Determinism Is Self Defeating

[The Grand Nudger]

While you can predict that the rock will ultimately roll to the bottom of the hill, you cannot predict the precise path that it will take.

That's fine. What we -can- predict is definitely evidence of deterministic behavior so long as we can continue to predict it. As I mentioned to someone else, we can always imagine that the moment we lose predictive ability things behave in an entirely different way than they did before.

Then we look at the emergent system represented by a conscious being capable of making random choices.

Good luck with predicting that.

"random choices" would be more an issue of the pov of the observer in this case. Again could be an inability to measure - but it could, as above, be that things are behaving differently -before- and -after- we are capable of measuring them. Perhaps something is bootstrapping itself - a special exception.

Therefore it is impossible to prove that the universe is deterministic.

If, on the other hand, you can provide such a proof......

Lets not go so far as to call it impossible, as though our competence was a description of the fabric of the cosmos. Lets say that we are simply incapable of proving such at this time (as in the examples above). That doesn't mean that we can't collect evidence, or that what we can measure and predict should not be considered when we ponder what can't be.