In the future, the main direction of human civilization's development will focus on underground space. Although humanity has previously made significant progress in aerospace technology, marine technology, and surface civilization construction, over time, underground space will become a key area for human exploration, and we will open the door to the exploration of underground space on celestial bodies.

Fifty years from now, if humanity masters the relevant technologies for developing underground space, we will begin constructing it. At that time, the scene may look like this: large-scale underground cities will rise in an orderly manner, resembling a massive three-dimensional city; lush green forests will be scattered throughout, akin to the “green lungs” of Earth, teeming with life. Even the vast oceans on the surface could be “contained” underground; in fact, the amount of water contained underground is many times greater than that in the oceans on the surface. When humanity begins to develop underground space, these abundant water resources will be discovered.

The resources that primarily support the continuous development of human civilization are mostly hidden underground, rather than in outer space. For example, underground contains various materials needed for civilizational development, rich mineral deposits, and energy sources. Additionally, underground space is much more extensive and of better quality compared to the surface; it can shield against various adverse environments, creating a more suitable space-time environment, which is far superior to the conditions in outer space.

However, at present, humanity still finds it difficult to venture into underground space, with psychological barriers being the biggest obstacle. Nevertheless, I believe that in a few years, as humanity opens the "virtual door" and overcomes psychological challenges, we will truly realize that while underground space may seem small, it is actually vast and boundless. It is like the center of the universe, containing endless potential and possibilities, waiting for humanity to explore and develop.