To recap: the KCA is based on the central premise that "whatever begins to exist has a cause." But quantum mechanics provides us with at least two examples of things that begin to exist without causes: radioactive decay results in the decay products beginning to exist, and vacuum fluctuations result in the virtual particles beginning to exist. In the latter case, the particles are created literally from nothing, but that's just a detail, a little icing on the cosmological cake. The KCA premise isn't about whether or not things that begin to exist are fashioned from previously existing materials. It only speaks of causes. And quantum events don't have causes — at least not local causes — as shown by Bell's theorem. Bell's theorem actually does more than rule out local causes, it rules out all local hidden state models, not just causal ones. So there are only two possibilities: either quantum events are not (locally) caused, or quantum mechanics is wrong.
But Bell's theorem does not rule out non-local hidden state, and so it does not rule out non-local causes. Indeed, what Bell's theorem shows us is that quantum states are in general non-local: an entangled system is a system with a single quantum state spread out over multiple locations. So could this be the source of quantum causality?
No, it couldn't. Non-local causality is ruled out both by relativity and by the no-communication theorem. For a non-local state to be causal, the causal effect would have to propagate faster than the speed of light, otherwise it would just be an ordinary run-of-the-mill everywhere-local chain of causation. Some popular accounts of entanglement would have you believe that this (faster-than-light causality) does happen, but it doesn't. Measuring one member of an entangled pair does not change the state of its partner. So non-local quantum states cannot be causal.
There is one last possibility: maybe there is some other kind of state in the universe, some non-local non-quantum state. As I noted at the end of part 1 we can never rule out this possibility on the basis of any experiment. Indeed, we can even demonstrate a hypothetical non-local state that would account for all possible observational data: a cosmic Turing machine computing the digits of pi from wherever it happens to be that they correspond exactly with the outcomes of all experiments that have ever been done or will ever be done. Assuming pi is normal, this will always be possible.
This is the fundamental problem with hidden state: it's hidden. Our universe could be run by a cosmic Turing machine, or it could be a simulation built by intelligent aliens. We can't eliminate either possibility, nor a myriad others, on the basis of experiment.
When I have pointed this out to Christians their response has been: what difference does it make if we're in a simulation? The aliens were still created by God. But in fact this possibility is devastating not just to the KCA, but to all theological arguments. If the universe is a simulation, then I can accept all of the claims of theologians at face value, and still not get to God. I can accept that Jesus was a real historical figure, that he really did perform miracles, that he really was crucified and rose from the dead, that he really did claim to be God, that the scriptures are the literal truth, that the Flood really happened, that the earth is 6000 years old. I can accept all of that and still not believe in God because all of that could have just been built in to our simulation by the aliens who designed it.
I can even accept the cosmological argument and still not believe in any particular god. I only have to accept the uncaused cause in the abstract. I cannot possibly know anything about God's true nature because all of the information I have at my disposal is filtered through the intelligent aliens who built this simulated universe that I live in. The information that I have access to may or may not reflect the actual metaphysical truth. In fact, the aliens that built our universe may themselves not know the metaphysical truth because they themselves could be living in a simulated universe built by meta-aliens.
There could be an arbitrary number of layers of simulation between us and the uncaused cause. For us to have accurate information about God, that information would have to somehow percolate down through all of those layers without being altered. It would be like a cosmic game of Chinese whispers. The odds of the truth emerging unscathed down here at the very bottom of the hierarchy are indistinguishable from zero.
It is worth noting that we may not be at the bottom of the hierarchy for long. We are on the verge of being able to create simulated universes of our own. When that happens, will the artificially intelligent inhabitants of that universe have souls? Unless we are 100% certain that the answer to that question is yes, how can we be sure that we have souls?
In sum, the KCA is completely untenable. Its central premise is refuted empirically by quantum mechanics. Even if this were not the case, the KCA only gets you to some unknown uncaused cause. The nature of the uncaused cause cannot be determined by any experiment, since no experiment can rule out the cosmic Turing machine.
Furthermore, the possibility of simulated worlds is devastating not just to the cosmological argument but to all religious arguments. Even if you accept all religious claims at face value, you still have to either show that information about God necessarily propagates reliably into a simulation, or somehow prove that our universe is not a simulation, that we are living in the One True Universe, and that any simulations we create will be the first level down. Otherwise, even in the face of miracles and revelations we cannot know if they are the work of God or the aliens who programmed our simulation. Or, what is most likely of course, of our own ancestors' imaginations.