12 ms·

A Twist on Schrödinger's Cat Paradox

114 points by mathgenius 6y ago

rbanffy 6y ago
I find the concept of consciousness applied here a bit disturbing. Shouldn't we treat the observation as information leaving the observed system and propagating causal effects to other systems? A data recorder is not conscious, but notes information that passes through it and, therefore, observes a single state instead of a superposition.
- __s 6y ago
  Yep, this is why quantum computers have to be kept at very low temperatures as opposed to asking everyone to look away from the computer while it operates
  - _def 6y ago
    What does a very low temperature accomplish in that context?
    - playeren 6y ago
      A set up for a punchline.
    - IncRnd 6y ago
      It accomplishes the quantum Ha Ha.
    - jtsiskin 6y ago
      Minimize particles bumping in to each other
    - rbanffy 6y ago
      Privacy.
- pdonis 6y ago
  > I find the concept of consciousness applied here a bit disturbing It's not just disturbing, it's going way, way beyond what the actual experiment tested. Articles like this (and even the underlying papers describing experiments like this) talk as if we are doing Wigner's friend type experiments involving actual humans. In fact the systems being experimented on are qubits, and the detectors are very simple detectors. The technical achievements involved in these experiments are certainly impressive, and experimenters should certainly continue pursuing these things, but the philosophical implications being claimed are IMO vastly overstated.
- Lichtso 6y ago
  I agree, however you have to keep in mind that the Copenhagen interpretation [1] was invented before Vitalism [2] was debunked. So it is not too surprising that it also has this idea of a fundamental difference between the rules guiding living (including conscious) and dead matter at its core. My usual argument against it is the mediocrity principle [3], we humans often fail to accept the insignificance of our existence. Thus, we tend to prefer theories which tell us that we are special. Just like the idea that we are able to trigger the collapse of the wave-function and the superposition, but a cat is not. 1: https://en.wikipedia.org/wiki/Copenhagen_interpretation https://en.wikipedia.org/wiki/Copenhagen_interpretation 2: https://en.wikipedia.org/wiki/Vitalism https://en.wikipedia.org/wiki/Vitalism 3: https://en.wikipedia.org/wiki/Mediocrity_principle https://en.wikipedia.org/wiki/Mediocrity_principle
  - missblit 6y ago
    Does the copenhagen interpretation actually require the observer to be conscious rather than, say, a macroscopic measuring instrument? Indeed the wiki article you link to says: > Although the Copenhagen interpretation is often confused with the idea that consciousness causes collapse, it defines an "observer" merely as that which collapses the wave function. Which seems like a very practical, albeit obviously incomplete, approach to take.
- elektropionir 6y ago
  Consciousness comes indirectly into quantum mechanics through the measurement postulate. You have to assume something special about measurement which breaks unitarity. Not all physicist are convinced, but it is the traditional way quantum mechanics is taught (all of the "transition probabilities" are really measurement probabilities). The problem is that you can't tell if your apparatus caused the collapse or if it was you that measured the apparatus that then caused the collapse. And because you can only know that something was "observed" when a conscious physicist makes that final readout you end up with a solipsistic situation where the only thing you can be certain of is that it was that last conscious observer that could have for sure collapsed the wave function. It could be that the collapse happened in the apparatus itself but as far as I know you have no way of telling the difference between it projecting the wave function of the measured system or you projecting the wave function of the apparatus into a pointer state. Basically consciousness sneaks in through the fact that there is no definition of what constitutes a measurement - what makes one physical process a measurement as opposed to all others that are unitary and the only thing you are certain of is that final "conscious" readout should count as measurement.
  - brummm 6y ago
    This is misleading at best. A measurement has nothing to do with a conscious observer taking the measurement. An automated experiment that could note down the result of an experiment would note down the result without any conscious observer having to check in and the result would be the exact same.
    - elektropionir 6y ago
      How do you know it would be the same? That's an assumption. The measurement problem is a problem because quantum mechanics postulates two types of processes "normal" unitary evolution and "measurements" that project out the wave function into eigenstates of the measured operator. This is obviously inconsistent since there is no definition, formal or operational of what process is a measurement and what process isn't a measurement. How do you know that your measurement apparatus isn't just evolving unitarily (which is what you would expect if it was a "normal" system) until someone looks at it to read out the results. Consciousness enters only in the fact that for anyone to know what happened to the experiment someone has to do the readout (otherwise you're just writing equations). At the point of readout you can't tell who or what did the collapse.
