Crisis in Physics Spurs Spirited Dialogue

Let me list some points of disagreement:

• "Great discoveries [in particle physics] are less frequent," Nagel says. Actually, the past few years have seen remarkable advances: the detection of oscillations of atmospheric neutrinos, the solution of the solar neutrino problem, the establishment of charge conjugation-parity violation in the B system, and affirmation of the standard model at CERN's Large Electron-Positron Collider and at Fermilab.

• The notion that "we do not really appreciate what is done in other areas" may be true of some physicists, but many faithfully attend weekly physics colloquia that cover every subfield. Because physics knowledge has expanded so much in recent years, it is more difficult to remain well informed even within one's own field, but that knowledge explosion is, in my opinion, a good thing, not a crisis.

• Nagel says that "small physics . . . has gotten even smaller." I think some areas that used to be small physics have actually gotten bigger rather than smaller. For example, many condensed matter physicists now use synchrotron light or neutron sources and sophisticated beam lines, devices that require substantial teams to build and operate. In my opinion, most of experimental physics has gotten bigger.

• "To study . . . condensed matter physics, . . . does one need to know the standard model?" Nagel rightly answers, "Of course not." On the other hand, some older reductionist results, like the fact that atoms are made of nuclei and electrons, do seem useful. Note that the tools of particle physics (like particle accelerators) may be useful to areas such as condensed matter physics. I cannot believe that a condensed matter or plasma physicist would not marvel at the beauty of the standard model and the intellectual accomplishment it represents, even if it had no impact on his or her own work.

• Nagel also mentions "the growing split between theory and experiment in all areas of physics." It is my impression that theory and experiment have been working very well together in many areas. I just read a piece about recent theoretical work done to explain experimental observations on the new superconductor MgB₂. The combination of theory and experiment that led us to our present understanding of solar neutrino astrophysics is extraordinary.

Despite these disagreements, I fully agree that closer interaction between the practitioners of various areas of physics is desirable. James Langer, former president of the American Physical Society, had urged that the March meeting be an example to other APS divisions to meet together to allow improved cross-fertilization and give young people the opportunity to see many different subfields. My division, particles and fields, has decided to hold every second divisional meeting within the APS April meeting, starting with the 2003 gathering in Philadelphia.

The real crisis arises from the inadequate funding of the physical sciences. In arguing for improved funding, we physicists should push for all of science and, within that, for all active areas of physics. I strongly agree that, in our talks, we ought to always explain why others in different fields should care about what we are doing.

As a particle physicist, I was a bit surprised to hear Sidney Nagel speak of particle physics as holding "pride of place" in the discipline. I am not sure that my condensed matter physics colleagues would have characterized the field that way, even when the Superconducting Super Collider seemed alive and well. Perhaps what Nagel has hit upon is that very large projects take on a symbolic significance, and their cancellation can't but have implications for the morale of the whole discipline of physics.

In the nearly ten years since the SSC was cancelled, the field of particle physics has remained vibrant and exciting. The Large Electron-Positron program at CERN and the Linear Collider at SLAC, after elevating the standard model to a precision branch of science, have recently shut down. The current experimental programs on B physics at both SLAC and KEK, Japan's High Energy Accelerator Research Organization, have been enormously successful. Recent data from Kamiokande and the Sudbury Neutrino Observatory in Canada have provided compelling evidence for neutrino masses and mixing.

The upgraded Tevatron is running at Fermilab and has the potential to make major discoveries. On the theoretical front, particle physicists have worked hard in the past few years to understand the flood of new data, have made predictions for new facilities, and have addressed difficult questions about black holes, electric- magnetic duality, and other issues.

The international community, with vigorous US participation, is working on CERN's Large Hadron Collider, which is currently scheduled to begin running in 2007. And in the last few years, an international consensus has crystallized as to the future after the LHC. The picture certainly has some clouds, particularly involving funding--but overall, there is cause for optimism.

Nagel raises a number of other important issues. Our parochialism is not new. When I was a graduate student, it was the nuclear physicists who ridiculed both condensed-matter and applied physics; my particle-theorist teachers admonished me that condensed matter had much to teach us, and even suggested that we might occasionally be able to contribute something to that field as well. The split between small and big science is inevitably a source of tension. It is important that researchers in big collaborations working on very large projects and those on smaller-scale efforts support each other. In my department, it is not uncommon to find, for example, our high-energy lab lending some of its resources to research in condensed matter (including soft condensed matter), and to find condensed matter physicists providing advice on detectors and detection strategies. But the exchange could be better.

As for hiring, when we serve on search committees in others' subfields, we must often defer to colleagues, but I find that we usually have enough in common to exchange useful advice. A candidate search can be an opportunity to learn about what is interesting to our colleagues.

Nagel does not mention another field that has altered the physics landscape during the past decade. When I was a student, astrophysics was peripheral and cosmology disreputable. Today, many physicists, both theorists and experimentalists, from other subfields are spending much of their time on these subjects.

