New observations of the cosmic microwave background radiation show that the early universe resounded with harmonious oscillations

Just as musicians can distinguish a world-class violin from an ordinary one by the richness of its overtones, cosmologists can elucidate the shape and composition of the universe by examining the fundamental frequency of the primordial sound waves and the strength of the overtones. The CMB reveals the angular size of the most intense temperature variations—how large these hot and cold spots appear across the sky—which in turn tells us the frequency of the fundamental sound wave. Cos- mologists can precisely estimate the actual size of this wave at the time of recombination because they know how quickly sound propagated in the primordial plasma. Likewise, re- searchers can determine the distance CMB photons have trav- eled before reaching Earth—about 45 billion light-years. (Al- though the photons have traveled for only about 14 billion years, the expansion of the universe has elongated their route.)

Wayne Hu and Martin White whole paper and Cosmic Symphony website.