As of August 2018, the series comprises nine novels and 53 shorter works, including short stories and novellas (most collected in three
anthologies). All are set within a fictional chronology that spans from the
Big Bang to the eventual
heat death of the universe and the singularity portrayed in
Timelike Infinity. An
omnibus edition of the first four novels (
Raft,
Timelike Infinity,
Flux, and
Ring), entitled
Xeelee: An Omnibus, was released in January 2010. In August 2016, the entire series of novels and stories (up to that date) was released in a single
e-book volume,
Xeelee Sequence: The Complete Series. Baxter's ''
Destiny's Children series is also part of the Xeelee Sequence''.
Conception Baxter first conceived of the Xeelee while writing a short story in the summer of 1986 as a hobby (eventually published in
Interzone as "The Xeelee Flower" the following year). He introduced powerful off-stage aliens to explain the story's titular artifact. In developing the backstory, he began to outline the elements that would later define the Sequence: a universe populated by intelligent species living in the shadow of the incomprehensible Xeelee.
Setting and themes The series introduces several notable species and civilizations, including the Squeem, a group-mind aquatic species; the Qax, whose biology depends on the interactions of
convection cells; and the Silver Ghosts, colonies of symbiotic organisms encased in reflective skins. Several stories explore humans and
posthumans in extreme environments: at the heart of a
neutron star (
Flux), in a
parallel universe where
gravity is much stronger (
Raft), and within
eusocial hive societies (
Coalescent). The
Xeelee Sequence explores numerous ideas from
theoretical physics and
futurology, including
artificial wormholes,
time travel,
exotic-matter physics,
naked singularities,
closed timelike curves,
multiple universes, advanced
computing and
artificial intelligence,
faster-than-light travel,
spacetime engineering,
quantum wave function entities, and the higher levels of the Kardashev scale. Thematically, the series addresses existential and philosophical issues such as the struggle for survival in an unknowable universe, the impact of war and militarism on society, and the consequences of an unpredictable technological future for humanity. ==Plot summary==