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05:09

Q: Should we flag comments like "Thank you"?

This is how flagging is described in help centre: Flagging is a way of bringing inappropriate content to the attention of the community. Are comments like, "Thank you","Good question", "Nice answer", etc. inappropriate content? Should we flag them?

5 hours later…

Slereah

09:55

Grandma's shelf-stable blackberry pie meson recipe was a huge seller until her farm was shut down by a joint FDA/NRC investigation.

Evil John Rennie

10:36

(removed)

1 hour later…

Slereah

11:43

Really the idea that simultaneity is a hard notion has little to do with relativity itself, it's a notion that stems from the lack of instantaneous interaction with your environment

It is baked in special relativity, but it is also true of classical mechanics if you just assume that there's no instantaneous interaction you can find

Jim

so if you just assume it's true, then it's true? Thanks for clearing that up

ACuriousMind

@Slereah sure but instantaneous interactions are not inconsistent with Newtonian mechanics, but they are with relativity

Slereah

@ACuriousMind But on a practical level, we knew that we didn't make any instantaneous measurement in the 19th century

ACuriousMind

sure, but there was nothing egregious that prevented you from thinking in terms of absolute simultaneity

Slereah

I mean sure, but even then, if you wanted to find the synchronization of everything, you had to take that into account

ACuriousMind

11:55

while the idea of a universal now is fundamentally incompatible with relativity, not just practically incompatible

Slereah

You couldn't just say that you observed something, so that event happened at $t$

ACuriousMind

@Slereah sure, but that's more of an engineering hurdle (how to give everyone synched clocks) than a philosophical problem

Slereah

IIRC that was one of those thing people had to start thinking about when the telegraph became a thing

you had some primitive form of Einstein synchronization in some telegraph formula

Not sure how fast a telegraph signal goes

What's the propagation speed in copper

"In copper at 60 Hz, v ≈ 3.2 m/s. "

That's frighteningly bad

"For copper cables, the speed is about 0.5 c."

Well which is it!

I guess it depends on many factors, but 3.2 m/s and 0.5c is a pretty large difference

unless $v$ is the drift velocity or something but that article seemed to imply it was the propagation speed

ACuriousMind

12:16

I highly suspect the small value is the drift velocity

Slereah

I suspect also, otherwise it would probably take a while for the lights to go on when I press a button

3 hours later…

Bohemian relativist

15:14

does "coupled" in physics contexts refer to "entangled"?

The idea that topology could be used to characterize the phase of matter was also used by Haldane (currently at Princeton University in New Jersey) in his work on spin chains—one-dimensional systems of coupled atoms found in magnetic materials.

Slereah

It can mean a few different things

Usually that they influence each other

the equation of motion of one is dependant on the other

bolbteppa

Quantum Heisenberg model

The quantum Heisenberg model, developed by Werner Heisenberg, is a statistical mechanical model used in the study of critical points and phase transitions of magnetic systems, in which the spins of the magnetic systems are treated quantum mechanically. It is related to the prototypical Ising model, where at each site of a lattice, a spin σ i ∈ { ± 1 } {\displaystyle \sigma _{i}\in \{\pm 1\}} represents a microscopic magnetic dipole to which the magnetic moment...

That's the basic spin chain model

5 hours later…

fqq

20:35

@Bohemianrelativist No, it means the same as "interacting", as in their dynamics are not independent. For quantum systems it implies that they will be entangled most of the time. But you can have stuff that is entangled but no longer interacting, e.g. the usual examples of teleportation etc

ACuriousMind

entangled is a description of a state, coupled is a description of dynamics - they're different categories

fqq

yes

3 hours later…

Bohemian relativist

23:57

@fqq what about spin-orbit coupling? Does the coupling here mean entanglement if the spin-orbit coupling refers to the spin-orbit coupling of atoms in a lattice?

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