The Thirteenth Floor. (Score 1)

If you haven't seen Thirteenth Floor, Then go rent it now. Because it's about a virtual world. A "virtual brain". Your brain is downloaded onto the computer system, And you interact with the other "computer simulated people" BUT! The computer simulated people don't realise they are just computer data. One of them finds out and you can imagine the rest. The interesting thing is, The people that made the simulation are in a simulated world themselves. So how do we define what is a REAL person and what is not? If something thinks/feels that it is real, What makes it not? And how do we know we are real? (Kind of like the matrix I guess.)