The European: The mission of CERN is to conduct experiments that push the limits of physics. What are the challenges for the coming decade?
Heuer: In the area of particle physics, we need many years to run our experiments and analyze the data. In the past fifty years, we have developed the Standard Model of particle physics. It describes the microcosm as we know it: the matter particles and the forces between them. But we are still missing one cornerstone to explain how elementary particles get their mass. We think that the Higgs mechanism could provide the answer to that question. The manifestation of that mechanism is something called the Higgs Boson – a particle that is thought to exist but hasn’t been found in experiments yet. Our goal is to find the Higgs Boson. If we succeed, then we will conclude the theory of the Standard Model.
The European: What consequences would that discovery have for our understanding of the physical world? Is it an achievement on par with Rutherford’s discovery of the atomic nucleus, with the Michelson-Morley experiment, with Newton’s prism experiments?
Heuer: It would be a very big step in physics because it would complete the Standard Model. And if we fail to find it, we would need to develop a new mathematical formalism to explain how particles get their mass. Either way, the impact would be significant. But the Standard Model only describes around five percent of the universe. Around a quarter of the universe is so-called “dark matter”, three quarters are “dark energy”. So an even bigger step would be to find traces of dark matter in the laboratory. I hope that we will achieve that within the next few years.
The European: CERN is a gigantic laboratory and it is hard to imagine that we would build something bigger in the near future. Does the future belong to theoretical physics, because the questions we are trying to answer cannot be examined through experiments anymore?
Heuer:Theory and experiment need each other. But the question is less about size and more about power. The Large Hadron Collider (LHC) is a very powerful microscope with very good resolution power. It can work with very small wavelengths, which means very high energy levels. But we don’t need to build bigger particle accelerators to achieve even higher energy levels; it can also be done through new technologies. The LHC tunnel – a structure with a 27 kilometer circumference – used to house another accelerator with much lower energy levels ten years ago. Now we are using the same infrastructure with different particles and new acceleration technologies to achieve more energy per unit length. So we have not reached the end of the development of experimental physics. To the contrary: If the LHC experiments yield results, we will have a much better understanding of the relevant energy levels and can custom-build the next generation of accelerators.
The European: What fascinates you about these very theoretical questions?
Heuer: It’s a quest for knowledge. The questions we are examining have been asked since the beginning of mankind. We are humans, we want to understand the world around us. How did things begin? How did the universe develop? That distinguishes us from other creatures. If you go outside at night and look up into the sky, you cannot help but dream. Your fantasy develops, you are naturally drawn to these questions about being and existence. And at the same time, our work has very practical consequences. When antimatter was introduced into the theoretical framework 83 years ago, nobody thought that this had any practical relevance. Yet today, the concept is used in hospitals around the world on a daily basis. Positron Emission Tomography (PET) is based on the positron, which is the anti-particle to the electron. Or take the internet. The idea of a worldwide network started in 1989 here at CERN, because we needed that kind of digital network for our scientific work. That’s the beauty of our research: We gain knowledge but we also gain the potential for technological innovation.
The European: When CERN first launched the LHC, some people were concerned that the experiments might lead to the creation of a black hole. From today’s perspective, that seems very irrational – like, for example, the fear before the first tests of an atomic bomb that the blast might set the earth’s atmosphere on fire. Are those fears a natural component of a quest for the unknown – a modern equivalent to sea monsters and giant squids?
Heuer: They are fully understandable. Research necessarily charts new territory, otherwise it would not be very interesting. I like the fact that people think critically about our research, and I understand that they might have fears. It is our job as scientists to explain what we are doing, how we are doing it, and that there are no dangers involved.
The European: But can you expect to address emotional reactions with very rational, theoretical arguments?
Heuer: You can discuss theories for ages, but by definition they have not been proven. So before any experiment, we have to think about the possible consequences based on those theories. But what convinces everybody are experimental facts. They are given by the laws of the universe that have existed for billions of years. Our experiments are bound by the same laws. So we can say: Look at the universe, these processes have been going on since the beginning – and we still exist. There is no reason to believe that a replication of the same processes on a smaller scale should have any different consequences.
The European: Can something as vast and as complex as the universe ever be reduced to the scope of human mental capacities, or are there natural limits to what we can know?
Heuer: That is a difficult question. Every time we discover something, we open the door to new knowledge but find new sets of questions that are more complex and dig deeper into the subject. So there is no real limit, the process of discovery never stops. Maybe the time to answer these questions, i.e. to open these new doors, will increase, but eventually we will be able to open them.
The European: What are the questions that might emerge behind the next set of doors?
