Because if our alternate world had the same physical stuff and the same physical laws, then people would be like us, not p-zombies. Something has to change.
Yes, something is different. What's different is that in our world, certain physical processes are accompanied by consciousness, and in the p-zombies' world, they aren't. But that's not anything that our current scientific theories deal with. It's not anything that could be called physics. Physics says that nerve impulses work in a certain way, and the p-zombies' nerve impulses work the same way. There's just no consciousness to go along with those nerve impulses. But physics doesn't say there should be.
As I said, if you're allowed to make arbitrary changes to a person's brain as you "remove his consciousness," then sure, you can make him answer yes, at least to trivial philosophical questions.
No, no changes to the physics of the brain. Changes to the way the world works, so that the same physics isn't accompanied by consciousness.
Then why would it answer "yes" to the question of whether it is conscious, unless it has been rigged? Not to mention, how can it hear the question if it is missing all experiences?
It doesn't hear anything consciously. But it has eardrums that vibrate when sound waves hit them, and it has all the rest of the mechanisms of the ear, and all the same nerves in its brain, etc. And all of those follow the same physical laws as our bodies do, so the physical result is the same: it says whatever we would say.
Yes, that's epiphenomenalism. It's silly because it suggests that there is some subset of mental experience that does not form memories, yet here we are talking about those very experiences.
But no mental experience happens without a corresponding physical process in the brain, and so we can always say that it's that physical process which results in the formation of the memory, rather than the mental experience itself. (By "formation of the memory", I mean a physical change in the brain.) And then, since our brain is different from what it would have been in the absence of that experience-and-corresponding-physical-process, our subsequent behaviour and conscious memories, which depend on our brain, also are different from what they would have been, which difference we describe as remembering and talking "about" the experience.
But actually it isn't the experience per se that results in our talking "about" it; it's the physical brain changes which accompanied it. So a p-zombie would also talk "about" it, even though it had no experience to talk about, because it did have the physical changes to its brain.
Either do one of the following: