| The expansion of the Universe appears to be accelerating and the origin of the agent of this acceleration, dark energy, is still unknown. Baryon acoustic oscillations can be used to study dark energy with direct measurements of redshifts of individual galaxies, by observing the 21cm line or by detecting optical emission. This proceeding describes the Hubble Sphere Hydrogen Survey (HSHS), an alternative approach, based on the 21cm brightness which would allow mapping of most of the observable universe while avoiding the effort of creating a redshift catalog of galaxies. |
