Praxis Archives – Page 125 of 181

Amazing particles and light

Promising developments in hadronic physics, microwave superconductivity, free-electron lasers and efficient energy-recovery techniques in accelerators were beckoning me – after 25 colourful years at Berkeley, including two spent at CERN. I was also concerned about the longevity of a profession in which I had personally invested. I had seen the attrition of talents, many of whom I mentored, to other professions, driven by socio-economic realities of large particle accelerators. This inspired me to motivate accelerator-science practitioners to diversify their portfolio by developing the small and mezzo-scale engines that would drive emerging nano- and bio-sciences. Today, on the eve of another personal transition as I prepare to take the helm at the UK’s Cockcroft Institute, new developments and challenges once again invite comment.

I observe a few key developments contributing at the frontier of “discovery”, while others attest to “innovation” and “diversification”. These include: development of electron, proton and ion beams of unprecedented precision based on normal and superconducting material technology and advanced feedback control; diversification and growth of synchrotron radiation sources worldwide; evolution of sophisticated table-top laser-plasma acceleration techniques with necessary control to produce giga-electron-volt electron beams; demonstration of self-amplified spontaneous emission for the planned X-ray free-electron lasers; demonstration of efficient energy use and recovery in superconducting linacs; and production of ultra-short femtosecond flashes of electrons, infrared light and X-rays for studies of ultra-fast phenomena – to name but a few.

We have consolidated the “discovery” sector and diversified the “innovation” sector

I also admit to occasional sombre worries that perhaps accelerators will be just a passing moment in history. But I was always awakened by the realization that particle accelerators have been and must continue to be singularly distinctive instruments of discovery and innovation, in various measures. What we are witnessing is a mere partitioning of the balance between these values in the context of the evolving human condition. We have consolidated the “discovery” sector and diversified the “innovation” sector. The fundamental value of accelerators, articulated in my 2002 Viewpoint, remains invariant: they package and focus energy and information in patterns of space–time bursts to serve a multitude of human pursuits – hence their universal, timeless appeal. Amazing particles and light, carrying focused energy and information in special staccato-fashion, beam into matter and life, illuminating what our eyes do not see and manipulating what our hands cannot.

Throughout the 20th century, fundamental discoveries were enabled by bold conception and realization of ever-larger particle accelerators, which today must be consolidated into just a few carefully selected facilities so large that they can only be supported internationally. Hence the emergence of but a few grand future machines: the Large Hadron Collider, the X-ray free-electron lasers, a potential International Linear Collider (ILC- or CLIC-based), and neutrino/muon facilities. This consolidation is a must for mastering the global resources necessary to discover fundamentals at the core of the physical world: hidden dimensions, symmetries and structures; origins of mass, dark matter and dark energy; unification of gravity; and exotic states of matter.

In parallel with that consolidation, we continue to anticipate tremendous diversification in the innovation sector of clever techniques and merger of technologies in creating unique bursts of particles and light. These efforts will lead not only to novel affordable scientific devices (for example, energy-recovery and laser-plasma-based compact high-brightness particle and light sources), but also to an increasing set of affordable instruments and processes that more directly enrich our everyday lives (such as novel medical imaging, diagnostics, therapy and radiation oncology; micro-machined instruments for use in medicine, scientific research, information technology and space exploration; designer nano-materials; and knowledge of complex protein structures for drug discovery).

The vision is one of discovering the secrets of the hidden energy and matter in the universe’s evolution; of understanding the protein as the molecular engine of life through studying its energetics and structural folding; of innovating new eco- and bio-friendly materials for human use; and of eliminating radioactive waste and dependence on fossil fuels. Extraordinarily clever particle accelerators drive this at all scales from “small” to “mezzo” to “grand”.

Is this just a dream? Inspired by US poet Carl Sandburg, I respond: “Nothing happens, unless first a dream.”

Quantum Optics: an Introduction

by Mark Fox, Oxford University Press. Hardback ISBN 9780198566724, 9.95 ($89.50). Paperback ISBN 9780198566731, £24.95 ($44.50).

