A Science in Context magazine explains the cosmological principle as a theory that states that the universe appears the same in every direction because the universe is infinite and centerless. The earth appears to be in the center because the universe expands, but any part of the universe would also appear that way. Other cosmological theories arose, such as Einstein's perfect cosmological principle, but they were not in line with the Big Bang theory because they did not include an expanding universe. Through the process of elimination, the ordinary cosmological principle is the best way to explain isotropy (cosmological principle). Joseph Silk, former professor of astronomy at Oxford University, describes the cosmological principle in detail in his book Infinite Cosmos. “One of the motivations behind the cosmological principle is the need to dethrone ourselves as privileged observers from the Earth's privileged point of view.” The cosmological principle requires homogeneity, which means that the universe should appear relatively the same to any observer anywhere in the universe (Seta 8). Ultimately, the cosmological principle is used to explain isotropy and requires