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Number 410, January 13, 1999 by Phillip F. Schewe and Ben Stein
IS THE FINE STRUCTURE CONSTANT CHANGING? The inherent strength of the electromagnetic force is characterized by a parameter called the fine structure constant (denoted by the Greek letter alpha), defined as the charge of the electron squared divided by the product of Planck's constant and the speed of light. The size of alpha determines how well atoms hold together and what types of light atoms will emit when heated up. And just as the elastic band keeping a swimsuit snug will gradually relax with time, so it is reasonable to ask whether an atoms' elasticity (or alpha) might also vary with time, an idea broached by Paul Dirac in 1937. A group of scientists at the University of New South Wales in Australia (John Webb, jkw@edwin.phys.unsw.edu.au) test this proposition by sampling ancient light emitted by ancient atoms, and comparing them to modern light from modern atoms. In particular they looked at the relative spacing of doublets of absorption lines in the spectra of several types of atoms in distant gas clouds lying in front of still more distant quasars. The spacings, not easy to tease out from the faint spectra, are proportional to alpha squared. After taking into account Doppler effects owing to the expansion of the universe, the Australian scientists find that there is a consistent change in alpha with increasing redshift (z), especially above a z of one. Owing to the caution needed in claiming a "measurement" of alpha change, the researchers prefer to think of their result as constituting a new upper limit on the fractional alpha change for z>1 of about 2 parts in 10,000. (Webb et al., Physical Review Letters, 1 February 1999.)
HYDROGEN BONDS IN WATER HAVE COVALENT PROPERTIES, new experiments have shown directly for the first time, confirming a controversial prediction of great importance to understanding water and the many other structures such as DNA which contain hydrogen bonds. Within a single water molecule, hydrogen and oxygen are held together by "sigma" bonds, which are strongly covalent, meaning that electrons are shared between atoms. Between groups of water molecules, however, are much weaker "hydrogen bonds." These bonds are principally electrostatic attractions between positively charged hydrogen--which readily gives up its electron in water--and negatively charged oxygen-- which receives these electrons--in a neighboring molecule. In the 1930s, after quantum mechanics had forever changed the world view of physics, famous chemist and Nobel Laureate Linus Pauling proposed that electron clouds associated with hydrogen and sigma bonds would somewhat overlap with one another, affecting each other's properties. However, the extent of this effect has been contentious and experimentally untested--until now. Shining intense synchrotron x rays on a single crystal of ice from several different directions, and plotting the energy spectrum of the scattered x rays, a US-France-Canada team (Eric Isaacs, Lucent Technologies) observed wavelike interference fringes. The presence of these fringes means that the electrons participating in the hydrogen bond are at least in part quantum mechanically shared (covalently) between neighbors just as Pauling had predicted. Since hydrogen bonds play a significant role in determining water's properties, this experiment is likely to shed light on the mysteries of water (such as the fact that water expands upon freezing) which have been so important to the advent and evolution of life on this planet. (Isaacs et al., Physical Review Letters, 18 January 1999; additional information at www.aip.org/physnews/preview/1999/h-bond/h-bond.htm)
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