1. From slowdown to speedup.
- Author
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Riess, Adam G. and Turner, Michael S.
- Subjects
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TYPE I supernovae , *CATACLYSMIC variable stars , *GRAVITY , *GALAXY clusters , *DARK energy , *GENERAL relativity (Physics) , *ASTRONOMY - Abstract
Distant supernovae are revealing the crucial time when the expansion of the universe changed from decelerating to accelerating. From the time of Isaac Newton to the late 1990s, the defining feature of gravity was its attractive nature. Gravity keeps us grounded. In 1998, however, researchers discovered the repulsive side of gravity. By carefully observing distant supernovae--stellar explosions that for a brief time shine as brightly as 10 billion suns-astronomers found that they were fainter than expected. But has the cosmic expansion been speeding up throughout the lifetime of the universe, or is it a relatively recent development--that is, occurring within the past five billion years or so? The answer has profound implications. Over the past decade, researchers have carefully calibrated the intrinsic luminosity of type la supernovae, so the distance to one of these explosions can be determined from its apparent brightness. Astronomers can deduce the recession velocity of a supernova by measuring the redshift of the light from the galaxy in which it lies. Although the space telescope remains the only means to probe the early history of cosmic expansion, more than half a dozen ground-based programs are trying to improve the precision of the measurement of recent cosmic speedup enough to reveal the physics of dark energy. INSETS: EXPANDING SPACE;How Can Gravity Be Repulsive?;THE TRANSITION POINT.
- Published
- 2004
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