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Quantum observers with knowledge of quantum mechanics break reality
- sebringj 8y agoThought this might be interesting about many-worlds https://www.hedweb.com/everett/everett.htm#believes https://www.hedweb.com/everett/everett.htm#believes if Feynman and Hawking and others are on board with it. I keep seeing with the string theorists and cosmologists that seem to be the leaders in the field are leaning toward many-worlds as the most sensible explanation. It then makes this article seem less interesting if the majority fall into copenhagen but the ones actually doing the real work are more in the many-worlds camp than not.
- visarga 8y agoIs Hawking still onboard?
- diminoten 8y agoUnfortunately, Hawking passed away in March of this year. :(
- escherplex 8y agoDepends. In an Everett (or Steins;Gate) sense, possibly. In a Bohm sense, probably not. :-) But string modeling has to be tested somehow and here you're dealing with essentially VR spaces and forms supervening on a quantum substrate with inascertainable so-called hidden variables. Probably need better brains to tackle this one.
- sebringj 8y agoRight it becomes not science if it cannot be tested or verified i wonder if quantum computers are helping though in the sense as its a practical use of being in many states at once although not in the macro sense
- sebringj 8y ago:) maybe in spirit? I don't know but that may be a real question in the sense of this. Funny.
- deckar01 8y agoI know they are trying to dumb it down, but I think they are leaving out some fundamental elements of the puzzle here. Bob interprets the message incorrectly sometimes and no reason is offered for why or how often. They say the observers get contradicting answers sometimes, but that revelation seems anticlimactic considering I have no reason the believe Bob's observer should observe outcomes matching Alice's observer any more often than Bob himself can "guess" the result. I might need to dig into the original paper: https://www.nature.com/articles/s41467-018-05739-8 https://www.nature.com/articles/s41467-018-05739-8
- roywiggins 8y agoOn first glance it seems like they're building a sort of Godel sentence- a self-referential experiment that forces things to end up looking contradictory.
- AstralStorm 8y agoIsn't the measurement enough to change the quantum state of the system? What is "got told" in this experiment? Does it involve creating an entangled state? In which way? Otherwise, the story is classical information, which means a measurement must have been done or said story is not tied to quantum state at all. The whole idea sounds like making classical guesses is supposed to somehow affect quantum states in a predictable or any way.
- Severian 8y agoI was thinking something along similar lines. Hawking had a lecture[1] regarding Godel, which indicate incomplete or inconsistent models of systems. What we may think as inconsistent is probably an incomplete model. Or as Hawking addressed in the lecture: " According to the positivist philosophy of science, a physical theory is a mathematical model. So if there are mathematical results that can not be proved, there are physical problems that can not be predicted." [1] http://www.hawking.org.uk/godel-and-the-end-of-physics.html http://www.hawking.org.uk/godel-and-the-end-of-physics.html
- roywiggins 8y agoHold on, what on Earth do they mean by a "quantum message"?
- roywiggins 8y agoAh: "In each round n = 0, 1, 2, … of the experiment, agent F¯¯¯¯ tosses a coin and, depending on the outcome r, polarises a spin particle S in a particular direction. Agent F then measures the vertical polarisation z of S" https://www.nature.com/articles/s41467-018-05739-8 https://www.nature.com/articles/s41467-018-05739-8
- jhanschoo 8y agoIs the point of this so that the whole situation in boxes remain an unobserved quantum state rather than classical?
- scotty79 8y agoI think people trying to interpret quantum mechanics are mislead by saying that probability wave upon observation collapses to precise value that upon next measurement stays exactly the same. That's unrealistic because no measurement is of perfect precission. Next measurement will give slightly different value. So we really can't tell if we have one exact value or still a probability wave just reshaped to very narrow thing by interaction needed to do the measurement. We can make probability wave wider and fuzzier again just by scattering particle we measure of some other unmeasured particle. That's how I understand quantum mechanics wave-particle duality. That there's no duality. There are just waves that interact and reshape each other through that interactions. And the only reason that we think of them sometimes as sort of little billiard balls is because annoyingly equations that govern evolution of narrow and sharp probability waves look (not accidentally) exactly the same as primary school level math that governs billard balls.
