Superluminal Travel Requires Negative Energies

Ken D. Olum
Phys. Rev. Lett. 81, 3567 – Published 26 October 1998
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I investigate the relationship between faster-than-light travel and weak-energy-condition violation, i.e., negative energy densities. In a general spacetime it is difficult to define faster-than-light travel, and I give an example of a metric which appears to allow superluminal travel, but in fact is just flat space. To avoid such difficulties, I propose a definition of superluminal travel which requires that the path to be traveled reach a destination surface at an earlier time than any neighboring path. With this definition (and assuming the generic condition) I prove that superluminal travel requires weak-energy-condition violation.

  • Received 1 May 1998


©1998 American Physical Society

Authors & Affiliations

Ken D. Olum*

  • Institute of Cosmology, Department of Physics and Astronomy, Tufts University, Medford, Massachusetts 02155

  • *Email address:

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Vol. 81, Iss. 17 — 26 October 1998

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