Number 664, December 3, 2003
by Phillip F. Schewe, Ben Stein, and James Riordon
The Top Physics Stories of 2003
The first three on our list concern the sharpening of our understanding
of the big bang era, evidence for new quark groupings, and progress
in manipulating quantum gases. At the largest size scale, new observations
from the Wilkinson Microwave Anisotropy Probe (WMAP), the Sloan Digital
Survey and other telescopes have reduced the uncertainties in the values
of such cosmic parameters as the Hubble constant, the age of the universe,
and the fractions of total energy vested in the form of dark and luminous
matter (PNU #624;
659).
Going to the opposite extreme, at the level of elementary matter, new
data indicate that quarks needn't appear only in clumps of three (baryons)
or two (mesons). Work at SLAC (US) and KEK (Japan) hint that quarks
might also exist in "tetraquark" states (643),
while experiments in Japan, the US, Russia, and elsewhere provide evidence
for a "pentaquark" state (644).
The third top story concerns the creation of the first ever Bose Einstein
condensate (BEC) consisting of paired-fermion-atom molecules. This work
is potentially important because mastering the interactions between
fermion atoms in the BEC state might provide insights into the nature
of superconductivity and superfluids (663).
Other notable physics stories from the past year include the controversy
over the use gravitational lensing of distant radio waves by Jupiter
to measure the speed of gravity (620);
advances in the use of attosecond laser pulses in studying chemical
reactions (625);
the use of microfluidics---essentially the science of fluids on a chip---in
processing bio-particles such as blood cells and DNA molecules (627);
evidence for the focusing of light in left-handed materials, materials
with a negative index of refraction, and vindication of earlier research
in this area (628);
first fusion reactions in Sandia's Z machine (632);
LIGO's first scientific publications report no gravity wave events but
do succeed in establishing new upper limits on various wave production
processes (632);
building a laser based on a single atom at rest (654);
amphoteric refraction, both positive and negative refraction, in a single
material (657);
and new work with photonic crystals, including the effects of shock
waves (634)
and energy shifting (646).
Relativistic Chaos
A new study shows that general relativity, a theory in which observers
in different reference frames measure time differently, is not incompatible
with chaos theory, in which events unfold in absolute time. Chaos is
an ordinary word with lots of meanings. In physics, however, the meaning
is more precise: a system---a weather system, say---is chaotic if a
very slight change in initial conditions sends the system off into a
very different history. How different? The degree to which a system
is chaotic can be encapsulated in a parameter called the Lyapunov exponent:
when it is positive the system is chaotic and to some extent unpredictable;
for a negative value, the system becomes nonchaotic---a small perturbation
will not radically change its history. What has worried physicists for
many years was the fear that a shift in a frame of reference might so
alter the time parameter as to change the Lyapunov exponent from null
or negative to positive or vice versa. In other words, the change of
frame would seem to make a chaotic system nonchaotic or vice versa.
Now, the work of Adilson
Motter of the Max
Planck Institute for Complex Systems in Dresden, Germany lays this
matter to rest. He shows that over a wide range of conditions, a change
of time parameter does not alter the Lyapunov exponent enough to change
chaos in a system. Motter believes that this is good news since the
equations of general relativity are nonlinear, as are those of chaotic
systems, and many common situations described by general relativity,
such as the motion of massive bodies near black holes or a nonuniform
expansion of the universe at the time of the big bang ("mixmaster
universe model," see PNU #158)
are expected to be highly chaotic. (Physical
Review Letters, 5 December 2003)
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