The Simulation Argument

In 2003, philosopher Nick Bostrom published a deceptively simple argument. If future civilizations become capable of running vast numbers of conscious ancestor simulations — detailed computer models of their past — and actually choose to run them, then simulated beings could vastly outnumber real ones. In that branch of the argument, a randomly selected observer like us would probably be simulated.

Bostrom framed it as a trilemma — exactly one of these must be true: civilizations almost always go extinct before reaching simulation capability, advanced civilizations almost never choose to run simulations, or we are almost certainly living in a simulation.