‘‘Sonoluminescence’’ from the early Universe

Abstract

The tens of microkelvin variations in the temperature of the cosmic microwave background (CMB) across the sky are snapshots of the Universe at 400<th>000 years of age and a Rosetta Stone for unraveling its earliest history. During the first 400<th>000 years the lumpy distribution of dark matter excited gravity-driven acoustic oscillations of the ordinary matter. Pressure provided by the photons in the CMB, which were tightly coupled to the ordinary matter, acted as the restoring force for these compressional modes. During an oscillation, photons were alternately compressed and heated, and rarefied and cooled. Ordinary matter and photons decoupled at 400<th>000 years, and CMB photons streamed freely to us, creating a snapshot of modes caught at maximum compression (hot spots) and maximum rarefaction (cold spots) at this early time. The pattern of hot and cold spots on the CMB sky today is being used to determine the curvature of the Universe, the Hubble constant, the total amount of ordinary matter and of dark matter, and to test theories of the early Universe including inflation.