View Full Version : As World Turns it Drags Time and Space

The Blond Beast
Friday, October 22nd, 2004, 10:28 PM

An international team of NASA and university researchers has found the first direct evidence the Earth is dragging space and time around itself as it rotates.

Image above: The Grace Satellite's Orbit - This image shows the orbit track of the twin GRACE satellites. In one month its track will densely cover the entire globe. The shaded part of the image is night time. The un-shaded is daytime. The names on the image are ground stations from where scientists talk to the satellite. Credit: Univ. of Texas, GRACE Science Data System

The researchers believe they have measured the effect, first predicted in 1918 by using Einstein's theory of general relativity, by precisely observing shifts in the orbits of two Earth-orbiting laser-ranging satellites. The researchers observed the orbits of the Laser Geodynamics Satellite I (LAGEOS I), a NASA spacecraft, and LAGEOS II, a joint NASA/Italian Space Agency (ASI) spacecraft.

The research, reported in the journal Nature, is the first accurate measurement of a bizarre effect that predicts a rotating mass will drag space around it. The Lense-Thirring Effect is also known as frame dragging.

The team was led by Dr. Ignazio Ciufolini of the University of Lecce, Italy, and Dr. Erricos C. Pavlis of the Joint Center for Earth System Technology, a research collaboration between NASA's Goddard Space Flight Center, Greenbelt, Md., and the University of Maryland Baltimore County.

Image above: Gravity's Complex Picture and Lageos Satelllite - The relief indicates the deviation of the true gravitational field from that of a perfect spheroid with uniform mass distribution. Red is higher deviation, blue is lower deviation. INSET: The LAGEOS satellite provided the data to test the Einstein theory. The GRACE mission provided the underlying gravitational data. Click on image to enlarge. Credit: Artwork by F. Ricci (Univ. of Roma, "La Sapienza") and I. Ciufolini (Univ. of Lecce), Earth model courtesy of GFZ-Potsdam, Germany

"General relativity predicts massive rotating objects should drag space-time around themselves as they rotate," Pavlis said. "Frame dragging is like what happens if a bowling ball spins in a thick fluid such as molasses. As the ball spins, it pulls the molasses around itself. Anything stuck in the molasses will also move around the ball. Similarly, as the Earth rotates, it pulls space-time in its vicinity around itself. This will shift the orbits of satellites near Earth." The study is a follow-up to earlier work in 1998 where the authors' team reported the first direct detection of the effect.

The previous measurement was much less accurate than the current work, due to inaccuracies in the gravitational model available at the time. Data from NASA's GRACE mission allowed for a vast improvement in the accuracy of new models, which made this new result possible.

"We found the plane of the orbits of LAGEOS I and II were shifted about six feet (two meters) per year in the direction of the Earth's rotation," Pavlis said. "Our measurement agrees 99 percent with what is predicted by general relativity, which is within our margin of error of plus or minus five percent. Even if the gravitational model errors are off by two or three times the officially quoted values, our measurement is still accurate to 10 percent or better." Future measurements by Gravity Probe B, a NASA spacecraft launched in 2004, should reduce this error margin to less than one percent. This promises to tell researchers much more about the physics involved.

Image above: ILRS Network Map - This is the map of international laser ranging network stations that collected the LAGEOS satellite data, which were used for this experiment. Credit: International Laser Ranging Service, Central Bureau/NASA

Ciufolini's team, using the LAGEOS satellites, previously observed the Lense-Thirring effect. It has recently been observed around distant celestial objects with intense gravitational fields, such as black holes and neutron stars. The new research around Earth is the first direct, precise measurement of this phenomenon at the five to 10 percent level. The team analyzed an 11-year period of laser ranging data from the LAGEOS satellites from 1993 to 2003, using a method devised by Ciufolini a decade ago.

The measurements required the use of an extremely accurate model of the Earth's gravitational field, called EIGEN-GRACE02S, which became available only recently, based on an analysis of GRACE data. The model was developed at the GeoForschungs Zentrum Potsdam, Germany, by a group who are co-principal investigators of the GRACE mission along with the Center for Space Research of the University of Texas at Austin.

LAGEOS II, launched in 1992, and its predecessor, LAGEOS I, launched in 1976, are passive satellites dedicated exclusively to laser ranging. The process entails sending laser pulses to the satellite from ranging stations on Earth and then recording the round-trip travel time. Given the known value for the speed of light, this measurement enables scientists to precisely determine the distances between laser ranging stations on Earth and the satellite.

NASA and Stanford University, Palo Alto, Calif. developed Gravity Probe B. It will precisely check tiny changes in the direction of spin of four gyroscopes contained in an Earth satellite orbiting 400-miles directly over the poles. The experiment will test two theories relating to Einstein's Theory of General Relativity, including the Lense-Thirring Effect. These effects, though small for Earth, have far-reaching implications for the nature of matter and the structure of the universe.

Monday, October 25th, 2004, 10:47 AM
You can't drag infinity.

Gorm the Old
Sunday, November 7th, 2004, 03:53 PM
This sounds suspiciously like the "aether-drift" hypothesis, supposedly disproven by the Michelson-Moreley experiment of the late 19th century except that they're now calling the "luminiferous aether" space and time. This is a good example of the "reification" of concepts. Neither space nor time (nor that illegitimate hybrid, "space-time") is a thing. Both are concepts expressing relationships, space expressing relationships between bodies of matter and time between events. The rotation of the Earth can no more "drag" these intellectual abstractions than it can "drag" independence or beauty.