杏吧原创

OUR Universe may have a twin. Li-Xin Li of Princeton University in New Jersey
has calculated that our Universe and its sibling could be akin to two soap
bubbles connected by a thin tube. 鈥淭o an observer situated far from the
connecting tube, the interior of a bubble would look just like our Universe,鈥�
says Li.

To find out what our Universe may be like, physicists look for mathematical
solutions to Einstein鈥檚 equations of gravity. Li has found an exact solution
that predicts a pair of low-density, or 鈥渙pen鈥� universes. The discovery, he
says, was 鈥渧ery surprising鈥�.

The universes would have been the result of two identical big bangs. Li
stresses, however, that the twins are not really shaped like bubbles. 鈥淏ubbles
have positive curvature and are finite but the space of my universes is actually
negatively curved, like a saddle, and infinite,鈥� he says.

A bridge known as a 鈥渨ormhole鈥� connects the universes, says Li, and could
provide a test of whether or not we live in a twin. Its presence would have an
effect on the cosmic microwave background radiation鈥攖he afterglow of the
big bang. We wouldn鈥檛 see obvious hot or cold spots in the CMB, but there should
be subtle changes in the pattern of temperatures at different length scales.

鈥淚t鈥檚 conceivable that we might actually see stars or galaxies disappearing
down the wormhole into the other universe or, alternatively, stars and galaxies
from the other universe appearing unexpectedly in our own,鈥� says Li. 鈥淚t would
even be possible for a spacecraft to go back and forth between the
耻苍颈惫别谤蝉别蝉.鈥�

鈥淚t鈥檚 certainly a very intriguing idea,鈥� says Max Tegmark of the University
of Pennsylvania in Philadelphia. 鈥淟i鈥檚 solution deserves close
颈苍惫别蝉迟颈驳补迟颈辞苍.鈥�

Einstein鈥檚 equations might also permit lots of universes all connected
together, says Li. Some cosmologists have argued that our Universe is just one
of a large ensemble of universes鈥攁 鈥渕ultiverse鈥濃�攅ach dancing to the
tune of slightly different laws of physics. 鈥淢y universes have the same laws of
physics,鈥� says Li, but he doesn鈥檛 rule out finding universes with different
laws.