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http://www.sciencedaily.com/releases/2011/05/
110504150655.htm
NASA's Gravity Probe B Confirms Two Einstein Space-Time Theories
ScienceDaily (May 4, 2011) NASA's Gravity Probe B (GP-B) mission has
confirmed two key predictions derived from Albert Einstein's general theory of
relativity, which the spacecraft was designed to test.
The experiment, launched in 2004, used four ultra-precise gyroscopes to measure
the hypothesized geodetic effect, the warping of space and time around a
gravitational body, and frame-dragging, the amount a spinning object pulls
space and time with it as it rotates.
GP-B determined both effects with unprecedented precision by pointing at a
single star, IM Pegasi, while in a polar orbit around Earth. If gravity did not
affect space and time, GP-B's gyroscopes would point in the same direction
forever while in orbit. But in confirmation of Einstein's theories, the
gyroscopes experienced measurable, minute changes in the direction of their
spin, while Earth's gravity pulled at them.
The findings are online in the journal Physical Review Letters.
"Imagine the Earth as if it were immersed in honey. As the planet rotates, the
honey around it would swirl, and it's the same with space and time," said
Francis Everitt, GP-B principal investigator at Stanford University. "GP-B
confirmed two of the most profound predictions of Einstein's universe, having
far-reaching implications across astrophysics research. Likewise, the decades
of technological innovation behind the mission will have a lasting legacy on
Earth and in space."
GP-B is one of the longest running projects in NASA history, with agency
involvement starting in the fall of 1963 with initial funding to develop a
relativity gyroscope experiment. Subsequent decades of development led to
groundbreaking technologies to control environmental disturbances on
spacecraft, such as aerodynamic drag, magnetic fields and thermal variations.
The mission's star tracker and gyroscopes were the most precise ever designed
and produced.
GP-B completed its data collection operations and was decommissioned in
December 2010.
"The mission results will have a long-term impact on the work of theoretical
physicists," said Bill Danchi, senior astrophysicist and program scientist at
NASA Headquarters in Washington. "Every future challenge to Einstein's theories
of general relativity will have to seek more precise measurements than the
remarkable work GP-B accomplished."
Innovations enabled by GP-B have been used in GPS technologies that allow
airplanes to land unaided. Additional GP-B technologies were applied to NASA's
Cosmic Background Explorer mission, which accurately determined the universe's
background radiation. That measurement is the underpinning of the big-bang
theory, and led to the Nobel Prize for NASA physicist John Mather.
The drag-free satellite concept pioneered by GP-B made a number of
Earth-observing satellites possible, including NASA's Gravity Recovery and
Climate Experiment and the European Space Agency's Gravity field and
steady-state Ocean Circulation Explorer. These satellites provide the most
precise measurements of the shape of Earth, critical for precise navigation on
land and sea, and understanding the relationship between ocean circulation and
climate patterns.
GP-B also advanced the frontiers of knowledge and provided a practical training
ground for 100 doctoral students and 15 master's degree candidates at
universities across the United States. More than 350 undergraduates and more
than four dozen high school students also worked on the project with leading
scientists and aerospace engineers from industry and government. One
undergraduate student who worked on GP-B became the first female astronaut in
space, Sally Ride. Another was Eric Cornell who won the Nobel Prize in Physics
in 2001.
"GP-B adds to the knowledge base on relativity in important ways and its
positive impact will be felt in the careers of students whose educations were
enriched by the project," said Ed Weiler, associate administrator for the
Science Mission Directorate at NASA Headquarters.
NASA's Marshall Space Flight Center in Huntsville, Ala., managed the Gravity
Probe-B program for the agency. Stanford University, NASA's prime contractor
for the mission, conceived the experiment and was responsible for the design
and integration of the science instrument, mission operations and data
analysis. Lockheed Martin Corp. of Huntsville designed, integrated and tested
the space vehicle and some of its major payload components.
For more information about Gravity Probe B, visit:
http://www.nasa.gov/mission_pages/gpb/ and http://einstein.stanford.edu/
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NASA (2011, May 4). NASA's Gravity Probe B confirms two Einstein space-time
theories. ScienceDaily. Retrieved May 5, 2011, from
http://www.sciencedaily.com /releases/2011/05/110504150655.htm
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Disclaimer: Views expressed in this article do not necessarily reflect those of
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