Questions tagged [locality]
The locality tag has no usage guidance.
170
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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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1answer
52 views
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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1answer
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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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1answer
75 views
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 ...
4
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2answers
191 views
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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1answer
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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
112 views
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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2answers
182 views
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 ...
2
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2answers
110 views
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 ...
2
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0answers
92 views
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 ...
2
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2answers
67 views
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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0answers
26 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
90 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 ...
0
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1answer
169 views
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 ...
2
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1answer
84 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
125 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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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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10answers
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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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0answers
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Non-locality of the Madelung equations?
As far as I understand, the Madelung equations
$$
\frac{\partial \rho}{\partial t} + \nabla \cdot \rho \mathbf{u} = 0 \\
\frac{\partial \mathbf{u}}{\partial t} + \mathbf{u} \cdot \nabla \mathbf{u} = -\...
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3answers
237 views
How exactly does the proof of Bell's theorem fail if you remove the locality assumption?
In this paper Bell derives his famous inequality using the assumtions of locality and realism. In order to understand how the locality assumption affects the derivation of the inequality, and why it ...
2
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0answers
35 views
Are there any black hole information loss solutions that do not resort to non-locality?
It seems as though all solutions to the information paradox resort to non local effects. What solutions do we have that preserve locality?
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1answer
54 views
Local operators in quatum mechanics
I was reading about LOCC recently, wherein two parties (Alice and Bob) are only allowed to apply local unitaries in their corresponding qubits and communicate classicaly.
To motivate this situation, ...
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1answer
94 views
Why do we only time-evolve one operator in the Lieb-Robinson bound?
Background
The Lieb-Robinson bound is said to provide some notion of causality in non-relativistic quantum systems with bounded local interactions. Formally, it can be stated as follows.
Theorem (...
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0answers
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Decomposition of rank-2 field and local interactions
Any rank-2 tensor can be decomposed in the following way
$$
\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}^{...
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 ...
5
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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 = ...
2
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1answer
69 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
76 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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53 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 ...
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0answers
42 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
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
267 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 ...
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1answer
68 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
114 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
95 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 ...
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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
126 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 ...
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3answers
194 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 ...
5
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1answer
209 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
42 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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101 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 ...
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0answers
52 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
115 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 ...
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0answers
111 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
$$\frac{\delta F[\phi]}{\delta \phi} [f(x)] = \lim_{\varepsilon \to 0} \frac{F[\phi + \varepsilon f ] - F[\phi]}{\varepsilon}$$
...
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0answers
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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 \...
2
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1answer
149 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 ...
asked May 29 '17 at 15:46
Quantum spaghettification
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