Dmitry67 said:
What is a smallest system which can be considered a 'measurement device' in terms of CI. How many atoms does it consist of?
To avoid confusion, I don't declare myself as CI.
But I think I'm reasonably close to CI, atl east relative to Dmitry to add my comments fwiw.
The question has some complications, but I'll give a simple answers and add that the
real answers can only be made in a evolutionary context.
I take "measurement device" to be synonmous to "observer" here. This means you ask, what the smallest possible observer is?
The first thing I'd note is that this question is always raised by a second observer. In this case Dmitry, who happens to be human. But in that case, there is only one first hand observer, and that's Dmitry. So when his observer reads the "measurement device", he is in fact observing another observer, which is nothing but a part of the first observer environment.
The question becomes, what is the smallest part of the environment with some varying degree of coherence, that the first observer can _distinguish_?
In this case, we can fapp replace Dmitry with any human. So in my opinnion the question Dmitry raises here, is the same as ask, what are the smallest possible constitutient in the universe? Certainly, it's not counted in atoms, it would be on subatomic level.
Of course, these "observers" are can not described as "classical". This may be a problem for the strict old school CI. But this is why I do not declare myself as CI. To me, classical observer, or classical measurement apparatous are only an idealisation, that is emergent within the view of another observer during special occasions. My view does not rely on "classical" observers.
So, the notion of the "set of all observers" is in my view, not objective. Because each observer, has their own inside view of other observers. And for those who point out that this implies a consistency problem, my response would be that this apparent "consistency problem" is not really so. It can instead be seen to be the cause of interactions beteween the observers. The apparent inconsistency of views, exerts a selective mutual pressure on all observers in the game, that can be interpreted as forces. Pretty much like the idea of gauge theory, but with the difference that there exists no objective gauge symmetry. Instead it's much more self-referencing and self-evolving symmetry idea.
The key is to go from a realist birds view of symmetries of nature, to an instrinsic frogs view. To make this strange suggestion work, the implication is that all structures are evolving, and it's not evolving globally as per some objective law. It evolves differentially as per subjective(or local, meaning almsot the same thing here) beliefs. The result is both evolving beliefs, and evolving evolution rules.
The similarly to GR, dynamics in spacetime and dynamics OF spacetime is clear, but I'm picturing taking it yet another step, to apply to generic structures, in an intrisic information view.
/Fredrik