The Fermi paradox was a contradiction first pointed out by physicist Enrico Fermi. During lunch with his colleagues in 1950, he discussed a contradiction between the lack of evidence for extraterrestrial civilizations and the high probability that life must have existed on other planets.
The age and vastness of the universe make it likely that extraterrestrial life has occurred somewhere. Fermi questioned why space craft or probes are not seen if advanced extraterrestrial civilizations exist in the Milky Way galaxy.
Some scientists seek proof of extraterrestrial civilizations, while proposing that life could exist without our knowledge. Other scientists believe that intelligent extraterrestrial life either does not exist or is so rare that we will never find it.
Since 1960, various efforts have tried to find evidence of extraterrestrial intelligence. Our lack of interstellar travel capability makes this challenging. Therefore, scientists search for evidence such as radio transmissions, which can travel vast distances.
To human scientists, radio technology and radio telescopes are a natural step for intelligent, technologically-advanced species. It is believed that our intense television and radio communication broadcasts might attract the attention of an extraterrestrial civilization. In turn, we continue to seek radio waves from them. To date, there has been no success.
In recent years, advances in technology have allowed us to examine planets outside of our solar system. Spectrographic analysis allows us to examine the atmosphere of these planets. Scientists search for evidence of air pollution, a possible sign of technological advancement.
However, it is very difficult to observe these planets directly. The first claim of direct observation was made in 2004. Instead, the existence of these planets is usually inferred from observing the effects they have on their stars. This allows us to only deduce the mass and orbit of the planet. The planetary environment can only be roughly approximated.
Several attempts have been made to theoretically explain this paradox. Some believe that the absence of evidence proves extraterrestrials do not exist. Others try to explain the silence without ruling out the possibility of extraterrestrials. These explanations often include assumptions about alien technology and behavior.
The simplest explanation is that we are truly alone in the galaxy.
It is also possible that no other civilizations have arisen. This is known as the “Rare Earth” hypothesis. According to this belief, earth is unique. In this view, many coincidences lined up to permit complex life on Earth. In the long history of life on Earth, only one species has developed the technology to make spaceflight and radio technology possible. The incredible intelligence of the human species may be nothing more than an ecological surprise. Even if intelligence is widespread, technology is not.
Some believe that intelligent life exists only to destroy itself through warfare or other catastrophe. To them, any extraterrestrial intelligence that may exist could have already destroyed itself. Even if it had not destroyed itself, it is likely that these aliens would be super predators, much like Homo sapiens. Perhaps it is their nature to destroy others, much as it is ours.
Both religious and philosophical traditions often believe that human beings were created alone. While some Jewish and Christian thinkers believed that extraterrestrial life was a possibility, many did not. Instead, they saw human beings as unique, part of God’s great plan.
Of course, it is possible that advanced extraterrestrial civilizations exist on other planets without our knowledge. Perhaps our limited technology does not allow us to communicate with them; perhaps we just don’t understand them.
Even if such civilizations exist, it is possible that they are too far away to maintain a two-way conversation with us. If messages take several thousand light years to pass between the two planets, communication becomes difficult. In that time, entire civilizations can rise and fall.
All in all, our inability to use technology for communication has existed for less than 100 years. Prior to that, we were still cooking food over fires. For most of human history, technology has involved finding various clever ways of banging rocks together. It is entirely possible that we haven’t been looking for long enough, or listening for long enough, to find the proof we so anxiously seek.