From: LARRY KLAES (ljk4_at_msn.com)
Date: Mon Dec 13 2004 - 12:30:54 PST
----- Original Message -----
From: physnews_at_aip.org<mailto:physnews_at_aip.org>
To: ljk4_at_MSN.COM<mailto:ljk4_at_MSN.COM>
Sent: Monday, December 13, 2004 11:48 AM
Subject: Physics News Update 712
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 712 December 13, 2004 by Phillip F. Schewe, Ben Stein
IS SPECIAL RELATIVITY WRONG? The centennial of Albert Einstein's
LASER LIGHTNING ROD. Lightning on demand, drawing down a bolt of
***********
AUTO-SUBSCRIPTION OR DELETION: By using the expression
This archive was generated by hypermail 2.1.6
: Mon Dec 13 2004 - 12:42:15 PST
miracle year of 1905 has arrived and so it is pertinent to ask how
one of his most famous theories is doing. Physicists don't
necessarily believe that Einstein's rules about the nature of
spacetime are mistaken, but as part of the continual scientific
effort to extend what is known about the universe physicists search
for subtle hints of a departure from expected behavior. Special
relativity predicts that clocks traveling in various directions and
with various fixed speeds relative to each other will tell time
differently, but in such a way that spacetime has no preferred or
distinguishable direction, a proposition known as Lorentz
invariance. Physicists, always on the lookout for departures from
received opinion, and also motivated by theoretical suggestions that
such effects might be expected, take this as an invitation precisely
to search for such a special direction or to find that the variation
of clock rates does not adhere to Einstein's equations. Such
effects are described by the "Standard-Model Extension" (SME) and
they can come in several forms. One disproof of special relativity
would be the finding that matter and antimatter behaved
differently. Another would be a birefringence violation: observing
that light with different polarizations travels at different
velocities through vacuum. Still another disruption of the
Einsteinian view would occur if the universe were pervaded by an
underlying oriented energy field, one that interacted weakly with
known particles so as to favor one direction over another.
A new experiment puts this latter violation to its most stringent
test yet. As so often happens when searching for extremely subtle
effects, no departure from known physics was found but a new upper
bound could be established. Ronald Walsworth and his
Harvard-Smithsonian colleagues, in conjunction with theorist Alan
Kostelecky at Indiana University, look at how atoms prepared in
special magnetic states (the precision of their light emissions
allow them to serve as "clocks") vary in their timekeeping when
moving at certain velocities (or "boosts") relative to the
hypothetical Lorentz-symmetry-violating fields that may permeate the
universe. In this case the two clocks consist of a sample of
helium-3 atoms and a sample of xenon-129 atoms held in a container
within a fixed magnetic field. The clock rate in each case is the
rate at which the atomic nuclei precess in the magnetic field. The
emissions from one atomic species were fed into a feedback mechanism
for controlling the magnetic field, so in effect the one set of
atoms (or, to be more precise, their nuclear spins) acted as a
reference clock while the other species served as the test clock.
The whole apparatus, and the absolute orientation of the applied
magnetic field in spacetime (and along with it the orientation of
the atoms and their emissions) change as the Earth rotates daily and
as the Earth takes its annual course around the sun. Furthermore,
to achieve the necessary level of precision (based on the light let
loose by the atoms), the Harvard researchers achieved the difficult
experimental feat of having the two atom samples operate in a maser
mode (that is, they performed like a laser) within the same
container. The existence of a Lorentz-violating field, one that
like a magnetic field favors a particular orientation in an
otherwise isotropic spacetime, could cause the two clocks to become
more out of synch as they move relative to the Lorentz-violating
field. The main result of the experiment was to put a stringent new
limit on a coupling of material particles (primarily the neutron) to
such fields. The upshot: no Lorentz "boost" violations are seen at a
level of one part in 10^-27. (Cane et al., Physical Review Letters,
3 December 2004; previous relativity test summarized at
http://www.aip.org/pnu/2003/split/623-2.html
at 617-495-7274, rwalsworth_at_cfa.harvard.edu<mailto:rwalsworth_at_cfa.harvard.edu>; background articles in
Physics Today, July 2004, Scientific American, Sept 04; Harvard
website at
www.cfa-www.harvard.eduWalsworth/Activities/DNGM/DNGM2.html<http://www.cfa-www.harvard.eduwalsworth/Activities/DNGM/DNGM2.html>;
Kosetlecky site,
http://www.physics.indiana.edu/~kostelec/faq.html#30
lightning for performing scientific studies, is usually done by
firing a rocket into an overhead cloud. The rocket spools out a
long wire, providing a conducting path between the charged-up cloud
and the earth below. Soon this might be done using laser pulses. A
team of French and German scientists has performed experiments in
the lab in which a laser beam ionizes air molecules between an
artificial thunderhead (a high voltage electrode) with another
electrode, the equivalent of "earth" (a grounded electrode), several
meters away. The experiment is unique in that it can trigger
megavolt discharges across self-guided plasma filaments in air
generated by laser pulses. (Here are the potent characteristics of
natural lightning: peak power of ten megawatts, peak voltage of 100
MV, peak currents of tens of kilo-amps.) One of the lab results is
the surprising discovery that rain does not much perturb the
triggering or guiding of the discharge process. Next the team will
perform open-air lightning experiments. The aim of this work will
be to obtain the ability to trigger lightning before it occurs
naturally at sensitive sites such as airports or electrical
substations. (Ackermann et al., Applied Physics Letters, 6 December
2004; contact Jerome Kasparian, Universite Lyon,
jkaspari_at_lasim.univ-lyon1.fr<mailto:jkaspari_at_lasim.univ-lyon1.fr>)
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.
Physics News Update appears approximately once a week.
"subscribe physnews" in your e-mail message, you
will have automatically added the address from which your
message was sent to the distribution list for Physics News Update.
If you use the "signoff physnews" expression in your e-mail message,
the address in your message header will be deleted from the
distribution list. Please send your message to:
listserv_at_listserv.aip.org<mailto:listserv_at_listserv.aip.org>
(Leave the "Subject:" line blank.)