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Questions tagged [locality]

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Local fields vs particles

I have heard it said that Richard Feynman was a proponent of a particle approach to QFT while Julian Schwinger preferred a local fields description. What is meant by “local fields”? Surely when one ...
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Euclidean view in curved manifold

Let's suppose I am an ant who lives in a 2D curved space. Locally the world seems 2d-euclidean to me, but it is not if I consider a large portion of space. Now let's consider a human being who lives ...
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Why is there no gauge-invariant local operator in GR?

I have a hard time understanding why the bulk locality is a question. I know some operator which depends on a particular coordinate $x$, $O(x)$, and its correlation function like $ \langle O(x)O(y) \...
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Don't these experiments suggest that locality has to be abandoned in the quantum realm?

First a quick recap because maybe my understanding/assumptions are flawed (you can jump to the question highlighted in bold below if you like to): Bell's inequalities require that an accurate(ly ...
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How come subatomic particles interact with each other while not being in contact? [closed]

Although electrons stays away from protons an atom remains electrically neutral But two atoms one positively charged and another negatively charged remain so until they comes in contact. Can the ...
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2answers
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Could there exist a “locality” field? [closed]

What I mean is (and I'm a layperson on the subject), can there exist a field that pervades the universe - like the Higgs field - that interacts with particles to give them "distance" or "space" ...
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Why using time-ordering causality? and what is Difference between Locality and Causality?

In QFT, the time-ordering causality is generally used. There are 4 ways to bypassing the pole called time-ordering, anti-time-ordering, retarded and advanced. But in many case only time-ordered ...
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Could you explain the linear correlation in Bell's theorem for a hidden variable? [duplicate]

Could you please explain why, in experiments with electron spin and light polarity, the expected correllation for a hidden variable would be linear (red line below) Answers with the least math ...
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2answers
154 views

What is a local operator in quantum mechanics?

In quantum mechanics, what exactly is meant by "local" operator? What about a "global" or a "non-local" operator? Are these the same? Can you also also help me understand what exactly is a local ...
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3answers
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Difference between an entangled pair of photon and two magnets in a box? [duplicate]

I try to understand quantum entanglement and especially what it’s called « Action at a distance » from my understanding, if you have a pair of entangled photon, after measuring the polarization of ...
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Why do physicists say information can't travel faster than light speed?

I often hear in physics videos light speed is the ultimate speedlimit two parts of the universe can communicate at, or even that speed of light is actual speed of causality. Where does that notion ...
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2answers
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How Maxwell theory of electromagnetism solved action at a distance problem?

According to wikipedia Maxwell's equations were an essential inspiration for Einstein's development of special relativity. Possibly the most important aspect was their denial of instantaneous action ...
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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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Locality and relativity - a paradox?

The equations of nature are supposed to exhibit locality in the sense that the action depends on fields and their derivatives. i.e. comparing the values of fields at local points. But two points on a ...
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2answers
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Physics solely in terms of local observables

Practically all of the physics equations I've encountered are written in terms of what might be called "remote observables", such as the distances between objects in Euclidean space or between events ...
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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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1answer
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Reality, locality, and universality in the EPR paradox

Apologies if this has been asked before. I did some searching but didn't see it anywhere asked quite like this. Thanks in advance for any insights. Caveat: I am an organic chemist and thus ...
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1answer
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Does Bell's theorem imply nonlocality using a false assumption? [closed]

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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1answer
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Why does the Lagrangian Density have to be a polynomial of the field?

In a lecture, a professor appeared to have said that the Lagrangian can only contain terms that have powers of $\phi$ and a term with $\partial_\mu \partial^\mu \phi$ . I imagine this would make any ...
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Localization of photon

Is the photon localized at the instant of its Emission (release)? by an accelarating charge by Atom´s emission
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Is it possible to define background independent fluid dynamics equations?

Imagine a lake, and you measured the distance from each molecule to it's neighbours for molecules to within say 3 molecular radii. Taking this data you could reconstruct the positions of the ...
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How do we know quantum entanglement works no matter the distance?

It is said quantum entanglement works regardless of distance. 2 particles can be entangled and information is shared instantaneously, even if they are lightyears away from each other. But how do we ...
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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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3answers
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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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Are there any black hole information loss solutions that do not resort to non-locality?

It seems as though all solutions to the information paradox resort to non local effects. What solutions do we have that preserve locality?
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1answer
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Local operators in quatum mechanics

I was reading about LOCC recently, wherein two parties (Alice and Bob) are only allowed to apply local unitaries in their corresponding qubits and communicate classicaly. To motivate this situation, ...
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1answer
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Why do we only time-evolve one operator in the Lieb-Robinson bound?

Background The Lieb-Robinson bound is said to provide some notion of causality in non-relativistic quantum systems with bounded local interactions. Formally, it can be stated as follows. Theorem (...
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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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What does it mean be gravity propagates with $c$? [duplicate]

I know that gravity propagates with speed of light. Does it mean that if Earth's orbit will disturb after 2 years if a supermassive black hole suddenly appears 2 light years away? Is this related to ...
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1answer
206 views

Where is locality used in CHSH/Bell's inequality?

