For the past half-century, humanity has been listening for alien radio transmissions, but so far we appear to be the only ones broadcasting into the void. Astrobiologists now seek to narrow down the search by looking for other technological and biological signatures. In this video, I explore some of the methods by which they hope to do so, and why the great silence of the universe is such a mystery.
During this part of the video I state that "as of the making of this video, [Voyager 1] is the only probe to have reached interstellar space." This is technically not true. When this video was published on November 30, 2018, both Voyager 1 and Voyager 2 had entered interstellar space. Voyager 1 did so back in 2012 and Voyager 2 on November 5, 2018. However, the date of Voyager 2's crossing was not publicly disclosed until December 10, 2018. So, when this video was published, Voyager 1 was still the only probe KNOWN to have entered interstellar space.