I defined "computation" above as Turing-computation. It's the only useful & rigorous definition I know of.
What does the equality of computation & physics even mean? What is physics? To me, physics consists of a number of large scale models of the world that remain incomplete. Also: if you consider the possibility of radical emergence (new rules coming into play at particular transitions in the history of the universe: eg nucleosynthesis, origin of life, and so on) then there is..
... no closure to physics (it remains forever incomplete) & is therefore not formalizable in a way the term "computation" suggests.
This is why I find any broad & vague application of the term misleading & restricting. By considering physics as computation, you limit yourself to the syntactic, symbolic realm (a small world where everything is well-defined), but the world we actually live in is full of ill-defined problems, ambiguity, & relevant cues are hard to come by.
Basically, you can have two attitudes towards computation:
(1) You can use computational models as tools to understand the world, with all the limitations of the approach that implies.
(2) You can come to live in your computational model and mistake it for the world. That's what computationalism is. That's why I call it deluded. It mistakes the map for the territory. It commits what is called the equivalence fallacy.
This immediately & radically restricts the questions ...
... you can ask, and the explanations you consider scientific. Our physical theories become complete descriptions of the world. You become trapped in your small world.
That's why computationalists can't even see the point of the argument I'm trying to have with them. The world is large and open-ended, but you can only get a shallow understanding of why that is if you live within your limited model.
Concrete examples:
Stephen Wolfram has a model called the "Ruliad," which he considers to be a model of not just this world, but all possible world. But it's 100% computational. So: nope. It remains trapped in a small world and does not even begin to describe what is possible in the real (large) world.
https://writings.stephenwolfram.com/2021/11/the-concept-of-the-ruliad
Similarly, Sara Walker and Lee Cronin have come up with an interesting computational model of chemical complexification during the history of the ...
... universe, which is called "assembly theory." But instead of seeing this as what it is (an interesting model) they claim it is a new theory of physical time.
https://aeon.co/essays/time-is-not-an-illusion-its-an-object-with-physical-size
In both cases, the models are really interesting, but it is a mistake to claim they *are* the world. This is my main point here.
Computation is a powerful tool to model the world. But I have no idea what someone means when they say "physics *is* computation." Probably, it does not mean anything.