Many of our fellow citizens have an image of science and of scientists that we physicists would find hard to recognize. They tend to think of science as something rigid, soulless and generally dull, which is generated in an objective and often solitary manner by cold, passionless people. While they may be willing to see some nobility in "pure" science, this reluctant generosity does not usually extend to its "dirty" offshoot, technology. Absurd as this looks to us, I think it is worth examining these dangerous misconceptions more closely – how they arise, what their consequences are and what might be done to improve other people's understanding of what we do.
This paper examines how black holes might compute in light of recent models of the black-hole final state. These models suggest that quantum information can escape from the black hole by a process akin to teleportation. They require a specific final state and restrictions on the interaction between the collapsing matter and the incoming Hawking radiation for quantum information to escape. This paper shows that for an arbitrary final state and for generic interactions between matter and Hawking radiation, the quantum information about how the hole was formed and the results of any computation performed by the matter inside the hole escapes with fidelity exponentially close to 1. Comment: 9 Pages, TeX
At the 1927 Solvay conference, three different theories of quantum mechanics were presented; however, the physicists present failed to reach a consensus. Today, many fundamental questions about quantum physics remain unanswered. One of the theories presented at the conference was Louis de Broglie's pilot-wave dynamics. This work was subsequently neglected in historical accounts; however, recent studies of de Broglie's original idea have rediscovered a powerful and original theory. In de Broglie's theory, quantum theory emerges as a special subset of a wider physics, which allows non-local signals and violation of the uncertainty principle. Experimental evidence for this new physics might be found in the cosmological-microwave-background anisotropies and with the detection of relic particles with exotic new properties predicted by the theory. Comment: 12 pages, 4 figures
Back in the 1970s Stephen Hawking of Cambridge University in the UK made the theoretical discovery that small black holes are not "completely black". Instead, a black hole emits radiation with a well defined temperature that is proportional to the gravitational force at its surface. The finding uncovered a deep connection between gravity, quantum mechanics and thermodynamics. Later, Bill Unruh of the University of British Columbia in Canada proposed that quantum particles should emit thermal radiation in a similar way when they are accelerated. According to Unruh, a particle undergoing a constant acceleration would be embedded in a "heat bath" at a temperature T = a/2πck, where is the Planck constant divided by 2π, a is the acceleration, c is the speed of light and k is the Boltzmann constant. But is it really possible to detect such radiation?
This article is a follow-up of a short essay that appeared in Nature 455, 1181 (2008) [arXiv:0810.5306]. It has become increasingly clear that the erratic dynamics of markets is mostly endogenous and not due to the rational processing of exogenous news. I elaborate on the idea that spin-glass type of problems, where the combination of competition and heterogeneities generically leads to long epochs of statis interrupted by crises and hyper-sensitivity to small changes of the environment, could be metaphors for the complexity of economic systems. I argue that the most valuable contribution of physics to economics might end up being of methodological nature, and that simple models from physics and agent based numerical simulations, although highly stylized, are more realistic than the traditional models of economics that assume rational agents with infinite foresight and infinite computing abilities.
Conventional thinking says the universe is infinite. But it could be finite and relatively small, merely giving the illusion of a greater one, like a hall of mirrors. Recent astronomical measurements add support to a finite space with a dodecahedral topology.
