It may sound like something from a second rate horror movie, but a zombie apocalypse is all too possible. But the zombies would be made of metal and plastic.
Many horror movie fans (and many video game fan) are familiar with the zombies depicted in movies like Night of the Living Dead: soulless, silent beings of decaying flesh who stalk around, scaring the daylights out of people. But philosophers speak of another type of zombie: what they call a philosophical zombie. The term philosophical zombie is used to mean a being who resembles a human but who does not really experience pain or pleasure, and does not have any real consciousness or inner self or true emotions. A philosophical zombie may appear to feel pain or pleasure (but does not really do so), and may appear to feel joy or sadness, but really feels nothing. Philosophers use this concept in various thought experiments designed to throw light on metaphysical issues.
As far as we know, there has never been a real philosophical zombie. But later in the century there may be many of them. The philosophical zombies that may come into existence are android robots. Within fifty years or so we will probably see robots that resemble human beings. Such robots may well seem to have some of the same emotions that we have, and some people will think that they will feel pleasure and pain as we do. But it would seem that such robots will not really have any real inner life or any real self. They will merely be simulations of beings who feel pleasure and pain, rather than beings that really do. An advanced android robot may say, “I feel happy when I see that,” but it won't really feel any happiness or pleasure at all, because it won't really have any inner self. In short, advanced android robots will be a technological implementation of the concept of a philosophical zombie.
Robots are philosophical zombies
Given these philosophical zombies of metal and plastic, there is then a possibility of what we might call a zombie apocalypse. We can define a zombie apocalypse in this context as the replacement of all human life (beings who actually have an inner self, and who really feel pleasure and pain) with soulless, insentient beings (robots) who don't actually feel any pleasure and pain. This would be a type of apocalypse because it would wipe out the main thing of value on the planet – the existence of beings with an inner self who are enjoying themselves and feeling real emotions such as love and joy.
To help clarify why such an event might be a kind of apocalypse, let us imagine an alien planet that undergoes a strange evolution. It starts out with a protoplasmic race of intelligent, sentient, feeling beings who live lives filled with real pleasure. But then for some reason these intelligent beings become obsessed with building model train sets everywhere around the planet. They finally fill the whole planet with an insanely intricate system of billions of model trains that can run independently (using solar power) on a vast system of little train tracks arranged all over the planet. The entire race of protoplasmic beings then kills itself for some reason. What is left is the system of model trains, which keeps running on and on for many centuries.
Clearly if this happened on such a planet it would be a kind of apocalypse. There would still be endless amounts of purposeful activity on the planet, as the model trains continued to run on their little tracks, going along their little routes. But such activity would not have any real value. The main thing of value on the planet (the pleasure in the lives of the protoplasmic beings, and the consciousness and feelings of such beings) would have been lost, and replaced by a mere mechanical, insentient swarm of activity. It would make relatively little difference if such a planet were to be wiped out by an asteroid collision, because nothing like a human life would be lost.
Having imagined this strange planet, let us compare it to a planet on which humans have entirely been replaced by robots (something that could happen not too many centuries after the first really impressive model of android robot was introduced). It would seem that such a planet is really not much different from the “toy train” planet just imagined. If all humans had been replaced by robots, the robots might scurry around the planet doing all kinds of elaborate things. But it would seem that they would not have any real inner selves, that they would not really feel any pleasure or pain, and would not have any real emotions. Consequently, such a horde of robots existing without humans would apparently not have any more real value than the horde of toy trains whizzing around on the previously imagined planet filled with toy trains. So if humans were to be entirely replaced by robotic beings who were philosophical zombies (incapable of any real pleasure, feelings, or inner self), then it would seem to be an apocalypse essentially as bad as the apocalypse previously imagined on the toy train planet.
This, then, is the “zombie apocalypse” that might really happen one day. As the metal and plastic “philosophical zombies” took over, Planet Earth might change from a planet with billions of man-years of pleasure experienced every year to an all-robot planet with zero man-years of pleasure experienced every year. From the philosophical standpoint of hedonism (which regards human pleasure as the main value), such a result would be something apocalyptic, a disaster about the same as if an asteroid were to hit and kill all human beings.
A person might argue that one day we will be able to prove that there could never be such a “zombie apocalypse,” by one day proving that advanced robots really are sentient and really can feel pleasure and have inner selves. But it would seem that such a thing can never be proven. Consider the question: how is it that you really know that the people you see around you are beings with real pleasures and real inner thoughts and real inner selves, rather than just images in your mind? You basically reason that such people look like you, and apparently originated in the same way you did; and since you know that you have inner thoughts and feelings, and that you really experience pleasure, you infer that the people you perceive also have inner thoughts and feelings and experience real pleasures and pains (even though you cannot directly experience such things by “living in their shoes” and being them). Such reasoning is respectable when applied to humans, but it would be wrong to apply any such reasoning to robots. We are not anything like robots, did not originate in the same way, are not made of the same materials, and we can never live “in the shoes” of a robot, experiencing things as they do. So we will never have any adequate warrant for concluding that a robot really feels pleasure or feels emotion in the same way we do.
We can avoid this type of “zombie apocalypse” by remembering that robots are just tools to help humans, rather than things to be valued like a human life. Even though robots might think faster, process facts faster, run faster, and work more efficiently at many tasks than human beings, from a value standpoint they must be considered mere philosophical zombies. Better to lose an entire alien planet consisting of nothing but robots that have no pleasures, emotions, or inner selves, than to lose a single bus load of humans that have pleasures, emotions, and inner selves.