About the author: Professor Stephen W. Hawking is probably the only living scientist today who needs no introduction to the publics in this world.
Professor Stephen Hawking presented the following statements by the invitation of Professor Shing-Tung Yau.
(Photo: Flickr / Lwp Kommunikáció)
Particle physics is definitely not a dying field. It is however an entirely different enterprise than it was in 1980. Since then, the standard model looks to be essentially confirmed and this may give the impression that the field is complete. However, that is far from being true. There are phenomena that are just not included in the standard model. Some are CP violation, neutrino oscillations, dark matter. In theory, the problems are immense: how to include gravity, the recently discovered dualities of quantum field theories, quark confinement, dark energy, black holes, early-universe cosmology. It is a different world but one that offers huge challenges to ambitious young people interested in how our Universe works. China has an incredible opportunity to become the world leader here --- don’t waste it. A good example is to build the Great Collider that can lead high energy physics for the next fifty years.
【The Chinese translation (by Hong-Jian He & Zhongzhi Xianyu) had been published in Math. Sci. History & Culture magazine (Wechat version) web link】
粒子物理学绝对不是一个行将就木的领域，也与它在1980年代的面貌完全不同。从那以后，标准模型看起来基本上已被证实，这给人一种该领域已经完成的印象。然而，这绝不是真实情况。自然界还存在标准模型无法解释的许多现象，其中包括CP破坏，中微子振荡，和暗物质，等等。同时我们还有大量理论上的难题：如何包含引力、量子场论中新近发现的各种对偶、夸克禁闭、暗能量、黑洞、和早期宇宙学。这是一个非同寻常的领域，它对于有志向、有兴趣探索我们的宇宙如何运行的年轻人提出了巨大的挑战。在这方面，中国有成为世界领导者的绝佳机遇 —— 不要错过它。一个很好的范例就是建造巨型对撞机，它将在今后五十年中引领高能物理学。
霍金完成了许多意义深远的杰出研究工作，获奖无数。主要的贡献有他与罗杰·彭罗斯（Roger Penrose）共同合作提出的彭罗斯-霍金奇性定理，以及他关于黑洞辐射的理论预测（现称为霍金辐射）。他结合广义相对论与量子力学，对量子宇宙学进行了先驱性研究。他关于黑洞面积不减定理的理论预言得到最近 LIGO 引力波实验观测的支持。LIGO 是尖端大科学项目成功进行重大基础科学前沿探索的又一个范例。
Hawking and Yau (Photo: CMSA Blog)
About the Interviewee: Professor Gerard 't Hooft is a renowned theoretical physicist at Utrecht University, the Netherlands. He is among the founders of the standard model of particle physics, and was awarded Nobel Prize in Physics “for elucidating the quantum structure of electroweak interactions” (together with Martinus Veltman) in 1999. He has also received numerous other prestigious prizes and awards, including Heineman Prize of American Physical Society (1979), Wolf Prize (1981), Pius XI Medal (1983), Lorentz Medal (1986), Spinoza Prize (1995), Franklin Medal (1995), Gian Carlo Wick Commemorative Medal (1997), HEP Prize of European Physical Society (1999), Ettore Majorana Prize (2011), Lomonosov Gold Medal (2011), and 1st Prize of Gravity Research Foundation (2015). He is the author of many popular science books, including “In Search of the Ultimate Building Blocks”, and the recent books “Playing with Planets” and “Time in Powers of Ten”.
About the Interviewer: Hong-Jian He, Professor of Physics at Tsinghua University, working in particle physics, cosmology, quantum gravity and their interface.
by photographer Alex Kok
Below are our interview questions (Q) and the answers (A) of Professor ’t Hooft.
Q1: Professor 't Hooft, it is our great pleasure to have this interview with you. I newly read your very thoughtful article “Imagining the Future, or How the Standard Model May Survive the Attacks” . In particular, you discussed new thinking about the Higgs boson and hierarchy problem. You also commented on the possible hint from the LHC. The LHC Run-2 has been performing well to collide proton beams at 13TeV energy, and has collected about 10% of the planned full Run-2 data. Even though no new physics is announced at the ICHEP conference in this summer, would you like to comment on your expectation of possible new findings at the on-going LHC?
