The h Bar

3:00 PM

@Qmechanic think youd make a great guest spkr plz consider it sometime :) physics.meta.stackexchange.com/questions/7783/… note general idea of sessions was proposed by mod DZ :)

0celouvsky

@vzn he's never going to do that

vzn

@0celouvsky why not (you think) ... ps your invitation is standing/ open also :)

0celouvsky

He wants to stay anonymous

Also why do you think he never spends time with us? He clearly despises chat

ACuriousMind

@vzn Qmechanic obviously values his anonymity, so it is very likely he won't be willing to do an AMA since divulging additional information about oneself weakens the prospect of remaining anonymous.

vzn

@0celouvsky was just musing on that. that is really no major obstacle to the sessions. actually nonanonymous users are almost the non-majority at this point. but do admit the sessions (by nature) create a more personal connection etc...

Slereah

3:08 PM

@ACuriousMind if the group is $GL$ what does the tangent bundle being trivial mean

ACuriousMind

@Slereah That you can reduce the structure group to the trivial group - a bundle with a reduction to the trivial structure group is necessarily trivial in the usual sense since all transition functions are trivial so all local objects are in fact global.

vzn

@ACuriousMind ok am the 1st to respect those who prefer "anonymity," but not sure Qmechanic values it more highly than others around here etc, havent seen him express anything particular on that, maybe others have...? anyway though as my grandfather used to say cant get hung for trying :| (grandmother didnt exactly like that expr either)

Slereah

whaaat

how does one reduce $GL(3,R)$ to $I$

Bernardo Meurer

@JohnRennie Lol, I love refactoring

@YashasSamaga I use GCC mainly, sometimes Clang

I have stocked up energy drinks and food

I am not leaving the room this weekend

Yashas Samaga

I am surprised that GCC gave you those errors.

It is a bug if it did.

0celouvsky

3:14 PM

@vzn that's a double negative or something

ACuriousMind

@Slereah "reducing the structure group" means picking all transition functions to be in the reduced group. If the bundle is trivial, then that's a vacuously true statement since there are no transition functions.

vzn

@BernardoMeurer reminds me of those hackathon scenes in Social Network have you seen that movie? luv it... actually you remind me of one of the characters

0celouvsky

Most people here are not anonymous

vzn

@0celouvsky lol but not incorrect. too hard for you to parse mr advanced topology-math? :P

0celouvsky

Why does everyone think I like topology the best?

Slereah

3:15 PM

@ACuriousMind Is there an example where the bundle structure is $O(n)$ that can't be reduced any further?

vzn

@0celouvsky uh, because you chat about it all day/ year long? (not that theres anything wrong with that... aka seinfeld)...

0celouvsky

@Slereah Möbius band

ACuriousMind

@Slereah A generic non-orientable manifold will do

Slereah

Hm

Under what circumstances is it trivial?

ACuriousMind

E.g. for Lie groups

0celouvsky

3:16 PM

@Slereah structure group is SO iff orientable IIRC

@Slereah contractible manifolds

Slereah

Ah

Well I am not that illuminated but I'm slightly less confused

I thought trivial was ~ orientable

0celouvsky

Nope, S2 is famously nontrivial

Slereah

At first I thought the whole $GL$ thing was related to coordinate change but I'm guessing from the examples that's not the case

I guess the harder question then is why is a vector bundle with the structure group $GL(n, V)$?

Bernardo Meurer

@vzn Who do I remind you of?

I haven't seen the move, no

0celouvsky

The structure group has to do with the way the fibers fit together

Less to do with coordinates

Bernardo Meurer

3:21 PM

@JohnRennie I'm going to wrap all the graphics stuff on a struct too :D

It's going ot be so neat and organized!

ACuriousMind

@Slereah By definition of the structure group - look at the transition functions of a vector bundle and note that they lie in GL(n)

Note that the statement "the structure group can be reduced" is different from "the structure group is". That I can reduce the structure group of a trivial vector bundle to the trivial group does not mean that the structure group of the vector bundle is not GL(n) anymore.

0celouvsky

That's a good point Bajoran

Slereah

Wait

>trivial if contractible
>S2 is famously nontrivial

Isn't $S^2$ contractible???

ACuriousMind

No???

0celouvsky

No

It has nontrivial homology

Slereah

3:24 PM

Oh is it different from simply connected

0celouvsky

Yes!!!

