The Philosophical Zombie Argument is a  thought experiment in the philosophy of mind,  

particularly in discussions about  consciousness and physicalism.

Proposed by philosopher David Chalmers,  the argument presents the concept of a  

"philosophical zombie," which is an entity  that is indistinguishable from a normal  

human being in every way except that it lacks  conscious experience, qualia, or sentience.

The zombie behaves and appears  exactly like any other human;  

it can speak about its emotions, respond to pain,  

and behave as if it is conscious, but it does  not actually have any subjective experience.

The core of the zombie argument  is to challenge physicalism,  

the doctrine that everything is physical or that  the real world consists only of physical entities.

Chalmers uses this argument to suggest that  

conscious experience cannot be fully  explained by physical processes alone.

If it is conceivable that there could be  a physical duplicate of a person without  

consciousness, then consciousness  must involve something non-physical.

This leads to the conclusion that physicalism  is false, as the existence of such zombies  

would mean that physical facts do not  exhaustively account for mental facts.