The h Bar

I dislike that the highest-voted answer does not address the question of what to do with duplicate answers or answers not appropriate to the desired level, and think it may be highest-voted precisely because it doesn't take a stand on that.

heather

@0celóñe7 are you talking about the metric tensor or metrics in metric spaces?

@ACuriousMind well, i really don't see how what to do with duplicate answers is a question. if it's not at the level asked for, it's NAA.

perhaps that's just me, though.

ACuriousMind

4:15 PM

@heather Our site has a long tradition of giving at least some answers that pretty much fly over OP's head, and in some of the prior meta posts I linked there was unanimous support for my position that answers should not be restricted by OP saying "I don't understand this".

vzn

@heather does anyone have more info on DSs (online) talk? url? chat.stackexchange.com/transcript/71?m=39539674#39539674

heather

@ACuriousMind I think that's kind of defeating the whole point of an answer.

if it doesn't help the OP or most people who will read it...

@vzn please stop editing that. anyway, the url will be posted when it starts.

ACuriousMind

@heather OP $\neq$ most people, and if it helps some people who read it (and is actually an answer to the question), I think it's worth having.

heather

no, i disagree.

ack. sorry.

Leaky Nun

heh

heather

4:18 PM

if you generalize that @ACuriousMind

you end up with: no matter what level of answer, it should be allowed.

now, say a researcher posts an answer with the highest insanest amt of math ever in response to how to explain something to a 5 year old.

ACuriousMind

@heather Yes, that is precisely my personal belief.

heather

is that really an answer

no, of course not.

that's entirely ignoring the question.

ACuriousMind

Well, it's easy to judge that in the extreme cases. There's a large grey area in between.

heather

my rule is consistent, yours isn't, that's what i'm saying.

and besides - that doesn't mean content is lost forever. encourage those people to post a question and self-answer.

ACuriousMind

@heather Of course my rule is consistent - because I also think that questions are duplicates no matter the level of explanation asked for.

heather

4:20 PM

or post the answer to an already existent question at the right level.

@ACuriousMind ah, i thought we were discussing answers with the assumption that they were not duplicates =)

what i'm saying is that if we decide questions of different levels aren't duplicates, answers should answer at the level asked for.

end of story.

whether or not questions of different levels aren't duplicates is a separate question, and so far people seem to be leaning in the affirmative (i.e., aren't duplicates).

Secret

Use this for the missing time:

ACuriousMind

@heather You see, I think you're right that the only consistent policy if we declare these questions not-duplicates is to delete answers that are not of the "right" level. But then again, this meta answer I wrote a while back and linked in the question is at +11/-0 and explicitly says that all answers at all levels should be allowed. So I don't know what to make of the voting on the newer thread.

heather

opinions change.

i think people are now in favor of questions of different levels not being duplicates.

does level not matter? does it make sense to teach a highschooler graduate material? no, not at all.

0celóñe7

@heather metric tensor

it doesn't induce a metric space structure on spcaetime

ACuriousMind

@heather See, the old question wasn't framed in these terms - I said answers of all levels should be allowed, but didn't touch on the duplicate issue at all.

heather

4:33 PM

i think we've lost track of the fact that this site is for answering questions.

ACuriousMind

My conclusion would be that people indeed hold the inconsistent beliefs that "These questions shouldn't be duplicate" and "Answers of all levels should be allowed"

Which would also explain why your answer is voted below AFT's, since yours explicitly contradicts the latter belief but AFT's doesn't.

heather

or, you could say that people have changed their minds. it is, as you say, the older question that contradicts what people are voting in the newer.

::shrugs:: i don't know.

honestly, i got frustrated with that question because of kyle kanos' comments.

ACuriousMind

@heather That's exactly the problem! I don't know either because almost no one except for the people who wrote answers commented. I can't see a way to extract consensus or even majority opinion here because several different things would be consistent with the voting behaviour

heather

@0celóñe7 you could say that a metric just explains how points relate to each other.

@ACuriousMind sometimes meta is very frustrating =P

0celóñe7

@heather that's what "describes the local geometry" means

heather

4:37 PM

@heather a way of defining distance, time, volume, curvature, etc - sort of the line that connects the points on a graph, explaining exactly how everything relates.

