According to the cosmological principle, there is no special place or direction in the universe when viewed on the cosmic scale. The assumption enabled Copernicus to propose that Earth was not the center of the universe and modern scientists to assume that the laws of physics are the same everywhere. Due to the cosmological principle, scientists also assume that the universe is “homogeneous” – having a uniform structure throughout – and “isotropic” – having uniform properties throughout.
But a few recent studies have found the possible existence of cosmological anisotropy: specifically, that the universe’s expansion is accelerating at a faster rate in one direction than another.
In the most recent study, scientists have analyzed data from 557 Type 1a supernovae and found, in agreement with some previous studies, that the universe’s expansion seems to be accelerating faster in the direction of a small part of the northern galactic hemisphere.
A valuable tool for cosmologists, Type 1a supernovae serve as “standard candles” due to their consistent peak luminosity, allowing researchers to measure their distance with high accuracy. Observations of these supernovae famously revealed in 1998 that the universe is not only expanding, but is doing so at an accelerating rate. And now, some observations of Type 1a supernovae at different locations in the sky hint that the acceleration is not uniform in all directions.