- brummm 6y ago
  It's a huge issue that observer is interpreted to be something like a person. An observation is a certain kind of interaction that causes the quantum state to collapse. It has nothing to do with consciousness.
  - jbay808 6y ago
    In what sort of physical system does this interaction occur? Can you make an observer out of carefully arranged doped silicon? How does it manage to trigger a collapse rather than ending up in a superposition itself?
- klmadfejno 6y ago
  I'm not well informed on this, and I don't think consciousness is relevant here so by all means I hope someone corrects me. But I'm not sure it's that simple. As I understand it, you can have something set up to measure a property like momentum, then obfuscate it, and the eventual outcome will be an uncollapsed system. Putting on my baseless assumptions hat, it seems to me the world just behaves as a weighted average of all possible pasts, that reality isn't "branching" into many worlds on measurements so much as just being a giant vector space of electron states that have some discrete gaps in an otherwise continuous space due to precise measurements being made, and that the phenomenon of particle-wave duality is just an artifact of some rounding the universe does under the hood when averaging together these possible pasts to render a given state*, and that any attempt to understand the casuality of the particles will fail because they don't arrive from a single cause, but a space of causes, which we can at best constraint to single points. https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser
boxed 6y ago
I read and skimmed and read and I gave up finding the substance. Can someone summarize?
- refulgentis 6y ago
  honestly, i felt the same way after a good 15-20 minute read - I think it's one of those where you have to read it a few times, leave space in between, and Google as soon as you start getting confused
  - boxed 6y ago
    There's too much filler background too...
monktastic1 6y ago
I haven't read the new paper in enough detail to comment, but also mentioned is the Renner-Frauchiger paper, which Scott Aaronson heartily debunks here: https://www.scottaaronson.com/blog/?p=3975 https://www.scottaaronson.com/blog/?p=3975 The primary error there is one that people can't seem to stop making for some strange reason: if you don't measure a property X, and instead measure a (non-commuting) property Y, you are not free to say what X "would have been," and -- especially egregiously -- to use that to demonstrate a contradiction. There is no "would have been" in QM. Either you measure it or you don't, and even after you do, the value becomes invalid after it evolves or a complementary variable is measured. Secondly, Wigner's friend was not a single particle. Asking what a single particle "experienced" only makes sense if you are a panpsychist (or "panpsychic" as amusingly misspoken in the article). In any case, it has no bearing on the essence of Wigner's question.
- TheOtherHobbes 6y ago
  I think RF is a bit more subtle than that, and I'm not convinced that Scott Aaronson has really "debunked" it. "But clearly, even if no one literally measures Charlie in the {|0〉,|1〉} basis, he’s still there, thinking either the thought corresponding to |0〉 or the thought corresponding to |1. And likewise Diane. Just as much as Alice and Bob, Charlie and Diane both exist even if no one measures them, and they can reason about what they know and what they know that others know. So then we’re free to chain together the “certainties” of Alice, Bob, Charlie, and Diane in order to produce our contradiction." You can't use this argument without also explaining what "thinking" means - because in fact it makes no sense unless you assume consciousness exists as a quantum state which allows a phenomenon called "thinking." And philosophically and practically, that's a very, very large can of wormns. So this ends up in the usual place: it's not obvious how using an idea no one understands - like consciousness - to explain another idea no one understands - like QM - is supposed to solve any of these problems.
  - Strilanc 6y ago
    In order to implement the measurement described in the thought experiment, you basically have to uncompute Charlie's state back to the start of the experiment (to disentangle him from the qubit you want to measure), do the measurement on the single qubit, then recompute Charlie forward. This means that when Charlie is making deductions about the current state of affairs, like "if my qubit is |0> then the other qubit is |+>, that thinking needs to be valid during the computation and during the recomputation. But the conclusions Charlie is making are not correct during the recomputation, e.g. it is no longer the case that if his qubit is |0> then the other qubit is |+> at that time, and as a result the whole argument (based on Charlie's reasoning being valid so that an outside agent can use his conclusions) falls apart. More details: https://algassert.com/post/1904 https://algassert.com/post/1904
