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Tufts University

Project Title

Does General Relativity Permit Exotic Phenomena

Project Summary

Is it possible to create a stable wormhole, or to travel faster than light or backward in time? General relativity indeed in principle allows space-time to be curved into configurations which permit such things, if we can construct the appropriate states of matter and energy whose gravity would produce the desired curvature. These states all require unusual matter with negative energy density, but that by itself does not rule them out, because negative energy densities are known, for example between parallel plates in the Casimir effect. But these exotic phenomena require more than just any kind of negative energy; they require that the total energy density be negative when we add up all contributions over the complete path of a light ray. The goal of this work is to prove that this total can never be negative, or never sufficiently negative to allow for exotic phenomena, and thus that faster-than-light travel and backward time travel are impossible.

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