In Big Bang cosmology, the observable universe consists of the galaxies and other matter that we can in principle observe from Earth in the present day, because light (or other signals) from those objects has had time to reach us since the beginning of the cosmological expansion. Because the universe is isotropic, the distance to the edge of the observable universe is roughly the same in every direction—that is, the observable universe is a solid sphere (a ball) centered on the observer, regardless of the shape of the universe as a whole. Every location in the universe has its own observable universe which may or may not overlap with the one centered around the Earth.