Questions tagged [locality]

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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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How constraint to first-order derivative in Lagrangian is a consequence of demand to get local theory?

In Physics From Symmetry Section 4.2 Restriction, the Author said that It is sometimes claimed that the constraint to first-order derivatives is a consequence of our demand to get a local theory, but ...
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Are infinitesimal dilatation transformations local?

In quantum field theories, a local transformation of a scalar field $\phi(x)$ is a transformation that involves the field and its derivatives at same point. See for instance Weinberg's QFT textbok, ...
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Are anyons non local?

Studying anyonic statistics in 2 dimensions, I naturally thought to ask the question of whether anyons are non local, since as we braid one around another, no matter the distance between the two, one ...
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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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Meaning of 'Local' density in Liouville's theorem

Liouville's theorem is commonly stated as $$\frac{d\rho}{dt} = \frac{\partial{\rho}}{\partial{t}} + [\rho, H]$$ Where, $H$ is Hamiltonian of the system, $\rho$ is the density, $[...]$ is the usual ...
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Many Worlds locality and EPR experiment

I've read in Sean Carroll's book (Something Deeply Hidden) that the Many-Worlds interpretation of quantum mechanics might be the only way to avoid instantaneous effects of entanglement, by having the ...
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2answers
260 views

In Cosmology, what does it mean to be 'local'?

I'm trying to make a point that there is curvature of spacetime from the metric expansion that contributes to the dynamics of a galaxy. This curvature would be in addition to the curvature caused by ...
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Why should the split property hold in AQFT?

In algebraic quantum field theory, one assigns complex unital $*$-algebras (or von Neumann algebras) $\mathfrak{A}(O)$ to open regions $O$ of Minkowski spacetime. I am reading an article by Chris ...
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Thought experiment in relativistic quantum mechanics?

Background Consider the following thought experiment in the setting of relativistic quantum mechanics (not QFT). I have a particle in superposition of the position basis: $$ H | \psi \rangle = E | \...
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What does it mean that gravity is '“local”? [closed]

What is "local" defined to be? Why don't larger systems affect smaller ones? ie. Don't we need to consider the gravitational pull from all other objects in the universe? Is this "...
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Locality of the Turbulent Energy Cascade

Locality appears to be an omnipresent feature of physics, including within turbulent fluid dynamics. In 1941 Kolmogorov postulated that the turbulent energy cascade is driven by scale-local ...
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Please explain the meaning of below statement

Newtons second law is a local law. (In the book,it says that it means that it applies to a particle at a particular instant without taking into consideration any history of the particle or its motion.)...
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71 views

The conditions under which a stress tensor $T^{\mu\nu}$ exists

I used to believe that the existence of the stress tensor in a QFT has to do with translation invariance: "If a theory is translation invariant, then one can construct a conserved $T^{\mu\nu}$ by ...
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Does local mean infinitesimally small?

I have studied General Relativity and there is one thing that I have trouble comprehending. What does local really mean? I will give some examples: The Hessian The Hessian is a way to compute the ...
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How do unitarity and locality break in theories involing gravity?

In the science-pop article A Jewel at the Heart of Quantum Physics https://www.quantamagazine.org/physicists-discover-geometry-underlying-particle-physics-20130917/, there is a footnote, with the ...
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What exactly means “local”? How local (and memoryless) is “local”?

Local and memoryless are easily defined in quantized space and time: Local: What happens from one time step to the next in one "cell" of quantized space is only influenced by the state of ...
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How is the non-local nature of quantum entanglement explained?

From what I understand, Einstein tried to introduce real but hidden variables to remove the apparent non-local nature of quantum entanglement, but Bell's inequality showed local realism isn't possible....
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On the computation of functionals in QFT

Using the Gaussian (path)-integral $$ \int \mathcal{D}\eta e^{i\int_{t_i}^{t_f} dt \eta(t) O(t) \eta(t)} = N [\operatorname{det} O(t)]^{-1/2} $$ my book claims that we can compute the following ...
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Why can't light travel three days into the future then transmit that information back to us prior to us arriving at that position? [closed]

Example: If a football game between the Pittsburgh Steelers @ Tennessee Titans will happen in 3 days Sunday 10/25/2020 at 1pm, why can't light leave today 10/22/2020 and go to where the Earth will be ...
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What is the main reason for the locality of Einstein's equivalence principle?

Einstein's equivalence principle (EEP) states: "Locally, a free-fall frame in a gravitational field is equivalent to an inertial frame in space in the absence of a gravitational field". ...
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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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Locality & Effective field theories

I know that in general locality is a much desired/needed feature of a field theory, e.g. Standard Model. What I would like to know is which principle forbids non-local terms in a Lagrangian density. ...
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Why Locality meant jointly observable?

Tobias Osborne's lecture around 20:00, he mentioned that the ideal of "Locality" could be expressed as such If $x-y$ were space-like, then for all observable $A_{j,x}$ and $A_{k,y}$ were ...
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Lattice differentiation and Locality

Assume we define the locality of a theory in the following way: Assume we have a theory of real scalars, so this theory is non local if the action has terms like $$\int d^dx\,\phi(x)V(x-y)\phi(y).$$ ...
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Rewriting the equation governing local transport into $\nabla (\ln(\sigma)) \cdot \nabla U_0 =− \nabla ^2(U_0)$

A paper concerning local sheet conductivity and sheet current density says the equation governing local transport $$\nabla \cdot \vec{j} = − \nabla\cdot(\sigma \nabla U) = 0,$$ where U denotes the ...
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What is a “quasi-local” charge?

Could someone please tell me what is a quasi-local charge? For instance, why are Brown-York charges called quasi-local?
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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
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QFTs without Lagrangian

I have been reading other questions in this site, but I have not found answers to all my questions about theories without Lagrangians. What do we mean exactly when we say that they do not have a ...
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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
93 views

What is the mathematical meaning of locality?

I have read on the Principle of locality Wikipedia page that: "The special theory of relativity limits the speed at which all such influences can travel to the speed of light, c. Therefore, the ...
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1answer
168 views

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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5answers
425 views

Is wave function collapse non-local or local?

Imagine a particle in a very large box which takes years to travel from one end to the other. Alice and Bob are outside the box, on opposing ends. Each can remove their side of the box to check if the ...
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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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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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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
95 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 ...
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2answers
200 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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Replication of Single Particle QM with Local Hidden Variables

In learning device-independent QM from [https://arxiv.org/abs/1303.3081], Scarani tells us that all quantum statistics involving one particle can be reproduced with local (hidden) variables. He then ...
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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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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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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 ...
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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 ...
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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 ...
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2answers
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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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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 ...
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195 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 ...