Famously, the rich angular power spectrum of the intensity of the cosmic microwave background (CMB) reveals the state of the universe a mere 10¹³ s after the big bang. In its fine-angular scale details, the CMB also encodes details of the CMB’s interactions with the rest of the universe in the subsequent 4x10¹⁷ s. The CMB is slightly polarized by Thomson scattering when there is any local quadrupolar anisotropy in the distribution of the scattering electron population. The CMB polarization at large angular scales may probe the universe as early as 10^-32 s. Inflation is the only proposed primordial source for the as-yet undetected odd-parity polarization patterns known as B-modes. At small angular scales, the polarization provides fresh cosmological information. The Atacama Cosmology Telescope (ACT) is a special-purpose 6m telescope situated at 17,000 ft in the dry Atacama Desert of northern Chile, at a latitude of 23 degrees South. ACT’s millimeter-wave detectors measure both polarization and intensity at very fine angular scales (arcminutes). I will describe ACT and its data in the context of other CMB measurements, their scientific impact, and the potential discovery space.

Argonne Physics Division Colloquium Schedule