New Theory May Burst Some Cosmic Bubbles : Astronomy: Princeton scientists believe they have solved the baffling mystery of some giant structures in the universe. It’s a matter of simple gravity, they say.
In recent years, scientists have been baffled by the discovery of huge bubbles in the universe that seem to be devoid of matter and by giant walls of galaxies that stretch on for hundreds of millions of light-years. No one could determine what mysterious forces would have created such giant structures.
Some theorists have suggested that massive explosions might have swept some areas clean, creating the bubbles and pushing matter together to form great walls of galaxies.
But scientists at Princeton University believe they now have the answer. Aided by a powerful computer, they have concluded that nothing more than gravity was needed to form the great structures that astronomers are now finding throughout the universe.
“There was no violent pumping of energy into the early universe” to create the features, astrophysicist J. Richard Gott said in a telephone interview. He said research he has conducted with his graduate student, Changbom Park, shows that gravity, acting on very slight fluctuations in the distribution of matter a fraction of a second after the Big Bang, would account for the great structures now seen in the universe.
“Gravity works very quietly,” Gott said. “It just takes time.”
The finding could prove anticlimactic for scientists who have searched for an exotic explanation for the huge voids, which have tantalized the world of astronomy ever since they were discovered four years ago. The discovery of the bubbles was hailed literally around the world by the popular press as well as scientific journals because it suggested that something terribly mysterious had happened in the earliest universe, creating giant structures that staggered the imagination.
But if the Princeton team is correct, it was nothing more than the normal functioning of one of the four fundamental forces of nature.
During the lifetime of the universe, simple gravity would have caused small pockets of matter to accumulate other particles, growing into stars and clusters of stars and even great walls of galaxies such as one discovered last year that is more than half a billion light-years long.
By simulating the accretion of matter over the lifetime of the universe, Gott and Park have created computer images that are remarkably similar to observational data from astronomers in the field. Their work is being published today in the British scientific journal of the Royal Astronomical Society.
At stake is the credibility of the basic cosmological models that theorists have used for years to comprehend the universe. Gott’s findings fit nicely with current theories. If he is wrong, theorists will have to come up with a new explanation for why a universe that began as a tightly compacted--and presumably homogeneous--primordial soup would have led to the development of such irregular structures as scientists are now finding.
Other scientists who are using computers to try to simulate the evolution of the universe tend to grant the Princeton research considerable credibility, but not everyone is convinced.
“I retain some healthy skepticism,” said astrophysicist Margaret Geller, who along with John Huchra of the Harvard-Smithsonian Center for Astrophysics in Cambridge discovered the “bubbles” several years ago and the “Great Wall” of galaxies announced last November. Geller said in a telephone interview that she had seen some of Gott’s earlier work and she does not think the images emerging from his computer match the observational data.
Edmund Bertschinger of the Massachusetts Institute of Technology, who has carried out research similar to Gott’s but on a smaller scale, also remains a little skeptical but believes the great mystery may well be much closer to being resolved.
“It (the Princeton work) should be treated as preliminary because nobody else has done a simulation this large,” Bertschinger said. “But it’s interesting work and it suggests that gravity is capable of making more complicated structures than we had thought.”
Gott insisted that his findings also fit nicely with the first results from the Cosmic Background Explorer (COBE), a spacecraft launched in November to study the background radiation left over from the Big Bang. One of the things COBE is looking for is evidence of cataclysmic events like energy-releasing explosions that could have swept particles from the Big Bang into tighter formations, leading eventually to the formation of such things as galaxies.
The first results from COBE, released in mid-January, showed no trace of such events.
And that has puzzled scientists who had expected COBE to find some evidence of extraordinary events in the background radiation left over from the Big Bang.
“I’m completely mystified (by) how the present-day structure has come to exist without having left some trace,” John C. Mather of NASA’s Goddard Space Flight Center said in announcing the first results during the winter meeting of the American Astronomical Society in Arlington, Va. “There should have been some kind of energy release (after the Big Bang). But there isn’t anything there.”
That wasn’t necessary, Gott said this week, because his research shows that gravity alone could have led to the formation of structures like the Great Wall.
“I was not at all surprised by COBE,” he said. “It is just what I would have expected.”
Gott’s research is based on the assumption that even in the earliest universe there would have been some slight fluctuation in the concentration of matter. At least one part in every 200,000 should have been a little different, he said.
“These (fluctuations) led to density fluctuations that can start to grow and they keep growing” because some areas would have slightly higher mass--and thus stronger gravitational pull--than others,” Gott said.
Gott and Park used the Princeton computer to simulate what would have happened if the earliest universe had had even slight fluctuations in density.
The computer was told to simulate the effect of gravity on 4 million particles over a slice of the universe 2 billion light-years across. The data included slight fluctuations in density, and the computer was programmed to follow the evolution of the particles for the equivalent of 13 billion years. It took the computer 14 hours to complete the task.
By the time the simulated universe had reached the theoretical age of today’s universe, the computer was spitting out images that Gott says “look astonishingly like the observations” of Geller and Huchra.
While the Princeton findings are not as exotic as some theories offered by other cosmologists, the end result is “wonderful,” Gott said.
“It means these superclusters (of galaxies) are fossil remnants of the pattern of fluctuations that existed in the early universe,” he said. “It’s our earliest look back at the beginning of the universe.”