This is a modern text on quantum optics for advanced undergraduate students. It provides explanations based primarily on intuitive physical understanding, rather than mathematical derivations. There is a strong emphasis on experimental demonstrations of quantum optical phenomena, in both atomic and condensed-matter physics. Other topics include squeezed light, Hanbury–Brown–Twiss experiments, laser cooling, Bose–Einstein condensation, quantum computing, entangled states and quantum teleportation. The book also includes worked examples and exercises.

The New Physics for the 21st Century

By Gordon Fraser (ed.), Cambridge University Press. Hardback ISBN 9780521816007, £30 ($60).

Seventeen years ago a book called The New Physics illuminated – vividly for the layperson and sensibly for the student – a series of scientific advances and philosophical obsessions, and it trailed them as signposts for the future. As so often happens, the future went off in a somewhat different direction. While Paul Davies was editing the first volume, physicists wondered loudly and publicly about dark matter and cosmic strings; black holes and the end of time; grand unification theory and cosmic inflation; the new window on the universe by the yet to be launched Hubble Space Telescope; and the claim by the Nobel prize-winner Luis Alvarez that an asteroid had crashed into the planet 65 million years ago and ended both the Cretaceous era and the dinosaurs. In fact, Alvarez and his planet-bruising bolide never got a mention in the Davies volume, but at the time there seemed quite a lot else to be getting on with.

CCEboo1_01-07 — The New Physics for the 21st Century by Gordon Fraser

What a difference the decades make. In the past 17 years, experimental physicists have delivered a fifth state of matter in the Bose–Einstein condensate; slowed light down first to walking speed and then to a complete standstill; dropped the idea that time might run backwards and instead proposed interminable heat death in an ever expanding cosmos; demonstrated quantum entanglement and teleportation; mapped the fluctuations in the cosmic background radiation; introduced branes and apparently dropped cosmic strings; and discovered dark energy in a big way – so big that it accounts for three-quarters of everything. Nanotechnology emerged as both engineering obsession and practical investment, amid royal alarm in the UK about global death by grey goo. The Hubble telescope went up with a faulty mirror, and NASA launched its International Space Station but seemed to run out of steam. Global warming – physics at a practical level for most people – announced its arrival with a procession of record temperatures globally, and the debate about the Cretaceous catastrophe flowered into a much larger argument about asteroid impact-warning and deflection.

Physics never seemed so glamorous, but student numbers continued to fall and university departments continued to close. The old New Physics didn’t look so new and now CERN’s own Gordon Fraser has produced a companion volume of 19 essays, just as substantial, just as wide-ranging, and in some cases just as much fun.

Physics is not easy (it is after all done by PhDs, not dilettantes) but each essay begins comprehensibly and even enticingly, before diving quite briskly into mathematics, hard argument and occasionally hostile language. (Did Michael Green, writing about superstring theory, really have to head a section “beyond the naive perturbative approximation”?) Chris Quigg looks at particle physics and puts the Large Hadron Collider handsomely in its scientific context. But Fraser plays no special favourites. Nanoscience is there, and the Grid, and there are welcome surveys of biophysics and medical physics; the last essay is a reminder that without the physics of imaging, some neuroscience would be little more than voodoo.

All the classical preoccupations – cosmology, astronomy, gravity and the quantum world – get a fresh look. Robert Cahn’s survey of the physics of materials is a big help for the benighted. Ugo Amaldi ends the volume with a handsome canter through the connections between physics and society, and echoes many of the themes tackled in the book’s previous 18 chapters. The bad news is that physics still has an image problem. The good news is that this time Alvarez gets a mention, although not for bolide impacts, dinosaurs or the present concerted international effort to identify and track near-Earth objects. No, he gets a mention for not solving the world’s energy crisis: to be fair, for admitting that, for a few exhilarating moments, he thought that he had solved the world’s fuel problems for all time by fusing a proton with a deuteron to form helium-3. This anecdote appears, a little unkindly, under the heading “usable knowledge”.

Experimental Techniques for Low-Temperature Measurements: Cryostat Design, Material Properties, and Superconductor Critical-Current Testing

By Jack W Ekin, Oxford University Press. Hardback ISBN 9780198570547, £65 ($125).

