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Isn't the universe deterministic? And is that not what science requires us to take as a basic premise? We have to have ideas of ‘object’ and ‘cause’, and you just follow them along. They can fit everything and build to arbitrary complexity, and the universe is just very big – therefore we can think of the universe as a complete causal system. Right?
This is like saying you have a complete domino cascade, but if I ask to see it, you cannot show me. If various sections of dominos are missing, you do not have a complete system after all.
You might say: “I am not talking about a model of the universe, I am talking about the universe itself”. Then what are you doing? When you spoke, were you actually giving me the universe itself? No. “Talking about the universe” is a model of the universe.
When you say ‘the universe is such-and-such’ you are really saying that you have a model of it that is such-and-such. And if you say it is (fully) deterministic, you have to be able to give all its rules.
A reply might be that at each point the next step is taken – there is no choice or randomness, there is only one possible step to take: that is what deterministic means. But if you do not know what that particular step is, how can you think of it as determined? The machinery can be as rigid and entire as possible, but if you do not know it, what does ‘deterministic’ mean? You cannot call it deterministic in a meaningful way.
Determinism pretends to be somehow abstract, as if to claim to have something without actually delivering. But really, either you have the complete system or you do not. If you say that a system is lawful, rule-following, deterministic, but then say that you cannot tell me what particular rules it is following, what are you telling me about the system? Nothing at all. Such a use of the words ‘lawful, deterministic’ is a bluff. It is no good saying that you could have it in principle. Again, either you do or not. If you only have it ‘in principle’, then you do not have it, and it does not exist.
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But you cannot even have it in principle either! It would be like claiming to have a ‘complete map’. Every rock? Every blade of grass? Every atom? … But then it would not be a map, it would be the thing itself. And then how could you have it?
Imagine your object to be modelled is some software, and your model is super accurate: it is just an exact copy of that software running on another machine. You run it as a prediction of what the other will do. But even then, someone could unplug the other computer mid way, and the model would fail and its limitation would be exposed. Can you close that gap? Only if you made the model the very same thing as what it models. But then it is not a model anymore.
A model and its object is a relation of two things, one a simplification of the other, and that relation would have disappeared. What would such a model do, what could you do with it? It cannot predict itself, it cannot say anything about itself, because that would be circular. A statement about the universe is a model of the universe. And to say the universe is deterministic is to say you have an absolutely complete model of the universe. But that would be a model of the universe that would have to include the model itself, and that would be circular.
So either you do have a model, but it must be incomplete – because models necessarily are; or you are delusorily saying you have an idea of a complete model (which you do not really have) which would have to be impossibly circular.
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When people say the universe and physics are deterministic, what they really mean is: they regard it as something that could be puzzled out, that it is approachable as to some degree understandable. The sensible interpretation of the word ‘deterministic’ is: ‘has at least some regularity, not completely random’. But to think, as is common, that ‘in principle everything is determined’ – this is really a figurative expression, and a bad way to describe the matter.
Determinism in that figurative sense is an illusion and does not work. It suggests something OK – about things, causes, models – but then confuses you about how and what they apply to. Resist any persuasive feeling of it, and arguments built on it. The universe cannot be deterministic.