Radio astronomy is undergoing a period of rapid advances because of digital techniques that allow an improvement in sensitivity of several orders of magnitude. The universe nearby and the initial conditions of the universe have now been characterized at great precision thanks to modern galaxy surveys and precision measurements of the cosmic microwave background. But the intermediate epoch, sometimes dubbed the “Dark Ages,” remains largely unexplored. However precision measurements using the 21cm line will allow a detailed three-dimensional characterization of this intermediate epoch.

POLARBEAR (PB) was the first experiment deployed as part of this program and delivered in the last couple of years some of the most interesting results in the field. This single-telescope, single-frequency observatory operating with O(1000) high-sensitivity detectors is going to be progressively replaced by a more powerful Simons Array (SA), composed of three telescopes, observing in at least three frequency bands and furnished with roughly O(10,000) detectors.