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Finding the door to a parallel universe

New Scientist

If there were a portal linking us to a parallel universe or some other region of space, how would we spot it? One suggestion is that it will give itself away by the curious way it bends light.

The existence of wormholes linking different regions of space was suggested in 1916 by the Austrian physicist Ludwig Flamm as a possible solution to equations of general relativity, which Einstein had published that year. They have since become accepted as a natural consequence of general relativity, which predicts that matter entering one end of a wormhole would instantly emerge somewhere else, so long as the wormhole is somehow propped open.

Though no direct evidence for wormholes has been observed, this could be because they are disguised as black holes. Now Alexander Shatskiy of the Lebedev Physical Institute in Moscow, Russia, is suggesting a possible way to tell the two kinds of object apart. His idea assumes the existence of a bizarre substance called "phantom matter", which has been proposed to explain how wormholes might stay open. Phantom matter has negative energy and negative mass, so it creates a repulsive effect that prevents the wormhole closing.

According to Shatskiy's calculations, the way phantom matter deflects light would give the wormhole a signature that astronomers could look out for. The gravity of an object with a positive mass, such as an ordinary black hole, focuses light rays passing close to it as if it were a giant concave lens - an effect known as gravitational lensing. Phantom matter's negative mass would have the opposite gravitational lensing effect to normal matter, making any light passing through the wormhole from another universe or point in space-time diverge, and emerge from it as a bright ring. Meanwhile, any stars behind it would shine through the middle. Shatskiy suggests that his idea might offer a way for future space-based observatories such as Russia's planned Millimetron Project to look for wormholes at the centre of large galaxies.

Other researchers point out that the idea relies on several untested assumptions. "It is an interesting attempt to actually think of what a real signature for a wormhole would be, but it is more hypothetical than observational," says Lawrence Krauss at Case Western Reserve University in Cleveland, Ohio. "Without any idea of what phantom matter is and its possible interactions with light, it is not clear one can provide a general argument." Critics also point out that even if phantom energy does exist, other objects might create a similar light signature. "The basic mechanism would not distinguish wormholes from negative energy 'stars'," says Don Marolf at the University of California, Santa Barbara.

What's more, today's telescopes would struggle to see the signature in enough detail, says astronomer Daniel Holz at the University of Chicago, though he doesn't reject Shatskiy's idea out of hand. "It's an interesting thing to think about, maybe after a few beers."

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Author: Amarendra Swarup

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THIS ARTICLE APPEARS IN NEW SCIENTIST MAGAZINE ISSUE: 2 FEB 2008. EMBARGOED UNTIL WED, 30 JAN 2008, 13:00 HRS EST US (18:00 HRS GMT)

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