Gravity Test Flawed, U.Missouri-Columbia Physicist Says (Forwarded)

University of Missouri-Columbia

06.01.07

Gravity Test Flawed, MU Physicist Says

Existence of gravitomagnetic field related to Einstein's theory of general
relativity, origin of universe

COLUMBIA, MO -- Albert Einstein's theory of general relativity has
fascinated physicists and generated debate about the origin of the universe
and the structure of objects like black holes and complex stars called
quasars. A major focus has been on confirming the existence of the
gravitomagnetic field, as well as gravitational waves. A physicist at the
University of Missouri-Columbia recently argued in a paper that the
interpretation of the results of Lunar Laser Ranging (LLR), which is being
used to detect the gravitomagnetic field, is incorrect because LLR is not
currently sensitive to gravitomagnetism and not effective in measuring it.

The theory of general relativity includes two different fields: static and
non-static fields. The gravitomagnetic field is a non-static field that is
important for the understanding of general relativity and the universe.

"If the existence of the gravitomagnetic field is confirmed, then our
understanding of general relativity is correct and can be used to explain
things such as quasar jets and accretion disks in black holes," said Sergei
Kopeikin, associate professor of physics in MU's College of Arts and
Science. "General relativity explains the origin of the universe, and that's
important for all humankind, irrespective of religion or creed. We all live
in the same world, and we must understand this place in which we live."

Kopeikin said there are four techniques used to test for the gravitomagnetic
field. The first, called Gravity Probe B, used a gyroscope in orbit around
the earth to measure for the field. It is supported by NASA and took nearly
40 years to develop; scientists recently conducted the experiment and are
now analyzing the results. A second experiment involved satellites called
LAGEOS and detected a gravitomagnetic field with a precision not exceeding
15 percent. A third experiment was developed by Kopeikin and other
scientists in 2001 and used Very Long Baseline Interferometry (VLBI) to test
for the gravitomagnetic field of Jupiter; this experiment detected the field
with approximately 20 percent precision.

LLR is a recent testing technique. It involves shooting a laser beam at
mirrors called retroflectors, which are located on the moon, and then
measuring the roundtrip light travel time of the beam. In a response to a
paper about LLR, Kopeikin argued in a letter published in Physical Review
Letters that the interpretation of LLR results is flawed. He said analyses
of his own and other scientists' research reveal that this approach to the
LLR technique does not measure what it claims.

The LLR technique involves processing data with two sets of mathematical
equations, one related to the motion of the moon around the earth, and the
other related to the propagation of the beam from earth to the moon. These
equations can be written in different ways based on "gauge freedom," the
idea that arbitrary coordinates can be used to describe gravitational
physics. Kopeikin analyzed the gauge freedom of the LLR technique and showed
that the manipulation of the mathematical equations is causing scientists to
derive results that are not apparent in the data itself.

"According to Einstein's theory, only coordinate-independent quantities are
measurable," Kopeikin said. "The effect the LLR scientists claimed as
detectable doesn't exist, as it vanishes in the observer's frame. The
equations add up to zero, having nothing to do with the real data. The
results appear this way because of insufficient analytic control of the
coordinate effects in the sophisticated computer code used for numerical LLR
data processing. We need to focus on the real physical effects of gravity,
not the mathematical effects depending exclusively on the choice of
coordinates."

A reply from the scientists who support LLR also has published in Physical
Review Letters and argues that there are aspects of the technique that cause
them to believe it merits worth.

Related Links

* National Aeronautics & Space Administration
http://www.nasa.gov/
* NASA: Gravity Probe B
http://www.nasa.gov/mission_pages/gpb/
* NASA: LAGEOS 1 & 2
http://msl.jpl.nasa.gov/QuickLooks/lageosQL.html
* Physical Review Letters
http://prl.aps.org/