October 9, 2003
Cosmic Soccer Ball? Theory Already Takes Sharp Kicks
n an unusual logjam of contradictory claims, a revolutionary new model of the universe, as a soccer ball, arrives on astronomers' desks this morning at least slightly deflated.
In a paper being published today in the journal Nature, Dr. Jeffrey Weeks, an independent mathematician in Canton, N.Y., and his colleagues suggest, based on analysis of maps of the Big Bang, that space is a kind of 12-sided hall of mirrors, in which the illusion of infinity is created by looking out and seeing multiple copies of the same stars.
If the model is correct, Dr. Weeks said, it would rule out a popular theory of the Big Bang that asserts that our own observable universe is just a bubble among others in a realm of vastly larger extent. "It means we can just about see the whole universe now," Dr. Weeks said.
But other astronomers, including a group led by Dr. David Spergel of Princeton, said a continuing analysis of the same data had probably already ruled out the soccer ball universe. They promised to post their results soon on the physics Web site arXiv.org/list/astro-ph.
"Weeks and friends are making a dramatic claim, perhaps one of the biggest science stories of the century," said Dr. Neil Cornish, a physicist at Montana State University, "but extraordinary claims require extraordinary support."
For now, the two groups, who have been in intense communication the last few days, disagree on whether the soccer ball universe has been refuted. What is amazing about this debate, they all agree, is that it will actually be settled soon, underscoring the power of modern data to resolve issues that were once considered almost metaphysical.
"This is what got Giordano Bruno burned at the stake," said Dr. Max Tegmark, a cosmologist at the University of Pennsylvania. "Is space infinite or not?"
In Nature, Dr. Weeks and his colleagues write: "Since antiquity, humans have wondered whether our universe is finite or infinite. Now, after more than two millennia of speculation, observational data might finally settle this ancient question." The other authors are Dr. Jean-Pierre Luminet of Paris Observatory; Dr. Alain Riazueleo of the French atomic energy center CEA, in Saclay, France; Dr. Roland Lehoucq of the Paris Observatory and CEA; and Dr. Jean-Phillippe Uzan of the University of Paris.
The evidence for and against a finite universe resides in a radio map of the baby universe produced last February by a NASA satellite, the Wilkinson Microwave Anisotropy Probe. It shows that 400,000 years after the Big Bang, the event in which space and time emerged, the universe was laced with faint waves and ripples, which are the origin of modern galaxies and other cosmic structures. In an infinite universe, according to theory, waves of all size should appear in the sky, but in the Wilkinson data there was a cutoff: no waves larger than about 60 degrees across appeared in the sky.
If the universe were a musical instrument, it would be inexplicably missing its low notes, perhaps, some cosmologists have suggested, because it is too small to play them. The universe is finite rather than infinite, they speculate. Like a violin that cannot produce deep cello notes, the universe cannot produce waves larger than itself.
In such a universe, if you went far enough in one direction, you would find yourself back where you started, on the other side of the universe, like a cursor disappearing off the left side of a screen and reappearing on the right.
One simple example of this is a torus, or a bagel shape, which is what you get when you wrap the left and right and top and bottom sides of the screen around so that they meet.
In the Nature paper, Dr. Weeks and his colleagues propose that three-dimensional space has 12 sides, like a soccer ball, or more technically a dodecahedron. This model would fit with the cutoff of large waves observed in the Wilkinson satellite data. Each face is "glued" to its opposite number. (Don't try this at home.) A spaceship crossing one face or panel of the soccer ball would enter the other side of the ball. After traveling 74 billion light-years it would find itself back where it had started.
While the lack of cosmic low notes is suggestive, cosmologists say there is a definitive test of finite universes in the Wilkinson map. When the cosmic radiation intersects the edges of the universe, it would make identical circles, like a balloon squashed in a box, on opposite sides of the sky. In the case of a bagel, there would be two circles in the map, on opposite sides of the sky. In the case of Dr. Weeks's dodecahedron, there would be six pairs of circles, each about 35 degrees in diameter.
"This is a much higher bar to clear," Dr. Cornish said.
Dr. Tegmark said: "What's nice is it's so testable. It's the truth or it's dead. The data is even out there, on the Internet. It's just a question of sifting through it."
But so far the circles have not showed up.
Earlier this year, Dr. Tegmark and his wife and colleague Dr. Angelica Oliveira-Costa, Dr. Mattias Zaldarriago, of Harvard, and Dr. Andrew Hamilton of the University of Colorado, searched the Wilkinson data for oppositely matched circles. The results, they said, ruled out the possibility that the universe was shaped like a bagel, no doubt disappointing New Yorkers who would like to have imagined a cosmic connection with their breakfast.
Dr. Tegmark said that the results also ruled out Dr. Weeks's dodecahedron. "We ought to have seen those circles in our study," he said.
Meanwhile, a more thorough analysis of the data, looking for all possible circles, has been undertaken by Dr. Spergel, who was part of the original Wilkinson team, Dr. Cornish, and Dr. Glenn Starkman of Case Western Reserve University in Cleveland. The study, about two-thirds complete, had already eliminated many simple models of so-called "small universes," including a dodecahedron when the Nature paper hit their desks last week, Dr. Spergel said.
"No soccer ball, no doughnuts, no bagels," he said.
But Dr. Weeks said there were potential gaps in the circle search methods. For one thing, if the dodecahedron were slightly larger, he said, the circles would be smaller and would not show up in Dr. Spergel's search. But until all the papers are posted on the archive or published where everybody can read them, these claims cannot be evaluated.
Dr. Weeks said that astronomers from both teams would join this fall to test the circle search, using simulated data. If the models are false, they could be ruled out as early as November, he said.
Dr. Cornish said that, although it was the scientific community that would ultimately decide, his team was confident of its results. "I don't see any wiggle room," he said.
But because it is such a "truly spectacular claim," he said, they are planning in the next few days to run a special test focused on the particular model. The test could detect very small circles. "We can push it to where there's no chance," Dr. Cornish said.
The prospects for the finite universe, he added, look bleak.
The stakes for cosmology, should the soccer ball or some other variety of small universe prevail, are not small at all. A small universe, everybody agrees, would present severe problems for the prevailing theory of the Big Bang, known as inflation, which posits that the cosmos underwent a burst of hyperexpansion in its first moments.
Moreover, Dr. Weeks said, a small universe would eliminate one popular variant of the theory known as eternal inflation, in which bubble universes give rise to one another endlessly in what some cosmologists call a "multiverse."
"This puts the whole universe in view," he explained. "It wouldn't rule out other universes. There could be others. They would be totally unrelated, without any contact between them."