# A strong no-go theorem on the Wigner’s friend paradox

@article{Bong2019ASN, title={A strong no-go theorem on the Wigner’s friend paradox}, author={Ko Bong and An{\'i}bal Utreras-Alarc{\'o}n and Farzad Ghafari and Yeong-Cherng Liang and Nora Tischler and Eric G. Cavalcanti and Geoff J. Pryde and Howard M. Wiseman}, journal={Nature Physics}, year={2019}, volume={16}, pages={1199 - 1205} }

Does quantum theory apply at all scales, including that of observers? New light on this fundamental question has recently been shed through a resurgence of interest in the long-standing Wigner’s friend paradox. This is a thought experiment addressing the quantum measurement problem—the difficulty of reconciling the (unitary, deterministic) evolution of isolated systems and the (non-unitary, probabilistic) state update after a measurement. Here, by building on a scenario with two separated but…

## 90 Citations

### Events in quantum mechanics are maximally non-absolute

- PhysicsQuantum
- 2022

The notorious quantum measurement problem brings out the difficulty to reconcile two quantum postulates: the unitary evolution of closed quantum systems and the wave-function collapse after a…

### Quantum erasing the memory of Wigner's friend

- PhysicsQuantum
- 2021

It is argued that the three apparently incompatible properties used to question the consistency of quantum mechanics correspond to two logically distinct contexts: either assuming that Wigner has full control over his friends' lab, or conversely that some part of the labs remain unaffected byWigner's subsequent measurements.

### No-go theorem based on incomplete information of Wigner about his friend

- PhysicsPhysical Review A
- 2023

The notion of measurements is central for many debates in quantum mechanics. One critical point is whether a measurement can be regarded as an absolute event, giving the same result for any observer…

### A no-go theorem for the persistent reality of Wigner’s friend’s perception

- PhysicsCommunications Physics
- 2021

The notorious Wigner’s friend thought experiment (and modifications thereof) has received renewed interest especially due to new arguments that force us to question some of the fundamental…

### The View from a Wigner Bubble

- PhilosophyFoundations of Physics
- 2021

In a recent no-go theorem [Bong et al., Nature Physics (2020)], we proved that the predictions of unitary quantum mechanics for an extended Wigner’s friend scenario are incompatible with any theory…

### A"thoughtful"Local Friendliness no-go theorem: a prospective experiment with new assumptions to suit

- Philosophy
- 2022

A recent paper by two of us and co-workers [1], based on an extended Wigner’s friend scenario, demonstrated that certain empirical correlations predicted by quantum theory (QT) violate inequalities…

### Demonstration of quantum correlations that are incompatible with absoluteness of measurement

- PhysicsPhysical Review A
- 2023

Exploiting the tension between the two dynamics of quantum theory (QT) in the Wigner's Friend thought experiment, we point out that the standard QT leads to inconsistency in observed probabilities of…

### Wigner's Friend Depends on Self-Contradictory Quantum Amplification

- Physics
- 2022

In a recent paper, Żukowski and Markiewicz showed that Wigner’s Friend (and, by extension, Schrödinger’s Cat) can be eliminated as physical possibilities on purely logical grounds. I validate this…

### The Invalid Inference of Universality in Quantum Mechanics

- Philosophy
- 2021

The universality assumption (“U”) that quantum wave states only evolve by linear or unitary dynamics has led to a variety of paradoxes in the foundations of physics. U is not directly supported by…

### Wigner’s friend and Relational Quantum Mechanics: A Reply to Laudisa

- Physics, PhilosophyFoundations of Physics
- 2021

Relational Quantum Mechanics is an interpretation of quantum mechanics proposed by Carlo Rovelli. Rovelli argues that, in the same spirit as Einstein’s theory of relativity, physical quantities can…

## References

SHOWING 1-10 OF 53 REFERENCES

### A No-Go Theorem for Observer-Independent Facts

- PhysicsEntropy
- 2018

A no-go theorem for observer-independent facts, which would be common both for Wigner and the friend is derived and is analyzed in the context of a newly-derived theorem arXiv:1604.07422, where Frauchiger and Renner prove that “single-world interpretations of quantum theory cannot be self-consistent”.

### Experimental test of local observer independence

- PhysicsScience Advances
- 2019

This result implies that quantum theory should be interpreted in an observer-dependent way, through recent no-go theorems that construct an extended Wigner’s friend scenario with four observers.

### Testing the reality of Wigner's friend's experience

- PhysicsMicro + Nano Materials, Devices, and Applications
- 2019

In this thought experiment, an observer is considered (Wigner’s friend) who is able to per- form measurement on the quantum system and assign a quantum state that does not ascribe a well-defined value to the outcome of the friend’'s observation, in apparent contradiction with the friend's perspective.

### On the Quantum Measurement Problem

- Physics
- 2017

In this paper, I attempt a personal account of my understanding of the measurement problem in quantum mechanics, which has been largely in the tradition of the Copenhagen interpretation. I assume…

### Significant-Loophole-Free Test of Bell's Theorem with Entangled Photons.

- PhysicsPhysical review letters
- 2015

A Bell test is reported that closes the most significant of loopholes that provide loopholes for a local realist explanation of quantum mechanics, using a well-optimized source of entangled photons, rapid setting generation, and highly efficient superconducting detectors.

### On the Einstein-Podolsky-Rosen paradox

- Physics
- 1964

THE paradox of Einstein, Podolsky and Rosen [1] was advanced as an argument that quantum mechanics could not be a complete theory but should be supplemented by additional variables. These additional…

### Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometres

- PhysicsNature
- 2015

The data imply statistically significant rejection of the local-realist null hypothesis and could be used for testing less-conventional theories, and for implementing device-independent quantum-secure communication and randomness certification.

### Nonlocal correlations as an information-theoretic resource

- Physics
- 2005

It is well known that measurements performed on spatially separated entangled quantum systems can give rise to correlations that are nonlocal, in the sense that a Bell inequality is violated. They…

### The Quantum Moment Problem and Bounds on Entangled Multi-prover Games

- Mathematics2008 23rd Annual IEEE Conference on Computational Complexity
- 2008

It is proved that a hierarchy of semidefinite programs similar to the one given by Navascues, Pironioand Acin converges to the entangled value of the game and it would follow that the languages recognized by a multi-prover interactive proof system where the provers share entanglement are recursive.

### The Problem of Hidden Variables in Quantum Mechanics

- Physics
- 1967

Forty years after the advent of quantum mechanics the problem of hidden variables, that is, the possibility of imbedding quantum theory into a classical theory, remains a controversial and obscure…