The Depths of Time
Roger MacBride Allen
 Humans have invented a way of traveling great distances by creating artificial wormholes that send ships several decades into the past. A wormhole would send a ship 70 years into the past. While the crew is in hibernation the ship would travel for 70 years, covering several light years, and wakening the crew when it reached its destination, arriving only a couple of months after leaving. These wormholes are guarded by a special organization - The Chronologic Patrol - in order to prevent unauthorized travel into the past and possible time-contaminations and paradoxes.