Cosmology and astrophysics highlight the issue of reductionism. The two fields are not exactly reductionist, but neither are they simply emergent. They are phenomenological in the most exciting sense. We are finding that the data fit into a fantastic picture. Cosmologists have used an impressive array of techniques from various fields to attack and apparently solve the classic problem of galaxy formation. Yet we don't yet know the physical laws that account for dark matter, dark energy, inflation, and the very origin and nature of the universe. The reductionists, both theorists and experimentalists, are attacking these questions vigorously.

In the end, Nagel's article gives me some hope for optimism. I, too, could list what I find to be the burning questions, and there would be a surprising amount of overlap. The question Nagel mentions of systems far from equilibrium arises frequently in particle physics and cosmology. Most recently it has been raised by the discovery--by astronomers, cosmologists, and astrophysicists--of a nonzero cosmological constant. Particle physicists and astrophysicists are proposing that these questions be studied further, using technologies developed in part by condensed matter physicists. So, while we face many challenges, ours remains a rich and exciting field.

Sidney Nagel claims that the goal of physics to find the basic underlying laws of nature has slowly been eroded--particularly in the US--since the demise of the Superconducting Super Collider.

The crash of a few commercial giants indeed depresses the stock market, but physics is not a stock market! Cancellation of the SSC cannot be used to define the vitality of the field. The edifices of particle physics still stand and are used by our cosmology colleagues with great benefit to our worldview. Inflationary theory of the Big Bang has its origins in the theories put forward by Peter Higgs about the sought-after Higgs particle. It is most likely that particle physicists will find dark matter, if indeed it exists in particle form. The symbiotic relationship between particle physicists and cosmologists is yielding a most active research domain nowadays.

Otherwise, I find Nagel's excellent analysis a very valuable admonition to all physicists that they keep in mind the unity of physics and not be distracted by petty interdisciplinary arguments.

As a solid-state physicist, I suggest an alternative interpretation of the changes that Nagel portrays as the lost hegemony of high-energy particle physics. That hegemony was always at least partly in the imagination of the high-energy community, and the community's change in perception may reflect a loss of rose-colored glasses now that its funding situation is tight.

I recently spent a few years teaching in a small four-year college, and I can affirm the continued existence of common ground among physicists. The school combined all the natural sciences into one department, and it became reasonably clear that even a nuclear theorist and a solid-state experimentalist share some important views of science. That level of agreement is less common between life scientists, chemists, and geologists. The strong mathematical emphasis of a physics education promotes a quantitative, analytical approach to problem solving. Also, although Nagel is correct that the reductionist approach to science no longer goes unchallenged, it is still a strong enough feature of the physicists' worldview to provide some "family resemblance" among most physicists. In facing the fractures in the physics community, we would do well to remember that we do indeed have much in common.

Prominent research physicist Sid Nagel writes about the fragmentation of physics, but does not include the growing separation between physics and physics education.

Over the past 30 years, the American Association of Physics Teachers, once a society of physicists interested in teaching, has become largely a society of educators interested in physics. The number of AAPT members who are research physicists has declined while the number of physicists from high schools and two-year colleges has increased.

On past occasions, top physicists like Ed Purcell and I. I. Rabi could be seen at AAPT meetings. Now, noted research physicists rarely come to a meeting unless they are being honored and asked to give an invited talk. And the joint AA American Physical Society meetings that brought research physicists and physics educators together are no more.

The 2002 conference of the International Research Group on Physics Teaching (GIREP) in Sweden, with a thoroughly international group of participants, had as a theme the flight from physics. Physics enrollments and degrees are down in most countries, and not one research physicist of note was among the 400 conference participants.

The undergraduate physics curriculum once united physicists. We bragged that, unlike the chemists, any physicist could teach any undergraduate physics course. The knowledge base provided by the undergraduate curriculum gave physicists in all research areas the ability to move from their frontier research position, take a few steps back toward that base, and find common ground with physicists in other specialties. That ability is no longer available. The chain of logic from a specialty back to a common base is too long. So we do not talk to each other--hence Nagel's crisis.

My introductory physics text of the 1950s, Sears and Zemansky (Addison-Wesley, 1955), is a black-and-white version of current physics textbooks. My introductory texts in chemistry and biology, however, bear no resemblance to current textbooks in those fields. Students are introduced to chemistry and biology in ways that represent the disciplines as they are today. Physicists, though, introduce students to their discipline as they did 50 years ago. Yet look at how physics has changed.

If we reform the structure and content of undergraduate physics to represent more accurately what contemporary research physicists do, we might establish a new knowledge base that would provide common ground for our discipline. Then, perhaps, we could talk to each other once again.

Nagel replies: I am delighted to see such a varied response to my Opinion piece. My intention had been to start a productive discussion, and it seems that has now begun.

