Humans often wonder if we are the only ones out here. This seems a reasonable thing to ponder considering the numerous number of stars and planets in our galaxy and in the entire universe. Our natural interest in outer civilization similar to that of humankind is part of the reason why topics such as aliens and UFO sightings easily grab the attention of the public. For example, in September 2019, people tried to raid the military base known as Area 51 in hopes of finding secretly kept aliens. Although this event was done as a joke, it clearly shows the public’s interest in extraterrestrial civilization.
In the search for extraterrestrial intelligence (known as SETI), an astronomer named Frank Drake formed an equation to estimate the number of civilizations in the Milky Way Galaxy. The simplified version of this equation is shown below.
N_HP is the number of planets in the galaxy that could potentially have life, f_life is the fraction of these planets that actually contain life, f_civ is the fraction of planets that contain life that have civilizations that were capable of interstellar communication at some point in time, f_now is the fraction of such planets that have a civilization in the present moment
This equation cannot be used to actually calculate tangible numbers, but we can use the fact that most civilizations fade away soon after reaching the intelligence level that allows them to make interstellar communication to reach a reasonable conclusion. This fact implies that f_now is extremely small (very close to zero), and allows us to conclude that we are really the only civilization that is intelligent AND active at the moment.
This conclusion, however, is just based on one simplified equation and not sophisticated enough accommodate for all other factors we know about extraterrestrial life. We may be missing something big because we haven’t reached a certain intelligence level yet, and it would be interesting to see how further advancements in technology affects the search for extraterrestrial intelligence.