The experiment is the Baryon Oscillation Spectroscopic Survey (BOSS), which is using the 2.5-meter (100-inch) Sloan Digital Sky Survey telescope.
The original Sloan survey compiled the most detailed three-dimensional map to date of a large swath of the universe. It used bundles of digital fibers to observe more than one million galaxies. The data included each galaxy’s location on the sky and its distance from Earth.
A team of astronomers used the observations of how galaxies are distributed through space to search for evidence of baryon acoustic oscillations. Observations of 46,000 luminous red galaxies, which are especially bright and red, across several billion light-years of space revealed a slight excess of galaxies that are 500 million light-years apart. This distance is like the crest in a ripple from a rock thrown into a still pond. As the universe expands, the size of these ripples should increase with it, so measuring the size of the ripples at different times will reveal how the expansion of the universe has changed.