George Trilling and Michael Dine assert that particle physics is exciting and may be as productive now as in the past. Those are also the main points made by Joseph Lykken in his Opinion piece (Physics Today, November 2002, page 56). Drasko Jovanovic points out the important symbiosis between particle physics and cosmology. I am happy to see such arguments made. I hope physicists from all different areas will become eloquent (yet avoid exaggeration) about their optimism for the future. We need to make clear why we find our fields exciting and why the achievement of our goals can open up new vistas for research. Particle physics is perhaps especially important in this regard simply because it may not appear to an outsider to have the same vibrancy it had during the development of the standard model. I commend Trilling, Dine, Jovanovic, and Lykken for starting the process of making the case for their field.

The executive committee of the American Physical Society's division of condensed matter physics, with input from its counterpart in the division of particles and fields, has organized a symposium entitled "Dreams for the Future of Physics: Where Are We? Where Are We Going?" This will be presented in a plenary session at the 2003 APS March Meeting in Austin, Texas, and I hope it becomes an ongoing tradition. The symposium's objective is to build a greater sense of continuity in physics by communicating the goals of a few major fields--condensed matter physics, nuclear and particle physics, cosmology and astrophysics, physics in biology, and string theory--and presenting some of the most pressing open questions in those fields. I hope that this symposium will not only be exciting but will also teach us how to convey the enthusiasm we feel for our own specialties to a more general public.

Trilling questions the existence of a widening gap between big and small science. Although increasing sophistication of apparatus occurs in condensed-matter as well as particle physics, so that one can correctly make the claim that both fields are simultaneously getting bigger, a different trend occurs that is not as often noticed. Many soft condensed matter experiments actually use extremely simple apparatus. Such experiments depart from the more technically demanding condensed matter experiments using dilution refrigerators, accelerators, reactors, and the like. Thus the poles of big and small physics have moved farther apart.

Of course, as Trilling says, all physicists should marvel at the intellectual achievement of the standard model. They should also marvel equally at the intellectual achievement represented by semiconductors and superconductors, critical phenomena, polymers, Bose-Einstein condensates, greater understanding of the universe, and others. Likewise, I agree that we all use tools that were developed by others. Not only do condensed matter physicists use accelerators, but particle physicists use superconductors and solid-state detectors. In this vein, I agree with Larry Merkle that we physicists do have much in common, but also find, as does he, that it is difficult to identify exactly what is the glue that holds us together.

The split that I see between theory and experiment is not the kind Trilling mentions. Simply put, I do not think that we train our students to do both kinds of physics. Very few, if any, of our "superstars" do both theory and experiment. In the past we had many great examples (starting with Galileo and Newton, going through Faraday, and up to Fermi) of such a cohesive approach. I do not think such a dichotomy exists in biology-related sciences; that is partly why those are such exciting fields for young scientists these days. The separation of theory from experiment has, of course, gone on for a long time; arguably, the separation occurs because physics has become a mature discipline.

There have been consequences to the split between theory and experiment. I cannot speak for other fields, but in my own area of condensed matter physics, we tend to think of theorists as the intellectual leaders. That is certainly not always true, but is true more often than I would like. I find it disappointing that we experimentalists have often yielded the intellectual leadership to theorists. This issue is complicated and may again be entwined with the maturity of physics. But I do not think it an accident that, of the physicists the general public knows and admires from the 20th century, nearly all are theorists. Richard Feynman and Stephen Hawking are only the two most recent examples. We physicists have raised them up as our common heroes for public admiration. I am uncomfortable that, for many decades, we have not had experimentalists that we have recognized as heroes across all disciplines.

John Rigden's letter also relates to the maturity of physics. I agree with his opinions, and I wish I had devoted more of my essay to education reform. That topic underlines one of the unappreciated problems of regarding physics as a mature discipline: Maturity may be admirable in many ways, but it may also be a final stage preceding dramatic decline. Educating bright students and training new researchers is the lifeblood of any science. If our curriculum, the artery bringing this lifeblood to our field, has become as rigid as Rigden maintains, we have a classic sign of impending doom. Because we certainly believe that our field has a bright future as well as a distinguished past, we must find ways of revitalizing our curriculum and keeping our field rejuvenated.

A further indication of the crisis in physics has recently appeared: the spate of horrendous data fabrication and scientific misconduct that has reportedly riddled such high-profile research as that of Jan Hendrik Schön on molecular-scale transistors and of Victor Ninov on element 118. As physicists, we have been trained to guard against errors in science in our own work and in that of others. We are probably pretty good at that, although greater care can always be taken. However, guarding against a hoax is entirely different from guarding against a mistake. Can we any longer trust that researchers are reporting their results to the best of their ability? The physics community on the whole seemed rather pleased when Alan Sokal, in Social Text, perpetrated a hoax about postmodern physics. The joke, if there ever was one, has now gone sour. We physicists are as easily duped and as open to ridicule as are our academic colleagues across campus.