杏吧原创

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 鈥渨ormholes鈥濃�攇ateways to distant regions
of space鈥攕hould 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鈥檚 theory of
gravity suggests such wormholes could exist, but they would need lots of matter
with negative mass鈥攁nd therefore repulsive gravity鈥攖o keep them
open.

Nobody knows whether negative mass can exist in such large amounts, but if it
does, one way to detect it would be through an effect called 鈥済ravitational
lensing鈥�. Unlike normal matter, whose gravity makes light bend towards it,
negative mass would make light bend away. Several years ago, John Cramer of the
University of Washington in Seattle showed that wormholes would deflect light
from stars behind them to form a bright curve called a 鈥渃austic鈥�.

In practice, however, it would be tricky to spot unambiguous signs of these
caustics. But now a team led by Diego Torres of Princeton University in New
Jersey has found another lensing effect that鈥檚 much more distinctive.

Torres and his colleagues have worked out that when light from a distant
source passes a wormhole, the different colours in the light should be magnified
in a peculiar way, making the coloured pattern we see on Earth very different
from an image lensed by normal matter. 鈥淚t鈥檚 a way of searching for a
negative-mass object,鈥� says Torres. He thinks it might be possible to see this
effect in existing databases of images or in future targeted searches.

鈥淚t鈥檚 a very nice result and a valuable contribution to the line of
investigation I and my colleagues initiated in 1995,鈥� says Cramer. He adds that
scientists searching for heavy lumps of matter called MACHOs in the outskirts of
our Galaxy are already looking for lensed images in several colour bands. 鈥淪o at
least part of what is being recommended is already in place,鈥� he says.

鈥淚f such mass was found, it would tell us something very profound about
fundamental physics,鈥� adds Torres. He stresses that the pattern his team has
described is the hallmark of negative mass of any kind, not necessarily of
wormholes. However, if negative mass is found to exist, the case for wormholes
would be much stronger, whether they were built as a transport system by aliens
in a hurry, or formed naturally in the big bang.