Locality Definition and 83 Threads

Suppose we have in a box a particle that is travelling left and right at some speed, bouncing off the walls of the box. The wall on the right is then removed such that the particle would be free to escape the box. Does the wave function of the particle get "updated" instantly the moment the...

Hi. To close the locality loophole in Bell tests, detector settings may be changed randomly "just before the photon arrives". Or I have read about a delayed choice quantum eraser with a Mach Zehnder interferometer where the second beam splitter was put into the setup or taken out "when the...

Unfortunately one of the threads about entanglement and Bell tests has again been closed prematurely. It has not been clarified what "locality" means. In the physics community, not involved in philosophical arguments about foundations of QT, it's clearly defined as the property of a...

Hi. As far as I know, entanglement can initially only be created locally, for example by creating two photons at one place in a crystal, or by local forces. Sure, there's entanglement swapping, but the initial entanglement was still created locally. But I only know examples. Is there a general...

Consider experiments that demonstrate violations of Bell inequalities. I'm wondering about the spatial extent of the wave function of the particles BEFORE measurement. I assume the spatial extent is "very large," and my main question is whether they overlap. If the wave functions do overlap...

Bostelmann, H., Fewster, C. J., & Ruep, M. H. (2021). Impossible measurements require impossible apparatus. Physical Review D, 103(2), 025017.

I would like to pose a question (previously posed to DrChinese in a personal message) regarding Bell Locality. From PeterDonis in another thread: Bell assumes that local realism requires the factorizability of the joint probability function. Most of the efforts to justify this assumption have...

Hi, Translated from German magazine "Spektrum der Wissenschaft", September 2009, p. 33 (original see below): That doesn't sound right. EPR even have "physical reality" in the title, though they might not mean with it the exact same thing as Bell. Why would we need Bell's argument if EPR...

Apologies if there are already an abundance of threads on related questions. I have tried searching for threads on here and have read quite a few, as well as reading other sources. I've kind of reached a point where I need help to parse some of the information that I have been reading and to get...

Summary: Bell's theorem is often interpreted as a claim that either locality or realism is wrong. A recent theorem claims that realism is a consequence of the assumption of locality, so that locality must be wrong in any case. Recently, Bricmont, Goldstein and Hemmick wrote two (quite similar)...

In a paper much discussed on this forum (https://www.physicsforums.com/threads/does-the-bell-theorem-assume-reality.964219/),Roderich Tumulka, "The Assumptions of Bell’s Proof" (http://de.arxiv.org/abs/1501.04168) argues that locality entails two specific types of realism, which he calls R1 and...

OK, so I'm trying to work out a few ideas regarding locality. I've studied at the undergrad level in the past (including quantum), but with professors that slaved away at proving math constructs and never bothered to indulge in clarifying the context of any concepts, so I'm pretty weak here...

Does anybody know if there is work being done on quantum locality vs nonlocality. Specifically, approaching the Planck scales there is no nonlocality. That is all points in space and time are local. This would also provide an explanation for Einstein Minkowsky's space time. Any material /...

From what I understand, the most reasonable explanation of the violation of the Bell inequalities is that nature is non local. If we accept this, is there a reasonable argument that nature is not deterministic? I.e. could it be that the probabilistic predictions from QM are just averaging --...

I’m reading in the lay literature that experiments on Bells inequality have shown that 2 entangled particles pass information simultaneously and therefore break the special relativity rule of c and therefore indicate a break from the concept of locality. I’m sure I didn’t phrase that sentence...

Does the definition of locality in the QM sense include the prohibition of retrocausality?

How do we express the locality of a vector space in general relativity? I mean, it's not clear what the boundaries of a given vector space are. To put in another way, we could, in principle, blindly consider that we have the entire of ##\mathbb{R}^4## at our disposal to describe, say, the...

When there are EPR/Bell test inequality violations and no signal faster than light, the terms: Bell Non Locality, Quantum Non Locality, Weak Locality and the Cluster Decomposition Principle: Initial state of space like systems can be factorized. Subsystems remain space like separated. Then final...

Through Bell's inequality, we can see that any hidden variable theory of QM will have to satisfy the inequality, but as it doesn't, wave function must be the whole story and so we have to do away with realism. So when a measurement is done on one detector in the EPR experiment, the wave function...

Hi. Bell formulated local realism as follows: The probability of a coincidence between separated measurements of particles with correlated (e.g. identical or opposite) orientation properties can be written as $$P(a,b)=\int{d\lambda\cdot \rho(\lambda)\cdot p_A(a,\lambda)\cdot...

Hi. A while ago, I apparently had a wrong idea about the meaning of realism. I stood corrected: I'm still struggling with those subtleties. Would following formulation be more appropriate: "Realism means, that every observable ##x## is attributed a probability distribution ##p_P(x)## that...

Hi. In most articles on Bell's inequalities, both the reality and locality assumptions are thrown at the reader from the beginning. DrChinese however starts with only the reality assumption and shows that it doesn't comply with QM IF it were possible to measure two non-commuting observables...

I am studying the history of Quantum Mechanics and was reading about particle entanglement. What I would like to know is how did Einstein see that particle Entanglement meant that particles would be affected by spooky action at a distance. I guess that spooky action at a distance may also be...

As far as I understand, given that there is such a thing called entanglement, we know that there are non-local interactions. The line that this is usually followed with is "since no information traveled faster than light , locality isn't violated". I have a few interrelated questions about...

In quantum field theory (QFT) from what I've read locality is the condition that the Lagrangian density ##\mathscr{L}## is a functional of a field (or fields) and a finite number of its (their) spatial and temporal derivatives evaluated at a single spacetime point ##x^{\mu}=(t,\mathbf{x})##...

