Questions tagged [locality]
The locality tag has no usage guidance.
2
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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 ...
0
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1answer
41 views
Localization of photon
Is the photon localized at the instant of its Emission (release)?
by an accelarating charge
by Atom´s emission
0
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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 ...
0
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0answers
25 views
Non-locality of the Madelung equations?
As far as I understand, the Madelung equations
$$
\frac{\partial \rho}{\partial t} + \nabla \cdot \rho \mathbf{u} = 0 \\
\frac{\partial \mathbf{u}}{\partial t} + \mathbf{u} \cdot \nabla \mathbf{u} = -\...
9
votes
3answers
205 views
How exactly does the proof of Bell's theorem fail if you remove the locality assumption?
In this paper Bell derives his famous inequality using the assumtions of locality and realism. In order to understand how the locality assumption affects the derivation of the inequality, and why it ...
2
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0answers
33 views
Are there any black hole information loss solutions that do not resort to non-locality?
It seems as though all solutions to the information paradox resort to non local effects. What solutions do we have that preserve locality?
0
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1answer
38 views
Local operators in quatum mechanics
I was reading about LOCC recently, wherein two parties (Alice and Bob) are only allowed to apply local unitaries in their corresponding qubits and communicate classicaly.
To motivate this situation, ...
0
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0answers
23 views
What are good books to study the basics of Local Realism?
I am trying to have a general understanding of the concepts of Local Realist theories and hidden variable models. I do not need a detailed developement of one of these theories, but only a general ...
3
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1answer
83 views
Why do we only time-evolve one operator in the Lieb-Robinson bound?
Background
The Lieb-Robinson bound is said to provide some notion of causality in non-relativistic quantum systems with bounded local interactions. Formally, it can be stated as follows.
Theorem (...
4
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0answers
65 views
Decomposition of rank-2 field and local interactions
Any rank-2 tensor can be decomposed in the following way
$$
\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
29 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
votes
1answer
175 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
votes
1answer
47 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
62 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#...
1
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0answers
47 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
32 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" ...
1
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0answers
92 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
139 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
vote
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 ...
1
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0answers
82 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 ...
1
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0answers
77 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
983 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
123 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 ...
2
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3answers
123 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
votes
1answer
141 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} = - \...
-1
votes
1answer
36 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?
1
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0answers
73 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
votes
0answers
37 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
votes
1answer
92 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
votes
0answers
94 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
114 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
votes
1answer
98 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
vote
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
votes
1answer
198 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
207 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
197 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}...
-1
votes
2answers
298 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
votes
2answers
255 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
102 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
votes
0answers
121 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)]|...
1
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1answer
182 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 ...
1
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1answer
233 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 ...
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0answers
44 views
Local degrees of freedom and second quantisation
In quantum field theory, the degrees of freedom $\phi({\bf{x}},t)$ are local. This means that the the dynamics of the field in a given region of spacetime is not governed by events outside its ...
3
votes
1answer
106 views
Geometry and integral laws of physics
Reading the English translation of Einstein's seminal paper on GR.
http://einsteinpapers.press.princeton.edu/vol6-trans/90?ajax
This paragraph below on p78 doesn't make much sense to me.
Could you ...
1
vote
3answers
597 views
Are fields (electric or magnetic) real? [closed]
Are fields (electric or magnetic) real or they are just theoretical concepts to explain lot of stuff which couldn't be explained by Newtonian action at a distance approach?
7
votes
1answer
207 views
$\phi^{n}$ quantum scalar field theories where $n$ is not an integer
Consider a quantum scalar field theory with interaction terms of the form $\phi^{n}$, where $n$ is not an integer.
Where are some examples of widely-studied quantum field theories which involve such ...
