Questions tagged [locality]
The locality tag has no usage guidance.
74
questions
140
votes
11
answers
21k
views
How fast does gravity propagate?
A thought experiment: Imagine the Sun is suddenly removed. We wouldn't notice a difference for 8 minutes, because that's how long light takes to get from the Sun's surface to Earth.
However, what ...
- 3,930
122
votes
10
answers
23k
views
Why is quantum entanglement considered to be an active link between particles?
From everything I've read about quantum mechanics and quantum entanglement phenomena, it's not obvious to me why quantum entanglement is considered to be an active link. That is, it's stated every ...
- 1,401
105
votes
12
answers
13k
views
Why are differential equations for fields in physics of order two?
What is the reason for the observation that across the board fields in physics are generally governed by second order (partial) differential equations?
If someone on the street would flat out ask me ...
- 8,523
39
votes
5
answers
3k
views
Can the Hubble constant be measured locally?
The Hubble constant, which roughly gauges the extent to which space is being stretched, can be determined from astronomical measurements of galactic velocities (via redshifts) and positions (via ...
- 435
95
votes
10
answers
15k
views
Quantum Entanglement - What's the big deal?
Bearing in mind I am a layman - with no background in physics - please could someone explain what the "big deal" is with quantum entanglement?
I used to think I understood it - that 2 particles, say ...
- 1,544
42
votes
5
answers
8k
views
Why are infinite order Lagrangians called 'non-local'?
And in what sense are they 'non-local'?
- 2,645
8
votes
1
answer
3k
views
What is meant by a local Lagrangian density?
What is meant by a local Lagrangian density?
How will a non-local Lagrangian look like?
What is the problem that we do not consider such Lagrangian densities?
- 26.8k
33
votes
4
answers
3k
views
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 ...
- 2,125
22
votes
6
answers
4k
views
Quantum entanglement and spooky action at a distance
When quantum entanglement is explained in "layman's terms", it seems (to me) that the first premise, that we have to accept on faith, is that a particle doesn't have a certain property (the particle ...
- 323
28
votes
6
answers
30k
views
Bell's theorem for dummies, how does it work?
I've been reading up on theoretical physics for a few years now and I feel like I am starting to get an understanding of particle physics, at least as much as you can from Wikipedia pages. One thing ...
- 453
5
votes
1
answer
1k
views
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?
- 3,023
11
votes
1
answer
672
views
Where is locality used in CHSH/Bell's inequality?
A very similar question is asked here, but I'm still confused :(
From Bell, in a hidden variable model, $A = A(\lambda, a)=\pm 1$ is the observed spin of the first particle around axis $a$, and $B = ...
- 113
13
votes
1
answer
4k
views
Local versus non-local functionals
I'm new to field theory and I don't understand the difference between a "local" functional and a "non-local" functional. Explanations that I find resort to ambiguous definitions of locality and then ...
- 243
11
votes
4
answers
3k
views
Do electrostatic fields really obey "action at a distance"?
In an electromagnetic theory class, my professor introduced the concept of "action at a distance in physics".
He said that:
If two charges are at some very large distance, and if any one of the ...
- 245
37
votes
2
answers
7k
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 ...
- 7,398