>Date: Thu, 13 Apr 2000 11:37:31 -0400 (EDT) >From: AIP listserver <[EMAIL PROTECTED]> >To: [EMAIL PROTECTED] >Subject: update.479 > > >PHYSICS NEWS UPDATE >The American Institute of Physics Bulletin of Physics News >Number 479 April 13, 2000 by Phillip F. Schewe and Ben Stein > >DARK ENERGY AND THE MICROWAVE BACKGROUND. The >theory of general relativity introduced the notion that spacetime could be >warped or curved by the presence of matter. Locally, stars or any object >with mass will curve space, but the expansion of the universe itself may >introduce a curvature of its own. This is how cosmologists summarize >things: a static universe with no matter (if such a thing were possible) >would have no curvature. If, however, the empty universe were expanding >it would have negative overall curvature. Increase the mass density from >zero and the curvature would be less negative. Add still more mass and you >might reach a net zero curvature. The ratio of matter to the critical matter >needed for zero curvature is called omega; the popular version of the big >bang model, featuring a very rapid expansion in an early "inflation" phase, >predicts that omega should equal 1 exactly. A new paper in Physical >Review Letters by Scott Dodelson of Fermilab and Lloyd Knox of the >University of Chicago (773-834-3287) provides the theoretical underpinning >for the higher-precision mappings of the cosmic microwave background >(CMB) reported over the past nine months. The paper was prepared just as >the first of the observational results appeared last summer: a Princeton- >Pennsylvania collaboration taking data from Cerro Toco in Chile. Their >findings (preprint astro-ph/9906421) can be plotted as the size of the >observed fluctuations in the CMB as a function of the angular size of the >fluctuation region (actually astrophysicists usually transform the data so that >it can be plotted against the size of angular moment, or "l"). These data and >those of the "Boomerang" (preprint 9911444 and 9911445; also see Update >460) and "Viper" (preprint 9910503) groups sit right on top of a theoretical >curve drawn by Dodelson and Knox corresponding to the case where omega >equals 1 and the net curvature of the universe is zero. With the contribution >of matter (luminous and dark) to the density of the universe expected to be >about one-third the critical value (of omega=1), this presents a stronger- >than-ever argument in favor of the existence of yet another form of energy, >often called "dark energy," to provide the missing two-thirds of the energy >needed to make omega=1. This dark energy would also provide the >"negative pressure" or repulsiveness needed to make the expansion of the >universe greater than in the past, a development suggested independently by >studies of distant supernovas. (Dodelson and Knox, Physical Review >Letters, 17 April; Select Article.) > >STORAGE OF HARD X RAYS IN A CRYSTAL RESONATOR, at least >for as many as 14 back-and-forth cycles, has been achieved by physicists at >the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. >The resonator consists of a pair of vertical walls (each 70% reflective) 150 >mm apart carved from a single crystal of silicon, thus ensuring the perfect >alignment of rows of atoms in both walls. X rays with an energy of 15.8 >keV from the ESRF machine arrive in the resonator in bursts only 10^-10 >seconds in duration and with a wavelength of only 7.8 x 10^-11 m. The x >rays are retained by multiple Bragg scattering between the walls. Previously >lower energy "soft" x rays had been stored in resonators but this is the first >time for higher energy x rays. The new resonator also serves to sharpen the >range of energy of x rays transmitted as compared to the range for the >incoming x rays. Plenty of x-ray optics applications are expected. (Liss et >al., Nature, 23 March 2000.) > >THE LONGEST COMET TAIL ever recorded, more than 570 million km, >has come to light in the form of a fluctuations in magnetic fields and in the >amount and species of charged particles detected by the Ulysses spacecraft >on 1 May 1996. A puzzle at first, the fluctuations are now attributed to >Ulysses' inadvertent passage through the wake of Comet Hyakutake. The >long tail is much greater than that of the previous record holder, the Great >March Comet of 1843. If Hyakutake's tail had been visible on Earth at that >point in the Comet's trajectory, it would have arced more than 80 degrees >across. (Jones et al. and Gloeckler et al., Nature, 6 April 2000.) > >TSUNAMIS IN LAKE TAHOE. One thinks of skiing and hiking in >reference to this lake nestled between Sierra mountain peaks. Nevertheless, >a system of faults near the lake might conspire to generate monster waves in >the event of a magnitude-7 earthquake in the area. Simulations by >researchers at the University of Nevada indicate that a tsunami and follow- >up waves lasting perhaps for hours could produce wave heights as high as >10 m. (Ichinose et al., Geophysical Research Letters, 15 April 2000.) > > >UPDATE SUBSCRIPTION REMINDER. You can add or delete your >email address from our distribution list automatically by sending a message >to [EMAIL PROTECTED] and specifying either "add physnews" or "delete >physnews." For viewing and searching through all past Updates you should >visit our website at http://www.aip.org/physnews/update. >
