Next Steps for Cosmology

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Science  09 May 2014:
Vol. 344, Issue 6184, pp. 586-588
DOI: 10.1126/science.1252724

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Experiments on the ground, balloons, and satellites have revolutionized our knowledge of the Big Bang by measuring the fossil glow from the first instants of the universe, the cosmic microwave background (CMB) radiation. Infinitesimal fluctuations in the photon temperature have been found, revealing the seeds of all large-scale structures, from galaxies to clusters of galaxies and superclusters. The detected wiggles in the distribution of the temperature fluctuations measure the gravitational coupling between dark matter, baryons, and radiation as the universe emerged from its opaque fireball phase. These measurements, pioneered by the Cosmic Background Explorer (COBE) (1) and then greatly refined by its successors, the Wilkinson Microwave Anisotropy Probe (WMAP) (2) and Planck (3) satellites, have allowed precise determinations of the key parameters of our universe—age, dark matter, dark energy content, and even the number of different types of neutrinos, as well as the strength and distribution of the primordial density fluctuations. Less than two decades ago, it was debated whether the major constituent of the universe, dark energy, even existed. Now its contribution is measured to an accuracy of a few percent.