Some of the invited lectures, suitable for a nonspecialist audience, that I have given are:
The Unimaginably Strange Behaviour of Free Electrons
Individual electrons give rise to wave-like interference patterns although they are always detected as discrete particles. Beyond this central "mystery" of quantum mechanics are other manifestations of quantum behaviour equally strange. Electrons interact with magnetic and electric fields through which they do not pass. They cluster in classically inexplicable ways although emitted seemingly at random. Two (or more) electrons constituting a single system can exhibit unusual long-range correlations long after the particles have separated. In this lecture I discuss examples of such behaviour in the context of novel types of particle interferometry. I also show one of the original videos made of the "famous" one-electron-at-a-time quantum interference build-up experiment I designed for the Hitachi Advanced Research Lab when I was their first Visiting Senior (later, Chief) Researcher for quantum physics.
Brighter Than a Million Suns: New Directions in Particle Interferometry
I have proposed new kinds of multiparticle quantum interference experiments that require for their implementation bright sources of degenerate particles. The brightest particle beam currently available is an atomic-sized field-emission electron source developed for point-projection electron microscopy by means of which electron Fresnel diffraction patterns can be observed. Point-projection imaging has the remarkable property of providing high-resolution non-aberrant images without the use of lenses or mirrors. Applying this method of imaging in the optical domain, I have shown it possible to isolate different structural symmetries in different focal planes. With the availability of appropriate massive particle sources, extension of this imaging method should greatly facilitate diffractive analysis of complex structures.
Light Reflection from a Chiral Medium: Exorcising A "Maxwell Demon"
Chiral systems display a preferential handedness; i.e. they are not superposable on their mirror image. Such systems can be found at all scales throughout the physical world, from the elementary particles (e.g. parity violation in beta decay) to the molecules critical to living organisms (e.g. left-handed amino acids and right-handed sugars) to the macroscopic objects of daily use (e.g. left and right handed gloves and right-handed scissors). Chiral molecules interact inequivalently with right and left circularly polarised light to display "optical activity", a complex of phenomena first noticed early in the 19th century and now thought to be well understood. I have shown, however, that the widely accepted "textbook" description of light reflection from chiral media violates fundamental physical laws. In this lecture I discuss my theoretical resolution of this controversy and experiments based on light reflection testing the electrodynamics of chiral media.
Through a Fog Brightly: A Penetrating Look at Scattered Light
The need to see through turbid media - media rendered cloudy by diffusive scattering from suspended small parlticles - is frequently encountered in science, technology, and medicine. Selective detection of phase-modulated polarised light provides a way to penetrate optically dense turbid media and reveal the presence and surface features of embedded objects invisible to ordinary viewing in ambient light. If the liquid medium is comprised of chiral molecules (e.g. aqueous solution of glucose), the prevailing expectation would be that the resulting optical activity would be "washed out" by random scattering from particles in suspension. I have shown, however, that, surprisingly, diffusive light scattering can lead, not to a diminution of optical activity, but to its enhancement relative to the transparent liquid devoid of suspended particles.
How Light Behaves When It Is Against a Wall: Amplification by Reflection
Can more light reflect from a surface than is incident upon it without violating the law of conservation of energy? Surprisingly, the answer is "yes" - if the reflecting surface is in contact with an underlying material whose molecules are excited, and the angle of incidence at the surface is carefully adjusted to fall within a certain range close to the critical angle. For a passive medium (no gain), critical angle is the angle at which 100% of incident light energy is reflected. However paradoxical it may seem, even if no light energy is transmitted, there is a nonvanishing "evanescent" field penetrating the underlying medium. In marked contrast to the operation of a laser, whereby light propagating through an excited medium stimulates emission, enhanced internal reflection results from emission stimulated by an evanescent wave. When originally proposed, light amplification by reflection generated considerable controversy regarding both its theoretical description and experimental detection. In this lecture, I discuss the correct theory developed by my student and me and our experimental tests that resolved this controversy.
Coins, Computers, and Quanta: Unexpected Outcomes of Random Processes
When purportedly random processes give rise to surprisingly nonrandom outcomes, how can one tell whether the processes are truly random? One way is to convert the process into a "coin toss", i.e. into a succession of binary events, and to examine the sequences of heads and tails. By this means, I have examined one of the most fundamental aspects of quantum mechanics. Quantum mechanics predicts that the transformations of atomic nuclei occur randomly without any underlying regularity that can reveal which nucleus is about to decay or when. An investigation of the randomness of (a) beta decay of Cs-137, (b) electron-capture decay of Mn-54, and (c) alpha decay of Po-214, as well as several non-nuclear processes, leads to some thought-provoking results. Begun initially as a student project to simulate by computer a simply stated but perplexing probability problem, the enquiry evolved into a test of fundamental physical law. The emphasis on encouraging curiosity and integrating research activities into course instruction is a basic part of my philosophy of teaching.
"Keep It Together! Keep It Together! Keep It Together!" Shedding Light on Dark Matter
Astronomers believe that about 99% of the mass of the universe is non-luminous, i.e. cannot be seen through telescopes covering the full range of accessible electromagnetic frequencies. Observations of relic radiation from the fireball that gave rise to the universe and of the red-shifted light from Type Ia supernovae provide evidence that the unseen matter is different from ordinary matter (i.e. protons, neutrons, and electrons). The nature of this exotic "missing mass" is one of the most fundamental problems of astrophysics. In contrast to presently favoured models of cold dark matter comprising highly massive particles, I will explain why I believe that dark matter may consist in large part of very low\ mass particles that form a quantum fluid known as a Bose-Einstein condensate. If my theory is confirmed, then such a condensate, currently touted as existing only in a few terrestrial laboratories, will instead be the most common form of matter in the universe.
