The original world established the first human civilization.
It was a stable and peaceful era, with neither capability nor erosion phenomena. People struggled to crawl under a few basic physical laws, barely managing to establish a base on the Moon and eventually landing on Mars.
However, this seemed to be the limit for humanity.
The Oort Nebula at the edge of the solar system was like an abyss, making it difficult for people to cross, and it's only a light-year from Earth. In comparison to the Milky Way where the Sun resides, it's a mere drop in the ocean.
At that time, someone predicted that humanity might never be able to leave the solar system.
