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<b>Wormhole 'No Use' For Time Travel</b><br /><br />LINK<br /><br />For budding time travellers, the future (or should that be the past?) is starting to look bleak. <br /><br />Hypothetical tunnels called wormholes once looked like the best bet for constructing a real time machine. <br /><br />These cosmic shortcuts, which link one point in the Universe to another, are favoured by science fiction writers as a means both of explaining time travel and of circumventing the limitations imposed by the speed of light. <br /><br />The concept of wormholes will be familiar to anyone who has watched the TV programmes Farscape, Stargate SG1 and Star Trek: Deep Space Nine. <br /><br />The opening sequence of the BBC's new Doctor Who series shows the Tardis hurtling through a "vortex" that suspiciously resembles a wormhole - although the Doctor's preferred method of travel is not known. <br /><br />But the idea of building these so-called traversable wormholes is looking increasingly shaky, according to two new scientific analyses. <br /><br />Remote connection <br /><br />A common analogy used to visualise these phenomena involves marking two holes at opposite ends of a sheet of paper, to represent distant points in the Universe. One can then bend the paper over so that the two remote points are positioned on top of each other. <br /><br />If it were possible to contort space-time in this way, a person might step through a wormhole and emerge at a remote time or distant location. <br /><br />The person would pass through a region of the wormhole called the throat, which flares out on either side. <br /><br />According to one idea, a wormhole could be kept open by filling its throat with an ingredient called exotic matter. <br /><br />This is strange stuff indeed, and explaining it requires scientists to look beyond the laws of classical physics to the world of quantum mechanics. <br /><br />Exotic matter is repelled, rather