Questions tagged [non-locality]
The non-locality tag has no usage guidance.
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Non-locality of the wavefunction in QM and Twistor theory [closed]
Regarding locality, I don't think locality is a principle per se, but we often assume that the physical fields are local on spacetime, describable by partial differential equations and so on. But of ...
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Bohmian mechanics, Leggett inequality, realism and nonlocality
Very often it is said that the Bell inequality has ruled out the possibility of hidden variables (HV) in QM. This is incorrect since Bell inequality has ruled out local hidden variables: nonlocal HV ...
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EPR effect, non-locality, positivism and realism
In the framework of EPRB experiments, has an experimental verification been performed of the conservation of 2-time correlations of Bob's photons polarization despite Alice's polarization measurements?...
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Relativistic Schrödinger Equation: How is it relativistic and can it be useful? [duplicate]
As is well known, the usual Schrödinger equation,
$$\mathrm{i}\hbar\frac{\partial}{\partial t}\psi=-\frac{\hbar^2}{2m}\Delta\psi+V\psi,$$
is not relativistic. It can be derived formally by applying ...
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Measurable effects of the global structure of the SM
It is known that the Lie algebra of the SM is
$$
\mathfrak{su}(3)\oplus \mathfrak{su}(2)\oplus \mathbb{R}\,,
$$
so that the Lie group is
$$
G_{\text{SM}} = \dfrac{SU(3)\times SU(2) \times U(1)}{\Gamma}...
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How can the quantum state of one particle depend on the other in entanglement without non-locality? [duplicate]
There are many different interpretations of quantum mechanics. Some posit determinism and non-local influences between particles. Others do not, such as in the Copenhagen interpretation.
My question ...
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Could reducing entanglement by unitary operations allow for FTL-communication? (and why not?)
About the closure: This Question is about why manipulating 1 particle of an entangled pair unitarily can’t cause measurable consequences on the other and how this manifests in the concretely described ...
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Can a non-local theory be consistent with special relativity?
If there was a non-local theory that explained quantum entanglement correlations, does it follow that it would violate special relativity?
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All the logically possible ways to get around Bell-type inequalities
I'm a high school student, so my (mis)understanding here is not very rigorous or precise, but I will write it below so as to concretely frame my question:
Bell's theorem takes three assumptions ...
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Do Bell’s inequalities assume determinism?
I was watching a video of Tim Maudlin where he talks about how the CHSH version of Bell’s inequalities do not assume determinism and only assume locality. He said that it is a common misconception ...
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Why do particles need a signal to travel to another to affect it? [closed]
I was reading up on quantum entanglement, non locality, and how people interpret QM to still be local in the sense that it does not allow for faster than light communication signals.
I have two ...
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How do non-local correlations occur in QM without a cause? [closed]
The Copenhagen interpretation of QM ultimately amounts to asserting that non-local correlations occur without a cause since that cause would involve propagation of information faster than the speed ...
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Does local realism imply entangled photons are equal (or opposite)?
I'm watching a video about Bell's inequality and how there can be no local hidden variables. They explain it using photons and whether they pass through a polarizer or not when they're oriented at ...
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What was the fallacy in EPRs chain of arguments?
Let's say, there is an entangled system of two electrons with opposite spins; The joint system is in a state of eigenvectors for z-Spin ( $S_z$) with both particles far away from each other:
$$|\Psi\...
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Learning contextual data using a variational quantum circuit
This question is about contextuality in quantum mechanics, about non-quantum data also showing contextuality.
Definition for the specifics of the question as well as an example of contextuality in ...
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What is the consensus among physicists on whether quantum mechanics has non-locality? [closed]
According to this article here by the SEP,
Following Bell's work, a broad consensus has it that the quantum realm involves some type of non-locality (for examples, see Clauser and Horne 1974, Jarrett ...
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What does non-local transport mean in plasmas physics?
I found a lot of plasma physics works that talks about non-local transport, what is non-local transport in plasmas? What does non-local transport mean ? Some examples please.
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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 ...
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Quantum Mechanics without Complex Numbers in a multipartite setting
I was fairly convinced that usual QM formalism didn't necessitate the use of complex numbers and that ultimately they're just a matter of convenience and utility rather than anything fundamental. This ...
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Contradiction of propagation speed of gravitational waves with non-locality of gravity?
Although LIGO at 2016 verified the speed of a traverse gravitational wave being the speed of light in a vacuum $c$ there is also the fact that gravity is a non-local phenomenon, meaning that it is not ...
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Justification for the derivative expansion in the Exact Renormalization Group
In the Exact Renormalization Group formalism, specifically the formalism of Wetterich, one writes down an evolution equation for the effective average action $\Gamma_k[\varphi]$, see f.ex
$$
\...
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Difference between local and non-local optical model potential?
As far as I understand, local OMP (optical model potential) depends only on the relative position, and non-local OMP depends on relative position and momentum.
I am searching for more information so ...
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Can a point in the quantum set of correlations violate more than one independent facet Bell inequality?
Usually, depictions of the quantum set of correlations and the local polytope look something like:
In this image it looks like non-local points belonging to the quantum set (in yellow) violate only ...
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Is the possible Bell's test loophole of entangled particles communicating at a non instantaneous but FTL speed addressed and eliminated? [closed]
TLDR:
There seems to be a loophole in Bell's test that is not addressed or eliminated before we can successfully conclude that it proves that the Universe is unreal and non local. The entangled ...
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How can we be sure Bell's theorem disproves local realism when we are not sure whether the measuring apparatus is in some form of entanglement or not? [duplicate]
Bell's therorem seems to disprove localism because measuring, let's say spin of an entangled electron, seem to communicate the measurement to it's another pair instantaneously.
But isn't another thing ...
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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-...
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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, ...
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Does non-local hidden variable theory predict the outcome of an experiment? [duplicate]
I am trying to understand what decides the outcome of an experiment and if there is any theory (e.g. non-local hidden variable theory) that is able to predict the outcome.
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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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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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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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