A very similar question is asked here, but I'm still confused :( From Bell, in a hidden variable model, $A = A(\lambda, a)=\pm 1$ is the observed spin of the first particle around axis $a$, and $B = ...
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1answer
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What is the effect of the locality condition if a „Rindler observer“ hovers close to a black hole?

Consider a „Rindler observer“ hovering close to the event horizon of a black hole, whereby flat spacetime is assumed locally. Does this observer see the same Unruh radiation like a Rindler observer ...
2
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1answer
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Distinguish Definitions: Realism Scientific, Realism, and realistic

I was readying about study about bell's theorem, where I had the question about some definitions. Here's some of my summaries: Scientific Realism: (https://en.wikipedia.org/wiki/Scientific_realism#...
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Why can't a localized state thermalize?

I am trying to get my head around Anderson localization and many body localization, and currently am looking at this article. In the first paragraph the author states First, since a localized state ...
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How does one define locality in a discrete system?

Consider a discrete system, such as a spin chain or spin net. Generally I think we can define such as system as a (undirected) graph, with various quantum operators (such as spin operators) "living" ...
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1answer
192 views

In what sense is a separable potential maximally non-local?

A (rank-one) separable potential is an operator $V$ with the coordinate representation $$ \langle \mathbf r' | V | \mathbf r \rangle = - A u(r) u(r')$$ where $u(r)$ is a real-valued function. It is ...
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2answers
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Proof of cluster decomposition theorem

I have looked through a few lits but can't find a proof for cluster decomposition theorem, which states that asymptotically separated apart operators cannot influence each other. Is there a formal ...
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1answer
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Basic question about local algebras in AQFT

AQFT (algebraic quantum field theory) assigns "local algebras of observables" to bounded regions of spacetime, in particular to double-cone ("diamond") regions. These algebras' projection operators ...
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Relativity and Bell's inequalities

I am reading a collection of interviews taken with prominent physicists as in an aftermath of famous Alain Aspect experiment. Between them John Bell states that if local realism has to go, he would be ...
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Does Bell's theorem have anything to say about the locality or realism of Quantum Mechanics?

In the original paper written by Bell, it's clear to me that what he's really trying to answer is what class of Classical Theories (that obey the laws of classical probability theory) can replicate ...
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2answers
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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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1answer
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Why don't there seem to be any dimensionless fields in nature?

Scalar fields have dimension 1, spinor fields dimension 3/2, and vector bosons like the photon dimension 1. According to the principles of renormalizability (along with others), this restricts the ...
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Infinite derivatives, Locality and Lagrangian

Providing the derivative of a single valued function $f(x)$ is like providing its value at two infinitesimally close points. My question consists of two parts: Can Higher derivatives be thought of ...
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1answer
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Locality in the coulomb gauge of classical electrodynamics

In the coulomb gauge, the equations that describe the dynamics of $\Phi$ and $\vec{A}$ simplify to: $$ \Delta \Phi = - \frac{\rho}{\epsilon_0} \\ \Delta \vec{A} - \frac{\partial_t^2}{c^2} \vec{A} = - \...
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What is the relation between continuity?

What is the relation between continuity and locality if there is any, either in classical or quantum mechanics? Are they the same?
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Field redefinitions involving derivatives

Consider the field equation $(\partial^2-m_1^2)(\partial^2-m_2^2)\phi =0 $ Now let me make the field redefinition $\psi = (\partial^2-m_2^2) \phi$ The question is, will the S-matrix be invariant ...
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How does the EPE-DH interpretation of quantum mechanics account for interaction-free measurement?

The extended probability ensemble decoherent histories (EPE-DH) interpretation of quantum mechanics proposed by Murray Gell-Mann and James Hartle posits that there is one real fine-grained history of ...
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1answer
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Newton's laws of gravitation and instantaneous action

I have been recently comparing Newton's and Einstein's laws of gravitation. Most of the authors in physics seem to claim that Newton's laws were incorrect. One of the important aspects that they ...
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Under what circumstances is the functional derivative (of an action functional) an actual function?

In general, for a functional $F[\phi]$, the functional derivative is $$\frac{\delta F[\phi]}{\delta \phi} [f(x)] = \lim_{\varepsilon \to 0} \frac{F[\phi + \varepsilon f ] - F[\phi]}{\varepsilon}$$ ...
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Malament theorem in curved spacetime?

Malament's theorem roughly assert that given a very general theory of a point particle, characterized by some operator $P_D$ such that for a region of space $D$ at a given time $t$, $P_D | \Psi \...
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1answer
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How local is local in the Hypothesis of Locality?

A while back I asked this question Freely falling frame and the use of special relativity? which I later answered using the Hypothesis of Locality which I used to state that $E=-p_\mu u^\mu$ in any ...