Interview with Nobel Laureate Steven Weinberg — Discussing High Energy Colliders


-- Steven WeinbergHong-Jian He

[This article will be published in ICCM Notices, and the Chinese translation had been published in Math. Sci. History & Culture (数理人文) magazine (Wechat version)].

About the Interviewee: Steven Weinberg is a renowned theoretical physicist and a great master of modern physics. He is currently the Josey Regental Chair Professor in Science at the University of Texas at Austin, where he is on faculty of the Physics Department and Astronomy Department. He is a major founder of the Standard Model of particle physics, and was awarded the Nobel Prize in Physics in 1979 (together with Sheldon Glashow and Abdus Salam) “for their contributions to the theory of the unified weak and electromagnetic interaction between elementary particles, including, inter alia, the prediction of the weak neutral current”. His research on elementary particles and cosmology has been honored with numerous other prizes and awards, including National Medal of Science (1991), J. R. Oppenheimer Prize (1973), Heineman Prize of APS (1977), Elliott Cresson Medal of Franklin Institute (1979), James Madison Medal of Princeton University (1991), and Benjamin Franklin Medal of American Philosophical Society (2004). He has been elected to American National Academy of Sciences and Britain's Royal Society, as well as to the American Academy of Arts and Sciences. He has also served as consultant at the US Arms Control and Disarmament Agency, and the JASON group of defense consultants. He taught at Columbia, Berkeley, MIT, and Harvard where he was Higgins Professor of Physics, before coming to Texas in 1982.

He is the author of over 300 articles on elementary particle physics. His books include Gravitation and Cosmology (1972); The First Three Minutes (1977); The Discovery of Subatomic Particles (1983, 2003); Elementary Particles and The Laws of Physics (with R. P. Feynman) (1987); Dreams of a Final Theory --- The Search for the Fundamental Laws of Nature (1993); a trilogy, The Quantum Theory of Fields (1995, 1996, 2000); Facing Up --- Science and its Cultural Adversaries (2002); Glory and Terror --- The Growing Nuclear Danger (2004); Cosmology (2008); Lake Views: This World and the Universe (2010); and To Explain the World --- The Discovery of Modern Science (2015), etc. His book “Dreams of a Final Theory” was written for the support of building the Superconducting Super Collider (SSC) in USA. His article “Big Crisis of Big Science” was written in 2012 in which he discussed the importance of big projects for the sciences and high energy physics as well as the lessons of the SSC.

About the Interviewer: Hong-Jian He, Professor of Physics at Tsinghua University, working in particle physics, cosmology, quantum gravity and their interface.

The Interview


Below are our interview questions (Q) and the answers of Professor Weinberg (A).

Q1: Professor Weinberg, it is our great pleasure to have this interview with you. I recently reread your article “Particle Physics, from Rutherford to the LHC”, first published in Physics Today [1], where you explained why the new physics is required to go beyond the Standard Model (SM) of particle physics for which you were a major founder, “It is clearly necessary to go beyond the standard model. There is a mysterious spectrum of quark and lepton masses and mixing angles that we have been staring at for decades, as if they were symbols in an unknown language, without our being able to interpret them. Also, something beyond the standard model is needed to account for cosmological dark matter.” These are indeed what the particle physics community has been striving for over the past thirty years, through the major high energy colliders including Tevatron in USA and LEP & LHC in Europe. The LHC Run-2 has been performing very well to collide proton-proton beams at an energy of 13TeV, which has collected about 10% of the planned full data sample of the Run-2 so far. Even though no new physics is announced at the ICHEP conference in August, would you like to comment on your expectation of possible new findings at the on-going LHC?

A1: It is impossible for anyone to know whether there are significant new discoveries that will be within the capabilities of the LHC. From the beginning, there had been strong reasons to anticipate that the LHC would be able to discover the mechanism by which the symmetry governing weak and electromagnetic forces is broken – either elementary scalar fields, as in the original electroweak theory, or new strong forces, as in technicolor theories. In either case, the observed strength of weak forces gave a powerful indication that new scalar particles or new strong forces would be observable at the LHC, as turned out to be the case. Indeed, this provided a guide in planning the LHC.

But, although there are several other phenomena of great importance that might be discovered at the LHC, including dark matter particles and superpartners of known particles, we have no strong reason to suppose, even if they exist, that they would be within the reach of the LHC. We will just have to wait and see.

