In parallel with the Physics of the Observer Program and RFP announced by FQXi, we will host an online Workshop on Quantum Observers from 9th January 2016 to 19th January 2016. The workshop will bring together leading experts in the field, and address the most pressing issues in understanding quantum observers and solving the measurement problem. Selected presentations in the workshop will be published in *International Journal of Quantum Foundations*.

**Note**: This is not a public workshop. Group content and activity will only be visible to members of the group, most of who are invited. If you would like to participate in the workshop, please log in or contact us.

Rovelli is correct that psi-ontology versus psi-epistemology is at the heart of the confusion about quantum theory. Psi-ontology has to deal with the measurement problem and collapse of the wave function, as Rovelli points out, while psi-epistemology leaves us asking, “Knowledge ABOUT WHAT?” Likewise, quantum information theory per Griffiths’ post leaves us asking, “Information ABOUT WHAT?” Leifer writes, “If we are to maintain psi-epistemic explanations, then we instead need to look for retrocausal ontological models that posit a deeper reality underlying quantum theory that does not include the quantum state.” Along these lines, Price, Spekkens and Corry have each introduced toy models and we have recently posted a full-fledged model here http://www.ijqf.org/archives/2087. Since the problem has resisted decades of intense study by very intelligent scholars, we are going to have to seriously consider more radical approaches than have thus far received attention in the foundations community. So, in summary, the biggest problem facing quantum foundations is an unwillingness to venture outside a comfort zone.

I agree that we have to go outside our comfort zone, but I respectfully disagree that psi-epistemic models constitute the correct sacrifice of our comfort. The possibilist transactional interpretation or PTI is a psi-ontic model that calls on us to sacrifice our tenaciously held and yet unexamined assumption that all of reality must be encompassed by spacetime. As I've argued in the literature and in my CUP book, the most natural and uncluttered approach to solving the riddles of QM is to simply admit that it's describing sub-empirical, extra-spatiotemporal processes. No new formal structures (hidden variables) are required for this account.

I have argued in the literature that PTI solves the measurement problem by giving a rigorous physical account of what constitutes 'measurement'--i.e., it provides a physical referent for von Neumann's 'Process 1' transition from a pure to a mixed state. Then 'collapse' is the process (via a form of spontaneous symmetry breaking) by which spacetime events are created; that is why collapse is not a spacetime process, and why it defies a causal, mechanistic explanation. (In that aspect, PTI agrees with RBW that there is fundamental acausality at the root of the quantum-to-classical transition.)

Remember that Bohr himself said that quantum process "[transcend] the frame of space and time" (Jammer 1993, 189). That doesn't mean they aren't real. They are just not spacetime processes. Of course, Bohr assumed that we could not or should not talk about things that are not in spacetime. But why not? Heisenberg also proposed 'potentia'.

Is the idea that one could actually give a physically grounded, observer-independent solution to the measurement problem considered suspect because it has resisted solution for so long? That would be a shame. All one needs to do is take seriously the idea that absorption is a real physical process (i.e. the direct-action picture of fields). And absorption is not a primitive notion in PTI; it is rigorously defined at the relativistic level. (An extra dividend of the direct-action approach is a solution to the problem of Haag's Thm, see my recent paper in the 2nd issue of IJQF.)

PTI certainly qualifies as "outside our comfort zone!" I did not mean to imply otherwise. [RBW is itself a form of direct action, so we took the liberty of referencing your IJQF paper for that in http://www.ijqf.org/archives/2087. Have you yet extrapolated PTI's implications for physics? I would like to see a PTI approach to quantum gravity, for example.

Bohm's original pilot-wave theory from around 1953 really does away with all the confusion surrounding collapse, the cut etc of Bohr's Copenhagen interpretations and its spin-offs including John Cramer's TI with "actualization" replacing "collapse".

Bohm's version is completely ontological. Antony Valentini has one strategy for getting beyond the Born probability rule to the new post-quantum realm of signaling entanglement. Rod Sutherland has also applied what is essentially Yakir Aharonov's "weak measurement" using Wheeler-Feynman inspired advanced and retarded quantum information fields to get a retro-causal version of Bohm's pilot wave - particle duality completely consistent with the global Lorentz group symmetry of special relativity. There is no need for a preferred frame of reference hidden by the statistical noise inherent in the Born rule. In other words, Abner Shimony's "passion at a distance" need no longer be invoked. We do not even need to think of configuration space for entangled quantum systems as anything more than a convenient short-hand tool - not as a fundamental ontological structure.

Some references to what I alluded to above:

https://www.academia.edu/12876280/V7_Updated_June_13_2015_Retrocausal_Back-Reaction_Post-Quantum_Entanglement_Signaling

https://www.academia.edu/12967176/References_and_post-script_for_post-quantum_entanglement_signaling

http://arxiv.org/abs/1408.2836

http://arxiv.org/abs/quant-ph/0203049

Antony Valentini http://arxiv.org/find/hep-th/1/au:+Valentini_A/0/1/0/all/0/1

arXiv:1502.02058 [pdf]

Naive Quantum Gravity

Roderick I. Sutherland

Subjects: General Relativity and Quantum Cosmology (gr-qc); Quantum Physics (quant-ph)

arXiv:1411.3762 [pdf]

Lagrangian Formulation for Particle Interpretations of Quantum Mechanics

Roderick I. Sutherland

Subjects: Quantum Physics (quant-ph)

arXiv:quant-ph/0601095 [pdf]

Causally Symmetric Bohm Model

Rod Sutherland

Comments: 35 pages, 5 figures, new sections 12 and 13 added

Subjects: Quantum Physics (quant-ph)

Free Will and Retrocausality in the Quantum World http://prce.hu/centre_for_time/jtf/retro.html