"Ringworld" by Larry Niven

    "Ringworld" was written in 1970 and has won the "triple crown" of science fiction awards for that year.  Although Niven had published before this volume, and also the "Known Space" universe in which the action takes place has been created by Niven before and used in other stories, this novel has become the work by which Niven is identified in the wider reader community.  The main invention in the novel, a RingWorld, is a sub-case of the Dyson Sphere, which postulates that a sufficiently advanced civilization will outgrow planets as living spaces, as the planets with appropriate gravity (not too big, not too small) do not have enough space to house properly all the members of an expanding, technologically advanced, star-travelling civilizations.  Dyson proposed building of a humongous sphere that would enclose a sun/star at a distance which would be comfortable for the temperature requirements of the sentient species that builds the sphere.

     Dyson sphere has many problems.  It needs artificial gravity across the habitable surface.  It might be difficult to keep the sphere centered on the star in the middle.  And you can't see the stars.  Niven simplified the concept by imagining only a circular strip of the sphere, a ring, orbiting around the central sun.  Gravity would be provided by the centrifugal force and you can see the stars.  This was a great invention at the time, and Niven received many accolades.  However in 1971 MIT students and other readers pointed out that even though the ring is much simpler than a sphere, it is still a rigid structure, and as such does not actually orbit around the central sun, affected by its gravity and eventually will become un-centered and destroyed.  Niven made this a central plot of his next Ringworld novel, "Ringworld Engineers".  Afterwards, further simplifications have been proposed, such as having half-rings or partial rings, which would not be rigid structures and would actually orbit the central sun moved by its gravity.

   Niven is well-known for his vivid descriptions of alien races, and in this book he describes the K'zint, a feline-like, 8 foot tall creatures with internal genitalia, and Pierson Puppeteers, herbivores with two heads on long necks and a brain held in their main trunk, which are currently the most technically advanced species in the Know-Space.  The Puppeteers are genetically afraid, as they originate from herbivore, herd animals and are trying to eliminate every potential threat to their existence, no matter how trivial it might sound.  The fear of death and injury is their main motivator and the ones that do not have it to an extreme extent, like Nessus, are considered insane by the rest of the species.  They performed experiments on both the K'zind and humans, trying to breed the former for less aggression and the latter to develop a sort of "Psychic Luck."  These characterstics come handy when Nessus takes Luis Wu and Speaker-to-Animals with Teella Brown to the RingWorld, but eventually it turns out that even the Puppeteers' intelligence and technology could not predict all the consequences that ensued.

   The novel ends when Luis Wu, Speaker-to-animals and Nessus (who has been decapitated and is not known if he survived) leave the RingWorld while Teella Brown stays there for good with her new chosen mate, The Seeker.  Niven didn't intend to write sequels, but bowing to fan pressure, he wrote 3.  Each of them could be read as an independent work though, while connected to the rest.