Embargo notice: Please do not report on the results mentioned in this press release until the time of the respective press briefing. For more information contact Phillip Schewe, 301-209-3092, pschewe@aip.org, or Ben Stein, 301-209-3091, bstein@aip.org, at the American Institute of Physics, or Randy Atkins at the American Physical Society, 301-209-3238, atkins@aps.org. College Park, MD, April 19, 2000 -----The following is a summary of the press conferences scheduled for the American Physical Society (APS) April Meeting in Long Beach, California April 29-May 2, 2000. The pressroom at the meeting will be room 201B in the Long Beach Convention Center. Press conferences will be held in room 201A. Pressroom hours: Sat-Tues 8 AM to 5 PM. Pressroom phone numbers: 562-499-7780 and 81. Fax: 562-499-7784. The meeting website, including all the abstracts, is www.aps.org/meet/APR00/#general. See also the APS virtual pressroom at www.aps.org/meet/APR00/baps/vpr. Journalists intending to attend the meeting should send in their request for a press badge, if they haven't already done so, to Ben Stein at bstein@aip.org. Saturday, April 29, 12 BEST MEASUREMENT OF THE GRAVITATIONAL CONSTANT/ BEST TEST YET OF SPECIAL RELATIVITY Jens H. Gundlach of the University of Washington (206-543-4080) will report a long-awaited higher precision measurement of the gravitational constant, usually denoted by the letter G. It is almost 10 times the precision of previous measurements, and also offers an the best determination yet of the Earth's mass. (For more information, see the lay language paper by Gundlach and colleagues at http://www.aps.org/meet/APR00/baps/vpr/layp11-03.html) Einstein's theory of special relativity rests on two postulates: (1) that the laws of physics are the same for all reference systems moving at a constant velocity with respect to each other and (2) the speed of light through vacuum is a constant independent of the speed of the light source. Kenneth Brecher of Boston University (617-353-3423) uses the sharpness of arriving wave pulses from distant gamma-ray bursters to affirm the second postulate to within one part in 10^20 (paper B16.13). Presenting an overview of recent adjustments made to the fundamental physics constants (Paper W10.03), Peter Mohr of NIST (301-975-3217, mohr@nist.gov) will explain how conflicting experimental results have made the recommended value for G, the gravitational constant,10 times less precise than before. At the other extreme, he will describe how the Rydberg constant (which helps prescribe an atom's spectrum of wavelength values) is known 100 times more accurately than in 1986, thanks to breakthroughs in measuring visible light. Sunday, April 30, 12 INTERGALACTIC ACCELERATION LANES FOR COSMIC RAYS? Presenting the very first low-frequency (75 MHZ) radio telescope images of a region that is part of the Great Wall of galaxies, Phil Kronberg of the University of Toronto (416-978-4971, kronberg@physics.utoronto.ca) and his colleagues present the clearest, most unambiguous evidence yet for intergalactic magnetic fields outside galaxy clusters. The new images suggest the possibility (still speculative at this point) that vast intergalactic zones like these may serve as the mysterious acceleration sites for ultra-high energy cosmic rays, which have confounded physicists in recent years. In separate work to be published later this year, Kronberg and colleagues have found that the rarefied intergalactic regions in typical clusters have magnetic fields that are, amazingly, at least as strong as those within the much denser disk of our Milky Way. This means that a significant additional amount of energy, in a previously invisible form, is stored within the intergalactic gas in galaxy clusters. Angela Olinto of the University of Chicago (773-702-8206, olinto@oddjob.uchicago.edu) will describe what is known about the history of magnetic fields in the universe. Studying the magnetic fields within galaxies, Russell Kulsrud of Princeton University (rkulsrud@astro.princeton.edu) will report on a new problem that has emerged: Evidence is ruling out the previously held scenario that a galaxy's magnetic field grows from a weaker field as it develops over billions of years. This only seems to leave the possibility that the precursors to galaxies billions of years ago must somehow have possessed magnetic fields roughly as strong as those in galaxies that we observe today. (Session B7, Saturday) Monday, May 1, 10 WHAT DID ASTRONOMERS KNOW AND WHEN DID THEY KNOW IT? At this briefing we view the heavens from the vantage point of the second, tenth, fourteenth, and twentieth centuries all at once (Session Q22). James Evans of the University of Puget Sound (jcevans@ups.edu) argues that the second century astronomer Ptolemy is the first true scientist since he combined the highly theoretical Greek astronomy with the more practical but limited observations of the Babylonians to make the first system in which a mathematical model predicts planetary positions. George Saliba of Columbia University (212-854-4166; gas1@columibia.edu demonstrates the Medieval Moslem astronomers did not merely pass along the ancient Greek models to later Europeans. Owen Gingerich of Harvard ((617-495-7216; ogingerich@cfa-harvard.edu) looks at how aesthetic principles helped to sculpt Copernicus's model of the solar system, which, despite its being centered around the sun, actually was quite old fashioned in its insistence on perfectly circular and constant-velocity trajectories. Finally Virginia Trimble of the University of Maryland and UC Irvine (vtrimble@astro.umd.edu; 949-824-6948), chair of Session P8 ("Triumph of Twentieth Century Astrophysics") will provide the modern view. Monday, May 1, 1 SEARCH FOR NOVEL GRAVITY AND EXTRA DIMENSIONS Just in the past two years an exciting new theory of quantum gravity has made startling, testable predictions. The model supposes the existence of extra spatial dimensions (with a characteristic size of perhaps a millimeter) in which gravity, but not other forces, might be operating. One practical implication is that at high-energy collisions at labs like CERN, and maybe even Fermilab, one manifestation of extra dimensions would be a conspicuous disappearance of energy, implying that some of the collision energy had been converted into gluons which disappear into the extra dimension. Another implication of the new model, one that can be probed with tabletop experiments, suggests that the gravitational force might depart from Newton's inverse square law (the force being inversely proportional to the square of the distance between two objects) at distances smaller than 1 mm. Speakers here from Session V12 include Nima Arkani-Hamed of LBL (510-486-4665; arkani@thsrv.lbl.gov), one of the authors of the theory paper that launched the model (this paper, in only 18 months, was the 1990s' most cited paper dealing with physics beyond the standard model); John C. Price of the University of Colorado (303-492-2484; john.price@colorado.edu) will present the first preliminary results from his tabletop experiment; he has not yet found evidence for anything anomalous, but will report the sharpest limit yet on the existence of new forces operating over the 50-150 micron range. Meanwhile, Gregory Landsberg of Brown University (401-863-1464; landsberg@hep.brown.edu) will report on the search for extra dimensions at Fermilab and CERN. Eric Adelberger of the University of Washington (206-543-4294) will join several other speakers on the subject of measurements of gravity at the millimeter level and below. ####