5 ms·

Imaging Bell-type nonlocal behavior

160 points by karxxm 7y ago

ZeroCool2u 7y ago
Large versions of the images from the paper: Figure 2: https://advances.sciencemag.org/content/advances/5/7/eaaw2563/F2.large.jpg https://advances.sciencemag.org/content/advances/5/7/eaaw256... Figure 3: https://advances.sciencemag.org/content/advances/5/7/eaaw2563/F3.large.jpg https://advances.sciencemag.org/content/advances/5/7/eaaw256... Figure 4: https://advances.sciencemag.org/content/advances/5/7/eaaw2563/F4.large.jpg https://advances.sciencemag.org/content/advances/5/7/eaaw256...
feiss 7y ago
I know this must be nuts, could someone ELI20?
- human20190310 7y ago
  This video by Veritasium covers the entanglement concept at a non-expert level: https://www.youtube.com/watch?v=ZuvK-od647c https://www.youtube.com/watch?v=ZuvK-od647c
- indutny 7y ago
  In this image: https://advances.sciencemag.org/content/advances/5/7/eaaw2563/F1.large.jpg?width=800&height=600&carousel=1 https://advances.sciencemag.org/content/advances/5/7/eaaw256... they describe their apparatus. The light comes from bottom left, then gets into Beam Splitter (BS) and splits in two. The top-left detector has a pre-selected filter and a measurement device after a delay line. As far as I understand, this device gives binary output: either light received or not. The top-right detector captures whole image of the light ray, but does so only if the left detector has seen light. The result is that the image from the top-right detector is highly correlated with the pre-selected filter of the top-left detector, even though they're placed in different arms of Beam Splitter! https://advances.sciencemag.org/content/advances/5/7/eaaw2563/F2.large.jpg?width=800&height=600&carousel=1 https://advances.sciencemag.org/content/advances/5/7/eaaw256...
  - Kovah 7y ago
    Thank you for the setup explanation. I understood what is happening and it is totally fascinating, even if I do not - and probably never can - understand why or how this is happening.
- zwkrt 7y ago
  A bell inequality is a feature of quantum systems by which they break our understanding of classical probability. A good reference is here [1]. The basic idea is to imagine a Venn diagram where the sum of the parts adds up to more than 100%. Bell inequalities are nifty because they heavily imply that our classical notions of “local realism” must be incomplete. Namely, that either quantum objects experience instantaneous action-at-a-distance (locality), or they do not have actualized measurement values when they aren’t being actively measured (realism). This paper is showing a way to produce a visual image of a bell inequality and explores ways that these inequalities can be used for other visual techniques. [1] https://youtu.be/zcqZHYo7ONs https://youtu.be/zcqZHYo7ONs
  - perl4ever 7y ago
    The point at which I disconnected from understanding physics is not the actual theory, but the stuff people say about locality. I mean, once you have the concept of fields, they're not local, right? So aren't people saying "what is not nonlocal must be local" which doesn't seem like a substantive principle. Every time I read about the struggle between realism and locality, it makes me feel unhappy because I have a choice between assuming it's me that's really dumb or everyone else. I can't understand why it should be a real problem.
    - SiempreViernes 7y ago
      Since you have a finite speed for information to propagate, locality can always be defined as "within the lightcone", and so locality is well defined, even for fields.
