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Planck all sky cosmic microwave background map highlighting the spatial anomalies
Credit: ESA and the Planck Collaboration


The Anomalous Universe?

A firm belief underpinning modern cosmology is that the Universe is uniform, and the same in all directions. This "cosmological principle" fails on small scales (the local Universe is much hotter in the direction of the sun than in the opposite direction), but it is believed to hold if you look at big enough sections. Maps of the relic radiation over the entire sky obtained by the Cosmic Background Explorer (COBE), the Wilkinson Microwave Anisotropy Probe (WMAP), and now the Planck spacecraft mostly support this view, and have confirmed the standard ideas of the geometry and makeup of the Universe. Mostly confirmed, that is. There were interesting hints from WMAP that something was not quite right with this picture; that the small fluctuations in the temperature of the Universe, the small fluctuations that give rise to all the structure we see around us, were not uniformly distributed. More precise observations with the Planck satellite confirmed and refined the WMAP results, but also (somewhat astonishingly) confirmed the presence of spatial asymmetries in the cosmic microwave background. Planck found that one of the two hemispheres of the Universe appears to have a significantly stronger signal on average than the other hemisphere. Planck also confirmed the presence of a peculiar 'cold spot' seen by WMAP, a surprisingly large, low-temperature region in the cosmic radiation. The image above shows Planck's all sky map with the hemispheric asymmetry enhanced, and with the "cold spot" encircled. These odd features may have a prosaic explanation; or they could indicate that the fundamental assumption of the cosmological principal is a poor one. That would seem to indicate the Universe has a preferred direction. If so, what preferred it?
Published: February 17, 2014


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Page Author: Dr. Michael F. Corcoran
Last modified Monday, 24-Feb-2014 07:17:56 EST