NASA / SCIENCE PHOTO LIBRARY NASA / SCIENCE PHOTO LIBRARY
Parameters of the universe. List of some fundamental cosmic parameters as determined by the Wilkinson Microwave Anisotropy Probe (WMAP) in 2003. The data include the time since the birth of the universe (to), 13.7 billion years; the rate of expansion of the universe (71 kilometres per second per megaparsec) and the temperature of the cosmic microwave background (Tcmb), 2.725 Kelvin. The WMAP data also indicate that around 73% of the universe is made up of "dark energy", an unexplained force that is pushing the universe apart. Another 23% is made up of "dark matter", as yet undetected particles. The visible universe forms just 4% of its structure.
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