Multivac is an Earth-bound supercomputer that solves complex resource problems, successfully finding a way to run the entire planet on solar power. Designed by humans, the machine is logical, precise, and entirely devoid of human emotions. As it answers inquiries from its human operators, it begins a long-term process of calculating whether the universe's increasing entropy can be reversed.

Humanity functions as a collective entity characterized by an insatiable curiosity and a persistent desire to overcome the physical limitations of the universe. Expanding from Earth to colonize planets and eventually entire galaxies, the human race continually pushes the boundaries of exploration. Despite achieving near-immortality and vast technological marvels, the species remains anxious about the eventual exhaustion of cosmic energy.

Alexander Adell is a maintenance technician who monitors the massive Multivac computer system. Possessing a highly optimistic view of technology, he believes his species' energy problems are permanently solved by solar power. A casual, alcohol-fueled debate with his colleague prompts him to formally ask the computer if entropy can be reversed.

Bertram Lupov is a maintenance attendant working alongside Alexander Adell to manage the Multivac system. Unlike his optimistic coworker, Lupov maintains a cynical and realistic perspective on the laws of physics. He argues that no energy source lasts forever because the universe itself will eventually succumb to entropy and burn out.

Jerrodd is a human explorer participating in the mass migration to other planets as Earth's population expands. He relies entirely on a Microvac system to pilot his family's ship and manage their journey. As a father, he attempts to comfort his children when they become terrified by the concept of dying stars.

Jerrodine is an interstellar traveler leaving Earth to settle on a newly colonized world. She journeys through hyperspace with her husband and daughters, representing humanity's outward expansion into the wider galaxy.

VJ-23X is a futuristic human dealing with the exponential growth of the immortal human population. Tasked with analyzing the rapid filling of the known universe, he recognizes the impending energy crisis this expansion creates. He jokingly proposes asking the Galactic AC for a solution to entropy.

MQ-17J is an official calculating the energy requirements of a rapidly expanding, immortal human race. Taking his colleague's offhand joke seriously, he decides to officially submit the question of reversing entropy to the Galactic AC.

Zee Prime is an advanced human who exists in an era where people project their consciousness out of their physical bodies. While engaging in astral wandering, he becomes curious about the original galaxy where humanity began. His discovery of the dying original sun fills him with sudden dread, prompting him to collect hydrogen to build new stars.

Dee Sub Wun is an ethereal human consciousness hailing from a distant galaxy. Encountering a stranger during astral travel, Dee Sub Wun joins in examining the ancient origins of humanity and observing the diminished state of Earth's original sun.