Dear all, I enjoyed last week's discussion session after the talk and thought some of you might be interested in the following papers about magnetism and spontaneous symmetry breaking: David Wallace (2018) Spontaneous Symmetry Breaking in Finite Quantum Systems https://arxiv.org/abs/1808.09547 Jasper van Wezel (2019) An Introduction to Spontaneous Symmetry Breaking https://arxiv.org/abs/1909.01820 Baptiste Savoie (2014) A rigorous proof of the Bohr-van Leeuwen theorem in the semiclassical limit https://arxiv.org/abs/1403.2834v3 J.H. van Vleck (1977) Quantum Mechanics: the Key to Understanding Magnetism https://www.nobelprize.org/uploads/2018/06/vleck-lecture.pdf Also, during the discussion, the question arose of whether I consider spontaneous symmetry breaking an experimental test of Everett. I don’t, but that being said, I think that spontaneous symmetry breaking should be incorporated into decoherence theory, and that decoherence theory aligns much more naturally with Everettian quantum theory than with other frameworks. –Sam On 19 May 2023 at 14:29:56, William Schober (william.schober(a)usi.ch) wrote: Hi everyone, Next Wednesday, 24 May, at 14:30 in D5.01 we're happy to have Sam Kuypers from our group give a talk at the CQI seminar. Sam will talk about the history of scientific models of magnetism, and why decoherence plays an important role in their modern understanding. Title and abstract below. As always you can join us online at https://meet.jit.si/cqi-demon-M6QW9V7YY. Looking forward to seeing you there, Will Speaker: Sam Kuypers Title: On Magnets and the Multiverse Abstract: Imagine a world where refrigerator magnets, compasses, and magnetic storage devices don't exist. Surprisingly, this is precisely the universe implied by classical physics: as Bohr and van-Leeuwen demonstrated, a classical system's magnetisation invariably vanishes to zero in thermodynamic equilibrium. Hence, quantum models, such as the Heisenberg spin-chain model, were invented to explain the phenomenon of magnetism. In this talk, I shall explore those models' history and intricacies. And I shall clarify why those quantum models require decoherence to explain the structure of magnetic materials.