peter_d_sherman 6y ago
>"Because the two photons appear to communicate faster than the speed of light — something prohibited by his theories of relativity—this phenomenon deeply troubled Albert Einstein, who dubbed it “spooky action at a distance.” These concerns remained theoretical until the 1960s, when physicist John Bell devised a way to test if reality is truly spooky—or if there could be a more mundane explanation behind the correlations between entangled partners." [...] Such “Bell tests” have since been carried out, with a series of watertight versions performed in 2015, and they have confirmed reality’s spookiness." Logic: If you believe that the Bell Test is correct -- you must equal-and-oppositely believe that the speed of light is NOT the upper limit of speed in the universe, that is, that Faster-Than-Light (FTL) speeds are possible. Conversely, if you believe that speed maxes out with the speed of light, and that nothing can travel faster than the speed of light -- then you equal-and-oppositely believe that the Bell Test is wrong. But, you cannot believe that nothing can travel faster than the speed of light AND that the Bell Test is correct, simultaneously -- as this would result in a logical paradox... (Choose one, but not both at the same time...)
- AnotherGoodName 6y ago
  The trick is to talk in terms of communicating information faster than the speed of light. Both relativity and quantum theories agree that there's no communication of information faster than the speed of light. Two wave-functions collapsing to opposite states lightyears away doesn't actually allow two people to communicate in an FTL way.
  - Lichtso 6y ago
    Exactly, so it becomes a question of the very inner working of the universe itself: How does the universe spontaneously assign the states consistently without communicating and also without assigning the states beforehand. This is precisely why the experiment was proposed, to show this conflict in our understanding of the constraints.
    - 3pt14159 6y ago
      If one bends a piece of paper such that two faces nearly meet then pokes a pin through the page and makes two holes in the page essentially simultaneously from the perspective of the two dimensional beings on the page it appears that the two events happened far apart and that "something must be moving information at faster than the speed of light" when the reality is more complex. That's how I mentally think about entanglement. I doesn't need to operate through the universe as I understand (or operate within) it.
cloudking 6y ago
In Schrodinger's Cat Paradox isn't the cat itself an observer? It has eyes, therefore it would observe the poison and be dead.
- wongarsu 6y ago
  If the cat is an observer, then is the bottle of poison also an observer? Are the cells of the cat? Are the atoms of those cells? What is it that gives the cat observer status? The intent of the thought experiment was to show that the Kopenhagen Interpretation of quantum physics is ridiculous. In the many-worlds interpretation for example there is no paradox, as time goes on more and more worlds exist where the cat died at some point.
  - cloudking 6y ago
    Going off the double slit experiment, it seems the definition of an observer is something that can take in light, interpret and measure it. The examples given are eyes and cameras. (I'm not claiming I understand this, just trying to)
    - Green_man 6y ago
      "observation" isn't important, it's enough interaction to decohere the superposition, or in another sense, entangle it with the environment. A polarization filter could be considered an "observer" in some sense, but I think focusing on observation results in a less clear and truthful understanding of what a measurement is. A polarization filter rather interacts with the light in a strong enough way to force conditional behavior based on its polarization. This results in photos that have a superposition of different polarizations to probabilistically become one of the polarizations, wrt the respective amplitudes of each polarization for that photon.
    - wongarsu 6y ago
      The double slit experiment works with much more than just light. It works just as well with electrons, and even with large molecules (the current record seem to be molecules of 2000 atoms each) [1]. That gives you a pretty wide range of observers under your definition. 1: https://en.wikipedia.org/wiki/Double-slit_experiment#Other_variations https://en.wikipedia.org/wiki/Double-slit_experiment#Other_v...
rdiddly 6y ago