Slereah

dang it

0celouvsky

Contractible means the identity map is homotopic to a constant

vzn

@BernardoMeurer imdb.com/character/ch0209107 you two might even look a little alike...

ACuriousMind

Contractible means there's a deformation retract to a point, i.e. you can deform the space continuously into a point.

Bernardo Meurer

3:25 PM

@vzn His nose is much bigger :P

0celouvsky

That's what I just said!

ACuriousMind

In particular the homology/homotopy group are obstructions to that, but there are silly spaces with vanishing homotopy that are not contractible

Slereah

$S^2$ isn't very silly

0celouvsky

@Slereah btw it's an abuse of terminology to call trivial loops contractible since they're not actually contractible. Nullhomotopic is the correct word.

vzn

@BernardoMeurer anyway very fun movie am sure youll get big kick out of it, it has hot chicks + hackers + coders what more could you want... got big box office years back... actually significantly launched star eisenberg into stardom... now hes doing stuff like joker in batman vs superman & woody allen movies with scarlett johanssen etc... (not bad either!)

ACuriousMind

3:27 PM

@Slereah It also doesn't have vanishing homotopy.

$\pi_2(S^2) = \mathbb{Z}$.

0celouvsky

But I think people call them contractible anyway

@ACuriousMind is that just degree theory?

Slereah

But then again who cares for $\pi_n, n > 1$ :p

0celouvsky

@ACuriousMind why not just say H2 is Z

Much easier than homotopy

Slereah

What does the group being reducible mean, anyway

I'm not sure that it's ever really explained

Bernardo Meurer

@vzn I didn't watch it back in the day out of my disgust for Zuckerberg and his company

Slereah

3:29 PM

Is it that there's a local trivialization cover with those transition functions?

like at least one

rob

@EmilioPisanty Thanks for the heads-up. One of the moderator tools is a list of recently-rejected migrated questions, but I forget to look at it very often.

ACuriousMind

@0celouvsky Same thing by Hurewicz.

@Slereah Yes, precisely

Slereah

Ah I see

That makes more sense

Would a cover of $R^2$ be for instance the cover of all $(a, b) \times (c,d)$?

0celouvsky

@Slereah why don't you read a book on algebraic topology and differential geometry?

Slereah

Money ain't good right now

ACuriousMind

3:31 PM

@Slereah I don't understand the question. $\mathbb{R}^n$ is simply connected so all connected covers are just $\mathbb{R}^n$.

@Slereah Read Hatcher. It's good and free.

Slereah

no money for more math book

0celouvsky

@Slereah hatcher is free online

ACuriousMind

Free as in gratis.

vzn

@BernardoMeurer the movie is not incompatible with disgust for zuckerberg, one might say quite to the contrary :P ... he was said not to have liked it... hes nearly the villain of the movie... some compared it to citizen kane, a not flattering comparison to/ swipe at zuckerberg... (& btw am not an unmitigated fan myself...)

0celouvsky

@ACuriousMind is it malware tho??

Slereah

3:32 PM

Ah I see

Jaime Gallego

Howdy y'all

Bernardo Meurer

@ACuriousMind M A L W A R E

Slereah

I guess $R^n$ is a much simpler cover if you want to make sure everything connects nicely :p

Bernardo Meurer

@vzn Still, I don't want to give him my view

To me Zuckerberg could die and take his company policies with him

Slereah

Is $\Bbb R^n \setminus \{p, q, ...\}$ also of trivial bundle?

0celouvsky

3:33 PM

What

Slereah

For a countable number of points

0celouvsky

What base should it be?

vzn

@BernardoMeurer hate his "open office" fanaticism (seen in the movie), its spreading like a infection/ virus to a cube near me... now even )( cubes are too much... @#%&

0celouvsky

What is it with people writing 500 page books? It's not possible to get past 200 and still be interested

Slereah

pirates Hatcher with great hacking skills

@0celouvsky Don't get Abramowitz then

0celouvsky

3:34 PM

@ACuriousMind ^illegal activity

@Slereah I own it!