This research describes a three dimensional quantum cellular automaton (QCA) which can simulate all other 3D QCA. This intrinsically universal QCA belongs to the simplest subclass of QCA: Partitioned QCA (PQCA). PQCA are QCA of a particular form, where incoming information is scattered by a fixed unitary U before being redistributed and rescattered. Our construction is minimal amongst PQCA, having block size 2 x 2 x 2 and cell dimension 2. Signals, wires and gates emerge in an elegant fashion. Comment: 15 pages, 11 figures. Companion website with animated examples: http://www.grattage.co.uk/jon/3DQCA
This review forms the microlensing part of the 33rd Saas-Fee Advanced Course "Gravitational Lensing: Strong, Weak & Micro'', which was held in April 2003 in Les Diablerets. It contains an introduction to the lensing effects of single and binary stars and it summarizes the state-of-the-art of microlensing observations and prospects at the time of the meeting. Stellar microlensing as well as quasar microlensing are covered. Comment: 93 pages, 51 figures; to appear (April 2006) in: Kochanek, C.S., Schneider, P., Wambsganss, J.: "Gravitational Lensing: Strong, Weak & Micro", Proceedings of the 33rd Saas-Fee Advanced Course; G. Meylan, P. Jetzer, P. North, eds. (Springer-Verlag, Heidelberg); pp. 457
This is a popular review of some recent investigations of the Kondo effect in a variety of mesoscopic systems. After a brief introduction, experiments are described where a scanning tunneling microscope measures the surroundings of a magnetic impurity on a metal surface. In another set of experiments, Kondo effect creates a number of characteristic features in the electron transport through small electronic devices -- semiconductor quantum dots or single-molecule transistors which can be tuned by applying appropriate gate voltages. The article contains 5 color figures, photo of Jun Kondo, but no equations.
One of the things that makes physics such a fascinating subject is the way in which new results come out of old and well established equations. Two new effects recently reported arise out of something as familiar as Maxwell's equations.
Few people were left unaffected by the soaring oil prices of summer 2008. Motorists were the hardest hit as the price at the pumps reached an all time high, but nobody could avoid paying more for their food as higher transport costs were passed on from the retailer to the consumer.
Nuclear fusion, which offers a potentially safe, environmentally friendly and economically competitive energy source is discussed. Energy is released through a chain of reactions that begins with the fusion of two protons into a deuteron. There is a quicker route to fusion involving the nuclei of deuterium and tritium. The International Fusion materials Irradiation Facility (IFMIF) is doing its best to speed the development of fusion power.
Energy manifests itself in many forms in the cosmos, chief among these being kinetic, thermal, gravitational, nuclear and magnetic. Magnetic energy is associated with electric currents flowing in conducting matter, such as the ionised gas of the insides of stars, or the deep liquid metal interiors of planets like the Earth. In the absence of electromotive forces (like those in the humble chemical battery), these electric currents, and the magnetic fields they generate, will always decay and the magnetic energy will in turn be converted to heat.
The 20th century has been a period of scientific revolution, unmatched in scope by anything that has come before, save perhaps the Copernican revolution in the 16th century. Ever since Newtonian physics was overthrown at the beginning of this century we have been living through a period of transition, during which the new theory that will replace Newtonian physics as a unified framework for the description of everything in nature has been steadily coming into focus. Big pieces of this theory have been discovered, such as relativity quantum theory the Standard Model of particle physics, and the standard big-bang cosmology But it is very clear that we do not yet have the full theory, because that must be based on a single theoretical framework, and such a framework is still lacking. Thus, as humanity emerges into a new century, the completion of the new theory that will finally replace Newtonian physics remains the primary goal of theoretical physics.
The second law of thermodynamics states that the entropy of an isolated system increases until it reaches a maximum. Entropy is traditionally associated with disorder but recent experiments, computer simulations and theories have illustrated how the disordering effect of entropy can lead to highly ordered superstructures in certain alloys.
Forty years ago cosmology was the realm of a handful of astronomers and two numbers were the holy grail: the Hubble constant, which describes the expansion of the universe, and the deceleration parameter, which describes how this expansion is slowing down due to gravity. Today, cosmology is an exciting area of research that attracts scientists ranging from astronomers and astrophysicists to experimental particle physicists and string theorists. The Hubble constant and the deceleration parameter have still not been measured, although they may be soon. The new holy grail, however, is to show that all structure in the universe evolved from quantum fluctuations.
Twenty years ago last month Danny Shechtman of the Technion Institute in Israel announced the discovery of a new metallic alloy. At the time Shechtman had been on sabbatical leave at the National Bureau of Standards in Washington DC, investigating the properties of mixtures of metals that had been melted together and rapidly cooled. He found that one of these alloys – aluminium manganese – displayed a diffraction pattern with 10-fold rotational symmetry. However, such symmetries were supposed to be forbidden by the laws of crystallography.
