more about me

My interest in science—all science, but especially physics and chemistry—developed very early. I grew up absorbed in the books of James Jeans, Arthur Eddington, George Gamow, and other physicists and astronomers. The physics books, math books, and course notes of my father, who trained in mechanical engineering, could be found throughout the house and intrigued me with their arcane symbols and details about materials and structures. From these beginnings and throughout my life, I have been attracted by the intricacies of physical phenomena and driven to understand their underlying causes.

I began my higher education at Michigan State University on a four-year Alumni Distinguished Scholarship, at the time one of ten (if I recall correctly) awarded annually based on a wide-ranging series of tests and subsequent interviews. Looking back over a long scientific career of many projects, papers, and books, I don't think I ever worked as hard as during those four years at Michigan State. I majored in chemistry with minors in physics and math, graduating at the end of four years with both a bachelor's degree in chemistry (having completed an honour's thesis on my research in synthetic organic chemistry) and a master's degree in physical chemistry.

Although chemistry was to interest me throughout my career, there was never any doubt in my mind as to what I really wanted to do. And so, I became a physicist (Ph.D. Harvard University). Working primarily at academic institutions, I have had the good fortune to be able to research whatever problems interested me—and in the course of my career I have chosen eclectically.

As a Harvard graduate student in the research group of Prof. Frank Pipkin, I started out in atomic physics, working on a method to study short-lived excited quantum states of neutral atoms by means of an atomic beam combined with microwave and optical spectroscopy. By studying hydrogen, the simplest atom of the periodic table, I investigated quantum electrodynamics (QED), which provides a theoretical account of all electromagnetic processes with breathtaking accuracy. It is known now that QED is but part of a more inclusive theory that encompasses the weak and strong nuclear interactions in addition to electricity, magnetism, and optics.

The physicist who, more than any other, served as a role model for me was Enrico Fermi, a scientist as adept with theory as he was at home in the laboratory. I never knew Fermi personally, but like him, I wanted to do both theoretical and experimental work with comparable facility, an ambition not common among physicists. Thus, for example, while conducting experiments on the hydrogen atom, I also worked on a comprehensive quantum theory of single- and multi-photon interactions of atoms with radiofrequency, microwave, and optical fields. My early theoretical and experimental work in atomic physics was eventually published as my fourth book, Probing The Atom: Interactions of Coupled States, Fast Beams, and Loose Electrons (Princeton, 2000). The title, a lightly mischievous play of words, was inspired by the originally conceived title “Base Pairs” of James Watson’s famous book.

I would add that, besides Fermi, I was influenced in several ways by my thesis advisor, Frank Pipkin. Seeing how he conducted research in what were effectively three distinct fields of physics—atomic, nuclear, and high energy—reinforced my determination to follow my own broad interests as they evolved over time. Moreover, he was a kind and accessible mentor who encouraged me to proceed in my own way at my own pace, but was always available when I needed his advice. I kept these traits in mind when I had my own research students to guide.

In the years that followed, quantum physics constituted a significant part of my research. I investigated a broad spectrum of intriguing quantum phenomena in a wide variety of ways—with electron interferometry, electron microscopy, radiofrequency and microwave spectroscopy, coherent laser spectroscopy, nuclear magnetic and electron paramagnetic resonance, atomic beams, radioactive nuclei, and of course pencil, paper, and computers. One of the most satisfying experiences of this phase of my career resulted from the time I spent in Japan as Visiting Chief Researcher in quantum physics at the Hitachi Advanced Research Laboratory near Tokyo. At Hitachi, I proposed to the electron microscopy group an experiment to demonstrate the buildup of an electron interference pattern one electron at a time. This classic two-slit interference phenomenon—which is one of the most dramatic illustrations of the wave-particle duality of nature—was designated in 2002 the “most beautiful experiment in physics” by readers of Physics World, the flagship publication of the Institute of Physics. My investigations of quantum mechanics became the subject matter of my second book, More Than One Mystery: Explorations in Quantum Interference (Springer, 1995) and sixth book, Quantum Superposition: Counterintuitive Consequences of Coherence, Entanglement, and Interference (Springer, 2008).

Being fascinated with the behaviour of light from childhood onward, I have also done extensive research in physical optics, conducting and analysing numerous experiments on the reflection, refraction, diffraction, interference, polarisation, and scattering of light. For example, using polarised light and a device known as a photoelastic modulator, invented by my French colleague and friend, Prof. Jacques Badoz, I devised a method for detecting and imaging hidden objects immersed in a light-scattering medium of the opacity of whole milk. The same methodology made it possible for Jacques and me to observe and measure for the first time the difference with which a naturally chiral substance reflects left and right circularly polarised light, thereby completing, in a sense, the epochal 19th Century work of Augustin Fresnel, who first demonstrated the difference with which a chiral substance refracts circularly polarised light. A chiral molecule is one which is not superposable on its mirror image, just like a right-handed glove cannot be superposed on a left-handed glove without turning it inside out. Since molecular chirality is a signature of all life on Earth (and possibly elsewhere as well), this research provided a versatile new way to explore systems critical to biology and medicine, as well as materials science.

