Astrophysicists Monday proposed an alternative theory for explaining the composition of most of the universe, which could have implications for all of cosmology.

"It suggests a new answer to one of the more important problems in cosmology," said Charles Alcock of the Lawrence Livermore National Laboratory in Livermore, Calif. "One of the more important questions you can ask about the universe is, `What is it made of?' That influences all of the subsequent work one has to do on the origin of galaxies."Current models propose that 90 percent of the universe consists of so-called "exotic" or "dark" matter, which is particles that have not been observed or understood.

But the new models suggest that the bulk of the universe is comprised of material that has been seen, said Alcock, who presented his work at a meeting of the American Astronomical Society.

"We can't prove one or the other is correct. But the alternative (models) say it is not necessary to invoke exotic material," said Alcock in a telephone interview before his presentation.

The work is based on experiments aimed at determining what took place within the first 15 minutes of the birth of the universe, particularly the distribution of nuclear particles during the gigantic explosion known as the Big Bang, he said.

Past studies have led astrophysicists to conclude that nine-tenths of the matter in the universe must be material that is invisible and not observed on Earth or at least well understood.

But by studying nuclear reactions, Alcock and other researchers found evidence suggesting that most of the matter in the universe is comprised of material that has been seen and understood, he said.

"It's entirely possible that all the material in the universe is made up of material we've already encountered," said Alcock. "We've theorized it's made up of the same basic building blocks of the Earth, the sun and everything we've seen in the past."