p1234 writes "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. 'US expert Dr Lawrence Krauss, from Case Western Reserve University in Cleveland, Ohio, points out that the idea rests on untested assumptions. He told New Scientist magazine: "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. Without any idea of what phantom matter is and its possible interactions with light, it is not clear one can provide a general argument."'"