Heuer: It’s about the constituent parts of the universe. We are looking into the question of what is driving the universe apart in all directions. Was there a single force at the beginning of the universe? At the moment we know of four fundamental forces but we have indications that they all stem from one single force at the very beginning of the universe. Another very intriguing question is why there is no more antimatter in the universe. We know that there must have been a very small asymmetry at the very beginning of the universe. We have ideas about the necessary conditions for this asymmetry, but we don’t know much about it yet. How did it happen that there is only one part in 10 billion more matter than antimatter? This one part forms our universe, our world, whereas all the rest was annihilated when matter and antimatter combined. Without this asymmetry, there would only be energy but no physical matter.
The European: The Higgs Boson has been described as the “God particle”. Many scientists dislike the name. Why?
Heuer: It is too flamboyant and misleading. Why should it be a “God particle”? It is one of the building blocks of the Standard Model, the cornerstone without which the model would not be valid. But there is nothing divine to it. I think the name primarily serves as a publicity tool to attract the attention of publishers.
The European: Let us talk about the idea of the divine. For much of human history, religion and science were deeply intertwined. Galileo was expelled from the church for questioning those links. How would you separate the two realms?
Heuer: We separate knowledge from belief. Particle physics is asking the question of how did things develop? Religion or philosophy ask about why things develop. But the boundary between the two is very interesting. I call it the interface of knowledge. People start asking questions like “if there was a Big Bang, why was it there?” For us physicists, time begins with the Big Bang. But the question remains whether anything existed before that moment. And was there something even before the thing that was before the Big Bang? Those are questions where knowledge becomes exhausted and belief starts to become important.
The European: What is the difference between justified opinion and belief?
Heuer: Justified opinion or knowledge is something that you can at least partially prove. Belief or philosophical thought cannot be examined through experiments.
The European: For Aristotle, physics was the primary science that could tell us almost anything about the cosmos. But he also thought that all things had an innate capacity – the telos – to develop to their full potential. And so it fell to philosophy to investigate the nature of things.
Heuer: At the edge of physics, it becomes linked to philosophy. But in the case of particle physics, it is really not a question of “believing” but of deducing something from a larger theoretical framework or from experimental data. Once you can prove something, it is no longer a question of philosophy.
The European: Scientific theories are postulated and then either supported or falsified by experiments. Isn’t there one component of theory that is always ahead of the realm of confirmation, that requires a Kierkegaardian leap of faith precisely because it seeks to expand the scope of our understanding?
Heuer: Not always. But the interplay between theory and experiment is very interesting. Sometimes the theory is indeed ahead of the experiment and we must later try to find proof for the validity of the theory through data analysis. But when the analysis yields results that could not be expected from the theory, then it must follow the experiment and devise new formulas to explain our observations. In the history of particle physics, we have discovered several unexpected particles that were only later explained by theories. They were like the missing pieces of the puzzle, except that we did not know they were missing.
The European: What still puzzles me is the following problem: A theory can only be falsified; it can never be proven. You can tweak the theory, you can establish an experimental record that supports it. But you will never have an ultimate confirmation of its validity.
Heuer: It is a question what you define as full proof. If all experimental evidence points to a given fact, that you can say that within certain boundary conditions the theory is correct. Take Newton’s law of gravity: Within our velocity regime, it is correct. But when you apply the logic of relativity theory, it loses its validity. This means Newton’s laws are a low velocity approximation of the more embedding theory of relativity.
The European: Do you think it is conceivable that we will eventually learn something about before the Big Bang?
Heuer: I doubt it.
The European: How do you make sense of that paradox? You want to expand the realm of knowledge but at some point, there is a definite boundary that you cannot cross. Do you simply have to accept the fact that nothing was prior to the Big Bang?
Heuer: I wasn’t saying there was nothing, I am saying that we don’t know anything about what was before – if there was a before. But here we are crossing the boundary between knowledge and belief. I think many famous scientists have struggled with this question and people today also struggle with it.
The European: So at the very borders of human knowledge, science and belief tend to converge?
Heuer: In the scientific community we don’t tend to discuss such things too often. But the more we investigate the early universe, the more people are trying to connect science to philosophy. That is a good thing. Since we are struggling with the limits of knowledge, maybe philosophy or theology struggle also with our research. I think it is important that we open a constructive dialogue. We are currently planning seminars and workshops to do exactly that. My hope is that we can reach a common understanding of what we are talking about.
The European: Do you think that your arguments – scientific arguments – have been dismissed by the humanities?
Heuer: Science is not much talked about in society today. It is largely separated despite the fact that society depends on science and its results and developments. This was very different at the beginning of the 20th century when science was a discussion topic in private households. Maybe the amount of information is becoming so overwhelming that people are submerged.
The European: Einstein was basically a rock star of modern science…
Heuer: Exactly, that’s a dynamic that we are missing today. But I think the public interest in the work at CERN might give us an opportunity to discuss science in a societal context. Questions about the boundaries of human knowledge give us an opportunity to open a dialogue with the general public, to bring science back into society. If scientists satisfy the public interest, then the interest can keep growing. It’s a circle that we have to perpetuate.