 The development of the universe from the Big Bang to its present form depended on two factors: the laws of physics and the initial conditions at the time of the Big Bang. Both factors appear to have been carefully arranged so that the universe would be capable of supporting life. Had certain constants in the physical laws been slightly different, intelligent life would never have been able to evolve. For example, had the forces that bind the nuclei of atoms together been slightly stronger or weaker, only hydrogen would exist. There would be no carbon, oxygen, or other elements available to form complex molecules or organisms. Similarly, had the expansion speed of the Big Bang been slightly different, the universe would have either simply collapsed back in on itself soon after the Big Bang, or else dispersed into diffuse dust. Stars and planets would never have formed (Rees 1999).