You’ve probably seen those experiments where scientists are able to levitate foam balls, or tiny drops of water, using nothing but ultrasonic sound waves. It’s utterly mesmerizing to watch something ...

In fiction, magic makes levitation easy. With a simple swish-and-flick of his wand, Ron Weasley yanks a troll’s club high above its head in Harry Potter and the Sorcerer’s Stone. Through graceful ...