Refreshments at 3:45pm, talk begins at 4pm

Abstract:
I will discuss how the acoustic oscillations that propagate in the photon-baryon fluid during the first million years of the Universe provide a robust method for measuring the cosmological distance scale.  The distance that the sound can travel can be computed to high precision and creates a signature in the late-time clustering of matter that serves as a standard ruler.  Galaxy clustering results from the Sloan Digital Sky Survey reveal this feature at a variety of redshifts.  I will review our recent work on the theory and practice of the acoustic oscillation method, describe our latest cosmology results from SDSS-III on the expansion history of the Universe, and introduce the upcoming Dark Energy Spectroscopic Instrument (DESI) project.

Host: Paul Schechter

Image: This is one slice through the map of the large-scale structure of the Universe from the Sloan Digital Sky Survey and its Baryon Oscillation Spectroscopic Survey. Each dot in this picture indicates the position of a galaxy 6 billion years into the past. The image covers about 1/20th of the sky, a slice of the Universe 6 billion light-years wide, 4.5 billion light-years high, and 500 million light-years thick. Color indicates distance from Earth, ranging from yellow on the near side of the slice to purple on the far side. Galaxies are highly clustered, revealing superclusters and voids whose presence is seeded in the first fraction of a second after the Big Bang. This image contains 48,741 galaxies, about 3% of the full survey dataset. Grey patches are small regions without survey data.

Image credit: Daniel Eisenstein and the SDSS-III collaboration