In simple language, Enrico Fermi felt that despite the existence of many billions of Earth like planets with the possibility of life to evolve in them, has life elsewhere evolved, and if they did why haven’t we received any sign of their existence? This is the Fermi paradox.
There are about 100-400 billion stars in the Milky way galaxy. For every star in our galaxy, there is a whole other galaxy out there in the universe. This means that there are approximately 100-400 billion “observable” galaxies in our universe. For a better picture, altogether for every grain of sand on every beach on Earth there are 10,000 stars out in our universe.
For the purpose of creating a same kind of scenario, there are 500 billion billion stars similar to our sun. The percentage of these sun like stars to be orbited by earth like planets is 50%, more conservatively a 22%. This means that there is a habitable Earth like planet orbiting at least 1% of the total stars in the universe, which brings us to 100 billion billion Earth like planets. Again, for a better picture, there are 100 Earth like planets for every grain of sand on every beach on Earth.
Imagine that like Earth, after billions of years, 1% of Earth like planets develop life. Among them, 1% of the planets hold life as intelligent as us on earth. This would mean that there are 10 million billion intelligent civilizations in the observable universe.
Considering just our galaxy, there are 1 billion Earth like planets home to 1,00,000 intelligent civilizations.
So why haven’t we received even a clue that shows a possibility of existence of intelligent life, let alone a proof.
Scientists have proposed various possibilities for why we exist in isolation.
- The Great Filter. There is a stage that all attempts at life must hit in order to go beyond and evolve to type 3 civilizations, which is either extremely rare or extremely impossible.
- Super intelligent life of type 2 and type 3 civilizations may have already visited Earth, but before humans could attain intelligence.
- The galaxy is already colonized, and Earth is in an isolated rural area kind of situation.
- Like in Hollywood movies, there are scary predators in the galaxy and intelligent life prefer to keep to themselves rather than broadcast their location.
- There is the possibility of existence of only one higher intelligent life like a super predator which will terminate other civilizations once they get past a certain technological level.
- We have established that we are still technological infants, so maybe there is a lot of activity in space, but our technology is not sufficient enough to detect those transmissions or maybe we are listening for the wrong things.
- The many, many controversies regarding the government hiding the obvious from the public to avoid global panic.
- Super intelligent life is aware of our existence and are observing us closely – “Zoo Hypothesis”
- Super intelligent life exists among us here on earth, but we, then again are too primitive to perceive them.
- Maybe we are completely wrong about our reality. We are just a computer simulation pre-programmed by super intelligent life. Or, we could be the alien life planted here on earth as an experiment.