The Intervening Universe

This lecture covers the concept of the Intervening Universe, focusing on the Event Horizon Telescope, cosmic microwave background, lookback time, and the Global mm-VLBI Array. It explores the collaboration between two VLBI arrays, GMVA and EHT, observing at different wavelengths and reaching high angular resolution. The lecture delves into the absorption of light by quasars, the size comparison of the M87 black hole with our solar system, and the energy levels of hydrogen atoms. It also discusses the optical depth, line transitions, and the specifics of radio astronomy, including the Jansky Very Large Array and the Square Kilometer Array.