Number 206, December 8, 1994 by Phillip F. Schewe and Ben Stein
PLANETS AROUND BETA PICTORIS? Beta Pictoris is the only star for which
a circumstellar dust disk has been directly imaged. Previously, transitory
absorption features were observed in the star's spectrum. Attributing these
to the fleeting passage of comets is complicated by the puzzling fact that
there are many more red shifts (90% of the sample) than blue shifts among
the features. Performing computer simulations, astronomers have now been
able to explain the asymmetry in the features by invoking the presence
of at least two planets in orbit around Beta Pictoris. (Harold F. Levison
et al., Nature, 1 December 1994.)
AN ELECTRONIC MICRO-REFRIGERATOR , a device that removes hot electrons
from already-cold metal electrodes, has been built by scientists at the
National Institute of Standards and Technology in Boulder, Colorado (contact
John Martinis, 303-497-3597). In their experiment, the NIST researchers
removed hot electrons flowing through a copper electrode. Attached to the
copper electrode is the refrigerator, a "tunnel junction" consisting
of a superconducting aluminum metal separated from the copper electrode
by means of a thin barrier. Only electrons higher than a certain energy
can travel through the barrier. In the NIST setup, electrons approach the
tunnel junction, and the higher-energy ones leave the metal through the
tunnel junction. The remaining electrons circulate through an electrical
circuit and return to the copper electrode through a superconducting lead
contact which allows electrical current to flow without the transmission
of heat from the circuit. In the first demonstrations of this method, Martinis
and colleagues lowered the temperature associated with the electrons from
100 mK to 85 mK. This technique, analogous to blowing the hot steam molecules
from a cup of coffee to make the coffee cooler, has the potential to cool
low-temperature electronic devices further so that they can make more sensitive,
less noise-laden measurements. Such devices could include the instruments
on the balloon-borne experiments that measure the cosmic background radiation.
(M. Nahum et al., Applied Physics Letters, 12 December 1994.)
EINSTEIN'S GENERAL THEORY OF RELATIVITY does not fit well with quantum
mechanics, but it does persist as the prevailing theory of gravity and
has been vindicated in many experimental tests. Nevertheless, scientists
try to build a better theory or at least to find flaws in Einstein's equations.
Two researchers, Huseyin Yilmaz of Tufts University and Carroll Alley of
the University of Maryland (301-405-6098), believe they have discovered
a case in which general relativity provides a nonsensical result, namely
that the gravitational attraction between two infinitely wide (but thin)
parallel plates in close proximity would be zero. Furthermore, they propose
a gravity theory of their own, one which, they claim, is compatible with
quantum mechanics. Other relativity experts, such as Clifford Will of Washington
University (314-935- 6244) and William Unruh of the University of British
Columbia, dispute Yilmaz's assertions and claim that general relativity
is in good health. Yilmaz and Alley hope to use small unexplained discrepancies
in the performance of the Global Positioning System (the satellite-based
navigation network) and new tests involving the travel times of laser beams
over different paths to test their theory. (Science News, 3 December 1994.)
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