A1: In one way, LHC did what was expected: it found the Higgs particle, often regarded as the last missing link in the Standard Model, but then it did something unexpected as well: it showed that there seem to be no other particles with such properties, while most theoreticians did expect them, and so there was a surprise after all. Then, many of us expected the Standard Model soon to require modifications in the form of new particles. We had several kinds of theories for that, of which the supersymmetry theory was the most advanced and detailed of all. To the contrary, there seem to be no new particles at all.
Will this be the new world at the TeV scale? We did not expect that. LHC is like the Michelson-Morley experiment, which, by giving no result at all, led to Eistein’s relativity theory. Now, I am considering that possibility seriously again: new theories that should explain the non-existence of heavy particles. I hope that this will turn out to be wrong again, since new particles will be giving us much more information, information that may reveal new principles of nature.
Q2: Since you mentioned  that the Higgs boson (125GeV) is an important clue and given the fact that the LHC with pp collisions could not measure the Higgs boson precisely, would you feel crucial to build up an e+e- Higgs Factory such as the CEPC ? You visited China many times before, and on February 23, 2014, you joined the Panel Discussion Meeting on “After the Higgs Boson Discovery: Where is Fundamental Physics Going”, held at Tsinghua University, Beijing. What is your viewpoints on this subject now?
A2: My viewpoints have not changed much. The value of 125 GeV is special because it is close to what one could have expected from theories based on conformal invariance, a theory that might one day explain to us the absence of heavy fundamental particles. If they are indeed absent, we need other clues to find the truth, and one of these clues could be obtained from precision physics. An e+e- Higgs factory would be quite suitable for obtaining precision data that would be more difficult to produce in other machines.
Q3: Regarding the lessons of Superconducting Super Collider (SSC) in USA, perhaps, you may have seen an article “The Crisis of Big Science”  by Steven Weinberg in 2012? 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 made vital negative impacts on American HEP in particular and in its whole fundamental science in general. Would you like to share your views with the publics regarding the lessons of SSC and LHC?
A3: I do not quite share Weinberg’s interpretation of recent history of our science. His rather gloomy mood on how big science failed applies to some unfortunate events such as the cancellation of the American Superconducting Super Collider, which has turned out to be too large and too costly to be operated by a single nation. However, many other big projects were extremely successful. LIGO has spectacular successes, various space probes and telescopes found lots of exciting things in the universe, such as gigantic black holes colliding at cosmic distances, and less far away asteroids, dwarf planets, comets, and thousands of exoplanets. Of course I see the LHC as a great example of how big science can still be successful, and clearly nobody can be blamed for the nonexistence of particles at the TeV scale. We still do not understand why this should be, so we strongly applaud initiatives for the next, greater machine.
Q4: Perhaps, you already heard about the current Chinese plan of the “Great Collider” project , 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. Many colleagues worldwide think that this is a truly promising direction for the next step forward in HEP . — Would you like to share your views on the CEPC Project with the Chinese community?
A4: We do have to live with the fact that science, no matter how big, evolves and its focus will change along with this evolution. If large particle accelerators and other large projects such as ITER will eventually not be further pursued, then this must be for sound scientific reasons. Perhaps we will find other ways to find answers to our questions. But today I do think we are not ready yet to give up hopes that higher energy machines will lead to important insights. It’s far too early to abandon that direction, but we do have to be united in our searches. The SSC might have been too ambitious at its time, and it might be too preposterous for us to ask China to succeed where the USA failed. But I would actually be pleased if China and Europe went into a friendly competition for building and operating the most powerful scientific instrument in the world – in that case, we scientists would all prosper from it. On the other hand, perhaps CERN’s present success is telling us that international collaboration, safeguarded by very strict regulations, is the way to go.
Q5: You probably have heard the on-going public debate in the Chinese community on whether this Collider should be built in China at all . This debate was provoked by the Chinese-American theoretical physicist C. N. Yang in this fall , who has been strongly against any collider project in China, including the current CEPC-SPPC project led by IHEP director Yifang Wang. 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. (As Yifang Wang showed in his refutation , the IHEP team estimated 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.) — Would you like to share your opinion with the Chinese publics?
