Starship Asterisk*

HEAPOW: The Anomalous Universe? (2014 Feb 17)

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 anround 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 principle is a poor one. That would seem to indicate the Universe has a preferred direction. If so, what preferred it?

Chris Peterson wrote:I've never been particularly overwhelmed by this discovery, since I can't think of any reason why "local" can't be extended to the entire observable Universe. Given that what we can see almost certainly represents only a tiny fraction of the entire Universe, why should we necessarily expect absolute uniformity at this scale?

BDanielMayfield wrote:How can you be so certain, or what causes you to believe that the entire Universe is so much larger than the fraction we can observe?

geckzilla wrote:It's counterintuitive the way we always see news about "the earliest galaxies" or "the faint microwave background leftover from the Big Bag" or other things of this nature. Makes it sound like we're looking at the edge. Also, age since the Big Bang? Makes it seem like there is a definite edge even if we can't see quite that far...