Hypothesis that reality could be a computer simulation
The simulation hypothesis proposes that what one experiences as the real world is actually a simulated reality, such as a computer simulation in which humans are constructs. There has been much debate over this topic in the philosophical discourse, and regarding practical applications in computing.
I don't really like it unless it's like in Greg Egan's short story "Wang's Carpets" in which the simulation is naturally occurring, and the laws of physics of the outer reality are completely different from the embedded one.