Questions tagged [locality]
The locality tag has no usage guidance.
252
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Equivalence of two entangling operators with respect to local operators
Suppose that $U_1$ and $U_2$ are two (entangling) operators that act on a quantum system consisting of several qubits. Is there any criterion to tell if these two are equivalent up to applying ...
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Can action be local in a non-relativistic theory?
Say we have a theory of a particle with action $$\int dt\mathcal{L(x,\dot{x})} = \frac{m}{2}\int dt\dot{x}^2$$Action is local if the integrand of the system depends only on the particle's position and ...
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What do we mean by causality when we say that entanglement measurements are uncaused? [duplicate]
I’m having a hard time wrapping my head around how the measurement of particle A does not affect the state of an entangled particle B even if no superluminal speeds exist.
Suppose Alice makes a ...
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Highest order derivatives (corrections) dictate causality?
My question seems simple but I am having trouble finding resources/papers on the topic (I am guessing my wording is poor). I am trying to find material (and perhaps a physical proof even) that in a ...
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Questions regarding action at a distance
There seems to be two concepts in action at a distance
The existence of an mediating medium (energy or matter) through which action is transmitted
The finiteness of the speed at which the action is ...
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How to interpret Poisson bracket of fields in terms of causality?
In quantum field theory, the fact that space-like separated observables commute, i.e. $[\hat {\phi (x)}, \hat{\phi(y)}]=0$, is taken as the test for causality. The equivalent statement for classical ...
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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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How does locality on space time manifold M put constraints on functions on configuration space of fields?
I am reading David Skinner's notes on AQFT. In Chapter 1 page 3, he mentioned that "purely from the point of view of functions on $C$, locality on $M$ is actually a very strong restriction", ...
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Is Quantum randomness true randomness? [closed]
I would like you guys to read it, and see whether it makes sense, and correct me if anything is wrong.
I'm not an expert on these topics, so I understand if very wrong. It would be wonderful if you ...
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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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Well-definedness of commutation relation in commuting local Hamiltonians
I'm reading the famous paper by Haah: Local stabilizer codes in three dimensions without string logical operators. In the last sentence of the introduction, he wrote:
A logical operator is a Pauli ...
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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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Are field theories necessary to make accurate predictions or do they just make calculations easier?
For example, if we really wanted to, could we, at least in principle, model electromagnetism just considering interactions between charged particles without using the EM field? That is, is it ...
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Understanding superdeterminism
I was reading about superdeterminism and it was a bit counter-intuitive. The idea of having a hidden variable on the measurement device is very rational. For example, if we emit light to a constrained ...
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Is a super-deterministic universe local or nonlocal? [closed]
Bell predicted predetermined (nonlocal) choice as the criteria for a super-deterministic universe.
...our belief that we are free to choose to do one experiment rather
than another, absolutely ...
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Understanding this abstract Lagrangian of effective field theory
I'm learning Wilson's approach to renormalization and the Effective Field Theory. Typically, the theory is defined by a Lagrangian valid up to some scale $Λ$. I saw these two definitions for 4-...
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Ostrogradsky instability and fractional derivatives
Are fractional derivatives (or even more generally differentegrals) also under the scope of the Ostrogradsky instability theorem?
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How does Bell's theorem disprove realism?
I am told that the the violation of Bell's inequalities prove that the universe cannot have local realism. That is to say, the universe cannot both be local and real.
I understand how Bell's theorem ...
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What does it mean to say the universe is not locally real? [duplicate]
Pardon me if this is a naive question.
What is difference between saying space-time is not locally real, and saying it is not real?
The proposal that the universe is not locally real seems to imply ...
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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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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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Non- Local operators and Entanglement
Given a separable state, $|\psi\rangle$ = $|a\rangle\otimes|b\rangle$, operating on this state with a local operator of the form, $A\otimes B$ will not lead to an entangled state. Is the converse true?...
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Locality and local gauge invariance
I was reading this question on the Physics Stack Exchange, and I'm still not quite sure how I can understand the relationship between locality and local gauge invariance using this example. Consider ...
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How to understand the principle of locality from a common example?
I'm reading the definition of the principle of locality from its Wikipedia page:
The principle of locality states that an object is influenced directly only by its immediate surroundings.
This ...
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Is Gauss law for gravity local?
in Newtonian gravity, the gravitational field obeys the equation
$$\nabla^2 \phi = 4 \pi G \rho$$
David Tong in his notes on general relativity claims that this equation works well when $\rho$ is not ...
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In an entangled system, what happens to Alice's wavefunction right after Bob makes a measurement?
