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Questions tagged [non-locality]

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How is Mermin's magic square computed?

BACKGROUND The Peres-Mermin magic square consists of different combinations of tensor products of Pauli operators being applied on an arbitrary bipartite state. Suppose we're considering the entry in ...
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Is there a systematic method to derive Bell's inequalities?

BACKGROUND The purpose of Bell's inequalities is to put bounds on certain combinations of classical measurement probabilities. One can then show that quantum entanglement can yield probabilities that ...
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Does reality express non-local realism, local non-realism or non-local non-realism? [closed]

So I read that Bell's tests prove that reality cannot follow the requirements of both realism and locality. My understanding is that: Realism: Objects have definite properties before they are ...
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60 views

How are contextuality and locality related?

I know how quantum non-locality is defined in Wikipedia quantum nonlocality is a characteristic of some measurements made at a microscopic level that contradict the assumptions of local realism ...
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Can bipartite mixed entangled states show Hardy nonlocality?

I understand that apart from maximally entangled states, all pure entangled states yield Hardy correlations for certain measurement settings. Can the same be told for mixed entangled states?
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Can a single photon behave in a non-local way?

Most discussions of quantum non-locality center on entangled pairs of particles which are described by a single wave function and thus, in some way, are to be regarded as one quantum object such that ...
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Non-local operators [duplicate]

As the title suggests I am interested on how to identify that an operator in QFTs is a non-local operator. I have already read similar questions/answers to the topic in stackexchange, but they didn't ...
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43 views

Fractional derivatives in a QFT Lagrangian

There are is at least one question asking about fractional powers of fields in QFT (and why they're not expected to occur), and several others asking about the physical relevance of fractional ...
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132 views

Does Bell's theorem imply nonlocality using a false assumption?

In https://arxiv.org/abs/1409.5158, the author concludes that Bell tests cannot refute local realism, because they employ a wrong analysis. He says: "The quantum joint prediction cannot be ...
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Non-local field redefinition and effects on path-integral measure

Consider the partition function $$ Z[0] = \int \left[\mathcal{D}A_\mu\right]\left[\mathcal{D}\pi\right] e^{-i \int d^4x \left(-\frac{1}{2}(\partial\pi)^2-\frac{1}{4}F_{\mu\nu}F^{\mu\nu}+ \frac{a}{M^2}...
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Non-locality of the Madelung equations?

As far as I understand, the Madelung equations $$ \frac{\partial \rho}{\partial t} + \nabla \cdot \rho \mathbf{u} = 0 \\ \frac{\partial \mathbf{u}}{\partial t} + \mathbf{u} \cdot \nabla \mathbf{u} = -\...
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Does a pilot-wave theory need to be stochastic in a discrete space-time?

I have found an article about Bohmian mechanics on a lattice with discrete space and time, the link of which is given below: https://arxiv.org/abs/1606.02883 Here the motion of quantum particles is ...
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Have fractional order differential models been explored as an alternative to standard gravitational field theory?

Since Einstein introduced his field equations and general theory of relativity, experimental evidence, at least on the cosmic scale has repeatedly supported the theory. Nevertheless, many seeking to ...
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Decoherence: faster than light?

The answer to this question suggest that one can solve the measurement problem by decoherence. If I understand it correctly the decoherence appears when the quantum state interacts with the ...
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The non-locality of Quantum Mechanics

I often heard physicists mentioning the EPR paradox or the quantum entanglement when talking about the non-locality of quantum mechanics, but wasn't quantum mechanics already non-local from the ...
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How exactly does the proof of Bell's theorem fail if you remove the locality assumption?

In this paper Bell derives his famous inequality using the assumtions of locality and realism. In order to understand how the locality assumption affects the derivation of the inequality, and why it ...
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Recharacterizing spooky action at a distance as a time loop invariant?

Caveat: I'm not a physicist and am a little fuzzy on what exactly what I'm asking here. But I'm hoping someone smarter than me can at least clarify (or dismiss) the question as stupid... :) This ...
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Is there a relation between the factorisation of the joint conditional probability distribution and Bell inequality?

