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Please tell me about "Action at a distance" in Electrodynamics [closed]

I am confused about how test charge informed about source charge. So I research on it. Web said me that it is "Action at a distance phenomenon". What is this? I am a first year Undergraduate ...
Arpan Purkait's user avatar
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1 answer
60 views

How is information defined when considering locality in quantum mechanics?

$\newcommand{\ket}[1]{|#1\rangle}$ My question is a follow-up from this discussion about the presence of non-local correlations in a theory that is deemed local. The first answer talks about the ...
UVcatastrophe's user avatar
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Is there any restriction for locally mapping a given 2-qubit density matrix into a desired 2-qubit density matrix with lower entanglement?

Suppose we're given a 2-qubit density matrix($\rho_{4\times4}$). we can apply two local maps on each of these qubits seperatly. So the output is density matrix($\rho^{\prime}_{4\times4}$). I'm ...
xhian's user avatar
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1 answer
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Definition of “quasi-locality” in Wilsonian RG scheme

I’m studying about the holographic RG with this paper. In that paper they say Wilsonian action expects quasi locality, but I’m not sure what “quasi-locality" exactly means. If quasi-locality ...
Positron3873's user avatar
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Can you model relativistic interactions without locality?

Assume $c=1$ I've been doing relativity by myself so I may be making some assumptions here that I would not have if my learning had been more extensive. One such assumption is that you can model the ...
NaiDoeShacks's user avatar
2 votes
1 answer
123 views

Is conservation of energy a local law in Quantum field theory? [closed]

From Wikipedia, "The local energy conservation in quantum field theory is ensured by the quantum Noether's theorem for the energy-momentum tensor operator. Thus energy is conserved by the normal ...
KleinMoretti's user avatar
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Lorentz invariance (LI) of time ordering operation

At Srednicki after eq. (4.10), we have a discussion about that the time ordering operation. Have to be frame inv. I.e it has to be LI. He wrote that for timelike separation we don't have to worry ...
Alon Buzaglo Shoub's user avatar
1 vote
2 answers
126 views

On the notion of Local Causality

In 1976, John Bell proved that any locally causal theory can't account for certain observed correlations, he formulated the local causality hypotesis in terms of "local beables". In ...
Davyz2's user avatar
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4 answers
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Confusion around Bell's Theorem and Locality

I recently got interested in foundational aspects of quantum mechanics and I have some questions: Bell's theorem proves that any local, deterministic theory with statistical independence can't account ...
Davyz2's user avatar
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1 vote
1 answer
191 views

$SO(3,1)$ is locally $SU(2)\times SU(2)$, what does *locally* mean here?

I am learning Lie group and Lie algebra. I saw in a YouTube video "Supersymmetry lecture 02" from OpenCourseWare (OCW) at University of Cambridge at 11:17 that $SO(3,1)$ is locally $SU(2) \...
Fermion's user avatar
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Equivalence of two entangling operators with respect to local operators

Suppose that $U_1$ and $U_2$ are two (entangling) operators that act on a quantum system consisting of several qubits. Is there any criterion to tell if these two are equivalent up to applying ...
george doultsinos's user avatar
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What do we mean by causality when we say that entanglement measurements are uncaused? [duplicate]

I’m having a hard time wrapping my head around how the measurement of particle A does not affect the state of an entangled particle B even if no superluminal speeds exist. Suppose Alice makes a ...
user avatar
2 votes
1 answer
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How to interpret Poisson bracket of fields in terms of causality?

In quantum field theory, the fact that space-like separated observables commute, i.e. $[\hat {\phi (x)}, \hat{\phi(y)}]=0$, is taken as the test for causality. The equivalent statement for classical ...
Rain Deer's user avatar
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Newton's second law - local laws and non-local laws

What are local laws? I was reading this line in a book... Newtons second law is a local law. This means that it applies to a particle at a particular instant without taking into consideration any ...
Aditi Bansal's user avatar
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How does locality on space time manifold M put constraints on functions on configuration space of fields?

I am reading David Skinner's notes on AQFT. In Chapter 1 page 3, he mentioned that "purely from the point of view of functions on $C$, locality on $M$ is actually a very strong restriction", ...
Kuro_'s user avatar
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1 vote
1 answer
306 views

Is Quantum randomness true randomness? [closed]

I would like you guys to read it, and see whether it makes sense, and correct me if anything is wrong. I'm not an expert on these topics, so I understand if very wrong. It would be wonderful if you ...
Nathan's user avatar
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1 answer
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Are field theories where free energy density depends on 2nd-order derivative non-local?

