One of the best and weirdest experiments in the history of pop music is happening right now not in some top secret A&R bunker but under our noses, in places as banal as YouTube and The Ellen DeGeneres Show. That's where Sia has appeared recently to perform her hit ''Chandelier.'' Or more accurately, hasn't appeared: In the song's video, which has more than 45 million views, she sings unseen while a rubber-band-bodied tween in a Sia-style wig dances as her stand-in. On Ellen, the singer kept her back to the crowd, like a toddler in time-out. (On Late Night With Seth Meyers, Lena Dunham was her avatar.) After years of writing for other artists (Beyoncé, Rihanna, Britney), Sia knows the Faustian bargain of fame. But she wants it both ways ubiquity for her songs, anonymity for herself. So with 1000 Forms of Fear, she's decided to vanish in plain sight, forcing us to ask: In the pop universe, is it possible to be a star and a black hole at the same time?
If anybody can, it's Sia. Fear shows off her ear for stentorian melodies, her quirky way with lyrics (''I'm your groundhog/And I'm skating on thin ice,'' she sings on ''Cellophane''), and her astonishing voice, with its unplaceable accent. (She's an Aussie, but in her top register she can sound like a Jamaican baby throwing a hissy fit.) Still, there's something missing. Maybe it's texture; all the heartbreak lyrics and Big Choruses can get samey. Maybe it's freshness, since she's already farmed out her style to so many other acts. Or maybe it's the artist herself. Fear is less a self-portrait than a sketch of an Everywoman. Sia's happy to bare her heart and soul in broad strokes just as long as she never has to show her face. B