In another phase of my optics work, I devised a method of lensless diffractive imaging by which to isolate and project symmetry patterns from a complex object with high noise content. Since no lenses are used, this method of imaging can be useful for structure determinations with spectral sources for which effective lenses may be difficult or impossible to produce, such as in X-ray and neutron diffraction. I described these and other optical investigations in my third book, Waves and Grains: Reflections on Light and Learning (Princeton, 1998).

From about 2000 onward, I became interested professionally in the same basic themes that I encountered in the books that first drew me to physics, namely nuclear physics and the evolution of the universe, galaxies, and stars. I investigated longstanding problems in astrophysics concerning dark matter, dark energy, and the internal structure of collapsed stars that have exhausted their nuclear fuel. I discuss this research in my fifth book, A Universe of Atoms, An Atom in the Universe (Springer, 2002) as well as in the long final chapter of Quantum Superposition (2008).

As a nuclear physicist, I studied a variety of low-energy nuclear processes such as alpha decay, beta decay, and electron capture decay of different nuclides. One objective of these studies was to test what is perhaps the most fundamental distinction between quantum and classical physics: viz. whether quantum processes occur completely randomly or not. It has often been stated (see, for example, Wikipedia) that random processes are devoid of any order or patterns. That is actually not the case. Certain patterns of recurrence are the hallmarks of a random process. By showing that these patterns are exhibited in a wide range of nuclear decay processes, my work has demonstrated that individual nuclear disintegrations indeed appear to be entirely unpredictable. In fact, as currently known, there is no process more random than spontaneous nuclear decay.

Another nuclear system I investigated, with practical as well as theoretical ramifications, is the decay and diffusion of the chemically inert gas radon and its radioactive progeny. Radon isotopes, created in the decay chains of uranium and thorium in underground layers of rock such as granite, subsequently seep into buildings and are principal sources of lung cancer in nonsmokers. I have devised and tested a simple, accurate method for measuring indoor radon concentration (i.e. decays per volume), employing nothing more sophisticated than two Geiger-Mueller (GM) counters—the most commonly available, overall least expensive, and most easily operated nuclear instrumentation. Prior to this work, standard references on radioactivity regarded measurement of radon concentrations with GM counters as not possible.

Besides measuring radon concentrations, I solved analytically and numerically complex statistical problems concerning the diffusion of a radioactive gas. I answered in particular the two major questions essential to mitigating problems arising from the release of such a gas: First, if the point of release is known, where will the gas likely be an arbitrary time later? Second, in how much time will the gas cover a specified distance? It may sound like the same question is being asked in two different ways, but the solutions call for mathematically very different statistical analyses.

My research in nuclear physics—in particular, the investigations of different kinds of radioactive decay—made me realise that I needed to become more proficient in statistical analysis than I was before. Although I taught courses in statistical physics, which dealt nearly exclusively with physical systems in equilibrium, the research I was engaged in called for mathematical methods to treat complex time-varying stochastic processes. And so I undertook an intensive self-instruction. As a university student, I became glassy-eyed with boredom at just the mention of the word statistics; this was one subject I scrupulously avoided, despite having a course schedule heavily laden with mathematics, physics, and chemistry. But later, as a professional scientist, the subject became much more interesting to me when I perceived it as necessary to my own work. Generally speaking, I think this incentive is the strongest motivation for acquiring knowledge.

The more intensively I studied statistical theory, the more applicable I found it to problems outside nuclear physics as well. And the more problems I worked on, the more statistical methods I became familiar with. Physics and statistics became for me a mutually reinforcing pair of interests. Over time, my initial study of the statistics of nuclear decay branched into a network of diverse explorations embracing not only fundamental physics, but also issues relating to recreation, education, health and medicine, finance, sports, air travel, and other topics. I discuss this aspect of my work in my seventh book, A Certain Uncertainty: Nature’s Random Ways (Cambridge, 2015).

With the start of the COVID pandemic in 2020, I retired from teaching in order to devote more time to research, much of which entailed the application of physical principles and statistical methods to medical and epidemiological issues. One study was to determine the infectivity of SARS-CoV-2; i.e. the probability of an infected person to shed virus day by day following the onset of symptoms or the first positive antigen test. The outcome would be highly useful to agencies like the CDC or organisations like the WHO, as it led to a rational and rigorous approach for determining self-isolation times. Regrettably, a recalcitrant public ignored such information, and agencies that should have been promoting sound public health revised key numbers downward, ultimately to the point of making no recommendations at all.

