# On Formalisms and Interpretations

Veronika Baumann1,2 and Stefan Wolf1

1Faculty of Informatics, Università della Svizzera italiana, Via G. Buffi 13, CH-6900 Lugano, Switzerland
2Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria

One of the reasons for the heated debates around the interpretations of quantum theory is a simple confusion between the notions of formalism $\textit{versus}$ interpretation. In this note, we make a clear distinction between them and show that there are actually two $\textit{inequivalent}$ quantum formalisms, namely the relative-state formalism and the standard formalism with the Born and measurement-update rules. We further propose a different probability rule for the relative-state formalism and discuss how Wigner's-friend-type experiments could show the inequivalence with the standard formalism. The feasibility in principle of such experiments, however, remains an open question.

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### Cited by

[1] Igor Salom, "To the rescue of Copenhagen interpretation", arXiv:1809.01746 (2018).

[2] Arne Hansen and Stefan Wolf, "The Measurement Problem Is the "Measurement" Problem", arXiv:1810.04573 (2018).

[3] Nuriya Nurgalieva and Lidia del Rio, "Inadequacy of modal logic in quantum settings", arXiv:1804.01106 (2018).

The above citations are from SAO/NASA ADS (last updated 2019-01-23 05:17:05). The list may be incomplete as not all publishers provide suitable and complete citation data.

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