A weeklong series of ideas for improving urban life. Whenever a new tower starts muscling its way toward the sky, it drains a bit more light from the streets and parks below, so walking along a sidewalk can sometimes feel like pacing the bottom of a deep well. But what if, even in the densest thickets of Manhattan, skyscrapers could be designed to shrink, or even bleach out, the shadows they cast? Imagine a structure that bends like a rubbery dancer...