Questions tagged [non-locality]

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114 views

Is nonlocality consistent with scale invariance?

For sure I'm excluding gravity at first step, the question is that if nonlocality is compatible with scale invariance. At the classical and quantum levels for field theory in Minkowski spacetime. Then ...
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2answers
154 views

Why is Pilot Wave Theory nonlocal?

I have read that the Pilot Wave Theory is nonlocal and can therefore be excluded. Why is the PW Theory nonlocal? Isn't QM also nonlocal, as we can see it from entanglement? I already googled the ...
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4answers
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Computer analogy to non-locality in quantum mechanics

It is not uncommon to say that the non-locality of quantum mechanics is equivalent to the following computer analogy: if you are trying to model an entangled two spin system, then even if the spins ...
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47 views

Nonlocality in the Many Worlds question

David Wallace and Lev Vaidman have said the MWI is nonlocal. "The overall story about locality in Everettian quantum physics, then, is this: the dynamics of the theory are local: there is no ...
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4answers
163 views

What is wrong with violation of locality (EPR paradox)?

When studying the EPR paradox, at some point we must resign ourselves that Reality and Locality can not be both true in the current theory of quantum mechanics. A lot has been said in Physics.SE about ...
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Does quantum entanglement necessitate that two particles communicate their state with one another?

I often hear it said that quantum particles, like an electron-positron pair or two entangled photons, which are entangled with one another communicate or transfer information about their state ...
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1answer
114 views

Is QFT "more" non-local than QM, at least mathematically?

Could physics still be local? Here's what I mean: The Schrodinger/Dirac equations allow for quantum entanglement, right? So in that sense they are non-local physically. But they are mathematically ...
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67 views

Non-locality and Twistor functions

Is there a nice intuitive way to visualize the concept of non-locality associated to twistor functions? And how is it related to the type of non-locality we encounter in Quantum Mechanics?
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1answer
46 views

Local vs Nonlocal electrodynamics

I am having a hard time to understand the difference between local and nonlocal electrodynamics. Does the former refer to the case when the charge (i.e electron) can be localized and the latter refer ...
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38 views

Has there been experimental evidence that entangled state collapses simultaneously?

If we observe the observable of one particle among two particles which are entangled each other and separated far away, we can determine the value of the other particle’s same observable from the ...
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1answer
72 views

Where does the negative cosine relation for quantum mechanical CHSH correlations come from?

I have been lately looking into Bell's inequality. I have noticed a recurring graph that depicts the correlation of two spins when measured at different angles, for the quantum and the classical case: ...
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Many worlds is nonlocal too after all according to some physicists?

Not a physicist but I have understood that MWI is unique in that it preserves local dynamics. There is a wavefunction - not in spacetime but in some more abstract space. But the worlds with spacetime ...
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59 views

Renormalization of non-local product of operators

In Unraveling hadron structure with generalized parton distributions by Belitsky and Radyushkin, appendix G, eq. (G.47) it is said that for renormalization of an on-local product of operators such as ...
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Are violations of realism the same thing as contextuality?

I am basically looking for a counter-example where we'd get contextuality but not violations of realism (and vice-versa). If no such counter-examples exist, then it seems to me that they're really one ...
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2answers
82 views

How to rule out all forms of "realism"?

Thus, we see that local causality condition (1) is mathematically equivalent to the assumption of joint probabilities, $p(A_1,A_2,B_1,B_2)$. The latter is a form of realism: complementary observables ...
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1answer
37 views

Does non-local interepretations of quantum mechanics imply FTL communication? [closed]

For example the pilot wave theory... And if this is the case then does FTL commuincation imply time travel (i.e: information going back in time).
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Is it possible to use Quantum Monte Carlo for non local interactions?

