Can Wigner's friend lie?

[Neoholographic]

I think this is an interesting thought experiment. It's a variation of the Wigner's friend experiment which could go down as one of the most important thought experiments in science. There's been a lot of papers on Wigner's friend lately. I think it supports the consciousness or awareness of the observer in QM is needed to fully explain quantum mechanics.

Quote

 

A thought experiment ask, is Quantum Awareness fundamental to the universe?

Orch Or and other theories of consciousness need to be looked at with an open mind. In this article, I want to talk about a thought experiment that I came up with called, Can Wigner’s Friend Lie? This thought experiment is a twist on the Wigner’s friend thought experiment by Nobel prize winning Physicist Eugene Wigner. Wigner’s friend says, his friend in a laboratory carries out a quantum measurement on a system like an electron or photon. In this case, he’s performing a polarization measurement on a photon and he will observe if the photon is in vertical or horizontal polarization. He carries out the measurement and writes down in his notebook that he measured vertical polarization of the photon at 1 PM. In the lab, Wigner’s friend has caused the wave function to “collapse.” For Wigner outside of the lab, it’s a different story. Wigner can look at the photon and a record of his friend’s measurement and do an interference measurement and measure interference. Wigner can conclude that his friend didn’t carry out a measurement in the lab and the wave function Wigner measures is in superposition according to the linearity of the quantum mechanical equations. So the laboratory is in a superposition that includes Wigner’s friend who measured verticlal polarization and Wigner’s friend who measured horizontal polarization. Wigner’s wave function didn’t collapse although the wave function for his friend in the lab clearly collapsed and he has written down a record of this result. Wigner can only carry out an interference measurement and measure interference as long as he doesn’t have any knowledge and isn’t conscious of his friend’s measurement. If his friend calls and says,”Hey Wigner, I measured vertical polarization.” Wigner can no longer measure interference. How is the quantum system aware of what Wigner knows or doesn’t know about it’s state?

 

Quote

I have a strong QA postulate and a weak QA postulate. A weak QA postulate says this Quantum Awareness becomes more dynamic when it interacts with human brains. It becomes self awareness. A strong QA postulate would be a more robust Quantum Awareness that may be more self aware than we are. We can test this by a thought experiment I call,”Can Wigner’s Friend Lie?” It would essentially be the same set up as the Wigner’s friend experiments, but Wigner’s friend would call Wigner and say,”Hey Wigner, I measured horizontal polarization.” Wigner’s friend actually measures vertical polarization and the question is, can Wigner still measure interference when his friend lies to him about the results of his measurement? We already know that Wigner can’t measure interference once he has knowledge of his friend’s measurement. The question is, is this Quantum Awareness so robust that it even knows when Wigner is being lied to and he actually doesn’t have knowledge of the state of a quantum system even when Wigner doesn’t know he’s being lied to?

https://hwimberlyjr.medium.com/can-wigners-friend-lie-c3fabeaa7bbc

This would be an interesting experiment. If Wigner's friend calls and tells Wigner the truth about what was measured and the Wigner can't carry out an interference measurement, then the friend calls him and lies about the measurement and Wigner can still carry out an interference measurement, that would be huge. You would have to connect the wave function to the knowledge of an observer and what an observer knows or doesn't know about it's state.

Here's some more recent Wigner friend studies:

Experimental test of local observer independence

Quote

The scientific method relies on facts, established through repeated measurements and agreed upon universally, independently of who observed them. In quantum mechanics the objectivity of observations is not so clear, most markedly exposed in Wigner’s eponymous thought experiment where two observers can experience seemingly different realities. The question whether the observers’ narratives can be reconciled has only recently been made accessible to empirical investigation, through recent no-go theorems that construct an extended Wigner’s friend scenario with four observers. In a state-of-the-art six-photon experiment, we realize this extended Wigner’s friend scenario, experimentally violating the associated Bell-type inequality by five standard deviations. If one holds fast to the assumptions of locality and free choice, this result implies that quantum theory should be interpreted in an observer-dependent way.

https://advances.sciencemag.org/content/5/9/eaaw9832

Quantum erasing the memory of Wigner's friend

Quote

The Wigner's friend paradox concerns one of the most puzzling concepts of quantum mechanics: the consistent description of multiple nested observers. Recently, a variation of Wigner's gedankenexperiment, introduced by Frauchiger and Renner, has lead to new debates about the self-consistency of quantum mechanics. We propose a simple single-photon interferometric setup implementing their scenario, and use our reformulation to shed a new light on the assumptions leading to their paradox. From our description, we argue 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 by Wigner's subsequent measurements. The first context may be seen as the quantum erasure of the memory of Wigner's friend. We further show these properties are associated with observables which do not commute, and therefore cannot take well-defined values simultaneously. Consequently, the three contradictory properties never hold simultaneously.

https://arxiv.org/abs/2009.09905

Wigner's friend is destroying the notion of materialism once again and posing serious questions about the role of the observer, consciousness and is there really an objective reality. 