It is accepted that infinite order of derivatives in field theory lead to non-local effects while finite number of them local. reference within physics stack exchange Let’s take a lattice with next-...
Sudipta Nayak's user avatar
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Is there any limit to the utility of quantum measurements in the sense of a Lieb-Robinson bound?

So the Lieb-Robinson bound of 1972 derives an emergent maximum speed $v \ll c$ of the propagation of quantum information under time evolution generated by some local Hamiltonian $H(t)$. Basically, ...
just a phase's user avatar
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Well-definedness of commutation relation in commuting local Hamiltonians

I'm reading the famous paper by Haah: Local stabilizer codes in three dimensions without string logical operators. In the last sentence of the introduction, he wrote: A logical operator is a Pauli ...
Waterfall's user avatar
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Why does it make sense to add/subtract the results of measuring in 2 different bases in Bell's inequality when each observer only measures 1 property?

In the CHSH inequality, we construct an experiment whereby two observers each receive a particle and measure two given properties of their particles, for which the outcomes are ±1. We then consider ...
David's user avatar
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6 answers
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Are field theories necessary to make accurate predictions or do they just make calculations easier?

For example, if we really wanted to, could we, at least in principle, model electromagnetism just considering interactions between charged particles without using the EM field? That is, is it ...
Mikayla Eckel Cifrese's user avatar
2 votes
4 answers
1k views

Understanding superdeterminism

I was reading about superdeterminism and it was a bit counter-intuitive. The idea of having a hidden variable on the measurement device is very rational. For example, if we emit light to a constrained ...
user123456789's user avatar
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1 answer
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Is a super-deterministic universe local or nonlocal? [closed]

Bell predicted predetermined (nonlocal) choice as the criteria for a super-deterministic universe. ...our belief that we are free to choose to do one experiment rather than another, absolutely ...
Manuel Morales's user avatar
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1 answer
101 views

Understanding this abstract Lagrangian of effective field theory

I'm learning Wilson's approach to renormalization and the Effective Field Theory. Typically, the theory is defined by a Lagrangian valid up to some scale $Λ$. I saw these two definitions for 4-...
IGY's user avatar
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1 vote
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Ostrogradsky instability and fractional derivatives

Are fractional derivatives (or even more generally differentegrals) also under the scope of the Ostrogradsky instability theorem?
riemannium's user avatar
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2 votes
2 answers
918 views

How does Bell's theorem disprove realism?

I am told that the the violation of Bell's inequalities prove that the universe cannot have local realism. That is to say, the universe cannot both be local and real. I understand how Bell's theorem ...
Eli Yablon's user avatar
1 vote
1 answer
4k views

What does it mean to say the universe is not locally real? [duplicate]

Pardon me if this is a naive question. What is difference between saying space-time is not locally real, and saying it is not real? The proposal that the universe is not locally real seems to imply ...
PeterJ's user avatar
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1 vote
2 answers
162 views

How is the non-locality of a theory apparent from its mathematical form?

I am reading Relativistic Quantum Mechanics by Bjorken and Drell and on page 5 they present the following attempt at a relativistic Hamiltonian for a free particle \begin{equation} i\hbar\frac{\...
NeonGabu's user avatar
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2 votes
0 answers
258 views

How localized are photons in a quantum field?

Are photons or other quanta at least somewhat localized in a quantum field? My limited understanding of quantum field theory is that photons or other fundamental particles (quanta) are excitations of ...
kdtop's user avatar
  • 317
2 votes
1 answer
85 views

Non- Local operators and Entanglement

Given a separable state, $|\psi\rangle$ = $|a\rangle\otimes|b\rangle$, operating on this state with a local operator of the form, $A\otimes B$ will not lead to an entangled state. Is the converse true?...
Paranoid's user avatar
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2 votes
1 answer
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Locality and local gauge invariance

I was reading this question on the Physics Stack Exchange, and I'm still not quite sure how I can understand the relationship between locality and local gauge invariance using this example. Consider ...
IGY's user avatar
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0 votes
2 answers
254 views

How to understand the principle of locality from a common example?

I'm reading the definition of the principle of locality from its Wikipedia page: The principle of locality states that an object is influenced directly only by its immediate surroundings. This ...
IGY's user avatar
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2 votes
2 answers
96 views

Is Gauss law for gravity local?

in Newtonian gravity, the gravitational field obeys the equation $$\nabla^2 \phi = 4 \pi G \rho$$ David Tong in his notes on general relativity claims that this equation works well when $\rho$ is not ...
Brain Stroke Patient's user avatar
2 votes
1 answer
231 views

In an entangled system, what happens to Alice's wavefunction right after Bob makes a measurement?

