8 ms·

How Schrödinger’s Cat Became Such a Violent Fable

49 points by bilifuduo 10y ago

M_Grey 10y ago
Two deeply unrelated quotes that I find apply here. The first is from a segment on a Christmas special of the British radio comedy panel show, The Unbelievable Truth, and the second is Einstein's. "Schrodinger, philosophic science whiz popped a kitty in his a pretty kitty and says ‘If you open the box, the 'lectric shocks.’ 'Don’t touch the box… the cat is now a paradox.’ 'Both dead and alive is the feline situation’ 'But its status will be changed by the act of observation’ The main thing that we learn from that: Schrodinger did not like cats." -Rufus Hound “[I advocate] that one conceives of the psi-function [i.e., wavefunction] only as an incomplete description of a real state of affairs, where the incompleteness of the description is forced by the fact that observation of the state is only able to grasp part of the real factual situation. Then one can at least escape the singular conception that observation (conceived as an act of consciousness) influences the real physical state of things; the change in the psi-function through observation then does not correspond essentially to the change in a real matter of fact but rather to the alteration in our knowledge of this matter of fact.” -Albert Einstein
- wyager 10y ago
  In said quote, Einstein advocates hidden variable theory, which was disproven. https://en.m.wikipedia.org/wiki/Bell_test_experiments https://en.m.wikipedia.org/wiki/Bell_test_experiments I would strongly advise people who do not have extensive tuition in Quantum Mechanics to refrain from speculating about the consequences of QM. I have been taking QM classes for several years now, and the most valuable thing I've learned is that almost everyone's understanding of QM is based on bad ad-hoc analogies, and it takes years of study to progress to gradually less ad-hoc analogies. Different mathematical models inform different "interpretations" of QM. If you can't tell the difference between a rigged and non-rigged Hilbert space, you certainly don't have enough background to speculate on classical QM, and I'm not at the point where I could even tell you the background required to speculate on modern QFT.
  - M_Grey 10y ago
    Did you think I was endorsing the contents of either quote? I wasn't.
  - selimthegrim 10y ago
    All three volumes of Weinberg?
  - aluhut 10y ago
    You could replace QM with "magic" and it could be a dialogue by one of those fancy mages in any fantasy story. Do you see a way to "sell" QM to the public in a way that would reflect the diversity of the ideas and the concepts in a better way? Something that could replace what we have now? Does it make any sense at this point to do this at all?
  - jostylr 10y ago
    Local hidden variable theories are not possible, but any local theory is not possible, assuming definite outcomes of experiments (many worlds might be considered local, but there is no definite outcome). Non-local hidden variable theories are quite possible, do quite well in explaining a number of facets of QM, and, in fact, inspired Bell's work. Nevertheless, Einstein certainly was no fan of the non-locality though he did not know of Bell's argument, of course.
    - tiglionabbit 10y ago
      Non-locality can't be right though, since locality is defined by the speed of light, and nobody will tell you that sending information faster than the speed of light is possible. Many worlds it is, then.
      - M_Grey 10y ago
        Non-locality doesn't imply that you can transmit information FTL, in fact you can't without classical channels. You can send random bits with entangled particles, but that is the precise opposite of information.
      - 10y ago
- codethief 10y ago
  Regarding the quote by Einstein: This turned out to be (partly) wrong. While the wave function can hardly be an object of reality (since its collapse depends on the observer, i.e. is not Lorentz invariant) and is thus rather a descriptive means for us, uncertainty in the quantum sense has nothing to do with a lack of knowledge. Put differently, there is a difference between a physical system being in a superposition of states A and B or being either in state A or state B (but not both of them at the same time). There're various experiments that can distinguish between both.
