John Henry

Assuming that the universe is fully interconnected, so any closed system is subject to external influences, and given that any system of modelling is a part of the universe and therefore smaller than it, is it impossible to make any predictions with complete certainty?

To give an example of what I mean, you could have a simple model of a toy railway, which would predict that it would start and stop when you pressed the appropriate buttons, and would keep going round the same loops until you interfered. Such a model would not predict that your brother might come and kick the train off the rails. You could extend the model to include your brother and make predictions involving the possibility of him kicking the train off the rails. However, the new model would not take into account the fact that he might get hit by a meteor, etc...

Eventually, for a completely reliable model of where your train would go, you would need to model the whole universe, which would surely be impossible to do with anything smaller than the unioverse itself.