Known Space is an ever-evolving "future history," a cycle made up of some 40 short stories and novels set in a 60-light-year radius of space centered on Earth. The Known Space timeline spans from the 1970s, and mankind's first explorations of the solar system, to the year 3101, when humanity lives comfortably on dozens of worlds alongside a colorful collection of alien species.
The term "Known Space" first appeared in "At the Core" (1966), the second adventure of star pilot Beowulf Shaeffer. Known space officially became "Known Space" in "A Relic of the Empire." Niven writes "This is the story that joined early Known Space to Late Known Space; and all for the sake of a practical joke. Stage tree logs belong to the Slaver Empire and thus to World of Ptavvs. Easy interstellar travel belonged to the Beowulf Shaeffer era. I wanted to watch a bonfire made from stage tree logs. In a previous life I expect I was a pyromaniac."
The Assumptions Behind Known Space
The Core of the Milky Way is exploding, in an out-of-control chain reaction of supernovas. In 20,000 years the galaxy will be awash with radiation. This knowledge has influenced the behavior of many races and individuals in Known Space, sometimes in subtle ways.
For Further Reading: Protector, "At the Core"
One-and-a-half billion years ago, a race of telepaths called the Thrintun used their overwhelming psychic power to rule the galaxy. Tellingly, they came to be known as Slavers. A certain slave race, the Tnuctipun, were allowed limited freedoms because of their skill with biogenetic engineering and other sciences. The Tnuctipun used that freedom and that skill to wage war against their oppressors. When this brutal war was finally over, no sentient creature survived anywhere in the galaxy. Plants from that era can still be found throughout the galaxy, including Sunflowers and Stage Trees, and even one bio-engineered animal, the Bandersnatch. Explorers sometimes come across Stasis Boxes, Thrint vaults containing artifacts from the war. Opening a Slaver Stasis Box is usually more trouble than it's worth.
One theory claims that the yeast left behind on many Slaver colony worlds evolved into life as we know it. As evidence, consider the fact that several of the modern races in Known Space have compatible DNA - they can eat one another, as demonstrated in more than one bloody war between species.
For Further Reading: World of Ptavvs, "A Relic of the Empire," "The Handicapped"
Speaking of ancestors, humanity is descended from a race from the core of the galaxy called the Pak. The Pak have three stages of life: infant, breeder, and protector. Infant is self-explanatory; breeder is what we know as homo Habilis. Protector is the next stage of life, attained with the help of a virus called "tree-of-life," which gives the Pak long life, extra brainpower, thicker skin and an overwhelming urge to protect its own bloodline at the expense of all others.
A colony of Pak landed on Earth millions of years ago, but tree-of-life failed to grow properly and the protectors died out, leaving homo Habilis to evolve unchecked into homo Sapiens. The Pak still exist in other parts of the galaxy. The protectors would view humanity as a dangerous mutation to be exterminated. The supernova chain reaction at the core of the galaxy has sent Pak refugee fleets fleeing in the direction of Known Space. How this situation will resplve itself is still a question.
The Pak are also the species most likely to have built the Ringworld; certainly it was populated with Pak Breeders, who were then left to evolve unchecked.
For Further Reading: Protector, The Ringworld Engineers
Technology has reached near-miraculous levels, especially in the later stories of Known Space. Hyperdrive is available in the later stories, as are transfer booths (they look like phone booths, but instead of making a call you dial in a location and teleport) and sonic stun weapons. Many human worlds in Known Space don't like weapons, so they keep only what they need for law and order, and for protection from occasional attacks by aliens. Lift Belts help you get around, Autodocs keep you alive and sane (based on the assumption that chemicals can control brain activity), and boosterspice keeps you young.
Known Space is exciting. Hyperdrive permits the discovery of new stars, planets, and aliens. Niven strives to keep his science "hard," relying on the laws of physics rather than some sort of cheap sci-fi doubletalk. Within those limits he's managed to build a fun little universe.