This is a lecture held at Harvard by Professor Abraham (Avi) Loeb, chair of the Astronomy department.
Are we alone? Probably not, out of modesty – keeping in mind that about a quarter of all stars host a habitable Earth-size planet. Upcoming searches for primitive life will aim to detect oxygen or methane in the atmospheres of transiting planets. Searches for intelligent life will aim to detect artificial signals in the radio or optical bands, as well as artifacts such as megastructures, solar cells that are used to re-distribute light and heat on tidally-locked planets, industrial pollution or artificial light beams. Our own civilization is starting to study the feasibility of interstellar travel using a powerful laser beam pushing on a lightweight sail, the so-called Starshot Initiative.