Gravity Probe B

surfaced in 1991 summed it up succinctly: "There is an unresolvable philosophical difference in how scientists view this mission."

George Keiser, a senior research associate who is the Stanford project's chief scientist, says, "General relativity is in some ways quite different from other aspects of physics because a large number of people have quite a bit of confidence in general relativity, partly because of Einstein's personality and partly because it is such an elegant theory. "Einstein inspires trust. He was a brilliant physicist. He has such a reputation that any experiment which contradicts his theory immediately raises questions." To anticipate those questions, Keiser says, "what we have been trying to do is make sure we have enough cross-checks and to have a very high degree of confidence in our experimental results."

In an act of sustained genius that forms the raw material of a modern scientific legend, Einstein, between his 25th and his 38th birthdays, basically rebuilt the entire universe in his mind. He called his theory of gravity, published in 1916 when he was 37 years old, "the happiest thought of my life."

Overturning centuries of conventional wisdom about the fundamental laws of nature, Einstein conceived of a universe in which gravity is not a force so much as a distortion in the very fabric of space caused by a massive object - a sinkhole in the celestial quagmire. A planet or star churns that invisible fabric as it rotates, dragging space and time around it like a pinwheel.

It was the product of a thought experiment, he later wrote, in which he brooded on the plight of a man falling from a building.

"If one considers an observer in free fall, for example, from the roof of a house," Einstein wrote. "There exists for him during his fall no gravitational field - at least in his immediate vicinity."

From that deceptively simple starting point, he opened a door into a weird realm of black holes, time warps and superstrings.

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