Quantum theory has already withstood quite a few experimental tests and despite this there are some paradoxes in it that are difficult for scientists to answer. Now researchers from Korea present an elaboration of Wigner's Friends Paradox and raise questions about the integrity of the theory and the possibility that it will be able to describe everything
Probably no physical theory exists with such a large amount of experimental confirmations as quantum mechanics. The successful theory has been "proven" again and again for a hundred years in a wide variety of precise experiments, but still the physicists are not really satisfied and see the holes in it. Although the theory admirably explains the tiny world, it fails to explain the world governed by everyday physical laws. When you try to apply the laws of the quantum world to our world, you sometimes get internal contradictions. The ambition of the physicists to try to unify the quantum theory that explains the tiny world with Einstein's theory of relativity that explains the vast world full of stars must begin with the resolution of the paradoxes and an attempt to understand quantum mechanics on its own.
towards huge bodies
How is it possible to combine forces between two teachings that are so different but precise in their delineation? One possibility is to examine and conduct quantum experiments on larger and larger bodies and hope that they will reveal inconsistencies in the experiment. But for this to happen physicists have to work under many restrictive conditions and constraints. Everyday bodies cannot reveal their quantum properties because the wavelength of these bodies is almost non-existent. To "solve" or bypass the limitations, researchers use an idea that Einstein bequeathed to scientists - thought experiments. This is exactly what the researchers from Korea suggested in an article published in Nature Communication. The thought experiment expands the paradox of Wigner's friends - observer A measures the spin of a particle and observer B measures the system containing the spin and the first observer. Observer A cannot know what Observer A measured and this is where the paradox begins. In such a case, observer A can measure a different spin than observer B. The extension that the researchers published in a recently published paper contained more stages and more observers that increase the gap between the measurements.
For clarification we will focus on the question where exactly is the paradox? Well, the paradox is right there in the measurement principle of quantum mechanics. As soon as a quantum system is measured, it "collapses" to the same measured value, that is, its probabilistic property disappears. This means that when we measure it again, we will get the same result. Therefore, if observer B (who is an indirect observer) measures the system that has already been measured, he should receive the same value as observer A, because observer A has already measured the system. Instead it measures an arbitrary value with a probability of half, whether the spin was up or down. How? The question arises when the spin wave function collapsed? Is it in viewer A or viewer B? Where was the system really measured? Wigner tried to explain his paradox with "awareness" (and I will leave the interpretation of this to the curious reader). According to him, the first observer is the one who predetermined the measurement results for all the other observers even before the particle was indirectly measured by them. Here, of course, comes another problem in contradiction to the principle of causality - what comes before what? Cause versus effect? The act of measuring against the measured value? Another paradox that is difficult for us to answer.
It is likely that the curious reader will ask himself whether the second observer who is now measuring a different system that includes the first observer and the spin should not have a different value, is this a new quantum state? Well, here precisely the question arises, what is a measurement? And what is its effect on the environment? This is precisely why the elaborate paradox was presented in the paper as the researchers added more and more secondary observers. If this claim is true, the entire system containing a huge number of secondary observers is in a state of superposition between states until the last one observes. Who is the last one? And if the latter does not "decide", how does this fit with the principle of causality? Is only the latter "aware"? (As Wagner asked, who is the conscious one that collapses the wave function in the system?)
Confusing conclusions
The researcher Renner who wrote the article found that his thought experiment polarized scientists. He was surprised to find that some of his colleagues were really enthusiastic and excited about the article and probably because of the conclusions written in it - the article claims that quantum theory is not as universal as it aspires to be, and in large systems it fails to explain the principle of measurement in our macroscopic world. How do two observers measure two different things? How does a theory that explains so much contain an internal contradiction? Maybe in fact the article contains an error in the calculation? Maybe he is wrong in physics? And maybe there are other options that don't appear here? These days researchers are trying to examine the math of the article and see if there are any errors.
Renner also feels discomfort with this interpretation he wrote in the article and he believes it will be resolved at some point. "When you look to history, paradoxes are resolved from unexpected places" he explains. The theory of relativity, for example, which solved several contradictions in Newton's theory and changed everything we knew about the idea of time.
"Our work now focuses on testing the assumptions, did we make wrong assumptions, who knows? Maybe our paradox is true and it will make us change the perception of space and time again. When we think about our theories again and again, we manage to reveal reality as it is."
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Read the works of the physicist David Bohm.
In the paragraph "Towards enormous bodies", it is written:
".. viewer A cannot know what viewer A is measuring and this is where the paradox begins."
