THE IDEA that the Universe may be shaped like a torus--rather like a bicycle inner tube--has long fascinated cosmologists. But a theorist in Japan is now arguing that the inner tube may also be twisted in a fourth dimension.
His claim is based on studies of the patterns made by quasars in different parts of the sky, which he says look like images of each other reflected in a distorted way, as if in a fairground mirror.
Imagine that the Universe is a flat strip of paper. Now put a single twist into the strip and join its ends together. This makes a continuous surface in which the inside of the loop becomes the outside. An ant could crawl around and arrive back at its starting place after travelling twice round the loop. This is the classic Mobius strip.
Now imagine that the strip is a cylinder joined at both ends to form a circle--a torus, or inner tube. The tricky bit is to imagine twisting the inner tube in a fourth dimension to create a toroidal Universe in which the inner and outer surfaces become continuous, as in a Mobius strip. But it's worth the effort, because according to Boud Roukema, a theorist at the National Observatory of Japan, that may be the shape of the Universe.
The way to tell if the Universe is "multiply connected" like this is to look in different directions on the sky at objects hundreds of millions of light years away. Quasars are about the only things bright enough and distant enough to fit the bill. If you see the same geometrical pattern in different directions (not necessarily in opposite directions, because the Universe may be crumpled as well as toroidal), you will know that it is indeed multiply connected.
Roukema has analysed the patterns made by quasars on different parts of the sky--the quasar equivalent of constellations. He has found two pairs of constellations where the patterns in different directions look like distorted images of each other (Monthly Notices of the Royal Astronomical Society, vol 283, p 1147).
Roukema admits that with such a small sample, the effect could be due to chance. But if he is right, the implication is that our Universe is not only toroidal, but twisted.
Should the idea be taken seriously? Malcolm MacCallum of Queen Mary and Westfield College in London says that the mathematics is sound, and "the general idea is not very surprising"--at least, not to a mathematician. It is worth pursuing the possibility, researchers believe, because if Roukema is correct, cosmologists will be able to see the same quasars by light which has taken different times to reach us around the twisted Universe--in other words, to see them at different stages of their evolution.
John Gribbin
From New Scientist, 4 Jan 97