Over the half-century since its discovery, the Cosmic Microwave Background (CMB) has been a cosmological goldmine, yielding measurements of the properties of the early universe that are unrivaled in both precision and accuracy.
The Simons Observatory is a new cosmic microwave background experiment being built on Cerro Toco in Chile, due to begin observations in the early 2020s. I will describe the scientific goals of the experiment, motivate its design, and forecast its performance. The Simons Observatory will measure the temperature and polarization anisotropy of the cosmic microwave background with arcminute resolution over approximately 40% of the sky in six frequency bands: 27, 39, 93, 145, 225 and 280 GHz. In its initial phase, three small-aperture (0.5-meter diameter) telescopes and one large-aperture (6-meter diameter) telescope will be fielded. These instruments will host a total of 60,000 cryogenic bolometer detectors. I will discuss some of the key science goals of the Simons Observatory, including the characterization of primordial fluctuations, determination of the number of relativistic species, and measuring the mass of neutrinos. I will also discuss other tests of fundamental physics — some of which may be best measured using Cosmic Microwave Background observations such as the ones we are embarking upon.