I Is this a new theory, an enhanced theory or just philosophy?

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ftr

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I get new notification from new scientist usually about some virus or some weird anthropology theory. Once in a while a physics subject and this time I got this "https://www.newscientist.com/article/mg24132220-100-schrodingers-kittens-new-thought-experiment-breaks-quantum-theory/"
Can somebody make sense of it and whether it is saying anything profound. It is perplexing for me that many people are debating exactly what is being measured, then boom all these bright ideas come along. No concrete setup and strange unexplained symbols, I guess if you are from Oxford etc you can do that without being called crackpot. :frown:

a video since the article is behind a paywall.

 
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Quantum theory cannot consistently describe the use of itself

Daniela Frauchiger, Renato Renner

(Submitted on 25 Apr 2016 (v1), last revised 5 Oct 2018 (this version, v2))

Quantum theory provides an extremely accurate description of fundamental processes in physics. It thus seems likely that the theory is applicable beyond the, mostly microscopic, domain in which it has been tested experimentally. Here we propose a Gedankenexperiment to investigate the question whether quantum theory can, in principle, have universal validity.
https://arxiv.org/abs/1604.07422

It is this paper. I will look at it.

At the first glance, I suspect that the authors of the paper have forgotten that the agent F may make an error in her "quantum theoretical analysis of the state". A quantum system is not a deterministic digital computer. We cannot assume that F always performs correct logical steps.
 
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ftr

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I am sorry, I inserted the link to a wrong arxiv.org paper. I have now corrected my first message.

Assumption (C)
Suppose that agent A has established that

Statement A(i): “I am certain that agent A0
, upon reasoning within the same theory as the one I am using, is certain that x = ξ at time t.”

Then agent A can conclude that

Statement A(ii): “I am certain that x = ξ at time t.”
Frauchiger and Renner introduce the assumption C above. But if the agent A0 is inside the quantum mechanical experiment, then how can we say that "A0 is certain"? Everything within the experiment is probabilistic, also the reasoning done by the logic gates inside the head of A0.

The authors seem to think that A0 is a deterministic computer in the style of classical physics.

In the Many Worlds interpretation, there is a branch where the memory of A0 contains "2 + 2 = 4 is true". There is another branch where it contains "2 + 2 = 4 is false". What do Frauchiger and Renner mean when they say that A0 is certain about something? In which branch?
 

ftr

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Thanks, I need to read and see If I can understand, but I am more convinced now that probability interpretation is the root of all these gymnastics like theories. Go TI ( generalized to the geometric probability concept where probability plays a useful role but not fundamental) all this magic disappears.
 

jtbell

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The Frauchiger-Renner paper has been discussed extensively here, e.g.:



 
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The talk is based on this paper: https://arxiv.org/abs/1701.07449

The highly abstract nature of this paper which treats theories as objects themselves and is not per se about objects within theories and then gives a proof of a theorem, and establishes different limits for different principles means that this is essentially a philosophical paper, i.e. de facto a fundamental research paper which happens to be about physical theories.
No concrete setup and strange unexplained symbols, I guess if you are from Oxford etc you can do that without being called crackpot. :frown:
The "strange unexplained symbols" are an alternative diagrammatic notation for mathematics and is widely used in computer science and network theory. John Baez has written extensively on such diagrams in blogs, articles and books.

More well known examples of concrete applications in physics of such diagrams are Feynman diagrams and the Penrose graphical notation for tensor calculus.
 
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https://www.scottaaronson.com/blog/?p=3975
Scott Aaronson thinks that Frauchiger and Renner forget that the measurement which W-overline makes, changes the quantum state of the whole system.

I think we should put W-overline inside the lab of F-overline and treat both as quantum systems rather than "observers". The only observer is W.

The Frauchiger & Renner paradox is so complicated that it is easy to make mistakes at many points. The Physics Forums discussions which are quoted above have found several possible sources of error.
 

vanhees71

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The observer W-overline is not needed. W can do both measurements.

The laboratories L-overline and L are in an entangled state. Measuring L-overline will change the state of L. The reasoning in the paper may overlook this.
 
The Many Worlds interpretation may cast some light on this. If an "observer" inside a quantum test system "measures" that the spin is up, that does imply that the spin is up in all branches of the Many Worlds. It does not cut off the branches where the spin is down.

In the paper of Frauchiger and Renner, in Table 3 they start from an assumption that F-overline has measured a quantum system having the value "tails". They further assume that F measures spin up, z = +1/2.

Then they let various "observers" deduce that w(igner) will measure "fail".

But all the branches of Many Worlds continue to exist. An "observer" inside one branch who measures "tails" cannot assume that he has been able to collapse the wave function so that the other branches were cut off. There is another incarnation of the "observer" in another branch who measured "heads". Neither incarnation may assume that the other one does not exist.

If we assume that F-overline measured "tails", and we cut off all the other branches of Many Worlds, that is equivalent to having an outside observer who measured "tails". Then we can legitimately cut off all the other branches. Then it is a correct deduction that wigner will measure "fail".

Thus the error in the paper is that F-overline applies quantum mechanics in a wrong way. She cannot assume that she is the only incarnation in the network of Many Worlds.

A simpler example of a wrong deduction: let us prepare an electron spin in a superposition of states up and down. Let us keep the electron in a totally isolated box with an "observer" incarnation F. If F "measures" the spin up, does she know that I will measure the spin up when I open the box? Of course not. She may be in the branch which did not "happen" for my measurement.

The authors in Table 4 admit that they do not know if Many Worlds satisfies their axioms.

