Carlo Rovelli on the relational interpretation of QM
Bruce Kellett
Interpretation of Quantum Mechanics (RQM)
https://www.youtube.com/watch?v=syb3WfSGRoE
A more detailed account is given in this paper from a Royal Society meeting:
arXiv:1712.02894v5
Rovelli's RQM is an interesting alternative perspective -- similar to
QBism, but without the extreme instrumentalism of that approach. I think
that RQM contains some interesting insights, in particular, the
rejection of "object realism" about the Schrodinger wave function.
Following Dirac and Heisenberg, Rovelli thinks that the Schrodinger
equation is an essentially misleading attempt to render the discreteness
of the quantum in terms of a continuous wave. At best, the wave
function is simply a book-keeping device, keeping records of past
interactions.
I go along with much of this -- it is certainly better than QBism in
that it retains a viable form of realism -- but Rovelli comes seriously
unstuck when he attempts to give a fully local account of the EPR
correlations.......
arXiv:quant-ph/0604064v3
Bruce
Lawrence Crowell
This is a ψ-epistemic interpretation. It considers all systems as quantum mechanical. In that setting all systems can be needle states or observers. This will then mean a system of observers are on different paths or amplitudes and do not share the same outcome. This is somewhat related to Qbism, where different observers may have different Bayesian regressions or a sequence of measurements. This has some interesting prospects for quantum complexity, where a state |A〉 = H_1H_2...H_n|B〉 for a sequence of Hadamard gates. This defines the complexity C(A,B) as a path or geodesic. The Wigner friend issue means there can be an ambiguity over which path is extremizes the complexity.
This has a weak effect on the macroscopic world. As Heisenberg pointed out there is no sharp boundary between the quantum and classical domains. There is no matter how much we might object some quantum uncertain fuzz around classical reality. This means we could find some irreducible errors in needle states for qubit systems that approach the mesoscopic domain. These irreducible errors may reflects some tiny level of this epistemic uncertainty between observer's account of reality.
LC