The antenna was surrounded by a big green meadow that formed a small oasis in the desert of northern China, but this meadow had not been specially planted. Once the gravitational-wave system had been completed, it began sending continuous, unmodulated emissions that were indistinguishable from the gravitational waves emitted from supernovae, neutron stars, or black holes. The density of the gravitational beam had a peculiar effect in the atmosphere: Water vapor collected above it, so that it frequently rained in the antenna’s vicinity. At times, the rain only fell within a radius of three or four kilometers, and a small, circular raincloud would hang in the air above the antenna like a giant flying saucer, leaving the brilliant sunshine in the surrounding area visible through the rain. And so this area grew lush with wild vegetation. But today, Luo Ji and his family did not witness that spectacle. Instead, they saw white clouds gather over the antenna, only to dissipate when the wind blew them away from the beam. Yet new clouds were continually forming, making the round patch of sky seem like a time wormhole to some other cloud universe. Xia Xia said that it looked like the white hair of a giant old man.

As the child ran about on the grass, Luo Ji and Zhuang Yan followed behind, until they reached the antenna. The first two gravitational-wave systems were built in Europe and North America, and employed magnetic levitation that suspended them a few centimeters from the base. But this antenna used antigravity, and could have been raised up into space if so desired. The three of them stood on the grass beneath the antenna, looking up at the huge cylinder curling up over their heads like the sky. Its large radius gave the bottom a low curvature, which meant there was no distortion in the reflected image. The setting sun now shone beneath the antenna, and, in the reflection, Luo Ji could see Zhuang Yan’s long hair and white dress fluttering in the golden sunlight like an angel looking down from the sky.

He lifted up the child and she touched the antenna’s smooth surface, pressing hard in one direction. “Can I make it turn?”

“If you push long enough, you can,” Zhuang Yan said—then, looking at Luo Ji with a smile, asked, “Right?”

He nodded at her. “With enough time, she could move the Earth.”