Story, first published: Wonder Stories, Dec. 1931
"World of the Red Sun" is a time-travel action adventure yarn, very much crafted to the taste of Wonder Stories readers. The two scientist-heroes equip their airplane as a time machine. Instead of traveling a few thousand years, a glitch in their instruments sends them five million years into the future to land in the ruins of what was once Denver. They are captured by a horde of primitives who possess "the eyes of furtive beings ... of hunted beasts." The travelers soon learn that all men are slaves of Golan-Kirt, a creature of pure evil, "He-Who-Came-Out-of-the-Cosmos" to rule by fear. The new arrivals must do trial by combat with Golan-Kirt, but their opponents turn out to be only figments of their own imaginations-a machine gun, marching soldiers, and a lion. Golan-Kirt himself is a fraud, an imposter, the naked brain of a 1930s' mad scientist who has ruled by fear for five million years. The intrepid timetravelers easily dispatch the madman by laughing at him. Despite the protests of the natives who want them to remain to help restore civilization, they attempt to return to the twentieth century.
And here the epilogue of this first story foreshadows some of that ironic despair for the success of the human race so dependent on its technology, which Simak would develop more concretely in City twenty years later. The instruments of the time travelers fail again, and they are sent farther into the future, where they find an eroded statue honoring them as saviors of the race. Like the Time Traveller in Wells's Time Machine, the two then realize that they are "alone at the end of the world." Such a downbeat ending was quite unusual for Gernsback fiction.
Ewald, Robert J.: When the Fires Burn High and the Wind is from the North, p.23-24