"Does the cat experience superposition?" Questions like these have always seemed to me like mistaking the map for the terrain. Quantum mechanics is a model, an abstraction of reality, trying to cope with uncertainties in reality that our observation & measurement technologies can't really settle. It's interesting but not to be taken quite so literally. Right? I dunno, clearly I'm not a physics expert. But I'm not a music expert either (actually I am but let's pretend), but I know that the sounds that please or impress advanced academic peers/mentors/funders rarely overlap with those that please the rest of the world. The Art and Architecture departments are like that also, and I suspect but can't prove that e.g. Economics, and more to the point, Physics, are too. I probably sound like I'm verging dangerously close to anti-intellectualism here, which I don't really want to do in the current cultural climate, but if anything it's the opposite: We should remember that believing someone implicitly just because they're an intellectual is also anti-intellectual. It's an appeal to authority which is one of the classic logical fallacies. Someone is not necessarily immune to institutional pressures (nor are they even necessarily an honest person) just because they're an intellectual. But you need to conduct your own research or at least a survey of the existing research before you can call yourself even a legitimate skeptic (as opposed to just a troll)! Which is why I'm stopping short of actually saying anything... so hey, my apologies for the time-wastage!
lisper 6y ago
Here are a couple of things that are very rarely explained in QM pedagogy but which are very helpful in understanding Shroedinger's cat: 1. The wave function does not exist in physical space, it exists in configuration space. Configuration space is the same as physical space only in the one very special case of a single non-entangled particle. The intuitions of physical space do not generally carry over into the general case of configuration space. 2. In order to produce interference you have to split up the wave function into two pieces and then bring those pieces back together again with a phase change. But since the wave function exists in configuration space, "bringing it back together again" becomes increasingly difficult as the number of entangled degrees of freedom grows. As a practical matter, it is effectively impossible to do this once the number grows beyond a few hundred (this is why building quantum computers is hard). But an actual macroscopic observer consists of O(10^23) degrees of freedom, and is also entangled with their environment. This is the reason that large systems behave classically and don't exhibit interference. 3. Whether or not a system is in a superposition is not a physical fact about the system, it is a consequence of the measurement you choose to make. A vertically polarized photon (for example) is in a superposition relative to a measurement axis rotated away from the polarization axis. For a more complicated system, the measurement axis, like the wave function itself, is in configuration space. But we can only do measurements in physical space. This is the reason that in order to see interference in an entangled system it is necessary to do multiple physical measurements and look at the correlations between them. Doing those kinds of measurements on actual macroscopic objects is way beyond the current state of the art, and may well be impossible even in principle. But this is the sort of thing that is contemplated in the theory behind these experiments. This is the reason that single particles are used as stand-ins for Wigner's friend.
- taneq 6y ago
  Is physical space an actual thing? Or is it just a statistical interpretation of configuration space?
  - lisper 6y ago
    That is a really good question! The answer is: no one knows. There is at least one serious interpretation of QM that says that the 3-D physical space that we know is just one of many possibilities [1]. [1] https://arxiv.org/abs/1812.06451 https://arxiv.org/abs/1812.06451
toxicFork 6y ago
It's silly to take Schrödinger's Cat literally. It's a convenience to explain states within equations. When you say "the cat is both alive and dead at the same time", you're simply saying "in this equation, do not assume that this variable will be one or zero, calculate the results for both conditions", and the final outcome will possibly be one of these calculated results. The more such variables you have, the more different results you may get.
lostmsu 6y ago
> “The paper is an important philosophical study,” If that line would be in the beginning, I would not have bothered to read the article :/
jungletime 6y ago
I have a pretty basic understanding of this. I think of QM measurement, like trying to find the highest wave in the ocean. At at any moment, there might be some n number of waves that are the highest. But not until the exact moment you measure the answer exists.
bookofjoe 6y ago
https://archive.vn/ycC6W https://archive.vn/ycC6W
Gravityloss 6y ago
The Schrödinger's cat paradox is a joke. Basically every time it's posted in some popular science article, it's a waste of time. The superposition collapses way before the cat is affected, when more than a handful of atoms is concerned, way before the hammer even moves.

