archive: SETI FW: [ASTRO] Physics News Update - September 15, 1998

SETI FW: [ASTRO] Physics News Update - September 15, 1998

Larry Klaes ( lklaes@zoomtel.com )
Thu, 17 Sep 1998 19:04:07 -0400

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From: Ron Baalke
Sent: Thursday, September 17, 1998 4:38 PM
To: astro@lists.mindspring.com
Subject: [ASTRO] Physics News Update - September 15, 1998

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 391 September 15, 1998 by Phillip F. Schewe and Ben
Stein

ANOMALOUS ACCELERATION. Data from several spacecraft,
including Pioneer 10 and 11, Galileo, and Ulysses, provide
evidence for an unexplained, weak, long-range acceleration, a new
report shows. Position and velocity information is derived from
radio signals sent from the craft to the Deep Space Network back on
Earth. Any change in velocity over time can be ascribed to a
variety of known sources: the sun and planets, the solar wind, the
Milky Way, the Kuiper belt, etc. But even after taking this all into
account, as well as other possibilities such as the presence of dark
matter in the solar system (only a millionth of a solar mass of dark
matter could reside within the orbit of Uranus, it is estimated) or
gas leakage from the vehicles themselves, a small acceleration in the
direction of the Sun---8 x 10^-8 cm/sec^2 for Pioneer 10---remains
unaccounted for. Signs of this anomaly first appeared in the
Pioneer tracking as long ago as 1980; Pioneer 10 was launched in
1972 and is presently 70 astronomical units from Earth. Now six
space scientists, armed with many years of Pioneer data,
supplemented with trajectory information from Galileo and Ulysses,
have carried out the first thorough analysis of the problem and find
the anomaly to be as persistent as ever. (The Voyager spacecraft
are less useful for determining acceleration anomalies.) The
researchers doubt but do not rule out the possibility of a novel
gravitational effect or other kind of new physics. Alternative
explanations include subtle systematic errors in the data analysis or
unexpected aspects of space navigation. Further work on this
problem may extend to the observed motions of planets, comets,
and the proposed Pluto Express craft. (John D. Anderson et al.,
Physical Review Letters, tentatively 5 October 1998; contact John
Anderson at JPL, 818-354-3956, john.d.anderson@jpl.nasa.gov; or
Michael Nieto at Los Alamos, 505-667-6127, mmn@mmn.lanl.gov;
journalists can obtain copies of the article from AIP Public
Information.)

THE MOST ACCURATE MEASUREMENT YET OF THE
PLANCK CONSTANT, the number which describes the
bundle-like nature of matter and energy at the atomic and subatomic
levels, has been carried out by NIST physicists, instantly improving
the accuracy of related fundamental constants (such as electron
mass, proton mass, and Avogadro's number) and paving the way
for a quantum-based definition of mass. Carrying out an
experiment first proposed by Brian Kibble of the National Physical
Laboratory in England (011-44-171-594-7845), a NIST group
(Edwin Williams, 301-975-4206) determined Planck's constant,
otherwise known as h, by using a "moving-coil watt balance," an
apparatus with a kilogram mass connected to a metal coil in a
magnetic field. Injecting a current through the coil created an
upward magnetic force which exactly balanced the downward force
of gravity on the mass. In a second step, the group allowed the coil
to move downward, measuring its velocity and the voltage it
generated. In both steps, the electrical power associated with the
mechanical motions of the system contained quantities proportional
to Planck's constant, allowing the researchers to extract the value
of h while cancelling out factors such as the geometry of the setup.
The team calculated a value for h of 6.62606891 x 10-34
Joule-seconds, with an uncertainty of 89 parts per billion, two times
better than previously published measurements. Their watt-balance
setup ultimately promises to lead to a definition of the kilogram
based on quantum units, rather than one based on the stalwart
physical artifact currently stored in France. (Physical Review
Letters, 21 September 1998; figure at
www.aip.org/physnews/graphics)