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4:00 PM
Make it an ISO standard
 
Sobolev spaces are $\mathrm W^{k,p}$
 
*Wobolev spaces
 
@Slereah dubstep?
@Черенки well what do you want to learn about
 
It's chat session time!
Welcome, everyone. Do we have any new users - new to the site, or to chat, or to both - in the room?
 
Yes hello I am new
My name is Oliver Twist
 
4:04 PM
@Slereah Then why did you name yourself "Slereah"? :P
 
Slereah is his idol
 
It's my nickity name
 
@Slereah how do I explain what spacetime is on a poster
 
Hm, well, if it's just you two then it's not a chat session, it's just chat as usual ;P
 
trying to explain math to biology people -- help
 
4:06 PM
HALP
 
@Slereah do you want me to put that on my poster
 
i don't like that one as much as the 3-d one
 
what poster
 
What is the fractional part of $-1.7$? $0.3$ or $0.7$?
 
4:06 PM
I have to explain the Einstein equations
oh no
@Mr.Xcoder -0.7
 
In any case, don't forget that today we will also have @Mithrandir24601's AMA - at 8pm UTC
2
 
@ACuriousMind that works ;-)
 
@0celóñe7 really?
 
The best way to represent spacetime is to use the lattice version of spacetime
It's fairly evocative
 
@Mr.Xcoder No, I have no idea what you are talking about
 
4:07 PM
Turns out I can pop in sporadically
 
Although of course it doesn't help much with the time part
what with the signature
 
@Slereah how does one explain what a metric is
 
@DavidZ Did you have anything you wanted to discuss? I thought about it and found I don't have anything to put on the agenda
 
a symmetric matrix thatr varies from point to point in spacetime and gives information about the local geometry?
 
vzn
4:08 PM
@DavidZ show up 15m beforehand to say you may not be available? (lol) looks like youre not missing much.
 
@0celóñe7 Use the submanifold way
With 2D manifolds
And fundamental forms
It's not too hard to understand if you know basic vector calculus
 
@Slereah Hmm, the more background I put on the poster, the less I have to pretend that my research was worth it
@Slereah this is for a general science audience
they might not even know calculus
 
Then just throw them the usual spacetime as a curved fabric
or use the lattice one
 
@ACuriousMind what are your thoughts on your meta post, with whether or not level of post matters?
 
ie
@heather this
It's slightly better
 
vzn
4:10 PM
fyi announcement for all Mithrandirs talk is today 4hr from now see bottom of schedule chat.stackexchange.com/rooms/info/71/the-h-bar?tab=schedule physics.meta.stackexchange.com/questions/10085/…
 
@0celóñe7 then say a metric is a way to measure distance...
when you told me that i thought it was pretty clear =)
 
@Slereah Is one supposed to lie to children and then have a footnote with the details?
@heather but that's not true for spacetime
"spacetime distance" is a pretty vacuous concept
 
Just say it gives the measure of distances and times
Which is roughly true
 
@heather I think the result seems to be "no consensus, learning towards not-duplicate in some cases".
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.
 
@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.
 
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
 
@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.
 
@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.
 
no, i disagree.
ack. sorry.
 
heh
 
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.
 
@heather Yes, that is precisely my personal belief.
 
is that really an answer
no, of course not.
that's entirely ignoring the question.
 
Well, it's easy to judge that in the extreme cases. There's a large grey area in between.
 
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.
 
@heather Of course my rule is consistent - because I also think that questions are duplicates no matter the level of explanation asked for.
 
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).
 
Use this for the missing time:
 
@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.
 
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.
 
@heather metric tensor
it doesn't induce a metric space structure on spcaetime
 
@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.
 
4:33 PM
i think we've lost track of the fact that this site is for answering questions.
 
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.
 
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.
 
@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
 
@0celóñe7 you could say that a metric just explains how points relate to each other.
@ACuriousMind sometimes meta is very frustrating =P
 
@heather that's what "describes the local geometry" means
 
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?
 
not children
 
how general is the general audience?
 
