Apropos of *Wigner has many friends...*: **Renato Renner**: *It’s hard to think when someone Hadamards your brain*: "Hi Scott: There are currently many who are blogging about our result, so I started to use my little quantum random number generator on my desk: outcome 0 means I don’t react to it, outcome 1 means I write a reply. For your blog the outcome was 1! Now, we are already in a situation that involves superposed agents...

## #quantummechanicswignerhasmanyfriends

Wigner has many friends, and they can disagree: **Daniela Frauchiger and Renato Renner**: *Quantum Theory Cannot Consistently Describe the Use of Itself*. **Lidia del Rio**: *Journal club: Frauchiger-Renner No-Go theorem for Single-World Interpretations of Quantum Theory*: "In this talk I will go over the recent paper by Daniela Frauchiger and Renato Renner, "Single-World Interpretations of Quantum Theory Cannot Be Self-Consistent" (arXiv:1604.07422)...

...The paper introduces an extended Wigner's friend thought experiment, which makes use of Hardy's paradox to show that agents will necessarily reach contradictory conclusions-unless they take into account that they themselves may be in a superposition, and that their subjective experience of observing an outcome is not the whole story. Frauchiger and Renner then put this experiment in context within a general framework to analyse physical theories. This leads to a theorem saying that a theory cannot be simultaneously (1) compliant with quantum theory, including at the macroscopic level, (2) single-world, and (3) self-consistent across different agents. In this talk I will (1) describe the experiment and its immediate consequences, (2) quickly review how different interpretations react to it, (3) explain the framework and theorem in more detail...

**Scott Aaronson**: *It’s Hard to Think When Someone Hadamards Your Brain*: "So: a bunch of people asked for my reaction to the new Nature Communications paper by Daniela Frauchiger and Renato Renner, provocatively titled 'Quantum Theory Cannot Consistently Describe the Use of Itself'...

## For the Weekend: Scott Aaronson's Take on Quantum Mechanics

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## Weekend Reading: John Bell (1989): Against "Measurement"

**John Bell** (1989): *Against "Measurement"*:

Uncertainty over terms such as 'apparatus' is still rife in serious discussions of quantum mechanics, over 60 years after its conception:This article is published with the permission of Plenum Publishing, New York; it will appear in the proceedings of

62 Years of Uncertainty(Erice, 5—14 August 1989):

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