Zombies: inconceivable, conceivable but not metaphysically possible, or metaphysically possible?
Accept or lean toward: [..]
Accept or lean toward: metaphysically possible 217 / 931 (23.3%)
What does "metaphysically" mean in this context?
Imagine a being that acted exactly like a human, it spoke, laughed, etc. - everything that you'd imagine a human being to do. However, it does not actually feel or think.
For example, if you were to prick one of these "zombies," they would say "ouch," recoil, perhaps berate you, but the zombie does not actually feel pain - it's a purely mechanical process.
Metaphysics is concerned with the nature of being, properties, identity, etc. What one means by whether such zombies are metaphysically possible is really an answer to the question: are such zombies really any different than how we are?
You can think of zombies as the analog to robots (as is canonical with most AI questions). Robots are essentially philosophical zombies, should we get them to a level of sophistication such that they would be indistinguishable from a human being. Whether such robots could be considered "living," "thinking," or "feeling," is a question to be answered by philosophy.
If you're more interested read about John Searle's Chinese Room thought experiment. It gives a great example of what you're thinking of.
John Searle's Chinese Room, Turing Test, physicalism, Conway's Game of Life
Sadly, this question is not related to the possibility that chemical spills can cause the dead to rise and eat brains.
There is a stronger version of possibility: nomological possibility, which means something like "possible under the laws of nature". It is nomologically impossible for information to be transmitted faster than the speed of light.
In the context of the philosophy of mind, this question is about whether or not it's possible (in some metaphysically possible world) for there to be fully functioning humans, but minus experience. If so, then experience is a true explanandum.
See [1] for an account of these modal truth states, [2] for an account of philosophical zombies.
[1] http://plato.stanford.edu/entries/modality-epistemology/
For all interested in the zombies, check out David Chalmers website: http://consc.net/zombies.html
The guy has stated one of the most famous arguments about the consciousness in his book The Conscious Mind.