Why is the temperature of the universe 2.726 Kelvin?
The Cosmic Background Explorer satellite has recently made the most accurate measurement of the temperature of the universe, determining it to be 2.726 +/- 0.01 kelvin. In trying to understand why the temperature has this value, one is led to discover the most fundamental features of the universe-an early, radiation-dominated epoch, enormous entropy per nucleon, synthesis of the light elements around 3 minutes after the bang, and a small excess of matter over antimatter-as well as some of the most pressing issues in cosmology today-the development of structure in the universe and the identification of the nature of the ubiquitous dark matter.
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