In the summer of 1950, four scientists from Los Alamos National Laboratory, established as part of the Manhattan Project to develop atomic weapons in the United States, were walking to lunch. They were discussing UFOs and laughing at those who believed they were real. The conversation turned to other topics. However, when they were about to sit down at the table, Enrico Fermi, one of the creators of the nuclear reactor and winner of the Nobel Prize in Physics, suddenly blurted out: ‘So where is everybody?’ The researcher was referring to the inhabitants of other planets in the universe. Over the next decades, various scientists developed Fermi's idea.

 A chain of reasons emerged for why a collision between Earthlings and aliens seemed inevitable:

There are billions of Sun-like stars in the Milky Way.

It is very likely that planets with conditions similar to Earth's circulate around many of them.

Many of these stars, and thus the planets orbiting them, are many times older than the Sun. If Earth is not unique, life should have evolved on them even earlier.

Some of these civilizations are likely to have advanced interstellar travel technology.

Even with the relatively slow rate of development of interstellar travel, the entire Milky Way can be explored in a few million years.

Since many other ‘suns’ and the planets around them are billions of years older than the solar system, Earth should have already been visited by aliens, or at least their exploration vehicles.

However, we have not yet discovered any contacts with extraterrestrial civilizations or traces of their activity. This is the Fermi paradox.

Hypothetical explanations for the paradox

Since the 1950s, scientists have produced various hypotheses that attempt to make sense of the Fermi paradox. Here's what the most interesting explanations look like.

There is no life outside the Earth

Other planets could not have developed a civilization similar to ours. Earth is unique because many factors coincided on it at once: from the right climate to evolution.

There is no intelligent life outside of Earth

Even if there is life on other planets, it does not have intelligence similar to humans. A large brain is not the crown of evolution, it is rather illogical, as it consumes a lot of energy. Humans, primates, whales, dolphins, octopuses and squids are in the minority compared to millions of other ‘non-intelligent’ species. Moreover, only humans have been able to reach out to the cosmos. As researcher Charles Lineweaver notes, ‘dolphins had about 20 million years to build a telescope, but they didn't get there.’

Periodic extinctions

There have been five mass extinctions on Earth, when huge numbers of species disappeared in a planet-wide short period of time. Other inhabited planets in the Milky Way have faced similar problems. The causes are many, from asteroids to volcanic eruptions. Because of all this, the galaxy has not developed a similar civilization to Earth's.

Intelligent life did not come to technology

Humans have the best technology in the universe due to a number of evolutionary factors and the availability of resources on Earth. Intelligent life on other planets has not been able to build telescopes or spaceships.

Any intelligent life comes to self-destruct

Soon after civilization comes to radio and space technology, it self-destructs. The rapid development of weapons of mass destruction can lead to the death of all life. The most obvious example on Earth is nuclear technology. Because of similar scenarios, intelligent life on other planets has not reached the level of development of ours.

Alien life may be over-advanced

Humans simply cannot yet detect signals from other civilizations. Just 500 years ago, even a simple radio message would have looked like magic and no one, not even the most advanced scientists, would have been able to receive it. What if aliens are bombarding us daily with information about their existence, but our technology is simply not advanced enough to recognize it?

The aliens have isolated themselves from the world around them

Advanced civilizations from other planets through technology similar to the digitalization of the brain have ‘moved’ into their analogue of the virtual world and have no plans to get out of it.

Earth is being deliberately avoided

Alien civilizations have long known that the Earth is inhabited. However, they prefer not to interfere, but simply observe humans, waiting for them to reach at least the minimum level of development necessary for contact. This idea has been called the ‘zoo hypothesis’. Konstantin Tsiolkovsky wrote about it in 1933: ‘What is the basis for the denial of intelligent planetary beings of the universe? We are told: if they were, they would have visited the Earth. My answer is: perhaps they will, but the time has not yet come for them to do so. The time must come when the average degree of humanity's development will be sufficient for the celestial inhabitants to visit us. We are not going to visit wolves, poisonous snakes or gorillas. We only kill them. The perfect animals from heaven don't want to do the same to us.’