Quotes of the Day

Back in the late 1970s, the National Enquirer ran this screaming front-page headline: "DID A REAL-LIFE STAR WARS CREATE HUGE HOLE IN SPACE?" There was a grain of truth behind the nonsense, believe it or not. Astronomers had just found a chunk of the universe that seemed weirdly empty — no galaxies, no clouds of gas, no nothing. In the decades since, they've found lots more. The universe, we now know, resembles a cosmic Swiss cheese, with galaxies organized into sheets and filaments surrounding mostly empty spaces. And while it was surprising at first, theorists have explained pretty convincingly how gravity made it all happen: the cosmos started out with some areas of slightly higher density than average, and as the universe expanded, gravity sucked more matter into those areas, leaving surrounding regions comparatively empty.

What they can't explain is a discovery announced a few days ago by Lawrence Rudnick, an astronomer at the University of Minnesota. He and a couple of colleagues have found what they think is another void in space — but at about a billion light-years across (that's 6 billion trillion miles, give or take), it's many times bigger than any void ever seen. It's so big, in fact, that if it's really there, it could cause real problems for all current models of the universe; the 14 or so billion years since the Big Bang isn't long enough for gravity to have cleared out a space this huge.

That's a big "if," however, as Rudnick readily acknowledges. The uncertainty comes from the fact that his discovery is circumstantial. What he and his colleagues actually found was that there's a surprising scarcity of radio galaxies — galaxies that put out unusual amounts of radio energy — in a part of the sky marked by the constellation Eridanus. That seemed odd, since radio galaxies tend to be spread about pretty evenly. Then they took a look at an entirely different set of data: microwaves emitted shortly after the Big Bang, as seen by the WMAP (or, NASA's Wilkinson Microwave Anisotopy Probe) satellite. There was a "cold" spot in the microwaves right at the same place where there weren't enough radio galaxies.

That could hardly be a coincidence, Rudnick thought, and the simplest solution was a great void in space. That would explain why there weren't many radio galaxies in that part of the sky. And microwaves crossing a huge void would lose some of their energy, in a complex process involving the reduced gravity inside. The exciting part is that the void is so huge that current theory simply can't explain it — and astronomers just love this kind of challenge.

But it's probably too soon to break out the supercomputers. In an e-mail, David Spergel, a theorist with the WMAP project and the chair of the astrophysics department at Princeton, explains that the microwave signal from the Big Bang has intrinsic hot and cold spots. It's possible that this particular part of the microwave sky was significantly colder than average to begin with. If so, Rudnick's "void" could actually be a region that's merely less dense than average, not completely empty.

And that means Rudnick's chances of fulfilling a lifetime dream might have to wait. All the publicity he and his colleagues have gotten for finding a HUGE HOLE IN SPACE is very nice. "But my real goal," he says, "is to be on Car Talk."

• Michael D. Lemonick
• Scientists find an enormous empty swath in space. How does it change what we know about the origins of the universe?