Editing A Brief History of Time (section)

=== Chapter 10: Wormholes and Time Travel ===
Hawking discusses whether [[time travel]] is possible. He shows how physicists have attempted to devise possible methods by humans with advanced technology may be able to travel [[Faster-than-Light|faster than the speed of light]], or travel backwards in time. [[Kurt Gödel]] presented Einstein with a solution to general relativity that allowed for time travel in a rotating universe. [[Einstein–Rosen bridges]] were proposed early in the history of the theory. These [[wormholes]] would appear identical to black holes from the outside, but matter which entered would be relocated to a different location in spacetime, potentially in a distant region of space, or even backwards in time. However, later research demonstrated that such a wormhole would not allow any material to pass through before turning back into a regular black hole. The only way that a wormhole could theoretically remain open, and thus allow faster-than-light travel or time travel, would require the existence of [[exotic matter]] with negative [[energy density]], which violates the [[energy condition]]s of general relativity. As such, almost all physicists agree that faster-than-light travel and travel backwards in time are not possible.