The Universe: Where Did It Come From? Where Is It Going?
Cosmology - the study of the universe - has undergone a profound change in recent years from a largely speculative activity to an empirical science supported by numerous observations with far-reaching implications. Among the studies pointing to a coherent picture of the origin and fate of the universe are the observations of catastrophic stellar explosions, a universal ocean of extra-galactic microwave radiation, and primordial elements forged in an unimaginably hot fireball of creation. In this lecture, I will discuss qualitatively what physicists believe to be the early history and ultimate destiny of the universe - and why they hold these beliefs.
Inside Story of a Black Hole and Other Dark Matters of the Cosmos
Stars, like living organisms, have lifetimes of various durations. The death of a star can be a spectacular event, leading to the outflow of prodigious quantities of energy and to exotic end states of unimaginably high density. The strangest state of all is a black hole in which the pull of gravity is so strong that not even light can escape, and the laws of physics as they are currently known may appear to fail. (When a ball of matter of more than 2 million million million million million kilogrammes - the mass of the Sun - is predicted to collapse to a size many powers of ten small than the full stop at the end of this sentence, one might conclude that something is not working out right.) This lecture is about some of the strangest denizens of the cosmos...red giants, white dwarfs, neutron stars, and black holes...and how, in the last case, the laws of physics may be saved.
Condensates in the Cosmos: Quantum Stabilisation of Relativistic Stars and Galactic Dark Matter
According to prevailing theory, a sufficiently massive star at its thermonuclear endpoint cannot achieve hydrostatic equilibrium through the pressure exerted by its constituent particles (principally neutrons) and must collapse to form a stellar black hole whereby all its matter and energy inescapably descend into a central singularity. Avoidance of this fate is a hoped-for outcome of the quantisation of gravity, an as-yet far from complete undertaking. My theoretical work, however, suggests the possibility that known quantum processes may intervene to arrest complete collapse and lead to equilibrium states of macroscopic size and finite mass-energy density. One such process entails the transformation of an even number of neutrons (or quarks in the event of nucleon disruption) into a boson condensate in equilibrium with the fluid of degenerate fermions. An analogous process is currently believed to give rise to neutron superfluidity and proton superconductivity in neutron stars. Fermion condensation in a star otherwise destined to become a black hole facilitates hydrostatic equilibrium in at least two ways. First, the removal of fermions from the system causes the Fermi level to drop and the fermion degeneracy pressure to depend more strongly on fermion density. More importantly, a self-gravitating boson condensate cannot collapse; much of it therefore remains outside the sphere of infalling fermionic matter and contributes neither pressure nor weight. This latter characteristic may also be recognized in the behaviour of galactic dark matter comprising a condensate of very low mass bosons.
The Climes, They Are A'Changin' - Causes and Consequences of Global Warming
The Question of global climate change - whether it is actually occurring and, if so, for what reasons - is one of the most controversial and contentious issues debated in the US today. Public discussion gives an impression that there is great uncertainty over the matter even among scientists. In reality, this is not the case. The unequivocal scientific consensus is that release of anthropogenic greenhouse gases into the atmosphere is among the principal causes of accelerated global warming. In this lecture, I discuss the evidence for this conclusion and what measures need be taken as part of an effective solution.
Are Crowds Wise? Testing whether "One of Us is Smarter Than All of Us"
Numerous individuals over the ages have provided quotable pithy insults regarding the collective intelligence of people acting in groups. (The title of this lecture plays on one such example: "None of us is dumber than all of us.") A recent best-selling book, however, argued for the provocative idea that "...groups of [ordinary] people are smarter than an elite few, no matter how brilliant," with respect to such matters as prediction, problem solving, decision making, and other cognitive activities. If valid, the implications for how best to make wise economic, political, educational, judicial, scientific, technological, and military choices (to state a few possibilities) are far reaching. To find out for myself whether collective intelligence is reliable, I engaged groups of students in several stages of short exercises. In this lecture, I discuss my experimental test and resulting simple statistical model that suggests the circumstances under which one might expect the "wisdom of crowds" hypothesis to be valid.
Self-Directed Learning: A Heretical Experiment in Teaching Physics (...or almost anything else)
I have developed an educational framework in which (1) curiosity-driven enquiry is recognised as an essential activity of both science and science teaching; (2) the principal role of the instructor is to provide students the incentive to learn science through their pursuit of personally meaningful questions; (3) the commission of errors is regarded as a natural concomitant to learning and is not penalized; (4) emphasis is placed on laboratory investigations that foster minimally restrictive free exploration rather than prescriptive adherence to formal procedure; (5) research skills are developed through out-of-class projects that involve literature search, experiment, and the modeling of real-world physical phenomena; (6) the precise and articulate use of language is regarded as seminal to communication in science (as it is in the humanities) and is promoted through activities that help develop written and oral language skills; (7) the evaluation of student performance is based on a portfolio of accomplished work rather than on the outcome of formal testing. It is not easy to teach in this way, but, where my experiment has been attempted (in high schools, colleges, universities, graduate and medical schools, and in secular home-schooling environments), the results, I am told, have been highly satisfactory.