By Charles W. Petit
More than 60 years ago, G. H. Hardy, an English mathematician besotted with abstraction, wrote, " `Imaginary' universes are so much more beautiful than this stupidly constructed `real' one." Were Hardy around today, he'd find plenty of company. From astronomers peering out into space to particle physicists inspecting atomic innards, the more scientists study the universe, the more preposterous, random, and, yes, ugly it becomes.

But hold it. How can the universe be thought ugly? This realm of wheeling galaxies whose stars explode gloriously to seed space with the building blocks of life? A cosmos that bore at least one planet on which mortals find joy in sunsets? Mathematically minded scholars admire such things, too. But for generations they have expected to discover a few simple, elegant rules from which the cosmos's workings spring.

Today, that search is going to extreme lengths, as scientists posit hidden realms, such as extra dimensions or parallel subuniverses, that could help make sense of our apparently random cosmos. They're also planning giant experiments that may turn up hints of these shadow universes. "Some wonderful discoveries are out there, and we are building machines to do this very soon," exults Maria Spiropulu, a young experimental physicist at the University of Chicago's Enrico Fermi Institute.

Cosmology desperately needs such a revelation. Once an academic playground where theorists freely speculated about the nature of the universe, the field now swarms with real data. Astronomers and physicists are busy compiling the universe's stats--its age, composition, and the nature and strength of the forces at work in it. But instead of becoming simpler, as scientists had hoped, this new portrait of the universe is an ever more random-seeming hodgepodge of apparently unconnected constants, particles, forces, and masses.

Fading glow. The last straw for noted physicist John Bahcall of the Institute for Advanced Study in Princeton, N.J., came last March, when NASA trucked out what, by any measure, was a genuine triumph. A satellite called the Wilkinson Microwave Anisotropy Probe had plotted, in unprecedented detail, tiny temperature variations in the microwave background radiation that fills the sky. This fading glow of the big bang reveals our universe at about 370,000 years (less than a 10,000th of its current age) and holds clues to its exact age and mix of matter and energy (box, below). The agency had invited Bahcall to comment. He dutifully noted his pride. "Every astronomer will remember when they first heard the results from WMAP," he said. Then he confessed. He had hoped against hope that growing evidence of the nature of our universe would turn out to be wrong. "The WMAP results have convinced me," he said. "We have to learn to understand this unattractive universe because we have no other choice."

Bahcall later explained: "It really is strange and--to our perhaps uneducated eyes--arbitrary, ugly, or accidental. To live in a universe where only 4 percent of matter is ordinary matter I find awkward at best, implausible at the least, but there it is." Even worse, he said, was WMAP's confirmation that most of the substance of the universe consists of a mysterious "dark energy" that is pushing all of space apart. "If I didn't have all of these facts in front of me, and you came up with a universe like that, I'd either ask what you've been smoking or tell you to stop telling fairy tales."

WMAP's data on the universe at large only underscore the puzzles physicists find right down to the smallest scales of matter. One is the "hierarchy" problem of the immense disparity in forces. The gravitational pull of an electron on a proton is less than a trillionth of a trillionth of a trillionth of their electromagnetic attraction. Why these forces are so vastly different is, to scientists, just plain weird. Similarly, physicists have long known that there is no such thing as empty space. Even the vacuum boils with particles and antiparticles appearing and disappearing in a subatomic quantum foam. That foam could generate "vacuum energy"--an antigravity effect very much like that dark energy astronomers have now detected. Trouble is, standard physics suggests that the vacuum energy, if it exists at all, should be incredibly larger than what is observed, by a factor of 1 followed by 55 zeroes.

Then there is the "fine-tuning" problem. The universe appears marvelously constructed to produce stars, planets, and life. Scientists have calculated that if the force binding atomic nuclei were just 0.5 percent different, the processes that forge atoms inside stars would have failed to produce either carbon or oxygen--key ingredients for life. If gravity were only slightly stronger or weaker, stars like our sun could not have formed. Yet physicists see no reason why the constants of nature are set just so.