Q2: We know you was the major supporter of the SSC [2]. Early last month, we recommended the Chinese translation of your review article “The Crisis of Big Science” (2012) [3] to the Chinese publics. The cancellation of SSC by US congress in 1993 was a great loss for the high energy physics (HEP) community in USA and worldwide; it seems to have made vital negative impacts on American HEP in particular and in its whole fundamental science in general. On the one hand, SSC was designed to collide proton-proton beams at a center of mass energy of 40TeV, which is a factor 3 larger than the current Run-2 colliding energy (13TeV) of Large Hadron Collider (LHC) at CERN, Geneva. Perhaps, it should not be so unexpected and disappointed that the LHC Run-2 has not found any new physics beyond the Standard Model (SM) so far, because we all know that the SSC with 40TeV colliding energy was designed to ensure a much more solid new physics discovery reach at TeV scales. As expected by many physicists, if the SSC had not been canceled in 1993, it would probably have already made revolutionary discovery of new physics beyond the SM and thus have pointed to a new direction for fundamental physics in 21st century. Since you have witnessed the full history of the SSC and the subsequent developments of the LHC so far, would you like to share your views with the Chinese community regarding the lessons of the SSC and LHC?

A2: Even after the SSC program had been approved by the US government, it continued to meet opposition from several directions. Part of the opposition came from those who generally prefer small government and low taxes, and therefore tend to oppose all large government projects, especially those projects for which there is no large number of immediate beneficiaries. The project would obviously provide economic benefits to people in its neighborhood, but these persons would be limited in number. One US senator commented to me that at that moment, before the site of the SSC had been decided, all 100 members of the Senate were in favor of it, but that once the site was chosen, the number of senators in favor would shrink to two, the two senators from the state of the chosen site. Even before the final site had been determined, one member of the House of Representatives who had favored the SSC turned against it once it was clear that the SSC would not go to his own district. All this was standard politics, perhaps of a sort that is not restricted to the US.

Much more disturbing was opposition from within the scientific community. No one argued that the SSC would not do important scientific research, but some urged that the money needed for the SSC would be better spent in other fields, such as their own. (It did not provide much consolation when the SSC was cancelled that the funds saved did not go into other areas of science.)

There was implicit opposition to the SSC from advocates of the LHC, who pointed to the financial savings from their use of an existing tunnel. The smaller circumference of this tunnel limited the LHC energy to only about one third of that possible for the SSC, but proponents of the LHC argued that the LHC could make up for its lower energy by operating at higher intensity, though this higher luminosity obviously carried its own difficulties, due to the several particle collisions in each intersection of bunches.

One explanation that is sometimes given for the cancellation of the SSC is that its projected costs kept increasing. This was certainly charged by some of the opponents of the SSC, but I don't believe it was a fair criticism. The only real increase in the cost of the project was approximately ten percent, made necessary by a calculation of the aperture needed for the SSC beam. Whatever increased cost there was beyond that came from the slowdown of funding from Congress, which required an extension of the time for construction, and hence an extended time in which construction personnel had to be employed.

The SSC project was killed chiefly by competition from a program that masqueraded as science, the International Space Station. This was to be administered at the Johnson Manned Space Flight Center, in Houston, Texas. It was not politically possible to support two large technological projects in Texas, and the Space Station was chosen. In the end, it cost ten times what the SSC would have cost, and has not led to any important scientific research. (The one possible exception, the Alpha Magnetic Spectrometer, could have been operated as well or better, and much more cheaply, on an unmanned satellite.)

The LHC has been a great success, with the discovery of the Higgs boson. Whatever the LHC’s chances for further important discoveries, it is clear that the much greater energy of the SSC would have provided a better chance for the future.

Q3: Perhaps, you already heard about the current Chinese plan of the “Great Collider” project [4], whose first phase is called CEPC, an electron-positron collider of energy 250GeV, running in a circular tunnel of circumference about 100km long. It has a potential second phase for a proton-proton collider with energy up to 100TeV (SPPC). This proposal was officially ranked as the “First Priority HEP Project” at the recent “Strategy Plan Meeting for Future High Energy Physics” of the Chinese Particle Physics Association, held on August 20-21, 2016. This plan has received worldwide supports of the international HEP community since its inception [5]. — You probably have heard about the on-going public debate in the Chinese community on whether this Collider should be built in China at all [6][7][8]. This debate was provoked by the Chinese-American theoretical physicist C. N. Yang in September, 2016 [7], who has been strongly against any collider project in China, including the current CEPC-SPPC project led by IHEP director Yifang Wang. Attached below are English translations of Yang’s recent public article [7], and Yifang Wang’s refutation [8]. It’s clear that Yang’s major objection is that this collider would cost too much for China, and a misconception of him was to stress the cost of the potential second phase SPPC. (The IHEP team estimated [8] the CEPC cost to be about 6 billion US dollars invested over 10 years and its 25% will come from international collaboration. The SPPC would be built during 2040s if the required technologies become mature by then.) As anyone may recall, the funds of the LEP and LHC at CERN were approved separately and in sequence. --- It will be extremely helpful for the Chinese community to learn your viewpoints and advice from international side.  Would you think that the fund invested for CEPC worthwhile? and what would this contribute to the world and to the society of China?

