Questions tagged [locality]
The locality tag has no usage guidance.
260
questions
-3
votes
0
answers
70
views
Please tell me about "Action at a distance" in Electrodynamics [closed]
I am confused about how test charge informed about source charge. So I research on it. Web said me that it is "Action at a distance phenomenon". What is this? I am a first year Undergraduate ...
0
votes
1
answer
60
views
How is information defined when considering locality in quantum mechanics?
$\newcommand{\ket}[1]{|#1\rangle}$
My question is a follow-up from this discussion about the presence of non-local correlations in a theory that is deemed local. The first answer talks about the ...
0
votes
0
answers
54
views
Is there any restriction for locally mapping a given 2-qubit density matrix into a desired 2-qubit density matrix with lower entanglement?
Suppose we're given a 2-qubit density matrix($\rho_{4\times4}$). we can apply two local maps on each of these qubits seperatly. So the output is density matrix($\rho^{\prime}_{4\times4}$).
I'm ...
- 27
1
vote
1
answer
57
views
Definition of “quasi-locality” in Wilsonian RG scheme
I’m studying about the holographic RG with this paper.
In that paper they say Wilsonian action expects quasi locality, but I’m not sure what “quasi-locality" exactly means.
If quasi-locality ...
- 61
0
votes
0
answers
62
views
Can you model relativistic interactions without locality?
Assume $c=1$
I've been doing relativity by myself so I may be making some assumptions here that I would not have if my learning had been more extensive.
One such assumption is that you can model the ...
- 312
2
votes
1
answer
123
views
Is conservation of energy a local law in Quantum field theory? [closed]
From Wikipedia,
"The local energy conservation in quantum field theory is ensured by the quantum Noether's theorem for the energy-momentum tensor operator. Thus energy is conserved by the normal ...
- 51
0
votes
0
answers
35
views
Lorentz invariance (LI) of time ordering operation
At Srednicki after eq. (4.10), we have a discussion about that the time ordering operation. Have to be frame inv. I.e it has to be LI.
He wrote that for timelike separation we don't have to worry ...
1
vote
2
answers
126
views
On the notion of Local Causality
In 1976, John Bell proved that any locally causal theory can't account for certain observed correlations, he formulated the local causality hypotesis in terms of "local beables".
In ...
- 407
7
votes
4
answers
3k
views
Confusion around Bell's Theorem and Locality
I recently got interested in foundational aspects of quantum mechanics and I have some questions:
Bell's theorem proves that any local, deterministic theory with statistical independence can't account ...
- 407
1
vote
1
answer
191
views
$SO(3,1)$ is locally $SU(2)\times SU(2)$, what does *locally* mean here?
I am learning Lie group and Lie algebra. I saw in a YouTube video "Supersymmetry lecture 02" from OpenCourseWare (OCW) at University of Cambridge at 11:17 that
$SO(3,1)$ is locally $SU(2) \...
- 53
0
votes
1
answer
70
views
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 ...
0
votes
0
answers
71
views
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 ...
user385269
2
votes
1
answer
89
views
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 ...
- 519
0
votes
1
answer
148
views
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 ...
- 13
0
votes
0
answers
22
views
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", ...
- 11
1
vote
1
answer
305
views
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 ...
- 55
2
votes
1
answer
78
views
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-...
- 134
1
vote
0
answers
46
views
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, ...
- 873
1
vote
0
answers
58
views
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 ...
- 508
0
votes
0
answers
45
views
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 ...
- 103
16
votes
6
answers
3k
views
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 ...
- 2,327
2
votes
4
answers
1k
views
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 ...
0
votes
1
answer
275
views
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 ...
0
votes
1
answer
101
views
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-...
- 1,783
1
vote
0
answers
53
views
Ostrogradsky instability and fractional derivatives
Are fractional derivatives (or even more generally differentegrals) also under the scope of the Ostrogradsky instability theorem?
- 6,611
2
votes
2
answers
914
views
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 ...
- 671
1
vote
1
answer
4k
views
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 ...
- 231
1
vote
2
answers
162
views
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{\...
- 229
2
votes
0
answers
257
views
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 ...
- 317
2
votes
1
answer
85
views
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?...
- 427