Scientists say they have again found
evidence that a spinning body changes the
surrounding geometry of the universe,
confirming Einstein's general theory of
relativity. But this time, the evidence doesn't
come from a distant black hole — instead, it
comes from satellites orbiting Earth itself.
THE NEW FINDINGS, published in Friday's issue of
the journal Science, are based on precise observations using
two laser-ranging satellites known as LAGEOS and
LAGEOS II. The satellites are covered with target
reflectors that bounce laser beams back to observers on
Earth. By timing how long it takes for the laser light to make
the round trip, scientists can measure orbital distances down
to a matter of millimeters.
An Italian-American-Spanish team of astronomers
took advantage of the LAGEOS system as well as new
models of Earth's gravitational field to test the theory of
relativity.
One of the implications of relativity is that the rotation
of a spinning body “drags” the geometry of space and time
in its vicinity. The orbit of an object going around that
spinning body would shift slightly with each revolution, and a
small gyroscope on the orbiting satellite would appear to
wobble.
The bottom line is that there are twists in space and
time in the vicinity of spinning bodies such as planets and
stars.
This phenomenon, known as “frame-dragging” or the
“Lense-Thirring effect,” was confirmed last November by
X-ray observations of five black holes and several spinning
neutron stars. The effects reported in Science are far closer
to home, but far more subtle.
The researchers took a series of measurements of the
LAGEOS satellites' position, noting how the orbit changed
over four years' time. The changes were measured in
thousandths of a degree of arc — in fact, one of the trickiest
aspects of the calculations involved accounting for the slight
gravitational effects of the moon, the sun and planets.
The result was that researchers indeed spotted an
orbital perturbation that was sufficiently close to Einstein's
predictions.
The results represent yet another vote of confidence in
Einstein's theories as a way of explaining how the universe
works. Further experiments, using yet-to-be-launched
satellites such as LAGEOS III and Gravity Probe B, should
provide an even better understanding of the Lense-Thirring
effect and its implications for precise measurements of time
and orbital trajectories.
Authors of the new study include Ignazio Ciufolini and
Federico Chieppa of the University of Rome; Erricos Pavlis
of the University of Maryland-Baltimore County; and
Eduardo Fernandes-Vieira and Juan Perez-Mercader of the
Laboratory of Space Astrophysics and Fundamental
Physics in Madrid, Spain. |
