by Gennady A Mesyats, Springer. Hardback ISBN 0306486539, 7227 (£157, $249).
Meysat provides an in-depth coverage of the generation of pulsed electric power, electron and ion beams, and various types of pulsed electromagnetic radiation, with a wide range of methods for producing up to 1014 W of power for pulse durations from 10-10 to 10-7 s. The physics of pulsed electrical discharges, properties of coaxial lines, spark gap switches, various plasma and semiconductor switches and their use in pulse generators are covered, as well as the production of high-power pulsed electron and ion beams, X-rays, laser beams and microwaves.
by John F Hawley and Katherine A Holcomb, Oxford University Press. Hardback ISBN 9780198530961, £33.99.
The new edition of this thorough, descriptive introduction to the physical basis for modern cosmological theory includes the latest observational results and provides the background material necessary to understand their implications, with a special focus on the concordance model. Emphasis is given to the scientific framework for cosmology, beginning with the historical background and leading to an in-depth discussion of the Big Bang theory and the physics of the early universe.
par Patrick R Girard, Presses Polytechniques et universitaires romandes. Broché ISBN 288074606X, 68CHF (€45.50).
Ce livre propose une introduction pédagogique à ce nouveau calcul, à partir du groupe des quaternions, avec des applications principalement dans les domaines de le relativité restreinte, de l’eacutelectromagnétisme classique et de la relativité geacuteneacuterale. C’est le premier ouvrage sur le sujet reacutedigé en langue française depuis près de 30 ans. Il s’adresse aux eacutetudiants, professeurs et chercheurs en physique et en sciences de l’ingeacutenieur.
par Constantin Piron, Presses Polytechniques et universitaires romandes. Broché ISBN 2880746116, 42CHF (7euro28).
Cet ouvrage constitue une introduction à la theacuteorie des champs quantiques très diffeacuterente des exposeacutes habituels le plus souvent formels. Reacutedigé par l’un des speacutecialistes francophones en la matière, il est particulièrement clair et didactique, illustré de nombreux exemples et exercices corrigeacutes.
by Leonard Susskind and James Lindesay, World Scientific. Hardback ISBN 9812560831, £17 ($28). Paperback ISBN 9812561315, £9 ($14).
Black holes have attracted the imagination of the public and of professional astronomers for quite some time. The astrophysical phenomena associated with them are truly spectacular. They seem to be ubiquitous in the centre of galaxies, and they are believed to be the power engines behind quasars. There is little doubt of their existence as astronomical objects, but this very existence poses deep and unresolved paradoxes in the context of quantum mechanics when one tries to understand the quantum properties of the gravitational field.
For many readers, the title of this book may sound odd because the contents have little to do with the astrophysical or observational properties of black holes. If you look for nice pictures of galaxy centres and gamma-ray bursts, you will find none. If, however, you are looking for the deep paradoxes in our understanding of quantum-field theory in nontrivial gravitational environments, and the riddles encountered when trying to harness the gravitational force within the quantum framework, then you will find plenty.
At the end of the 19th century, Max Planck was confronted with serious paradoxes and apparent contradictions between statistical thermodynamics and Maxwell’s electromagnetic theory. The resolution of the puzzle brought the quantum revolution. When Albert Einstein asked himself what someone would observe when travelling at the same speed as a light beam, the answer revealed a fundamental contradiction between Newtonian mechanics and electromagnetic theory.
The resolution of these problems led to the relativity revolution, first with special and then general relativity. Sometimes experiment itself is not the only way towards progress in our understanding of nature. Conceptual paradoxes often provide the way to a deeper view of the world.
In the 1960s, largely due to Roger Penrose and Steven Hawking, it became understood that under very general conditions, very massive objects would undergo gravitational collapse. The end state would be a singularity of infinite curvature in space-time shrouded by an event horizon – the last light surface that did not manage to leave the region. The horizon is a profoundly non-local property of a black hole that cannot be detected by local measurements of an unaware, infalling observer.
