Titles and Abstracts

Adlam, Emily

Quantum Mechanics and Global Determinism

ABSTRACT: It is proposed that certain features of quantum mechanics may be perspectival effects, which arise because experiments performed on locally accessible variables can only uncover a certain subset of the correlations exhibited by an underlying deterministic theory. This hypothesis is used to derive the no-signaling principle, thus resolving an open question regarding the apparently fine-tuned nature of quantum correlations. Some potential objections to this approach are then discussed and answered.


Cohen, Eliahu

Uncertainty vs. determinism in quantum systems with two boundary conditions

ABSTRACT: In this talk I will briefly present and then reconcile two parallel routes that my colleagues and I have been working on: Relativistic independence [1,2] and the Two-State Vector-Formalism (TSVF) [3,4]. The former highlights the immense explanatory power of indeterminism in quantum mechanics (and beyond), especially for deriving the strength of quantum correlations, while the latter gives the impression of retrospective determinism with the help of a backward evolving wavefunction. A restricted form of reconciliation between the two was given in [5], which I'll then discuss, but more recent results and open questions will be presented too.

[1] A. Carmi, E. Cohen, Relativistic independence bounds nonlocality, Sci. Adv. 5, eaav8370 (2019).
[2] E. Cohen, A. Carmi, In praise of quantum uncertainty, Entropy 22, 302 (2020).
[3] Y. Aharonov, E. Cohen, E. Gruss, T. Landsberger, Measurement and collapse within the Two-State-Vector Formalism, Quantum Stud.: Math. Found. 1, 133-146 (2014).
[4] Y. Aharonov, E. Cohen, L. Landsberger, The Two-Time Interpretation and macroscopic time-reversibility, Entropy 19, 111 (2017).
[5] Y. Aharonov, E. Cohen, F. Colombo, T. Landsberger, I. Sabadini, D.C. Struppa, J. Tollaksen, Finally making sense of the double-slit experiment, Proc. Natl. Acad. Sci. USA 114, 6480-6485 (2017).


Hall, Michael

Retrocausality for fun and profit
 
ABSTRACT: It is shown that the optimally efficient models of Bell nonlocality, in terms of the quantity of information transfer required, must be implemented retrocausally. This provides a type of Ockham's Razor argument for retrocausality. The information costs of fully causal and of superdeterministic models, relevant to constructing physical devices that subvert device-independent cryptographic key distribution and randomness generation, are also considered.
 

 't Hooft, Gerard

Deterministic quantum mechanics: the missing math
 
ABSTRACT: Discussions on the interpretation of quantum mechanics often avoid talking about the equations. Here we show what it means to have a deterministic Hamiltonian and choose an ontological basis for Hilbert space. The most difficult feature to understand is how such a theory can obey locality constraints. In principle, the `cellular automaton" should meet all requirements but a stronger formalism will be needed for constructing effective theories and models.
 

Kaster, Ruth E.

What do we mean by "Retrocausation"?

ABSTRACT. This talk considers the use of the term "retrocausation" in connection with various approaches to interpreting quantum theory. It is noted that the physical meaning of the term depends, to a great extent, on what we mean by "causation" a notoriously elusive concept. Causation can be understood in a dynamical sense or in a purely relational sense, where the latter pertains to a static ontology. It is argued that many purported dynamical "retrocausal" pictures are subject to deflation to a static picture, and that an appropriate sort of ontological expansion can allow retrocausal models to retain a form of causal dynamism.


Kent, Adrian

Quantum reality via late-time photodetection

ABSTRACT: I describe new postulates for realist versions of relativistic quantum theory and quantum field theory in Minkowski space and other background spacetimes. According to these postulates, quantum theory is supplemented by local variables that depend on possible outcomes of hypothetical measurements on the late-time electromagnetic field in spacelike separated regions. I illustrate the implications in simple examples by using photon wave mechanics, discuss possible extensions to quantum field theory, and review recent related work.


Kinney, David

Corroboration Conditions for Cyclic Bayesian Networks

ABSTRACT: Since the 1980s, Bayesian Network models have been used to represent the causal structure of systems. Verma and Pearl (1988) prove that in an acyclic Bayesian Network, there is a one-to-one correspondence between sets of variables that stand in the d-separation relation to one another in a graphical structure and sets of variables that are conditionally independent of each other in a probability distribution that is Markov to that structure. This result provides clear corroboration conditions for acyclic Bayesian Network models. However, Neal (2000) shows that the same result does not hold for cyclic Bayesian Networks. This poses difficulties for the corroboration of theories that posit causal loops. Expanding on work by Clarke et al. (2014), I show that cyclic Bayesian Networks can be re-written as acyclic, Dynamic Bayesian Networks that are infinitely long in two directions. These models allow us to use to Verma and Pearl’s result to state probabilistic corroboration conditions for theories with causal loops. I discuss the implications of these results for superdeterminism.


Palmer, Tim

Invariant Sets, Noncomputability and Superdeterminism

ABSTRACT: A superdeterministic model is one that violates the Statistical Independence (SI) assumption and in so doing allows a locally causal interpretation of the violation of Bell’s inequality. Such a violation is typically seen as conspiratorial, or one that denies experimenter free will, or one that is simply unscientific. However, whilst the existence of such conspiracies etc imply a violation of SI, they are not implied by a violation of SI. In particular, we consider a class of theory where SI is only violated when comparing real-world ensembles of particles (prepared in some quantum state and measured in some particular way) with counterfactual ensembles of the same particles (prepared in the same quantum state but measured in some different way). Such violation need involve no conspiracy or violation of experimenter free will in the real world. However, to make theoretical sense of such an idea, such counterfactual states have to somehow be mathematically distinct from real-world states. This can be achieved if states of the world lie on a dynamically invariant fractal subset of state space, an idea motivated by chaos theory. In this case, the property of belonging to the invariant set is algorithmically undecidable. A local state-space representation of an invariant set is constructed. In such a representation, disallowed counterfactual Hilbert states have either irrational squared amplitudes or irrational phases.

 


Price, Huw
Interventionist causation, Bell's Theorem, and the 'free will' loophole

ABSTRACT: Bell's Theorem requires the assumption that the properties of a quantum system are statistically independent of the settings of future measurements of the system. This independence assumption is commonly taken to follow from a further assumption, namely, that observers have 'free will' in choosing these measurement settings. The possibility that this 'free will assumption' might fail is regarded as a loophole in Bell's argument for non-locality – a loophole claimed to be closed or at least narrowed in recent experiments in which the settings are determined by remote astronomical events. In this short talk I'll explain why an interventionist about causation should regard this thinking as confused, in several ways. Interventionism itself rests on something similar to the free will assumption. Far from closing the associated loophole in Bell's argument, however, interventionism gives us new reason to take seriously the possibility that nature exploits it.


Wharton, Ken
All Useful Superdeterminstic Models are Retrocausal


ABSTRACT: Using the causal model framework popularized by Judea Pearl, one can mathematically distinguish superdeterministic models from retrocausal models. (See arXiv:1208.4119, 1906.04313.) To be useful, all superdeterminstic models must be supplemented with future inputs (measurement settings), which transforms them into retrocausal models (i.e. models with future-input-dependence). Attempting only a "forward-time" analysis on such models is shown to lose all meaningful aspects of "causation" except bare temporal order. These conclusions will be supported using analogous classical scenarios: statistical mechanics with boundary constraints, and retarded/advanced potentials in electromagnetism. The implication is that superdeterminists should not be averse to hidden retrocausation.