This extensively illustrated book presents a step-by-step approach to the design and construction of low-temperature measurement apparatus. The main text describes cryostat design techniques, while an appendix provides a handbook of materials-property data for carrying out designs. Tutorial aspects include construction techniques for measurement cryostats, operating procedures, vacuum technology and safety. Many recent developments in the field not previously published are covered in this volume.

Rooted in symmetry: Yang reflects on a life of physics

Chen Ning Yang first came to CERN in 1957, the year he shared the Nobel Prize in Physics with Tsung-Dao Lee for their proposal that the weak interaction violates parity symmetry – at a fundamental level, the mirror symmetry between left and right is broken. Almost 50 years later, Yang was again at CERN speaking to a packed auditorium about his thoughts on the important themes in physics over the second half of the 20th century. He can do so with authority: he not only knew great physicists such as Wolfgang Pauli and Paul Dirac, but he has also made many fundamental contributions to physics from the 1950s onwards.

CCEint1_01-07 — Above: Yang at the site of the CMS detector with spokesperson-elect Jim Virdee. Above right: Yang delivering his colloquium. Right: at lunch theorist André Martin illustrates a point while Yang and Jack Steinberger (right) listen attentively.

When Yang arrived at CERN in 1957 the theory group was housed in a hut at Cointrin by the villa visible still behind fences surrounding the airport, and he recalls meeting people such as Jack Steinberger, Oreste Piccioni and Bruno Ferretti. But the visit also had a personal significance for Yang, who had lived in the US for 12 years, having left his native China in 1945. In the US he had gained his PhD, working under Edward Teller at Chicago University, and by 1957 he was married with a six-year-old son. It was a time of difficult relations between China and the US, with no possibility for Yang and his new family to meet with his parents in either country. However, the trip to Geneva offered Yang the opportunity to arrange for his father to come from China for a six-week visit and meet his wife and son. This happy experience was repeated on further visits to CERN in 1960 and 1962.

Throughout his long career Yang made many contributions to physics, achieving two of his best-known contributions to particle physics – Yang–Mills theory and parity violation – by the time he was 34. Yang says that he was fortunate to come into physics when the concept of symmetry was beginning to be appreciated.

In the 1920s people did not like the concept of symmetry, as they were sceptical of its new mathematics of groups – there were those who even talked of “the group pest”. But in the 1930s physicists began to realize that symmetry was necessary to describe atomic physics; in particular, symmetry groups explained the structure of the Periodic Table. By the 1940s its application had extended to nuclear and particle physics.

Yang worked on group theory for his PhD thesis under Teller, and this firmly anchored his interest in groups and the emerging field of symmetry in particle physics. He now reflects: “When young, the best thing that you can do is to launch yourself into a field that is just beginning.” This is exactly what Yang did.

Yang–Mills theory

By 1954 he had written with Robert Mills what he still regards as his most important paper, laying out the basic principles of what has become known as Yang–Mills theory. The theory is now a cornerstone of the Standard Model of particle physics, but at the time it did not agree with experiment. “We couldn’t escape the question of the mass of the spin-1 particles that come out of it,” recalls Yang, “although we did discuss it at the end of the paper and implied that there may be other reasons for the mass not being zero.” So why did they write the paper? Yang says that he appreciated the beauty of the structure and believed that it should be published. Samuel Goudsmit, who together with George Uhlenbeck had discovered the electron’s spin, was the editor and speedily published the paper.

On the subject of his Nobel prize-winning work with Lee, Yang says he was very proud of the paper on parity violation. “It caused a great sensation because of its ‘across the board’ character,” he recalls. “It was relevant to nuclear physics as well as high-energy physics. There were hundreds of experiments in the following two years.” The paper was published on 1 October 1956, and on 27 December C S Wu and her colleagues had the results that demonstrated that the parity is violated in weak decays. Yang says that Wu contributed more than just her technical expertise: “She did not believe the experiment would be so exciting, but believed that if an important principle had not been tested, it should be. No-one else wanted to do it!”

Since 1957 Yang has visited CERN many times and has seen the latest accelerator installations, each larger and more complex than the previous generation. This time he was taken to see preparations for ATLAS and CMS, the huge general-purpose detectors being built for the LHC. Yang says that seeing these installations is “very educational for a theorist who doesn’t tangle with these complex detectors and the engineers who are putting it all together”. He was “more than impressed” he says: “It is quite unbelievable. My only regret is that I may not be around to see the results.”