Classically, black holes were supposed to be black. However, in the early 1970s Jacob Bekenstein and Hawking showed that black holes must necessarily have very unsettling properties. As Bekenstein argued, if the second law of thermodynamics is supposed to hold, then an intrinsic entropy must be assigned to a black hole. Since entropy measures the logarithm of the number of available states for a given equilibrium state, it is logical to ask what these states are and where they came from.The entropy in this case is proportional to the area of the black-hole horizon measured in Planck units (a Planck unit of length is 10-33 cm). This is vastly different from the behaviour of ordinary quantum-field theoretic systems.
Meanwhile, Hawking showed that if one considers the presence of a black hole in the context of quantum-field theory, it radiates thermally with a temperature inversely proportional to its mass, so the hole is not black after all. If the radiation is truly thermal, this raises a fundamental paradox, as Hawking realized. Imagine that we generate a gravitational collapse from an initial state that is a pure state quantum-mechanically. Since thermal radiation cannot encode quantum correlations, once the black hole fully evaporates it carries with it all the subtle correlations contained in a pure quantum state. Hence the very process of evaporation leads to the loss of quantum coherence and unitary time evolution, two basic features of quantum-mechanical laws.
These puzzles were formulated nearly 30 years ago and they still haunt the theory community. It was, nevertheless, realized that resolving these puzzles requires deep changes in our understanding of both quantum mechanics and general relativity, and also a profound modification of the sacrosanct principle of locality in quantum-field theory.
This book is precisely dedicated to explaining what we have learned about these puzzles and their proposed solutions. Assuming that some of the basic features of quantum mechanics (such as unitary evolution) and general relativity (such as the consistency of different observers’ observations, no matter how different they may be) do indeed hold, the authors analyse the conceptual changes that are required to accommodate strange phenomena such as black-hole evaporation.
In the process, they masterfully present a whole host of subjects including quantum-field theory in curved spaces; the Unruh effect and states; the Rindler vacua; the black-hole complementarity principle; holography; the Maldacena conjecture and the role of string theory in the whole affair; the notion of information in quantum systems; the no-cloning theorem for quantum states; and the general concept of entropy bounds.
A remarkable feature of this book is that relatively little specialized knowledge is required from the reader; a cursory acquaintance with quantum mechanics and relativity is sufficient. This is impressive, given that the authors cover some of the hottest topics in current research.
The technical demands are low, but conceptually the book is truly challenging. It makes us think about many ideas we take for granted and shakes the foundations of our understanding of basic physics. It provides a rollercoaster ride into the treacherous and largely uncharted land of quantum gravity. This book is highly recommended for those interested in these fascinating topics.
The authors end with the sentence: “At the time of the writing of this book there are no good ideas about the quantum world behind the horizon. Nor for that matter is there any good idea of how to connect the new paradigm of quantum gravity to cosmology. Hopefully our next book will have more to say about this.” We hope so too.
On 21-24 September, in co-operation with several other scientific institutions, the Masaryk University in Brno is organizing
a memorial symposium in honour of the Czech physicist George Placzek, who was born on 26 September 1905 and died on 9 October 1955, soon after his 50th birthday. Placzek was an outstanding scientist who made substantial contributions to the fields of molecular physics, scattering of light from liquids and gases, the theory of the atomic nucleus and the interaction of neutrons with condensed matter. He belongs among the important physicists of the 20th century, setting an example not only through his discoveries, but also by the stimulating style of his scientific work.
George Placzek was born in Brno, Moravia, in what is now the Czech Republic but which in 1905 was part of Austro-Hungary. The oldest son of Alfred and Marianne Placzek, he spent his childhood in Brno and in Alexovice, where the family owned a textile factory, Skene & Co. He had a brother, Friedrich, one year younger and a sister, Edith, 12 years younger. The family was well integrated into the mixed Czech-German language environment around Brno. George studied in the Deutsches Staatsgymnasium in Brno between 1918 and 1924 and then went to the University of Vienna, with three semesters away in Charles University, Prague. He graduated in 1928, having defended his doctoral thesis, which dealt with the determination of density and shape of submicroscopic test bodies, with distinction.
