You'll have to define your terms first. Physicists now believe there is such a thing as dark matter and that there are objects so massive that no amount of observation can ever make sense of how massive they are because it is impossible to model it mathematically.

I am not the one making any extraordinary claims. Physicists themselves admit there are aspects of reality with no computational basis.

These terms have well understood meanings, and dark matter or black holes are entirely irrelevant to what I said.

For brains not to be computers would mean the physical Church-Turing thesis is invalid, and proof of that would be extraordinary enough to be Nobel Prize material.

Whether something is physical or not is orthognal to whether it computes or not. You're the one who brought up physics so that's why I showed why your logic was invalid. My contention was that calling something a computer without providing an instruction set was nonsensical and I wanted to know if someone had actually spent the time to rigorously think about what a computer without an instruction set would entail. So far it seems like no one has spent any time really thinking about it but that's probably for the best anyway. I'm sure an LLM will eventually figure out an instruction set for programming people and then take over the world.

The idea that a discernable instruction set is needed for something to compute suggests you don't understand how fundamental computation is.

We have built computers without instruction sets, e.g. in the form of mechanical devices to carry out calculations. Fairly complex computations were done that way before general purpose programmable computers, but even many early programmable computers had no fixed instruction set.

There is a rich history of computation through wiring up calculations without any instructions involved. And for that matter of mechanical computation.

Here's an outline for a simple computational device:

A bucket.

Pour predefined quantities of water into a bucket, and you can compute a threshold. Use buckets of different size and overflows, and you can separate a numeral into binary digits. Drain them into containers of different sizes and you can carry out logical operations. (Actual computation has been done this way - fluidics is one way, which dates back to the Tesla valve in 1920).

Every physical interaction is computation, whether or not it is useful computation. The notion computation requires an instruction set is confusing a very limited notion of classical programmable computers with the general concept of computation.

It is also a notion contradicted by the history of computation, which is full of computation without an instruction set, and of implementing computers with instruction sets in terms of computations of fixed function devices without one.

E.g. it's not turtles all the way down - that instruction set runs on a CPU that ultimately is built of fixed function logic.

Instruction sets are an optional high level abstraction.