The locality tag has no wiki summary.
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QFT basics for Klein-Gordon fields
I am teaching myself QFT from Peskin for next years maths course and I have two questions:
What is a c-number? Is it a complex number, and if so why does it mean, ...
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Gravity versus light [duplicate]
I've read this problem somewhere but don't remember where I saw it, but anyways...
So Earth revolves around the sun, and let's hypothetically remove the sun (make it disappear) would Earth just ...
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2answers
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Solar Catastrophe [duplicate]
Consider all of sudden the sun vanishes. What would happen to planetary motion. Will it continue to move in elliptical path or move in a tangential to the orbit immediately after sun vanishes or move ...
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Do all the 4 forces of nature act at the same speed? [duplicate]
It is believed that gravity, the weakest of the four forces propagates at the speed of light, cf. e.g. this Phys.SE post. One would expect (perhaps erroneously) that the other, stronger, forces acted ...
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How soon that a force affect another object?
Imagine this scenario: I have 2 objects in vacuum without any force exerted upon them not even a possible gravitational force between them.
Now if one of them gets a gravitational or magnetic force, ...
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2answers
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Algebraic/Axiomatic QFT vs Topological QFT
Can anybody please tell me a good source investigating the relation between Algebraic/Axiomatic Quantum Field Theory (AQFT) and Topological Quantum Field Theory (TQFT)? Or is there none?
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1answer
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Is this field redefinition for free scalar field theory non-local?
The action of free scalar field theory is as follows:
$$
S=\int d^4 x \frac{\dot{\phi}^2}{2}-\frac{\phi(m^2-\nabla^2)\phi}{2}.
$$
I have been thinking to redefine field as ...
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1answer
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Definition of Local Function
Now a days I am studying Srednicki's QFT book. In its third chapter it is written that
Any local function of φ(x) is a Lorentz scalar, [...] .
Now my question is: What is a local function?
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2answers
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How does locality decouple the UV and IR behaviour of a QFT?
I came a comment in this paper: Scattering Amplitudes and the positive grassmannian in the last paragraph of page 104 which says:
"One of the most fundamental consequences of space-time locality is ...
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3answers
155 views
What was wrong with action a distance?
It is usually said that the idea of fields was introduced (electric and magnetic fields) in electricity and magnetism after Coulomb's law to cure the conceptual problems of action at a distance.
...
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1answer
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Theories with non-vanishing commutators outside the lightcone
I'm reading Weinberg's new book on Quantum Mechanics, and in Chapter 8.7 "Time-Dependent Perturbation Theory" he derives the usual Dyson series for the $S$ matrix when the interaction Hamiltonian ...
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1answer
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Does this Bell's experiment actually disprove LHVT
I'm watching some archived video lectures on QM in Coursera given by Umesh Vazirani from UC Berkeley and I have a question regarding a Bell's experiment (I guess something close to this) described in ...
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1answer
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How to tell local and unlocal in QFT?
I'm taking QFT course in this term. I'm quite curious that in QFT by which part of the mathematical expression can we tell a quantity or a theory is local or unlocal.
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Could we get rid of explicit fields derivatives in Quantum Field Theories?
For instance, if we choose the following scalar field Lagrangian, which is (I hope) Lorentz-invariant, where $l$ is a a length scale, and with a $(-1,1,1,1)$ metric:
$$ \mathfrak{L}(x) \sim ...
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1answer
89 views
Other ways of checking whether particular system result in non-locality
In quantum mechanics, when hamiltonian $H$ is constrained ($H = \sqrt{m^2 - \hbar^2 \nabla^2} $) so that it would produce simple "relativistic" model of quantum mechanics, we can show that it results ...
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1answer
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What would it take for a physical phenomenon to be telekinetic?
I've just watched an episode by MinutePhysics called "Real World Telekinesis". In it, Neil Turok (I wonder if that is his actual name; I remember playing a game called "Turok: Dinosaur Hunter" on ...
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2answers
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$\nabla$ and non-locality in simple relativistic model of quantum mechanics
In Wavefunction in quantum mechanics and locality, wavefunction is constrained by $H = \sqrt{m^2 - \hbar^2 \nabla^2} $, and taylor-expanding $H$ results in:
$$ H = \dots = m\sqrt{1 - \hbar^2/m^2 ...
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1answer
238 views
Wavefunction in quantum mechanics and locality
Every wavefunction of a form $\Psi(x)$ can be described as a superposition of multiple free particle solutions.
