The accelerating expansion of the Universe is the most surprising recent cosmological discovery, and led to the Nobel Prize in Physics in 2011. Pertaining to this acceleration, scientists have identified these top-level questions: (1) Is this acceleration caused by a breakdown of General Relativity or by a new form of energy? (2) If dark energy is causing the acceleration, is its energy density constant in space and time?
Cosmology and Large-Scale Structure
For the first time, eBOSS will enable high-precision distance measurements at epochs spanning the emergence of Dark Energy in the universe. Critically, the 1<z<2.2 expansion has never been probed using any method at comparable accuracy previously. eBOSS will also provide new tests of General Relativity on cosmological scales through redshift-space distortions, new probes of inflation from limits on non-Gaussianity in the primordial density field, and new constraints on the summed mass of all neutrino species — possibly providing the first cosmological detection of the neutrino mass.
By targeting quasars and galaxies in the redshift window 0.6<z<3.5, eBOSS will produce the largest volume map of the Universe (covering approximately 11 Gpc3 and the strongest cosmological constraints to date from the baryon acoustic oscillation (BAO). BAO yields cosmological distance measurements with low systematic errors, which the SDSS-III program BOSS has currently produced at high precision to z<0.6 and at z~2.3. Using the BOSS spectrographs, eBOSS targets luminous red galaxies between 0.6<z<0.8, emission lines galaxies between 0.6<z<1, quasars between 1<z<2.2, and Lyman-alpha quasars above z>2.2. We plan to obtain, respectively, 0.9%, 1.8%, 2.0% and 1.5% precision distances — greatly expanding the redshift range relative to BOSS, and doubling the accuracy of the BOSS measurements at the highest redshift using a denser set of Lyman-alpha forest quasars.