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
 
Hopefully you don't need to explain what a riemann curvature tensor is
 
well, one can explain it. how well one can explain it is another story, i'm guessing ;)
 
4:44 PM
what is going on
 
@Secret something which describes how different spacetime is at a point from normal flat space would be my go at it.
 
why do we want to explain metric tensor to the general audience
 
@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?
 
@BalarkaSen gmt
 
@0celo pls no gmt
 
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
 
that's holonomy, not really curvature
it's one of the global phenomenons of curvature, i guess
 
@BalarkaSen holonomy is quite related to curvature
 
yes! solved the last problem in the mechanics section of my textbook =D
::celebrates::
 
there's a formula for the deviation of a vector as it parallel transports that involves curvature
 
@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
 
4:49 PM
(approximate formua for small loops)
 
@0celóñe7 "i know bro. it's everyday bro." - jake paul from h3h3 podcast
 
now part II and part III and part IV and part VIII...
 
@BalarkaSen did u watch the compilation?
 
@ACuriousMind that's rather unsatisfying...there's not any way to "ask it again" or something like that?
 
What is the hardest thing in GR to explain to a Layperson?
 
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
 
@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?
 
@Secret ricci curvature
 
@ACuriousMind erm...magic?
 
I have no clue what it is
 
@0celóñe7 nah, just clips from it where he got the most roasts
 
4:51 PM
@BalarkaSen I mean the vid I sent you
 
@heather "Insanity is doing the same thing over and over again and expecting different results" :P
 
@ACuriousMind insanity is repeating that quote over and over again and expecting different results =P
 
@0celóñe7 oh yes i saw it
did you watch the one i sent you in response?
 
@BalarkaSen The exact formula is $$\Delta v^i=-\int_\gamma \Gamma^i{}_{kj}v^j\, dx^k.$$ For a small enough loop this is $$\approx -\frac{1}{2}R^i{}_{jkl}(p)v^j_0 \int_\sigma dx^k\wedge dx^l$$
 
@heather I...don't think I've used that quote here before...
 
4:53 PM
where $\partial\sigma=\gamma$
 
@0celóñe7 [swedish curses]
 
vzn
missing new physics section of mtg... :( anyone have any to share?
 
@ACuriousMind i was referring to the general overuse of the quote.
 
@BalarkaSen what
 
i picked that up from when pewdiepie reacts to jump scares in his playthroughs
 
4:54 PM
@vzn well, china launched a satellite for quantum communications, did experiments, it works, published in
let me see
 
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...
 
ah, physics today, vol 70, issue 8, pg 14-16
 
@0celóñe7 thats not even scary
 
@BalarkaSen if you were playing it, it would be
 
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
 
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
 
Alright, time to define spacetime
A spacetime is a tuple $(M,g,\nabla,\mu,\tau,T)$...
 
?, metric, connection, ?, proper time, ?
 
@Mithrandir24601 I thought you said the seminar was at 10:00 PST...
 
@heather in 5 minutes...
or maybe slightly less
 
5:00 PM
@Secret manifold, metric, connection, orientation, time orientation, matter
 
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
 
@Mithrandir24601 ah, sorry. timezones are confusing =)
 
will drop link in five minutes
need to go to bathroom etc. before starting.
 
so, we're having the ama and the seminar at the same time?
ugh, that's not very convenient
 
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
 
oh
2 mins ago, by heather
@Mithrandir24601 ah, sorry. timezones are confusing =)
 
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
 
what aboot Hausdorff
 
@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...(?)
 
makes sense to me, though the layperson is going to stratch heads without you standing next to it to explain
 
that's the convention in analysis
 
@vzn dude, really, dont edit pings please
 
but I forgot second countable
@AccidentalFourierTransform why not?
 
5:06 PM
its annoying
 
@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.
 
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
 
yeah I noticed
 
5:07 PM
Seminar on quantum computing with superconducting circuits: hangouts.google.com/hangouts/_/mqgg7qrsuvgepm2e2sinq7f5oie
That's a google hangouts link
 
Pushing the company software, eh? ;)
 
@DanielSank GDP!!!!!!!!!!
 
