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2:00 PM
@JohnRennie MMA released an update!
I'm so proud of my accomplishment
 
@rob be careful with that, though. If it's two stinkers by 100+ rep, there's sometimes not much point there
@0celouvskyopoulo7 whatcha mean, blew up?
 
@EmilioPisanty Got a lot of views, upvotes, MMA released an update in response
 
@0celouvskyopoulo7 the views is HNQ
 
Oh, it went HNQ
How do you know?
 
'cause that's how I saw it
I think
 
2:02 PM
aha
@JohnRennie what's this file on my flash drive
Sounds ominous af
 
@0celouvskyopoulo7 that looks like wcry
 
what's that?
 
shut everything down pull all the plugs run like hell
 
@0celouvskyopoulo7 you been living under a rock these past four days?
 
2:04 PM
You mean PDE papers? Yes.
 
@EmilioPisanty So...you're fuckin' with me?
 
@0celouvskyopoulo7 yes
 
Gonna run Avast just to make sure...
 
wcry looks like this
 
2:06 PM
@EmilioPisanty WCry is windows only
it relies on W32 API
(Right?)
 
Lol that broken English
 
@BernardoMeurer yes
 
Heck the vulnerability is on SMB
@EmilioPisanty So why would he be worried running MacOS about WCry?
 
but if 0celo7 doesn't know what wcry is after all that hue and cry then he deserves the scare
 
@EmilioPisanty So I performed that fix that the wolfram dev suggested. Did that disable packlet updates?
 
2:08 PM
Great news everyone! WCry 2.0 functions PERFECTLY under Wine, you can infect your Linux desktops too if you are so… https://twitter.com/i/web/status/863359375787925505
 
Although there's this, lol
 
this is hilarious though
 
@EmilioPisanty lol
 
@EmilioPisanty Idk, I read the font page of reddit every few hours, and didn't see it.
 
2:08 PM
@0celouvskyopoulo7 why would news about ransomware be on a typesetting section?
=P
 
I'm guessing /r/fonts is a thing and that's what you're talking about
 
Ok, there's a megathread on r/technology
@EmilioPisanty Oh, lol
I meant front page :P
 
bizarre thing to check every few hours but everyone has their pet peeves
@0celouvskyopoulo7 anyways - I'm not really sure what paclets are, to be honest with you
 
@EmilioPisanty You're not exactly digging for gold there :P
 
2:10 PM
@ACuriousMind ah, it's an alternative definition of gold
 
Cocaine?
 
I mean, look at this marvellous rant
 
> Are not reproducible results fundamental to science? [closed]
 
user228700
(Jesus Christ is that creepy or what?)
 
2:11 PM
Guys! I finally have a feel for what curl means. Can I please post my geometrical interpretation here? (I spent two days breaking my head over this)
(i.e., would anyone be interested:P or kind enough to read it)
 
@ShaVuklia curl
 
aha:P
I'm gonna drop it here. sorry, no f's given:
It's easy to show that the $k$ component of the curl $\nabla\times F$ at a given point $(X,Y)$ equals $\int \vec F\cdot d\vec r$ divided by $dx\,dy$, where our curve is an infinitesimal rectangle parallel to the $x$-$y$ plane, starting from the point $(X,Y)$, and then (in counter-clockwise direction) $(X+dX,Y)$, $(X+dX)$, $(Y+dY)$, $(X,Y+dY)$.
So for the $k$ component of the total curl of a surface $A$, we can approximate this by considering the curl of $N$ patches of the surface - which boils down to integrating when we consider the limit $N\to\infty$ and $dxdy\to 0$, so we have $\int_A(\n
just look at it:P it's a perfect explanation
 
@Kaumudi.H that's a bummer, if I'd seen that video last year I'd totally have gone
that's creepy as hell, yes
 
@EmilioPisanty cogold
gold*
 
nope, just alternative gold
it perfectly fits the new definition of 'alternative'
 
user228700
2:15 PM
@EmilioPisanty Ah, were u in Germany last year? :-) I too have a strange desire to visit it and freak the heck out.
 
@Kaumudi.H I lived in Berlin up until January
 
user228700
Ah, I see.
 
But seriously, though, there's plenty of more interesting stuff to see & do in Berlin
though if abandoned places are your thing, Berlin is probably the best place for it
 
user228700
@EmilioPisanty Oh wow.
 
user228700
Haha, no, abandoned places aren't really my thing although I do have a little fascination with them. It's a moot point anyway; I don't know when I'll get to visit Germany, if ever. Thanks for the link though!
 
