It's like measuring the thickness of asheet of paper held edge-on 100 miles away. Tomeasure this angle reasonably well, GP-B needed a fantastic precision of 0.0005arcseconds. If the gyroscopesweren't so spherical, their spin axes would wobble even without the effects ofrelativity.Īccordingto calculations, the twisted space-time around Earth should cause the axes ofthe gyros to drift merely 0.041 arcseconds over ayear. These pingpong-sized balls of fused quartz and silicon are 1.5 inches across and nevervary from a perfect sphere by more than 40 atomic layers. The fourgyroscopes in GP-B are the most perfect spheres ever made by humans. Inpractice, the experiment is tremendously difficult. But ifspace is twisted, the direction of the gyroscope's axis should drift over time.By noting this change in direction relative to the star, the twists ofspace-time could be measured. Free from external forces,the gyroscope's axis should continue pointing at the star-forever. Put aspinning gyroscope into orbit around the Earth, with the spin axis pointedtoward some distant star as a fixed reference point.
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