Quantum Time Waits For No Cosmos —- John Gribbin

The man Sagan turned to for advice, in the summer of 1985, was Kip Thorne, at CalTech. Thorne was sufficiently intrigued to set two of his PhD students, Michael Morris and Ulvi Yurtsever, the task of working out some details of the physical behaviour of what the relativists know as “wormholes”. At that time, in the mid-1980s, relativists had long been aware that the equations of the general theory provided for the possibility of such hyperspace connections. Indeed, Einstein himself, working at Princeton with Nathan Rosen in the 1930s, had discovered that the equations of relativity — Karl Schwarzschild’s solution to Einstein’s equations — actually represent a black hole as a bridge between two regions of flat spacetime — an “Einstein-Rosen bridge”. A black hole always has two “ends”, a property ignored by everyone except a few mathematicians until the mid-1980s. Before Sagan set the ball rolling again, it had seemed that such hyperspace connections had no physical significance and could never, even in principle, be used as shortcuts to travel from one part of the Universe to another. Morris and Yurtsever found that this widely held belief was wrong. By starting out from the mathematical end of the problem, they constructed a spacetime geometry that matched Sagan’s requirement of a wormhole that could be physically traversed by human beings. Then they investigated the physics, to see if there was any way in which the known laws of physics could conspire to produce the required geometry. To their own surprise, and the delight of Sagan, they found that there is.

http://www.lifesci.sussex.ac.uk/home/John_Gribbin/Time_Travel.html

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