Suppose two entangled particles are far apart. One is with Alice and the other is with Bob. The relative velocity between Alice and Bob is zero (and spacetime is flat), so that we can define a notion ...
Ryder Rude's user avatar
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2 votes
3 answers
375 views

Don't Bell experiments rule out local non-realism too? [duplicate]

Bell experiments rule out local realism (hidden variables). But it seems to me that it also rules out local non-realism (no hidden variables). Local non-realism makes 2 claims; Two distant events can'...
Juan Perez's user avatar
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2 votes
1 answer
111 views

How to tell if a theory is "local"?

Suppose I have a collection of $N$ quantum systems, which I would like to think of as lattice sites. If you tell me that these $N$ sites have some particular embeddings $\vec{x}_i$ in $\mathbb{R}^d$, ...
pseudo-goldstone's user avatar
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3 answers
102 views

Cluster decomposition $\stackrel{?}{=}$ Translation invariance

In Weinberg Volume 1 (section 4.4), Weinberg argues for a certain structure of the interaction Hamiltonian by demanding that it produce an $S$-matrix satisfying cluster decomposition. The proposed ...
phonon's user avatar
  • 169
3 votes
1 answer
754 views

Proof that conservation of momentum is Lorentz invariant

In classical mechanics, if $$\frac{\mathrm d}{\mathrm d t}\sum_i m_i\vec{v_i}=0$$is true for one frame of reference, then it is easy to prove that this is true for all frames (since different frames ...
Filippo's user avatar
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1 vote
2 answers
226 views

Why is the local component of sound particle-velocity not associated with a local component of pressure?

A sound wave can be described by the pressure field or the sound air particle velocity (acoustic flow). Both are intrinsic to any sounds, i.e. there is no sound wave if no pressure or no particle ...
Noil's user avatar
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1 answer
421 views

How does the many-worlds interpretation solve spooky action at a distance?

If we take the classic example of two particles that are entangled with up spin and down spin, and we separate these particles a few light years apart and then observe them one after the other, they ...
simon lombard's user avatar
2 votes
1 answer
150 views

Is there something that violates "time locality"?

The way I understand locality is that for an object to influence another object away from it, it has to do so through the space that separates them. It can shoot out an EM wave to the other object, ...
Guilherme Mendonça's user avatar
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1 answer
84 views

Local nature of physical laws

All the laws in physics are local in nature and that's why their formulation follows differential equations. My doubt is whether the locality is a proven theorem or it is a postulate?
rkn's user avatar
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1 vote
0 answers
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Is causality a consequence or a constraint in physics?

I wonder if causality is a constraint that we must add to physical models (if needed), or is it a consequence of Lorentz invariance and locality (or something else). In other words, which properties ...
Noam Chai's user avatar
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1 vote
0 answers
49 views

What are the implications of rejecting the local tomography assumption?

Recently I presented on the paper by Renou, et. al. in Nature (Quantum theory based on real numbers can be experimentally falsified) developing an experimental technique for rejecting real ...
fiziks's user avatar
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1 vote
0 answers
140 views

Local algebra of AQFT vs Bisognano Wichmann Theorem

Maybe I am misunderstanding something really stupid, but I am finding it hard to think of local algebras in terms of wedge algebras. One of the claims (see, e.g., Section 3 and 4 of this paper) is ...
Evangeline A. K. McDowell's user avatar
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0 answers
115 views

How do Lieb-Robinson Bounds talk about locality without the position operator?

So we know when one goes from QM to QFT Lieb Robinson bounds become micro causality. But micro causality is a statement on the commutators assuming they are space-like, time-like or light-like. ...
More Anonymous's user avatar
1 vote
0 answers
41 views

Locality in Bell Experiments

I have a question about experiments that show a violation of Bell's inequalities. It's said that these experiments disprove local realism. However, immediately before the final measurement of the 2 ...
Mat's user avatar
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5 votes
1 answer
125 views

Conserved charge at null infinity associated with Large gauge transformation

I am reading Strominger's lecture notes "Lectures on the infrared structure of gravity and gauge theory" (https://arxiv.org/abs/1703.05448). At some point, following (I guess) the authors of ...
schris38's user avatar
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9 votes
2 answers
372 views

How are we able to use quantum field theory to study systems?

I've been trying to understand the concept of locality in QFT, and I was reading this paper by Edward Witten, where he explains (on pg 13) that the state space cannot be factored into a tensor product ...
Sandejo's user avatar
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0 votes
2 answers
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Must all field theories depend on the spatial derivate of the fields?

For instance, if I have encountered \begin{equation} \label{eqq2} \frac{\partial \mathcal{L}}{\partial (\partial_i \phi)} = 0 \end{equation} This tells us that $\mathcal{L}$ cannot depend on $\...
Lopey Tall's user avatar
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