Activities
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Seminars
| Seminar on Theoretical and Computational Physics:
| | Title | Discovery of a New Phenomenon Induced by Quantum Fluctuations in the Electromagnetic Vacuum
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| Speaker | Cesareo Dominguez
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| Affiliation | Emeritus Professor of Theoretical Physics, University of Cape Town
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| Date | Tuesday, 02-03-2010
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| Time | 10h00, Thứ Ba
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| Location | Meeting room on the 1st floor, Institute of Physics
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| Abstract | According to Quantum Electrodynamics, fluctuations in the vacuum have been known for a long time to induce nonlinear peculiar effects. Most of these effects are time-dependent and are being discussed with growing frequency in the current literature. A static phenomenon due to nonlinearity induced by the quantum vacuum has been predicted very recently. A neutron placed in an external constant electric field develops an induced electric dipole moment. This discovery is as much unexpected as it is spectacular. In addition, there is a very good chance of observing this effect in experiments being planned for the near future. This phenomenon is described here having in mind the layperson interested in Physics. First, a brief description is given of Classical Electrodynamics and the classical Cartesian vacuum, followed by Quantum Electrodynamics and the characteristics of the quantum vacuum. Finally an explanation of the discovery in non technical language is given.
CLASSICAL ELECTRODYNAMICS
Classical Electrodynamics, the theory describing electric and magnetic phenomena, is a linear theory so that the Superposition Principle holds. This means that the electromagnetic field produced by a collection of sources is obtained by adding linearly, one by one, the field produced by each source. One important consequence of this linearity is that two light rays crossing each other would never interact; they would be oblivious to each other. Another property of the classical theory, true also for any other theory at the classical level, is that the vacuum is a perfect void without any dynamical properties. In particular, the vacuum would have no electrical or magnetic properties. This picture of the vacuum led René Descartes (1596-1650) to coin the famous phrase: Nature abhors the vacuum. As explained next, none of this actually holds in the quantum world.
QUANTUM ELECTRODYNAMICS
In Physics, a theory is usually characterized by a function called the Lagrangian density,
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