Reality+: Virtual Worlds and the Problems of Philosophy

by David J. Chalmers

In the 20th century, the American philosopher Hilary Putnam and others updated Descartes’s idea with equipment from modern science. The evil demon was replaced by an evil scientist, and the person deceived by the evil demon was replaced by a brain in a vat. Like the brains that float in jars in the Steve Martin movie The Man with Two Brains, the brain is kept alive with a carefully balanced mix of nutrients. Putnam tells us that the brain’s nerve endings are “connected to a super-scientific computer.” The computer sends electronic impulses to the brain, bringing about the illusion that everything is normal. The brain experiences a richly detailed and well-populated world, but in fact it is alone in a laboratory.