Can you imagine a casual lunch conversation inspiring a series of world-changing scientific projects and hypotheses? This happened to the renowned physicist Enrico Fermi and his colleagues Emil Konopinski, Edward Teller and Herbert York at the Los Alamos National Laboratory. When talking about some dubious UFO sightings and their connection to the disappearance of municipal trashcans, Fermi, the creator behind the world’s first nuclear reactor, suddenly asked the famous question: "Where are they (aliens or extraterrestrial life forms)?" which later formularized into the Fermi paradox.
The paradox arises from the lack of evidence alongside the high probability of the existence of intelligent life forms besides humans. We already know that our galaxy has billions of stars that are similar to the Sun, and a certain percentage of these stars will have Earth-like planets. A fraction (which could be very small) of these exoplanets could harbor intelligent life, which may become capable of traveling or communicating interstellarly sooner or later. Following this line of thinking, one might reason that earthlings should have seen aliens arrive in spaceships or at least have received transmissions of greeting by now, just as Fermi concluded 67 years ago.
Although Fermi's name is most commonly associated with the paradox, Konstantin Tsiolkovsky a Russian Rocket Scientist implicitly raised the same issue in an unpublished manuscript from 1933. He was a strong believer in extraterrestrial civilizations despite the lack of evidence. For explanation, he proposed the so called “zoo hypothesis”: the human society has not reached the right development stage for other (more advanced) beings to contact us (sound familiar, Star Trek fans?).
An equation formulated by the American astrophysicist Frank Drake is closely associated with the Fermi paradox. As an attempt to find a systematic means to evaluate the probabilities involving the existence of alien life, Frank Drake came up with a way to calculate the odds in 1961. In the speculative equation, numerous factors are considered, from the rate of star formation in the galaxy all the way to the chance that a detectable, technologically advanced alien society appearing on a planet. But the problem with this equation is that a majority of these factors are still scientifically ambiguous. Therefore depending on who is using the equation, one might give an extremely optimistic or pessimistic estimate.
The theoretical underpinnings of the Fermi paradox are two lines of empirical evidence: there are many potential planets suitable for supporting life, and we see no evidence of life. The first point was an assumption in Fermi's time. The hunt for exoplanets has slowly heated up and revealed many fruitful discoveries. The finding of the Trappist-1 system and many other Earth-like exoplanets within our galaxy has convinced people that earth’s twin or siblings could be around the corner. The second part of the paradox that we see no evidence of extraterrestrial life is the major motivator behind the Search for Extra Terrestrial Intelligence (SETI) movement and the establishment of organizations whose goal is to find signs of both primitive and intelligent life.
The paradox also gave rise to many speculative concepts regarding extraterrestrial societies and the things of which they may be capable. The Kardashev scale was the brain child of Soviet astronomer Nikolai Kardashev. He classified civilizations into three levels of advancement, and the signature criterion is based on the amount of energy they collectively harness and put out. If other civilizations do exist, they may belong to lower levels of advancement, making their energy production difficult or impossible to detect using current Earth technology. American astronomer and physicist Ronald Bracewell hypothesized an autonomous space probe that is deployed by extraterrestrial life forms to travel between star systems and establish communication with other civilizations. In this case, we might shift our gaze closer to home in our attempts to detect alien technologies. The Dyson sphere, a concept popularized by physicist Freeman Dyson, is an artificial megastructure that covers an entire star and harnesses most of its power. Many different versions of this type of energy harvesting device appeared after Dyson’s published manuscript came out. The search for such megastructures is another avenue scientist are taking to solve the Fermi paradox. These ideas have received increasing exposure in the media, thanks to their connection to the Fermi paradox, and provide new imaginative avenues for our collective search for alien civilizations.
Video Credit: Kurzgesagt – In a Nutshell