Suppose two entangled particles are far apart. One is with Alice and the other is with Bob. The relative velocity between Alice and Bob is zero (and spacetime is flat), so that we can define a notion ...
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Don't Bell experiments rule out local non-realism too? [duplicate]
Bell experiments rule out local realism (hidden variables). But it seems to me that it also rules out local non-realism (no hidden variables).
Local non-realism makes 2 claims;
Two distant events can'...
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How to tell if a theory is "local"?
Suppose I have a collection of $N$ quantum systems, which I would like to think of as lattice sites. If you tell me that these $N$ sites have some particular embeddings $\vec{x}_i$ in $\mathbb{R}^d$, ...
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Cluster decomposition $\stackrel{?}{=}$ Translation invariance
In Weinberg Volume 1 (section 4.4), Weinberg argues for a certain structure of the interaction Hamiltonian by demanding that it produce an $S$-matrix satisfying cluster decomposition. The proposed ...
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Proof that conservation of momentum is Lorentz invariant
In classical mechanics, if
$$\frac{\mathrm d}{\mathrm d t}\sum_i m_i\vec{v_i}=0$$is true for one frame of reference, then it is easy to prove that this is true for all frames (since different frames ...
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Why is the local component of sound particle-velocity not associated with a local component of pressure?
A sound wave can be described by the pressure field or the sound air particle velocity (acoustic flow). Both are intrinsic to any sounds, i.e. there is no sound wave if no pressure or no particle ...
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How does the many-worlds interpretation solve spooky action at a distance?
If we take the classic example of two particles that are entangled with up spin and down spin, and we separate these particles a few light years apart and then observe them one after the other, they ...
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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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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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Is causality a consequence or a constraint in physics?
I wonder if causality is a constraint that we must add to physical models (if needed), or is it a consequence of Lorentz invariance and locality (or something else). In other words, which properties ...
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What are the implications of rejecting the local tomography assumption?
Recently I presented on the paper by Renou, et. al. in Nature (Quantum theory based on real numbers can be experimentally falsified) developing an experimental technique for rejecting real ...
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Local algebra of AQFT vs Bisognano Wichmann Theorem
Maybe I am misunderstanding something really stupid, but I am finding it hard to think of local algebras in terms of wedge algebras. One of the claims (see, e.g., Section 3 and 4 of this paper) is ...
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How do Lieb-Robinson Bounds talk about locality without the position operator?
So we know when one goes from QM to QFT Lieb Robinson bounds become micro causality. But micro causality is a statement on the commutators assuming they are space-like, time-like or light-like. ...
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Locality in Bell Experiments
I have a question about experiments that show a violation of Bell's inequalities. It's said that these experiments disprove local realism. However, immediately before the final measurement of the 2 ...
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Conserved charge at null infinity associated with Large gauge transformation
I am reading Strominger's lecture notes "Lectures on the infrared structure of gravity and gauge theory" (https://arxiv.org/abs/1703.05448). At some point, following (I guess) the authors of ...
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How are we able to use quantum field theory to study systems?
I've been trying to understand the concept of locality in QFT, and I was reading this paper by Edward Witten, where he explains (on pg 13) that the state space cannot be factored into a tensor product ...
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Must all field theories depend on the spatial derivate of the fields?
For instance, if I have encountered
\begin{equation}
\label{eqq2}
\frac{\partial \mathcal{L}}{\partial (\partial_i \phi)} = 0
\end{equation}
This tells us that $\mathcal{L}$ cannot depend on $\...
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How does string theory get around the argument in Weinberg's QFT?
In Weinberg's The Quantum Theory of Fields Vol. 1, an argument is presented that the three postulates of
Lorentz invariance
quantum mechanics
cluster decomposition principle
leads to quantum field ...
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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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Why does one work with the Lagrangian density in field theory?
Why is it necessary to introduce the Lagrangian density (integral of the Lagrangian over volume) when describing the dynamics of fields? Is there a specific reason for that or just for convenience?
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On the Bell's Theorem / Bell-type Inequalities and the Kochen-Specker Theorem
It appears to me that the Kochen-Specker theorem, if not Gleason’s theorem already, seals the fate of realism / value definiteness (with possibly the additional assumption of non-contextuality, ...
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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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Are all physically realistic Hamiltonians local?
My understanding of modern physics is that physicists think that, fundamentally, physical laws are local. For system A to interact with system B, they either need to be very close to each other or ...
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How did the local hidden variable theory resolve the EPR paradox?
I'm trying to understand the motivation for local hidden variable theory. The EPR paradox considers the following thought experiment, where we can express a state $|\psi \rangle \in H_{Alice} \otimes ...
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