Axis of evil (cosmology)
The "Axis of Evil" is a name given to an anomaly in astronomical observations of the Cosmic Microwave Background (CMB). The anomaly appears to give the plane of the Solar System and hence the location of Earth a greater significance than might be expected by chance – a result which has been claimed to be evidence of a departure from the Copernican principle.
The Cosmic Microwave Background (CMB) radiation signature presents a direct large-scale view of the universe that can be used to identify whether our position or movement has any particular significance. There has been much publicity about analysis of results from the Wilkinson Microwave Anisotropy Probe (WMAP) and Planck mission that show both expected and unexpected anisotropies in the CMB. The motion of the solar system, and the orientation of the plane of the ecliptic are aligned with features of the microwave sky, which on conventional thinking are caused by structure at the edge of the observable universe. Specifically, with respect to the ecliptic plane the "top half" of the CMB is slightly cooler than the "bottom half"; furthermore, the quadrupole and octupole axes are only a few degrees apart, and these axes are aligned with the top/bottom divide.
But when you look at CMB map, you also see that the structure that is observed, is in fact, in a weird way, correlated with the plane of the earth around the sun. Is this Copernicus coming back to haunt us? That's crazy. We're looking out at the whole universe. There's no way there should be a correlation of structure with our motion of the earth around the sun – the plane of the earth around the sun – the ecliptic. That would say we are truly the center of the universe.
Some anomalies in the background radiation have been reported which are aligned with the plane of the Solar System, which contradicts the Copernican principle by suggesting that the Solar System's alignment is special. Land and Magueijo in 2005 dubbed this alignment the "axis of evil" owing to the implications for current models of the cosmos, although several later studies have shown systematic errors in the collection of that data and the way it is processed. Various studies of the CMB anisotropy data either confirm the Copernican principle, model the alignments in a non-homogeneous universe still consistent with the principle, or attempt to explain them as local phenomena. Some of these alternate explanations were discussed by Copi, et al., who claimed that data from the Planck satellite could shed significant light on whether the preferred direction and alignments were spurious. Coincidence is a possible explanation. Chief scientist from WMAP, Charles L. Bennett suggested coincidence and human psychology were involved, "I do think there is a bit of a psychological effect, people want to find unusual things."
Data from the Planck Telescope published in 2013 has since found stronger evidence for the anisotropy. "For a long time, part of the community was hoping that this would go away, but it hasn’t," says Dominik Schwarz of the University of Bielefeld in Germany.
There is no consensus on the nature of this and other observed anomalies and their statistical significance is unclear. For example, a study that includes the Planck mission results shows how masking techniques could introduce errors that when taken into account can render several anomalies, including the Axis of Evil, not statistically significant. A 2016 study compared isotropic and anisotropic cosmological models against WMAP and Planck data and found no evidence for anisotropy.
In June, 2020, the 'axis of evil' observation was confirmed by a study conducted by Lior Shamir, which verified the same result via a different measurement. Shamir commented: "We have two different sky surveys showing the exact same patterns, even when the galaxies are completely different. There is no error that can lead to that. This is the universe that we live in. This is our home."
- Copernican principle – Assumption in Cosmology
- Cosmic microwave background – Electromagnetic radiation as a remnant from an early stage of the universe in Big Bang cosmology
- List of unsolved problems in physics – Wikipedia list article
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