2:18 PM
@Kaumudi.H yeah, it's a good read
@ShaVuklia yeah, that's pretty much it
 
see Purcell's EM textbook for a more formalized description of that understanding
 
@Emilio it took me two days though to finally see it:P like, I understood it for the $k$ component, but I couldn't see exactly what happened when we got a wobbly surface, without getting too vague when describing the loops
and I'll see what Purcell says on curl
 
@ShaVuklia and if you haven't got Div Grad Curl And All That, now might be a good time
 
user228700
 
2:24 PM
@Kaumudi.H not surprised
it's in a pretty urban area
at least by Berlin standards
 
user228700
Ohh, I see...
 
@ACuriousMind or, say, this gem
 
@Emilio nice. I think I might actually buy that book for the summer. Right now, I have to focus on my finals, but I really love the geometry behind calculus. So thanks for the recommendation
 
> Taking rep points away from me is not an insult , it makes me continue my unauthadox view on on this unanswered confusion
 
wait, why would I buy a book when I can just find it online:P
 
2:26 PM
@EmilioPisanty I'll grant you it's amusing.
> Imagine a world that is watching ours, theory is theory , what if theory was real, why do we breath
 
Hey @0celouvskyopoulo7
If u want to do a book
Do you see things to put in there
 
@ACuriousMind thank you
=P
 
I'm guessing Cauchy problem and Sobolev spaces
 
pretty close to my old commute, too
 
user228700
Ah, thanks! I watched some drone footage of the same and saw all of the urban places surrounding it.
 
2:29 PM
@ACuriousMind heck, even Kyle fell for it
> Add our stands, this is merely an odd statement.
 
@Slereah I would like to write a thing on Sobolev spaces....
There's a lot of stuff to write about though
 
Kau mu di!
 
Most probably
 
@Slereah I would structure it differently.
 
How would u
 
2:31 PM
I would put the basic geometry in an appendix like Straumann does.
 
user228700
@Avantgarde :-P Yeah?
 
Start the main book with Lorentzian vector spaces.
 
@Kaumudi.H that was just a hi
 
user228700
Hey :-)
 
which would you consider "basic geometry"
There is a lot of geometry
Is it basically all of chapter 1
Hm, what else could I put in
pp-wave spacetimes
for gravitational waves
Linearized gravity
I guess the first test of GR I should put in the experimental test is "a ball falls down"
 
2:40 PM
Well...why do you need Ehresmann connections
 
To define the connection on the bundle?
 
They offer no physical insight for vector bundles, and presumably you don't need principal $G$-connections
 
Don't I
What if I want to do gauge fields
 
@Slereah Connections on vector bundles are very straightforward
@Slereah You don't...
 
Don't I
Also I might want to explore torsion and non-metricity
 
2:43 PM
Then you still only need connections on vector bundles
You really don't want to have to deal with the tangent bundle of a principal bundle
 
$U(1)$ isn't a tensor bundle
 
there's too many details there
you'd need a whole chapter on Lie groups
 
MAYBE I WILL
 
I'm not talking about representation theory either
 
Or I will write "See book"
 
2:44 PM
I thought the whole point was to make this self-contained
 
We will see
I mean I still need to write it
Should I try writing it
I can probably get enough pages from that CTC book for a good start
 
So, if I were to write a GR book (which I have been thinking about, but it would be ridiculous for me to try), I would have many appendices.
Kind of like Wald and Yvonne
There's no need to bog down the main text with a bunch of basic topology and geometry
 
Basic topology, yeah
Differential geometry, tho
I dunno
 
Also, I think I would put the physical foundations in an appendix
No need for that to be in the main book
 
What do you call the physical foundations
 
2:48 PM
Derivation of the field equations, why we use $-+++$, etc
why particles follow geodesics
I think one could motivate all of that in ~20 pages or less
 
Depends what you mean by derivation of the field equations
Do you mean from the Lagrangian or from Newtonian gravity
 
"ELLIPTIC SYSTEMS IN SPACES $H_{s,\delta}$ ON MANIFOLDS WHICH ARE EUCLIDEAN AT INFINITY "
Oh Yvonne
what a nice title
in all caps too
 
What I definately don't want to do is the usual historic text
 
@Slereah Newtonian.
 