@0celóñe7 sure, but your version sounds more complicated. you said this was for a general audience/children maybe, right?

0celóñe7

not children

heather

how general is the general audience?

ACuriousMind

I feel the problem here is that you're being asked to explain something on part of a poster that really can't be explained to anyone who doesn't already know something about it in that space :P

Secret

Hopefully you don't need to explain what a riemann curvature tensor is

heather

well, one can explain it. how well one can explain it is another story, i'm guessing ;)

Balarka Sen

4:44 PM

what is going on

heather

@Secret something which describes how different spacetime is at a point from normal flat space would be my go at it.

Balarka Sen

why do we want to explain metric tensor to the general audience

heather

@0celóñe7's doing a poster @BalarkaSen

@ACuriousMind what do you think the next step is for that question, then, if no consensus can be drawn?

0celóñe7

@BalarkaSen gmt

Balarka Sen

@0celo pls no gmt

Secret

4:47 PM

My take will be how much your orientation will be rotated and shifted when you try to move around a closed path, while trying to keep your orientation fixed at all points.

Riemannian curvature tensor have so many components that it does not just capture how much spacetime deviates from the flat spacetime

Balarka Sen

that's holonomy, not really curvature

it's one of the global phenomenons of curvature, i guess

0celóñe7

@BalarkaSen holonomy is quite related to curvature

heather

yes! solved the last problem in the mechanics section of my textbook =D

::celebrates::

0celóñe7

there's a formula for the deviation of a vector as it parallel transports that involves curvature

ACuriousMind

@heather Well, just that: We have no consensus, so reviewers are free to vote as they like. It hasn't been a large point of contention before that we didn't have a policy on this and so I don't expect it will become one now

0celóñe7

4:49 PM

(approximate formua for small loops)

Balarka Sen

@0celóñe7 "i know bro. it's everyday bro." - jake paul from h3h3 podcast

heather

now part II and part III and part IV and part VIII...

0celóñe7

@BalarkaSen did u watch the compilation?

heather

@ACuriousMind that's rather unsatisfying...there's not any way to "ask it again" or something like that?

Secret

What is the hardest thing in GR to explain to a Layperson?

Balarka Sen

4:50 PM

yeah I think it was like if you take limit of the angle deviation you get by parallel transporting along loops at a point with limit as length tends to 0

you get Gaussian curvature (modulo 2pi shit factors) for surfaces

I dunno how this generalizes but w/e

ACuriousMind

@heather Of course it is unsatisfying, but why would we repeat asking the question without any reason to believe the voting or responses would be any more clear-cut?

0celóñe7

@Secret ricci curvature

heather

@ACuriousMind erm...magic?

0celóñe7

I have no clue what it is

Balarka Sen

@0celóñe7 nah, just clips from it where he got the most roasts

0celóñe7

4:51 PM

@BalarkaSen I mean the vid I sent you

ACuriousMind

@heather "Insanity is doing the same thing over and over again and expecting different results" :P

heather

@ACuriousMind insanity is repeating that quote over and over again and expecting different results =P

Balarka Sen

@0celóñe7 oh yes i saw it

did you watch the one i sent you in response?

0celóñe7

@BalarkaSen The exact formula is $$\Delta v^i=-\int_\gamma \Gamma^i{}_{kj}v^j\, dx^k.$$ For a small enough loop this is $$\approx -\frac{1}{2}R^i{}_{jkl}(p)v^j_0 \int_\sigma dx^k\wedge dx^l$$

ACuriousMind

@heather I...don't think I've used that quote here before...

0celóñe7

4:53 PM

where $\partial\sigma=\gamma$

Balarka Sen

@0celóñe7 [swedish curses]

vzn

missing new physics section of mtg... :( anyone have any to share?

heather

@ACuriousMind i was referring to the general overuse of the quote.

