Science and Health

Dark energy causes universe to expand: Scientist

(Xinhua)
Updated: 2011-05-20 08:01

CANBERRA - Australian scientist on Thursday said dark energy is real and causing space-time and the universe to expand.

A team of 26 scientists from 14 different institutions, including Dr Chris Blake from Australia's Swinburne University in Melbourne, is the first to have looked at the structure of the universe more than halfway back in time, to a period when this repulsive force, known as dark energy, began to dominate over the pull of gravity.

Dr Blake said the results of their four-year survey provides the first independent confirmation of both the existence of dark energy and its rate of expansion.

A hundred years ago scientists believed the universe was steady and unchanging.

Physicist Albert Einstein invented the cosmological constant to expand the fabric of space-time after his own equations for general relativity would not allow for the cosmos to remain static as expected in a steady state universe.

Soon afterwards, astronomer Edwin Hubble discovered the universe was actually expanding, consistent with Einstein's original general relativity theory.

"It (the study result) shows physicist Albert Einstein was right," Dr Blake told ABC News.

"Dark energy is a smooth cosmological constant throughout the universe, rather than a change in the laws of gravity."

Dark energy is the name astronomers gave in the late 1990s to an unknown cause of the Universe's accelerating expansion.

This mysterious energy, that defies gravity, makes up about 72 percent of the Universe, with the remaining 24 percent constituting dark matter, and four percent making up the planets, stars and galaxies.

To verify the supernovae findings, Dr Blake and colleagues spent four years using a powerful spectrograph at the Australian Astronomical Observatory to collect data on more than 240,000 galaxies going back over seven billion years to when the cosmos was less than half its current age.

"It (the data back in seven billion years) showed the growth of structure in the universe, the development of galaxy clusters and super clusters has slowed down (compared to nowadays)," Dr Blake said.

"This implies the most distant parts of the universe, which are further back in space-time, have ordinary matter and hence gravity is dominating. But today this antigravity dark energy has taken hold."

The researchers then looked at the distances between pairs of galaxies.

The average distance between galaxy pairs is about 500,000,000 light years, Dr Blake said, adding that "the average distance between these galaxy pairs has also been found to have grown because of the expansion of space-time, and that's further confirmation of an antigravity agent."

Dr Blake said although the exact physics required to explain dark energy still remains a mystery, confirming it exists is a significant step in understanding the origin, evolution and fate of the universe.

The paper will be published in the Monthly Notices of the Royal Astronomical Society.