But the detailed philosophical form of the simulation argument comes from Nick Bostrom, a philosopher who is currently the director of the Future of Humanity Institute at the University of Oxford.
Back in 2003 Bostrom wrote an article imaginatively titled "Are You Living In A Computer Simulation." Bostrom wanted to consider technologically mature civilizations, which for him meant cultures so advanced they build super-duper computers with fully conscious simulated minds living inside simulated realities. Think The Sims on super-duper steroids. These cultures, Bostrom reasoned, might then create ancestor simulations on their computers, meaning simulations of their own past. With these ideas in mind, Bostrom then made the final leap by considering the truth, or falsehood, of three statements:
Almost all civilizations at our level of development become extinct before becoming technologically mature.
The fraction of technologically mature civilizations that are interested in creating ancestor simulations is almost zero.
You are almost certainly living in a computer simulation.
So watch what happens as we run down the truth/falsehood list of these statements. If 1 is true then virtually no civilization becomes super-high tech before dying, which kind of stinks. If 1 is false but 2 is true, then virtually no ancestor simulations should exist. The use of "virtually" is important here because Bostrom's purely philosophical argument relies on probabilities and, in the end, it leads him to a remarkable place.
Now let's say statement 1 is false. That would means there are civilizations reaching heights of technology we can barely imagine today. Then add statement 2 as false. That would mean some of these technologically mature civilizations start creating super-duper simulations of their own past. With statement 1 and statement 2 false the conclusion has to be that there must exist ancestor simulations running out there right now full of simulated ancestor minds.