Structure of Universe Supports Accelerating Expansion
(From the May/June 2002 issue of StarDate magazine)
Comparing the structure of the universe today to its structure in the distant past supports the idea that “dark energy” is causing the universe to expand faster, according to an international team of astronomers.
Astronomers have known since the 1920s that the universe is expanding. Until recently, though, they believed that the combined gravity of all the stars, galaxies, and “dark matter” was acting as a brake, slowing the expansion. But in 1998, astronomers studying exploding stars in distant galaxies found evidence that the expansion rate is increasing. Current theory says this acceleration may be caused by a “negative energy” in the vacuum of space.
A team of 27 astronomers headed by George Efstathiou of the University of Cambridge, England, found support for the accelerating expansion in the changing geometry of space.
Team members analyzed the structure in the cosmic microwave background — the “afterglow” of the Big Bang in which the universe was born. This glow was produced when the universe was just 300,000 years old — long before the first stars or galaxies took shape.
They compared this early structure to that revealed in a survey of about 200,000 galaxies conducted with the Anglo-Australian Telescope in Australia. Although the distances to these galaxies vary, they provide a relatively good snapshot of the structure of the universe “today,” about 12 billion to 15 billion years after the Big Bang.
Changes in the geometry of the universe between the two epochs suggest that “dark energy appears to exist and to dominate over more conventional types of matter,” says Efstathiou. In a paper in the February issue of the Monthly Notices of the Royal Astronomical Society, the team reports that the presence of so much dark energy “significantly strengthens the case in favour of an accelerating universe.” — Damond Benningfield
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