According to cosmologists — physicists who study the origins of the universe — a mere four percent of all the stuff in the universe consists of conventional matter and energy. Of the remaining stuff in the universe, roughly 26 percent is dark matter — mysterious, invisible matter the gravitational effects of which alter the orbits of galaxies. And an overwhelming 70 percent of all stuff in the universe is the even more elusive dark energy. Accordingto Prof. Robert Kirshner, Harvard, understanding dark energy will allow cosmologists to understand the future of the entire universe.

Kirshner addressed a large crowd of faculty and students in Schwartz Auditorium on Monday, for the second physics colloquium of the semester. He revealed that scientists are now closing in on conclusive evidence that the universe is accelerating at an increasing pace — an idea in defiance of contemporary physics, which ultimately promoted the controversial idea of dark energy.

In the early ’90s, Kirshner worked on the High-Z Team, which examined the 14-billion year history of the universe by studying the light generated by supernovas in distant regions of the universe.

“If you want to look at the history of cosmic expansion,” Kirshner explained, “you want to look at the most distant objects.”

The team examined Type IA supernovas. Stars commonly orbit each other in pairs. When a tiny, dense white-dwarf star orbits a companion of normal size, it sucks matter off the companion until it reaches an unstable critical mass. At this point the star implodes, and a brilliant flash of light 400-billion times more luminous than the Sun occurs.

These intense flashes of light are readily visible through deep-space telescopes and flash at a rather specific brightness. By measuring how bright the flash appears here on earth, scientists can infer distance — a surprisingly difficult measurement for astronomers to make.

“Our ability [to study cosmic expansion] depends on our comprehension of the properties of the Type IA supernovas,” said Kirshner.

The team observed a vast number of supernovas across the visible universe. From this data, the team affirmed Edwin Hubble’ s claim that the universe is expanding and showed that the rate of this expansion is accelerating. The team revealed that the universe is continually growing faster and faster.

The team’s study showed that the movement of the supernovas away from the Earth correspond to the behavior of an expanding universe. However, when the team compared the observed intensity of the supernova light to their anticipated calculations, they noticed that the light emanating from the deeper regions of the universe is less intense than contemporary physics indicate it should be.

As a result, the team introduced a new problem into the astrophysics field, mainly, the question of why the universe’s expansion is accelerating.

The answer emerged as the theory of dark energy. “If you integrate the idea of gravity, the idea of slowing down, with dark energy, the idea of speeding up you can explain the history of cosmic expansion,” Kirshner explained.

Kirshner described a joint-venture between NASA and The Department of Energy to place a dark energy space telescope in orbit.

“My personal hope is that there will be a really good theoretical idea that will convince people to sharpen up this idea,” Kirshner said. “There is quite a bit of theory, but none of it helps us at this moment.”