The quest to detect extremely-redshifted 21cm radiation

I will first summarize the status of searches for 21cm radiation from z>6. Most 21cm efforts to date are aimed at detecting the reionization era (z~6-10), but two new efforts are targeting the signal from the era of the first stars (z~15-25). This talk will focus on three theoretical issues that have implications for the detectability of these signals and for what we will learn when we detect them. I will discuss: (1) what the reionization era observatories will teach us about this epoch, (2) whether the z~20 Universe shock heated (as has been suggested), which would eliminate the predicted strong absorption signal that the first stars efforts are targeting, and (3) whether the recently appreciated baryon-dark matter supersonic velocity difference could result in much larger fluctuations in the 21cm signal.