In 1974, Robert Nozick imagined a machine that could feed your brain any life you chose: famous composer, beloved parent, fearless explorer, every triumph feeling real.
Would you plug in forever? Most people hesitate, even when the machine promises happiness without pain.
Nozick spotted the catch.
A plugged-in brain receives sensations, but it cannot write music, raise a child, or cross Antarctica. So you feel a whole life happening while your body does nothing.