Physics

An Overview of Einsteins Predictions about Gravity



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While theoretical physicist have come up with new theories to explain the phenomena of gravity, scientists have not given up on Albert Einstein's general theory of relativity, or theory of gravitation.Everybody knows about the Albert Einstein's well established theory of relativity we now call special relativity which leads to E = mc2 (energy equals mass times the speed of light squared), and is a very well established experimentally.Einstein's also established the general theory of relativity to explain the gravitation and unlike special relativity, surprisingly few tests have been made quantitatively of the results of this theory. But that was until NASA launched Gravity Probe B in April 2004.

The data collected by Gravity Probe B during 17 months orbiting around the Earth is putting general theory of relativity to the test.Since October 2005, scientists have conducted painstaking data analysis and validation.

The preliminary results were announced in April 2007 for the geodetic effect are consistent with the prediction of general relativity to an accuracy of ~1.0 percent. This is on par with the only other measurement of this effect that was performed using the Earth-Moon system orbiting the Sun, but seen in a different and much more direct way. Moreover, the indications of frame-dragging measured thus far are also highly encouraging. However, for both measurements, the current level of experimental error must be significantly reduced and the measurements thoroughly cross-checked before being announced as final results.



Gravity Probe B had the the world's most accurate gyroscopes stowed away inside and was put into a polar orbit precisely aligned with a reference star.The gyros, a million times more accurate than the best on Earth, measured how the rotating Earth drags on the fabric of space-time.The probe also measured the frame-dragging to within one per cent. It measured the much larger space-warping effect called the geodetic effect to one part in 10,000, the most precise test yet of any relativistic effect.In the plane of the orbit, the direction of spin of the gyroscope will tilt by a certain predicted amount because space and time are curved. At right angles to the plane of the orbit, just parallel to the direction in which the Earth is rotating, space and time will be pulled around by the Earth - according to Einstein's theory.

To meet these exacting requirements, Gravity Probe B contains four spinning balls of fused quartz, each perfectly spherical to within 40 atomic layers. Each one is coated with a 1.27-micrometre layer of niobium, and cooled to 1.8 degrees above absolute zero to keep the metal film superconducting.
The superconducting layer creates a tiny magnetic field that pinpoints the axis of the spinning sphere. The experiment therefore required a shielding that reduces the strength of external magnetic fields by a factor of a trillion, electric fields to suspend the spinning spheres, and 2441 litres of superfluid helium coolant.

Let us see what final results have to say.

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