A5: It is important to have this discussion in China. I am sure that Prof. Yang understands China’s domestic and foreign political attitudes and problems, as well as its enormous potential as a world power, so he should be listened to. Yet I don’t quite follow his arguments. In planning the SSC, I suspect the scientists in the USA miscalculated the support they would receive from politicians, congress, and fellow scientists, at home as well as abroad. Maybe it was just a tiny miscalculation, but it was enough to topple the project. This does not have to mean that China will make the same mistakes. Instead, the Chinese should carefully study what went wrong with the SSC, and ensure a sufficiently stable political and financial basis for the realization of its ambitious plans. Then decide whether the plans can be realised. As for their benefit for humanity in general and China in particular, we should indeed not make too grand promises in that a giant new accelerator will bring many elementary breakthroughs, let alone new applications of big science that will boost China’s prosperity. That is not the main justification of these enterprises. What should be expected is that this accelerator, together with a number of other big science projects, will lead to joint investigations all over the world of humanity’s basic questions. Chinese scientists will take part in these discussions, bringing in their own observations and results. China will be part of a scientific intelligentsia discussing not only basic questions in physics, but in all sciences and problems faced by humanity.
Will it be worth-while to spend such amounts of money on a project whose purposes are obscure to a big majority of the population? This, the Chinese scientists and politicians must decide for themselves. I should warn the scientists in particular that, in my experience, this isn’t a zero-sum game. Money saved by cancelling this machine, will not be used for other branches of science, but most likely disappear into completely different activities, which you may or you may not agree about. Therefore, in my humble opinion all scientists should be in favor of reserving money for projects like this, just because it is money to be spent on fundamental science. If indeed China decides to go into this direction, other, totally different big science projects might follow.
I presume Prof. Yang observed that, while the LHC was built in a region that already had all the necessary infrastructure present, which will certainly have suppressed its costs, the new Chinese machine must be built from scratch. This will make it cost more, but then, such money is well-spent. A new city may arise, where scientists from all over the world pay frequent visits and discuss the world’s problems. If China could still be looked upon as a developing country now, it won’t be that anymore.
 Gerard ’t Hooft, “Imagining the Future, or How the Standard Model May Survive the Attacks”, Int. J. Mod. Phys. 31 (2016) 1630022.
 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).
 C. N. Yang, “China should not build a super-collider now”, September 4, 2016. Chinese version: web link.
 Yifang Wang, “It is Suitable Now for China to Build Large Collider”, September 5, 2016. English translation: web link
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.
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 , 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 . Early last month, we recommended the Chinese translation of your review article “The Crisis of Big Science” (2012)  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 , 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 . — 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 . This debate was provoked by the Chinese-American theoretical physicist C. N. Yang in September, 2016 , 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 , and Yifang Wang’s refutation . 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  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. 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.
 Steven Weinberg, “Particle Physics, from Rutherford to the LHC”, Phys. Today 64N8 (2011) 29-33. See also, Int. J. Mod. Phys. A28 (2013) 1330055.
 Steven Weinberg, Dreams of a Final Theory --- The Search for the Fundamental Laws of Nature, published in New York, USA: Pantheon Books (1992).
 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).
 C. N. Yang, “China should not build a super-collider now”, September 4, 2016. [Chinese version.]
 Yifang Wang, “It is Suitable Now for China to Build Large Collider”, September 5, 2016. [English translation].
 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.
如果你还有其他问题，我很乐意回答，也可以推荐你与一些著名的物理学家（如David Gross、Edward Witten和Nima Arkani-Hamed等）联系，你将会了解到他们与杨教授很不一样的看法。
About the author: Yifang Wang is the director of Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences (CAS).
[The original article in Chinese: webpage.]
Today (September 4th) “The Intellectuals” published Prof. Chen-Ning Yang’s article “It’s not suitable now for China to construct the large collider”. As an experimentalist and the current Director of Institute of High Energy Physics, Chinese Academy of Sciences (IHEP, CAS), I cannot agree with him. Prof. Yang is a respected scientist, but I have even more respect for science and rational. I apologize in advance if the following discussion would cause any impoliteness.
The first point of Prof. Yang is that the construction of large colliders is a bottomless money sink. During the construction of the Superconducting Super Collider (SSC) in the US, the prices went so high that this project had to be given up halfway, leading to a waste of 3 billion US dollars. The construction of LHC cost 10 billion US dollars. The large collider of China won’t be cheaper than 20 billion US dollars, and may become a bottomless money sink.
Concerning this point, there are actually three questions: First, why did SSC fail? Secondly, what’s the cost of China’s large collider? Thirdly, is our estimation reliable? Is it another bottomless money sink? Let me discuss them one by one in the following.
(1). Why did SSC fail ? Are all Large colliders bottomless money sinks?
