An investigation by the LIGO Scientific Collaboration and the Virgo Collaboration has significantly advanced our understanding of the early evolution of the universe. Analysis of data taken over a two-year period (2005-2007) has set the most stringent limits yet on the amount of gravitational waves that could have come from the Big Bang in the gravitational wave frequency band where LIGO can observe. In doing so, the gravitational-wave scientists have put new constraints on the details of how the universe looked in its earliest moments.