Travels in Europe
In 1928, Placzek set off on several years of travel through the main scientific centres of Europe. This was usual for post-docs at the time, although Placzek later markedly avoided countries in which Adolf Hitler was increasingly encroaching upon civil liberties and human rights. He spent three years with Hendrik Kramers in Utrecht, followed in 1930-31 by a short time with Peter Debye and Werner Heisenberg in Leipzig. He then joined a group of young physicists led by Enrico Fermi in Rome, where Edoardo Amaldi became his closest colleague. Then, in 1932, Placzek joined Niels Bohr in Copenhagen where he remained until 1938, with periods of research fellowships or visiting professorships at the universities of Kharkov, Jerusalem, Paris and elsewhere.
Placzek’s first scientific interest was in the scattering of light from molecules and the Raman effect. With Lev Landau, he investigated the fine structure of a monochromatic wave in liquids and gases, and together they derived the Landau-Placzek formula for the ratio of intensities of Brillouin and Rayleigh scattering of light. Then in the early 1930s, the scattering of slow neutrons in matter became topical and Placzek was attracted to this problem, first in Rome and later in Copenhagen, where at Bohr’s suggestion he and Otto Frisch studied the capture of slow neutrons.
Placzek’s work in Copenhagen made him a leading authority on neutron scattering and absorption in matter. In a series of experiments, Placzek and Frisch discovered that the absorption of neutrons depends strongly on the atomic mass of the material and the velocity of the neutrons, while for slow neutrons and light elements the neutron-capture cross-section is inversely proportional to the velocity. He also worked with Hans Bethe on a theory of neutron absorption resonances, deriving important laws and selection rules, and publishing a seminal paper on resonance reactions in 1937. Papers published later by Placzek with Bohr and Rudolf Peierls dealt with the general theory of nuclear reactions and rank among the classics. For example, the well-known optical theorem, connecting the imaginary part of a scattering amplitude with the total cross-section, bears the names of Bohr, Peierls and Placzek. Using the optical theorem and Bohr’s drop model of the nucleus, the trio developed a fundamental theory of neutron-induced nuclear reactions.
Hitler’s preparations for a systematic occupation of all countries bordering Germany endangered some members of Bohr’s international team, including Placzek. The Anschluss of Austria in the spring of 1938 and the seizing of a large region from Czechoslovakia through the Munich treaty in September of that year left no-one in the dark. Bohr decided to move part of his Copenhagen Institute to the other side of the Atlantic. Placzek left Copenhagen for the US in January 1939 and in Princeton, at the beginning of February, he met Bohr, who had been waiting for him impatiently.
Across the Atlantic
Placzek’s first encounter with Bohr on the other side of the Atlantic provides an interesting illustration of their personal relationship and scientific collaboration. While sources (e.g. Moore 1966, Wheeler and Ford 2000) do not agree exactly on what was discussed during breakfast on 3 February 1939, they do seem to have the same opinion on the following. Bohr found Placzek – “the institute’s always stimulating Bohemian” – sitting with Leon Rosenfeld. Their discussion focused on some exciting news from Europe. First, Frisch and Lise Meitner had recently suggested that most of the transuranic elements were produced by a new type of nuclear reaction – the capture of neutrons from uranium fission. Second, Placzek had suggested to Frisch in Copenhagen how he might confirm the existence of fission in a straightforward way, which Frisch promptly did on 13 January 1939.
Bohr, listening attentively, looked up with a big smile: “For one good thing, we’re free of transuranic elements.” Placzek, the sceptic, 20 years younger than Bohr, commented: “Yes, but now you’re in a worse mess. How can you reconcile it with your view of nuclear reactions?”. How, he asked, was Bohr going to explain why slow rather than fast neutrons should cause uranium to fission? Why should slow neutrons induce a modest fissioning in uranium, but be captured in thorium?
Bohr suddenly went pale, took Rosenfeld and set off across the campus to his office. He went to the blackboard and worked rapidly, making some rough sketches. In about ten minutes he stopped; he had the answer to the problem posed by Placzek, related to the fissioning of the nuclei. The fission cross-section for slow neutrons must be due to the small amount of the isotope uranium-235, the cross-section increasing as the wavelength of the neutrons increases with decreasing energy.
