I n the late twentieth century, humanity was evicted from Earth by the Invaders — an alien race that had evolved in a giant gas planet. For them, time itself is just another physical reality, the way three-dimensional space is for human beings. In their hierarchy of intelligence, the Invaders are at the top level, sharing it with other beings who, like themselves, had evolved in gas planets such as Jupiter. The second level of intelligence is occupied by whales and dolphins, and beneath them are land-dwelling races such as humanity. The Invaders routinely travel about the universe evicting landdwelling civilizations in favor of species similar to whales. Utterly beyond human comprehension, the Invaders are invincible; humanity can never return to Earth and must dwell on the other planets and moons of the solar system.

Soon after its eviction from Earth, humanity began to receive scientific...