The truly peaceful can find peace in a bustling city. And to attain that state, you need to empty yourself. - Liu Cixin

The Archean Eon was followed by the Proterozoic Eon, each billions of years; then the Paleozoic: the Cambrian’s seventy million years, the Ordovician’s sixty million years, the Silurian’s forty million years, the Devonian’s fifty million years, the Carboniferous’s sixty-five million years, and the Permian’s fifty-five million years; then the Mesozoic: the Triassic’s thirty-five million years, the Jurassic’s fifty-eight million years, and the Cretaceous’s seventy million years; then the Cenozoic: the Tertiary’s 64.5 million years and the Quaternary’s 2.5 million years. Then humanity appeared. Compared to the eons before, mankind’s history was but the blink of an eye. Dynasties and eras exploded like fireworks; the bone club tossed into the air by an ape turned into a spaceship. Finally, this 3.5-billion-year-long road full of trials and tribulations stopped in front of a tiny human individual, a single person out of the one hundred billion people who had ever lived on the Earth, holding a red switch.

The universe had once been bright, too. For a short time after the big bang, all matter existed in the form of light, and only after the universe turned to burnt ash did heavier elements precipitate out of the darkness and form planets and life. Darkness was the mother of life and of civilization. On Earth, an avalanche of curses and abuse rolled out into space toward Blue Space and Bronze Age, but the two ships made no reply. They cut off all contact with the Solar System, for to those two worlds, the Earth was already dead. The two dark ships became one with the darkness, separated by the Solar System and drifting further apart. Carrying with them the entirety of human thoughts and memories, and embracing all of the Earth’s glory and dreams, they quietly disappeared into the eternal night.

But more commonly, the technique is used to construct the equivalents of pits and city walls. Some reduced-lightspeed belts are large enough to traverse an entire arm of a galaxy. In places where the stars are dense, many reduced-lightspeed black holes can be connected together into chains that stretch for tens of millions of light-years. That’s a Great Wall at the scale of the universe. Even the most powerful fleets, once trapped, would not be able to escape. Those barriers are very difficult to cross.