To some, this is all good news. Perhaps, as many religious people say, God exists and wanted it this way--case closed. For many scientists, who try to avoid supernatural explanations, the accumulation of mysteries merely signals that the time is right for a breakthrough.

One of the newest, most daring hypotheses is that the explanation lies somewhere weird, near yet far: in extra dimensions. As in the land of Narnia in writer C. S. Lewis's novel The Lion, the Witch and the Wardrobe, behind obscure passages in this rambling mansion we call a universe may be hidden wings that make the house beautiful. "There may be a whole new universe of large, higher dimensions beyond the ones we can see and every bit as big and rich," says Joseph Lykken of the University of Chicago and the Fermi National Accelerator Laboratory.

Earlier this year, at a meeting of the American Association for the Advancement of Science, Spiropulu organized a session for Lykken and other, mostly young physicists to discuss such extra dimensions and how to find them. Sean Carroll, also of the University of Chicago, is fond of calling the universe preposterous. He explained the appeal of extra dimensions, saying, "One way to tackle a tough problem is to spread it out."

While it may sound like science fiction, extra dimensionality has a solid pedigree in string theory, born in the past 35 years as a way to simplify fundamental particles like quarks and electrons. Traditional physics regards them as points, with a diameter of zero. Zeros wreak havoc in equations, but if fundamental particles are seen instead as tiny vibrating strings and loops, their math quickly settles down. Among string theory's triumphs is that it unites the theory describing gravity, Einstein's general relativity, with the theory governing nature's other forces, quantum mechanics.

Wrinkle in time. Standard string theory requires at least seven extra dimensions, but, unlike the ones we know, they are "compacted," or wrapped into tiny arcs less than a trillionth the size of a proton. In the past few years, however, theorists have concluded that some extra dimensions could be as infinite as our familiar up, forward, and sideways. Another wrinkle in string theory, called M theory, holds that higher dimensions can form membranes--branes for short. Our universe might occupy one brane, while others, perhaps just a short "distance" away, may be home to different physics.

Confused? Don't feel bad. Even experienced physicists have a hard time visualizing such things. With branes, says Harvard University's Lisa Randall, another panelist at the meeting, "the [apparent] weakness of gravity starts to make perfect sense. It's not weak. It only looks that way to us." She and a colleague, Raman Sundrum of Johns Hopkins University, propose that gravity loses its strength as it leaks out of our familiar universe into the "bulk"--that unseen realm of higher dimensions. Other theorists, like Savas Dimopoulos of Stanford University, suggest that gravity originates in a parallel "braneworld" and seems weak to us because only a portion of its strength leaks onto our brane. Dimopoulos also thinks that dark matter, a mystery ingredient of the universe known only from its gravitational pull, is the shadowy echo of a parallel braneworld, or even a sign of folds in our own braneworld that allow gravity to take shortcuts to distant neighborhoods.

M theory has many other variants and oddball jargon, including flat branes, weak branes, colliding branes, skinny branes and, Spiropulu jokes, "my big fat Greek brane." But best of all, large higher dimensions like branes should be much easier to detect than the ultratiny packets of the original string theory. Experimenters see a good chance that a new, more powerful version of Fermilab's Tevatron particle accelerator or the European Large Hadron Collider, due in a few years, may slam protons, electrons, and other particles together so hard that signals of big extra dimensions will finally turn up. Such hints could take the form of so-called supersymmetric particles, predicted by string theory; "gravitons" that carry the force of gravity; or even tiny black holes that would evaporate instantly but leave a telltale signal.

Nobody pretends yet to know the answer. String theorist James Cline of Canada's McGill University sees rapid progress toward a new kind of physics, whatever it is. "There may be large extra dimensions; there may not be," he says. "These are wonderful times. New things are coming out every day. I think the chances that any one of the ideas around today is true are slim. But when we do find the right answer, it will look, and smell, just right."

In other words, it will be beautiful.