I wrote about this in my physics blog two days ago. The topic there is Bell's inequality. I claim that no one can assume that he is able to collapse the wave function, because if we prune the network of Many Worlds, then the predictions of quantum mechanics cannot be reproduced - we have removed information which is needed in calculating the future development of the network.
 
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ftr

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The talk is based on this paper: https://arxiv.org/abs/1701.07449

The highly abstract nature of this paper which treats theories as objects themselves and is not per se about objects within theories and then gives a proof of a theorem, and establishes different limits for different principles means that this is essentially a philosophical paper, i.e. de facto a fundamental research paper which happens to be about physical theories.

The "strange unexplained symbols" are an alternative diagrammatic notation for mathematics and is widely used in computer science and network theory. John Baez has written extensively on such diagrams in blogs, articles and books.

More well known examples of concrete applications in physics of such diagrams are Feynman diagrams and the Penrose graphical notation for tensor calculus.
Thanks, today I understood it better than the other day since my brain was overloaded with many scientific and non scientific issues.:frown:

I asked God the other day to grant me an extension one more year to finish some urgent matters, I feel he obliged. I really hate to ask him for four more years with millions brain cells thrown in to understand all this.:cry:


 
I analyzed the Fraulicher & Renner experiment more.

We can combine W-overline and W to a single external observer.

1. The assumption is that the external observer has made a weak measurement "ok" from the first lab.

2. Then it is trivial to show that if the external observer would measure the second lab, he would get z = +1/2.

3. If the external observer after 2 would proceed to measure the first lab precisely, he would trivially get "tails".

The measurement 2 affects the state of the system. The external observer did not make the measurements 2 and 3. If he does not do 2, but does 3, he will sometimes get "heads". No one in the experiment can deduce that the state of the first lab is "tails" if the external observer does not do the measurement 2.

Especially, the incarnation of F-overline who "measures" "tails" in the first lab cannot assume that her other incarnation who measures "heads" does not exist.

Thus, no one in the experiment can deduce that the external observer will weakly measure "fail" from the second lab. There is no paradox.

We could have guessed the resolution. Correct quantum mechanics predicts that sooner or later, the external observer will weakly measure "ok" from both labs. If the observers during that round "deduce" that it is not possible, then the observers are applying quantum mechanics in a wrong way.

Scott Aaronson has this quote on his blog entry:

“Unperformed measurements have no results.” - Asher Peres
 
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ftr

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I analyzed the Fraulicher & Renner experiment more.
I have few unrelated questions if you don't mind.
1. Is Fraulicher & Renner experiment related to the OP paper, if yes how.
2. Does this experiment will be affected if measured values are not eigenvalues based as discussed in TI threads.
3. Does it rule out any interpretations.
4. Can it apply to the continuous as position.
5. are these QM symbols used interpretation independent or not.
Sorry if the questions sort of not very clear.
 
Schrödinger’s cat has just had an upgrade, and if you had a feeling the original was weird, it has nothing on the new one. Instead of placing a cat into an indeterminate state of dead-and-aliveness, a new scenario doing the rounds involves pulling off a similar trick with people who are themselves performing and observing a Schrödinger’s cat-type experiment.
https://www.newscientist.com/article/mg24132220-100-schrodingers-kittens-new-thought-experiment-breaks-quantum-theory/

Has anyone on this forum read the New Scientist story? It is behind a paywall. Is it the Frauchiger & Renner experiment or something else?

UPDATE: Someone on Reddit wrote that it is the Frauchiger & Renner work.
 
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https://www.newscientist.com/article/mg24132220-100-schrodingers-kittens-new-thought-experiment-breaks-quantum-theory/

Has anyone on this forum read the New Scientist story? It is behind a paywall. Is it the Frauchiger & Renner experiment or something else?

UPDATE: Someone on Reddit wrote that it is the Frauchiger & Renner work.
I found the same thing here:

The question is @ftr, where did the following video come from in connection to the article:
a video since the article is behind a paywall.

 
My impression is that 90% of physics news which make headlines in popular media are wrong. The media picks up sensational claims.

It would be a sensation if an observer inside a test box could make a valid quantum mechanical reasoning which has a different result than the reasoning done by an outside observer.

The Frauchiger and Renner experiment uses observers who are bad at quantum physics: the observers make an error in their reasoning.
 

ftr

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The question is @ftr, where did the following video come from in connection to the article:
Since the article is behind a paywall, that was the best next thing I could do, consult uncle google! and arxiv for the authors. Poor kitten she is been in a limbo for a while now. One possible conclusion is to deny superposition because it leads to abject illogical absurdity even for micro-world, I don't think it can even be possible in a magical world.
 
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One possible conclusion is to deny superposition
You can't just wave your hands and "deny superposition". Superposition is a necessary consequence of the linearity of quantum mechanics. Denying it would mean throwing out quantum mechanics and coming up with a new theory from scratch that somehow managed to reproduce all of the successful predictions of QM, but avoided whatever you see as problems. Whatever else can be said about such a prospect, it's way out of scope for a PF discussion.
 

ftr

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Superposition is a necessary consequence of the linearity of quantum mechanics
Misunderstanding again,I am not denying it( can't, it is in the math) I just think it might be possible (or we should look for a way) to reinterpret it to take its "not even magic" away.
 
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Misunderstanding again
Well, you literally used the word "deny". How else are we supposed to interpret that?

I am not denying it
Then saying "deny superposition" was an extremely bad choice of words on your part.

I just think it might be possible (or we should look for a way) to reinterpret it to take its "not even magic" away.
I have no idea what this means.
 

ftr

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I ment its usual interpretation. I will post couple of papers later.
 

ftr

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I have no idea what this means.
What do you think of this write up. He has many papers and highly cited, I will dig for the appropriate ones.
 

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