I just have a brief question about QMC being applied to calculating expectation values. If I were to calculate the expectation value of an operator, like the energy via a Quantum Mote Carlo ...
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1answer
80 views

Non-locality of pre-Klein-Gordon equation

In Relativistic Quantum Mechanics, Bjorken and Drell state that expanding the square root in the equation $$-\hbar^2\frac{\partial^2\psi}{\partial t^2}=\sqrt{-\hbar^2c^2\boldsymbol{\nabla}^2+m^2c^4}\...
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1answer
62 views

If quantum entanglement causes the violations of Bell's inequality why don't we see perfect correlation?

From wikipedia: For example, if a pair of entangled particles is generated such that their total spin is known to be zero, and one particle is found to have clockwise spin on a first axis, then the ...
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91 views

How can quantum nonlocality be understood in the path integral formalism?

I have always had my difficulties (being bored, impatient) with the theoretical considerations around quantum nonlocality, especially Bell's inequalities. What makes it cumbersome for me is that these ...
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2answers
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How to take 'non-local' functional derivatives?

I am currently in the process of getting into linear response theory in general, and I have often met functional derivatives of the type $$\frac{\partial J[f(x)]}{\partial f(y)} = \chi(x,y).$$ I've ...
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1answer
48 views

Quantum Erasure - what causes the phase difference in the two interference patterns observable at Do?

In the Delayed Quantum Erasure experiment, I understand that the interference patterns that you would see at Do is associated to the entangled photons that eventually arrive at D1 or D2 (which-way ...
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1answer
55 views

How does quantum contextuality relate to realism?

According to Spekkens contextuality can be defined as follows: Suppose A, B and C are Hermitian operators such that A and B commute, A and C commute, but B and C do not commute. Then the assumption ...
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Does bohmian mechanics imply time-travel due to its nonlocal nature?

I know bohmian mechanics is non local in the sense two particles can affect each other instantaneously(faster than the speed of light). Does this imply that time-travel is possible?
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1answer
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Easiest way to see that superposition is necessary?

I have been discussing QM with a friend and wanted to explain why holding on to realism means we must accept non-locality. Essentially I got hung up on explaining Bell's Theorem in simple words. I ...
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2answers
124 views

How does relaxing counterfactual definiteness allows for CHSH inequality violation?

Scenario, I want to play a game with a group of students as a teacher, I ask two teachers to help. The students are from the central classroom, going to room A and room B where the teachers there asks ...
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A Venn diagram for: (non-)locality, (non-)realism, (non-)contextuality, (non-)signalling, (dis-)entanglement

I recently asked a (yet-unanswered) question about the relationship between state-dependence and violations of realism. The more I read on the subject, the more I find myself digging deeper in a ...
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2answers
207 views

How can a disentangled state be contextual?

I (re-)learned about Bell tests from the ground up based on this very intuitive lecture by Spekkens. In a nutshell, realism is violated whenever measurement statistics cannot be reproduced by ...
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1answer
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Question on hidden variable theory of QM [closed]

My understanding from careful study of Bells theorem is that there may be a deep subtlety that is not ruled out, but is probably very minimally studied in the literature. However the literature is ...
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1answer
128 views

Is Bell nonlocality compatible with, or even predicted by, quantum field theory?

Bell's theorem, together with experiments confirming the ordinary quantum mechanical distant correlation predictions which violate its conclusion for local theories, show that any entirely local ...
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1answer
80 views

Are following statements valid for quantum gravity?

In the concluding section of this post user Chiral Anomaly states following: On the other hand, since any stable marriage of quantum theory and gravity (in the sense of general relativity, not just ...
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1answer
101 views

Non-analytic functions and non-local Lagrangians

Infinite sums of increasingly higher-order derivatives, when present in Lagrangians, are typically taken as a sign of nonlocality. This is supposed to rule out fractional, negative and exotic (for ...
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What does it mean for an extended operator to possess "local excitations"?

In the context of defect conformal field theory, we consider in operator product expansions "local excitations" of the defect (see e.g. text between eq. $(1.1)$ and $(1.2)$ in the paper ...
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What is an "optimal ensemble" used to demonstrate quantum steering?

