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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 i
by 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 agoThe 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 agoSince 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 agoFields 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.
- perl4ever 7y agoOk, but if you think of a field as existing in space at a given time, then essentially all of it is not in your particular spot. Just saying "this field has a value elsewhere" means you are talking about something that is not near your given point. And having different values at different points is what I thought a field was.
- archgoon 7y agoAre you saying that electromagnetism is a nonlocal theory because it has a field? That is not the standard meaning of 'nonlocal'.