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Charting the Course for Elementary Particle Physics

By Harold T. Shapiro

Over the past 18 months I have been engaged in a very stimulating—and rewarding—intellectual adventure. I chaired the National Academies’ Committee on Elementary Particle Physics in the 21st Century that was convened in response to an informal request from DOE and NSF. The committee was charged to identify the compelling science questions that currently define the elementary particle physics scientific agenda and to recommend a 15-year implementation plan with realistic, ordered priorities to address them. The committee that was assembled included quite a few individuals from outside the field of particle physics; in fact, half the committee members were not experts in particle physics, and yet each one had an important perspective to contribute. As an economist with a long-time interest in science policy and as a former university president, I undertook this challenge seriously but with a commitment to ensure that our recommendations would represent responsible stewardship of public resources.

The final report of the committee, Revealing the Hidden Nature of Space and Time, was publicly released on April 26, 2006. The committee strongly recommended an aggressive, direct exploration of the physics of the Terascale, where “tera” refers to the trillions of electron-volts that the world’s most powerful accelerators can impart to fundamental particles. The strong attraction of Terascale physics is underscored by the convergence of interests from distinct scientific areas. From cosmology, there is growing interest in dark matter and dark energy. From particle physics, there is great interest in supersymmetry, in the origins of mass, and in Einstein’s dream that all the forces can be unified. This convergence is what makes the Terascale so persuasive. The intersection of scientific interests is often a signal that major new discoveries are on the horizon, and thus, the committee felt that explorations of the Terascale have enormous scientific potential.

Let me assume for the moment some general familiarity with the report (please see the excellent discussion in last month's APS News for details ), and use this space to briefly expand on three themes: (1) the role of particle physics in the physical sciences (as seen by an outsider), (2) leadership in an international arena, and (3) the medium-term challenge facing US particle physics.

In the committee’s judgment, the US program in particle physics, despite a long tradition of distinction, is now at a decisive crossroads. Not only has this program (like many others in the physical sciences) experienced a decade of stagnating support when programs elsewhere in the world were expanding, but also the most important experiments at SLAC and Fermilab are reaching the end of their useful scientific lives without a clear follow-on strategy in place. As a result, the intellectual center of gravity is moving abroad just when the scientific agenda is especially promising. In these circumstances it was the committee’s view that a failure to adopt a refreshed and compelling strategic vision and associated set of priorities would imply a decision to forgo leadership and commit ourselves to a much smaller effort in this critical scientific arena.

An outsider to particle physics (or even to the physical sciences in general) might naturally question the consequences of forgoing America’s tradition of leadership in particle physics. In my view, and one echoed by the committee throughout its report, there is a strong relationship between the health of US particle physics and the vitality of the nation’s overall science and technology portfolio. Consider these two observations. First, scientific discovery is an unpredictable process whose impacts are only fully recognized ten or twenty, sometimes even thirty, years down the road. In such an environment, the best investment strategies rely on a mixed or diversified portfolio. Indeed it was the committee’s view that a strong particle physics program not only would enable us to explore some of the most exciting issues on the scientific frontier, but was essential to the long-term vitality of the physical sciences. Historically certain important scientific and technological advances arose because of a synergy among particle physics and other developments in science and technology, but the committee does not claim that particle physics is the best or only path to drive such innovations. Rather, the committee argued that a strong program in particle physics is an essential element of an overall strategy to foster such breakthroughs.

Second, it seems to me that particle physics has several key attributes that give it a distinctive role in the physical sciences. For example, particle physics incorporates both imagination and technological and computing prowess at an unusual scale in order to address several of the most exciting questions of our time: What is the nature of space and time? What are the origins of mass? How did the universe begin? How will it evolve in the future? The quests and the techniques of particle physics, therefore, attract some of the best and brightest minds to futures in science, technology, engineering, or mathematics.

Thus, I would posit that the future of the US program in particle physics has consequences that extend far beyond the field itself. Particle physics is not elite, nor special, nor exclusive in this regard. However, the US program currently faces a set of strategic decisions that will determine, to a large degree, its future for a generation. These decisions will require the support of physics in general, if not all of the physical sciences together. Perhaps this is one of the reasons the National Academies saw fit to include such a diverse set of individuals on the committee. The committee recommended, unanimously, that the United States should not abandon its leadership role in particle physics, especially at a time when the scientific agenda is richer than it has been for a generation.

Let me say something further about leadership and the international arena. As the field of particle physics took shape in the middle of the century, America’s scientists focused on experiments designed to measure and explain the properties and forces governing the ultimate constituents of matter. Since then, even as the field became increasingly internationalized with very distinguished centers abroad, the United States has been home to some of the world’s most accomplished theorists, the most diverse array of experiments, and some of the largest particle accelerators. Moreover the United States has welcomed and greatly benefited from the intellectual and financial input of scientists from around the world. US leadership in particle physics both anchored and symbolized the growing distinction and reach of the overall American scientific enterprise.