Ask @BernardoMeurer

I have my dad's copy from back in the day

Slereah

I wonder what's the largest book I own that isn't just a list of things

Probably Kleinert's book on path integrals

It's a fucking brick

0celouvsky

Zee is pretty damn big

It could kill a man if skillfully weld

Slereah

Though to be fair it's basically 3 unrelated books

ACuriousMind

@Slereah Why would you pirate it? It's free on his homepage

0celouvsky

@ACuriousMind can verify that BBS is unreasonably heavy

vzn

3:36 PM

@Bernardo re "villain" try this out... o_O dailymail.co.uk/news/article-4134654/…

Slereah

It's a joke :p

Path integrals for QM, path integrals for polymers and path integrals for financial markets

I don't think anyone has read all the book

Bernardo Meurer

@vzn I refuse to read Daily Mail, or go on their website, but from the link I know what you are talking about

He's an asshole

0celouvsky

The polymers part sounds interesting

Slereah

What kind of weirdo gets a QM book and then thinks "I also want to model the market"

0celouvsky

@BernardoMeurer I bet you know my sister has a house

I'm apparently the only one she didn't tell

My family hates me

Slereah

3:37 PM

The polymer part is something like

Bernardo Meurer

@0celouvsky She didn't tell me either :)

Slereah

You sum over all configurations of the polymer?

vzn

@BernardoMeurer lol dont know what ppl have against dailymail, its at least as credible as anything in this chat room :P

0celouvsky

Oh, that's nice

Slereah

I think

Bernardo Meurer

3:37 PM

I sent her a text yesterday, no answer

ACuriousMind

@Slereah Simons of Chern-Simons fame is a mathematician, but also a hedge fund manager :P

0celouvsky

Me too ;_;

@ACuriousMind what????

Slereah

what a sellout

0celouvsky

A mathematician actually getting that GDP???

vzn

@ACuriousMind a billionaire in fact, who has heavily funded CS/ math research etc... theres an interesting/ rare youtube video interview

Bernardo Meurer

3:38 PM

@vzn It's a shitty news company that deceives the public and is dishonest

0celouvsky

CNN?

vzn

@0celouvsky lol exactly @#%& MSM

The only real news is @readDonaldTrump

vzn

hey people talk about vixra all the time in here, so why not dailymail? :P

John Rennie

3:40 PM

Vixra isn't to blame for Brexit

0celouvsky

@BernardoMeurer you betrayed me

vzn

@JohnRennie lol you think brexit passed because dailymail? o_O :P

John Rennie

The Daily Mail thinks so

0celouvsky

@ACuriousMind can you please just ban Bernardo?

Bernardo Meurer

@0celouvsky Why?

vzn

3:41 PM

@JohnRennie and donald trump (brexit fan!) got elected because breitbart news, right? :P

ACuriousMind

@0celouvsky What did you think where the Simons foundation gets its money from? ;)

0celouvsky

I don't know what that is

rob

Apparently Mathematics and Electronics are our most common migration targets, accounting for a little more than half of all migrated questions.
[Over the last 90 days](https://physics.stackexchange.com/admin/posts/migrated/stats) Mathematics has rejected 2/37 migrated questions, which seems pretty good.
Electronics has apparently rejected 4/19 questions from Physics, which seems big percentage-wise, but four bad migrations in three months doesn't seem like a terrible burden.
We seem to have rejected 10/18 questions from Mathematics, which isn't too surprising to me since their attitude tow…

ACuriousMind

@0celouvsky the upper right corner of the arXiv "gratefully acknowledges" support by it, for one. Never noticed that?

vzn

@ACuriousMind think that is a relatively new/ recent grant

0celouvsky

3:43 PM

Nope. Why would I read the top corner of arXiv?

Emilio Pisanty

@ACuriousMind the support acknowledgements on top right of arXiv change depending on your IP

Bernardo Meurer

@0celouvsky Why did I betray you?

ACuriousMind

@vzn Yeah, it wasn't always like that but it's been that way for several months at least

0celouvsky

Michelle knows I told you

ACuriousMind

@EmilioPisanty I...did not know that!

rob

3:44 PM

@EmilioPisanty No way ... really??

Emilio Pisanty

e.g. if your institution supports arXiv directly then it can show up on the top-right bit

Bernardo Meurer

@0celouvsky because I told her "I heard you got a house"

Emilio Pisanty

it did at Imperial

Bernardo Meurer

and Kat asked me in another chat if you had bitched to me that she hadn't told you directly

and I confirmed

vzn

@Slereah lol & what kind of weirdo buys the book?