The changing face of particle physics

As the detectors become larger and more complex they are also being built and run by physicists and engineers who are collaborating on a very large scale. How particle physics is done has changed a great deal in the 50 years since Yang’s first visit to CERN. “Now group members are named by countries,” Yang says. “We have progressed from teams of colleagues in an institute, to several institutes, to several countries.” At CMS in particular he was impressed by all the young people from different countries who were participating in data-taking tests during his visit.

Looking to the future, Yang believes that astronomy is going to be an exciting field because so many peculiar aspects not yet understood will provide many opportunities for exploration. More fundamentally, he thinks that while the nature of physics has changed in the 21st century it will continue to thrive, resulting in important contributions to science.

So what of high-energy physics? Is it coming to an end? Yang believes that the type of particle physics studied over the past 50 years is not likely to continue for two reasons: one external and one internal. He points out that his generation was fortunate in that they launched into the unknown where there was a great deal to be discovered. Now, he says, we have reached marvellous collaboration efforts with the LHC, but there are limits to what governments will support. This is the external factor: funding will limit expansion unless there is some bright new idea. “We need to reduce the budget by a factor of 10,” he says.

As for the internal factor, he sees that the subject faces more difficult mathematical structures. He notes that field theory today has become highly nonlinear and is very difficult compared with what was thought to be difficult in the 1940s.

In the meantime, what does he think will be the most important discovery at the LHC? “Everybody is focusing on the Higgs and most feel it will be discovered,” he observes. “But,” he adds, “it may be more exciting eventually if it is not discovered.”

Viewpoint

I started a company, Research In Motion, while I was still at the University of Waterloo in Ontario, Canada. By the late 1990s we had developed the BlackBerry handheld mobile device. As a result I found myself in a position where I could invest in an area that I am passionate about and one that could make a big difference.

Spot an opportunity. Having observed that research funding is usually thinly spread, I decided to start a theoretical-physics institute that would focus on science that is fundamental to all human progress and at which Canada can excel.

CCEvie1_01-07 — “There’s reason for balancing good science with good outreach.”

Promote scientific openness. My driving motivation for establishing the Perimeter Institute (PI), located next to the University of Waterloo, is that I feel fundamental science needs more support. What worries me is that governments all around the world seem to be listening to the same consultant. They ask scientists to do something that will benefit the economy within five years. Of course, governments are under pressure to balance budgets and be accountable – that’s reasonable. But some of that pressure is getting transferred to universities, with unfortunate results.

Science is a global enterprise based on co-operation and openness. If you say to universities that they must justify their research with patents and licences, you collapse that openness. Efforts to commercialize too early are making researchers more secretive, hampering their ability to excel, without necessarily helping business. I wanted to challenge this trend.

Concentrate on core competencies. A strategic decision we made when creating the Institute in 1999 was to focus on a couple of very specialized fields, quantum gravity and quantum foundations, because we felt these were areas where a relatively small, high-quality team could make a big difference. This is the same strategy that originally made BlackBerry a success: it focused on doing one thing – “push e-mail” – very well rather than competing on all features. So for the first few years, PI focused on recruiting top-class researchers in these two areas to ensure that research efforts were of international calibre within a relatively short period. As the Institute’s reputation builds, we are branching out a bit more.

Build a focal point. The other decision we made early on was to house the Institute in an outstanding building. Before we built it, we spent two years going around the world and talking to people in theoretical-physics institutes and theory departments at universities, asking them what works and what doesn’t. Based on this, we put together some specifications and organized a competition, where we really let the architects go wild. The result is a building with a design that has won several prizes and is internationally recognized.

Attract investment. I invested C$100 million of my own money in PI to get it started. For the longer term it was critical to get government support. Convincing government officials took a huge effort. Part of the challenge is that not many politicians understand basic science, let alone know how to value it. This means that a lot of funding is done almost entirely on your ability to explain the benefits and on their faith in you. Early on, all levels of government (local, provincial and federal) saw the benefit of PI and decided to support the Institute with a total of about C$55 million dollars. More recently, and now that the Institute is established, a further C$50 million in public investment was warmly received.