  - akvadrako 10y ago
    Just for the sake of anybody reading, your claims about the reality of the wave function are not settled science. Published in 2012, the PBR theorem[1] suggests with some caveats that 𝛹 must be interpreted physically or modified to make new predictions of which there is no evidence of. [1] http://www.nature.com/nphys/journal/v8/n6/full/nphys2309.html http://www.nature.com/nphys/journal/v8/n6/full/nphys2309.htm...
    - codethief 10y ago
      Thanks for the link![1] I should have been more precise. What is settled science is that the collapse of the wave function happens due to different causes for different observers. Example: Take two detectors A and B and place an apparatus in the middle that emits two entangled photons in opposite directions. In the lab frame, both particles will reach the detectors at the same time, so that both detectors cause the collapse of psi simultaneously. In contrast to that, two observers moving to the left and right respectively will see one of the photons reach its respective detector before the other photon reaches his. Thus, for one observer it's detector A causing the collapse (and B then only receives a disentangled photon) and for the second observer it's the other way around. Hence the causal chain of events is reversed (which is forbidden by special relativity). Now, the problem here is obviously the collapse of the wave function itself (and the faster-than-light propagation of the disentanglement which, however, is widely accepted). Since we still don't know how the collapse actually works[2], it's likely (and I think assumed by most physicists nowadays) that the non-unitary(!) collapse should be replaced with a different mechanism. (Such as decoherence[3] but there are still a lot of questions remaining.) So it is in this sense that I say that the wave function (in our formalism today) cannot be an actual part of reality because it only works until a collapse occurs. That doesn't mean, though, that the quantum states themselves (given by the wave function in intermediate times) can't correspond to reality. In fact, as I said myself, quantum uncertainty doesn't have anything to do with a lack of knowledge. That is, the view that quantum states merely represent statistical properties of an underlying state (which a priori might be part of a hidden variable theory) is wrong. While I think this was known before 2012, the PBR theorem gives a very general proof of that. [1] The full article without pay wall can be found here: https://arxiv.org/abs/1111.3328v1 https://arxiv.org/abs/1111.3328v1 [2] https://en.m.wikipedia.org/wiki/Measurement_problem https://en.m.wikipedia.org/wiki/Measurement_problem [3] https://en.m.wikipedia.org/wiki/Quantum_decoherence https://en.m.wikipedia.org/wiki/Quantum_decoherence
diyseguy 10y ago
Schrödinger's cat was a zombie
cyberferret 10y ago
I first came across the story when reading Douglas Adams' "Dirk Gently's Holistic Detective Agency" many decades ago. It spurred me to learn a bit more about philosophic science. Now it appears that every man and his cat spouts on about Mr. Schrodinger and his hapless kitty at the drop of a decayed subatomic particle... Verschränkung has become pop culture...
wodenokoto 10y ago
I've known about schrödingers cat for years, though my physics background is just high school + the odd popular science book. It wasn't until a few months ago that I learned on reddit that it isn't an explanation of quantum physics, but a critique. This explains why the cat isn't an observer that causes the wave function to collapse or why the cat isn't dead or alive, but we as outsiders can't know and thus simply think of it as both until we open the box.
erikpukinskis 10y ago
Has anyone written code that can do quantum decoherence of radiation in an OpenGL fragment shader? Edit: I'm imagining some kind of subset of QuTiP that could calculate photon (electron?) states from a wave function, ported to GLSL. Edit 2: Maybe a Born probability that would draw the interference pattern from the double slit experiment? Or a reduced density matrix or something? The word "matrix" makes me think it might be amenable to a GPU, but I don't really know GLSL or quantum physics.

