清华大学高等研究院学术报告 Colloquium, Tsinghua Physics

1. 清华大学高等研究院学术报告 Colloquium, Tsinghua Physics Two-slit diffraction with highly charged particles: Niels Bohr’s consistency argument that the electromagnetic field must be quantized Gordon Baym University of Illinois at Urbana-Champaign 8 月20 日（星期五）上午10:30 ，科学馆 322 报告厅 Abstract: Niels Bohr proposed a two-slit interference experiment with highly charged particles that argues that the consistency of elementary quantum mechanics requires that the electromagnetic field must be quantized. In the experiment a particle's path through the slits is determined by measuring the Coulomb field that it produces at large distances; under these conditions the interference pattern must be suppressed. The key is that as the particle’s trajectory is bent in diffraction by the slits it must radiate and the radiation must carry away phase information. Thus the radiation field must be a quantized dynamical degree of freedom. On the other hand, if one similarly tries to determine the path of a massive particle through an inferometer by measuring the Newtonian gravitational potential the particle produces, the interference pattern would have to be finer than the Planck length and thus undiscernable. Unlike for the electromagnetic field, Bohr’s argument does not imply that the gravitational field must be quantized. 报告人简介： Professor Baym received his bachelor's degree in physics from Cornell University in 1956, his A.M. in mathematics from Harvard in 1957, and his Ph.D. in physics from Harvard in 1960. He joined the Department of Physics at the University of Illinois as an assistant professor in 1963. Professor Baym has been a major leader in the study of matter under extreme conditions in astrophysics and nuclear physics. He has made original, seminal contributions to our understanding of neutron stars, relativistic effects in nuclear physics, condensed matter physics, quantum fluids, and most recently, Bose-Einstein condensates. His work is characterized by a superb melding of basic theoretical physics concepts, from condensed matter to nuclear to elementary particle physics. He has received APS Hans A. Bethe Prize (2002) “For his superb synthesis of fundamental concepts which have provided an understanding of matter at extreme conditions ” and Lars Onsager Prize (2008) “For fundamental applications of statistical physics to quantum fluids ”