Where the progression of the first chapters is done along the historical procedure
 
2:51 PM
I don't know any book that actually does that, except for Zee
 
There's too many books like that and I'm sick of reading about the history
 
and he puts a spin on the whole thing
Straumann talks about the history a bit but he never follows a "historical path" or whatever
 
I want everything rigorous from the get go, and only then do specific cases for applications
 
@dmckee If I have a #define in a parser.h, when I #include "parser.h in my main.c will the define be "seen" by main?
 
@BernardoMeurer Yes. The effect of #include is as of the text of the included file was inserted in place of the preprocessor directive.
Thus, the targets of #includes in header files are also effectively reproduced at that location.
 
2:53 PM
@dmckee That's what I thought! However it doesn't work well. I want to use strptime() from time.h, but for that I apparently need a #define _GNU_SOURCE 1 for reasons I don't understand.
 
I've even written a very simple unit testing framework in c-preprocessor
 
AH
Because I'm importing the parser AFTER time.h
 
Yep. Order matters.
 
@0celouvskyopoulo7 First two chapter of Straumann are kind of the historical path
 
2:54 PM
Why do I need #define _GNU_SOURCE 1 to use strptime()?
 
Hell he even does scalar gravity
 
It's part of POSIX ffs
 
@Slereah yeah we can forget about that...
So I would also do Basic Sobolev Spaces in an appendix
And then Weighted Sobolev Spaces should be a main chapter
 
Well I might bring up scalar gravity
But only in the chapter on alternative theories
And maybe the experimental one
 
No alternative theories
It's not a physics book
 
2:59 PM
@BernardoMeurer At a guess I would suspect it of being part of (or a residual of) of an effort to make the gnu library compatible across a bunch of different systems.
There is a lot of under-the-hood wonkiness in that library and much of it is about compatibility.
 
@dmckee What a PITA
 
pain-in-the-ass bread
 
@0celouvskyopoulo7 I'm afraid it is!
If I put the differential geometry in the appendix I'm afraid it would be more appendix than book
 
I don't see you getting away under 800 pages, honestly.
A solid GR book has a lot of stuff.
@Slereah Humor me, I will write a short outline...
 
dammit
 
3:11 PM
@EmilioPisanty what
 
overdupehammered again
 
@EmilioPisanty help
 
0
Q: If Quantum Mechanics and Special Relativity tend to "Classical" physics at everyday scales, how do magnets exist?

alexI'm aware that ferromagnetism, para-magnetism, etc. in materials could be properly explained only when a relativistic, quantum mechanical theory for the electron was developed, in which spin was a naturally arising, fundamental quantity. I suppose one could say all effects of QM and SR except th...

can folks peer-review that closure?
@AccidentalFourierTransform with what?
 
@EmilioPisanty a differential equation
 
@AccidentalFourierTransform fine, go ahead
 
3:12 PM
so, spherical harmonics, right
two differential equations
 
if it's $f''(x)+f(x)=0$ I can help
 
@Kaumudi.H I'll be around as usual, from about six a.m. to midday British summer time, and variable times in the afternoon/evening.
 
$Y=f(\theta)\Phi(\phi)$
 
fancier stuff, I dunno
 
@AccidentalFourierTransform Are you looking for existence/uniqueness or an explicit thing
 
3:12 PM
@AccidentalFourierTransform yeah
 
so, $L_zY=mY$ means $\partial_\phi \Phi=im\Phi$, so $\Phi=e^{im\phi}$
 
and $m\in\mathbb Z$ for univaluedness
 
I'm trying to agree but chat won't let me
yes
 
Is that link to show/hide the icons for inactive users new? Or have I only just noticed it?
 
3:14 PM
there we go
 
now, the other one, something like $(1-x^2)f''+\text{stuff}+\left[\frac{m^2}{1-x^2}+\ell(\ell+1)\right]f=0$
 
... yes?
it's pretty dangerous to just $+\mathrm{stuff}+$ stuff
 
with solution $f=c_1P_\ell^m+c_2Q_\ell^m$
 
Yeah it would be fairly hefty
 
3:15 PM
and $c_2=0$ for finiteness
bc $Q$ diverges at $x=\pm1$
 
yes yes yes
damn you, chat
 
but where does the quantisation condition on $\ell$ come from?
$P_\ell^m$ is finite for all $\ell\in\mathbb C$
 
@AccidentalFourierTransform from finiteness at the other pole
 
which other pole?
the Legendre function can be written as a series
which terminates for $\ell\in\mathbb N$
 
the one that is not the other other one
 
3:16 PM
for real $\ell$ it does not terminate, but the series converges and is finite in the interval (-1,1)
 
@AccidentalFourierTransform false
has a divergence at $x=-1$
 
let me see if MMA agrees :-P
 
Limit[LegendreP[\[Pi], 1, x], x -> -1]
(* \infty *)
so yes, that's it
 
user228700
@JohnRennie Nah, it wasn't to ask about how often you'd be around here.
 
