The cosmological principle is based on the assumption that the universe is isotropic T and homogeneous. In other words, the universe looks the same in all directions regardless of where it is being observed from, allowing astronomers to extrapolate from what is visible. Abiding by the principle, astronomers would say that matter is evenly spread. No structure should be able to exceed 1.2 billion light years in diameter either, as when you take into account the timescales involved in forming large objects through the process of gravitational instability, there simply has not been sufficient time in the 13.8-billionyear history of the universe for anything larger. But as PhD student Alexia Lopez from the Jeremiah Horrocks Institute at the University of Central Lancashire (UCLan) has noted – not once, but twice – such assumptions can be firmly challenged.
In 2021, Lopez and her colleagues were using data from the Sloan Digital Sky Survey, which has been cataloguing distant quasars. The multispectral imaging and spectroscopic redshift survey makes use of a telescope at the Apache Point Observatory in the Sacramento Mountains of New Mexico, and it’s capable of imaging 1.5 square degrees of sky at a time. Using this, it’s been possible to observe more than 600 galaxies and quasars at once. It enabled Lopez to make her first discovery: a giant, near-symmetrical arc of
