A Universe of Riddles.

Sean Paling clumps down the tunnel in hefty work boots, his path lit only by his miner's lamp. The temperature is a sweaty 37 degrees Celsius; the underground air has a thick, recycled quality to it. This is the bottom of Britain's deepest mine, 1,100 meters from daylight, a six-minute ride down a clanking elevator. "This is not what I signed up for when I became an astroparticle physicist," he says.

Maybe not. But strange and wonderful things are happening beneath the Yorkshire Moors, where scientists are chasing some of the great riddles of the universe. A brisk 10-minute walk from the mineshaft lies the cavernous extension of the Boulby Underground Laboratory for Dark Matter Research, which opened last summer at a cost of [Pound sterling]3.1 million. In brilliantly lit rooms hewn out of the rock, sheltered from the interference of cosmic rays that constantly rain down on the sunlit world aboveground, scientists tend supersensitive experiments. The task at hand: to search for a breed of subatomic particle needed to make sense of how the universe works.

There's been plenty of progress of late. But as things often go in cosmology, answers only seem to lead to new, more disturbing questions. In recent years scientists have figured out how old the universe is (13.7 billion years) and what it's made of (we'll get to that), they've confirmed that it all started with the big bang (though much may have gone on beforehand), and they've sent up the Wilkinson Microwave Anisotropy Probe (WMAP) to map the afterglow.

If that sounds reassuring, consider a paper in last week's issue of Nature. Dr. Jeffrey Weeks, a mathematician in New York, uses these very maps to argue that the universe may be shaped with 12 sides, and that passing through one side would only put you instantaneously on the opposite side, light years away from where you started. This notion of a finite hall-of-mirrors universe has elicited skepticism from some astronomers, but their alternative isn't much better: an infinite stretch of mini-universes, of which ours is only one. Before you get woozy, though, let's get back to basics:

How big is the universe?

It's getting bigger all the time, but the shocking news of recent years is that the pace of expansion is far greater than previously thought. In 1998, astrophysicists discovered that "Type 1a" supernovae--a class of exploding stars--were fainter than they should be given their distance from Earth. From this they concluded that universe's expansion hasn't slowed since the big bang, it's accelerated.

What would make that happen ?