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** FILE ** In an archival photo, Danish Atomic Scientist Niels Bohr discusses an equation at the University of Princeton, New Jersey, on March 21, 1950. Danish scientist Niels Bohr received the Nobel Prize in Physics in 1922 and his son Aage Bohr with American Ben Mottelson in 1974. (AP Photo / Alan Richard)
The pioneering quantum physicist Niels Bohr was a kind of quote machine, with many comments on the philosophical underpinnings of quantum physics that are cited whenever the theory comes up. Unfortunately, many of these quotes turn out to be a bit empty when you try to understand them and attach them to any sort of concrete meaning. One of the few that is good, it is "As it is wonderful that we have encountered a paradox.Now we have a hope to progress."
I say this largely because, as I often say here too often, I am an experimenter and, in my opinion, the emergence of a paradox is a good sign, because a paradox is by definition a situation where two lines the reasoning leads to mutually contradictory results. And since, as far as we know, there is only one real physical reality, it suggests the possibility of an experiment to determine which of them is correct and to progress. (It is possible that Bohr wanted to say something else, because, as stated above, it was (in) notoriously obscure.It's my interpretation, and that's my blog, so we're going to run with it.)
There has been a lot of buzz this week about a new article presenting a thought experiment that "breaks the quantum mechanics", in the panting terms of the lead authors of Nature and American scientist. The description of this gives the impression of a useful paradox in the above sense, so this might indicate some progress in the field.
Daniela Frauchiger and Renato Renner, from the Swiss Federal Institute of Technology in Zurich (Einstein's alma mater), entitled "Quantum theory can not systematically describe self-use," triggered all this excitement. Most reports on this subject reach levels of darkness close to Bohr-ian with regards to what is happening, so I went to the source (you can get a pdf preprint of ETH), which the overall implications but at least I have a better idea of what is happening in the experiment.
The basic scenario is an extension of the famous variant of "Wigner's friend" of the Schrödinger cat thought experiment. Wigner imagined a scientist who was looking at boxed cat in a sealed laboratory, and asked what a friend of this scientist should consider as the laboratory's quantum state before hearing the result of the experiment. It was mostly in the service of the somewhat sinister idea that consciousness plays a role in quantum physics, but the question of which agents perceive an experiment remains somewhat interesting even though most physicists have assigned a special role for human observers (or felines). .
The paper is a blizzard of confusing notation, but I will try to convey it to something like the traditional Alice and Bob phrasing common in quantum entanglement experiments. Alice prepares a quantum particle in her lab that is twice as likely to kill the cat, and a third chance to keep her alive (the paper confusingly uses "heads" and "tails" for these, but I am a dog, so I'll go back to Schrödinger's roots). If the cat lives, she sends Bob, in the other lab, a particle in a defined slowdown state; if the cat dies, she sends Bob a particle that has a 50% chance of being cast. Bob does a spin-down vs. spin-down measurement on the particle, which creates a complex state of entanglement of Bob's mental state, Alice's mental state and of the condition of the cat.
Meanwhile, outside of Alice's lab, her friend Ted is making a complicated move that has a 50% chance to return "OK" if Alice has detected a dead cat. And outside of Bob's lab, his friend Carol does the same measurement about measuring the particle that Alice sent her, again with a 50% chance of returning "OK" if Bob had measured the particle in its initial state. If Carol and Ted get "OK" measurements, the experience is interrupted, the doors are opened and everyone compares the results.
Perhaps the paradoxical aspect here concerns the conclusions that different people involved could draw from the cat's condition. The precise combination of the imbalance imbalance probability, the ambiguous spin state sent by Alice, and the ambiguous measurements made by Ted and Carol creates a situation in which everyone could reasonably conclude from the rules of quantum mechanics. The result indicates that the cat is dead, but in fact, there is a one in twelve chance that the cat is alive.
What does it accomplish, other than offering cat lovers a slight hope? Well, the authors argue that this result indicates an inconsistency between three philosophical assumptions at work in the schema: the assumption that quantum mechanics is correct, the assumption that any measure leads to a single result and what others will conclude according to quantum mechanics will give coherent results. With regard to the above scheme, the last hypothesis is that Carol and Ted, outside of these labs, can correctly predict what Alice and Bob will conclude based on the measurement results. According to them, it is not possible to interpret quantum mechanics successfully.
Illustration of observers trained in an entangled overlay in multi-world interpretation.Chad Orzel
This paradox makes it possible to distinguish the interpretations in a realizable experience. Unfortunately, it is not very clear. As they point out in the text, most of the major interpretations out there already break one or more of them – Many-Worlds, for example, infallibly allows multiple results, while the new interpretation "QBism" the quantum bayesianism "), the reality depends on the observer.This is probably Easier to explain the result in terms of some of them, but it's not clear to me that going through dozens of cats and finding that a handful of survivors could actually spread all.
There are a lot of things I'm not really sure about, though. On the one hand, since I can go through the calculations to show that the cat lives once in twelve, I'm not sure this is a surprise to our fearless experimenters. It seems that reasoning about the results of quantum mechanics should lead them to the same conclusion: the survival of the cat is unlikely but not impossible.
I also do not understand why everyone is talking about it says that the experiment is not feasible because it requires that Alice and Bob are humans or complex computers. Their role in this system seems pretty mechanical, so I do not know where the complexity comes from.
That said, stories about it include a bunch of quotes from people who are smarter than me and who spend a lot more time thinking about quantum foundations than me. They all seem to think that's very important, so there's probably an angle to what I do not see. Which means that although I am personally tempted to answer the title of this quote with a Betteridge law "No", the real answer is, quite rightly, a Bohr-ian "Maybe?"
