The Goldilocks Enigma: Why Is the Universe Just Right for Life?

by Paul C.W. Davies

Key Points The universe began with a hot big bang 13.7 billion years ago and is still expanding. The expansion is best envisaged as the stretching of space between the galaxies. Space is filled with heat radiation that is a remnant, or afterglow, of the hot early phase of the universe. The cosmic microwave back ground (CMB) radiation has been intensively studied, most notably by the WMAP satellite, because it contains lots of important data about the history and structure of the universe. Fluctuations in the CMB reveal the seeds of the large-scale structure of the universe (clusters of galaxies). The universe has no discernible center or edge. Because light travels at a finite speed, there is a maximum distance, or horizon, in space beyond which we cannot see. Gravitation is described by Einstein’s general theory of relativity in terms of warped space (strictly, warped spacetime). Spacewarps are familiar to astronomers. Even though space is warped locally, by stars and galaxies, overall the geometry of the universe seems to be flat (Euclidean). Einstein’s general theory of relativity then predicts that the universe should have zero total mass: the positive mass-energy of matter is exactly