It’s easy enough to find the interpretations that break counterfactual definiteness in order to maintain locality. But I’m not sure how to find the ones with something (perhaps information) moving backwards through time. The reason I ask is I’ve always had trouble with the idea that a...

I have a question with regards to quantum entanglement, and how it relates to the concepts of realism and locality. I am just an interested amateur who has self-studied QM in my free time, so perhaps I should first run my understanding by you first, to make sure it is accurate : the basic idea...

I'm familiar with Bell's Theorem.. have studied it over the years. I'd just like to confirm if my belief is correct. In short. It shows either particles don't exist before measurement or there are hidden variables.. you know all those non-counterfactual and locality arguments.. Specker theorem...

Why is it required that interactions between fields must occur at single spacetime points in order for them to be local? For example, why must an interaction Lagrangian be of the form \mathcal{L}_{int}\sim (\phi(x))^{2} why can't one have a case where \mathcal{L}_{int}\sim\phi(x)\phi(y) where...

I am struggling with the concept of phonons and if they should be considered (experimentally) to be treated as collective oscillations of a certain region instead of the whole crystal. I know the title comes off as a little strange -- since phonons are not localised to anyone atom, but consider...

This has been causing some confusion to me as the two concepts seem very similar, if not the same (especially when taking special relativity into account). As far as I understand, even in classical physics (i.e. even before considering QFT and the like), one requires that interactions are...

I've read in a set of lecture notes that the requirement of locality and unitarity in QFT imply that the vacuum must have a non-zero energy associated with it (http://arxiv.org/pdf/1502.05296v1.pdf , top of page 3 under heading "What is the problem?"). My question is, why does the locality and...

I am slightly unsure as to whether I have understood the notion of locality correctly. As far as I understand it locality is the statement that if two events occur simultaneously (i.e. at the same time) then no information can be shared between them (they are causally disconnected). Thus a...

First of all, sorry if this is in the wrong forum, wasn't quite sure which one to post it in given the question. My question is, given two space-time points ##x^{\mu}## and ##y^{\mu}##, if the events that occur at these points are simultaneous, i.e. ##x^{0}=y^{0}##, are the two events...

Hi, In all the discussions about EPR, Bell's inequality and interpretations of QM locality seems to be a property that nobody likes to drop light-heartedly. This is somehow understandable since SR is an extremely successful theory. But SR only says that we cannot transmit information faster...

my question is this: you know than in feynman path integra, you integrate eiS/hbar along all the fields. you also know that S is real and that it is the integral of local functions (fields and derivatives of fields). you also know that path integral generates an unitary and local...

In wikipedia it says that "Coulomb's law of electric forces was initially also formulated as instantaneous action at a distance, but was later superseded by Maxwell's Equations of electromagnetism which obey locality." I don't really understand in which sense Maxwell's equations solve the...

Hi, Bell demonstrated that there cannot be a local realistic theory that reproduces the expectation values of QM. I can see that a non-realistic theory is unsatisfactory, we would have to abandon the nice determinism we got so accustomed to in classical physics, from Newton to Maxwell to...

Just posted to the archives is a great new paper from a top experimental team. These are some of the same individuals that performed the now standard citation regarding a Bell test under strict locality conditions. They have now extended their concept to GHZ states, and also close the...

Can we have a local hidden variable theory explanation for Bells theorem? The outcomes of the mesurement (measuring the electron spin of an entangled electron pair as Red or Green) can be random initially without any correlation at all. But by the time we compare the results of the two...

I understand that relativity at least philosophically excludes the ability to use entanglement to instantaneously send information, but as I understand it, it seems only philosophically, and the hard problem is that you break the entanglement by measurement. (Before I go on, I'm sure that ^^...

hi i read an article by S.carlip about quantum gravity, arXiv:gr-qc/0108040v1 , in this article carlip stated: why we need quantum gravity what's problems of quantum gravity and two ways of quantization of GR. I couldn't realize some clues in section of "the problems of quantum gravity"...

As I understand it, EPR proposed their entanglement thought experiment as a means of demonstrating that Quantum Mechanics was incomplete, and hence that the Copenhagen interpretation (which says that the wave function is a complete description of the state of a system) was wrong. They postulated...

Quantum mechanics says that physical observables are self-adjoint operators. Is this correspondence a bijection, ie can we realize any such operator as a physical observable? There are obvious practical concerns with physically realizing certain contrived operators. But are there any...

By Bell’s theorem, an interpretation of QM must break either locality or causality. Linked below is the only interpretation I know of that chooses to maintain locality. (I don't know many.) Do you know of any others? CAUSALLY SYMMETRIC BOHM MODEL...

As per the Wheeler Feynman absorber theory, there cannot be electromagnetic radiation without an emitter and absorber. If we had only a single electron in the universe then disturbing it (accelerating it) would not produce any radiation since there was nothing to absorb it. Hence it would...

Drawing on a number of threads in this forum, and my very limited understanding of relativity, I am intrigued by the following thoughts: If I have understood correctly, in GR, c is supposed to be only a 'local global constant', and not exactly a Universal constant. Meaning that, two distant...

Sorry, I have 2 doubts about the EPR paradox. 1) Just check out if I am ok: What EPR proposed was that QM suggest that if two entagled particles, for example photons, prepaired in some special way, get away from each other then: a) if we measure their x-spin then one particle will get the...

I couldn't find out if the following article had been discussed (it is probably well known), but there were many threads on locality/non-locality, so it might be of interest. On first reading I like it quite a lot, made some things clearer for me, but it will need some thinking and probably a...

Bell's theorem is generally thought to show that the world cannot be both local and real. http://en.wikipedia.org/wiki/Bell%27s_theorem In simplistic terms, Bell derives an inequality which allegedly must be satisfied if the world is both local and real. In practice, it is found in...