- sixo 8y agoIf you make 3 subsequent measurements of different but related variables (like a vector component wrt to 3 different axes) the 3rd's probability distribution will depend on the value you observed in the 2nd observation in a way that cannot be replicated without the 2nd. Meaning it's not just matter of poor precision. See the Stern-gorlach experiment.
- kurthr 8y agoI think the problem he points out is that the measurement (e.g.the polarizer/slit/field) is never perfect. In fact the measurements are also made of materials at finite temperature with quantum effects so the subsequent probabilistic results won't be "exact". Of course you can design the measurements to be exponentially insensitive to those variations. However, when you build a sequence of measurements each exponentially sensitive to that variation you make setting up each individual measurement ever more difficult. It still doesn't prevent the thought experiment.
- Thespian2 8y agoA simple version of this (not the exact experiment) is to take three polarizing filters. Put one down, and see it reduces the amount of light passing through. Put a second one down, in line with the first, then rotate it to 90 degrees off. You will observe the light dim until the second filter is completely dark, blocking all the light which passed the first filter. Finally, take the third filter, and place it between the first two, at 45 degrees off, and suddenly light will pass through all three. This very clearly demonstrates that each filter reshapes the wave's polarization, not to a single orientation, but to a narrow band.
- laretluval 8y agoThis writeup is incomprehensible. Does anyone know of a better one?
- lisper 8y agoI'm working on it (definitely room for improvement there), but the original paper is long and it will probably take me the better part of the day to work through it (and I also have to get some work done). In the meantime, the same conclusion can be reached by a completely different argument: http://www.flownet.com/ron/QM.pdf http://www.flownet.com/ron/QM.pdf Same content in a video: https://www.youtube.com/watch?v=dEaecUuEqfc https://www.youtube.com/watch?v=dEaecUuEqfc UPDATE: Just found this: https://arstechnica.com/science/2018/09/quantum-observers-with-knowledge-of-quantum-mechanics-break-reality/ https://arstechnica.com/science/2018/09/quantum-observers-wi... By way of: https://news.ycombinator.com/item?id=18025438 https://news.ycombinator.com/item?id=18025438
- sctb 8y agoThanks! We've updated this submission to the Ars article from https://www.nature.com/articles/d41586-018-06749-8 https://www.nature.com/articles/d41586-018-06749-8.
- deleted 8y ago[deleted]
- skywhopper 8y agoI found this article impossible to make sense of. But what I did gather reminds me of the simultaneity paradox in relativity where it's possible for different observers of two events to perceive their relative order in time differently. So that observer 1 may see event A happen before event B, observer 2 may see event B happen before event A, and observer 3 may see events A and B happen at the same time.
- romaniv 8y agoThis is different, because relativity can actually be observed directly. Different interpretations of QM cannot.
- rotskoff 8y agoThis write up not only oversimplifies, but it totally neglects one of the more interesting motivations of the original paper [1]. The authors are probing whether or not quantum mechanics is consistent with a single-world interpretation---that is, whether or not there is a unique reality. Formally, the claim is that there is no physical theory that is (1) consistent with QM, (2) consistent with a single-world interpretation, and (3) logically self-consistent. 1. https://arxiv.org/pdf/1604.07422.pdf https://arxiv.org/pdf/1604.07422.pdf
- cs702 8y agoThe paper's title makes the claim succinctly: "Single-world interpretations of quantum theory cannot be self-consistent." Nature's headline does a terrible job at conveying this, really. I would have expected better from the people who edit headlines there.
- deleted 8y ago[deleted]
- phkahler 8y ago>> Formally, the claim is that there is no physical theory that is (1) consistent with QM, (2) consistent with a single-world interpretation, and (3) logically self-consistent. Does pilot wave theory fit the bill?
- nanofortnight 8y agoPilot wave theory (also known as Bohmian mechanics) imposes a single-world interpretation.
