This issue—​the issue of consciousness and whether a simulation could have it—​is harder than the others. For now, we can set the issue of consciousness aside by focusing on impure simulations—​that is, Matrix-​style simulations in which you’re a biosim connected to the simulation. Biosims are not themselves simulated. They have ordinary biological brains which will presumably be conscious like ours. Whether you’re an ordinary person or a biosim whose brain is in the same state, things will look and feel the same to you. If so, we can never prove we’re not living in a simulation.

What about the other way around? Could we prove we are in a simulation? In The Matrix, Neo realized he’d been living in a simulation when he took the red pill and woke up in a different reality. He shouldn’t have been so sure. For all he knows, his old world was nonsimulated and the red pill plunged him into a simulation.

Still, we certainly could get very strong evidence that we’re in a simulation. The simulators could lift the Sydney Harbor Bridge into the air and turn it upside down. They could show us the source code of the simulation. They could show us private episodes from our past, along with the simulation technology that produced them. They could show me a film of my brain hooked up to wires in the next reality up, with an associated readout of my thoughts and feelings. They could give me control of the simulation, so that I could move mountains in the world around me just by pressing some buttons.