The SSC of the US failed for multiple reasons, including the deficit in the government budget, the competition of funding with the space station project, the political struggle between the Democratic and the Republican party, the competition between Texas and other states for the hosting of the SSC, mismanagement, mistakes in the budget, soaring cost, and not sufficient international cooperation, etc. A detailed analysis and historic documents can be found in the reference [2, 3]. In fact, the budget overrun was definitely not the main reason for its failure. Rather it was quite accidental in special circumstances, mainly due to political reasons.
For the US, the cancellation of the SSC project was a big mistake. Consequently, the high energy physics community of the US lost the chance to find the Higgs boson, lost its foundation and opportunity for further development, and lost its leading position in the international particle physics community. This decision had extremely negative impact to big science projects at the US. It dampened the ambition and courage of an entire generation. The opposition to the SSC in the US at that time shares many common arguments with the criticism of the Chinese large collider project today. In fact, the cancellation of the SSC project didn’t lead to any increase of funding to any disciplines. Of course, the construction of the SSC didn’t lead to any decrease of funding to any other field either. Many people who opposed the SSC came to regret their opposition to the project.
After that, the Europeans built the Large Hadron Collider (LHC) with a great success. Even though there was a small budget overrun, it was not significant, showing that large colliders are not necessarily bottomless money sinks, and could be successful.
The decision making process and political system in China is very different from that of the US, and is actually advantageous for large construction projects. It has less uncertainty. China today has already done a number of things which the US would not or could not do. In the future, more achievements of this kind will happen. The failure of SSC doesn’t means that we are not able to build large colliders in China. Of course, we should learn from the experience of the SSC and be better prepared for the project, including better international cooperation, management and budget estimate.
(2). What’s the cost of this collider?
The large collider we proposed has two phases. The first phase is a Circular Electron Positron Collider (CEPC), which could be constructed during 2022 – 2030. Assuming a tunnel circumference of 100km, the construction cost is roughly 40 billion CNY (not including the cost of land, and the supporting infrastructure such as road, water, internet, power supplies, etc.). If we succeed in the CEPC project and there are hints of physics beyond the SM, and if the novel technology of super conducting materials will have matured so that their cost is reduced to an acceptable level (say, ~ 20 CNY/kA*m), we can start the second phase, the Super Proton Proton Collider (SPPC). The cost of this phase could be controlled to within 100 Billion CNY, and the construction could happen in 2040-2050. As an international project, we expect 30% of the total cost to be covered by international partners. Therefore, the Chinese government needs to invest 30 Billion CNY (3 Billion per year for 10 years) for the first phase and 70 Billion CNY (7 Billion/year) for the second phase (without taking into account inflation). The fact that there is a possible second phase gives this proposed project, CEPC-SPPC, a much longer lifetime. It could stimulate the development of corresponding technologies such as high-Tc superconducting materials. These two phases are highly complementary to each other, in both scientific goals and technology impacts. At this stage, the purpose to discuss SPPC is to make sure that our design, such as tunnel length and cross section, does not limit the option for the future upgrade.
(3). Is this estimate reliable? Would it repeat the failure of SSC?
In the past half a century, many accelerators have been successfully constructed all over the world (LEP, LHC, PEPII, KEKB/SuperKEKB, et. al). There were also some not-so-successful accelerator projects (ISABELLE, SSC, et. al). In this list, all failed projects are proton colliders, with no failed example of electron-positron colliders. The reason is that the proton collider is technologically much more complicated; it’s usually very hard to predict the advancement of the super-conducting technology and it is not easy to properly balance between the cost, technology, and the specification. If the spec is too high, it would result in cost overrun. On the other hand, the choice of low spec would appear to be too conservative.
There had been many successful examples of large construction projects in China. Since its founding 40 years ago, IHEP has carried out many big scientific projects with cost higher than 100 M CNY, including the Beijing Electron Positron Collider (BEPC), the Daya Bay Neutrino experiment, the China Spallation Neutron Sources and the ADS Injector. All these projects have been completed on time, and up to the spec. The actual cost has never exceeded the budget by more than 5%. We have a mature system and deep experience on budget estimate, construction and project management.
In fact, we employed two methods to estimate the cost of CEPC: 1). decomposing the project into a list of equipment, components and sub-systems; 2). making analogies and comparing with similar projects around the world. Both at the sub-system level and for the total cost, these cost estimates are consistent within 20%. In fact, once we finished the Preliminary Conceptual Design Report (Pre-CDR) for the CEPC (the first phase), we generated a list of more than 1000 items, based on which the cost estimate was done, and reviewed by domestic and international experts. If Prof. Yang has any doubt about this cost estimate, another review can be organized.
