It sounds like a joke, and certainly the title is tongue-in-cheek: György Ligeti composed his Poème symphonique not for a big, colorful French Impressionist–style orchestra, as the name suggests, but for 100 metronomes. The "score" is a satirically overelaborate list of instructions, but basically you just wind them up, set them to different tempi, and let them run until they stop. One metronome can be irritating, as every music student knows, but thousands of click-clacks in a hundred separate time-grooves take on a grippingly listenable life of their own. Clustering and reclustering, converging and diverging, swooping and shape-shifting—it's a musical lava lamp, a cloud of ticking robot gnats, the precise sonic equivalent of a school of fish or a flock of birds, making vast morphing shapes out of tiny individual elements. (Ligeti did similar things with voices and instruments, as everyone has heard who's seen 2001: A Space Odyssey.) In what's surely its weirdest program ever, the Seattle Symphony is presenting Poéme symphonique as part of a concert of works from the World's Fair year of 1962, alongside music by Morton Feldman (spare, quiet, inspired by minimalist visual art), Iannis Xenakis (visceral, earthy, inspired by probability theory and other mathematical models), and others. It's the launch of the SSO's [untitled] series of informal, late-night new-music concerts in the lobby, one of music director Ludovic Morlot's new initiatives; sprawl anywhere on the floor, and the bars will be open. Preceding the show, at 9 p.m., KEXP DJ Darek Mazzone will perform something from the recent avant-garde: the Concerto for Turntables and Orchestra by Gabriel Prokofiev (grandson of Sergei); and for those of staider tastes, the evening opens with an hour of Mozart and Haydn at 7.