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How did astronomers discover that the expansion of the universe was accelerating?

Steve Ciucci, Madison, Wisconsin
RELATED TOPICS: EXPANSION RATE
Astronomers used distant supernovae to determine that the expension of our universe was speeding up.
In the early 1990s, two teams of astronomers set out to measure the universe’s expansion history to predict its future. If the universal expansion was slowing down a lot, it would someday stop and reverse itself, ending in a hot Big Crunch. If, instead, the deceleration was small, the universe would expand forever (albeit at a decelerating rate).

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