In the real world, causality usually rules. But in the quantum world, or in the real world viewed through certain transformations (such as the transform from "sequency" to frequency [time domain to spectral domain]) causality does not necessarily have any meaning. For example, in the perceptual distinction between green and red, it is not necessary to introduce time or causality. And the point you made about quantum decoherence as "cause" of the wavefunction collapse is a kind of circular logic - in the sense that the first intervention (observation) still looms large as the "paradoxical cause" for things we more often call "spontaneous". That leaves the question of whether the Big Bang happens "spontaneously" or whether it's even absurd to tie causality to something that can't be properly said to have a beginning (since time [spacetime] is created in the expansion). The philosophical problem brought to bear by the Creationists, then, is that human experience is not sufficient to cast the Big Bang as an event which has a beginning of its own. It is a condition, true, and it does imply a timeline, once the expansion begins and spacetime is created; but it doesn't necessarily "have to have" a beginning of its own in order for the rest to follow. The presumed fallacy of creatio ex nihilo is an ancient concept, but still is rooted in modern religious ideation. But no one who complains of the presumed fallacy in these threads seems to be aware of this. I suppose it's OK to say "just about everything" is causal once the Big Bang happens, but the recasting of ancient superstition and myth as something that "has to be true" is, on closer inspection, just another fallacy. That being said (and OK it gets to be quite a mouthful) none of this really relates directly to the existence of a God. In fact, the proof that God can not possibly exist is far more straightforward: (a) there exist no definitions of God which are not created out of human imagination, (b) therefore all definitions of God are purely imaginary, (c) therefore any and all Gods so created can not possibly exist outside of fabrication, therefore (d) God can not possibly exist. By the same token, whether the wavefunction collapses spontaneously, or under some paradox tied to observation, or as a matter of quantum decoherence, or any other idea that connects to the idea of "cause", it still never helps the Creationist extricate herself from the quagmire, as reasoned above, that God cannot possibly exist. And by the same argument, the superstitious belief that her God created the universe can have no bearing on any implications of physical reality outside of her own imagination, and therefore, the existence of the universe can never be properly reasoned as the justification for a claim that God exists, and must be set aside as yet another fallacy. Indeed, religion is so deeply ingrained in the human imagination that it requires fallacy upon fallacy to keep it alive.