@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 :|
 
maturity at its finest
 
5:15 PM
You should ping vzn on that message.
And edit it a million times.
 
we should program a bot that pings him every time he edits a message :-P
 
@BalarkaSen gmt is bad because even explaining what the theorems are takes pages of crap
 
@DanielSank ...Google Hangouts does not work in Firefox?!
 
it's also hard to motivate an $\mathcal H^k$-rectifiable stokes theorem
 
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
 
5:38 PM
@ACuriousMind rm appears to be on hulu in america
I don't have that
 
they typically upload the episodes to mega and share them on reddit
the third season sucks btw
 
@AccidentalFourierTransform No it doesn't :P
 
yeah it became mainstream
it used to be cool
 
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
 
interesting
technical difficulties...
 
5:49 PM
@AccidentalFourierTransform are you suggesting piracy
 
Ok they're getting an ethernet cable in hopes that it helps.
 
nice
 
@0celóñe7 What about it?
 
@DanielSank I was excited to see you talk about it
 
@DanielSank: no microphone! sorry?
 
5:51 PM
No problem.
 
@DanielSank: I was just going to spectate
 
I have not plug in any microphone, I am also spectating until roughly 4:15
 
I wanted to spectate too but I cannot login
I think I forgot my password anyway :-/
 
I have a microphone but it's off
@JohnRennie we should ask about quantum SSDs
hahaha
 
6:09 PM
what is the command for the semi-direct sum symbol in latex?
Detexify did not help
 
what the heck is a semi-direct sum
 
@AccidentalFourierTransform Do you mean a semi-direct product $\ltimes$?
 
semidirect product is for groups
the linearisation is the semidirect sum
 
if acm doesn't know your algebra, you might be talking nonsense
 
ie, for the algebra
NO IM NOT ;_;
 
6:11 PM
@AccidentalFourierTransform Ah. I've never seen a special symbol for that
 
well, how do you write the Poincaré algebra for example?
 
I don't
 
@AccidentalFourierTransform I define the Poincaré group and then just say "the Lie algebra of this" :P
 
Yikes, my PC setup is pulling 14.3 A
no wonder I exploded the power last night
 
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?
 
lol
 
Ah
Nope, never seen that
@0celóñe7 That...is a lot
 
@AccidentalFourierTransform omg what the .... is that
 
@AccidentalFourierTransform $\oplus_\text{semi}$
 
@BalarkaSen A SEMIDIRECT SUM FFS
@0celóñe7 eww
 
@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
 
@BalarkaSen go ask ppl in the math.se chat please will you
 
That would be 1,7 kW power, which seems pretty high to me
 
@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
 
@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
 
6:20 PM
Hmm, the breaker box says 120
I think some palces have 110
 
220V>110V $\Rightarrow$ Europe>America confirmed.
 
@AccidentalFourierTransform more like Europe needs more voltage to get things working
we're more efficient
 
Wikipedia said the semidirect sum is used in lie algebra
 
@BalarkaSen @ACuriousMind what is this? bookstore.ams.org/gsm-177
 
@0celóñe7 Something I know nothing about :P
 
6:24 PM
and wikipedia is goddamn right
 
@Secret ...AFT already said that.
 
@ACuriousMind it says Galois
"Guido Schneider"
that name seems randomly generated
 
Ok sorry, I was moving between maths chat, this chat and Danielsank's seminar
> What on earth is faster than the universe :?
 
@0celóñe7 All names are pseudo-randomly generated :P
(Humans are pretty bad pseudo-random generators, though)
 
inb4: NINE NINE NINE NINE
 
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
 
@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
 
14
Q: Why are cosine and sine functions used when representing a signal or a wave?

gayathri gayiActually, 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?
 
you are already fourier transformed
so yeah
 
@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?"
 
> Thomas :?
 
6:31 PM
I.e. for what reason do functions that describe geometric relations in a triangle show up when describing periodic phenomena
 
@ACuriousMind are you telling me I can't randomly generate
 
@Secret Why not?
 
I see
 
"1 cup dry white wine"
this country is awful
 
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
 
6:39 PM
Play with quantum computers here:
Recommended by Danielsank
 
7
A: Why are cosine and sine functions used when representing a signal or a wave?

Eric TowersThe 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!?
 
@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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