0celóñe7

@BalarkaSen what

Balarka Sen

i picked that up from when pewdiepie reacts to jump scares in his playthroughs

heather

4:54 PM

@vzn well, china launched a satellite for quantum communications, did experiments, it works, published in

let me see

0celóñe7

Heart Attack Simulator

►

vzn

@heather yeah have noticed they (china) seem to be leading the world in that area... impressive quantum crypto advances but my feeling is that the idea its related to quantum computing is overhyped right now...

heather

ah, physics today, vol 70, issue 8, pg 14-16

Balarka Sen

@0celóñe7 thats not even scary

0celóñe7

@BalarkaSen if you were playing it, it would be

Balarka Sen

4:57 PM

also S.T.A.L.K.E.R is the game they ripped off of that movie i have on my top 5 list lol

or so i heard

heather

KATRIN, in Germany, for looking for the mass of neutrinos, is being tested right now, and will start collecting data next year, also according to Physics Today

0celóñe7

Alright, time to define spacetime

A spacetime is a tuple $(M,g,\nabla,\mu,\tau,T)$...

Secret

?, metric, connection, ?, proper time, ?

heather

@Mithrandir24601 I thought you said the seminar was at 10:00 PST...

Mithrandir24601

@heather in 5 minutes...

or maybe slightly less

0celóñe7

5:00 PM

@Secret manifold, metric, connection, orientation, time orientation, matter

vzn

Aug 17 at 1:34, by vzn

Large Hadron Collider finds 'direct evidence' of light interacting with ITSELF in physics breakthrough that confirms long-standing prediction / dailymail

Secret

hmm, interesting how we need to split orientation into spatial and temporal parts, but I guess my GR is not good enough to comment on that yet

heather

@Mithrandir24601 ah, sorry. timezones are confusing =)

DanielSank

will drop link in five minutes

need to go to bathroom etc. before starting.

AccidentalFourierTransform

so, we're having the ama and the seminar at the same time?

ugh, that's not very convenient

ACuriousMind

5:04 PM

@AccidentalFourierTransform Hm?

The AMA starts in three hours

vzn

@AccidentalFourierTransform Mithrandir AMA is later afaik (see earlier links/ starboard). DS seminar time was not announced beforehand afaik

AccidentalFourierTransform

oh

2 mins ago, by heather

@Mithrandir24601 ah, sorry. timezones are confusing =)

0celóñe7

Introduction. We say that a topological space $M$ is a topological manifold of dimension $n$ if each $p\in M$ has a neighborhood homeomorphic to an open set in $\Bbb R^n$. We say that $M$ is a smooth manifold if there exits a covering of $M$ by charts $(U_\alpha,\phi_\alpha)$, i.e. subsets $U_\alpha$ of $M$ with homeomorphisms $\phi_\alpha:U_\alpha \to \hat U_\alpha\subset\Bbb R^n$ such that for two charts $(U,\phi), (V,\psi)$, the map $\psi|_{U\cap V}\circ \phi^{-1}|_{\hat U\cap \hat V}$ is

a diffeomorphism.

that's like a 10th of the poster right there

AccidentalFourierTransform

what aboot Hausdorff

0celóñe7

@AccidentalFourierTransform All topological spaces are Hausdorff

vzn

5:05 PM

@AccidentalFourierTransform oh wait DS said 10:00 PST which is eve US, ~12 hr from now...(?)

Secret

makes sense to me, though the layperson is going to stratch heads without you standing next to it to explain

AccidentalFourierTransform

oh

0celóñe7

that's the convention in analysis

AccidentalFourierTransform

@vzn dude, really, dont edit pings please

0celóñe7

but I forgot second countable

@AccidentalFourierTransform why not?

AccidentalFourierTransform

5:06 PM

its annoying

Secret

@AccidentalFourierTransform Non hausedoff topological spaces only arises in time travel spacetimes (CTCs, etc.), which is probably not what 0celo will be presenting

vzn

getting AM/ PM mixed up sorry its after this mtg.

0celóñe7

hmm

vzn

← getting tired of ppl telling me not to edit my own msgs, turn off chat pings if you dont like them, they are just replies etc, consider reply/ edit features basic chat functionality... its annoying

AccidentalFourierTransform

yeah I noticed

DanielSank

5:07 PM

Seminar on quantum computing with superconducting circuits: hangouts.google.com/hangouts/_/mqgg7qrsuvgepm2e2sinq7f5oie

That's a google hangouts link

ACuriousMind

Pushing the company software, eh? ;)

0celóñe7

@DanielSank GDP!!!!!!!!!!