A3: I have tremendous respect for the scientific research carried out by C. N. Yang, but I do not agree with his arguments against the proposed CEPC. Some of them are familiar, being used again and again against large scientific projects.

Yes, society has many other needs, including environment, health, education, and so on. It always does. But it also has needs for arts and sciences that make its civilization worthy of respect.

Yes, no immediate practical applications are likely to follow from discoveries made at particle accelerators. But the projects themselves have important practical consequences in the form of technological spin-offs. Frequently cited examples include synchrotron radiation, used to study the properties of materials, and the World Wide Web.

A less frequently cited spin-off is intellectual. The fundamental character of elementary particle physics makes it very attractive to bright young men and women, who then provide a technically sophisticated cadre available to deal with problems of society. In World War II microwave radar, cipher-breaking computers, and nuclear weapons were developed by scientists who before the war had been concerned with problems of fundamental scientific importance rather than of military value. One of the best graduate students who started work with me on elementary particle theory later became interested in more practical problems, and has developed what may become the leading approach to isotope separation. The country that pursues only research of direct practical importance is likely to become unable to make not only discoveries of fundamental importance but also those of practical value.

One of Professor Yang’s arguments is that progress can be made without new accelerators by the search for beautiful geometric structures. This reminds me of a position taken after World War II by another great theoretical physicist, Werner Heisenberg. He argued against German spending on particle accelerators, on the grounds that progress could be made through theoretical studies of certain field theories[9]. It is true that without the impetus of new experimental results, in trying to understand the strong forces Yang and Mills did develop a field theory of a class that later turned out to be realized in nature. But the correct Yang-Mills theory of strong forces could not be guessed until accelerator experiments revealed a weakening of strong forces at high energy, and the relevance of Yang-Mills theories++ to the weak and electromagnetic interactions could not be confirmed without new accelerator experiments that discovered weak neutral currents. Theory can only go so far without experiment.

References


[1] Steven Weinberg, “Particle Physics, from Rutherford to the LHC”, Phys. Today 64N8 (2011) 29-33. See also, Int. J. Mod. Phys. A28 (2013) 1330055.

[2] Steven Weinberg, Dreams of a Final Theory --- The Search for the Fundamental Laws of Nature, published in New York, USA: Pantheon Books (1992).

[3] Steven Weinberg, “The Crisis of Big Science”, in The New York Review of Books, May 10, 2012. webpage For Chinese edition of this article (translated by Zhong-Zhi Xianyu), see: webpage

[4] Circular Electron Positron Collider (CEPC) and Super pp Collider (SPPC), (http://cepc.ihep.ac.cn).
See the recent science book for introduction of this subject: S. Nadis and S.-T. Yau, “From the Great Wall to the Great Collider --- China and the Quest to Uncover the Inner Workings of the Universe”, 2015, International Press of Boston, Inc., MA, USA (https://thegreatcollider.com).

[5] David Gross and Edward Witten, “China’s Great Scientific Leap Forward”, in The Wall Street Journal, September, 2015. webpage For Chinese translation of this article, see: webpage

[6] Shing-Tung Yau, “Comments on the Construction of a High-Energy Collider in China and Reply to Media’s Questions”, August 30, 2016. [English version], [Chinese version].

[7] C. N. Yang, “China should not build a super-collider now”, September 4, 2016. [Chinese version.]

[8] Yifang Wang, “It is Suitable Now for China to Build Large Collider”, September 5, 2016. [English translation].

[9] Note: This refers to, after the German atomic bomb project failed in World War II, Heisenberg's works on certain unified field theory of elementary particles since 1953 in which he tried to derive the so-called "world equation". As is well-known, his attempts ended up in vain and have been forgotten thereafter. See: Werner Heisenberg Biography (https://nobelprize.org); David C. Cassidy, “Uncertainty: The Life and Science of Werner Heisenberg”, Freeman (1992), cf. Appendix A.




(更新日期:2016-10-31)