Message-ID: <Pine.NEB.4.64.0612051644480.24658@panix3.panix.com>
From: Alan Sondheim <sondheim@panix.com>
To: Cyb <cybermind@listserv.aol.com>, Wryting-L <WRYTING-L@listserv.wvu.edu>,
Cyberculture <cyberculture@zacha.org>
Subject: Physics News Update 804 (fwd) stories of the year
Date: Tue, 5 Dec 2006 16:45:16 -0500 (EST)
---------- Forwarded message ---------- Date: Tue, 5 Dec 2006 15:22:10 -0500 From: physnews@aip.org To: sondheim@PANIX.COM Subject: Physics News Update 804 PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 804 December 5, 2006 by Phillip F. Schewe, Ben Stein, and Davide Castelvecchi www.aip.org/pnu THE PHYSICS STORY OF THE YEAR FOR 2006 was, we believe, the new high precision (0.76 parts per trillion uncertainty) measurement of the electron�s magnetic moment by Gerald Gabrielse and his colleagues at Harvard. Then in a second paper the same experimenters used the new moment in tandem with a fresh formulation of quantum electrodynamics (QED) provided by theoretical colleagues to formulate a new value for the fine structure constant (denoted by the letter alpha), the pivotal parameter which sets the overall strength of the electromagnetic force. The new value has an uncertainty of 0.7 parts per billion, the first major revision of alpha in 20 years. A comparison between this new value and values determined by other methods provides the best test yet of quantum electrodynamics (QED) (http://www.aip.org/pnu/2006/split/783-1.html; also see Physics Today, Aug 2006). Other top physics stories for the year, in no particular order, are listed below with links to pertinent PNU items (and sometimes figures) from the past year. These top stories include the observation of many more supernovas at redshifts of 1, thus establishing the idea that dark energy was around even in the early universe (http://www.aip.org/pnu/2006/split/802-1.html); the first direct measurement of turbulence in space (http://www.aip.org/pnu/2006/split/802-2.html); the best direct test of Einstein�s E=mc^2 formula (http://www.aip.org/pnu/2006/split/761-1.html); new WMAP measurements of the cosmic microwave background, including polarization information, help to sharpen cosmological numbers such as the age or the flatness of the universe (http://www.aip.org/pnu/2006/split/769-1.html); (http://www.aip.org/pnu/2006/split/794-1.html); first matter-antimatter chemistry (http://www.aip.org/pnu/2006/split/796-1.html); elements 116 and 118; 2006 Nobel prize in physics for Smoot and Mather (http://www.aip.org/pnu/2006/split/795-1.html); advances in plasmonics, or �two-dimensional light� (http://www.aip.org/pnu/2006/split/770-1.html); advances in the study of graphene, including the discovery of a new form of the Hall effect (http://www.aip.org/pnu/2006/split/769-2.html); progress at several labs in modeling gravity wave transmissions from black hole mergers, the kinds of events which LIGO or LISA would possibly detect (http://www.aip.org/pnu/2006/split/771-1.html); measuring the presence of virtual strange quarks inside protons (http://www.aip.org/pnu/2006/split/776-1.html); acoustic lasers (http://www.aip.org/pnu/2006/split/779-1.html); evidence for negative electrical resistance (http://www.aip.org/pnu/2006/split/780-1.html); a particle laser or �PASER� (http://www.aip.org/pnu/2006/split/792-1.html); hypersound (http://www.aip.org/pnu/2006/split/797-1.html); heaviest baryons discovered (http://www.aip.org/pnu/2006/split/798-1.html); investigating whether the electron/proton mass ratio changed over time (http://www.aip.org/pnu/2006/split/774-1.html); optical �cloaking� (Science, 8 Sept); telecloning, http://www.aip.org/pnu/2006/split/765-1.html; rare positronium ion, http://www.aip.org/pnu/2006/split/763-1.html; wireless energy transfer (http://www.aip.org/pnu/2006/split/801-1.html); the sharpest object ever made (http://www.aip.org/pnu/2006/split/788-2.html); chemical transistor, (http://www.aip.org/pnu/2006/split/786-1.html); radioactive scorpion venom for brain cancer therapy (http://www.aip.org/pnu/2006/split/782-1.html); liquid flowing uphill (http://www.aip.org/pnu/2006/split/772-1.html); and stock market criticality (http://www.aip.org/pnu/2006/split/765-2.html). POLARIZED AND UNPOLARIZED SUPERFLUID STATES. In many areas of science, such as the study of chemical reactions among atoms or the nuclear interactions among protons in collisions at an accelerator, the strength of the interaction between species is imposed by nature. In some cases, however, the researcher has some control over the interaction strength and can contrive exotic states of matter thereby. An important example of this dexterity is the study of nanokelvin fermionic atoms (atoms with a half-integral total spin value, such as 1/2). The Pauli exclusion principle forbids Fermi particles from distilling into a monolithic quantum fluid like a Bose-Einstein condensate (BEC). Paired up, however, fermions become bosons (integral-spin objects) and can condense. Fermi atoms, such as lithium-6, can marry in a variety of ways and this is what over the past few years has made them valuable to physicists in their effort to intervene in the basic interactions among particles. Typically the pairing is induced by adjusting an external magnetic field. The result can be a chemical bond: lithium atoms become tight diatomic molecules which then condense into a molecular BEC. Alternatively, the atoms might form weakly bound Cooper pairs of large size (many times the average interatomic spacing). Or the pairing can be some kind of in-between state. This in-between pairing regime is poorly understood but intensely interesting since discoveries there may offer great insights into basic condensed matter interactions. Theorists say that one potential route to discovering of exotic new atomic condensates is the use of unbalanced clouds with an excess of spin-up or spin-down atoms. Such systems are relevant to the study of magnetized superconductors and possibly even to pairing in cold quark matter at the centers of neutron stars. Recently, these systems have moved within reach of experiments, since in addition to being able to vary interaction strength, experimenters using cold atoms can vary the relative number of spin-up and spin-down atoms. One result of such an imbalance can be a separation into a two-phase gas consisting of a superfluid core of paired atoms surrounded by a normal-fluid mantle consisting of unpaired atoms. Randy Hulet (randy@rice.edu) and his colleagues at Rice University and Utrecht University have now, for the first time, found evidence for two distinct superfluid regimes in an imbalanced gas of fermionic lithium-6 atoms. At lower temperatures, a sharp boundary between the fully-paired superfluid core and the excess unpaired atoms is observed, as expected for a first-order phase transition (the kind of transition---such as water changing to ice---in which the internal energy of the substance takes a discontinuous jump). At a slightly higher temperature, the fully paired core and the normal fluid mantle are separated by a diffuse mixed-phase which is also superfluid. Moreover, while the higher-temperature gas maintains the long cigar shape (aspect ratio of 30) imposed by the fields of the atom trap, the superfluid core of the lower-temperature gas, under the action of surface tension between the superfluid and normal phases, deforms towards a more spherical shape (aspect ratio as small as 2). (Partridge et al., Physical Review Letters, 10 November 2006; text at www.aip.org/physnews/select) *********** PHYSICS NEWS UPDATE is a digest of physics news items arising from physics meetings, physics journals, newspapers and magazines, and other news sources. It is provided free of charge as a way of broadly disseminating information about physics and physicists. For that reason, you are free to post it, if you like, where others can read it, providing only that you credit AIP. 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