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Questions tagged [locality]

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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 ...
0
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0answers
21 views

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 ...
0
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1answer
76 views

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 ...
1
vote
1answer
123 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 ...
2
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1answer
75 views

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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1answer
60 views

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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0answers
25 views

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 ...
24
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10answers
9k views

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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0answers
33 views

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} = -\...
9
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3answers
218 views

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 ...
2
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0answers
33 views

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?
0
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1answer
41 views

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, ...
0
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0answers
26 views

What are good books to study the basics of Local Realism?

I am trying to have a general understanding of the concepts of Local Realist theories and hidden variable models. I do not need a detailed developement of one of these theories, but only a general ...
3
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1answer
87 views

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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0answers
67 views

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}^{...
0
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0answers
33 views

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 ...
0
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0answers
31 views

Is local realism an inaccurate description of the Universe? [duplicate]

Has the big Bell tests proven local realism wrong? References: The Big Bell Test: Global physics experiment challenges Einstein Crowdsourced quantum reality-check gets crowdsourced peer review
5
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1answer
182 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 = ...
2
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1answer
57 views

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
64 views

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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0answers
49 views

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 ...
2
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0answers
34 views

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" ...
2
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1answer
138 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 ...
2
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2answers
180 views

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 ...
1
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1answer
60 views

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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0answers
92 views

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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0answers
80 views

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 ...
13
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2answers
1k views

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....
3
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1answer
125 views

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 ...
3
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3answers
151 views

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 ...
3
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1answer
157 views

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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1answer
39 views

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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0answers
83 views

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 ...
3
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0answers
44 views

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 ...
3
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1answer
98 views

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 ...
2
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0answers
102 views

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 $$\frac{\delta F[\phi]}{\delta \phi} [f(x)] = \lim_{\varepsilon \to 0} \frac{F[\phi + \varepsilon f ] - F[\phi]}{\varepsilon}$$ ...
2
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0answers
119 views

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 \...
2
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1answer
110 views

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 ...
1
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1answer
43 views

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 ...
3
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1answer
213 views

Why infinite order derivative in Lagrangian density implies non-local?

There is a homework in field theory. It says that negative order of derivative( such as $\frac{1}{\nabla^2}$), fraction order of derivative ( such as $\nabla^{2/3}$ ) and infinite order derivative in ...
3
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2answers
1k views

How does the Earth know when to send a graviton to a newly born particle?

Pardon if this is a silly queston, but I'm reading this for the first time. It says that the force we perceive between two objects is an effect of the exchange of the force carrier particles. Even ...
2
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1answer
219 views

Why must the Einstein tensor $G$ be linear in the Riemann curvature tensor?

In the classic book by Misner, Wheeler and Thorne, they justify the form of the Einstein tensor, $G$, by the fact that it is the unique tensor which satisfies $G$ vanishes when spacetime is flat $...
2
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0answers
227 views

Local Hamiltonian

When I read the paper "Chaos and complexity by design", I found the following sentence in the Introduction part confusing: $$W(t)=\sum_{j=0}^{\infty}\frac{(it)^j}{j!}\underbrace{[H,\dots[H}_{j},W\...
3
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0answers
67 views

Product of Local Hamiltonians is Local

Let $H_1,H_2$ be local Hamiltonians (i.e. interactions are finite range). Let us form the product of the exponentials of both. By Baker-Campbell-Hausdorff, this defines a third Hamiltonian, $$e^{H_1}...
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2answers
337 views

Why does breaking Bell's inequality rule out all local hidden variables theories? [duplicate]

It seems that a hidden variables theory could reproduce Bell's experiments results, preserving locality, as long as it accepts that the superposition state(or at least a faux superposition) existed at ...
0
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2answers
279 views

Is there something wrong with Bell's inequality? [closed]

Repeating the title because that's what I posted on Reddit and didn't get an answer. But I guess the proper question is: is there something wrong with the experiment? The text over on Reddit: ...
2
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0answers
105 views

Locality of Wess-Zumino terms and Goldstone bosons

Suppose a theory with a fermion sector $\psi$ having some global chiral symmetry group $G$ without internal anomalies (i.e., a group whose algebra generators $t_{a}$ give zero coefficients $D_{abc}\...
3
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0answers
128 views

Is the vanishing commutator of observables outside the light cone only a necessary or also a sufficient condition for causality?

The equal-time commutator of observables in QFT has to vanish outside the light cone in order to ensure causality. Mathematically spoken, $[ \bar{\psi}(x)\Gamma_1\psi(x),\bar{\psi}(y)\Gamma_2\psi(y)]|...
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1answer
192 views

What evidence is there that The Big Bang was not just a local phenomenon?

This post is the second in a series of posts that met (decreasingly) with some contention from the physics community, do to my status as a pure mathematician at the very beginning of trying to discuss ...
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1answer
255 views

How can I derive the most general scalar field Lagrangian from locality?

My understanding of the principle of locality in a field theory demands that field degrees of freedom interact locally. For example, $\phi(x)$ at the spacetime point $\phi(x+\delta x)$ can interact ...