Physicalism is the somewhat outdated theory that everything we do or experience can be reduced down to physical components. The physicalist would believe that consciousness can be explained purely through physical matters. In other words, there is no mental component accompanying consciousness. An important term in the this discussion is what philosophers refer to as qualia. Qualia can be best thought of the as the distinct, subjective perceptions/feelings we associate with specific actions, or instances of conscious experience. So the feeling of pain when being hit, or the taste bitterness when drinking coffee, or the color of redness when seeing a rose are all examples of qualia.

Lets get into the zombies first. A philosophical zombie, as posited by David Chalmers, is a being that is exactly like a human, but lacks consciousness, and therefore has no qualia. Keep in mind, this zombie is exactly like us. If there was a LeBron zombie, that zombie would be completely indistinguishable from the real LeBron. Zombie LeBron would not only be a phenomenal basketball player, but he would act and talk in the same manner that the real LeBron does. Furthermore, Z-LeBron would react to stimuli in the same way. This is a little confusing, but stick with me. If Z-LeBron broke his ankle in a basketball game, he would react in the same way as regular LeBron would outwardly—however, he would lack the qualia of pain, i.e, he wouldn’t actually feel the pain. This is all to say that philosophical zombies are completely indistinguishable from normal humans. A Cartesian would say that everyone else in the world besides you could be a zombie, and you would have no way of knowing.

If the concept of a philosophical zombie seems in any way conceivable to you, Chalmers’ argument is working. You don’t have to agree that there are philosophical zombies in real life. All you have to concede is that the concept of them make sense. If this is you, and you think they are possible, you cannot be a physicalist as well. If consciousness is solely physical, then even the possibility of philosophical zombies should be illogical. This is because, under a physicalist logic, the zombies wouldn’t actually be zombies, and they would have a consciousness of their own, as consciousness is indivisible from physical structures.

In the future, it would be interesting if we could somehow put this to the test. I’m not sure there is even a way to measure the consciousness of another being in a quantitive way. If we could, and we also found a way to clone humans, we could make real-life zombies and test Chalmers’ assumption.