> Secondly it seems to me that applying something like Turing equivalence to things which are not computer programs is a category error which leads to him talking very obvious total nonsense.
Turing equivalence applies to all computation. "Computer programs" has nothing to do with it.
> How does a weather system compute anything at all for example? By any standard definition of these words it doesn’t
By every normal definition of these words it does. Any computation with a digital computer is us applying an interpretation onto physical computation in the form of basic physical interactions that carry out operations that we interpret in terms of logic.
And we have computing devices that makes this link more explicit, such as e.g. the Soviet "water integrator". Using physical interactions to compute is trivial, e.g. ranging from the trivial, with two pools of water merging is the computational equivalent of addition, to the slightly less trivial classic demonstration of Pythagoras theorem with tree interconnected triangles filled with fluid.
Every physical system carries out computations with every interaction, but most of them are useless to us. But every digital computer can carry out computations that are useless to us too, if we let them run chaotic programs on chaotic data.
> That’s cool but it’s not the universe.
It's not the universe, but that is irrelevant unless you can either disprove Turing equivalence or prove that the universe contains computation that exceeds the Turing computable. If you could, there'd likely be a Nobel prize with your name on it.
> 3. How does any of that make life indistinguishable from computation? All life that I’ve observed seems to be very easily distinguishable from computation, and I would suggest that anyone who finds this confusing should probably get out more.
If life does not exceed the Turing computable, then it can be fully simulated, to the point of giving identical responses to identical stimuli when starting from the same state and at that point if there is any distinction at all, it would need to require observing the internal processes of the entities involved.
Put another way: If life does not exceed the Turing computable, then you don't know whether or not you are simply a simulation, nor do you know whether or not the universe itself is.