SLAC, Kavli 3rd Floor Conf. Room
Current and forthcoming CMB experiments such as the South Pole Telescope, Simons Observatory, and CMB-S4 image, or will image, a large area of the sky on daily scales in the 60-250 GHz band to probe a wide variety of exciting physics in the early universe. Contaminating this view of the early universe are a wide variety of nuisances: many thousands of active galaxies, clusters, high-redshift dusty galaxies, and, even worse for the CMB, time-varying sources of all stripes. The usual approach is to cut them out of the maps and move on, but, following the particle physicist's dictum that "Everyone's Background is Someone Else's Signal", the view of these objects provided by CMB surveys turns out to be both novel and quite detailed. This talk will discuss a variety of the things we are beginning to do with these data, focusing on the implications for high-energy and multimessenger astrophysics, in particular for time-variable sources such as GRB afterglows and AGN.