114 points by mathgenius 6y ago

I find the concept of consciousness applied here a bit disturbing. Shouldn't we treat the observation as information leaving the observed system and propagating causal effects to other systems? A data recorder is not conscious, but notes information that passes through it and, therefore, observes a single state instead of a superposition.

__s 6y ago
Yep, this is why quantum computers have to be kept at very low temperatures as opposed to asking everyone to look away from the computer while it operates
- _def 6y ago
  What does a very low temperature accomplish in that context?
  - playeren 6y ago
    A set up for a punchline.
  - IncRnd 6y ago
    It accomplishes the quantum Ha Ha.
  - jtsiskin 6y ago
    Minimize particles bumping in to each other
  - rbanffy 6y ago
    Privacy.
pdonis 6y ago
> I find the concept of consciousness applied here a bit disturbing It's not just disturbing, it's going way, way beyond what the actual experiment tested. Articles like this (and even the underlying papers describing experiments like this) talk as if we are doing Wigner's friend type experiments involving actual humans. In fact the systems being experimented on are qubits, and the detectors are very simple detectors. The technical achievements involved in these experiments are certainly impressive, and experimenters should certainly continue pursuing these things, but the philosophical implications being claimed are IMO vastly overstated.
Lichtso 6y ago
I agree, however you have to keep in mind that the Copenhagen interpretation [1] was invented before Vitalism [2] was debunked. So it is not too surprising that it also has this idea of a fundamental difference between the rules guiding living (including conscious) and dead matter at its core. My usual argument against it is the mediocrity principle [3], we humans often fail to accept the insignificance of our existence. Thus, we tend to prefer theories which tell us that we are special. Just like the idea that we are able to trigger the collapse of the wave-function and the superposition, but a cat is not. 1: https://en.wikipedia.org/wiki/Copenhagen_interpretation https://en.wikipedia.org/wiki/Copenhagen_interpretation 2: https://en.wikipedia.org/wiki/Vitalism https://en.wikipedia.org/wiki/Vitalism 3: https://en.wikipedia.org/wiki/Mediocrity_principle https://en.wikipedia.org/wiki/Mediocrity_principle
- missblit 6y ago
  Does the copenhagen interpretation actually require the observer to be conscious rather than, say, a macroscopic measuring instrument? Indeed the wiki article you link to says: > Although the Copenhagen interpretation is often confused with the idea that consciousness causes collapse, it defines an "observer" merely as that which collapses the wave function. Which seems like a very practical, albeit obviously incomplete, approach to take.
elektropionir 6y ago
Consciousness comes indirectly into quantum mechanics through the measurement postulate. You have to assume something special about measurement which breaks unitarity. Not all physicist are convinced, but it is the traditional way quantum mechanics is taught (all of the "transition probabilities" are really measurement probabilities). The problem is that you can't tell if your apparatus caused the collapse or if it was you that measured the apparatus that then caused the collapse. And because you can only know that something was "observed" when a conscious physicist makes that final readout you end up with a solipsistic situation where the only thing you can be certain of is that it was that last conscious observer that could have for sure collapsed the wave function. It could be that the collapse happened in the apparatus itself but as far as I know you have no way of telling the difference between it projecting the wave function of the measured system or you projecting the wave function of the apparatus into a pointer state. Basically consciousness sneaks in through the fact that there is no definition of what constitutes a measurement - what makes one physical process a measurement as opposed to all others that are unitary and the only thing you are certain of is that final "conscious" readout should count as measurement.
- brummm 6y ago
  This is misleading at best. A measurement has nothing to do with a conscious observer taking the measurement. An automated experiment that could note down the result of an experiment would note down the result without any conscious observer having to check in and the result would be the exact same.
  - elektropionir 6y ago
    How do you know it would be the same? That's an assumption. The measurement problem is a problem because quantum mechanics postulates two types of processes "normal" unitary evolution and "measurements" that project out the wave function into eigenstates of the measured operator. This is obviously inconsistent since there is no definition, formal or operational of what process is a measurement and what process isn't a measurement. How do you know that your measurement apparatus isn't just evolving unitarily (which is what you would expect if it was a "normal" system) until someone looks at it to read out the results. Consciousness enters only in the fact that for anyone to know what happened to the experiment someone has to do the readout (otherwise you're just writing equations). At the point of readout you can't tell who or what did the collapse.
brummm 6y ago
It's a huge issue that observer is interpreted to be something like a person. An observation is a certain kind of interaction that causes the quantum state to collapse. It has nothing to do with consciousness.
- jbay808 6y ago
  In what sort of physical system does this interaction occur? Can you make an observer out of carefully arranged doped silicon? How does it manage to trigger a collapse rather than ending up in a superposition itself?
klmadfejno 6y ago
I'm not well informed on this, and I don't think consciousness is relevant here so by all means I hope someone corrects me. But I'm not sure it's that simple. As I understand it, you can have something set up to measure a property like momentum, then obfuscate it, and the eventual outcome will be an uncollapsed system. Putting on my baseless assumptions hat, it seems to me the world just behaves as a weighted average of all possible pasts, that reality isn't "branching" into many worlds on measurements so much as just being a giant vector space of electron states that have some discrete gaps in an otherwise continuous space due to precise measurements being made, and that the phenomenon of particle-wave duality is just an artifact of some rounding the universe does under the hood when averaging together these possible pasts to render a given state*, and that any attempt to understand the casuality of the particles will fail because they don't arrive from a single cause, but a space of causes, which we can at best constraint to single points. https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser

