Mar Capeáns, new director of CERN: "It's terrifying that we only know 5% of the universe."

Mar Capeáns, a doctor in physics born in Santiago de Compostela 58 years ago, is the new director of operations of the world's largest particle physics laboratory, Europe's CERN . Her main task in this new position will be to ensure "everything runs smoothly," as she puts it. This is a major challenge when dealing with an institution that brings together 20,000 scientists from 110 countries, including sworn enemies such as Israel (which funds it), Iran, and Palestine (which are academic collaborators). Spain is one of its 25 member states and contributes 7% of the annual budget, which totals around €1.2 billion.

Capeáns' mandate begins in 2026 and ends in 2030. During these years, the European laboratory based in Geneva (Switzerland) will face some of the greatest challenges in its history, such as multiplying by ten the power of its main particle accelerator, the LHC , which discovered in 2012 the last elementary particle that remained to be observed: the Higgs boson . The construction of the Future Circular Collider (FCC) will also be decided, a machine three times larger, which will be the largest new experiment on Earth. The technology that will be needed in its construction is not yet clear, but it could reveal what up to 25% of the universe is made of, of which almost everything is still unknown.

Looking back, Capeáns believes no other Spaniard has risen as high as she has in this organization, where she has worked for more than 30 years. She will be joined by five other directors from other areas, such as accelerators, technology, and international relations, led by Briton Mark Thomson , who succeeds Italian Fabiola Gianotti as director general. In this interview with EL PAÍS, conducted via videoconference, the scientist ventures into the future discoveries of the world's cathedral of physics.

Question: Does the current geopolitical tension threaten CERN's future?

Answer: The situation is very difficult. This laboratory has enjoyed a period of glorious stability in its 70 years of existence. This has been made possible by the increase in the number of Member States funding it [all European except Israel]. Nothing can be done here without collaboration, and therein lies our strength. We're starting to hear that budget allocations are going to be diverted from basic science, that there are contributions from countries we took for granted that may never arrive. It would be a shame to throw away 70 years of success, collaboration, and knowledge sharing. I believe that Europe today is a super Europe, where collaboration, listening to others, being competitive, but not leaving anyone out, remain fundamental values ​​that are more valid than ever.

Q. Will Europe build the FCC before China, which is planning a very similar accelerator?

A. CERN has three key objectives: to take advantage of the 2026-2029 technical break to improve the LHC, prepare for its restart in 2029 to obtain better results in particle physics, and define the long-term future. Among the possible options is the FCC, a 90-kilometer-diameter accelerator. Decisions must consider sustainability, international cooperation, and technological development, as these projects require years of preparation and joint investment. This process is extremely interesting and is being decided right now, as part of the European Strategy for Particle Physics. It's a bottom-up process, where countries or scientists can begin to say which scientific facility they believe will answer the biggest questions we have. And to that must be added the costs and the politics involved. Probably, a machine as large as the FCC will require an expansion of CERN, a different governance model, and external funding that doesn't come from member countries. All of this is being discussed now, and a conclusion will be reached by the end of the year. There seems to be a fair amount of consensus regarding the cost and effort that a circular machine can offer us. The Chinese will probably get there first in terms of construction. But when you build such a complex machine for physics, you need a cohesive scientific community, a historical infrastructure that only CERN has, and, in addition, an international community pushing forward. If we put these three things on the table, I think we're doing well.

Q. You arrived at CERN in 1992. That year, your professor, Georges Charpak , who had fought in the French resistance and suffered two years of internment at Dachau, after which he became an engineer and specialized in physics, won the Nobel Prize in Physics for creating a particle accelerator that formed the basis of the LHC. In 2012, this machine discovered the Higgs boson, which earned it the Nobel Prize in Physics just one year later . What could be the next big discovery from this laboratory?

A. What we're all looking for is dark matter . There are other goals, like understanding the Higgs particle or the asymmetry between matter and antimatter, but what keeps me awake at night is that, after so many years, we only understand 5% of the universe . I find that terrifying. We believe that with the LHC, especially in its next high-luminosity phase, we will be able to discover dark matter, and that would already help us explain 25% more of the universe. If I leave CERN with that, I'm already happy. And I'm sure there will be another Nobel Prize.

Q. What exactly would the LHC see?

A. New particles . What we would do is experimentally prove that these particles exist, and therefore, that dark matter exists, and therefore, all theories based on its presence would be automatically validated. This is closely related to cosmology, to astrophysics… We're all looking for the same thing.

Q. Could dark energy , which makes up the other 75% of the universe, be discovered?

A. It's much more difficult. There's no consensus on what dark energy is. We know it's there, but we don't know where to attack it.

Q. Above these discoveries would be the theory to unify gravity and quantum mechanics, is it possible to demonstrate it?

A. The history of particle physics is about unifying forces. It's one of the things that most attracts me to this field, that everything tends toward beauty and simplicity. And there could be nothing more beautiful and simple than having the four fundamental forces exist within a single theory. That's really what we're looking for, a theory that explains everything. With the equipment we have today, it's very difficult to prove its existence, but that's the goal we're pursuing.

Q. Some of these concepts are as broad and uncertain as those addressed by religion. Do you think there is room for God in this entire universe?

A. They're completely different topics. Some people need faith. Science, particle physics, doesn't seek to understand whether there is a God or not. What we want to understand is the origin of the universe from the perspective of the laws of physics. And within the CERN community, you have all spectrums and different religions; it's wonderful.

Q. How does your appointment influence Spain's role at CERN?

A. I'm convinced that CERN is the Spanish laboratory in Switzerland. I carry the legacy of many Spaniards who have worked here. Spain has a very strong scientific community, and it must be involved in everything we do. I always make sure there are Spaniards in relevant positions; that attracts young people, and it's key for them to see that. Much progress has already been made.

Q. US President Donald Trump is threatening to cut off your international scientific collaboration projects, including at CERN. How might this affect you?

A. If it's confirmed, we'll have problems. The United States is a very important partner, both financially and in terms of expertise. We work extensively with them on particle detectors, which are very complex, and we depend on them, just as we do on other countries. I hope these things will gradually improve, and that the community of particle physics scientists in the United States doesn't end up in a situation of weakness due to very short-term measures.

Q. Is a CERN like the one you have described compatible with the imminent remilitarization of Europe ?

A. Yes, it has to be. Europe can't afford to stop doing basic and fundamental science. We must help politicians understand that basic science is a long-term commitment, for young people and sustainability, with major economic and industrial repercussions. It would be a step backward to wipe this off the map. I've been at CERN for 30 years, and it seems impossible to me that this isn't understood. But we must be vigilant, because basic science shouldn't be negotiable.