# Questions tagged [locality]

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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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### 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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### 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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### 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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### 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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### Proof of cluster decomposition theorem

I have looked through a few lits but can't find a proof for cluster decomposition theorem, which states that asymptotically separated apart operators cannot influence each other. Is there a formal ...
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### Basic question about local algebras in AQFT

AQFT (algebraic quantum field theory) assigns "local algebras of observables" to bounded regions of spacetime, in particular to double-cone ("diamond") regions. These algebras' projection operators ...