The big bang has long been accepted by cosmologists as the most accurate theory of the universe's first moment of life: the explosion of a super-dense primeval atom. But the theory has large flaws, leading cosmologists to search for answers by considering what happened in the moments before the bang itself.
Alan H. Guth, the Victor F. Weisskopf Professor of Physics at the Massachusetts Institute of Technology, addressed this problem in the Hans A. Bethe Lecture, "The Inflationary Universe," March 4 in Schwartz Auditorium of Rockefeller Hall.
His theory, said Guth, adds a short prehistory to the standard big-bang model, which only describes the ancient explosion that set the expanding universe in motion. Inflation occurs, said Guth, when a space itself reaches extremely high temperatures, driving gravity's force backwards, making it repel instead of attract. Guth calls this strange space "a repulsive-gravity material." As the universe was born, a fragment of this matter, a billion times smaller than an atom, could have expanded blindingly fast, swelling to nearly the size of our present universe in a fraction of a second.
What happened to this strange, repulsive-gravity material? Guth theorizes that it could have decayed into the primordial soup of elementary particles.
At this point, Guth said, the standard big-bang model could take over and describe the expanding universe as it is viewed today. But the theory has problems, as Guth said he first learned at another Hans A. Bethe lecture, when he was a research associate at Cornell in 1978. The inflationary universe, he noted, is his attempt to produce viable solutions to three of big-bang cosmology's most enigmatic shortcomings.
One is the problem of the large-scale distribution of matter. When astronomers look to the limits of the visible universe they see a surprising amount of homogeneity, a uniform distribution of matter. The big bang, however, describes the universe as cooling too quickly to allow such an equal dispersion of matter, Guth said.
As he pointed out, a few drops of dye in a glass of water will eventually disperse equally throughout the water, unless the water freezes, in which case there will be islands of color through the ice. Because the big-bang theory depicts a universe that cooled too quickly to allow homogeneity, Guth said, there must have been a time before the explosion when the universe was small enough to evenly distribute its contents. This is Guth's period of inflation.
Another problem, he said, is the uneven uniformity of the universe on the small scale, such as within the Milky Way galaxy. Put simply, the sun is a concentration of matter, but for billions of miles out into in empty space there is no matter. The big-bang theory, Guth said, cannot account for this. But the inflationary universe theory can.
After the bang, Guth explained, the universe spread out uniformly in ripples which, as they intersected, combined to form areas of higher and lower ripples. These peaks and valleys increased and decreased the density of matter in certain areas of space. These variations enabled gravity to pull matter together into stars and galaxies, while leaving the areas of low density to become regions of empty space.
The third problem is what Guth called "flatness." This is the term used to describe the classically postulated shape of the universe, which is somewhere between a closed and an open universe. If the universe contains enough mass and hence gravity -- to halt the expansion caused by the big-bang explosion, it is said to be closed. If not, it is open.
Understanding of the flatness of the universe has undergone some dramatic modifications in recent weeks as several astronomers have concluded that the expansion rate of the universe is actually increasing, Guth said. Instead of upsetting the inflationary universe model, he said, the new findings strengthen it.
These theories suggest that the universe is still undergoing a less potent form of inflation as the space between us and distant stars expands, Guth said. This expansion correlates exactly to how he would expect repulsive gravity to act, constantly creating mass.
Guth was a pioneer of the idea of the inflation model in 1981. He has recently published a book, The Inflationary Universe: The Quest for a New Theory of Cosmic Origins.
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