Questions tagged [locality]
The locality tag has no usage guidance.
260
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
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
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
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
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
28
votes
10
answers
11k
views
How do we know quantum entanglement works no matter the distance?
It is said quantum entanglement works regardless of distance. 2 particles can be entangled and information is shared instantaneously, even if they are lightyears away from each other.
But how do we ...
- 389
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
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
21
votes
2
answers
4k
views
Locality in QFT vs "non-local" in QM
In quantum mechanics (QM), teacher always emphasizes on the "weird" parts, like EPR paradox, Bell inequality and so on. The Bell inequality tells us that QM is either nonlocal or non-realistic or both....
- 2,147
20
votes
1
answer
1k
views
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 ...
Pavel Safronov
20
votes
2
answers
2k
views
Locality in the scattering amplitude
Early in this talk by Nima Arkani-Hamed, he describes what locality means for scattering amplitudes. "Locality tells you that the only poles in the scattering amplitude occur when the sum of a subset ...
- 2,282
19
votes
3
answers
1k
views
Uncertainty principle - momentum so precise that uncertainty of position is outside light-cone?
Thought experiment: what happens if we measure momentum of a particle so precisely, that the uncertainty of its position becomes absurd?
For example, what if the uncertainty of the position exceeds 1 ...
- 645