Paratime series

The Paratime series written by H. Beam Piper consists of several short stories, one novella, and one novel; they deal with an advanced civilization that is able to travel between parallel universes with alternate histories, and uses that ability to trade for goods and services that their own, exhausted Earth cannot provide. Specifically, the Paratime series deals with the Paratime Police, the organization that protects the secret of paratime travel.

These stories were written by Piper:

Sequels not written by Piper

Some persons dispute He Walked Around The Horses and Genesis being Paratime stories, however Genesis is the account of a group of Martian colonists arriving on Earth between 75,000 and 100,000 years ago exactly as described by Piper in several of his Paratime Police stories. All of the names used in Genesis follow the conventions used in all of the Paratime stories but not used in Piper's other stories. Additionally the events in He Walked Around The Horses are referred to by Tortha Karf in the story Police Operation where he describes the event briefly to Verkan Vall.

In Piper's Paratime universe, there are an infinite number of timelines, but in each timeline, events occurred differently. They are grouped into five Levels, based on the probabilities of success of an attempt by Martians to colonize Earth 75,000 to 100,000 years ago; humans, on timelines where they are present, are the descendants of the Martian colonists. Timelines with points of divergence before the Martian colonization attempt are not discussed.

This is the level of complete success of the Martian colonization. However, in this level are several sectors of several thousand timelines each:

Home Timeline, and its associated Fifth Level Commercial, Fifth Level Passenger, Fifth Level Industrial Sector, Fifth Level Service Sector, is the home of the Paratime civilization. This is the only known timeline with paratime travel capacity, and protection of the Paratime Secret is the highest priority.

Venus and Mars are also colonized by the Home Timeline (or in the case of Mars, reclaimed), and paratime transport exists there as well.

The Dwarma sector is one where paratime travel was never discovered, and the Martian colonists settled down into a subsistence agriculture economy to survive. The culture is pacifistic and nonaggressive, though Dwarma peoples eat meat. One major event people remembered for years is when a farmer and trader contradicted themselves on the price of a pig; they raised their voices and shouted at each other. Verkan Vall and Hadron Dalla were planning a vacation in the Dwarma Sector when it was interrupted by the discovering of a paratemporal slave-trading ring in Time Crime. (In Home Timeline usage, family names precede personal names.)

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