The Simulation Argument, proposed by philosopher Nick Bostrom, suggests that we might be living in a computer simulation. It is based on the premise that if a civilization could reach a post-human stage and run many simulations of their evolutionary history, we would be statistically more likely to be in a simulation than in physical reality.
For example, imagine a highly advanced civilization that has the capability to simulate entire universes. They create countless simulations, each with its own unique set of physical laws and initial conditions. We are living in one of these simulations, and we have no way of knowing which one it is.