    - archgoon 7y ago
      Fields are neither local nor non local. Locality is about how information propagates. Classical Gravitation defines a force field that is nonlocal, as it propagates instantaneously. Move a mass from point a to point b, and the entire universe immediately updates the force they experience. Classical Electromagnetism defines a field that only propagates changes at a finite speed. If you move a charged mass from point a to point b, the change in the electric and magnetic fields radiate outward at the speed of light. One way to think about this is to observe that time update equations for E+M only rely on values infinitesimally near a point. If you need to compute the next time step on a grid, you only need to look at the neighbors of a point to figure out how to update a given point.
- kgwgk 7y ago
  https://static.scientificamerican.com/sciam/assets/media/pdf/197911_0158.pdf https://static.scientificamerican.com/sciam/assets/media/pdf... https://physics.aps.org/articles/v8/123 https://physics.aps.org/articles/v8/123 The first link gets bonus points for the 40-year-old advertisements included in the scan.
moedersmooiste 7y ago
Maybe a bit off topic, but i've always wondered why most physicists dismiss the possibility of superdeterminism to escape Bell's theorem. Are there any physicists here who would like to elaborate?
- steve76 7y ago
  If we had that, we should easily be able to speak to the dead! Spoiler Alert: Until further notice, you die!
- lisper 7y ago
  Not a physicist, but I've been studying QM as a hobby for thirty years. The problem with superdeterminism (SD) is that if QM is true then SD is not falsifiable. SD says that all experimental outcomes are deterministic but derive from hidden state, i.e. some sort of "Cosmic Turing Machine" (CTM) calculating the digits of pi or something like that. So now what? The CTM has to be perpetually hidden from us, otherwise we could examine its state and predict the outcomes of quantum experiments, and that would violate QM. So if QM is true, then the CTM necessarily has the same ontological status as an Invisible Pink Unicorn (IPU). In fact, the deterministic calculations underlying SD may well be carried out by a literal IPU. If QM is correct then there's no way to determine this, even in principle.
  - nabla9 7y ago
    Bell-inequality experiments still that leave room for hidden-variable models that fall short of full superdeterminism. Relatively recent experiment using photons from stars in the Milky Way "Cosmic Bell Test: Measurement Settings from Milky Way Stars" http://web.mit.edu/asf/www/Papers/Handsteiner_Friedman+2017.pdf http://web.mit.edu/asf/www/Papers/Handsteiner_Friedman+2017.... The experiment excludes local-realist models with local hidden variable younger than 600 light years. Similar test with cosmic microwave background could push the limit to the early universe.
  - corey_moncure 7y ago
    How do you tell if your code is running on a virtual machine or on bare metal?
dang 7y ago
A blog post is https://www.sciencealert.com/scientists-just-unveiled-the-first-ever-photo-of-quantum-entanglement https://www.sciencealert.com/scientists-just-unveiled-the-fi.... BBC article is https://www.bbc.com/news/uk-scotland-glasgow-west-48971538 https://www.bbc.com/news/uk-scotland-glasgow-west-48971538, discussed at https://news.ycombinator.com/item?id=20423884 https://news.ycombinator.com/item?id=20423884.