Serendipity has always been an attendant to great science. Arno Penzias and Robert Wilson discovered the cosmic background radiation after first mistaking it for the effect of pigeon droppings on their microwave antenna. US spy satellites detected gamma-ray bursts when surveying the sky for evidence of secret Soviet nuclear tests during the Cold War. Satyendra Bose arrived at Bose–Einstein statistics only after discovering that a mathematical error explained the experimental data concerning the photoelectric effect. In the words of science-fiction writer Isaac Asimov, "The most exciting phrase in science is not 'Eureka!', but rather, 'That's funny...'.
The Swiss polytechnic and university system is celebrating two of its Zürich graduates this year: Wilhelm Conrad Röntgen, who discovered X-rays a century ago, and Albert Einstein who, ten years later, introduced special relativity and the photon. These anniversaries occur in the same year as another important celebration for physics: in April, Marie Curie became the first woman to be buried in the French Pantheon.
Three days after Theodore Maiman demonstrated the first ruby laser at his laboratory in Malibu, California, in May 1960, a scientist a few miles away at the Lawrence Livermore National Laboratory came up with an idea for using lasers to harness the power source of the stars. Although details of Maiman's device would not emerge for several weeks, scientists already knew that a laser's ability to concentrate energy in time and space would be unprecedented. Might it be possible, the Liver more scientist wondered, to use lasers to fuse small atoms together to create a heavier, more stable atom-releasing huge amounts of energy in the process?
Classical chaotic dynamics has moved into yet another field. According to Ragnar Fleischmann, Theo Geisel and Roland Ketzmerick of Frankfurt University, Germany, the mathematical framework used to characterise chaotic dynamics can be applied to electron transport experiments in two-dimensional electron gases (2DEGs) that have been modulated by a periodic lattice of strong scatterers (Phys. Rev. Lett (1992) 68 1367). They have shown that chaos and nonlinear resonances are clearly reflected in the magnetotransport in lateral surface superlattices and from this they offer an explanation for a series of peculiar magnetoresistance peaks observed recently in "antidot arrays" on semiconductor heterojunctions.
Hydrogen is the dominant element in the universe, and in cold regions, such as giant molecular clouds, the molecular ion H3+ is the dominant ionic form of hydrogen. Over the past decade H3+ has received considerable attention because of its astronomical and fundamental importance and, more recently, its unusual photodissociation spectrum. Not only is H3+ the simplest polyatomic molecule (neutral H3 is unstable), but it can also be used to probe phenomena as diverse as chaos in the lab and the wind speed on Jupiter.
With the vast majority of scientific papers now available online, the author describes how the Web is allowing physicists and information providers to measure more accurately the impact of these papers and their authors. Provides a historical background of citation analysis, ISI's citation databases, and the impact factor. Discusses the strengths and weaknesses of Web of Science and other more recent citation data sources (e.g., Scopus and Google Scholar), the impact of the Web on citation analysis, and the emergence of new citation-based research assessment measures (e.g., h-index). Argues that the use of multiple Web-based citation tools allows more accurate visualizations of scholarly communication networks. Also argues that publishing a journal article is now only the first step in disseminating one's work.
We are all ecologists now, so when Martin Fleischmann and Stanley Pons announced on 23 March 1989 that at Utah, they had caused deuterium ions to fuse giving out heat using electrolysis in a simple cell at room temperature – cold fusion – we all wanted to believe it. At first we were a bit sceptical, but then came more information – they had measured excess heat and observed neutrons, gammas, and tritium. And next day there was independent confirmation from Steve Jones of nearly Brigham Young University. Other confirmations followed quickly. The early days of April were the high point when perhaps 500 million people had heard of cold fusion, Fleischmann and Pons, and had dreams of sea water yielding limitless amounts of heavy water that could provide energy without pollution.