Edited December 20, 2020 by Neoholographic

[Halc]

4 hours ago, Neoholographic said:

If Wigner's friend calls and tells Wigner the truth about what was measured and the Wigner can't carry out an interference measurement, then the friend calls him and lies about the measurement and Wigner can still carry out an interference measurement, that would be huge. 

That would indeed be huge, but it doesn't happen. If the friend is capable of calling Wigner, Wigner is effectively in the lab.  Decoherence has taken place.  Wigner cannot measure interference anymore as the wave function has collapsed. This has nothing to do with what the friend writes or says.

Quote

[Wigner’s friend] carries out the measurement and writes down in his notebook that he measured vertical polarization of the photon at 1 PM. In the lab, Wigner’s friend has caused the wave function to “collapse.” For Wigner outside of the lab, it’s a different story. Wigner can look at the photon and a record of his friend’s measurement and do an interference measurement and measure interference.

This cannot be. If Wigner can measure the system, the lab is not a contained system (not a Schrodinger’s box) and the wave function of the photon is collapsed already due to it already having been measured by the friend. Wigner doesn’t know the result of that measurement (a classic epistemological state), but the photon is not in superposition relative to Wigner.

If the lab is a perfect box (zero information coming out), then Wigner has nothing to measure.

The friend can lie all he wants. It will have no effect on the outcome of any experiment unless Wigner bases his decisions (what to measure) on the information from the friend.

 

Edited December 20, 2020 by Halc

[Neoholographic]

2 hours ago, Halc said:

That would indeed be huge, but it doesn't happen. If the friend is capable of calling Wigner, Wigner is effectively in the lab.  Decoherence has taken place.  Wigner cannot measure interference anymore as the wave function has collapsed. This has nothing to do with what the friend writes or says.

This cannot be. If Wigner can measure the system, the lab is not a contained system (not a Schrodinger’s box) and the wave function of the photon is collapsed already due to it already having been measured by the friend. Wigner doesn’t know the result of that measurement (a classic epistemological state), but the photon is not in superposition relative to Wigner.

If the lab is a perfect box (zero information coming out), then Wigner has nothing to measure.

The friend can lie all he wants. It will have no effect on the outcome of any experiment unless Wigner bases his decisions (what to measure) on the information from the friend.

 

Have you read the recent Wigner friend's experiments? There's no evidence of a universal collapse of the wave function. In fact, collapse may not occur at all and Wigner's friend in the lab has just become a part of the S+O system as Rovelli says in his Relational quantum mechanics.

All physical interactions are, at bottom, quantum interactions, and must ultimately be governed by the same rules. Thus, an interaction between two particles does not, in RQM, differ fundamentally from an interaction between a particle and some "apparatus". There is no true wave collapse, in the sense in which it occurs in the Copenhagen interpretation.

 

Because "state" is expressed in RQM as the correlation between two systems, there can be no meaning to "self-measurement". If observer O measures system S, S's "state" is represented as a correlation between O and S. O itself cannot say anything with respect to its own "state", because its own "state" is defined only relative to another observer, O'. If the S+O compound system does not interact with any other systems, then it will possess a clearly defined state relative to O'. However, because O's measurement of S breaks its unitary evolution with respect to O, O will not be able to give a full description of the S+O system (since it can only speak of the correlation between S and itself, not its own behaviour). A complete description of the (S+O)+O' system can only be given by a further, external observer, and so forth.

 

Taking the model system discussed above, if O' has full information on the S+O system, it will know the Hamiltonians of both S and O, including the interaction Hamiltonian. Thus, the system will evolve entirely unitarily (without any form of collapse) relative to O', if O measures S. The only reason that O will perceive a "collapse" is because O has incomplete information on the system (specifically, O does not know its own Hamiltonian, and the interaction Hamiltonian for the measurement).

https://en.wikipedia.org/wiki/Relational_quantum_mechanics

This is exactly what we see in the recent Wigner's friend experiments. The wave function "collapses" for Wigner's friend in the lab which is his fram of reference but it doesn't collapse for Wigner oustide of the lab. Wigner can still measure interference between his friend's record of what he measured and the photon that was measured. Here's some highlights from the paper.

Quote

Wigner can now perform an interference experiment in an entangled basis containing the states of Eq. 1 to verify that the photon and his friend’s record are indeed in a superposition—a fact from his point of view. From this fact, Wigner concludes that his friend cannot have recorded a definite outcome. Concurrently, however, the friend does always record a definite outcome, which suggests that the original superposition was destroyed and Wigner should not observe any interference. The friend can even tell Wigner that she recorded a definite outcome (without revealing the result), yet Wigner and his friend’s respective descriptions remain unchanged (6). This calls into question the objective status of the facts established by the two observers. Can one reconcile their different records, or are they fundamentally incompatible, so that they cannot be considered objective, observer-independent “facts of the world” (3, 4)?

Again, you're saying what some suspect to be the result but it wasn't. Wigner's friend in the lab did't destroy the superposition when he measured the photon. The friend can even tell Wigner that a recorded outcome occurred without revealing the results and Wigner can still measure interference as I said.

