Humans, from the perspective of the universe, are smaller than ants are to us. The universe is enormous, and we are one out of millions and millions of species that live on a very small planet, the Earth, that orbits a star out of billions. The Sun is one out of 100–400 billion stars that exist in the Milky Way Galaxy. Since there are estimated to be about 2 trillion galaxies, the total number of stars that exist in the universe is up to about 2 to 8 billion trillion. Through a rough calculation, a Sun-like star is classified as an F, G, or K-class star, which makes up around 20% of all stars in our galaxy. Each of these stars is estimated to have about 0.4 to 0.9 rocky planets, allowing us to estimate that there are 0.26 to 1.04 billion trillion Earth-like planets in the universe. We could predict with this huge number that extraterrestrial species, an alien, do exist in outer space. However, we have never discovered them despite all the work we have done. Then, where do they exist?

This particular question, about the existence and habitats of extraterrestrial species, is called the Fermi Paradox. The Fermi Paradox is named after the physicist Professor Enrico Fermi. Put simply, the nature of the paradox is the following: if the chance of life starting somewhere is relatively high, then why haven’t we seen any signs of anyone else’s existence in the universe? Few hypothetical explanations exist, and one of them is that “(Intelligent) Life is Rare”.

The Drake Equation, which is used to find the number of civilizations in our galaxy that emits a detectable electromagnetic signal, consists of 7 variables, including the average rate of star formation in our galaxy, the fraction of those stars that have planets, the number of planets per star that can support life, the fraction of planets on which life emerges, and so on. A breakdown of the Drake Equation shows that the chance of abiogenesis occurring is higher in planets like Earth, although the only model for us is Earth. However, something with a significantly lower chance is the emergence of intelligent life. Although it took only about 400 million years for life to appear on Earth, it took about another 4.1 billion years for intelligent life to form. There are a lot of hypotheses around this case, and of them is that the number of mass extinction events throughout the planet’s history caused natural selection, leading to the survival of the most complex forms of life to survive. Also, even if any intelligent life does exist out in the universe, that does not mean that they will build a spaceship and travel around the universe.

Another obstacle that blocks us from discovering extraterrestrial life is the difficulty of finding life due to the large size of the universe. Although we cannot observe the size of the whole universe, the Drake Equation itself shows us that the universe is vast. Humans only began exploring the universe after the invention of the radio telescope, which is around 85 years ago, a very short time compared to the time that the universe has existed. Signals of extraterrestrial species may have travelled around the Earth, but we wouldn’t have noticed it if it was sent during a period without developed civilizations on the Earth.

Not only that, extraterrestrial life may not be willing to communicate with other extraterrestrial species, unlike us, the humans. Humans have been transmitting different messages out into the universe that typically provide basic information about our planet and civilization. These messages from Earth may have already reached another intelligent species in our galaxy, but they might be refusing to answer them, out of concern for their safety. Another reason may be that there is simply nothing they benefit from by responding to our messages.

Through different theories and equations, such as the Drake Equation, it does seem logical to believe that extraterrestrial life exists in outer space, considering the fact that our planet is one out of a few billion trillion planets that exist in the universe. Humans are always starving for information about the universe, and thus will not stop on adventures to outer space, until we unveil the whole universe.