I am reading Wiseman et al. (2007) and Jones et al. (2007) papers on quantum steering. They relied on the existence of "optimal ensembles" for a Local Hidden State theory. They make use of ...
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1answer
157 views

Blocking quantum effects

A Faraday cage blocks electromagnetic fields, provided they are not intense enough to change the state to something non-conductive (e.g. slicing it in two with a laser). Is there any analogous system ...
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2answers
123 views

Why quantum mechanics doesn’t break locality in entanglement but hidden variables theories will?

What makes it so that quantum mechanics doesn’t break locality in entanglement yet hidden variable theories will? In Bell‘s inequality said that hidden variables theories need to break locality in ...
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1answer
38 views

Light in action-at-a-distance formulation of Electromagnetism

If it is possible to use Jefimenko's equations to formulate Electromagnetism as a non-instantaneous action-at-a-distance theory, what would electromagnetic radiation be in such a theory? Would it be a ...
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0answers
47 views

Concrete Example of Quantum Entanglement, Quantum Steering and Bell Nonlocality

I was reading the wikipedia page for quantum steering. The following is the mathematical way they have described the three notions: Is there any concrete example of these three concepts? Like, any ...
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2answers
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What is locality?

In QFT and statistical mechanics, one is usually interested in studying integrals of the form: $$Z(\phi) =\int d\mu_{C}(\phi')e^{-V(\phi+\phi')}$$ where $\mu_{C}$ is Gaussian measure with mean zero ...
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1answer
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Functional Analytic Square Root of Hamiltonian Alternative to Dirac

I was thinking about the history of the Dirac equation and asked myself, what happens if one simply considers the Schrödinger equation $$i\hbar\frac{\partial\phi}{\partial t}=\sqrt{-c^2\hbar^2\Delta+m^...
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1answer
299 views

Argyres-Douglas CFT

Adding of mass in supersymmetric gauge theories will affect structure of moduli space by creating new singular point (picture and some statements from Matteo Bertolini: Lectures on Supersymmetry): ...
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253 views

Is there a deep reason why action comes from a local lagrangian?

In both classical and quantum physics Lagrangians play a very important role. In classical physics, paths that extremize the action $S$ are the solutions of the Euler-Lagrange equations, and the ...
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Particle picture in position space in quantum field theory

When I operate $a^{\dagger}_k$ on vacuum, $|0\rangle$, I get a particle created in momentum space with a 4-momentum equal to $(\omega_k, \vec{k})$ where $\omega_k=\sqrt{m^2+\vec{k}^2}$ here I'm only ...
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1answer
205 views

Local and non-local interactions

When I look for the van der Waals interactions, they are defined as they are non-local interactions but no explanation for what they mean by non-locality. What would be the best way to understand this ...
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What is the difference between non-local optical response and local optical response?

Does anyone knows what is the difference between non-local optical response and local optical response in metal-dielectric-metal?
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255 views

Does Quantum Entanglement have a preferred reference frame?

What I mean by this is, with wave function collapse,--and by extension, collapse between two entangled particles--being nonlocal (instantaneous across space), in what reference frame does the ...
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1answer
221 views

What is the Hilbert space of the SYK model?

In reading a recent preprint [1] contrasting bosonic models with local (tensor product) Hilbert spaces with SYK-like models of fermions, I realized I was confused about something. While I have a vague ...
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1k views

Non-local potential

I read that the Schrodinger equation for a non-local potential is given by $$-\frac{\hbar^2}{2m}\nabla^2\psi(x)+\int V(x,x')\psi(x')dx'=E\psi(x).$$ In case of a local potential, $$ V(x,x')=V(x)\delta(...
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Are there any nonlocal one-body operators?

In case I have a one-body operator given by $$ \hat{O}=\int d^3r\int d^3r' \,\hat\psi^\dagger(\mathbf{r})\langle \mathbf{r}|\hat O|\mathbf{r}'\rangle\hat\psi(\mathbf{r}'), $$ are there any operators ...
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What is recessional nonlocality?

In laymen’s terms, what is recessional nonlocality? I understand recessional means to recede or retract away, and (correct me if I’m wrong) I understand locality has something to do with quantum ...