Excerpt (Einstein's Dreams, by Alan Lightman)

26 April 1905
In this world, it is instantly obvious that something is odd. No houses can be seen in the valleys or plains. Everyone lives in the mountains. At some time in the past, scientists discovered that time flows more slowly the further from the center of the earth. The effect is minuscule, but it can be measured with extremely sensitive instruments. Once the phenomenon was known, a few people, anxious to stay young, moved to the mountains. Now all houses are built on Dom, the Matterhorn, Monte Rosa, and other high ground. It is impossible to sell living quarters elsewhere. Many are not content simply to locate their homes on a mountain. To get the maximum effect, they have constructed their houses on stilts. The mountaintops all over the world are nexted with such houses, which from a distance look like a flock of fat birds squatting on long skinny legs. People most eager to live longest have built their houses on the highest stilts. Indeed, some houses rise half a mile high on their spindly wooden legs. Height has become status. When a person from his kitchen window must look up to see a neighbor, he believes that neighbor will not become stiff in the joints as soon as he, will not lose his hair until later, will not wrinkle until later, will not lose the urge for romance as early. Likewise, a person looking down on another house tends to dismiss its occupants as spent, weak, and shortsighted. Some boast that they have lived their whole lives high up, that they were born in the highest house on the highest mountain peak and have never descended. They celebrate their youth in their mirrors and walk naked on their balconies. Now and then some urgent business forces people to come down from their houses, and they do so with haste, hurrying down their tall ladders to the ground, running to another ladder or to the valley below, completing their transactions, and then returning as quickly as possible to their houses, or to other high places. They know that with each downward step, time passes just a little bit faster and they age a little more quicly. People at ground level, never sit. They run, while carrying their briefcases or groceries. A small number of residents in each city have stopped caring whether they age a few seconds faster than their neighbors. These adventuresome souls come down to the lower world for days at a time, lounge under the trees that grow in the valleys, swim leisurely in the lakes that lie at warmer altitudes, roll on level ground. They hardly look at their watches and cannot tell you if it is Monday or Thursday. When the others rush by them and scoff, they just smile. In time, people have forgotten the reason why higher is better. Nonetheless, they continue to live on the mountains, to avoid sunken regions as much as they can, to teach their children to shun other children from low elevations. They tolerate the cold of the mountains by habit and enjoy the discomfort as part of their breeding. They have even convinced themselves that thin air is good for their bodies and, following that logic, have gone on spare diets, refusing all but the most gossamer food. At length, the populace have become thin like the air, bony, old before their time.