We can see the following Fourier transform:
$$ \psi(x) = \int e^{ik\cdot x} \psi(k) dk ...
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1answer
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Tracking down the locality assumption in a CHSH inequality derivation
CHSH inequality requires both locality and realism. I will equate here realism with counterfactual definiteness.
Now counterfactual definiteness tells us that given two different measurements on the ...
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2answers
660 views
Definitions: 'locality' vs 'causality'
I'm having trouble unambiguously interpreting many answers here due to the fact that the terms locality and causality are sometimes used interchangeably, while other times seem to mean very different ...
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1answer
152 views
How is the 'cluster decomposition principle' implemented in holographic theories?
Since holographic theories are non-local by definition, how is this principle implemented?
Naively, it seems to me it is not, at least, in some sense.
I would appreciate an explanation as simple ...
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2answers
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What's the relationship between quantum entanglement and the relativity of time?
Apologies in advance for what may be a stupid question from a layman. In reading recently about quantum entanglement, I understood there to be a direct link between entangled particles, even at ...
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1answer
157 views
EPR paradox and uncertainty principle
In Wikipedia article EPR paradox,
The original paper purports to describe what must happen to "two systems I and II, which we permit to interact ...", and, after some time, "we suppose that there ...
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Non-Locality and Entanglement
Let’s consider a pair of particles [with their signals] comprising an isolated system. Any change in some property of either particle is due to the signal/s received from the other. Each particle has ...
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3answers
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Bell's theorem and why nonlocality is problematic
I generally hear it assumed that Bell's inequality implies violation of counterfactual definiteness, because locality is considered sacrosanct. I understand of course that measurable violations of ...
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3answers
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Assumptions in Bell's Theorem
It is often Stated that Bell's Theorem is equivalent to the statement: No theory of Local Hidden Variables can reproduce all of the predictions of quantum mechanics. I see nowhere in Bell's Theorem ...
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1answer
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How are fundamental forces transmitted?
How are the fundamental forces transmitted? In particular I wonder, are all "processes" local, i.e. without superluminal distant interactions? But if they are local, then particles would have to ...
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1answer
256 views
Relativity and Entanglement
Say we have two particles which are entangled so that they have opposite spins. If one is up, the other is down. They are sent off to two spatially separated observers A and B. Both observers can ...
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4answers
430 views
Locality in Quantum Mechanics
We speak of locality or non-locality of an equation in QM, depending on whether
it has no differential operators of order higher than two.
My question is, how could one tell from looking at the ...
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3answers
351 views
Special conformal transformations and locality
In the conformal symmetry, used in some QFT theories, the infinitesimal generators, applying to space-time, are all linear (translations, rotations, boosts, dilatation), except the special conformal ...
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4answers
228 views
Are Everettian branchings global or local?
Everett's theory of quantum mechanics is about the wavefunction of the whole universe holistically. If a branching occurs very far away at the Andromeda galaxy, do I also branch? Are branchings global ...
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1answer
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Is string theory local?
By locality I mean something like the Atiyah-Segal axioms for Riemannian cobordisms (see e.g. http://ncatlab.org/nlab/show/FQFT). I.e. to any (spacelike) hypersurface in the target we associate a ...
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How can a point-like particle “feel” gravity, if locally the curvature of spacetime is always flat?
I imagine a point-like particle can only experience the local properties of spacetime. But locally there is no curvature and no gravity, as it is often stated that
Locally, as expressed in the ...
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5answers
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What combinations of realism, non-locality, and contextuality are ruled out in quantum theory?
Bell's inequality theorem, along with experimental evidence, shows that we cannot have both realism and locality. While I don't fully understand it, Leggett's inequality takes this a step further and ...
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The speed of gravity?
Sorry for the layman question, but it's not my field.
Suppose this thought experiment is performed. Light takes 8 minutes to go from the surface of the Sun to Earth. Imagine the Sun is suddenly ...
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2answers
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Why is lagrangian density correct?
The textbooks I have available explain that due to the infinite degrees of freedom of a field, the relevant object in QFT is the lagrangian density. A lagrangian is then obtained for the field by ...
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Why quantum entanglement is considered to be active link between particles?
From everything I've read about quantum mechanics and quantum entanglement phenomena it's unobvious for me, why quantum entanglement is considered to be active link. I.e. it's stated every time that ...