boxed 6y ago

I read and skimmed and read and I gave up finding the substance. Can someone summarize?

refulgentis 6y ago
honestly, i felt the same way after a good 15-20 minute read - I think it's one of those where you have to read it a few times, leave space in between, and Google as soon as you start getting confused
- boxed 6y ago
  There's too much filler background too...

monktastic1 6y ago

I haven't read the new paper in enough detail to comment, but also mentioned is the Renner-Frauchiger paper, which Scott Aaronson heartily debunks here: https://www.scottaaronson.com/blog/?p=3975 https://www.scottaaronson.com/blog/?p=3975 The primary error there is one that people can't seem to stop making for some strange reason: if you don't measure a property X, and instead measure a (non-commuting) property Y, you are not free to say what X "would have been," and -- especially egregiously -- to use that to demonstrate a contradiction. There is no "would have been" in QM. Either you measure it or you don't, and even after you do, the value becomes invalid after it evolves or a complementary variable is measured. Secondly, Wigner's friend was not a single particle. Asking what a single particle "experienced" only makes sense if you are a panpsychist (or "panpsychic" as amusingly misspoken in the article). In any case, it has no bearing on the essence of Wigner's question.

TheOtherHobbes 6y ago
I think RF is a bit more subtle than that, and I'm not convinced that Scott Aaronson has really "debunked" it. "But clearly, even if no one literally measures Charlie in the {|0〉,|1〉} basis, he’s still there, thinking either the thought corresponding to |0〉 or the thought corresponding to |1. And likewise Diane. Just as much as Alice and Bob, Charlie and Diane both exist even if no one measures them, and they can reason about what they know and what they know that others know. So then we’re free to chain together the “certainties” of Alice, Bob, Charlie, and Diane in order to produce our contradiction." You can't use this argument without also explaining what "thinking" means - because in fact it makes no sense unless you assume consciousness exists as a quantum state which allows a phenomenon called "thinking." And philosophically and practically, that's a very, very large can of wormns. So this ends up in the usual place: it's not obvious how using an idea no one understands - like consciousness - to explain another idea no one understands - like QM - is supposed to solve any of these problems.
- Strilanc 6y ago
  In order to implement the measurement described in the thought experiment, you basically have to uncompute Charlie's state back to the start of the experiment (to disentangle him from the qubit you want to measure), do the measurement on the single qubit, then recompute Charlie forward. This means that when Charlie is making deductions about the current state of affairs, like "if my qubit is |0> then the other qubit is |+>, that thinking needs to be valid during the computation and during the recomputation. But the conclusions Charlie is making are not correct during the recomputation, e.g. it is no longer the case that if his qubit is |0> then the other qubit is |+> at that time, and as a result the whole argument (based on Charlie's reasoning being valid so that an outside agent can use his conclusions) falls apart. More details: https://algassert.com/post/1904 https://algassert.com/post/1904

