Steven Poole in The Guardian:
Elon Musk thinks you don’t exist. But it’s nothing personal: he thinks he doesn’t exist either. At least, not in the normal sense of existing. Instead we are just immaterial software constructs running on a gigantic alien computer simulation. Musk has stated that the odds are billions to one that we are actually living in “base reality”, ie the physical universe. At the end of last year, he responded to a tweet about the anniversary of the crude tennis video game Pong (1972) by writing: “49 years later, games are photo-realistic 3D worlds. What does that trend continuing imply about our reality?”
This idea is surprisingly popular among philosophers and even some scientists. Its modern version is based on a seminal 2003 paper, Are We Living in a Computer Simulation? by the Swedish philosopher Nick Bostrom. Assume, he says, that in the far future, civilisations hugely more technically advanced than ours will be interested in running “ancestor simulations” of the sentient beings in their distant galactic past. If so, there will one day be many more simulated minds than real minds. Therefore you should be very surprised if you are actually one of the few real minds in existence rather than one of the trillions of simulated minds.