[dchftcs]

A more concise explanation is that, computation is the transformation of information. Any transformation of information is computation, and is thus subject to some theory of computation. A physical process involves the transformation of information, so can be studied with a theory of computation.

[andsoitis]

> A physical process involves the transformation of information, so can be studied with a theory of computation.

A rock rolling downhill has state-dependent future behavior you could describe informationally, but nothing is gained by modeling it with automata theory instead of Newtonian mechanics, and it isn't computing in any substantive sense.

[dchftcs]

Quantum mechanics is pretty fundamental but you wouldn't use it to describe a rock rolling down hill either.