Alternate Realities is a 2000 omnibus collection of three short science fiction novels by American writer author C. J. Cherryh: Wave Without a Shore (1981), Port Eternity (1982), and Voyager in Night (1984).

All three novels are set in Cherryh's Alliance-Union universe and share a common theme of people encountering and coping with a reality different from their own.

Wollheim encouraged Cherryh to experiment in this way during the late 1970s and early 1980s because he felt that the science fiction market would support such unusual offerings at the time.

Port Eternity is a romantic thriller set aboard the space yacht Maid of Astolat, owned by an extremely wealthy woman.

Cherryh originally named the story Involutions, because it "spirals in upon itself", but after discussing the title with her publisher, Wollheim's suggestion of Port Eternity was adopted.

[5] Port Eternity and Voyager in Night are part of C. J. Cherryh's Age of Exploration series, a collection of three science fiction novels that share a common theme, but are unrelated to each other.