Number 733, June 16, 2005
by Phil Schewe and Ben Stein
Light May Arise From Tiny Relativity Violations
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@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; text at www.aip.org/physnews/select),
the authors propose that the very existence 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@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/)r
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