I will present galaxy clustering results from the Sloan Digital Sky Survey that reveal the fossil imprint of sound waves that propagated through the cosmic gas in the first million years of the Universe. The scale of this feature can be computed and hence the detection in the galaxy clustering serves as a cosmic yardstick, giving a geometric distance to the galaxies in the survey. I will discuss the implications of this measurement for the composition of the universe, including dark energy and spatial curvature, and the prospects for future redshift surveys to use the acoustic signature to map the expansion history of the universe. This talk is intended for a general audience.