Questions tagged [non-locality]
The non-locality tag has no usage guidance.
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Quantum Entanglement: Is Non-locality Inherent or Does It Violate Causality? [duplicate]
Dear Physics Stack Exchange community,
I am intrigued by the concept of quantum entanglement and its implications for our understanding of the fundamental nature of reality. I have come across various ...
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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 ...
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Does a measurement violate conservation law? [duplicate]
(Edited according to the discussion with @naturallyInconsistent. The edited part is highlighted in italic.)
We have an experimental bench and we assign a coordinate system $(x,y)$ to it.
We shall call ...
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Does a nonlocal deterministic hidden variable theory imply retrocausality?
I've had this idea for a while, and recently I stumbled upon a short paper from N. Gisin that formulated this idea, but I could not find a meaningful discussion on the problem. The paper that I found ...
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What's mechanism of "spooky action at the distance"? [duplicate]
Nobel prize 2022, a local theories of hidden variables are ruled out, Einstein's "spooky action at a distance" seems to be a reality.
Is there ANY explanations of this behavior of quantum ...
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Have spin-correlation experiments been done on entangled particles other than photons?
I know that Bell experiments on spin correlations have been done with entangled photons, but have spin-correlation experiments ever been done on entangled particles other than photons?
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Is numerical optimization useful in (highly nonlocal) Lagrangian dynamics?
It is well known that many equations of physics can be formulated as an extremalization principle, i.e. that the equations arise from an action $S = \int L(t,x(t))dt$ with a time-dependent Lagrangian $...
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How can two phonons be entangled when the atoms in the crystal are not?
It is my understanding that you can use phonons to make a gaussian packet, which would behave like a quantum particle. I also believe that you can make two such packets and entangle them, that is ...
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Are functions of commuting measurement operators equivalent to the same functions on the outcomes of those operators?
I.e., is it the case that for all states $\hat{\rho}$, we have that $F(\hat{A}_i, \hat{A}_j, \hat{A}_k, \hat{\rho}) \equiv F(a^{(l)}_i, a^{(m)}_j, a^{(n)}_k)$, where $a^{(l)}_i, a^{(m)}_j$ and $a^{(n)}...
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What is the difference between nonlocality and entanglement?
I'm a bit confused about the difference and relation between (quantum) nonlocality and entanglement.
To give some context about my confusion, I was reading this paper: Brunner, Nicolas, et al. "...
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Is degeneracy of eigenvalues required for the Kochen-Specker theorem?
I'm wondering why the operators for the Kochen-Specker theorem are 3-dimensional while they only produce two eigenvalues $\{0,1\}$. Is this degeneracy always needed regardless of the dimensionality of ...
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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{\...
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Local fields in relativity with pure creation operators
The Wikipedia page on the Spin-Statistics theorem states that
In relativity, there are no local fields that are pure creation operators or annihilation operators.
In this answer at SE Phys, in a ...
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Are spinors intrinsically nonlocal?
I would prefer a purely classical answer since I don't think quantum mechanics (quantum field theory etc.) are necessary to answer this question and such answers will likely complicate matters. If you ...
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Nonlocality of a bug on movie screen
I am currently learning quantum mechanics using Griffiths. In the appendix, he goes to talk about EPR and Bell's inequality, and that experimental verification of Bell's inequality rejects the "...
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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 ...
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In the Bell CHSH experiment, why are Alice and Bob not allowed to pre-arrage their measurements?
From Nielsen and Chuang, Chapter 2:
Imagine we perform the following experiment, illustrated in Figure 2.4. Charlie prepares
two particles. It doesn’t matter how he prepares the particles, just that ...
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Quantum mechanics: does many-worlds interpretation remove nonlocality? Bell-type experiment
Trying to make sense of many-worlds interpretation and see if it removes nonlocality or solves other problems. It appears to me that branching is equivalent to collapse... so trying to see what I'm ...
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How are the different derivations of Bell's inequality related?
I wanted to ask about two different derivations for bell's inequality for the known CHSH inequality.
One derivation is the one bell originally used in 1971
this derivation is thoroughly written in ...
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Why is quantum non-locality so surprising when quantum mechanics is a non-relativistic theory to begin with?
Ignore the fact that Quantum Field Theory (QFT) is compatible with Special Relativity (SR) for a second. Imagine we are back in a time before the construction of QFT. If Quantum Mechanics (QM) is the ...
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Is there any way to write a non-local operator nicely?
Consider the boundary(the real axis) of the 2d CFT or the D-brane. They were non local object but with well known description.
Consider the following expression,
$$\langle 0| \phi_1(z_1) \phi_2(z_2)|B\...
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Measurement of the spin of the EPR pair in two orthogonal directions and how did Einstein tackle this?
Let us consider two types of measurement in the EPR experiment. In Bohm's description of this experiment, the state of the electron-positron (called the EPR pair) is given by
$$
|{\rm EPR} \rangle =\...
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Nonlocal Gravitational energy: How to localize nontrivial topology in GR?
Ok, This question has been beaten to death. I just wanted to look at it from a slightly different angle: Einstein, Rosen, and later Wheeler considered the possibility of particles as spacetime ...
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Non-local Euler-Lagrange equations and Noether theorems
Following up my Noether theorem issues: how can Euler-Lagrange and Noether theorems be formulated for non-local lagrangians?
Two examples from the literature:
Example 1. Let $L(\phi, F(\phi))=-\dfrac{...
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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, ...
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Are only local hidden variables at odds with special relativity?
So hidden variables in quantum mechanics are at odds with special relativity. I can understand this to be the case with local hidden variables, but does this also hold for non-local ones? Often one ...
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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?
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Effective action as a generating functional and its derivative expansion
On page 381 of Peskin and Schroeder, equation (11.90) reads
$$ \frac{\delta^2 \Gamma}{\delta \phi_{cl}(x)\delta \phi_{cl}(y)} = iD^{-1}(x,y).\tag{11.90}$$
I am having a bit of trouble interpreting ...
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Locality of interactions and their high energy behavior
In a classic Georgi review of EFT, I have read the following quote
The result of eliminating heavy particles is inevitably a
nonrenormalizable theory, in which the nontrivial effects of the heavy
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Lagrangian depending on running integral
In the theory of calculus of variations, the Lagrangian generally depends on the unknown function and its first derivative. This assumption leads to the Euler-Lagrange equations.
However, I found that ...
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Interpretations for Interaction-free measurements
So I read several papers on IFM by Vaidman, Dicke, and many others, In all of them I think the Pilot wave theory is able to adequately justify the observations, but then I came across several papers ...
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Could Planck scale wormholes be a solution for non-locality?
When two entangled particles are separated, an observation made on one particle seems to be able to act at a distance to determine the state of the other particle. Is it possible, or has anyone in ...
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Non-local connection Between $D$ and $E$ (Kramers-Kronig relations)
I'm trying to solve next exercise from Jackson's Electrodynamics, Chapter 7, page 348, 3th edition:
Consider the non-local (in time) connection between $D$ and $E$,
$$\vec{D}(\vec{x},t)=\epsilon_0 \...
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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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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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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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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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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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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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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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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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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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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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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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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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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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