The Drake Equation is “an attempt to estimate the number of extraterrestrial civilizations in our galaxy with which we might come in contact.” It was theorized by Dr. Frank Drake, who is best known for being the founder of SETI, or the Search for Extra-Terrestrial Inteligence. Drake proposed the equation in 1960, the same year the physicist Enrico Fermi proposed his Fermi Paradox, which asks why “if a multitude of advanced extraterrestrial civilizations exist in the Milky Way galaxy, evidence such as spacecraft or probes are not seen.” One suggestion for the reason for this is called the Zoo Hypothesis, which suggests that aliens may be present but that they might “generally avoid making their presence known to humanity, or avoid exerting an influence on human development, somewhat akin to zookeepers observing animals in a zoo.” Another suggestion is known as The Great Filter, which “acts to reduce the great number of potential sites to the tiny number of intelligent species actually observed (currently just one: ours). It might work either by one or more barriers to the evolution of intelligent life, or a high probability of self-destruction.” While SETI implies a more passive search, METI (Messaging to Extra-Terrestrial Intelligence), is described as follows: “The science known as SETI deals with searching for messages from aliens. METI science deals with the creation of messages to aliens. […] [METI] pursues not a local and lucrative impulse, but a more global and unselfish one—to overcome the Great Silence in the Universe, bringing to our extraterrestrial neighbors the long-expected annunciation ‘You are not alone!’” Attempts at METI include the beautiful Arecibo Message and the highly symbolic Pioneer Plaque, both well worth a look.