In another project with significant medical implications, I derived the exact statistical distribution of the body mass index (BMI), which is the most widely used medical risk factor for an extensive array of diseases and conditions associated with either excess or deficient weight. This probability function provides a means for the CDC and WHO to determine BMI cut-off points that accurately reflect the health risks of people from diverse demographics. In a closely related investigation, I also determined theoretically the joint probability distribution of human height and weight, which are correlated variables. This project not only resolved rigorously an anthropometric problem dating back to the origins of modern statistics—i.e. the question of how human physical attributes vary in a population—but was also essential to practical application of the BMI by the medical community. Moreover, it is a study that may shed light on biological mechanisms of human growth.

One of my greatest pleasures as a physicist was to recognize a significant conceptual problem, work out the theory of it, and then, whenever possible, go into the lab and test it. It is indescribably satisfying to find that the esoteric mathematical symbols created in one’s mind and scribbled on a sheet of paper actually foretell accurately what Nature will do.

There is an individual, personal dimension to the research choices that scientists make. I am a physicist who has chosen to work primarily at an undergraduate college, where teaching takes up most of one’s time, and there are no graduate students or postdoctoral fellows to help with research. Having made that decision, I understood from the outset that a research programme in competition with well-funded, well-staffed scientists at universities or national laboratories would never be successful. However, as I wrote in the last essay of Waves and Grains:

"The likelihood of succeeding as a scientist under conditions of severely parceled time and inadequate resources depends critically on the projects one chooses to investigate. It is at this point where a wide-ranging curiosity can mean the difference between a satisfying career and a life of frustration."

Thus, with wide interests, there are wide choices—and I have been a scientist with very wide interests.

In more than a few instances I came to a project serendipitously, having been captivated by a particular unresolved controversy in which different researchers arrived at conflicting conclusions as to whether some phenomenon took place or not, or, if it did, then how. Among the controversies treated in my papers and books are the following consequential issues:

• Amplified reflection — can more light reflect from a surface than is incident upon it? Answer: Yes (Waves and Grains)
• Chiral optics — are two widely used sets of relations that describe an optically active medium equivalent? Answer: No (Waves and Grains)
• Quantum mechanics — does it conflict with special relativity? Answer: No (Quantum Superposition)
• Nuclear decay — does the disintegration of one radioactive atom influence the subsequent decay of another? Answer: No (A Certain Uncertainty)
• Dark matter — can it comprise very low-mass particles, rather than very high-mass particles? Answer: Conceivably Yes (A Universe of Atoms)
• Dark matter and dark energy — are they somehow related? Answer: Conceivably Yes (A Universe of Atoms)
• Stellar collapse — can a massive star that has exhausted its nuclear fuel collapse to form a hole in space-time where the laws of physics break down? Answer: Almost certainly not (Quantum Superposition and more recent published papers with colleagues)

The last question above is the question of black holes, a topic that has grasped the attention of news media to such an extent that to much of the public the entire field of physics is reduced to oracular pronouncements by celebrity theorists regarding the collapse and disappearance of matter. This collapse leads to a host of paradoxes concerning energy, entropy, information, and travel through space and time. These paradoxes are usually the product of an overactive imagination and a mathematical virtuosity unguided by the compass of experimental physics. The problem of collapsed stars is a fascinating one which has by no means received a definitive theoretical treatment. Nevertheless, there are quantum processes that can halt the internal collapse of a star to create an equilibrium end state of finite size and density that still appears externally as a hole in space.

My career as a physicist has also afforded me the pleasure of numerous close collaborations with colleagues throughout the world. Because of my work as a scientist, my children have grown up as world citizens whose homes have ranged geographically from New Zealand to Finland and throughout the US, Europe, and the Far East. To accommodate this travel, my wife (also a Harvard Ph.D) and I undertook the education of our children ourselves from kindergarten through high school, and this homeschooling experience has not only made for close family ties among us, but has had a profound positive influence on my teaching students at college and university.

If there is one overarching lesson that I have learned from my career as a physicist, it is that the universe is governed by comprehensible physical laws. Nothing supernatural is needed to make sense of the world. If only this lesson could be inculcated everywhere myth, superstition, religion, and tradition impede the teaching of science and lead to unsound public policy decisions and the repression of human rights.

Trinity's science quad. Left, bottom, and right: Math, Computer Science, and Engineering; Biosciences; and Physics.