LIGO searches for the ripples of space-time called gravitational waves. Albert Einstein first predicted these waves in his 1916 general theory of relativity, but for years their effects were regarded as too small to measure. LIGO, supported by the National Science Foundation, now participates in an international quest to uncover the messages that gravitational waves will bring from highly energetic distant events. These messages may revolutionize our understanding of black holes, neutron stars and the processes that formed the universe. .