For the SPPC, we only used the comparison and analogy method, since it is not the main objective now, but only a future possibility. It is meaningless to talk about its construction cost now. We have to wait until the technology is mature enough. How could it become a bottomless money sink?
The second point of Prof. Yang is that, China is still a developing country, and there are still livelihood issues to be solved. A Large collider is not that urgent and should not be considered now.
For any country, especially one with the size of China, it is essential to balance the short-term needs and the long-term plans. The livelihood is certainly an essential issue and it is in fact the main part of the government budget. Meanwhile, we also need to invest in long-term needs, with a reasonable fraction of GDP on basic science, in order to ensure the potential of long term development, and stimulate becoming a leader of the world. A terrible example is the Qing Dynasty. At that time, China had the largest GDP of the world, capable of buying anything from abroad. However, China was not developed in science. Though China bought lots of advanced weapons from abroad, it was still defeated miserably and its livelihood fell all the way down to the bottom of the world.
For centuries, the studies of microscopic structure of matter, from molecules, atoms to nucleus and elementary particles, led the development of science to a large extent. Nowadays, such research takes the form of particle physics, which aims to reveal the fundamental building blocks of matter and their interactions. Particle physics adopted and stimulated the development of technologies such as accelerators, detectors, cryogenics, superconducting materials and cavities, micro wave equipment, vacuum systems, power supplies, precision machinery, automation, computing and networks. Because of its huge impact to science and the boost to the technology development, high energy physics is a very significant and unique field. By constructing the CEPC, China will play a leading role in this important flagship field. In addition, Chinese industries could manufacture related high-technology products and lead the world. Meanwhile, the CEPC will also attract, and train thousands of top scientists and engineers, forming a science and technology center. The CEPC is indeed an urgently priority for China.
In fact, the impression of China to the world is rich and at same time too practical. A big country without contribution to the civilization cannot have big impact and influence in the world. This will in turn affect China’s interests. On the other hand, as a fraction of GDP, the cost of the large collider (CEPC and even SPPC) didn’t exceed that of BEPC, and is lower than that of other constructed and planned facilities (LEP, LHC, SSC and ILC) in the world.
The CEPC provides a unique opportunity for China to assume the leadership in the field of high energy physics in the world. First, the Higgs boson discovered at LHC has a mass that is perfectly suited to allow a circular electron positron collider to be a Higgs factory. Meanwhile, this collider could be upgraded to a proton collider, providing a science program that could last for 50 years. Secondly, we have a time window of roughly 20 years with relatively mild international competition, since Europe, the US and Japan are all occupied by other particle physics projects. Thirdly, with the BEPC, an electron-positron collider, we accumulated sufficient experience and a well-trained team which are just right for CEPC. This window of opportunity will last for only about 10 years. It is hard to predict when would be the next time if we miss it. Meanwhile, China has excellent experiences in large underground projects, and the economy is still in rapid growth. During this restructuring period, there are needs to invest on science. Therefore, CEPC is a well suited project for China now.
The third point of Prof. Yang is that the construction of CEPC will largely squeeze the funding for other disciplines of basic science.
Currently in China, the funding for basic science is roughly 5% of the total R&D spending, while that fraction for developed countries in the world is typically 15%. As a large developing country moving towards a developed one, I think China should gradually increase this ratio to 10% and eventually to 15%. In terms of numbers, there is still a big room for the funding of basic science to increase (roughly 100 B CNY per year). Therefore, construction of the CEPC would not crowd out the funding for other disciplines.
On the other hand, how should we spend the funding from such an increase? It is well known that a significant percentage of our funding is spent on purchasing equipment, especially from abroad. If we suddenly increase the funding uniformly to all disciplines, or toward some disciplines that strongly rely on the international apparatus, it is very likely that such an increase will also boost the GDP of foreign countries. To the contrary, if we invest on the large accelerator for 10 years with a total budget of 30B CNY, more than 90% of the money will be spent in China. Such a spending will stimulate our companies to have technology progresses and more market sharing, train thousands of scientists and engineers that could design and manufacture the needed apparatus, and help the development of other disciplines. In fact, such an investment will not change significantly the balance among different fields. In the long run, it will rebalance the funding distribution to a level comparable to the norm in the world (currently particle physics and nuclear physics are significant low in China relative to the rest of the world). The Chinese government is now calling for proposals to host large international scientific projects. CEPC is an excellent candidate, and not in conflict with other disciplines of basic science.
