What is it like to be Wigner's friend? By Dr. Caslav Brukner

The Nobel Prize in physics in 2022 went to scientists who, for over 40 years, have carried out a series of experiments indicating that, contrary to materialist expectations, physical entities do not have standalone existence but are, in fact, products of observation. This result is extraordinarily relevant to our understanding of the nature of reality, and so Essentia Foundation, in collaboration with the Institute for Quantum Optics and Quantum Information, Vienna, of the Austrian Academy of Sciences (home to Prof. Anton Zeilinger, one of 2022's Nobel Laureates in physics), organized a conference discussing the implications of this result. The conference was hosted by IQOQI-Vienna’s Dr. Markus Müller and featured seven other speakers.

In this presentation, Prof. Caslav Brukner, PhD, also from the IQOQI-Vienna, discusses what it may be like to be Wigner's friend, the famous character of an important thought experiment in foundations of quantum entanglement.

Copyright © 2022 by Essentia Foundation. All rights reserved.

[spotteryk]

Very interesting presentation, but is still not basic enough for most viewers who are asking awkward questions. The box represents a system, and our first mission is to discuss what a system is. In physics, the universe is a perfectly closed system in which matter/energy/information is neither created nor destroyed, only transformed from one state to another. This ideal notion of a system isn't true of the kinds of systems we experience, even under the most stringent laboratory conditions. We are always dealing with systems in our lives. Anything you can name can be called a system; A cat is a system; a box is a system, a cat in a box is a system. So we must be clear about what system(s) we want to observe and how it may interact with other systems. Systems have two possible states: Basis states and Superposition states, where a basis state is the state of the system at the moment it is observed and data is collected, and a Superposition state is all possible states for that system when NO observation is made. A deck of cards is a system, and there are many possible poker hands (permutations) of that system, some will be dealt with a higher probability than others. The rarest hands, like a flush or straight are therefore better to have. In any case, it is the observer who defines and creates the system in the first place.

[rooruffneck]

Hope we get the roundtable discussion.

[kwsmith]

It seems to me that its not like anything to be Wigner's friend because Winger's friend is not something that one can be. One can only be an observer that observes herself to be Wigners friend. The root of the problem is that there is absolutely no evidence whatsoever that the third person perspective exists and so it can't have observations. We always knew this on some level of course but it seemed silly to point out because its so useful to talk as the third person exists and no problems ever arose that could not be explained away. For example, isn't it suspicous that you can't observe two moments in time simultaneously and indeed no facts can be shared unambiguously between two moments in time even in the classical world? What is nature hiding? She's hiding that moments in time are not a thing, they are part of the description of a perspective and have no independent existence. Perspectives are related to other perspectives by correlation or if you like entanglement but there is not some universal box in which they sit. If fact "they sitting" is already slipping into the false shorthand of the third person.

[cornfall]

Thank you for your expert presentation. Would you discuss how Wigner’s friends 1, 2, 3, … (continuing evermore or practically far enough for engineering) are cartoons representing (1) Maiman 1960 mirrors in a laser — a coherent quantum state — with then ( measurement or collapse?) tunneling out a projected beam of light and (2) de Keninck mirrors in PGA SIBGRAPI 2021.