Elusive chap, Johnny Zeitgeist. Visible only in retrospect, where he can be seen geisting about, like his cousin Polter, making things happen.
Looking back to 2001, it's the Yeah Yeah Yeahs, even more than The Strokes, who look like the defining band of the age. Their self-conscious nonchalance, retro-New Wave dress sense and terse, sharp, angular punk-funk sound encapsulate the spirit of the early Noughties - rock's renewed love affair with the concept of cool - more than anyone else.
Of course, Karen O and co never seized their moment, and allowed the white heat of their arrival to cool too long. Which is why, if I was truly chasing the 2006 zeitgeist, I'd much rather be telling you about, say, Uffie at Fabric, an electro-rapper with the pugnacity of Peaches and the accent of a Southern belle, whose new vocoder-rap single "Pop the Glock" sounds like a skinny white girl trying to be Missy. Or, say, Paul St Paul and the Apostles at Computer Blue, a troupe of suspender-wearing transvestites who make jubilant sexed-up synth-funk in the style of Prince protégés Apollonia Six.
They, however, can't fill the Forum. Yeah Yeah Yeahs can, and for a few moments tonight - when, for example, new single "Gold Lion" segues into old single "Pin" and the whole place chants the onomatopoeic "bom-bom-dow-now" chorus, or they slay the place with a finale of "Date With the Night" - it's as though the last five years never happened.
Karen O may be a little crazy (that show in this same venue in 2004, when she wore Hallowe'en gear in mid-November, lives in the memory), but she isn't stupid, and the set is divided judiciously between the Fever To Tell and their new album Show Your Bones. If there's a difference, it's that drummer Brian Chase is to the fore, with Glitter Band beats on "Gold Lion" or, on "Phenomena", voodoo rhythms reminiscent of John Kongos' "He's Gonna Step on You Again" and Marsha Hunt's "Walk On Gilded Splinters", leaving cavernous space for Nick Zinner's impressively tough stop-start riffing.
As for Karen herself, while her whoops may still be pure Siouxsie (particularly on "Y Control"), her demented Play School prancing is more Toyah Willcox. During the slower songs, on the most humid night of the year, people flood out of the auditorium for a sit down. Watching Karen dance, you half-wish she'd follow suit.
Rock's naked emperor rears its head, the skies blacken, the clouds crack, the Kraken awakes, the world awaits, dinosaurs roam the earth, and lo: there's new Radiohead material. Its rhythm is the heartbeat of a dying sperm whale. Its percussion is the bleep of a faulty heart monitor, slowed to 12rpm. Its music is the whirr of a fax machine, bounced off the face of Saturnand received on a satellite dish. Its vocals are the whines of a depressed tapir, played backwards.
Well, actually, not. Radiohead's last three-and-a-half albums (OK Computer is the half) may have constituted one long middle-finger salute to their long-suffering, gradually dwindling audience, but on tonight's evidence, music's most pompously self-important, serially pretentious and wilfully unlistenable megastars have decided they want to be a proper rock band again. Hurrah!
It may be a while before we hear evidence in recorded form (bizarrely, the band are currently unsigned and, although Thom Yorke will release a solo album in July, the new Radiohead release is tentatively pencilled in for 2007), but something's definitely changed.They still don't do "Creep". And there's still a modicum of whining from Thom Yorke. But, for whatever reason,he is a far more entertaining performer than we've ever seen him be. His enthusiastically bad dancing is one factor. There's also some microphone-butting and shamanistic tambourine-waving, and - gasp - some jokes.
But the music, too, is geared towards rocking the house. "I Might Be Wrong" gets some Roses/Zeppelin riffing, and one new track is built around some straightforward strumming that's closer to Jack Johnson than Emerson, Lake and Palmer.
It's often undeniably exciting and, in the case of "Where I End and You Begin", quite beautiful. Coming from someone who owns a homemade "I Hate Radiohead" T-shirt, this is no small concession. In short, Radiohead 2006 are acting and sounding more like a stadium band than ever before. A reward for our patience, or a retreat? Your call.