- phkahler 8y agoMy understanding is that it meets all 3 criteria. Hence the assertion that there is no theory that meets all 3 would be false.
- GorgeRonde 8y ago> And different researchers tend to draw different conclusions. “Most people claim that the experiment shows that their interpretation is the only one that is correct.” Exactly like in the experiment ... Edit: To be clearer, why not try to explain the way the paper is received with the very material the paper is about ?
- dschuetz 8y agoHere's another write-up of the same subject: https://arstechnica.com/science/2018/09/quantum-observers-with-knowledge-of-quantum-mechanics-break-reality/#p3 https://arstechnica.com/science/2018/09/quantum-observers-wi... "Quantum observers with knowledge of quantum mechanics break reality"
- lostmsu 8y agoThis article's comments section links to reviews of the paper, and, basically, the second reviewer nails it. In one of the outcomes authors examine, which gives the rise to the apparent contradiction, measurements do no commute, which means, according to QM it is impossible to get that set of results in real world.
- lisper 8y agoCan you please post the link to the reviews so we don't have to slog through all the comments?
- yorwba 8y agoThe reviews are here https://static-content.springer.com/esm/art%3A10.1038%2Fs41467-018-05739-8/MediaObjects/41467_2018_5739_MOESM1_ESM.pdf https://static-content.springer.com/esm/art%3A10.1038%2Fs414... The authors' final response to referee #2: We thank the referee for the clarification of their earlier comment, which we indeed misunderstood. It is of course correct that the observable of the measurement leading to z does not commute with the one corresponding to the measurement of w . This also means that the values z and w cannot be defined simultaneously (in the sense of “at the same time”). To explain how our argument avoids this problem, note first that the measurements take place at different times (as pointed out in the reply above). Concretely, z is measured at time n :10 and w is measured at time n :30. Note also that, in all statements we are using, we always explicitly specify the time at which a variable is supposed to have a given value. Whenever we are talking about z , the corresponding time lies (strictly) before n :30, whereas we only talk about what value w has at times after n :30. We hence never need to assume that z and w are available at the same time. To clarify this in the manuscript, we have changed the labelling of all statements. They now have a superscript which indicates at what time a statement has been made by an agent.
- dschuetz 8y agoI don't think that it breaks quantum mechanics. It shows once again that the results of the double slit experiments are still not completely understood. That idea in the article only means that the Copenhagen Interpretation is being challenged. It doesn't make all the discoveries in particle physics collapse.
- program_whiz 8y agoHere's my writeup, this is a first-attempt so please offer constructive criticism if wrong: 2 labs (L1 and L2), these are like the box of shrodingers cat, they are in quantum uncertainty. 2 lab workers (Alice, Jane) 2 outside observers (Bob, Frank) Time is denoted as T0, T1, ... T0 Alice in Lab1 randomly selects heads / tails T1 Alice uses heads / tails to setup a quantum particle S T2 Jane in Lab2 reads the state of S, infers heads / tails and stores this information in a new particle Z T3 Frank reads the state of Lab2 to infer Z, S, heads/tails and determines pass / fail (pass == was heads), lets call this variable W_frank T4 Bob reads the state of Lab1 to infer S, heads / tails, and then makes his own pass / fail (pass == was heads) and that's variable W_bob Since these are separate readings on untangled particles by Bob and Frank, they can get disparate readings W_frank != W_bob This is a problem since we "collapsed" the state of W_frank -> Z -> S -> Coin, but this doesn't necessarily imply that we can known with certainty that W_bob will match (i.e. forward collapsed Coin -> S -> W_bob). Basically its just that each lab is in a quantum uncertainty (Quantum Coin is heads/tails, S is in either state, Z is in either state until measured). And making the measurement should reveal this, but there's no guarantee both collapses will result in the same outcome (so in one case the coin was heads, and the other it was tails). My conclusions: 1. There is no randomness, we just suck at measuring still 2. We are in the "many worlds" but impossible branches can't happen (reality stays consistent somehow) -- so it won't happen even though its theoretically possible 3. The forward collapse does happen, we just haven't done the experiment to verify it. In other words, the pass/fail result would change to keep things consistent (the whole system is entangled). Including the memories everyone would have about it. So maybe this is happening constantly but we just don't know it because it changes even our memories about it. 4. This experiment fractures reality, and we realize we all live in a simulation and that's where "white holes" come from :P
- program_whiz 8y agoSo to clarify one info flow is: Alice: Coin -> S, Jane: Z, Frank: Pass / Fail The other is: Alice: Coin -> S, Bob: Pass / Fail
- kgwgk 8y agoI think their problem is considering that the labs L1 and L2 are isolated quantum systems because there is obvious entanglement through the state S. In the sequence of events that they present at T1 the observer in L1 prepares S, transfers it to L2, and knowing the current state of L2 predicts what the observer outside L2 will measure later assuming that L2 is left unperturbed (the actions of the internal observer do not affect the system). But this prediction is invalid because the protocol specifies that before the last observer enters the scene at T4 the system L1/L2 will be perturbed by another external observer (the observer outside L1 when he does his thing at T3, as you said he's effectively measuring Z).
