final Culture Novel The Hydrogen Sonata goes into greater depth than we've seen before on the process and consequences of a culture's subliming, in which they disappear from reality, and are presumed to gain access to some higher reality. It's a process that requires that an entire society make the decision collectively, and then nearly all of them must carry through roughly simultaneously, or it doesn't work somehow. The process is treated as some kind of graduation for civilizations, and its rhetorical role in the universe of the Culture is to make room for a constant influx of new civilizations arising anew. It's not absolutely required, and many societies have been around since the oldest known sublimations without making the choice.'s
The Hydrogen Sonata of the title is a composition designed to be played by someone with 4 arms on an eleven-stringed instrument. It's extremely difficult to play, and the focal character Vyr Cossont has been attempting to play it correctly all the way through as her life's project. The point, of course, is that she (and her civilization) is wealthy enough to be able to afford to work on completely frivolous projects like this.
The Gzilt, of which Cossont is a member, has voted to sublime, so Cossont has a limited time to finish her project. While she works on it, she gets embroiled in some shenanigans swirling around the circumstances of the sublimation. When a society decides to sublime, it's customary for others to clear the air if they had any unresolved grievances or issues. The Gzilt's progenitors, the Zihdren had a big secret, but they sublimed quite a while ago. Some Zihdren who missed the event would like to spill the beans, but other parties would prefer the secret remain hidden.
Cossont is reactivated by her old regiment who have heard what the Zihdren plan to say and want to know if it's true. The secret would undercut some of the Gzilt's most cherished beliefs about their civilization's rise. There's not a lot more I can say without giving away the plot. I enjoyed the adventure, and thought thatadventure around the galaxy was quite entertaining. There are interesting chases, fights between highly armed AIs, bizarre characters, awe-inspiring architectural feats, and plenty more.