[mjburgess]

I don't regard computation as a physical process, or a property of any kind. It's a description of a system, say like "salad" or "party", which whilst informative in conversation, doesn't map to any actual property of reality.

ie., there is no property shared by all salads, nor by all computers.

Saying, "everything is a computer" is a bit presocratic in its way, like "everything is water" or "everything is fire"

In practice, what we mean by "computer" is something which can transmit power in a programmable fashion.. this has more to do with our ability to control devices, and what those devices are, than anything in the "computer".

It turns out LCDs, keyboards, CPUs, etc. can all be joined up so I can do something with them.. I call this a "computer" and leave it there.

As far as the mathematical definition goes, all functions from ints->ints are computable.. this is eitehr useless or uniformative. It has no relevance for physics.