- jeletonskelly 8y agoOur simulation is written in a functional language using lazy evaluation, obviously. Observing a quantum state forces evaluation and consumes more memory on the machine running our simulation. If we observe too much the beings simulating us are going to kill -9 us.
- martin1975 8y agoI am happy and sad to hear this.
- pantalaimon 8y ago> There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. > There is another theory which states that this has already happened. - Douglas Adams, The Restaurant at the End of the Universe
- Myrmornis 8y ago> (Frauchiger has now left academia.) Tangential: why is that statement in the article?
- kgwgk 8y agoBecause she's no longer at ETHZ and normally they would add her current affiliation.
- AnimalMuppet 8y agoOnce one person has flipped the coin, it seems wrong to me to say that an observer outside the box sees a superposition of heads and tails, simply because the person outside the box doesn't know the result of the flip. I don't think that a human's ignorance is equivalent to a waveform superposition. This is true even if you replace the coin with the results of a quantum random number generator. The problem isn't that the coin is a macroscopic object (and therefore doesn't really do quantum superposition). The problem is that, once observed, there is no uncertainty in the output of the quantum random number generator. There's only human ignorance (for everyone except the one person in the innermost box). And as I understand it, experiment agrees with me. You take an entangled pair of photons, observe one, and you know what the same observation on the other photon will produce, even if the person making the observation on that photon doesn't. It could be that the write-up is creating confusion, or that I am confused, but something feels off here (and not just in a "that's too weird to be true" way).
- juris 8y agoThe tao that can be named is not the real tao.
- leoh 8y agoFrom the original paper: >Analysing the experiment under this presumption, we find that one agent, upon observing a particular measurement outcome, must conclude that another agent has predicted the opposite outcome with certainty. The agents’ conclusions, although all derived within quantum theory, are thus inconsistent. This indicates that quantum theory cannot be extrapolated to complex systems, at least not in a straightforward manner. It really sounds to me that what they're saying is that some phenomena can be described multiple ways. And in particular, it is likely to explain phenomena consistently as X in one setting and Y in another. This seems akin to the concept of two strings (A and B) being hashed to the same value; the creator of the hash had one value (A) and an observer has a rainbow table that believes the value is different (B) and both are right, but the observer is not able to understand the creator's intention. Is this analogy roughly correct? And if so, why is this so darn surprising?
- MrQuincle 8y agoThe original Maxwell daemon experiment didn't work because there was some "work" hidden in the formulation. A few days ago I was reading this https://phys.org/news/2018-09-quantum.html https://phys.org/news/2018-09-quantum.html (didn't get on the frontpage), but it's about the difficulty of disappearing quantum information. As a layman, I can imagine that decoherence plays a similar role in these thought experiments. Maybe perfect transfer of quantum information is impossible. It would be a nice merge of Schrodinger's cat with Maxwell's daemon. :-D