Big Bang Under Fire

By MICHAEL D. LEMONICK

The term Big Bang has become part of the standard scientific vocabulary, but it was first coined in the 1940s as a putdown. The idea that the universe actually had a beginning seemed just plain wacky -- especially since there was almost no evidence at the time to support it. Yet by the end of the 1960s, virtually all astrophysicists were convinced that the cosmos was born in a single massive explosion, and doubters were left out on the fringe.

In recent months, however, that fringe has been growing. A spate of articles in both the popular and scientific press point to disturbing discrepancies between recent astronomical findings and the Big Bang theory. A book by a renegade physicist even proclaims confidently that The Big Bang Never Happened.

What's in trouble is not so much the Big Bang itself but modern astronomy's account of what occurred afterward. How did the dense, superheated cloud of particles and radiation created by the explosion evolve into the complex modern universe of stars and galaxies?

According to the conventional explanation, the cosmos began to expand and cool immediately after the moment of the Big Bang. For 300,000 years or so, the expansion continued, but enormous numbers of tightly packed, free-ranging electrons created a dense fog that kept light from shining: the universe was hellishly hot, but utterly dark. Finally, the electrons were incorporated into atoms, and the light broke free in a gigantic flash. Astronomers can still see that ancient light, known as the cosmic background radiation, although it has cooled to about -270 degrees C (-454 degrees F) and is visible only to sensitive radio telescopes.

But new research suggests there is something wrong with this picture. Regions of the universe that had slightly higher density when the light broke free -- the areas that later accreted under gravity to form the galaxies and clusters -- should be detectable as slightly warmer regions of the background radiation. Yet the radiation has been analyzed in detail -- most recently by the Cosmic Background Explorer satellite -- and its temperature is utterly uniform. Meanwhile, powerful telescopes have revealed unexpected agglomerations of galaxies tens of millions of light-years across. How could such giant structures have arisen from the smooth-textured aftermath of the Big Bang?

One popular explanation postulates a major role for a mysterious, invisible substance called dark matter. Astronomers have learned about dark matter through indirect evidence: galaxies spin and orbit one another faster than the laws of physics allow, unless one presumes the presence of invisible matter that provides the extra gravity to hold things together. The extra gravity of dark matter could also have helped the galaxies grow faster out of the smoothness of the early universe. Even this explanation, however, does not sufficiently account for recent observations. "It is clear that there is something profoundly wrong with our theories," says Harvard astrophysicist Margaret Geller.

A few scientists believe it is the Big Bang theory itself that is wrong. Instead of a universe that exploded into being 20 billion years ago and grew by way of gravity's tug, they postulate a cosmos trillions of years old and shaped not by gravity but by electricity and magnetism. Their evidence comes mainly from lab experiments showing that electromagnetic forces can pull hot gases into distinct structures. Most astrophysicists dismiss this idea, but alternative schemes offered by mainstream thinkers are almost as wild. Many groups are exploring the idea that the Big Bang created strange energy formations, largely undetectable in the cosmic background radiation, variously dubbed cosmic strings, global textures or cosmological constants.

Yet the Big Bang theory remains essentially intact because it is based on + three fundamental pieces of evidence, none of which can be accounted for by any competing model. The first is the cosmic background radiation: its evenness and the mix of electromagnetic wavelengths it contains can only have come about, as far as anybody knows, if the universe was once dense, hot and small. The second is the fact that the universe is expanding. Calculating backward, one easily concludes that all the galaxies must have come from a single point. Finally there is the fact that hydrogen makes up 75% of the matter in the universe and helium nearly 25%. These elements can only be forged in a furnace as hot as the Big Bang, and the proportions correspond exactly to what the Big Bang model posits.

None of this means the Big Bang is the ultimate truth. Someone could come along tomorrow with a better explanation for the known facts, and that would delight astronomers. Says Princeton astrophysicist Bohdan Paczynski, a Big Bang supporter: "I'd love to disprove the Big Bang myself. It would make me instantly famous. But the evidence is just not there."