If civilizations ever build perfect simulations, simple logic says you're probably in one

Philosopher Nick Bostrom argued at least one of three things must be true: almost no civilizations reach the technology to simulate conscious minds, those that can decline to run such simulations, or nearly everyone with experiences like yours is simulated. If even one future civilization ran many realistic ancestor-simulations, simulated minds would vastly outnumber 'original' ones. Bostrom doesn't claim we ARE simulated — only that one of the three must hold.

— Nick Bostrom, Are You Living in a Computer Simulation? — Philosophical Quarterly, 2003