Your area.....what's your analysis of this? Thanks for your help ahead of time. X.
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.)
American Institue of Physics bulletin 517 12/21/2000
LIMITS ON THE COSMIC EVOLUTION OF THE FINE STRUCTURE CONSTANT. Denoted by the Greek letter alpha, the fine structure constant sets the absolute strength of the electromagnetic force at work inside atoms and in the cosmos. Besides this, alpha incorporates within itself several of the other important fundamental constants of nature, and is defined as 2 times pi times the charge of the electron squared, divided by the product of the speed of light and Planck's constant. If alpha has changed over the eons, then part of the redshift exhibited by the spectra of distant galaxies would not be attributable exclusively to the expansion of the universe, thus throwing off many astrophysics calculations. Hence it is desirable to troll for different physical constants in past epochs much as one scans core samples from Greenland to gather fossil bits of ancient air trapped in the ice layers A new comparison of the 21-cm-wavelength emission of hydrogen atoms in distant radio galaxies with that of terrestrial hydrogen reduces the systematic uncertainties by an order of magnitude relative to previous studies using this technique and suggests that any non-expansion contribution to redshifts would be in the fifth decimal at best. Equivalently, the measured limit on proportional change in alpha is less 3.5 x 10^-15 per year out to a look-back time of 4.8 billion years. This study was carried out by astronomers at the National Radio Astronomy (Chris Carilli, 505- 835-7000, ccarilli@nrao.edu), Max Planck Institute (Bonn), University of Colorado, Space Telescope Science Institute, Netherlands Foundation for Research in Astronomy, Kapteyn Research Institute (NL), Onsala Space Observatory (Sweden), and Harvard Smithsonian. (Carilli et al., Physical Review Letters, 25 December 2000)
American Institute of Physics bulletin 552 8/20/2001
Is alpha, like pi, a fundamental constant, or does it change over time? Pi, the ratio of a circle's circumference to its diameter (pi can be defined in other ways too) doesn't seem to be changing, but alpha, the symbol for the fine structure constant, might be.
Alpha is a measure of the intrinsic strength of the electromagnetic force and thus determines how strong an atom is bound and what kind of light is absorbed or emitted by the atom when an electron inside the atom moves from one internal quantum state to another.
In 1999 a group of scientists at the University of New South Wales in Australia reported some positive evidence that alpha was not staying the same (See Update 410). The evidence for a changing alpha--at the level of a part in 100,000, according to a new report being issued by the same group--consists of the spacings of pairs of absorption lines of metal atoms in gas clouds in front of quasars at various redshifts. The spacings are proportional to alpha squared. The new observations suggest that alpha is growing bigger.
This, if confirmed by further tests, runs counter to the law which prescribes that elasticized objects lose their holding power with the years. Swimsuits might droop with age, but atoms would get stronger as time goes by. (Webb et al., Physical Review Letters, 27 August.)
CERN: Are fundamental constants evolving?
Making a return appearance on the physics stage is a report of the possible evolution of the fine structure constant, a.
This constant, which governs fine structure in the emission and absorption spectra of atoms, is defined by other fundamental constants: the charge of the electron, the Planck constant and the speed of light. If , a were to vary, then at least one of the other "constants" would have to change as well. If the speed of light were evolving, this would have important implications for recent cosmological observations, such as the apparent need for negative gravitational pressure and a cosmological constant.
The new results are based on the spectroscopy of gas clouds using light from distant quasars and then comparing the spectral lines with those observed in the laboratory today. The results suggest that , a is evolving with time.
The reported fractional change is minute, being -0.72 ¥10-5 over the redshift range from z = 0.5 to 3.5. However, even such a minute change would have tremendous significance. The researchers have not yet identified any systematic effects that could otherwise explain the results.