Throughout history, astronomers and scientists have pondered the mysteries of the cosmos. Early astronomers, such a Ptolemy, believed that the Earth was the center of the universe with all other celestial bodies revolving around it. Then came Copernicus, another early astronomer, suggesting the earth revolved around the sun.

As the science and technology of astronomy advanced, new realizations about the universe unfolded.

Galileo, Kepler, Brahe, and Newton all were early scientists recreating the model and the understanding of the universe. In 1929, Edwin Hubble, using Einstein's General Theory of Relativity, made the major discovery that the universe is expanding.

Since that time, scientific theories have suggested that the expansion of the universe must have been happening at a decreasing rate.

Researchers postulated that gravitational forces of matter were causing this deceleration until another revolutionary discovery occurred in 1998.

That year, a team of scientists, after 10 years of examining the redshifts of supernovae that were billions of light years away, concluded that universal expansion was not slowing, but doing exactly the opposite: it was speeding up.

The discovery quickly spread through the scientific community, and made front-page news around the world. Scientists were challenged to discover what forces were causing the accelerated expansion.

Michael S. Turner, the Bruce V. and Diana M. Rauner Distinguished Service Professor and chair of the Department of Astronomy and Astrophysics at the University of Chicago is a cosmologist whose research focuses on understanding the forces behind this accelerated expansion.

"Our understanding of the universe is undergoing revolutionary change," Turner said. He explained the "revolutionary" changes as:

-- Expansion of the universe is speeding up, not slowing down.

-- Two-thirds of the universe is composed of dark energy.

-- Most matter in the universe is in some new, exotic form.

Turner will be presenting this year's 2002 Marker Lectures in Astronomy and Astrophysics from Sept. 16 to 18 at Penn State.

Titled "The New Cosmology," the lectures are sponsored by the Eberly College of Science. The three-part lecture series includes: "How the Universe Began," "The Dark Side of the Universe: Dark Matter and Dark Energy" and "Cosmic Inflation: The Dynamite Behind the Big Bang?"

Turner said the first lecture, "How the Universe Began" will appeal to all students, faculty and residents, while the latter two will have more of an appeal to people with backgrounds in astronomy and astrophysics.

"Dark energy is an unclear concept that is used to explain the acceleration of the universe," said Jane Charlton, associate professor of astronomy and astrophysics. The gravity of dark energy pushes instead of pulls, said Turner, fueling the accelerated universal expansion.

"This stuff is really, really weird," he said. "If there was a massive ball of it around, it would repel you." He added that 60 percent of the universe is dark energy. The new and exotic form of matter described by Turner is considered dark as well, Charlton said.

"The dark matter gives off gravitational forces, but not light that we can see," she said, explaining why it's called dark matter.

Scientists only know that it exists because of the influence it exerts on other objects. Dark matter comprises 30 percent of the universe, Turner said. Dark matter is a new form of stable matter produced in the big bang, and only 4 percent is made of particles like protons and neutrons. "Dark matter is what holds our galaxies together," Turner said.

With the explosive growth in technology and deeper understandings of math and science, Turner said many other questions also are being answered.

"We now know the age of the universe is 14 billion years old, give or take a billion years," he said. "We also know the shape of the universe is flat, not curved as once theorized." Even with all this new information recreating a model of the cosmos, Turner said there are many mysterious questions yet to be answered.

"What's so exciting about all of this ongoing research is that it illuminates how far we have come, and, yet how much is still waiting to be discovered about the intricacies of the universe," Ken Cavorsi (senior-science) said.

A former astrophysics major, Cavorsi said the subject still fascinates him. "We still don't know what happened before the Big Bang," he said.

"Or what actually went 'bang'."