I'm approaching the study of Bell's inequalities and I understood the reasoning under the Bell theorem (pdf : https://cds.cern.ch/record/111654/files/vol1p195-200_001.pdf) and how the postulate of ...
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Non-local field theory (of Jaffe type) vs strings

As it is well known expectation values of fields are distributions. One usually works with tempered distributions or even with Jaffe fields (https://doi.org/10.1103/PhysRev.158.1454), all defining ...
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In a Bell scenario, why can correlations be nonlocal only if there are at least two measurement settings to choose from?

In (Brunner et al. 2013), the authors mention (end of pag. 6) that a set of correlations $p(ab|xy)$ can be nonlocal only if $\Delta\ge2$ and $m\ge2$, where $\Delta$ is the number of measurement ...
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Local determinism vs. Local realism vs. Local causality

I found the following definitions for the three different terms. Do you find these definitions exhaustive, or can you suggest more precise formulations? Quoting the wikipedia page on Local realism: ...
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Can local hidden variables models be ruled out without invoking expectation values?

Bell's inequalities, in their standard form, are a statement about the limitations faced by a probability distribution that can be written as $$p(a,b|x,y)=\sum_\lambda p(\lambda) p(a,b|x,y,\lambda)=\...
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On the entanglement of photons polarization

I am trying to make my perception evolve to include non-locality, and this idea is one of the last that I want to invalidate in order to get there. When we emit two entangled photons and test their ...
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Can non-locality be considered an instantaneous propagation of the field?

I've read the article Quantum Entanglement, which is a summary of the basics of non-locality, as well a claim for the first "real" proof of its existence. I also have some background from self-...
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Decomposition of rank-2 field and local interactions

Any rank-2 tensor can be decomposed in the following way $$ \phi_{\mu\nu} =\phi_{\mu\nu}^{TT} + \partial_{(\mu}\xi_{\nu)} +\frac{1}{4}T_{\mu\nu}s+\frac{1}{4}L_{\mu\nu}(w-3s) $$ where $\phi_{\mu\nu}^{...
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Does photon absorption annihilate the associated EM wave instantly?

My Understanding A single photon has an associated electromagnetic wave. The wave is spread out in space, but the photon is considered a point particle. If the photon is absorbed, the entire wave ...
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How to deduce quantum non-locality from indeterminism?

In the paper ''Quantum non-locality as an axiom'' (Popescu, S. & Rohrlich, D. Found Phys (1994) 24: 379. https://doi.org/10.1007/BF02058098), it is stated that the conventional formalism of ...
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Why can't Faddeev-Popov ghosts be replaced with bosons?

Faddeev-Popov ghosts are introduced in the quantization of Yang-Mills theory to absorb the Faddeev-Popov determinant into the action, $$\det \Delta_{\text{FP}} = \int \mathcal{D} \bar{c} \mathcal{D} c ...
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316 views

Local and Non-Local Potentials

Can anybody explain the difference and concepts between local and non-local potentials in light of quantum mechanics?
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Finding the cost functional of a car-following model [closed]

I have a car-following model with delay $\ddot{x}_n(t)=\lambda [\dot{x}_{n-1}(t-T)-\dot{x}_{n}(t-T)]$, where $\ddot{x}$ is the acceletation, $\dot{x}_{n-1}-\dot{x}_{n}$ is the relative velocity, $\...
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EPR-Bohm paradox and Robertson uncertainty relation [closed]

Consider Bohm's version of the EPR paradox, where spin-1/2 are used. The bipartite system is in the state $$ \vert \Psi\rangle = \dfrac{1}{\sqrt{2}} \left( \vert \uparrow_x \rangle_A \vert \...
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Intuition behind non-local stress tensor

Starting from the following Reisz Fractional Integro-differential formula (see for example https://www.amazon.com/Fractional-Integrals-Derivatives-Theory-Applications/dp/2881248640, chapter 25) $$ I^{...
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Is there any basis in stating there are different levels of 'locality' or 'reality', within physics or physical theories?

EPR’s reality criterion and quantum realism has this paragraph (the paper has 0 citations, and I'm personally happy to call this metaphysics, but still!): A popular interpretation of Bell’s theorem ...
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Are contextual theories non-local and vice-versa?

