Scientists Put Copernican Principle to the Test

University of Oxford astrophysicists suggest that the widely accepted theory regarding the existence of dark energy and its role in the accelerated expansion of the universe is wrong. The alternative explanation they propose puts us in a special place in the universe; at the center of a void with very low matter density, in direct contradiction of the Copernican Principle. Supernovae studies should be able to settle the matter.
 Portrait of Nicolaus Copernicus
Portrait of Nicolaus Copernicus

One of the main tenets of cosmology holds that on large scales the universe is homogeneous and isotropic; i.e. uniform, with no preferred direction. This is a rephrasing of the Copernican Principle which postulates that we are not located in a special place in the universe, and in fact that no place in it is special. Another fundamental assumption is made in regard to the dynamics of the universe, as described by Einstein in his set of equations.

When supernovae data was analyzed in 1998, two teams of scientists each independently reached the conclusion that the universe’s expansion is accelerated. This conclusion was based on the two paradigms previously described. This acceleration was explained with the existence of a gravitationally repulsive substance, dubbed “dark energy.” Though this substance has yet to be detected, it is widely accepted that it is in fact the cause of the acceleration, and has been incorporated into the standard cosmological model.
If one were to reject the notion of dark energy, the two principles would be subject to question. This is precisely what three physicists at the University of Oxford are suggesting. If the Copernican Principle is disregarded and if we are located at the center of a spherical void, the accelerated expansion can be explained without introducing dark energy. If we are in fact located in such a place, we should be able to detect this by observational methods such as supernovae analysis.
The Oxford team performed such analyses. Their results are inconclusive, and while they lean lightly in favor of dark energy, they are far from definite. Additional data is needed, encompassing more supernovae and reaching deeper into space. Several projects that will yield such data are taking place or are being planned currently. They will have to be studied carefully and perhaps will be able to determine if the dark energy model is wrong or if we should stick to it a while longer.
TFOT reported on attempts to detect dark energy and other elusive substances, such as the Dark Energy Survey collaboration’s construction of one of the largest cameras to detect dark energy and NASA’s launch of the Gamma-ray Large Area Space Telescope designed to serve as a new multipurpose imaging space observatory. In other related articles TFOT has covered various supernova detections, among them the Swift Satellite’s real time observation of a supernova, the first ever, and the observation of the brightest supernova to date by NASA’s Chandra X-ray Observatory, as well as several ground-based optical telescopes.
Further information on the new study, published in the September 26th issue of the Physical Review Letters, can be found in the Arxiv website.