C3921 The Creation of High Technology Civilization

Setting the subway to a vacuum state would allow the speed to reach a very frightening level.

In a vacuum, it must be sealed. With the doors of a rubber subway, it is very difficult for air to enter the tunnel.

Due to the synthesis of crystals, regardless of hardness and toughness, all of a sudden, the idea of using synthetic crystals to make carriages and rails came up?

As expected