Present your product. In the long run, you can’t rely on faith alone. So although excellent science is crucial to success that’s really only half of the story. The other half of the Institute’s activities is about outreach. For example, PI has a summer-school programme for students from all over Canada and around the world. PI also goes on tour across Canada to give classroom instruction about physics to both students and teachers.

PI also has a programme of monthly public lectures. Sometimes we’ll have scientists like Roger Penrose discuss a weighty topic; other times we’ll have debates about science with well-known historians and journalists. Waterloo has a population of only about 100,000, yet every month we fill a 550 seat lecture theatre, and there’s always a queue outside on standby. That’s how much interest you can generate in science, if you make the effort to open it up for people and make the research accessible.

And that’s success. Because ultimately, these are the people who vote for the governments which fund the research. If they don’t benefit from and believe in what we’re doing, it’s always going to be an uphill struggle. So in addition to directly helping students, teachers and members of the general public, there’s reason for balancing good science with good outreach. We have to move beyond relying on faith.

Mike Lazaridis is founder and co-CEO of Research In Motion, makers of BlackBerry handheld devices, as well as chancellor of the University of Waterloo. Additional information about PI is available at
www.perimeterinstitute.ca.

Field Theory: A Path Integral Approach (Second edition)

by Ashok Das, World Scientific. Hardback ISBN 9812568476 £45 ($78). Paperback ISBN 9812568484 £28 ($48).

This book describes quantum-field theory within the context of path integrals. With its utility in a variety of fields in physics, the subject matter is primarily developed within the context of quantum mechanics before going into specialized areas. Adding new material keenly requested by readers, this second edition is an important expansion of the popular first edition. Two extra chapters cover path integral quantization of gauge theories and anomalies, and a new section extends the supersymmetry chapter, describing the singular potentials in supersymmetric systems.

Data Analysis: A Bayesian Tutorial (Second edition)

by D S Sivia and J Skilling, Oxford University Press. Hardback ISBN 9780198568315 £39.95 ($74.50). Paperback ISBN 9780198568322 £22.50 ($39.50).

Statistics lectures can be bewildering and frustrating for students. This book tries to remedy the situation by expounding a logical and unified approach to data analysis. It is intended as a tutorial guide for senior undergraduates and research students in science and engineering. After explaining the basic principles of Bayesian probability theory, their use is illustrated with a variety of examples ranging from elementary parameter estimation to image processing. Other topics covered include reliability analysis, multivariate optimization, hypothesis testing and experimental design. This second edition contains a new chapter on extensions to the ubiquitous least-squares procedure.

Relativity: Special, General and Cosmological (Second edition)

by Wolfgang Rindler, Oxford University Press. Hardback ISBN 9780198567318, £55 ($99.50). Paperback ISBN 9780198567325, £27.50 ($49.50).

Relativistic cosmology has recently become an active and exciting branch of research. Consequently, this second edition mostly affects the section on cosmology, and the purpose remains the same: to make relativity come alive conceptually. The emphasis is on the foundations and on presenting the necessary mathematics, including differential geometry and tensors. With more than 300 exercises, it promotes an in-depth understanding and the confidence to tackle basic problems in this field. Advanced undergraduates and beginning graduate students in physics and astronomy will be interested in this book.

Quantum Mechanics: Classical Results, Modern Systems, and Visualized Examples (Second edition)

by Richard W Robinett, Oxford University Press. Hardback ISBN 9780198530978, £39.95 ($74.50)

This second edition is a comprehensive introduction to non-relativistic quantum mechanics for advanced undergraduate students in physics and related fields. It provides a strong conceptual background in the most important theoretical aspects of quantum mechanics, and extensive experience of the mathematical tools required to solve problems. It also gives the opportunity to use quantum ideas to confront modern experimental realizations of quantum systems, and numerous visualizations of quantum concepts and phenomena. This edition includes many new discussions of modern quantum systems, such as Bose–Einstein condensates, the quantum Hall effect and wave-packet revivals.

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Yang–Mills theory

The changing face of particle physics