Today we do not doubt the existence of atoms and molecules – we can "see" them using scanning tunnelling and atomic force microscopes. At the beginning of this century, however, the reality of atoms was still a matter for debate. With simple yet brilliant experiments performed between 1907 and 1913, Jean Perrin resolved the issue by studying small particles suspended in solution. Using an ordinary light microscope he studied the behaviour of the smallest objects he could see – spherical colloidal particles of resin just 1 μm across, suspended in water. (A colloidal system contains small particles of one type of material in a continuous matrix of another type. They can be solid in liquid, like paint; liquid in liquid, like milk; and even gas in liquid, such as an aerosol.)
Topological insulators are electronic materials that have a bulk band gap like an ordinary insulator but have protected conducted states on their edge or surface. These states are possible due to the combination of spin-orbit interactions and time-reversal symmetry. The two-dimensional (2D) topological insulator is a quantum spin Hall insulator, which is a close cousin of the integer quantum Hall state. A three-dimensional (3D) topological insulator supports novel spin-polarized 2D Dirac fermions on its surface. In this Colloquium the theoretical foundation for topological insulators and superconductors is reviewed and recent experiments are described in which the signatures of topological insulators have been observed. Transport experiments on HgTe/CdTe quantum wells are described that demonstrate the existence of the edge states predicted for teh quantum spin hall insulator. Experiments on Bi1-xSbx, Bi<2Se3, Bi2Te3 and Sb2Te3 are then discussed that establish these materials as 3D topological insulators and directly probe the topology of their surface states. Exotic states are described that can occur at the surface of a 3D topological insulator due to an induced energy gap. A magnetic gap leads to a novel quantum Hall state that gives rise to a topological magnetoelectric effect. A superconducting energy gap leads to a state that supports Majorana fermions and may provide a new venue for realizing proposals for topological quantum computation. Prospects for observing these exotic states are also discussed, as well as other potential device applications of topological insulators.
Neural network computers have hardware architectures more like the human brain than those of current digital computers. This makes them much faster at pattern recognition, optimization problems and high-speed data retrieval from vast data–bases. Instead of being programmed, they are "trained" by the repeated presentation of data, usually in the form of images. This saves programming costs but the training time can be prohibitive if neural architectures have to be simulated on serial electronic computers. Faster training speeds are possible with electronic neural hardware, but to achieve fast learning and operation with many neurons optoelectronic hardware is needed. Such a system has now been demonstrated by a group from Trinity College Dublin in collaboration with Hitachi.
It is only over the last three decades that a coherent picture of the liquid state has emerged, much later than our understanding of both gases and solids. The difficulties in describing liquids arise from two of their key characteristics. First, liquids are dense phases of matter. The molecules constantly interact with many other molecules, making it impossible to develop an equation that describes how a liquid's behaviour changes with pressure, temperature and volume. Such an "equation of state" can easily be derived for a gas, in which molecules are assumed to collide with one molecule at a time. Second, molecular positions and orientations are random in liquids, making them intrinsically disordered. Thus they do not have a clear-cut reference state like the perfect lattice associated with crystalline solids. The disorder is, moreover, dynamical. Individual molecules diffuse away from their initial positions and, for sufficiently long timescales, this gives rise to collective motions and hydrodynamic flow.
A quantum computer would put the latest PC to shame. Not only would such a device be faster than a conventional computer, but by exploiting the quantum-mechanical principle of superposition it could change the way we think about information processing. However, two key goals need to be met before a quantum computer becomes reality. The first is to be able to control the state of a single quantum bit (or "qubit") and the second is to build a two-qubit gate that can produce "entanglement" between the qubit states. Now Xiaoqin Li at the University of Michigan and co-workers have passed a significant milestone in solid-state quantum computing by demonstrating a two-qubit logic gate using electron – hole pairs in a single quantum dot (X Li et al. 2003 Science 301 809–811).
Quantum matter is everywhere, from the interiors of neutron stars to the electrons in everyday metals. Like ordinary, classical matter, it is made up of many interacting particles. In classical matter, however, it is possible to think of each particle as an individual entity, whereas in quantum matter Heisenberg's uncertainty principle prevents us from telling individual particles apart: their behaviour can only be described collectively. In spite of this, many types of quantum matter are well understood from a theoretical point of view. For example, the "electron liquid" that is responsible for the flow of electricity through ordinary metals, the magnetic properties of many insulating materials and the normal and superfluid phases of helium at very low temperatures have all succumbed to the probing of theorists.
