In ancient times, before mankind had left the Earth, they had imagined the existences of various unique lifeforms other than humans in the outer space. They felt that these lifeforms would definitely be like humans, possessing great intelligence and developing a brilliant civilization. Therefore, they were referred to as aliens.
How naive and ignorant were they?
The universe was very big, filled with extraordinary things and various strange lifeforms. There were ghost civilizations formed from pure spiritual entities, robotic civilizations that used fire as the core of their lives, and even silicon-based civilizations that had extremely long lifespans...
Humans were just a part of the weakest carbon-based civilizations.
