Philosophical Zombies
01-Aug-2013: Original version

The concept of the philosophical zombie is one that was popularised by David Chalmers and discussed at length in Chalmers 1996. Since then the idea has been the subject of much debate with numerous classes of zombie and zombie world having been proposed. There is considerable disagreement as whether zombies are possible and what it would mean if they were.

What Are Zombies?

A philosophical zombie is the same as any other person except they lack phenomenal consciousness and its associated qualia.

Zombies are normally described as being "physically identical" with their conscious counterparts. This can be interpreted in two different ways: a zombie identical to a specific person ("particular zombies") or zombies indistinguishable from humans in general ("generic zombies").

Particular Zombies

The particular zombie is a copy of a specific person, down to the quantum level. Would such a copy be the same as the original? Is it possible to create such a copy without also duplicating the original consciousness? Would the zombie's actions be the same as those of the original?

There are problems with the conceivability of a particular zombie. Quantum mechanics tells us that it theoretically impossible to know everything about a system. So how can we ever say that one thing is truly identical to another at the quantum level? This is not just an issue of measurement, this is an issue of theoretical knowability. If some aspects of a system are undefined then how can we make a true copy of that system?

If we assume that issue can be overcome then we have the problem that a zombie copy in the same world as the original will occupy a different spacial location. The external influences on the copy will differ from those on the original which could influence behaviour.

Of course both of these effects would be extremely small. However they are differences and must be borne in mind whenever we claim that a zombie in the normal world is "identical" with the original.

Generic Zombies

Generic zombies are identical to "a" human, not necessarily a particular one. They will pass any physical test for humanity. The generic zombie is a weaker form of zombie than the particular.

Generic zombies could coexist in with us in the ordinary world without the problems affecting particular zombies. Is it possible that a person we pass in the street is a zombie? Is it possible that I am the only person in the world who possesses phenomenal consciousness? Since there is currently no objective test for consciousness this question cannot be answered by experiment.

Functional Zombies

A functional zombie is a still weaker form of zombie. Such a being would appear to be human and would react in ways that were indistinguishable from a human being. However if we cut them open we would find they were not human inside.

An example of this sort of zombie would be the humanlike android popular in science fiction. A functional zombie would be anything that passes a greatly extended Turing test.

Zombie World

Many discussions about philosophical zombies postulate not zombies in the ordinary world but an entire zombie world. This world is identical to ours in every physical respect, however its "human" inhabitants have no phenomenal consciousness. They go about their business the same as we do and to an outside observer their world is indistinguishable from ours. But there is no consciousness in that world.

Is such a world possible? And if it is, what does that mean for consciousness?

Physicalists argue that in such a world the inhabitants must have consciousness since consciousness is either equivalent to or caused by physical aspects which are identical in both worlds.

Others argue that a zombie world is conceivable and hence possible, therefore physicalism must be false. A zombie world is compatible with most forms of dualism. However epiphenomenal dualism would mean that consciousness would emerge in the same way in the zombie world as in ours.

A third way is to say that a zombie world is conceivable if by "physically identical" we mean "identical within the limits of current science". However if and when science expands to incorporate consciousness then the meaning of "physically identical" will change and a zombie world will no longer make sense.

References:
Chambers, David J. 1996. The Conscious Mind