I am wondering if every contextual theory that reproduces QM is NON-local and reciprocally. Otherwise, when is contextuality equivalent to non-locality? And moreover, how much nonlocality is encoded ...
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What's a comprehensive review of the implications of Bell-nonlocality on our notion of reality / Weltanschauung?

I am looking for a (preferably peer-reviewed) article that summarizes: the historic debates surrounding Bell-nonlocality, how nonlocality can/not be reconciled with our notation of reality, and ...
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What is space according to quantum mechanics?

We have a pretty good idea what space is in general relativity, yet the strange fact of non-locality in quantum mechanics tells a different story. Interestingly enough this non-locality doesn't seem ...
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Problem with argument for the existence of the electric field

In the Extended Third Edition of "Physics for Engineers and Scientists" by Ohanian and Markert (pp. 722-723), it is written: According to the naive interpretation of Coulomb’s Law, the electric ...
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How to build an Elitzur–Vaidman bomb tester?

I would like to personally recreate the Elitzur–Vaidman bomb tester experiment. Is that generally possible with maybe only a few thousand dollars to invest or maybe even for a few hundred? Any ...
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Locality in QFT vs “non-local” in QM

In quantum mechanics (QM), teacher always emphasizes on the "weird" parts, like EPR paradox, Bell inequality and so on. The Bell inequality tells us that QM is either nonlocal or non-realistic or both....
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176 views

How can quantum entanglement not be non-local?

I know this kind of question has been brought up many times.I have read many posts here regarding this but I still have a problem with a certain aspect of it so please bear with me. Lets consider the ...
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“Logical Conclusions” arising from hypothetical wormholes

EDIT In eternal (time independent) Schwarzschild black hole contains a wormhole called an Einstein-Rosen bridge. But since no real black hole is eternal, real black holes do not contain any ...
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287 views

What exactly are the high energy problems between general relativity and quantum field theory? [duplicate]

I know there are many questions on physics stack exchange devoted to the question of quantum gravity and reconciling GR and QFT, but don't mark this as a duplicate because my question is a bit more ...
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Is there non-locality in the AdS/CFT?

Many String theorists are trying to restore bulk locality in the AdS/CFT. So does that mean the CFT, the boundary, is non-local? Does matter travel faster than light on the CFT?
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Non-local field redefinition and $S$-matrix

It is known that for local field redefinitions for which the LSZ formula is valid: $$\langle 0|\phi(x)|p\rangle \neq 0$$ field redefinitions don't change the S-matrix. (See QMechanic's answer to ...
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How can non-locality of entanglement be explained only in terms of correlation?

I'd like to ask a very specific question about the entanglement nonlocality. I know that it is not possible to send a faster than light signal using this phenomenon, so that's not what I'm asking ...
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Are all instances of quantum non-locality problem artifacts of the use of classical concepts in quantum physics?

Consider experiments involving entangled spins, say two-spin 1/2 particles in the singlet state: $$\left|\psi\right> =\frac{1}{\sqrt{2}}\left[\left|\uparrow\downarrow\right> - \left|\downarrow\...
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Dimension of joint probability space in the Bell Scenario

In the Bell(CHSH) scenario with the normal two qubits+two measurement settings, how does the dimension of the joint probability space $ P(ab|xy)$ drops from 16 to 8? In general, for two d-dimensional ...
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Why Shy away from non-local nature of gravitational energy/momentum?

Feel free to tear me a new one, This is something that has been bothering me a while. The very nature of attempting to write gravitational energy/momentum (called the stress energy pseudotensor), ...
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166 views

Local and non-local counterterms in the ultraviolet and infrared limits of a quantum field theory

These is a question about the renormalization of a quantum field theory. See below equation (19.3) in page 176 of Thomas Hartman's notes on Quantum Gravity and Black Holes. When we renormalize a ...
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Does Bell's theorem include causal networks?

I am not an expert, so by causal networks I mean whatever it is that Wolfram talks about in its book. Regardless of the official definition, it basically means that spacetime is an emergent property ...