Quote

It was recently shown (4) that this question can be addressed formally, by considering an extension of the Wigner’s friend scenario as follows. Consider a pair of physical systems, shared between two separate laboratories controlled by Alice and Bob, respectively (see Fig. 1C). Inside these laboratories, Alice’s friend and Bob’s friend measure their respective system nondestructively and record the outcomes in some memory. Outside these laboratories, in each run of the experiment, Alice and Bob can choose to either measure the state of their friend’s record—i.e., to attest the facts established by their friend, and whose results define the random variables A₀ (for Alice’s friend) and B₀ (for Bob’s friend), or to jointly measure the friend’s record and the system held by the friend—to establish their own facts, defining variables A₁ (for Alice) and B₁ (for Bob). After comparing their results, Alice and Bob can estimate the probability distributions P(A_x, B_y) for all four combinations of x, y = 0,1. As in the original Wigner’s friend Gedankenexperiment, the facts A₁, B₁ attributed to Alice and Bob and A₀, B₀ attributed to their friends’ measurements may be inconsistent.

Again, there's no universal collapse of the wave function. This supports Rovelli and RQM which says these things are observer dependent. So "collapse" happens in Wigner's friend's reference frame but not for Wigner until he has knowledge of his friend's result. This is also in line with the quantum eraser delayed choice experiment and entanglement swapping experiments. This is exactly what happened when they carried out the experiment.

Quote

The observables A₀ and B₀ directly unveil the records established by Alice’s and Bob’s friend, respectively. The observables A₁ and B₁, on the other hand, correspond to Alice’s and Bob’s joint measurements on their friend’s photon and record, and define their own facts in the same way as Wigner in the original thought experiment confirms his entangled state assignment.

All of these quotes are taken from the published paper Experimental test of local observer independence: https://advances.sciencemag.org/content/5/9/eaaw9832

If decoherence occurred and some universal collapse independent of the observer, then they shouldn't be able to measure interference. This supports Quantum Awareness. The only thing that collapses the wave function for Wigner is when he gains knowledge about the outcome of his friends measurement in the lab. It would be more profound if his friend lied to Wigner about the result of his measurement and then Wigner can still measure interference. How is the system aware Wigner is being lied to when Wigner isn't aware of it? 

Edited December 20, 2020 by Neoholographic

[Halc]

There's no evidence of a universal collapse of the wave function.

Agree. You say this like I said otherwise. Anyway, it is also arguable that there’s no evidence against it either.

In fact, collapse may not occur at all and Wigner's friend in the lab has just become a part of the S+O system as Rovelli says in his Relational quantum mechanics.

MWI doesn’t conclude collapse at all. RQM does, per your quoted bits. Collapse is a relation under RQM.

I favor the RQM interpretation, so I’ll likely not give much argument to Rovelli unless he starts claiming he has some kind of evidence against the others.

This is exactly what we see in the recent Wigner's friend experiments. The wave function "collapses" for Wigner's friend in the lab which is his fram of reference but it doesn't collapse for Wigner oustide of the lab. Wigner can still measure interference between his friend's record of what he measured and the photon that was measured. Here's some highlights from the paper.

It would have been appropriate to include a description (and not just the diagram) of the experiment along with all these highlights you chose.

Wigner's friend in the lab did't destroy the superposition when he measured the photon.

Is this still going on about RQM? Because if so, there is no ‘the superposition’ to destroy or not. Your statement seems biased towards some interpretation other than RQM, in which case I’m not sure why you brought up RQM in which superposition is relational.

Also, I love how Alice, Bob and the friends are depicted as human observers while in the experiment performed, no humans were involved. The symbol just seems to be placed wherever a measurement is taken/recorded by some piece of apparatus, which seem to be these single-photon detector things.

Again, there's no universal collapse of the wave function. This supports Rovelli and RQM which says these things are observer dependent.

It would seem that any interpretation that predicts a different measured outcome would be falsified then. So there’s nothing special about RQM in this respect. Calling something a universal collapse or not is an interpretational assessment. One cannot measure such a thing directly. Copenhagen would simply say that the friends are on the wrong side of the Heisenberg cut, and thus did not cause the universal collapse like the external observers do.

So "collapse" happens in Wigner's friend's reference frame but not for Wigner until he has knowledge of his friend's result.

If decoherence occurred and some universal collapse independent of the observer, then they shouldn't be able to measure interference.

Under RQM, collapse happens Wigner becomes correlated with the friend (when decoherence occurs). This may happen whether or not he actually gains knowledge of the measurement result or not. This is why humans are not involved in the experiments since there is no practical way to prevent such correlation. Same with the cat in the box.

It would be more profound if his friend lied to Wigner about the result of his measurement and then Wigner can still measure interference.

If you set up the device to not actually base its signal to the outside to be based on the measurement result, then yes, interference (superposition) can still be measured. If it is simply a lie (always invert the result), then Wigner is correlated with the result and will not measure superposition. Wigner will have incorrect knowledge of the result but will know that superposition is gone.

 

Edited December 21, 2020 by Halc