Subspace Encounter

The book describes two "spaces" that exist simultaneously in the universe, each of three spatial dimensions, and each occupied by human beings of roughly equal technological standing.

Through their joint use of the fourth dimension, psychics (called "psiontists") in the two spaces become aware of each other, and meet to exchange technologies.

The book was published almost twenty years after Smith's death, and edited by Lloyd Arthur Eshbach.

[1] Dave Langford reviewed Subspace Encounter for White Dwarf #57, and stated that "one doesn't read Smith for literary graces, but this one is far inferior to the equally awfully written Lensman books because our hyperbrained Earthlings have it all too easy.

Kim Kinnison used to suffer for his victories (eg erethism, amputation, infection with hideous alien fungi): this lot gets their on a plate.