Cosmologists are getting a better handle on the age of the universe, one of the basic parameters of astronomy. Their latest calculation, based on the oldest light that telescopes can detect, is 14.0 billion years with an uncertainty of just 500 million years--the tightest age constraint yet, and slightly older than the going estimate of around 13 billion years.
Researchers arrived at the previous estimate by using the Hubble Space Telescope to measure how fast the universe is expanding and then extrapolating back in time to the big bang. But that approach has complications. It seems, from remote supernova explosions, that a strange repulsive force is making the universe grow more quickly today. That factor, as well as gauging the distances to galaxies, creates an uncertainty of about 10%.
Earlier this year, cosmologists realized that they could derive an independent age estimate by scrutinizing the cosmic microwave background, a primordial glow from the big bang that permeates space. Subtle ripples in this background hint at how the big bang shaped the universe (ScienceNOW, 30 April). The size of the ripples can reveal the universe's age via what cosmologist Lloyd Knox of the University of California, Davis, calls an "accidental and surprising correlation." Basically, the distant ripples appear to shrink as the universe expands, so researchers can infer the age of the cosmos from their angular size on the sky.
Knox and his colleagues are the first to combine data from four leading cosmic microwave background experiments, including the balloon-borne BOOMERANG mission and the Degree Angular Scale Interferometer (DASI) telescope in Antarctica. Their analysis, submitted to Astrophysical Journal Letters, yields a 68% chance that the universe is between 13.5 billion and 14.5 billion years old and a 95% chance that the age is between 13.0 billion and 15.0 billion years. Further studies of the cosmic microwave background from NASA's MAP satellite, launched in June, may narrow that uncertainty to a mere 100 million years, Knox says.
"This is a clever piece of work," says astronomer Adam Riess of the Space Telescope Science Institute in Baltimore, Maryland. "To break the 10% [uncertainty] barrier for our knowledge of cosmological quantities is a real step forward." He notes one caveat: The analysis hinges on the assumption that space is "flat"--an assumption supported by observations, but not yet confirmed. "If we allow the curvature to vary, the age becomes significantly less precise," Riess says.
Related sites
Text of Knox
et al. Paper
Text of Hubble
Space Telescope research on expansion of universe
BOOMERANG home
page
DASI home page
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