Shining Light into the Cosmic Dark Ages
The first billion years of cosmic history hold the key to unlocking many of the remaining mysteries in astronomy, cosmology and physics. Observational evidence from that epoch is poor, resulting in large uncertainty in astrophysical processes. Fortunately, observational effort is ongoing to map the Epochs of Reionization and Cosmic Dawn with the 21-cm line of neutral hydrogen. Recent discovery of the anomalously bright Cosmic Dawn signal by EDGES is very controversial and raises more questions than provides answers. Other experiments to probe Cosmic Dawn will hopefully clarify the picture. International effort includes HERA, SKA (radio), JWST (infrared), and the next generation X-ray observatories such as Athena and the projected Lynx mission. The wealth of data that these projects will generate will revolutionize our knowledge of the first billion years. In my talk I will describe what we can learn about the first billion years using the redshifted 21-cm line of neutral hydrogen. I will comment on the EDGES result. I will also mention possible synergies with other tracers.