How does this make sense? There is some divine being that only sometimes looks at the actual synapses to decide if it should feel nauseous or happy?
It's a debatable position in philosophy against the reductionism OP is describing, and maybe a bit magical but I'd find it the more interesting of the two positions to hold.
> If you fully understood the laws of physics at an atomic level, would it be sufficient to recognize a cpu as turing complete if you see one?
This is testable if you take an alternate universe with very few laws. Somewhat canonically, do you understand a Turing machine built in Conway's Game of Life if you understand the 2 rules of that game. (Or 4 rules, depending on how you count).
The only way to understand it is to play the game.
That view states, as you describe, that somehow the whole is more than just the sum of the parts. I reject that. Instead, my claim is that if the only parts you have are physical parts, you will not get consciousness. You need other parts too -- specifically, mental/consciousness parts.
(although, this sounds closer to a dualist view, while my view is more idealist)
One possibility: the experiences that God gives me at any moment are what they are because of the state of my brain. This isn't a sometimes thing, but an always thing. I see or experience what I do because of the state of my brain, but not only because of the state of my brain.
The problem is that the physical states alone don't entail anything about the experiential -- nothing about the phenomenology. The physical explanation leaves out things that are real and need explaining.
Much like there is no divine being that decides "I'm going to make this dense star a black hole", a black hole and the attached phenomena are consequences of matter and forces interacting.
Emotions are thoughts (brains and the attached phenomena) are consequences of matter and mind interacting.