From 1939 to 1942 Placzek was professor at Cornell University, Ithaca. Later he went to Montreal and Los Alamos, where he contributed to solving problems related to the moderation of neutrons in matter. He was apparently the only citizen of Czechoslovakia to take part in the Manhattan Project, being head of the Theory Group in Chalk River near Montreal, and then in Los Alamos from May 1945. Later he worked for some time in the General Electric Company in Schenectady and in 1948, he obtained a permanent position at the Institute for Advanced Study in Princeton.
In the last years of his life, Placzek went into more depth with his analysis of the elastic and inelastic scattering of light particles in liquids and crystals, aimed at investigating the physical properties of these media. Albert Messiah and Léon Van Hove were among his collaborators and friends in this period (Van Hove 1956, Messiah 1991). During this time, he also visited Europe to lecture on the moderation and diffusion of neutrons and in 1954, the book Introduction to the Theory of Neutron Diffusion, by K M Case, F de Hoffmann and Placzek appeared, based on a lecture course Placzek gave in Santa Monica and Los Angeles in the summer of 1949. In autumn 1955, Placzek died in Zurich while he was planning a several-month lecture tour through Italy for the academic year 1955-56.
During his scientific career, Placzek provided a quantum formulation of Raman light scattering, developed the ideas of molecular symmetry and its application in physics, and in collaboration with Bethe, Bohr and Peierls, contributed to the general theory of nuclear reactions. He systematically studied the behaviour of neutrons in nuclear reactions, neutron resonances, scattering and diffusion in matter, and the moderation and absorption of neutrons in crystals and liquids. He was among the first to suggest, independently of several others, that graphite might be used to moderate neutrons. Yet his name is not well known.
The importance of publication
Those who knew Placzek personally agree that his discoveries and results in physics, rich and important as they were, were not sufficiently published; only a small portion of his results appeared in print. As Van Hove points out, Landau’s and Placzek’s classic results on the scattering of a monochromatic wave in liquids were published in an incomplete form, and were only later discussed in more detail by Jacov Frenkel in his Kinetic Theory of Liquids. The same holds for the results on the general theory of nuclear reactions obtained by Bohr, Peierls and Placzek. Amaldi wrote about Placzek in 1956: “The redaction of an article represented an immense effort for him; even important results of his, which he had formulated clearly and in definite form, often remained unpublished.”
He was noted for strict moral principles and a great sense of tolerance
Edoardo Amaldi
This trait of Placzek’s corresponded to his desire always to deepen his analyses of the phenomena he studied. Moreover, many of his original ideas are implicitly contained in other papers. As an unmerciful critic, Placzek often served as the scientific conscience for his colleagues, stimulating their invention, criticizing their work and forcing them to formulate their scientific ideas clearly. He had a number of characteristics that made him a welcome collaborator and team member: a highly developed critical sense, an ability to understand new problems quickly and to confront them with relevant facts, an unselfish willingness to offer advice and, last but not least, a generous disinterest in participating in the result.
These attributes, as Amaldi explains, reflected Placzek’s character. He excelled in general erudition and in a culture anchored in fundamental ideas. He easily learned foreign languages and felt great affection for small nations. He was noted for strict moral principles and a great sense of tolerance.
What little remains
Despite Placzek’s long collaboration with Bohr there are only a few photographs and letters in the Niels Bohr Archive in Copenhagen. One possible explanation is that, before moving to America, Bohr obliterated all traces that could help the Nazis pursue the families of those who had fled from occupied countries. In Placzek’s fatherland, by the end of 2004, only a few documents had been found: a note in the register of births (containing the names of his parents and grandparents, the godfathers, the rabbi and the midwife), the regular notes of his studies in the Staatsgymnasium high school, and the distasteful entries in the book of the right of domicile. Placzek’s parents and his sister died in concentration camps during the Second World War, while his brother died eight days after the Nazis’ invasion of Czechoslovakia in March 1939. Recently, however, in connection with the double anniversary of Placzek’s birth and death, many interesting documents have been found about his relatives and the history of the whole family in Moravia and North America (Gottvald 2005). These will be presented at the symposium.
