This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
The discovery of the Higgs particle at the Large Hadron Collider (LHC) over half a decade ago marked a milestone in the long journey toward understanding the deeper structure of matter. Today, particle physics strives to push a diverse range of experimental approaches from which we may glean new answers to fundamental questions regarding the creation of the universe and the nature of the mysterious and elusive dark matter.
Such an endeavor requires a post-LHC particle collider with an energy capability significantly greater than that of previous colliders. This is how the idea for the Future Circular Collider (FCC) at CERN came to be—a machine that could put the exploration of new physics in high gear. To understand the validity of this proposal, we should, however, start at the beginning and once more ask ourselves: How does physics progress?
Many believe that grand revolutions are driven exclusively by new theories, whereas experiments play the parts of movie extras. The played-out story goes a little something like this: theorists form conjectures, and experiments are used solely for the purposes of testing them. After all, most of us proclaim our admiration for Einstein’s relativity or for quantum mechanics, but seldom do we pause and consider whether these awe-inspiring theories could have been attained without the contributions of the Michelson-Morley, Stern-Gerlach or black-body radiation experiments.
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This simplistic picture, despite being far removed from the creative, and often surprising, ways in which physics has developed over time, remains quite widespread even among scientists. Its pernicious influence can be seen in the discussion of future facilities like the proposed FCC at CERN.
In the wake of the discovery of the Higgs boson in 2012, we have finally of all of the pieces of puzzle of the Standard Model (SM) of physics in place. Nevertheless, the unknowns regarding dark matter, neutrino masses and the observed imbalance between matter and antimatter are among numerous indications that the SM is not the ultimate theory of elementary particles and their interactions.
Quite a number of theories have been developed to overcome the problems surrounding the SM, but so far none has been experimentally verified. This fact has left the world of physics brimming with anticipation. In the end, science has shown time and again that it can find new, creative ways to surmount any obstacles placed along its path. And one such way is for experimentation to assume the leading role, so that it can help get the stuck wagon of particle physics moving and out of the mire.
In this regard, the FCC study was launched by CERN in 2013 as a global effort to explore different scenarios for particle colliders that could inaugurate the post-LHC era and for advancing key technologies. A staged approach, it entails the construction of an electron-positron collider followed by a proton collider, which would present an eightfold energy leap compared to the LHC and thus grant us direct access to a previously unexplored regime. Both colliders will be housed in a new 100-kilometer circumference tunnel. The FCC study complements previous design studies for linear colliders in Europe and Japan, while China also has similar plans for a large-scale circular collider.
Future colliders could offer a deep understanding of the Higgs properties, but even more importantly, they represent an opportunity for exploring uncharted territory in an unprecedented energy scale. As Gian Giudice, head of CERN's Theoretical Physics Department, argues: “High-energy colliders remain an indispensable and irreplaceable tool to continue our exploration of the inner workings of the universe.”
Nevertheless, the FCC is seen by some as a questionable scientific investment in the absence of clear theoretical guidance about where the elusive new physics may lie. The history of physics, however, offers evidence in support of a different view: that experiments often play a leading and exploratory role in the progress of science.
As the eminent historian of physics Peter Galison puts it, we have to “step down from the aristocratic view of physics that treats the discipline as if all interesting questions are structured by high theory.” Besides, quite a few experiments have been realized without being guided by a well-established theory but were instead undertaken for the purposes of exploring new domains. Let us examine some illuminating examples.
In the 16th century, King Frederick II of Denmark financed Uraniborg, an early research center, where Tycho Brahe constructed large astronomical instruments, like a huge mural quadrant (unfortunately, the telescope was invented a few years later) and carried out many detailed observations that had not previously been possible. The realization of an enormous experimental structure, at a hitherto unprecedented scale, transformed our view of the world. Tycho Brahe’s precise astronomical measurements enabled Johannes Kepler to develop his laws of planetary motion and to make a significant contribution to the scientific revolution.
The development of electromagnetism serves as another apt example: many electrical phenomena were discovered by physicists such as Charles Dufay, André-Marie Ampère and Michael Faraday in the 18th and 19th centuries through experiments that had not been guided by any developed theory of electricity.
Moving closer to the present day, we see that the entire history of particle physics is indeed full of similar cases. In the aftermath of World War II, a constant and laborious experimental effort characterized the field of particle physics, and it was what allowed the Standard Model to emerge through a “zoo” of newly discovered particles. As a prominent example, quarks, the fundamental constituents of the proton and neutron, were discovered through a number of exploratory experiments during the late 1960s at the Stanford Linear Accelerator.
The majority of practicing physicists recognize the exceptional importance of experiment as an exploratory process. For instance, Victor “Viki” Weisskopf, the former director-general of CERN and an icon of modern physics, grasped clearly the dynamics of the experimental process in the context of particle physics:
“There are three kinds of physicists, namely the machine builders, the experimental physicists, and the theoretical physicists. If we compare those three classes, we find that the machine builders are the most important ones, because if they were not there, we would not get into this small-scale region of space. If we compare this with the discovery of America, the machine builders correspond to captains and ship builders who truly developed the techniques at that time. The experimentalists were those fellows on the ships who sailed to the other side of the world and then jumped upon the new islands and wrote down what they saw. The theoretical physicists are those fellows who stayed behind in Madrid and told Columbus that he was going to land in India.” (Weisskopf1977)
Despite being a theoretical physicist himself, he was able to recognize the exploratory character of experimentation in particle physics. Thus, his words eerily foreshadow the present era. As one of the most respected theoretical physicists of our time, Nima Arkani-Hamed, claimed in a recent interview, “when theorists are more confused, it’s the time for more, not less experiments.”
The FCC, at present, strives to keep alive the exploratory spirit of the previous fabled colliders. It is not intended to be used as a verification tool for a specific theory but as a means of paving multiple experimental paths for the future. The experimental process should be allowed to develop its own momentum. This does not mean that experimentation and instrumentation should not maintain a close relationship with the theoretical community; at the end of the day, there is but one physics, and it must ensure its unity.