Imagine staring out of your window on a strange scene of warped colours, bent light and regions that are in and out of focus. Either you have mistaken the window for the bottom of a pint glass, or your windowpane could be patterned with a series of nanometre-size holes. When photons strike a transparent solid that is patterned on the scale of the wavelength of light, they scatter at the interfaces and cause multiple interference. This can lead to intriguing optical properties where the normal laws of optics do not apply.
I read with interest Robert P Crease's article on "Discovery with statistics" (August p19), which described how the Cyrogenic Dark Matter Search (CDMS-II) presented its recent results on dark matter, and discussed the problem of identifying a definite signal in the future.
Experiments housed deep underground are searching for new particles that could simultaneously solve one of the biggest mysteries in astrophysics and reveal what lies beyond the Standard Model of particle physics.
Although superconductivity in carbon-60–the chief member of the fullerene family–has attracted a great deal of attention lately, the magnetic properties of the molecule have intrigued physicists since they were first reported in 1991. In the last nine years, several groups have confirmed that electron-doped carbon-60 is ferromagnetic. However, they have also noticed strange discrepancies in the molecule's magnetic properties. Now Bakhyt Narymbetov of the Institute for Molecular Science in Okazaki, Japan, and co-workers in Slovenia and Japan have succeeded in differentiating two distinct magnetic phases in a carbon-60 compound (B Narymbetov et al. 2000 Nature 407 883).
Is there something basically wrong with present-day radiology techniques? The answer would seem to be yes, on the basis of recent results from the National Synchrotron Light Source in the US. The results show that the limited quality of conventional X-ray images can be dramatically improved by exploiting synchrotron light (D Chapman et al. 1997 Phys. Med. Biol. 42 2015). Moreover, there is no need for a high radiation dose.
Why do physicists like distorting history? This embarrassing question cannot be avoided when one reads the brilliant article by Helge Kragh about how Max Planck developed his theory of black-body radiation (sec "Max Planck: the reluctant revolutionary" Physics World December 2000 pp31–35). Having destroyed several misconceptions, Kragh correctly remarks that what we often believe–and unfortunately teach is "closer to a fairytale than to historical truth".
Thermodynamics was developed in the mid 19th century to explain how steam engines worked in terms of macroscopic variables such as temperature, pressure and heat. Boltzmann and Gibbs later established the microscopic foundations of thermodynamics in terms of the statistical mechanics of large numbers (~1023) of atoms and molecules. But with today's increasing interest in nano-scale devices, it is crucial to ask if the concept of temperature is valid for systems that contain a relatively small numbers of atoms? According to a recent study by Michael Hartmann and Gunter Mahler of the University of Stuttgart and Ortwin Hess of the University of Surrey, the answer to this question is "no"(Phys. Rev. Lett. 93 080402).
In the late 1950s visionary physicist Richard Feynman issued a public challenge by offering $1000 to the first person to create an electrical motor "smaller than 1/64th of an inch". Much to Feynman's consternation the young man who met this challenge, William McLellan, did so by investing many tedious and painstaking hours building the device by hand using tweezers and a microscope.
Biological cells, molecules and organisms are complex systems that are increasingly capturing the imagination of physicists. Unlike many objects in the physical domain, biological systems cannot simply be described by the collective behaviour of individual components. The difference is that biological cells are living systems – a property that has less to do with the number of components they contain and more to do with the way these various components are arranged. Many physicists recognize that understanding this complexity is a fundamental challenge of biology.
The strong-force interactions between quarks and gluons inside hadrons are so powerful that they make the quarks and gluons behave in a highly complex way. Indeed, it is impossible to study this behaviour analytically. Physicists have therefore turned to numerical simulations performed on the world's fastest supercomputers. Recent progress in computing technology,: together with the development of new computational and theoretical techniques, means that these numerical calculations will become much more reliable over the next few years, opening up a whole new era of accurate predictions of the properties of hadrons. And by combining these predictions with experimental results, we will be able to test our understanding of the physics of the strong force in a way that has previously been impossible. The quantitative information that we can extract about the weak interactions will also pave the way to new physics.
