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General relativity from A to B Robert Geroch
Publisher: U.Chicago

To be sure, the Gravity Probe B experiment is a fantastic achievement that offers spectacular evidence in support of two distinct predictions of the general theory of relativity. If time travel is possible, then it is possible for you to kill your father before you were born. Gravity Probe B Proves General Relativity Still Valid. In particular, white dwarfs — like Sirius B, illustrated above — condense a Sun's worth of mass into a volume of only the Earth, creating spacetime that's curved 100 times more severely than at our Sun's photosphere. One of the most spectacular and successful ideas of the 20 Century was Einstein's General Relativity, or the idea that matter and energy determines the curvature of spacetime, and the curvature of spacetime in turn determines how gravitation works. If B-theory is true and special and general relativity are true, then time travel is possible. That's definitely true for physicists because the best interpretation of General Relativity supports B-Theory (though I've seen any physicist talk in terms of “A” or “B” Theory of Time). A gravity probe whose origins date to the era before human spaceflight has finally proved general relativity right, according to NASA. Well, they want to make an atom interferometer to measure the effects of general relativity, by starting with ultra-cold rubidium atoms and manipulating them with light pulses. The GP-B satellite was launched in April 2004 and collected a year's worth of data to determine if predictions of Albert Einstein's General Theory of Relativity are correct. [B][U]General Relativity - The theory of the gravitational force[/U][/B] The effect of gravity is indistinguishable from a state of constant acceleration, and disappears entirely in any frame of reference that is in freefall.