The Duke University Physics Department: Six Big Questions

Monday, August 29, 2011

Physics is a mature and evolving scientific discipline, which has witnessed many breakthroughs. In the 21st century, physics is poised for more discoveries and breakthroughs, many of which will come out of interdisciplinary research and teaching. In the last several years, faculty in our department have been working on better ways to articulate and present our work to prospective students, our undergraduate and graduate students, and others both inside and outside of Duke. The result is the following document, “Six Big Questions” which the faculty prepared and approved this summer to help guide our planning, research, teaching and communications as we move forward. --Professor Haiyan Gao, Chair of the Department of Physics

The Duke University Physics Department: Six Big Questions

What Are the Ultimate Laws of Nature?

Over the past century experimental observations and theory developments have driven remarkable changes in our understanding of the laws that govern the behavior of matter at small distances and the character of large cosmological structures. These two apparent disparate domains of nature are connected when theories of fundamental particles and forces on the microscopic scale are applied to the evolution of the universe. The next few decades will reveal a still deeper level of understanding of these ultimate laws of nature. This progress is being driven by a new generation of experimental tools such as the Large Hadron Collider that will probe matter with increased precision, energy, and sensitivity. The data provided may reveal new physics beyond our current understanding and will aid in the development of theories of the behavior of fundamental particles and their applications to understanding the timeline from the Big Bang to the fate of our universe.

Duke experimental physicists are exploring the properties of neutrinos, the origin of mass, the structure of matter, and fundamental symmetries. Duke theoretical physicists are exploring the strong force, extensions of the Standard Model, string theory, and the gravitational probes of cosmological structures.

What are the Principles and Applications of Quantum Physics?

A revolution in our understanding of quantum mechanics and its applications is shaping the future of fundamental science and engineering. Quantum physics determines the ultimate miniaturization scale and operating principles of nanodevices that function at the level of a single electron, single spin, single molecule, or single photon. The full range of phenomena permitted by the principles of quantum mechanics is coming to be understood only now, a century after its original discovery. New techniques are directly probing such cornerstones of quantum physics as quantum entanglement and quantum measurement. Quantum information processing—relying on entangled states of many particles—pushes the limits of our present experimental, theoretical, and computational approaches. One of the challenges is to control the interaction of these complex systems with their environments, which induce decoherence and dephasing; these processes generate the transition from the quantum-mechanical microscopic world to the classical macroscopic world. Yet another line of inquiry is leading to new materials with dramatic properties—graphene, topological insulators, and spin liquids, for instance.

Physicists at Duke are developing means of quantum information processing, studying nonlinear interaction between matter and light, investigating transport of charge and spin in nanostructures, and examining emergent behavior in interacting quantum systems, both in equilibrium and far from equilibrium. Some specific subjects of study include atomic and superconducting qubits; sub-diffraction limit optics and cloaking; “spintronics” and electronic transport in molecules, graphene, and quantum nanostructures; and the search for exotic phases of matter and quantum phase transitions.

What are the Features of Strongly Coupled Systems?

Many systems in nature are composed of strongly interacting components. In the quantum regime, examples include atomic nuclei, ultracold atoms, quantum liquids, and new exotic states of matter, such as the quark-gluon plasma and high-temperature superconductors. Very few quantum systems can be solved exactly, however, and these usually correspond to weakly interacting particles or excitation modes. Over the past decade, novel mathematical and experimental techniques have been developed to prepare, probe, and theoretically describe the intriguing features of strongly interacting systems. Among the amazing results is the insight that two of the coldest and hottest systems created under laboratory conditions share the property of being nearly perfect fluids with minimal viscosity. Another surprising discovery is the close connection between strongly coupled quantum systems and Einstein’s classical theory of gravity. Fascinating connections with both quantum information and graph theory have brought novel algorithms and insights into old methods. Duke physicists study many variants of strongly coupled quantum systems by experimental and theoretical techniques. The experimental activities include the investigation of ultracold atoms trapped in laser fields, the study of electrons in nanosystems and in materials containing strongly correlated electrons, as well as the exploration of the three-dimensional structure of nuclei and the nucleon using high-energy electron microscopes and intense gamma-rays. Theorists investigate transport properties of the quark-gluon plasma; use effective field theories to describe hadrons, nuclei, and atomic systems; develop novel algorithms for the simulation of strongly coupled systems of fermions; and apply methods derived from network theory and quantum information theory to model ground states of strongly coupled quantum systems.

How Do Statistical, Nonlinear and Complex Systems Work?

The vast majority of natural phenomena encountered in everyday life can be described in terms of nonlinear interactions, which are often a complex, collective consequence of underlying microscopic laws. Even when the nature of those interactions is well understood, the collective, macroscopic effects can be surprising. The surprises may come in two forms: (1) a collection of simple particles and interactions gives rise to intricate patterns and dynamical heterogeneity (such as turbulence); or (2) a heterogeneous network of interacting agents produces robust behavior with discernible coherent patterns (e.g., in granular materials or biological systems). Studies of these phenomena are pushing the boundaries of physics and revealing unexpected connections between seemingly disparate fields.

Physicists at Duke are exploring a broad and exciting range of complex behaviors.

Some examples include fluid flows, granular materials, gene networks, neural tissues, semiconductors, accelerator beams, and turbulent quark-gluon plasmas. (See also “What are the features of strongly coupled quantum systems?”)

What Does Physics Say About Biological Phenomena?

The application of physics to biology represents one of the most rapidly growing frontiers of physics. In fact, some of the most interesting unsolved problems in all of science are related to biology and physics such as: How did life arise and does life exist elsewhere in the universe? How are living creatures able to reproduce themselves faithfully over hundreds of millions of years, when the molecular mechanisms related to cellular reproduction are subject to fluctuations related to thermal noise and small numbers of components? How do the tens of thousands of genes and proteins in a cell interact to guide the structure and behavior of a cell or the self-assembly a complex organism? How do the neurons in a brain process information, and how do they do it more efficiently and in a much smaller volume than any existing electronic computer?

Duke physicists are excited about these and other biology-related questions, especially because their training in areas such as statistical mechanics, nonlinear dynamics, quantum mechanics, nanoscience, biophysics, and instrumentation provide numerous opportunities to make progress on these questions. Advances in biophysics also have applications to medicine, material science, computer science, electrical engineering, mechanical engineering, energy science, and other disciplines.

How Can We Use Physics to Benefit Society?

The search for the fundamental laws and explanations of natural phenomena often leads to technological breakthroughs of great benefit to society. In many cases, physicists also directly address important technological challenges in engineering, medicine, communications, information processing, finance, environmental science, and national security. A deep familiarity with the physical principles and the possibilities inherent in them is critical for the development of new techniques and for the design and implementation of practical devices and applications. The possibilities for advancement encompass the full range of sub-disciplines, from subatomic physics to condensed matter and complex systems.

Physicists at Duke are actively developing new physics-based techniques and technologies for communications; information processing; sensing with electromagnetic waves; neural networks and statistical modeling; nuclear energy production; detection of nuclear materials oriented towards homeland security; optimization of radiation risk versus benefits in medical imaging procedures; development of quantitative medical diagnostic procedures; applications of properties of granular materials to defense, industries and space-engineering; and the assessment of dynamic response of plants to changes in carbon levels in the soil and atmosphere.