The committee felt strongly that because of the increasing cost and complexity of particle physics experiments, and the need to deploy public funds in the most effective and responsible manner, it is more important than ever for all the major programs in particle physics to leverage their resources by working together internationally. The community of particle physicists has a strong tradition in this area, but that tradition needs to be enhanced. Moreover, the key sponsors of national and multinational programs need to allow for the serious consideration of new and imaginative arrangements. Such arrangements would not only serve the cause of scientific progress; they also may be the only way to provide scientists and their students in each region of the world with the opportunity to address those areas of particle physics to which they can make the greatest scientific contribution. This type of transformation cannot be accomplished by a single country or region: it requires the mutual collaboration of all major partners. Such transformations would strengthen the knowledge base of the entire US scientific enterprise.

If we are to take the current discussions about globalization, “the flat world,” and the growing interdependence of national efforts around the world, what does scientific leadership mean for the United States? After some thought, the answer becomes relatively clear for a field like particle physics. Leadership does not mean dominance, but rather taking initiative at the frontiers, accepting appropriate risks, and catalyzing partnerships both at home and abroad. That is, in articulating a strategy for the United States, we must find a path that leverages US strengths for the benefit of the not only the domestic program but also the global enterprise. We must move from a paradigm of “We’re going to build this, will you help us?” to one of “What can we build together that will benefit us all?” US leadership, together with that of our colleagues abroad, is important because it is critical to reaping the scientific, technological, economic, and cultural dividends that come from advancing the scientific frontier.

With these considerations in mind, the committee saw a critical role for the United States in fostering this new era of international partnership and coordination. Even as the Europeans have been finishing the Large Hadron Collider (LHC), particle physicists worldwide have been designing the next generation of particle accelerators. Known as the International Linear Collider (ILC), this new tool would consist of two accelerators that fire electrons and positrons at each other head-on, re-creating conditions that existed just a fraction of a second after the universe’s birth. The ILC would be of such a scale and complexity, similar to the LHC, that only a global, cooperative effort could make it possible. It was the committee’s judgment (echoing many others) that the ILC was a necessary tool to fully exploit the scientific opportunities of the Terascale. The committee believed that the potential role of the United States in building, supporting, and perhaps hosting the ILC was key to the continued distinction of the US program. In order to participate in such a global effort, the United States must surrender some degree of control—but this shift is precisely the form of leadership that I believe will be essential to shepherding in a new era of global scientific cooperation.

The committee’s report identifies a set of priorities that we believe will propel the United States to leadership in a way that adds value to the international effort. The committee’s strategy aims for a pivotal role in the ILC but is not without risks. Nature might not reveal its secrets so easily at the LHC, the necessary level of international cooperation and agreement might not coalesce, or fiscal and technical realities might make a linear collider untenable. The committee advocated for a firm step forward, however, in the face of these longer-term uncertainties. The committee recommended that the program invest some risk capital that would enable the United States to become the leading center for R&D relating to the ILC and prepare to mount a compelling bid to host the ILC if that still seems desirable down the road. While this path contains obvious risks the committee felt that the prospective benefits more than justified such actions. Indeed we could not identify an alternative program that could sustain our leadership position with a better risk-adjusted rate of return: the riskiest path is to simply maintain our current course.

The task of crafting a meaningful program that moves forward is a challenge that requires courageous decisions, but such courage and determination are some of the unavoidable prerequisites for leadership. In its strategic principles, the committee offers some general guidance to the US particle physics program and its sponsors. A key element of these principles is the discussion of the role that a so-called national program committee might play in helping to frame a national program that not only addresses the most compelling science but also best deploys US resources and talents. Implicit in this principle is the committee’s judgment that structuring the near- and mid-term program, within the recommended framework, is work best left to the physicists and their immediate sponsors.

Today, our nation faces some decisions about its future role in particle physics. The United States can choose to sacrifice its historical leadership in particle physics. Or we can make a strong commitment to current and future global efforts. The United States has an unprecedented opportunity, as a leader of nations, to undertake this profound scientific challenge.

Finally, I must express my thanks and gratitude to the members of the committee and indeed to everyone who contributed to the work of this committee. I am pleased with our final report and I hope that it continues to be of value to this important field of science for years to come.

Harold Shapiro is president emeritus and professor of economic and public affairs at Princeton University. His broad interests and experience range from chairing the board of trustees of the Alfred P. Sloan Foundation and the National Bioethics Advisory Committee to membership on the U.S. Olympic Committee.

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