But from the very beginning of the 2001 project, something was wrong.  Kubrick "was direct and honest with me concerning his desire to retain some of the 'temporary' music tracks which he had been using," North would later recall.  "Somehow I had the hunch," he said, "that whatever I wrote to supplant Strauss' 'Zarathustra' would not satisfy Kubrick."  He was right.  Neither the director nor the composer could finally live with a score that was part North's original work and part excerpts from classical pieces.  The "temporary" tracks were what Kubrick used in the completed film.

        Whatever the motivation behind it, Kubrick's decision to use preexisting classical music - like everything else about 2001 - went against the grain of the science-fiction film genre.  Most of what passed for science-fiction films before 2001 employed fairly conventional film music, though the best of them were often distinguished by futuristic experimentation, such as Bernard Herrmann's remarkable score for The Day The Earth Stood Still, the "electronic tonalities" created by Luis and Bebe Barron for Forbidden Planet, and the theramin-based "space music" that quickly became a cliché.

        "'The Blue Danube,'" Kubrick remarked in an interview, "gets about as far away as you can from the cliché of space music."  Both the most widely loved and the most frequently lampooned of the waltzes of Johann Strauss Jr., "The Blue Danube" was given new life when Kubrick associated it with the dancelike poetics of weightlessness.  So hauntingly perfect was his use of the Strauss waltz to accompany the graceful descent of spacecraft in silent space that today few people can think of either without the other.  Perhaps sensing the rightness of this conjunction of music and image, Kubrick reprised the waltz for the film's end titles, sending the audience away with something they could hum and deftly supplanting the disturbing open-endedness of his finale with comfortingly familiar rhythm and melody.

        There is a certain irony in Kubrick's decision to use a composition of Aram Khachaturian's in 2001 in preference to Alex North's music: North had scored Spartacus, Kubrick's film of the epic story of gladiator/slave rebellion that Khachaturian had himself scored for ballet.  Khachaturian worked on his Spartacus music beginning as early as 1950, producing three different versions - the final one of which was premiered in 1968, the same year that 2001 appeared.

        Much earlier, Khachaturian had composed the popular Gayane, a massive four-act ballet about crisis and reconstruction on a Soviet collective farm, filled with spirited Russian dances, of which the popular concert piece "Sabre Dance" is best known.  Kubrick's use of the languid, melancholic Adagio from Gayane to accompany the flight of Discovery toward Jupiter is a stroke of genius.  It amplifies the monotony of the astronauts' existence aboard the ship and adds an overtone of near-hopelessness.  The crew is, after all, not only in an empty and sterile environment but also millions of miles from home (and, as we later learn, doomed never to return).  The mood created by this use of the Khachaturian adagio finds a more recent echo in Oliver Stone's Platoon (1986): Samuel Barber's mournful Adagio For Strings floods the film with foreboding and despair as a yawning air transport disgorges its cargo of doomed recruits onto the shimmering-hot blacktop of Tan Son Nhut Air Force Base, Vietnam.

        The most experimental music to be found in 2001 is that of the contemporary experimental composer Gyorgy Ligeti, whose turbulent choral atonality combines, for Kubrick's purposes, the unease of inexplicable occurrence with the adventurous strangeness of the utterly new.  The choral phrases of the Requiem, each overriding the one before, create a layering of laments that emerge like the sound of battling winds.  This music accompanies the first appearance of the monolith and reflects the furor into which it sweeps the band of man-apes.  A portion of the piece is heard again as Discovery is guided by a floating monolith into Jupiter space.

        The less turbulent, more wondrous "Lux Aeterna" accompanies the low-level flight of the moon bus that carries Dr. Floyd to the site of the excavated monolith, and his team's "artifact."  The disorienting and adventurous "Atmospheres" expresses the danger and drama of Bowman's dizzying "light show" flight through Jupiter's atmosphere toward his destiny.  Another use of Ligeti's music occurs in the sequence in the 18th century room in which Bowman lives out his life: The presence of his extraterrestrial "zookeepers" was suggested by surreal, laughterlike sounds created by altering an excerpt from a Ligeti composition.  (Ligeti reportedly took successful legal action for the unauthorized modification of his music.)

        But unquestionably the most famous and most emphatically right musical choice in 2001: A Space Odyssey was the selection of the stirring introduction to Richard Strauss' "Also Sprach Zarathustra" to accompany the film's key moments of planetary alignment and intellectual propulsion.  Johann Strauss' "The Blue Danube" was already a widely popular piece before 2001; not so "Also Sprach Zarathustra," nor even Richard Strauss himself, both of only second-echelon importance even in narrow classical and operatic circles.  The opening to "Also Sprach Zarathustra" is but a brief introduction to a sweeping full-length orchestral tone poem celebrating Nietzsche's ambitious philosophical parable of the superman.  But by the time Kubrick was done with it, that fanfare was thoroughly and irrevocably associated in the popular mind will stellar spectacle.  The news media and NASA picked up on it; so did television commercials and the satirical impulses of comic filmmakers.  But even though widely quoted and parodied, nothing has shaken loose the power and appropriateness of Kubrick's choice, which not only embodied a philosophical and musical rightness but also introduced the music of Strauss to a far wider audience than it had enjoyed before.

        Becoming in the film a sort of musical emblem of the Nietzschean philosophical theme on which Strauss' tone poem was based, the fanfare from "Also Sprach Zarathustra" accompanies an alignment of astral bodies at the film's opening; the man-ape leader's triumph at discovering the power of the bone as tool and weapon; and the unforgettable finale, when the fetal Star-Child joins a new celestial confluence - and, turning gently, weightlessly, floats into film history.