<textbreak=Acknowledgements>
The author is greatly indebted to Ugo Amaldi, Giuseppe Cocconi, Torleif Ericson, Ales Gottvald, André Martin, Michelle Mazerand, Jack Steinberger, Valentin Telegdi and Jenny Van Hove for providing valuable information relating to George Placzek.
One of the things we do well in particle physics is collaborate with each other and internationally to carry out our science. Of course, individual and small collaborations are a trademark of modern scientific research and many of us have developed lifelong colleagues and friends from different cultures through our scientific interactions. Even during times when political situations have been constraining, scientific contacts have been maintained that have helped to break down those barriers. For example, during the heat of the Cold War, personal interactions were greatly hampered, yet scientific bonds persevered and some of those connections provided crucial ongoing contacts between Western and Soviet societies.
When I was a student at the University of California, Berkeley, I did my PhD research at the “Rad Lab”, now called Lawrence Berkeley National Laboratory. I recall being immediately surprised both by the number of foreign or foreign-born scientists at the lab and by how little it seemed to matter. For me, having grown up as a local Californian boy, this was an eye-opening experience and a terrific opportunity to learn about other cultures, customs and views of the world. After a while, I pretty much took it for granted that we scientists accept and relate to each other in ways that are essentially independent of our backgrounds. However, it is worth reminding ourselves that this is not the case in most of society and that we are the exception, not the rule.
I have often wondered what it is that unifies scientists. How can we work together so easily, when cultural, political and societal barriers inhibit that for most of society? After all, hostilities between countries and cultures seem to continue as an almost accepted part of our modern existence. I won’t theorize here on what enables scientists to work together and become colleagues and friends without regard to our backgrounds. Instead, I would like to briefly explore whether the nature of how we collaborate will, or should, change.
Particle physics is increasingly focused on the programmes at our big laboratories that house large accelerators, detectors and support facilities. These laboratories have essentially come to represent a distributed set of centres for high-energy physics, from which the intellectual and technical activities emanate and where physicists go to interact with their colleagues. Fermi National Accelerator Laboratory (Fermilab), Stanford Linear Accelerator Center (SLAC), the High Energy Accelerator Research Organization (KEK) and Deutsches Elektronen-Synchrotron (DESY) are examples of national laboratories that play this role in the US, Japan and Germany. CERN is a different example of a successful regional laboratory that has provided Europe with what is arguably the leading laboratory in the world for particle physics and with a meeting place for physicists from Europe and beyond.
One essential ingredient in the success of particle physics is that the accelerator facilities at the large laboratories have been made open to experimentalists worldwide without charge. This principle was espoused by the International Committee on Future Accelerators (ICFA) and, I believe, it has been crucial to widening participation.
It is interesting to contemplate how international collaboration might evolve as we go beyond the regional concept to a global one, like the International Linear Collider (ILC). The organizational principles for building and operating the ILC are not yet defined, but the idea is to form a partnership between Asian, American and European countries. Such an arrangement is already in place for the accelerator and detector R&D efforts. The general idea is to site the ILC near an existing host laboratory, to take advantage of the support facilities. However, the project itself will be under shared management by the international stakeholders. The experiments are expected to consist of large collider detectors similar to those at present colliders, but with some technical challenges that will require significant detector R&D over the next few years.
As we plan for the ILC, we want to ensure that we create a facility that will be available to the world scientific community. What needs to be done to ensure that we maintain the strong collaborative nature of our research and how do we create a true centre for the intellectual activities of our community? What should we require of the host country to assure openness to the laboratory and its facilities? How can we best include the broad community in the decision-making that will affect the facilities that are to be built? Is it time to consider new forms of detector collaboration and/or should we contemplate making the data from the detectors available to the broader community after an initial period (as in astronomy)?
