Expansion of the universe

 

Accelerating expansion of the universe

1. Observations show that the expansion of the universe is accelerating, such that the velocity at which a distant galaxy recedes from the observer is continuously increasing with time.
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3. The accelerated expansion was discovered during 1998, by two independent projects, the Supernova Cosmology Project and the High-Z Supernova Search Team, which both used distant type Ia supernovae to measure the acceleration.
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5. The idea was that as type Ia supernovae have almost the same intrinsic brightness (a standard candle), and since objects that are further away appear dimmer, we can use the observed brightness of these supernovae to measure the distance to them.
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7.  The distance can then be compared to the supernovae's cosmological redshift, which measures how much the universe has expanded since the supernova occurred.
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9. The unexpected result was that objects in the universe are moving away from one another at an accelerated rate. 
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11. Cosmologists at the time expected that recession velocity would always be decelerating, due to the gravitational attraction of the matter in the universe.
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15. More via Wiki.
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17. CMB = Cosmic Microwave Background here

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