I will attempt to explain what Philosophical Zombies are and why they matter.
Do not worry, philosophical zombies do not exist in reality, or at least we do not know of any. They are purely mental constructs used to make a “thought experiment” and draw conclusions. A philosophical zombie is defined as a being which has all the outside attributes of a human being but does not have a soul or a conscience.
Conscience is defined in a number of ways. A good definition is based on the feeling that “I am me and I am here,” a feeling which persists during the whole period in which we are awake. The problem which materialists (or naturalists or physicalists) have with this is that it is impossible to explain the existence of conscience as emerging from pure physical processes in the brain. This is called “the hard problem of conscience.”
Moreover, the existence of a conscience or soul cannot be explained in the context of Neo Darwinism. If some primitive form of an anthropoid existed from which humans evolved, why and at what point did conscience appear? Evolution claims that new features in a specie appear under a “selection pressure,” which is the need to become more fit. But how does conscience make us more fit as simple animals? On the contrary, conscience slows us down and burdens our brains with thoughts which do not help us to adapt to the environment or to immediate situations. As simple animals we would perform much better without conscience. Intelligence itself does not imply a conscience. Computers are intelligent, but not aware of themselves. For this reason, some scientists believe that conscience is a simple epiphenomenon, i. e. a collateral effect which has no role in the process in which it appears. An example of an epiphenomenon is the noise made by the car engine: it results from the running of the engine, but it is a collateral effect with no role in moving the car.
Even such a hypothesis (that conscience is an epiphenomenon) leaves the materialist with unanswered questions. According to the theory of evolution, the features which do not contribute to fitness disappear in time. Many believe that the so-called “junk DNA” is such a deposit of failed and unnecessary features. If not useful, over many generations they become corrupted and either disappear or become totally dysfunctional.
Our philosophical zombies are virtual beings which look and act just like normal humans but have no conscience or soul. They can act (just as machines) and even solve problems (just as computers). Theoretically they should be more fit and more efficient than us, humans. From a purely materialistic point of view, we should all be such zombies.
But we are not zombies. We KNOW we have a conscience or soul. This cannot be explained in a naturalistic paradigm.