peter_d_sherman 6y ago

>"Because the two photons appear to communicate faster than the speed of light — something prohibited by his theories of relativity—this phenomenon deeply troubled Albert Einstein, who dubbed it “spooky action at a distance.” These concerns remained theoretical until the 1960s, when physicist John Bell devised a way to test if reality is truly spooky—or if there could be a more mundane explanation behind the correlations between entangled partners." [...] Such “Bell tests” have since been carried out, with a series of watertight versions performed in 2015, and they have confirmed reality’s spookiness." Logic: If you believe that the Bell Test is correct -- you must equal-and-oppositely believe that the speed of light is NOT the upper limit of speed in the universe, that is, that Faster-Than-Light (FTL) speeds are possible. Conversely, if you believe that speed maxes out with the speed of light, and that nothing can travel faster than the speed of light -- then you equal-and-oppositely believe that the Bell Test is wrong. But, you cannot believe that nothing can travel faster than the speed of light AND that the Bell Test is correct, simultaneously -- as this would result in a logical paradox... (Choose one, but not both at the same time...)

AnotherGoodName 6y ago
The trick is to talk in terms of communicating information faster than the speed of light. Both relativity and quantum theories agree that there's no communication of information faster than the speed of light. Two wave-functions collapsing to opposite states lightyears away doesn't actually allow two people to communicate in an FTL way.
- Lichtso 6y ago
  Exactly, so it becomes a question of the very inner working of the universe itself: How does the universe spontaneously assign the states consistently without communicating and also without assigning the states beforehand. This is precisely why the experiment was proposed, to show this conflict in our understanding of the constraints.
  - 3pt14159 6y ago
    If one bends a piece of paper such that two faces nearly meet then pokes a pin through the page and makes two holes in the page essentially simultaneously from the perspective of the two dimensional beings on the page it appears that the two events happened far apart and that "something must be moving information at faster than the speed of light" when the reality is more complex. That's how I mentally think about entanglement. I doesn't need to operate through the universe as I understand (or operate within) it.

cloudking 6y ago

In Schrodinger's Cat Paradox isn't the cat itself an observer? It has eyes, therefore it would observe the poison and be dead.

wongarsu 6y ago
If the cat is an observer, then is the bottle of poison also an observer? Are the cells of the cat? Are the atoms of those cells? What is it that gives the cat observer status? The intent of the thought experiment was to show that the Kopenhagen Interpretation of quantum physics is ridiculous. In the many-worlds interpretation for example there is no paradox, as time goes on more and more worlds exist where the cat died at some point.
- cloudking 6y ago
  Going off the double slit experiment, it seems the definition of an observer is something that can take in light, interpret and measure it. The examples given are eyes and cameras. (I'm not claiming I understand this, just trying to)
  - Green_man 6y ago
    "observation" isn't important, it's enough interaction to decohere the superposition, or in another sense, entangle it with the environment. A polarization filter could be considered an "observer" in some sense, but I think focusing on observation results in a less clear and truthful understanding of what a measurement is. A polarization filter rather interacts with the light in a strong enough way to force conditional behavior based on its polarization. This results in photos that have a superposition of different polarizations to probabilistically become one of the polarizations, wrt the respective amplitudes of each polarization for that photon.
  - wongarsu 6y ago
    The double slit experiment works with much more than just light. It works just as well with electrons, and even with large molecules (the current record seem to be molecules of 2000 atoms each) [1]. That gives you a pretty wide range of observers under your definition. 1: https://en.wikipedia.org/wiki/Double-slit_experiment#Other_variations https://en.wikipedia.org/wiki/Double-slit_experiment#Other_v...