ACuriousMind

@vzn Can you really not see how one ping is useful to focus one's attention here if one is looking at another window, but that several in very quick succession because the same message keeps getting edited can be annoying? If people keep telling you not to do that, and you keep doing it, then really no one but you is to blame for you "getting tired" of that.

vzn

uh oh mod mad at me better run! nice chatting to some in here :|

AccidentalFourierTransform

maturity at its finest

Balarka Sen

5:15 PM

You should ping vzn on that message.

And edit it a million times.

AccidentalFourierTransform

we should program a bot that pings him every time he edits a message :-P

0celóñe7

@BalarkaSen gmt is bad because even explaining what the theorems are takes pages of crap

ACuriousMind

@DanielSank ...Google Hangouts does not work in Firefox?!

0celóñe7

it's also hard to motivate an $\mathcal H^k$-rectifiable stokes theorem

Secret

Nice work getting us chemist and biologist in!

$\lvert A\rangle \to \lvert A\rangle+\lvert B\rangle \to \lvert B\rangle$

Hmm, how does one implement this path?

Now that's new to me, QM is bad at basic arithmetic

0celóñe7

5:38 PM

@ACuriousMind rm appears to be on hulu in america

I don't have that

AccidentalFourierTransform

they typically upload the episodes to mega and share them on reddit

the third season sucks btw

ACuriousMind

@AccidentalFourierTransform No it doesn't :P

AccidentalFourierTransform

yeah it became mainstream

it used to be cool

Secret

I can here you @Danielsank, but, the sound from Ross and co are frozen, the reception sometimes lags a bit and your voice get drawn out

DanielSank

interesting

technical difficulties...

0celóñe7

5:49 PM

@AccidentalFourierTransform are you suggesting piracy

DanielSank

Ok they're getting an ethernet cable in hopes that it helps.

Secret

nice

DanielSank

@0celóñe7 What about it?

0celóñe7

@DanielSank I was excited to see you talk about it

John Rennie

@DanielSank: no microphone! sorry?

DanielSank

5:51 PM

No problem.

John Rennie

@DanielSank: I was just going to spectate

Secret

I have not plug in any microphone, I am also spectating until roughly 4:15

AccidentalFourierTransform

I wanted to spectate too but I cannot login

I think I forgot my password anyway :-/

0celóñe7

I have a microphone but it's off

@JohnRennie we should ask about quantum SSDs

hahaha

AccidentalFourierTransform

6:09 PM

what is the command for the semi-direct sum symbol in latex?

Detexify did not help

0celóñe7

what the heck is a semi-direct sum

ACuriousMind

@AccidentalFourierTransform Do you mean a semi-direct product $\ltimes$?

AccidentalFourierTransform

semidirect product is for groups

the linearisation is the semidirect sum

0celóñe7

if acm doesn't know your algebra, you might be talking nonsense

AccidentalFourierTransform

ie, for the algebra

NO IM NOT ;_;

ACuriousMind

6:11 PM

@AccidentalFourierTransform Ah. I've never seen a special symbol for that

AccidentalFourierTransform

well, how do you write the Poincaré algebra for example?

0celóñe7

I don't

ACuriousMind

@AccidentalFourierTransform I define the Poincaré group and then just say "the Lie algebra of this" :P

0celóñe7

Yikes, my PC setup is pulling 14.3 A

no wonder I exploded the power last night

AccidentalFourierTransform

ACuriousMind

6:14 PM

But honestly, I've simply never seen a symbol for that. If you tried detexify, you must've seen it somewhere. How does it look?

0celóñe7

lol

ACuriousMind

Ah

Nope, never seen that

@0celóñe7 That...is a lot

Balarka Sen

@AccidentalFourierTransform omg what the .... is that

0celóñe7

@AccidentalFourierTransform $\oplus_\text{semi}$

AccidentalFourierTransform

@BalarkaSen A SEMIDIRECT SUM FFS

@0celóñe7 eww

Balarka Sen

6:15 PM

NO GOD! PLEASE NO!!! NOOOOOOOOOO

►

0celóñe7

@ACuriousMind That's assuming a 100% PSU usage, I think I use like 2/3 of it

But god knows how much current my ceiling fan draws

oh and I didn't account for the desk light and overhead

AccidentalFourierTransform

@BalarkaSen go ask ppl in the math.se chat please will you

ACuriousMind

That would be 1,7 kW power, which seems pretty high to me

0celóñe7

@ACuriousMind 1.5 A x 2 for monitors

1.5 A for laptop charger

3 A for powered USB hub

max of 6.8 A for PC

+ desk lamp + overhead light + phone charger + fan

+ iPad

lots of power

@ACuriousMind Did you remember that we run at 110V in America

ACuriousMind

@0celóñe7 That one will only draw so much current if it is charging something at maximal current through every USB port connected, I think

@0celóñe7 Yes.

