Welcome to the 2021 Global 21-cm Workshop hosted by SSERVI-NESS.

Global 21-cm experiments have the potential to greatly expand our understanding of the reionization epoch and open new observations of the Dark Ages and the Cosmic Dawn.  Ongoing instrument development for ground-based and lunar-based missions is strengthening the capabilities of low-frequency radio receivers, yielding new techniques for modeling and characterizing instruments, and motivating the exploration of novel sites for deployments. In 2018, EDGES reported a broad, flat-bottomed absorption feature in their spectrum centered at 78-MHz. The origin of this spectral feature remains controversial. Its spectral shape and size characteristics are not predicted by standard cosmological models. Since then, the 21-cm community has devoted significant experimental and theoretical efforts to the confirmation and explanation of the feature. In addition, lunar farside instruments are being designed to probe down to 10 MHz and begin to sample the Dark Ages. Such observations may lead to new physics in this unexplored epoch.

This year, the Network for Exploration and Space Science (NESS) will host the 4th Global 21-cm Workshopvirtually at the University of Colorado Boulder.

This meeting will again serve as a platform to bring together recent developments and updates from different Global 21-cm groups. We will have talks focusing on theory, instrumentation development, observation techniques, data analysis, and related subjects from a diverse set of speakers with regard to career level, demographics, and geography.

Several discussion sessions will be hosted for exchanging ideas, addressing important issues being raised during the workshop, and ultimately providing some guidance to the global 21-cm community on what to tackle next.