3:18 PM
noice
 
;-) there you go
 
thanks!
for some reason, I thought that $P_\ell^m$ was symmetric around $x=0$
and I did check that it was finite at $x=1$
so I did what any physicists would do
 
user228700
@JohnRennie ...I was wondering about ur book collection (and if you could recommend a few books to me) but on second thought, never mind; I suspect I'm going to have too many books to read as it is.
 
I assumed that it must hold at $x=-1$ as well
 
@Kaumudi.H ah, OK, my business levels should be back to normal from tomorrow i.e. not very busy.
 
3:20 PM
@AccidentalFourierTransform it has specific symmetry for integer $\ell$
 
mislead by a false symmetry!
 
but not for arbitrary order
 
well now I know
 
user228700
@JohnRennie Wokay :-) Good to know.
 
3:21 PM
From more physical grounds, though, you've reduced the eigenvalue DE to some kind of wave problem in a 1D interval
 
you expect to need to impose finiteness at both ends
 
I'll be referencing this one next time anyone asks something about rotational motion
 
1. The Causal Theory of Lorentzian Manifolds
2. The Wave Equation
3. The Einstein Equations
4. The Cauchy Problem and Constraints
5. The Positive Mass Theorem
6. Spherically Symmetric Spacetimes
7. Singularity Theorems
8. Global Lorentzian Geometry
9. Cosed Timelike Curves

Appendices.

A. Topology
B. Smooth Manifolds
C. Semi-Riemannian Manifolds
D. Lorentz Metrics on a Compact Manifold
E. Riemannian Geometry
F. Natural Sobolev Spaces in R^n
G. Weighted Sobolev Spaces
H. Partial Differential Equations
@Slereah idk, that's a first thought
 
@AccidentalFourierTransform nice one
doesn't beat this one
but it's nice anyways
> Shipping Weight: 13 pounds
sounds about right
 
3:23 PM
oh I want it :-(
 
@Slereah That should fill roughly 2,000 pages.
 
user228700
@AccidentalFourierTransform How come he knows this stuff? His dad's usually not very smart...
 
user228700
 
@AccidentalFourierTransform I don't get it
 
@AccidentalFourierTransform you seen Hobbes & Bacon, btw?
 
3:25 PM
> you cant believe anything you read, I'm afraid
I HAVE A QUOTE FOR MY THESIS
 
@AccidentalFourierTransform which you're going to attribute to ... ?
"Dad"?
 
-3
Q: The Sun and Earth

CarolIf the Sun can hold at least a million or more Earths,how are we able to look up at the sky and see a perfect ball which is the Sun?

 
user228700
@JohnR: Anything especially great though?
 
3:28 PM
@SirCumference I created an account just to +1.
2
 
@0celouvskyopoulo7 wha...
 
user228700
Ah, didn't check my mail...
 
@Kaumudi.H :-)
 
> how are we able to look up at the sky and see a perfect ball which is the Sun?
 
user228700
@JohnRennie Ya know, the whole point of gchat was so we could avoid this mail delay thing :-P
 
3:30 PM
@Kaumudi.H yes, but gchat needs a call setting up whereas I can fling out an e-mail and you'll get it eventually whether you're around at the time or not.
 
@0celouvskyopoulo7 could use a bit more physics!
 
and more appendices
good books have more appendices than actual chapters
 
user228700
@JohnRennie Same with gchat. I check hangouts as many times as I do Gmail :-)
 
@Kaumudi.H after all you have three days (2½ now!) before the mail would become relevant.
 
@JohnRennie strptime() is amazing
 
user228700
3:32 PM
@JohnRennie 2.5 days?! A little more than 24 hours to go!!
 
No, two days, I keep forgetting the time difference.
 
user228700
The exam may be in 1.5 days but I only have to study for one more day.
 
OK :-)
 
user228700
Those extra 12 hours I'll spend sleeping and eating and etc.
 
@Slereah Ideally this would be published as a Graduate Text in Mathematics...
 