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** FILE ** In an archival photo, Danish Atomic Scientist Niels Bohr discusses an equation at the University of Princeton, New Jersey, on March 21, 1950. Danish scientist Niels Bohr received the Nobel Prize in Physics in 1922 and his son Aage Bohr with American Ben Mottelson in 1974. (AP Photo / Alan Richard)
The pioneering quantum physicist Niels Bohr was a kind of quote machine, with many comments on the philosophical underpinnings of quantum physics that are cited whenever the theory comes up. Unfortunately, many of these quotes turn out to be a bit empty when you try to understand them and attach them to any sort of concrete meaning. One of the few that is good, it is "As it is wonderful that we have encountered a paradox.Now we have a hope to progress."
I say this largely because, as I often say here too often, I am an experimenter and, in my opinion, the emergence of a paradox is a good sign, because a paradox is by definition a situation where two lines the reasoning leads to mutually contradictory results. And since, as far as we know, there is only one real physical reality, it suggests the possibility of an experiment to determine which of them is correct and to progress. (It is possible that Bohr wanted to say something else, because, as stated above, it was (in) notoriously obscure.It's my interpretation, and that's my blog, so we're going to run with it.)
There has been a lot of buzz this week about a new article presenting a thought experiment that "breaks the quantum mechanics", in the panting terms of the lead authors of Nature and American scientist. The description of this gives the impression of a useful paradox in the above sense, so this might indicate some progress in the field.
Daniela Frauchiger and Renato Renner, from the Swiss Federal Institute of Technology in Zurich (Einstein's alma mater), entitled "Quantum theory can not systematically describe self-use," triggered all this excitement. Most reports on this subject reach levels of darkness close to Bohr-ian with regards to what is happening, so I went to the source (you can get a pdf preprint of ETH), which the overall implications but at least I have a better idea of what is happening in the experiment.
The basic scenario is an extension of the famous variant of "Wigner's friend" of the Schrödinger cat thought experiment. Wigner imagined a scientist who was looking at boxed cat in a sealed laboratory, and asked what a friend of this scientist should consider as the laboratory's quantum state before hearing the result of the experiment. It was mostly in the service of the somewhat sinister idea that consciousness plays a role in quantum physics, but the question of which agents perceive an experiment remains somewhat interesting even though most physicists have assigned a special role for human observers (or felines). .
The paper is a blizzard of confusing notation, but I will try to convey it to something like the traditional Alice and Bob phrasing common in quantum entanglement experiments. Alice prepares a quantum particle in her lab that is twice as likely to kill the cat, and a third chance to keep her alive (the paper confusingly uses "heads" and "tails" for these, but I am a dog, so I'll go back to Schrödinger's roots). If the cat lives, she sends Bob, in the other lab, a particle in a defined slowdown state; if the cat dies, she sends Bob a particle that has a 50% chance of being cast. Bob does a spin-down vs. spin-down measurement on the particle, which creates a complex state of entanglement of Bob's mental state, Alice's mental state and of the condition of the cat.
Meanwhile, outside of Alice's lab, her friend Ted is making a complicated move that has a 50% chance to return "OK" if Alice has detected a dead cat. And outside of Bob's lab, his friend Carol does the same measurement about measuring the particle that Alice sent her, again with a 50% chance of returning "OK" if Bob had measured the particle in its initial state. If Carol and Ted get "OK" measurements, the experience is interrupted, the doors are opened and everyone compares the results.
Perhaps the paradoxical aspect here concerns the conclusions that different people involved could draw from the cat's condition. The precise combination of the imbalance imbalance probability, the ambiguous spin state sent by Alice, and the ambiguous measurements made by Ted and Carol creates a situation in which everyone could reasonably conclude from the rules of quantum mechanics. The result indicates that the cat is dead, but in fact, there is a one in twelve chance that the cat is alive.
What does it accomplish, other than offering cat lovers a slight hope? Well, the authors argue that this result indicates an incompatibility between three philosophical hypotheses at work in the scheme: the hypothesis that quantum mechanics is correct, the hypothesis that any measure leads to a single result, and the hypothesis that which to use quantum mechanics to reason what others will conclude according to quantum mechanics will give coherent results. With regard to the above scheme, the last hypothesis is that Carol and Ted, outside of these labs, can correctly predict what Alice and Bob will conclude based on the measurement results. According to them, it is not possible to interpret quantum mechanics successfully.
Illustration of observers trained in an entangled overlay in multi-world interpretation.Chad Orzel
This paradox makes it possible to distinguish the interpretations in a realizable experience. Unfortunately, it is not very clear. As they point out in the text, most of the major interpretations out there already break one or more of them – Many-Worlds, for example, infallibly allows multiple results, while the new interpretation "QBism" the quantum bayesianism "), the reality depends on the observer.This is probably Easier to explain the result in terms of some of them, but it's not clear to me that going through dozens of cats and finding that a handful of survivors could actually spread all.
There are a lot of things I'm not really sure about, though. On the one hand, since I can go through the calculations to show that the cat lives once in twelve, I'm not sure this is a surprise to our fearless experimenters. It seems that reasoning about the results of quantum mechanics should lead them to the same conclusion: the survival of the cat is unlikely but not impossible.
I also do not understand why everyone is talking about it says that the experiment is not feasible because it requires that Alice and Bob are humans or complex computers. Their role in this system seems pretty mechanical, so I do not know where the complexity comes from.
That said, stories about it include a bunch of quotes from people who are smarter than me and who spend a lot more time thinking about quantum foundations than me. They all seem to think that's very important, so there's probably an angle to what I do not see. Which means that although I am personally tempted to answer the title of this quote with a Betteridge law "No", the real answer is, quite rightly, a Bohr-ian "Maybe?"