Is this a typo?
Relativistic quantum mechanics is something that has been around for a long time
https://en.m.wikipedia.org/wiki/Relativistic_quantum_mechanics
Hello Nathan,
You are absolutely right. I don't think I mentioned this claim in the article, if so I would be happy for you to mention it and correct it.
There are several more or less successful attempts to combine them (among others the string theory) but there is still no theory that is accepted by consensus.
Noam Chai:
In my opinion, quantum is incompatible with *general* relativity. Quantum with private relativity (relativistic energies/velocities) already exists
Similar to what Gil was able to understand - a system also includes the viewers who are included in it.
If you have understood this, then do not limit your thought and go further, then the overall picture that cannot be generalized will become clear, that is, the entire cosmos - the conscious and the unconscious.
The system includes everything that is near and visible and known, but the system also includes everything that is far and unseen and unknown. Now we will ask whether the nearest has more influence on the behavior and will of the particle, or the wave?
Can it be measured at all?
Is it possible to differentiate between the movement/behavior/desire of the particle or wave while it is under examination and influence compared to its natural state without manipulation or measurement?
Is where the particle/wave allows us to measure a pure measurement?
Is there an influence for the relative who is aware of the test, or maybe someone who is in the system and is not aware of the measurement has an influence as well and is involved in the fact that it exists.
The real thought experiment is on the question of whether in such a system that includes the near and the far
And in addition to the conscious and the unconscious, is there even a point in measuring?
And hence is it possible to create a system or conditions in which the particle will cooperate and allow its measurement "of its own free will"?
In my opinion, the reason that in quantum mechanics it is not possible to predict what the particles will do is because the particles are made of different materials (each particle is made of one of the materials we see physically in nature) and each material has different laws of physics and chemistry
In my opinion, all the problems are solved if we start from the assumption that only the one viewer is in his (private) world and everything else, including other viewers who watched before or after him, are statistics in his world and therefore their viewing does not change anything.
You can add more complex dimensions but I want to keep it simple at this point.
Peace,
First, I don't think there is anything new in the claim about different measurement results of two observers. It seems that this topic was raised by Einstein in a confrontation with Niels Bohr.
Secondly, in the view of quantum mechanics, a system is not only what we define as a system, but the system is the whole of space which also includes the external observer. See Afka Aaronov-Bohm.
Third, it is quite possible that observer A measures one value and observer B measures another value because of the influence of observer A on the system.
Fourth, even if the two observers measure the same system they can measure different values when the wave function collapses due to the superposition of states.
Fifth, I think that quantum mechanics is not complete and its development is required to be completed since it talks about the universe as a whole system and in which the factors, observers and observed interact that affect the measured value.
Sixth, when collapsing the wave function one value out of several theoretically possible is measured. Why exactly is this value measured? What leads to his choice and whether it can be predicted is one of the important questions in the theory.
Seventh, referring to the system as a whole, the concept of time must also be included. In this context it is worth looking at what Prof. Yakir Aharonov suggests, the influence not only of the past but also of the future on the present. How this leads to the choice of the measured value, I do not know. The principle of free choice which he claims is not at the basis of living beings but of inanimate objects can change the measured value every time, and again how can this be predicted?
To Michael:
The paradox is found there in the measurement principle of quantum mechanics. Once a quantum system is measured, it collapses to the same measured value. When you measure it again, you will get the same result. Therefore, if observer B, who is an indirect observer, measures the system that has already been measured, he should receive the same value as observer A, because observer A has already measured the system. Instead it measures an arbitrary value with a probability of half, whether the spin was up or down. How? The question arises when the spin wave function collapsed? Is it in viewer A or viewer B? Where was the system really measured? Perhaps observer A predetermined what observer B would see because he was the one who collapsed the wave function and determined the measurement results for other observers? Wigner tried to explain his paradox with "awareness". I'll leave that to you to look for, but according to him the first observer is the one who predetermined the measurement results for all the other observers even before they measured the particle indirectly. Here, of course, comes another problem of causality - what comes before what? Cause versus effect? The act of measuring against the measured value? Another paradox that is difficult for us to answer.
I do not understand…
After all, when F measures the spin, the result in the end is the L system at all, since the very measurement makes it part of the system.
And so when W measures the L system he is actually measuring the L+W+w system, which is already a completely different system from the one that F measured.
And since there are internal interactions, there is a possibility that the measurement of the spin will give a different result between the systems.
So where is the contradiction?
There may be no answer. Everything is controlled by the name.