3:33 PM
@BernardoMeurer it looked pretty cool. Time conversions are the bane of every programmer's life. Why can't the world agree on a single format for writing times?
 
user228700
@JohnR: Anyhoo, thank you! :-) I was gonna ask if you have anything to recommend, having some idea of my taste but OK...
 
@Kaumudi.H what? you should never study in the last 48h before an exam!
sleep and eat and dance and play, but dont study
I mean, cmon!
 
It should combine the best bits of Yvonne, Straumann, HE, BEE, SW, Wald, my spherical work (assuming that goes anywhere), and it should put the Cantor/Yvonne/Bartle/Christodoulou theory of weighted Sobolev spaces/elliptic systems into book form.
 
user228700
@AccidentalFourierTransform x'D Says who? Had I followed that rule, I'd have failed. Consistently. (I have a thing for last-minute revision)
 
@AccidentalFourierTransform I'd be cautious about making judgements. The Indian examination system is a strange beast and rather different to the examination style we're used to in the West.
 
3:35 PM
@Kaumudi.H says someone who has failed many exams too, but is older than you >:| (:-P)
 
user228700
:-P OK, Sir.
 
user228700
> A strange beast
 
@JohnRennie ¯\_(ツ)_/¯
 
user228700
Fitting.
 
3:37 PM
@Kaumudi.H In the next update of Fabulous beasts and where to find them the Indian examination system is included in Appendix A.
 
user228700
Hahaha x'D
 
lol
 
dunno if you saw this
damn Indian testing taking over the chat again
 
@Kaumudi.H anyway, I have lots of books I think are truly wonderful but it's always a risky business recommending books to other people as tastes vary so widely..
 
@Kaumudi.H I can recommend books to you
 
3:39 PM
bourbaki
 
This is one of the most amazing books I read in a while:
 
user228700
@JohnRennie Hmm, OK.
 
the one book
 
I didn't think we were talking about math books
@BalarkaSen wanna write a Lorentzian geometric analysis book with me
 
3:40 PM
no
 
wtf why
 
user228700
@JohnRennie Looks interesting! :-)
 
It was one of those books I couldn't put down. The Minotaur is such a wonderful character in the book.
 
my favorite Minotaur story is House of Asterion. It's like 2 pages
 
user228700
@JohnRennie I see. I am yet to update my to-read list but once I do, I'll show you.
 
3:42 PM
is that a novel?
 
@Avantgarde yes. Well, it's a mixture of prose and poetry. But mostly prose.
 
@JohnRennie That's a good question, the UNIX time format is not very nice
seconds since 1970, lol
 
@BernardoMeurer it works. Though the rollover in 2038 may be an entertaining time :-)
 
That's going to be a mess
There's a party scheduled in Copenhagen for the rollover date
 
@JohnRennie Okay
 
3:46 PM
I want to be there
@JohnRennie If you go you'll have outlived the UNIX time standard! :P
 
Excel uses days since 01/01/1900. Windows uses seconds since the beginning of the Gregorian calendar or something ...
 
@BernardoMeurer another 21 years - that seems a reasonably modest ambition :-)
 
My favorite minotaur story is the original one
 
@JohnRennie We go, I buy you a beer :P
 
3:48 PM
When they put the monster bull baby in a maze
 
@Slereah Well it's ok
House of Asterion is a reinterpretation from the monster's perspective, really
 
Is the entire book just gibberisg
RAAAARGH
 
user228700
@JohnRennie 77. Really?
 
I always felt a bit sorry for the Minotaur. It wasn't his fault his Mum got a bit experimental one evening.
 
MOOOOO
 
3:49 PM
what book
 
The book written from the minotaur perspective
 
it's not a book, it's 2 pages. no it's not gibberish
 
@JohnRennie they should have made hip into hamburgers
 
it's the most beautiful 2 pages i have ever read
 
@Kaumudi.H 77 seems a fairly modest age to aim for.
 
3:50 PM
"Would you believe it, Ariadne? The Minotaur scarcely defended himself."
 
@Slereah hip?
 
Him
I am on the phone
 
bad typo
brings disturbing visions
 
user228700
@JohnRennie Reasonably modest. Ah. Yes. I misread your message.
 
3:55 PM
That's the translation I read. Weirded out by the links though
 
@BalarkaSen yes, I'm not sure the links add anything to the story ...
 
I mean it's an interesting idea to illustrate the story, but the images used there are plain weird
 
user228700
:-) That's a nice little poem.
 
Somewhere I have a collection of amusing little poems like that.
 

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