Research: Theoretical Physics: Introduction - People - Courses - Studies - Seminars - Preprints
Theoretical physics covers a wide field of phenomena, from subatomic physics at the smallest scale to physics of the universe at the largest scale. By use of mathematical methods and physical understanding the existing theories are studied, extended and developed further, and the new ideas that are introduced are confronted with observations and measurements. Simplified models are often studied in order to obtain better understanding of more complex theories and phenomena.
A main objective of theoretical physics is to attack the problems of physics that we consider as the most fundamental ones. The discovery at the beginning of the last century of the theory of relativity and of quantum mechanics changed in a basic way our understanding of Nature, and still these theories form the basis of much of the research in theoretical physics. That is also the case in our research group, where the focus of interest is particularly on fundamental quantum phenomena.
Elementary particles, and the forces that act between them, are theoretically described by a set of quantum field theories called gauge theories. These theories have a rather simple formulation, but in many cases the derivation of experimentally testable predictions are very difficult. This is particularly true for the theory of quarks and gluons, referred to as QCD (quantum chromodynamics). This is the theory of strong interactions, which bind the quarks together to form nucleons and cause the interactions between the protons and neutrons in the nucleus. However, in the case of weak and electromagnetic interactions predictions can be made with great accuracy. The methods of calculations that are often applied are perturbation methods and effective field theories. Much of the activity in theoretical particle physics that is going on in our group is based on the application of these methods.
At extremely high energies the effects of gravitation becomes important for interactions between elementary particles, and in this energy regime new and so far non-established laws of nature will most probably come into play. Many physicists are convinced that a theory of strings rather than of point particles will correctly describe these new phenomena. Some of the activity in the group is focussed on the study of certain aspects of string theory.
In quantum physics the interactions between particles can give rise to other types of phenomena than those described by classical physics. The coherent behaviour of the particles may give rise to new types of collective phenomena and new types of (quasi) particles.
Some of the activity in our group is aimed at the study of coherent quantum effects in low-dimensional electron systems. In such systems, where the motion is restricted to a plane (or to a line), the collective motion can give rise to vortices in the electron fluid, and these vortices behave as new types of particles with unexpected properties. They may be anyons (something intermediate between bosons and fermions), and may carry a fraction of the unit of electric charge. The quantum Hall effect is a particular measurable effect of a 2-dimensional electron gas in a strong magnetic field that is directly related to these phenomena. Also high temperature superconductivity is considered to exist due to coherent effects of a low-dimensional electron system.
Quantum information theory is a recent field of research activity in our group. Quantum mechanics gives rise to new ways to process and transmit information, and in recent years these new possibilities have been studied with increasing interest. In principle quantum computers can be designed that operate according principles that are basically different from those of a classical computer. The new possibilities are interesting for the promises they give for new types of technological applications, but also because the focussing on quantum physics and information gives a different approach to the study of fundamental quantum phenomena. One of the basic coherent effects which is important in this field is referred to as entanglement, and the study of entanglement in many-particle systems and in field theory is one of the on-going activities.
Atomic and molecular physics. This is a research activity with a long tradition in our group. The present activity is focussed more on the study of highly excited atomic states than on the properties of stable ground states. Also the study of interactions between atoms and the electromagnetic field is an active field of research, with importance for the understanding of optical and magnetic properties of matter. Some of the activity in the field of atomic and molecular physics is stimulated by the ongoing discussion of possible physical realizations of a quantum computer.
Dynamical systems and chaos theory. The ongoing activity in this direction is aimed at the numerical study of instabilities in non-linear systems. The objective is to obtain a better understanding of how chaotic behaviour is initiated.
Classical physics and gravitation. The research activities in this field are focussed on problems in classical mechanics and classical radiation theory. Various problems in classical gravitation theory and in cosmology are also studied.
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