Could different outcomes have different physics in Wigner's friend?

[Suekdccia]

TL;DR

Could different outcomes have different physics in Wigner's friend?

Summary: Could different outcomes have different physics in Wigner's friend?

Physicist Eugene Wigner said that consciousness was fundamental for physics and that laws of physics existed because of it. He said that "consciousness can change the usual laws of physics"

He also proposed the "Wigner's friend" mental experiment (analogue to Schrödinger's cat) where two observers could experience different realities or observe different outcomes for the same experiment.

But what about the laws of physics? Could these different realities differ in their laws of nature?

 

[PeterDonis]

Moderator's note: Moved thread to the QM foundations and interpretations forum.

 

[Demystifier]

Could these different realities differ in their laws of nature?

No.

 

[Quantum Alchemy]

Summary:: Could different outcomes have different physics in Wigner's friend?

Summary: Could different outcomes have different physics in Wigner's friend?

Physicist Eugene Wigner said that consciousness was fundamental for physics and that laws of physics existed because of it. He said that "consciousness can change the usual laws of physics"

He also proposed the "Wigner's friend" mental experiment (analogue to Schrödinger's cat) where two observers could experience different realities or observe different outcomes for the same experiment.

But what about the laws of physics? Could these different realities differ in their laws of nature?

That's an interesting question.

Recent experiments confirmed Wigner's Friend on a microscopic level. You then have the work of Frauchiger and Renner that shows the implications of Wigner's Friend if you apply it on a classical level.

I think the end result of these things is the wave function is real but non physical.

The wave-function is real but nonphysical: A view from counterfactual quantum cryptography

Counterfactual quantum cryptography (CQC) is used here as a tool to assess the status of the quantum state: Is it real/ontic (an objective state of Nature) or epistemic (a state of the observer's knowledge)? In contrast to recent approaches to wave function ontology, that are based on realist models of quantum theory, here we recast the question as a problem of communication between a sender (Bob), who uses interaction-free measurements, and a receiver (Alice), who observes an interference pattern in a Mach-Zehnder set-up. An advantage of our approach is that it allows us to define the concept of "physical", apart from "real". In instances of counterfactual quantum communication, reality is ascribed to the interaction-freely measured wave function (ψ) because Alice deterministically infers Bob's measurement. On the other hand, ψ does not correspond to the physical transmission of a particle because it produced no detection on Bob's apparatus. We therefore conclude that the wave function in this case (and by extension, generally) is real, but not physical. Characteristically for classical phenomena, the reality and physicality of objects are equivalent, whereas for quantum phenomena, the former is strictly weaker. As a concrete application of this idea, the nonphysical reality of the wavefunction is shown to be the basic nonclassical phenomenon that underlies the security of CQC.

https://arxiv.org/abs/1311.7127

A test later confirmed this and transferred information between points A and points B without a physical particle. An interesting question to answer next is can this transmission of information on the phase part of the wave function occur faster than light.

Direct counterfactual communication via quantum Zeno effect

Significance

Recent theoretical studies have shown that quantum mechanics allows counterfactual communication, even without actual transmission of physical particles, which raised a heated debate on its interpretation. Although several papers have been published on the theoretical aspects of the subject, a faithful experimental demonstration is missing. Here, by using the quantum Zeno effect and a single-photon source, direct communication without carrier particle transmission is implemented successfully. We experimentally demonstrate the feasibility of direct counterfactual communication with the current technique. The results of our work can help deepen the understanding of quantum mechanics. Furthermore, our experimental scheme is applicable to other quantum technologies, such as imaging and state preparation.

Abstract

Intuition from our everyday lives gives rise to the belief that information exchanged between remote parties is carried by physical particles. Surprisingly, in a recent theoretical study [Salih H, Li ZH, Al-Amri M, Zubairy MS (2013) Phys Rev Lett 110:170502], quantum mechanics was found to allow for communication, even without the actual transmission of physical particles. From the viewpoint of communication, this mystery stems from a (nonintuitive) fundamental concept in quantum mechanics—wave-particle duality. All particles can be described fully by wave functions. To determine whether light appears in a channel, one refers to the amplitude of its wave function. However, in counterfactual communication, information is carried by the phase part of the wave function. Using a single-photon source, we experimentally demonstrate the counterfactual communication and successfully transfer a monochrome bitmap from one location to another by using a nested version of the quantum Zeno effect.

https://www.pnas.org/content/early/2017/04/19/1614560114

So, in the case of Wigner's Friend, in the lab, he can collapse his wave function so to speak when he carries out a measurement. Wigner outside of the lab can look at the same particle and get an interference pattern and come to the conclusion that his friend hasn't carried out a measurement.

If the wave function is just a mathematical tool, why doesn't Wigner and his friend get the same outcome?

Also, Wigner can get an interference pattern unless his friend calls him from the lab and tells him that he carried out a measurement and tells Wigner the result of the measurement. Then Wigner no longer gets an interference pattern. It's like there's Bayesian updating of Wigner's wave function. Before this updating, Wigner can get alternative facts so to speak.

Can Wigner get alternative laws of physics? I would say no but if all is quantum as many Physicist believe, then you can have these things play out on a classical level where two humans may measure different outcomes for the same event and the two humans may believe their measurement is the true reality until there's Bayesian updating of the wave function. As Frauchiger and Renner pointed out, if this is the case, it would happen on a smaller scale yet still be noticeable.

 

[Demystifier]

The wave-function is real but nonphysical

If that statement can be made precise, it seems very interesting. I will study the paper.