rdiddly 6y ago

"Does the cat experience superposition?" Questions like these have always seemed to me like mistaking the map for the terrain. Quantum mechanics is a model, an abstraction of reality, trying to cope with uncertainties in reality that our observation & measurement technologies can't really settle. It's interesting but not to be taken quite so literally. Right? I dunno, clearly I'm not a physics expert. But I'm not a music expert either (actually I am but let's pretend), but I know that the sounds that please or impress advanced academic peers/mentors/funders rarely overlap with those that please the rest of the world. The Art and Architecture departments are like that also, and I suspect but can't prove that e.g. Economics, and more to the point, Physics, are too. I probably sound like I'm verging dangerously close to anti-intellectualism here, which I don't really want to do in the current cultural climate, but if anything it's the opposite: We should remember that believing someone implicitly just because they're an intellectual is also anti-intellectual. It's an appeal to authority which is one of the classic logical fallacies. Someone is not necessarily immune to institutional pressures (nor are they even necessarily an honest person) just because they're an intellectual. But you need to conduct your own research or at least a survey of the existing research before you can call yourself even a legitimate skeptic (as opposed to just a troll)! Which is why I'm stopping short of actually saying anything... so hey, my apologies for the time-wastage!

lisper 6y ago

Here are a couple of things that are very rarely explained in QM pedagogy but which are very helpful in understanding Shroedinger's cat: 1. The wave function does not exist in physical space, it exists in configuration space. Configuration space is the same as physical space only in the one very special case of a single non-entangled particle. The intuitions of physical space do not generally carry over into the general case of configuration space. 2. In order to produce interference you have to split up the wave function into two pieces and then bring those pieces back together again with a phase change. But since the wave function exists in configuration space, "bringing it back together again" becomes increasingly difficult as the number of entangled degrees of freedom grows. As a practical matter, it is effectively impossible to do this once the number grows beyond a few hundred (this is why building quantum computers is hard). But an actual macroscopic observer consists of O(10^23) degrees of freedom, and is also entangled with their environment. This is the reason that large systems behave classically and don't exhibit interference. 3. Whether or not a system is in a superposition is not a physical fact about the system, it is a consequence of the measurement you choose to make. A vertically polarized photon (for example) is in a superposition relative to a measurement axis rotated away from the polarization axis. For a more complicated system, the measurement axis, like the wave function itself, is in configuration space. But we can only do measurements in physical space. This is the reason that in order to see interference in an entangled system it is necessary to do multiple physical measurements and look at the correlations between them. Doing those kinds of measurements on actual macroscopic objects is way beyond the current state of the art, and may well be impossible even in principle. But this is the sort of thing that is contemplated in the theory behind these experiments. This is the reason that single particles are used as stand-ins for Wigner's friend.

taneq 6y ago
Is physical space an actual thing? Or is it just a statistical interpretation of configuration space?
- lisper 6y ago
  That is a really good question! The answer is: no one knows. There is at least one serious interpretation of QM that says that the 3-D physical space that we know is just one of many possibilities [1]. [1] https://arxiv.org/abs/1812.06451 https://arxiv.org/abs/1812.06451

toxicFork 6y ago

It's silly to take Schrödinger's Cat literally. It's a convenience to explain states within equations. When you say "the cat is both alive and dead at the same time", you're simply saying "in this equation, do not assume that this variable will be one or zero, calculate the results for both conditions", and the final outcome will possibly be one of these calculated results. The more such variables you have, the more different results you may get.

lostmsu 6y ago

> “The paper is an important philosophical study,” If that line would be in the beginning, I would not have bothered to read the article :/

jungletime 6y ago

I have a pretty basic understanding of this. I think of QM measurement, like trying to find the highest wave in the ocean. At at any moment, there might be some n number of waves that are the highest. But not until the exact moment you measure the answer exists.

bookofjoe 6y ago

https://archive.vn/ycC6W https://archive.vn/ycC6W

Gravityloss 6y ago

The Schrödinger's cat paradox is a joke. Basically every time it's posted in some popular science article, it's a waste of time. The superposition collapses way before the cat is affected, when more than a handful of atoms is concerned, way before the hammer even moves.