Particle Physicists are developing a number of different types of experiment to search for the very weakly interacting sub-e V particles (WISPs) that would help to reveal some fundamental states of matter and the contents of the universe. There are three basic types of WISP, which, because of their very weak interaction with everyday world, are said to occupy a hidden sector of nature. These include the 'axion-like particle' (ALP), more generalized form of the axion, 'photon-like particles', having a spin equal to one and hidden-sector analogues of photons, and 'minicharged particles' (MCPs), that are predicted to have an extremely small charge. The results of research experiments to study the WISPs, that are expected in near future, can help to eliminate many of the possible solutions of string theory, and to develop new insights in the area of elementary particle physics and cosmology.
As A result of extensive media coverage, all readers must surely by now be aware of the latest bandwagon to hit the physics trail – 'electrolytic fusion'. Martin Fleischmann and Stanley Pons and the Brigham Young University group have achieved popular fame apparently exceeding that achieved by Bednorz and Müller, the discoverers of high temperature superconductivity. Even those who, like ourselves, have merely admitted to being involved in this area, have found themselves being sought out by a variety of journalists – and few of our colleagues can claim to have had a prayer dedicated to them in the Morning Service on BBC Radio 4.
Particle physics was born in 1897 with the discovery of the electron by J J Thomson, and many experimental and conceptual strides have been made in the century or so since this discovery. Several layers of the cosmic onion have been peeled away, and our current understanding of the subject is summarized in the so-called Standard Model, which has been tested with high precision at particle-physics laboratories around the world. There is no confirmed measurement from any laboratory experiment that contradicts the Standard Model. However, we particle physicists find it very unsatisfactory because its very successes raise many fundamental questions that cry out for answers.
Gravity is truly universal. It is the force that pulls us to the Earth, that keeps the planets and moons in their orbits, and that causes the tides on the Earth to ebb and flow. It even keeps the Sun shining. Yet on a laboratory scale gravity is extremely weak. The Coulomb force between two protons is 1039 times stronger than the gravitational force between them. Moreover, Newton's gravitational constant is the least accurately known of the fundamental constants: it has been measured to 1 part in 104, while Planck's constant, which characterizes quantum mechanics, is known to within 1 part in 106.
A shortfall in the production of medical isotopes in Europe has forced hospitals to delay patient scans or offer alternative diagnostic tests. The problems began in August when all three nuclear reactors used to generate molybdenum-99, which then decays to form the key nuclear-imaging agent technetium-99m, had to be unexpectedly shut down at the same time. Technetium-99m is a radioactive isotope with a half-life of six hours that is used in about 80% of all nuclear medical tests to detect bone cancer, heart disease and poorly functioning kidneys. The three reactors in Europe that produce it are HFR (Petten; The Netherlands), BR2 (Mol; Belgium) and OSIRIS (Saclay; France) were shutdown together for an extended period in the second part of 2008. The problem was further compounded by the simultaneous closure of the IRE (Fleurus; Belgium), following a leak of radioactive iodine-131. The IRE is one of the two plants in Europe that extracts molybdenum-99 from uranium targets irradiated at the nuclear reactors.
Synchrotron radiation was first observed by physicists working on the GEC electron synchrotron at Schenectady, New York, in 1947. Since then the building of synchrotron sources has accelerated and there are now about 70 synchrotrons in operation, or under construction, in Europe, the US, Japan and Asia. The largest of these, the Spring 8 machine being built in Tsukuba in Japan, will measure over 1400 m in circumference. So why has synchrotron radiation become so popular? Today there is intense competition for just a few hours of beamtime and scientists are prepared to travel across the world to use it. In the UK, industrial users are willing to pay almost £5000 for a day's synchrotron radiation and spent about £0.5m for synchrotron-related activities last year.