160 points by karxxm 7y ago

Large versions of the images from the paper: Figure 2: https://advances.sciencemag.org/content/advances/5/7/eaaw2563/F2.large.jpg https://advances.sciencemag.org/content/advances/5/7/eaaw256... Figure 3: https://advances.sciencemag.org/content/advances/5/7/eaaw2563/F3.large.jpg https://advances.sciencemag.org/content/advances/5/7/eaaw256... Figure 4: https://advances.sciencemag.org/content/advances/5/7/eaaw2563/F4.large.jpg https://advances.sciencemag.org/content/advances/5/7/eaaw256...

feiss 7y ago

I know this must be nuts, could someone ELI20?

human20190310 7y ago
This video by Veritasium covers the entanglement concept at a non-expert level: https://www.youtube.com/watch?v=ZuvK-od647c https://www.youtube.com/watch?v=ZuvK-od647c
indutny 7y ago
In this image: https://advances.sciencemag.org/content/advances/5/7/eaaw2563/F1.large.jpg?width=800&height=600&carousel=1 https://advances.sciencemag.org/content/advances/5/7/eaaw256... they describe their apparatus. The light comes from bottom left, then gets into Beam Splitter (BS) and splits in two. The top-left detector has a pre-selected filter and a measurement device after a delay line. As far as I understand, this device gives binary output: either light received or not. The top-right detector captures whole image of the light ray, but does so only if the left detector has seen light. The result is that the image from the top-right detector is highly correlated with the pre-selected filter of the top-left detector, even though they're placed in different arms of Beam Splitter! https://advances.sciencemag.org/content/advances/5/7/eaaw2563/F2.large.jpg?width=800&height=600&carousel=1 https://advances.sciencemag.org/content/advances/5/7/eaaw256...
- Kovah 7y ago
  Thank you for the setup explanation. I understood what is happening and it is totally fascinating, even if I do not - and probably never can - understand why or how this is happening.
zwkrt 7y ago
A bell inequality is a feature of quantum systems by which they break our understanding of classical probability. A good reference is here [1]. The basic idea is to imagine a Venn diagram where the sum of the parts adds up to more than 100%. Bell inequalities are nifty because they heavily imply that our classical notions of “local realism” must be incomplete. Namely, that either quantum objects experience instantaneous action-at-a-distance (locality), or they do not have actualized measurement values when they aren’t being actively measured (realism). This paper is showing a way to produce a visual image of a bell inequality and explores ways that these inequalities can be used for other visual techniques. [1] https://youtu.be/zcqZHYo7ONs https://youtu.be/zcqZHYo7ONs
- perl4ever 7y ago
  The point at which I disconnected from understanding physics is not the actual theory, but the stuff people say about locality. I mean, once you have the concept of fields, they're not local, right? So aren't people saying "what is not nonlocal must be local" which doesn't seem like a substantive principle. Every time I read about the struggle between realism and locality, it makes me feel unhappy because I have a choice between assuming it's me that's really dumb or everyone else. I can't understand why it should be a real problem.
  - SiempreViernes 7y ago
    Since you have a finite speed for information to propagate, locality can always be defined as "within the lightcone", and so locality is well defined, even for fields.
  - archgoon 7y ago
    Fields are neither local nor non local. Locality is about how information propagates. Classical Gravitation defines a force field that is nonlocal, as it propagates instantaneously. Move a mass from point a to point b, and the entire universe immediately updates the force they experience. Classical Electromagnetism defines a field that only propagates changes at a finite speed. If you move a charged mass from point a to point b, the change in the electric and magnetic fields radiate outward at the speed of light. One way to think about this is to observe that time update equations for E+M only rely on values infinitesimally near a point. If you need to compute the next time step on a grid, you only need to look at the neighbors of a point to figure out how to update a given point.
kgwgk 7y ago
https://static.scientificamerican.com/sciam/assets/media/pdf/197911_0158.pdf https://static.scientificamerican.com/sciam/assets/media/pdf... https://physics.aps.org/articles/v8/123 https://physics.aps.org/articles/v8/123 The first link gets bonus points for the 40-year-old advertisements included in the scan.

moedersmooiste 7y ago

Maybe a bit off topic, but i've always wondered why most physicists dismiss the possibility of superdeterminism to escape Bell's theorem. Are there any physicists here who would like to elaborate?

steve76 7y ago
If we had that, we should easily be able to speak to the dead! Spoiler Alert: Until further notice, you die!
lisper 7y ago
Not a physicist, but I've been studying QM as a hobby for thirty years. The problem with superdeterminism (SD) is that if QM is true then SD is not falsifiable. SD says that all experimental outcomes are deterministic but derive from hidden state, i.e. some sort of "Cosmic Turing Machine" (CTM) calculating the digits of pi or something like that. So now what? The CTM has to be perpetually hidden from us, otherwise we could examine its state and predict the outcomes of quantum experiments, and that would violate QM. So if QM is true, then the CTM necessarily has the same ontological status as an Invisible Pink Unicorn (IPU). In fact, the deterministic calculations underlying SD may well be carried out by a literal IPU. If QM is correct then there's no way to determine this, even in principle.
- nabla9 7y ago
  Bell-inequality experiments still that leave room for hidden-variable models that fall short of full superdeterminism. Relatively recent experiment using photons from stars in the Milky Way "Cosmic Bell Test: Measurement Settings from Milky Way Stars" http://web.mit.edu/asf/www/Papers/Handsteiner_Friedman+2017.pdf http://web.mit.edu/asf/www/Papers/Handsteiner_Friedman+2017.... The experiment excludes local-realist models with local hidden variable younger than 600 light years. Similar test with cosmic microwave background could push the limit to the early universe.
- corey_moncure 7y ago
  How do you tell if your code is running on a virtual machine or on bare metal?

dang 7y ago

A blog post is https://www.sciencealert.com/scientists-just-unveiled-the-first-ever-photo-of-quantum-entanglement https://www.sciencealert.com/scientists-just-unveiled-the-fi.... BBC article is https://www.bbc.com/news/uk-scotland-glasgow-west-48971538 https://www.bbc.com/news/uk-scotland-glasgow-west-48971538, discussed at https://news.ycombinator.com/item?id=20423884 https://news.ycombinator.com/item?id=20423884.