Does anyone know how David Copperfields does the trick that makes 13 audience members disappear & reappear?

We recently saw Copperfield at the MGM in Las Vegas. In the finale, he randomly chooses 13 audience members, puts them each in a chair, which are all in the center of the state. He gives each of them flashlights, and surrounds them all by sheets. The entire time they are on stage, you can see the flashlights through the sheets. In an instant, they vanish, and instantaniously reappear in the back of the arena (near the main entrance). He supposedly swears everyone who participated to secrecy. I don't know if he has them sign a confidentiality contract. I don't know how he could force them to. does anyone know how he does this trick?