The fourth point of Prof. Yang is that SUSY particles and Quantum Gravity have not yet been discovered, and it is hopeless for the CEPC to discover such hypothetical particles.
The science goal of CEPC is not what Prof. Yang described. In fact, we described clearly the physics motivation in the “Preliminary Conceptual Design Report of CEPC-SPPC” which I delivered to Prof. Yang in person. In short, the Standard Model (SM) of the particle physics is only an effective theory at low energies. We aim at discovering the fundamental physics principles that underlying the SM. Although there are some experimental evidences for new physics beyond the SM, we still need more data to guide the direction for the future. Currently, most of the problems of the SM are related to the Higgs boson. Therefore, clues of new physics at deeper level shall come from the Higgs boson. CEPC can measure the Higgs boson to an accuracy of 1% level, which is a factor of 10 better than that of the LHC. Such a precision would allow us to determine the properties of the Higgs, and to check its consistency with the prediction of the SM. Meanwhile, CEPC may measure for the first time the self-coupling of the Higgs boson (indirectly) to determine the type of the electroweak phase transition, which is essential for the understanding of the early evolution of the Universe. In short, no matter if LHC discovers new physics or not, CEPC is badly needed and cannot be skipped in the advance of particle physics.
If there is any deviation from the SM observed at the CEPC, for example new coupling and/or new partners of Higgs boson, substructure of the Higgs boson, we could upgrade CEPC to SPPC to directly look for the cause of such deviation, which might be SUSY particles or any other new particles. For experimentalists, we care about theoretical predictions, but we never rely on them. It is too assertive to claim what particles can or cannot be discovered at the future collider. Most people from the international high energy physics community do not think that way either.
The fifth point of Prof. Yang is that major achievement of particle physics in the last 70 years did not offer direct benefit to human life, and it won’t have any in the future.
For 70 years, high energy physics had a lot of achievements. It developed lots of technologies that are closely related to people’s daily life. Without particle physics, there will be no synchrotron light source (coming from electron positron circular collider), free electron laser (coming from electron positron linear collider) and spallation neutron source, which are essential tools for the study of biology, geology, environment, material science, and condensed matter physics. Without particle physics, many medical apparatus such as MRI, PET and radiotherapy would not exist, would not be so advanced, or be invented much later. Many people would have a shorter life span, or their life quality would be severely reduced. Without particle physics, there would be no (or much delayed) touching screen, and therefore no smartphones; there will be no World-Wide-Web (WWW) and we would not be able to surf the web. There would be no e-commerce of course. In fact, WWW has changed profoundly the world and its economical outcome has been much more than all the investment in high energy physics before that.
In terms of the CEPC, how would it affect our daily life? With the 30 Billion CNY investment (3 Billions per year, starting from 2022 for 10 years), we could promote the following technologies in our domestic companies to a world leading position:
a) High Quality Super Conducting Cavity (used in almost all the accelerators)
b) High Efficiency, High power microwave power source(used in radar, broadcasting, communication and accelerators)
c) Large scale cryogenic systems (used in other fundamental researches, rocket engine, medical apparatus)
d) High speed, radiation-hard silicon detectors, electronics and ASICs
In the meantime, we can also lead the world in technologies such as precision machinery, microwave, vacuum, automation, data acquisition and processing, computing and networks. We can train thousands of top-level physicists and engineers, as well as attract thousands top-level scientists and engineers worldwide to form an international center of science. If SPPC is going forward, 7 Billion CNY will be investigated each year starting from 2040, it can promote the application of our technologies of high-Tc superconducting material and superconducting magnets which will be leading the world. The volume of this industry would be much larger than 70 Billion CNY(cost of SPPC). On top of that, there might be unexpected new discoveries and new technologies. The direct application of high energy physics discoveries cannot be predicted now. Indeed there should be no need to ask this question since the importance of the study of the structure of matter and elementary particles cannot be emphasized more. The Chinese may have laughed at the Greeks and the Europeans for their “useless” studies on atoms, gravity, quantum mechanics and the Higgs boson, but there is always a price to pay (which has been paid).
The sixth point of Prof. Yang is that the Institute of High Energy Physics (IHEP) did not have great achievements in the last 30 years. Over 90% of the works for the large collider will be dominated by non-Chinese and the possible Nobel laureates would not be Chinese.