Although I might've used 120V :P

0celóñe7

6:20 PM

Hmm, the breaker box says 120

I think some palces have 110

AccidentalFourierTransform

220V>110V $\Rightarrow$ Europe>America confirmed.

0celóñe7

@AccidentalFourierTransform more like Europe needs more voltage to get things working

we're more efficient

Secret

Wikipedia said the semidirect sum is used in lie algebra

0celóñe7

@BalarkaSen @ACuriousMind what is this? bookstore.ams.org/gsm-177

ACuriousMind

@0celóñe7 Something I know nothing about :P

AccidentalFourierTransform

6:24 PM

and wikipedia is goddamn right

ACuriousMind

@Secret ...AFT already said that.

0celóñe7

@ACuriousMind it says Galois

"Guido Schneider"

that name seems randomly generated

Secret

Ok sorry, I was moving between maths chat, this chat and Danielsank's seminar

> What on earth is faster than the universe :?

ACuriousMind

@0celóñe7 All names are pseudo-randomly generated :P

(Humans are pretty bad pseudo-random generators, though)

AccidentalFourierTransform

inb4: NINE NINE NINE NINE

Secret

6:27 PM

Update to old notation: ...? will be replaced with :? from now on to indicate wonder type questions that are not urgent to answer

:? is a lot more descriptive

Balarka Sen

@ACuriousMind what are you talking about? a generic username of a generic user of a generic chat in the internet is like "robloxnerd5677"

Random as shit

AccidentalFourierTransform

14

Q: Why are cosine and sine functions used when representing a signal or a wave?

Actually, in the mathematics sine and cosine functions are defined based on right angled triangles. But how will the representation of a wave or signal say based on these trigonometric functions (we can't draw any right angled triangles in the media, i.e., the air) then how can we say that?

am i the only one who has no idea what OP is trying to ask?

Balarka Sen

you are already fourier transformed

so yeah

ACuriousMind

@AccidentalFourierTransform No (seeing as there are 4 unclear close votes), but I think it's pretty clear that the question is "Wtf do triangles have to do with waves?"

Secret

> Thomas :?

ACuriousMind

6:31 PM

I.e. for what reason do functions that describe geometric relations in a triangle show up when describing periodic phenomena

0celóñe7

@ACuriousMind are you telling me I can't randomly generate

Thomas Klimpel

@Secret Why not?

Secret

I see

0celóñe7

"1 cup dry white wine"

this country is awful

Secret

Looks like vzn said about overhyped quantum computing is not far fetched at all

Guess the general public need to made aware that quanutm computing actually suck at basic arthmetic so that (metaphorically) they don't start throwing away all their classical computers

Secret

6:39 PM

Play with quantum computers here:

Recommended by Danielsank

algassert.com/2016/05/22/quirk.html

AccidentalFourierTransform

7

A: Why are cosine and sine functions used when representing a signal or a wave?

The trigonometric functions form a basis for the space of "reasonable signals". (For the purposes of this answer, "reasonable signals" are continuous functions having finite energy and bounded power.) The word "basis" here is meant exactly the way it is used in linear algebra. (This is explici...

the last few paragraphs are very wrong arent they?

you wont get the solutions to a homogeneous equation by Fourier transforming

and $\left( (2 \pi \mathrm{i} \omega)^2 + k^2 \right) \hat{f}(\omega) = 0$

does not imply

$\hat{f}(\omega) = \frac{1}{(2 \pi \mathrm{i} \omega)^2 + k^2}$

and, most importantly, Fourier transforming back does not lead to

$f(t) = A \sin(kt) + B \cos(kt)$

or am I going crazy

how did this get +7!?

ACuriousMind

@AccidentalFourierTransform You're not going crazy

I guess the correctness of the first part just makes the eyes gloss over at the end :P

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