The "axis of evil" is a name given to the apparent correlation between the plane of the Solar System and aspects of the
cosmic microwave background
In Big Bang cosmology the cosmic microwave background (CMB, CMBR) is electromagnetic radiation that is a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all spac ...
(CMB). It gives 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 as assumed in the concordance model.
Overview
The
cosmic microwave background
In Big Bang cosmology the cosmic microwave background (CMB, CMBR) is electromagnetic radiation that is a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all spac ...
(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
''Planck'' was a space observatory operated by the European Space Agency (ESA) from 2009 to 2013, which mapped the anisotropies of the cosmic microwave background (CMB) at microwave and infrared frequencies, with high sensitivity and small angu ...
that show both expected and unexpected
anisotropies
Anisotropy () is the property of a material which allows it to change or assume different properties in different directions, as opposed to isotropy. It can be defined as a difference, when measured along different axes, in a material's physic ...
in the CMB. The motion of the solar system, and the orientation of the plane of the
ecliptic
The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic agains ...
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
A quadrupole or quadrapole is one of a sequence of configurations of things like electric charge or current, or gravitational mass that can exist in ideal form, but it is usually just part of a multipole expansion of a more complex structure refl ...
and
octupole
A multipole expansion is a mathematical series representing a function that depends on angles—usually the two angles used in the spherical coordinate system (the polar and azimuthal angles) for three-dimensional Euclidean space, \R^3. Similarly ...
axes are only a few degrees apart, and these axes are aligned with the top/bottom divide.
Lawrence Krauss
Lawrence Maxwell Krauss (born May 27, 1954) is an American theoretical physicist and cosmologist who previously taught at Arizona State University, Yale University, and Case Western Reserve University. He founded ASU's Origins Project, now c ...
is quoted as follows in a 2006 Edge.org article:
The new results are either telling us that all of science is wrong and we're the center of the universe, or maybe the data is simply incorrect, or maybe it's telling us there's something weird about the microwave background results and that maybe, maybe there's something wrong with our theories on the larger scales.
Observations
Some anomalies in the background radiation have been reported which are aligned with the plane of our solar system. These are unexplained by the Copernican principle and suggest that the solar system's alignment is special in relation to the background radiation of the universe. 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 those data and the way they have been 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
The Wilkinson Microwave Anisotropy Probe (WMAP), originally known as the Microwave Anisotropy Probe (MAP and Explorer 80), was a NASA spacecraft operating from 2001 to 2010 which measured temperature differences across the sky in the cosmic mic ...
,
Charles L. Bennett
Charles L. Bennett (born November 1956) is an American observational astrophysicist. He is a Bloomberg Distinguished Professor, the Alumni Centennial Professor of Physics and Astronomy and a Gilman Scholar at Johns Hopkins University. He is t ...
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.
As of 2015, 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 2020, Lior Shamir of Kansas State University calculated that spin directions of