I raise such questions only as examples, not to imply that we should change the way we do business, but to encourage us to think hard about how we can create an exciting international facility that will best serve our entire community and enable productive and broad collaboration to continue in science.
With this issue, CERN Courier takes on a slightly different look, with the inclusion of articles in French. This is because CERN has, with regret, taken the decision to cease the publication of separate French and English editions. In the new bilingual edition, articles submitted in English will remain in English while French articles will be published in French. There will, however, be summaries of feature articles in the other language, and the news items, as here, will be listed in French.
During its meeting in Geneva on 17 June, the CERN Council agreed to take on the role of defining the strategy and direction of European particle-physics research, a task already present in the founding convention.
A strategic planning team is to be established in support of this role, consisting of the chair of the European Committee for Future Accelerators, the chair of CERN’s Scientific Policy Committee, CERN’s director-general, one member nominated by each of CERN’s member-state delegations, and representatives of the major European national laboratories. In spring 2006, the team will provide the CERN Council with a status report in Berlin, with a full report to follow later that year.
At the same meeting, the Council also heard from project leader of the Large Hadron Collider (LHC), Lyn Evans, who told attendees that all efforts are currently being made to ensure that the LHC will be ready for commissioning in the summer of 2007. CERN’s chief scientific officer, Jos Engelen, also reported that all the LHC’s experiments expect to be in a position to take data in 2007, and that the LHC computing grid is progressing according to plan.
In his presentation to the Council, CERN’s director-general, Robert Aymar, applauded the progress that is being made towards the LHC. However, while the laboratory is on course for LHC start-up in 2007, current expenditure profiles indicate that CERN’s budget could be entirely committed to paying for the project right through to the next decade. This subject will be discussed at the Council’s meeting in September.
On 24 May, Jonathan Dorfan, director of the Stanford Linear Accelerator Center (SLAC), announced a complete reorganization of the structure and senior management of the laboratory, which Stanford University has operated for more than 40 years for the US Department of Energy. The new organizational structure is built around four divisions: Photon Science, Particle and Particle Astrophysics, Linac Coherent Light Source (LCLS) Construction, and Operations.
“One thing that is recurrent in world-class scientific research is change,” Dorfan said. “Recognizing new science goals and discovery opportunities, and adapting rapidly to exploit them efficiently, cost-effectively and safely is the mark of a great laboratory. Thanks to the support of the Department of Energy’s Office of Science and Stanford University, SLAC is ideally placed to make important breakthroughs over a wide spectrum of discovery in photon science and particle and particle astrophysics. These fields are evolving rapidly, and we are remodelling the management structure to mobilize SLAC’s exceptional staff to better serve its large user community. The new structure is adapted to allow them to get on with what they do best – making major discoveries.”
Two of the new divisions – Photon Science, and Particle and Particle Astrophysics – encompass SLAC’s major research directions. As director of the Photon Science Division, Keith Hodgson has responsibility for the Stanford Synchrotron Radiation Laboratory, the science and instrument programme for the LCLS (the world’s first X-ray-free electron laser) and the new Ultrafast Science Center. Persis Drell, director of the Particle and Particle Astrophysics Division, oversees the B-Factory (an international collaboration studying matter and antimatter), the Kavli Institute for Particle Astrophysics and Cosmology, the International Linear Collider effort, accelerator research and non-accelerator particle-physics programmes.
Construction of the $379 million LCLS, a key element in the future of accelerator-based science at SLAC, started this fiscal year. A significant part of the laboratory’s resources and manpower are being devoted to building LCLS, with completion of the project scheduled for 2009. Commissioning will begin in 2008 and science experiments are planned for 2009. John Galayda serves as director of the LCLS Construction division.
To reinforce SLAC’s administrative and operational efficiency, and to stress the importance of strong and effective line management at the laboratory, a new position of chief operating officer has been created, filled by John Cornuelle. This fourth division, Operations, has broad responsibilities for operational support and R&D efforts that are central to the science divisions. Included in Operations will be environmental safety and health, scientific computing and computing services, mechanical and electrical support departments, business services, central facilities and maintenance.
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