49 points by bilifuduo 10y ago

Two deeply unrelated quotes that I find apply here. The first is from a segment on a Christmas special of the British radio comedy panel show, The Unbelievable Truth, and the second is Einstein's. "Schrodinger, philosophic science whiz popped a kitty in his a pretty kitty and says ‘If you open the box, the 'lectric shocks.’ 'Don’t touch the box… the cat is now a paradox.’ 'Both dead and alive is the feline situation’ 'But its status will be changed by the act of observation’ The main thing that we learn from that: Schrodinger did not like cats." -Rufus Hound “[I advocate] that one conceives of the psi-function [i.e., wavefunction] only as an incomplete description of a real state of affairs, where the incompleteness of the description is forced by the fact that observation of the state is only able to grasp part of the real factual situation. Then one can at least escape the singular conception that observation (conceived as an act of consciousness) influences the real physical state of things; the change in the psi-function through observation then does not correspond essentially to the change in a real matter of fact but rather to the alteration in our knowledge of this matter of fact.” -Albert Einstein

wyager 10y ago
In said quote, Einstein advocates hidden variable theory, which was disproven. https://en.m.wikipedia.org/wiki/Bell_test_experiments https://en.m.wikipedia.org/wiki/Bell_test_experiments I would strongly advise people who do not have extensive tuition in Quantum Mechanics to refrain from speculating about the consequences of QM. I have been taking QM classes for several years now, and the most valuable thing I've learned is that almost everyone's understanding of QM is based on bad ad-hoc analogies, and it takes years of study to progress to gradually less ad-hoc analogies. Different mathematical models inform different "interpretations" of QM. If you can't tell the difference between a rigged and non-rigged Hilbert space, you certainly don't have enough background to speculate on classical QM, and I'm not at the point where I could even tell you the background required to speculate on modern QFT.
- M_Grey 10y ago
  Did you think I was endorsing the contents of either quote? I wasn't.
- selimthegrim 10y ago
  All three volumes of Weinberg?
- aluhut 10y ago
  You could replace QM with "magic" and it could be a dialogue by one of those fancy mages in any fantasy story. Do you see a way to "sell" QM to the public in a way that would reflect the diversity of the ideas and the concepts in a better way? Something that could replace what we have now? Does it make any sense at this point to do this at all?
- jostylr 10y ago
  Local hidden variable theories are not possible, but any local theory is not possible, assuming definite outcomes of experiments (many worlds might be considered local, but there is no definite outcome). Non-local hidden variable theories are quite possible, do quite well in explaining a number of facets of QM, and, in fact, inspired Bell's work. Nevertheless, Einstein certainly was no fan of the non-locality though he did not know of Bell's argument, of course.
  - tiglionabbit 10y ago
    Non-locality can't be right though, since locality is defined by the speed of light, and nobody will tell you that sending information faster than the speed of light is possible. Many worlds it is, then.
    - M_Grey 10y ago
      Non-locality doesn't imply that you can transmit information FTL, in fact you can't without classical channels. You can send random bits with entangled particles, but that is the precise opposite of information.
    - 10y ago
codethief 10y ago
Regarding the quote by Einstein: This turned out to be (partly) wrong. While the wave function can hardly be an object of reality (since its collapse depends on the observer, i.e. is not Lorentz invariant) and is thus rather a descriptive means for us, uncertainty in the quantum sense has nothing to do with a lack of knowledge. Put differently, there is a difference between a physical system being in a superposition of states A and B or being either in state A or state B (but not both of them at the same time). There're various experiments that can distinguish between both.
- akvadrako 10y ago
  Just for the sake of anybody reading, your claims about the reality of the wave function are not settled science. Published in 2012, the PBR theorem[1] suggests with some caveats that 𝛹 must be interpreted physically or modified to make new predictions of which there is no evidence of. [1] http://www.nature.com/nphys/journal/v8/n6/full/nphys2309.html http://www.nature.com/nphys/journal/v8/n6/full/nphys2309.htm...
  - codethief 10y ago
    Thanks for the link![1] I should have been more precise. What is settled science is that the collapse of the wave function happens due to different causes for different observers. Example: Take two detectors A and B and place an apparatus in the middle that emits two entangled photons in opposite directions. In the lab frame, both particles will reach the detectors at the same time, so that both detectors cause the collapse of psi simultaneously. In contrast to that, two observers moving to the left and right respectively will see one of the photons reach its respective detector before the other photon reaches his. Thus, for one observer it's detector A causing the collapse (and B then only receives a disentangled photon) and for the second observer it's the other way around. Hence the causal chain of events is reversed (which is forbidden by special relativity). Now, the problem here is obviously the collapse of the wave function itself (and the faster-than-light propagation of the disentanglement which, however, is widely accepted). Since we still don't know how the collapse actually works[2], it's likely (and I think assumed by most physicists nowadays) that the non-unitary(!) collapse should be replaced with a different mechanism. (Such as decoherence[3] but there are still a lot of questions remaining.) So it is in this sense that I say that the wave function (in our formalism today) cannot be an actual part of reality because it only works until a collapse occurs. That doesn't mean, though, that the quantum states themselves (given by the wave function in intermediate times) can't correspond to reality. In fact, as I said myself, quantum uncertainty doesn't have anything to do with a lack of knowledge. That is, the view that quantum states merely represent statistical properties of an underlying state (which a priori might be part of a hidden variable theory) is wrong. While I think this was known before 2012, the PBR theorem gives a very general proof of that. [1] The full article without pay wall can be found here: https://arxiv.org/abs/1111.3328v1 https://arxiv.org/abs/1111.3328v1 [2] https://en.m.wikipedia.org/wiki/Measurement_problem https://en.m.wikipedia.org/wiki/Measurement_problem [3] https://en.m.wikipedia.org/wiki/Quantum_decoherence https://en.m.wikipedia.org/wiki/Quantum_decoherence

diyseguy 10y ago

Schrödinger's cat was a zombie

cyberferret 10y ago

I first came across the story when reading Douglas Adams' "Dirk Gently's Holistic Detective Agency" many decades ago. It spurred me to learn a bit more about philosophic science. Now it appears that every man and his cat spouts on about Mr. Schrodinger and his hapless kitty at the drop of a decayed subatomic particle... Verschränkung has become pop culture...

wodenokoto 10y ago

I've known about schrödingers cat for years, though my physics background is just high school + the odd popular science book. It wasn't until a few months ago that I learned on reddit that it isn't an explanation of quantum physics, but a critique. This explains why the cat isn't an observer that causes the wave function to collapse or why the cat isn't dead or alive, but we as outsiders can't know and thus simply think of it as both until we open the box.

erikpukinskis 10y ago

Has anyone written code that can do quantum decoherence of radiation in an OpenGL fragment shader? Edit: I'm imagining some kind of subset of QuTiP that could calculate photon (electron?) states from a wave function, ported to GLSL. Edit 2: Maybe a Born probability that would draw the interference pattern from the double slit experiment? Or a reduced density matrix or something? The word "matrix" makes me think it might be amenable to a GPU, but I don't really know GLSL or quantum physics.