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IF SOPHISTICATED aliens are commuting across the Galaxy using a superfast
transport network, we should be able to spot the terminuses. A multinational
team of physicists has shown that “wormholes”—gateways to distant regions
of space—should stamp a coloured hallmark on light from distant stars as
it travels past them on its way to Earth.

One way extraterrestrials might travel through the Universe would be to use a
hypothetical short cut through the fabric of space-time. Einstein’s theory of
gravity suggests such wormholes could exist, but they would need lots of matter
with negative mass—and therefore repulsive gravity—to keep…