Perplexing observations beamed back by a NASA spacecraft are fuelling debates about a mystery of biblical proportions – is our Universe infinite? Scientists have announced tantalising hints that the Universe is actually relatively small, with a hall-of-mirrors illusion tricking us into thinking that space stretches on forever.

However, work by a second team …

However, work by a second team seems to contradict this, and scientists are now busy trying to resolve the conundrum. “Whether space is finite is something people have been asking since ancient times, and probably before that,” says mathematician Jeffrey Weeks from Canton, New York. “If we resolved this and confirmed that space is finite, this would be an enormous step forward in our understanding of nature.”

At the centre of the debate are observations by NASA’s Wilkinson Microwave Anisotropy Probe (WMAP), which was launched in 2001. The probe measures temperature ripples in the “cosmic microwave background”, the afterglow radiation from the big bang fireball.

Astronomers are interested in how strong different sizes of ripples are, as this reveals vital information about the early Universe, and might tell us how big the Universe is today. Many astronomers suspect that the Universe is infinite.

In that case, the microwave background ripples should have an unlimited range of sizes. But while WMAP’s observations of small-scale ripples have matched predictions for an infinite Universe almost perfectly, the large-scale measurements have not. On the largest scales, WMAP has shown that the ripples almost disappear (see graphic, top).

Hall of mirrors

It could just be down to chance….

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