experimental outcomes requiring urgent interpretation. Recent data from CERN's experiments have produced anomalies in measurements of particles known as B mesons, results suggesting potential deviations from Standard Model predictions that physicists have struggled to reconcile with existing theory. Additionally, experiments examining muon behaviour have yielded measurements that deviate from theoretical expectations, with these discrepancies persisting across multiple experimental collaborations and data collection periods. These measurements themselves remain technically challenging, sitting at the boundary of current experimental precision, yet they simultaneously hint at possible new physics awaiting discovery. The laboratory must determine whether these anomalies represent glimpses of undiscovered particles or phenomena, or whether they emerge from currently unaccounted experimental uncertainties. This investigative imperative directly influences decisions about resource allocation and whether CERN should invest in upgrading existing experiments or constructing fundamentally new detection systems.

For the scientific community and informed publics tracking particle physics developments, Thomson's leadership carries immediate implications regarding the organisation's near-term trajectory. CERN currently operates the High-Luminosity Large Hadron Collider upgrade project, scheduled for completion around 2029, which will dramatically increase the rate at which collision events are observed and measured. This upgrade enables physicists to accumulate data sufficient to either confirm whether observed anomalies constitute genuine physics breakthroughs or emerge from statistical fluctuations within current datasets. Thomson must navigate decisions about concurrent technical initiatives, including proposals for future collider facilities that would dwarf existing infrastructure in scale and cost. The European Strategy for Particle Physics, which guides the laboratory's agenda, undergoes periodic revision; Thomson's influence over strategic planning during his tenure will determine whether CERN pursues incremental improvements to current facilities or commits to ambitious new construction projects. These decisions directly determine which scientific questions researchers can address over the next ten to twenty years and which mysteries remain beyond experimental reach.

Thomson's appointment reflects a broader inflection point within fundamental physics research more generally. The discipline confronts a generational challenge: successive large-scale experiments have discovered fewer transformative particles and phenomena than theoretical frameworks predicted. The Standard Model's persistence despite incomplete explanations has prompted serious disciplinary debate about whether continued investment in ever-larger particle colliders represents optimal resource allocation for fundamental research. Alternative approaches to probing physics beyond the Standard Model, including precision measurement campaigns, cosmic observation techniques, and quantum information technologies, have gained credibility as complementary or substitute research pathways. CERN's decisions under Thomson's leadership will implicitly signal the broader scientific community's confidence in particle collider methodology versus alternative investigative approaches. The laboratory's strategic choices consequently influence funding priorities and research direction across national physics programmes internationally, as institutions worldwide calibrate their own investments relative to CERN's positioning and priorities. This pattern extends beyond particle physics into adjacent disciplines, as decisions about big science infrastructure reverberate through interconnected research ecosystems.

Looking forward, several specific developments merit close monitoring to assess Thomson's strategic effectiveness and CERN's institutional trajectory. The completion of the High-Luminosity LHC upgrade in 2029 represents a crucial milestone, as data accumulated thereafter will definitively address whether current anomalies reflect genuine new physics or emerge from experimental artifacts. Simultaneously, CERN's deliberations regarding proposed Future Circular Collider, a facility potentially costing billions of euros and requiring construction timelines extending into the 2040s, will crystallise the laboratory's fundamental vision for particle physics research beyond current capabilities. The European Strategy for Particle Physics underwent revision in 2020 and will undergo further assessment as Thomson establishes his research priorities; observers should monitor whether strategic updates emphasise collider-based approaches or favour diversified methodologies incorporating precision measurements and alternative detection technologies. Thomson's success ultimately depends upon navigating these institutional decisions while maintaining scientific credibility, international collaboration frameworks involving thousands of researchers across dozens of nations, and political support from contributing governments during an era of constrained public science funding. The choices made during his tenure will determine whether particle physics continues its historical trajectory of experimental discovery or enters a different investigative paradigm.