My partner and I went to see David Copperfield last night. He is a great performer, and it was very entertaining. And part of the entertainment is of course to try to figure out how it is done.
Here are some ways it could be done...
Transporting to Perth
What we see: We are shown live footage from a beach near Perth, and DC promises to bring someone with him there and back during the course of the evening. The woman is pre-selected, and we watch a brief video explaining that her estranged father wants to re-establish connection. A randomly selected audience member chooses two letters, and DC writes them on his forearm. He also takes a polariod photo of a group of audience members holding a postcard written by a couple of them. DC and the young woman is hidden behind curtains, then vanishes, and a little later shows up on the live footage from the beach near Perth. The woman runs into the water, and DC shows the letters on his arm and the polaroid photo they brought with them.
How it can be done: The woman and DC have doubles on the beach in Perth. Before the transportation, DC's double writes the two letters on his arm, learning which two letters to write via a communication link from back-stage, and the polariod is digitally transfered and printed on the beach.
Guessing numbers in advance
What we see: DC tells us has audience members select random numbers and answer a personal question, which he writes on a large screen on stage. Then, he opens a well sealed box, takes out a large piece of paper and an audio cassette, walks over to the edge of the stage (with his back touching the black curtains there), unfolds the piece of paper, and puts the cassette into a tape player. Amazingly, on the piece of paper is written the numbers and information given by the audience members, and the audio tape has him saying the numbers out loud. He also shows two license plates with the numbers on them.
How it can be done: Someone back-stage writes the numbers on a piece of paper and a voice-double reads them in on a tape. When DC walks up the black curtain, he is given the paper and tape and switches them with the ones he pulled out from the box, distracting the audience and using sleight-of-hand. A machine back-stage puts the numbers on blank license plates.
Vanishing audience members
What we see: A group of randomly selected audience members sit on a platform on stage, curtains are drawn around them, and they shine of the curtain with flashlights. When the curtains are raised, they are gone.
How it can be done: The group is led out through the black back curtains as soon as the curtains are lowered around them. The flashlights are simulated by a simple mechanical and electronic device behind the curtains, creating the appearance of the volunteers still being there. (The only question is, what do you do if a stubborn volunteer refuses to go...?)
None of this takes anything away from the performance or the entertainment, if anything, trying to figure it out only adds to it. Especially since none of us knows how he really does it.