Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A static universe or "Einstein universe" is one in which space is neither expanding nor contracting. Albert Einstein proposed such a model as his preferred cosmology in 1917. He added a positive cosmological constant to his equations of general relativity to counteract the attractive effects of gravity on ordinary matter, which would otherwise cause the universe to either collapse or expand forever. This motivation evaporated after the discovery by Edwin Hubble that the universe is in fact not static, but expanding; in particular, Hubble discovered a relationship between redshift and distance, which forms the basis for the modern expansion paradigm. According to Gamow this led Einstein to declare this cosmological model, and especially the introduction of the cosmological constant, his "biggest blunder".