PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 733  June 15, 2005
by Phillip F. Schewe, Ben Stein
        
LIGHT MAY ARISE FROM TINY RELATIVITY VIOLATIONS, according to a new theory.
Speaking most recently at last month's American Physical Society meeting of
the Division of Atomic, Molecular, and Optical Physics in Nebraska, Alan
Kostelecky of Indiana University (812 855-1485, KOSTELEC{at}INDIANA.EDU)
described how light might exist as a result of breaking an assumption of
relativity theory known as Lorentz symmetry.  In Lorentz symmetry, the laws
of physics stay the same even when you change the orientation of a physical
system (such as a barbell-shaped molecule) or alter its velocity. 
According to special relativity, the speed of light is the same in every
direction, a notion that current experiments verify to a few parts in
10^16.  However, if physicists find variations in the speed of light with
direction, this would provide evidence for broken Lorentz symmetry, which
would radically revise notions of the universe.
Broken Lorentz symmetry would give spacetime a preferred direction.  In its
simplest form, broken Lorentz symmetry could be visualized as a field of
vectors (arrows) existing everywhere in the universe.  In such a picture,
objects might behave slightly differently depending upon their orientation
with respect to the vectors.  In a recent paper, published in Physical
Review D (Bluhm and Kostelecky, Physical Review D, 71, 065008, published 22
March 2005), the authors propose that the veryexistence of light is made
possible through a vector field arising from broken Lorentz symmetry.  In
this picture, light is a shimmering of the vector field analogous to a wave
blowing through a field of grain (see animation at
http://www.physics.indiana.edu/~kostelec/faq.html).  The researchers have
shown that this picture would hold in empty space as well as in the
presence of gravity (curved spacetime) which is often ignored in
conventional theories of light.  This theory is in contrast to the
conventional view of light, which arises in a space without a preferred
direction and as a result of underlying symmetries in particles and force
fields. Kostelecky says that the new theory can be tested by looking for
minute changes in the way light interacts with matter as the earth rotates
(and changes its orientation with respect to the putative vector field). In
addition, Kostelecky says that neutrino oscillations might arise from
interactions between neutrinos and the background vector field, as opposed
to the conventional explanation, which invokes neutrino mass as the
explanation for the oscillations.  Experimentalist Ron Walsworth of
Harvard-Smithsonian comments that the nice thing about Kostelecky's work is
that he proposes detailed experiments to test his theories; and that the
results of such experiments, no matter how they turn out, promise to deepen
our understanding of physics. (For more information, see article by
Kostelecky in the Scientific American, September 2004; as well as Indiana
University Press Release, March 21).

WATCHING RAPID MELTING AT THE ATOMIC SCALE.  At last month's CLEO/QELS
optics meeting in Baltimore, Dwayne Miller of the University of Toronto
(dmiller{at}lphys.chem.utoronto.ca) described how he and his colleagues are
capturing the first atomic-level view of the melting process, one of the
simplest transformations of matter, on the timescale of femtoseconds, or
quadrillionths of a second.  Rapidly heating metals and watching how their
atoms rearrange themselves can provide insights into extreme states of
matter, e.g., of matter that approaches fusion temperatures or under the
extreme conditions in the interiors of planets.  In the University of
Toronto setup, an intense, ultrafast pulse of laser light melts the target
material.  This pulse is followed by a beam of electrons that diffracts off
the atoms in the sample to provide information on the positions of the
atoms at any given instant.  The experiments are revising scientists' basic
knowledge of what happens during rapid melting.  Raising the temperature of
solid aluminum to approximately 1000 degrees in less than 1 picosecond, the
researchers found that the aluminum atoms, initially arranged in an
face-centered cubic lattice (much like oranges in a grocery display), are
vigorously shaken by the heating caused by the laser beam, with the atoms
at the corners shaken off first, followed by those closer inside (see
Siwick et al, Science, 21 November 2003). Recently, the researchers have
begun to investigate the melting and the equation of state of pure carbon,
the element with the highest melting point; the results might help answer a
question in planetary science, namely whether liquid carbon exists inside
Neptune and Uranus.  (Presentation CTuAA1, "Femtosecond Electron
Diffraction: An Atomic-Level View of Condensed Phase Dynamics";
http://lphys.chem.utoronto.ca/)

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