It has been more than 40 years since the establishment of the IHEP. Benefiting from the construction of the Beijing Electron Positron Collider (BEPC), IHEP had been developed significantly with focus on particle physics, astrophysics, multi-discipline research and applications. For particle physics, a major investment to facility at IHEP is the Beijing Electron-Positron Collider (240 M CNY, 1984), its upgrade (640 M CNY, 2004) and the Daya Bay neutrino experiments (170 M CNY, 2007). The total is about 1 Billion CNY. Comparing to other disciplines, for example biology, condensed matter physics and astrophysics as mentioned by Prof. Yang, the funding level of particle physics is not higher (in total or per person). Meanwhile, the output of particle physics, partially measured by national and international awards and honors, is no less than other disciplines. Though such an investment is orders of magnitude lower than that of leading countries, the scientific output is somehow comparable. At least IHEP is one of the four leading particle physics laboratories in the world (CERN, Fermilab, KEK, IHEP).
In the year of 2012, Chinese scientists first independently proposed the CEPC-SPPC project. The international community of particle physics responded strongly to this proposal and gave strong support. We launched the conceptual design afterwards and completed mainly by ourselves, with some international participation, the “Preliminary Conceptual Design Report” (pre CDR) in 2015. Hence we believe that in the future，more than 70% of the works for the large collider will be completed by Chinese, at least the same as the fraction of the Chinese investment. If Prof. Yang still has no confidence, please consult with leaders of major particle physics labs in the world.
In fact, IHEP has over 30 years’ experiences with the electron positron collider. CEPC is proposed after much deliberation. Those who participated the design and construction of BEPC in 80’s agree that it was much more difficult to construct the BEPC in 80’s than to construct the CEPC today. We believe that the younger generation today would do even better and we have the confidence, capacity and courage to accomplish the CEPC by ourselves. On the other hand, we should encourage international participations for this project.
Concerning to the second phase of the hadron collider (SPPC), we admit that we don’t have much experience and need more effort. However, we still have 20 more years, and should be able meet the minimum target of “accomplish works proportional to the funding contribution”. According to our record of progress in the last 30 years, this goal should be achievable.
About the possibility of Nobel Prize to Chinese, I think it is not predictable. It is not the motivation of the investment to basic science by our country, nor that of the individuals who do the research. We ultimately try to understand and reveal fundamental principles of the nature. The Higgs boson is discovered at CERN and its discovery granted the Nobel Prize to Mr. Higgs from the University of Edinburg. We hope that China can host a research institute with the similar scale, scientific output and technology capabilities like CERN. It is not important whether we have our University of Edinburg and Mr. Higgs to win a Nobel Prize.
The seventh point of Prof. Yang is that the future of particle physics lies in the direction of “new concept of acceleration” and “theory of geometry”, not in colliders.
The “new concept of acceleration” (such as plasma acceleration) is indeed promising for the future accelerators. Given enough time, maybe in several decades, such technologies might be applicable to fixed target experiments or other experiments that do not require high quality beams. For high energy colliders, both beam quality and energy efficiency of these novel technologies still have a long way to go. In the meantime, high energy physics should not halt to wait for the maturity of these technologies. And about the “theory of geometry” or “string theory”, they are too far away from being able to be tested by experiments, it is not an issue for us (experimental particle physicists) to consider now.
People always have different opinions about the future direction of particle physics. China does not have Nobel Laureates in physics now, but there are many in the world. Obviously Prof. Yang holds a view different from the majority of them, not only now, but also in the past. Prof. Yang has been pessimistic about particle physics since 1960s, and missed the major discoveries of the Standard Model of particle physics. In 1970s, Prof. Yang opposed the construction of high-energy accelerators in China . Fortunately, Mr. Deng Xiaoping took the suggestions of Prof. T.D. Lee and other prominent scientists. As a result, it became possible to have today’s IHEP, BEPC, Daya Bay, and their great results, as well as large science facilities such as synchrotron light sources and the spallation neutron source serving the science community of the whole country. Facing the future, we should listen more to the young scientists working on the front line of the research, who will make our science flourish and grow into a leading position in the world.
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 M．Riordan, L. Hoddeson and A. Kolb, Tunnel Vision --- The rise and fall of the Superconducting Super Collider, The University of Chicago Press，2015.
 IHEP Annual Report, 1972--1979 (in Chinese).