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findingDulcinea Staff
NASA's Gravity Probe B confirms one of the central predictions of the general relativity theory: gravity bends space and time.
30 Second Summary
Gravity Probe B has provided the first experimental evidence of the geodetic effect, one of two key propositions of Einstein’s general relativity theory.
In the most commonly used analogy for general relativity, space is compared to a rubber mat stretched flat. The surface of the mat bends if a heavy object is placed on it. In a similar way, the Earth bends what Einstein called “space-time.”
The NASA probe contains four ultra-precise gyroscopes to measure that curvature. The orbit of the satellite is actually a very slow fall to Earth. Because that fall is over curved space-time, the axes of the gyroscopes move differently to how they would were the surface of space-time flat. Like a ship going prow-first into a whirlpool, the axes are tipped on the approach to earth.
Over the next eight months, the probe will return data to test the second key prediction of general relativity: frame-dragging. Does the Earth’s spinning drag space-time, making it spin like the whirlpool in the above analogy?
In the most commonly used analogy for general relativity, space is compared to a rubber mat stretched flat. The surface of the mat bends if a heavy object is placed on it. In a similar way, the Earth bends what Einstein called “space-time.”
The NASA probe contains four ultra-precise gyroscopes to measure that curvature. The orbit of the satellite is actually a very slow fall to Earth. Because that fall is over curved space-time, the axes of the gyroscopes move differently to how they would were the surface of space-time flat. Like a ship going prow-first into a whirlpool, the axes are tipped on the approach to earth.
Over the next eight months, the probe will return data to test the second key prediction of general relativity: frame-dragging. Does the Earth’s spinning drag space-time, making it spin like the whirlpool in the above analogy?
Headline
The final results of the experiment will appear in December 2007, when scientists expect to confirm frame-dragging––a phenomenon much harder to detect than the geodetic effect.
Source: Scientific American
Key Players
“Gravity Prove B is the relativity gyroscope experiment developed by NASA and Stanford University to test two unverified predictions of Albert Einstein’s general theory of relativity.” NASA provides elegant animations illustrating the curvature of space-time.
Source: NASA
Albert Einstein was born in Germany on March 14, 1879. He received the Nobel Prize in Physics in 1921. “At the start of his scientific work, Einstein realized the inadequacies of Newtonian mechanics and his special theory of relativity stemmed from an attempt to reconcile the laws of mechanics with the laws of the electromagnetic field.”
Source: Albert Einstein
Related Links
The earth is not round, says Scientific American. Our planet is in fact a “bumpy spheroid.”
Source: Scientific American
Reference Material
The John F. Kennedy Space Center in California launched the satellite on April 20, 2007. The launch and mission is can be followed at the John F. Kennedy Space Center site.
Source: The John F. Kennedy Space Center
The “special theory of relativity” shows that time and length are not absolute, but their values vary; it also produced the world’s most famous equation, E=MC2, describing the equivalence of mass and energy. The “general theory of relativity” demonstrated mathematically the curvature of space and time.
Source: Einstein Online
The short answer to the question of what is the General Theory of Relativity is that “according to Einstein the presence of a gravitational field alters the rules of geometry in space-time. The effect is to make it seem as if space-time is ‘curved’.”
Source: Stanford University
As with much of science, general relativity is counter-intuitive. Time can travel at different speeds for different people; two people can measure the same object with perfect accuracy and produce different results; mass and energy are different expressions of the same force. This section of the NASA Web site tries to shed some light on these difficulties.
Source: NASA
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