15 September 2026
Title: A solution to the preferred-basis problem based on the
WAY theorem
Abstract: The preferred-basis problem is an issue that arises in several fields of
quantum foundations: decoherence theory (including its later
developments like quantum Darwinism), consistent histories, the
quantum-to-classical transition, as well as in some discussions about
the measurement problem and the interpretation of QM. From a “3rd person
perspective”, it can be formulated as follows: given the laws of
physics, in which bases do systems preferably entangle and therefore
mutually decohere? That is: about which observables does information
accurately flow between systems? Equivalently, from a “1st person
perspective”, it amounts to understand which measurements can actually
be performed, while the vast majority of bases in the Hilbert space can
not be probed in practice (e.g. Wigner’s non-classical supermeasurement
on his friend). While a variety of models already exist, they remain
arguably insufficient, in the sense that they rely on the choice of some
specific Hamiltonians which clearly favour one basis or another from the
start. In this talk, we propose a universal solution to the
preferred-basis problem, merely assuming the existence of a global
symmetry (a conserved additive charge), based on the Wigner-Araki-Yanase
(WAY) theorem and some basics of quantum reference frames. We further
discuss the implications of this result for the quantum-to-classical
transition.
By Antoine Soulas (online)
29 September 2026
Paper: M. Girard, G. Cheng, CJ Cao: Demystifying Objectivity with Operator Algebra Quantum Error Correction link
By Marin Girard (online)
13 October 2026
Title: Subquantum physics and the Spin-Geometry theorem
By Nathan Cohen
27 October 2026
Paper: C-J Cao, O. Friedrich, M. Girard, N. Loizeau, A. Singh: Wave packets from the spectrum link
By Oliver Friedrich (online)
10 November 2026
Paper:
By Ted Jacobson (online)
24 November 2026
Title: Boltzmann Brains and the Quantum Theory of Everything
Abstract: Physicists don't spend as much time worrying about Boltzmann Brains as they should. The ΛCDM model predicts a future thermal de Sitter phase, which arguably implies fluctuations into minimal systems that dominate the total number of observers in the universe. There is controversy over whether such fluctuations happen - depending on one's views about the foundations of quantum mechanics - and if so, whether they rule out such cosmologies. I will argue that: (1) they don't happen in infinite-dimensional Hilbert space; (2) they do happen in finite-dimensional Hilbert space; (3) they rule out such cosmologies because of cognitive instability, not because of mismatch with the data; and (4) a fine-tuned cyclic cosmology can avoid the problem.
Paper1: K. Boddy, S. Carroll, J. Pollack: De Sitter Space Without Dynamical Quantum Fluctuations link
Paper2: S. Carroll, N. Diachenko, S. Dulani: Toward a Phenomenologically Acceptable Quantum Cyclic Universe link
By Sean Carroll (online)
8 December 2026
Paper: TBD
By TBD
TBD November - December 2026
Paper: TBD
By Caslav Brukner
Add new papers here
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C-J Cao, X-L Qi, B. Swingle, E. Tang: Building bulk geometry from the tensor Radon transform link
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D. Schmid, Y. Ying, M. Leifer: Coppenhagenish interpretations of quantum mechanics link
L. Catani, M. Leifer, D. Schmid, R. W. Spekkens: Why interference pheonomena do not capture the essense of quantum theory link
S. Carroll, A. Singh: Quantum mereology: Factorizing Hilbert space into subsystems with quasiclassical dynamics link
L.Hausmann, R. Renner: Against probability: A quantum state is more than a list of probability distributions link