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Gravity Probe B

Testing Einstein's Universe

Special & General Relativity Questions and Answers

How does a body actually bend space-time?

Einstein developed general relativity, which describes the gravitational field, with the mathematical idea that there was no difference in the mathematics, between the role played by the gravitational field, symbolized by


and the metric tensor defining the geometry of space-time. Without the gravitational field, space-time would not exist. That being the case, whenever we ask how space-time gets to be curved by matter, we are simply asking the equivalent question 'how does the gravitational field change?'. The mathematics provide us with the framework we need to interpret questions such as 'what does it mean for space-time to be curved?' by letting us rephrase the question in terms of our old friend the gravitational field. Presumably, a body produces a gravitational field the same way that other bodies produce the other fundamental forces, however, we have no experimental proof that a quantum description for the gravitational field is a reachable goal anytime soon.

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All answers are provided by Dr. Sten Odenwald (Raytheon STX) for the NASA Astronomy Cafe, part of the NASA Education and Public Outreach program.