Emilio Pisanty

3:45 PM

@rob I think that overall the status quo is OK

rob

@EmilioPisanty Yeah, that was my conclusion as well.

But thanks for bringing it up.

Emilio Pisanty

I guess the question is whether the EE migration load is getting too big for manual mod migration, but that's a call for y'all

@rob not me, cf. Jim's edit on the front page of meta

@vzn web.archive.org/web/20121207042137/http://arxiv.org

present at least since December 2012

John Rennie

@Kaumudi.H: I succumbed to temptation! :-)

vzn

@EmilioPisanty ok didnt notice it before, they made it into a top banner recently

Emilio Pisanty

@vzn if 2012 counts as recently ;-)

rob

3:50 PM

@EmilioPisanty Oh, how about that. At least we were using the same numbers.

vzn

@EmilioPisanty it was a footnote for years, a new prominent top banner recently... someones decision to make funding more visible ala wikipedia donation requests

Emilio Pisanty

@vzn not sure what you're talking about

Slereah

@vzn me

Emilio Pisanty

it was on the top banner since December 2012

the design is unchanged since that date

vzn

@EmilioPisanty ok sorry! think they changed the top banner some recently mentioning simons. ofc web banners/ layouts change all the time. didnt realize/ notice simons funded the site long ago.

Slereah

3:54 PM

The reduction of a bundle being the existence of a cover that has the reduction as structure group, is that cover unique for all sections, or is it just that, for a given section, there always exists such a cover?

since the big thing I suppose is that the sections have to fit together

0celouvsky

What sections?

This doesn't have to do with sections

Slereah

I guess it doesn't matter since you don't need sections to define the structure groups

vzn

anyway arxiv is an old site going back to early 1990s or so right? simons funding is maybe more "recent" wrt that timeline

Emilio Pisanty

@vzn sigh I'm not sure how many different ways I can say this. There's nothing "recent" about the mention of Simons on the top banner - the "restructuring" took place 4+ years ago. Go look at the original link I sent you, please.

rob

@EmilioPisanty Maybe I'm getting hold, but four years feels recent to me. :-)

0celouvsky

3:57 PM

This is a boring conversation

@BernardoMeurer when am I teaching you Lebesgue integrals on R^1?

Emilio Pisanty

@0celouvsky agreed

vzn

@EmilioPisanty they had a new top banner recently asking for donations, a major design chg. cant remember how it cited simons or not.

Slereah

let's talk about physics instead

did u know that objects fall down

Balarka Sen

Is lifting structure group to a cover called a "reduction" too? Eg, a spin structure imposed on an oriented Riemannian bundle.

Slereah

Well no

Objects try to rejoin their layer of element

as u well know from Aristotle

The layer of earth, the layer of water, the layer of air and the layer of fire

ACuriousMind

3:58 PM

@BalarkaSen It is a subset of "reduction" if you define reduction not with respect to subgroups $H\subset G$ but morphisms $H\to G$, yes.

Slereah

Followed by the layer of ether

vzn

@0celouvsky and technical topology is so much more interesting

Balarka Sen

@ACuriousMind Ah, ok, got it.

Slereah

if you find some ether, does that mean you can ride that bitch to space?

or is ether immune to violent actions

0celouvsky

I bet the final form of physics is Aristotilean

Balarka Sen

3:59 PM

@vzn It is interesting and not technical to those who understand it. It is technical and uninteresting to those who don't.

John Rennie

Inhaling ether can cause instant heart failure.

Bernardo Meurer

@JohnRennie Did you see my comment on wrapping the graphics on a struct?

0celouvsky

@vzn Lebesgue measure is not topology

Bernardo Meurer

@0celouvsky After my exams,

so May

John Rennie

Yes. More refactoring eh? :-)

Slereah

3:59 PM

@0celouvsky so it turns out every quantum field has a natural motion towards its layer of quantum field

0celouvsky

@BernardoMeurer let's do it when we're in Cali

Slereah

The center of the universe has all the fermionic sector

Then above the EM fields

Bernardo Meurer

@0celouvsky Deal :)

0celouvsky

Ill bring the measure theory tomes

Slereah

etc etc

ACuriousMind

4:00 PM

@0celouvsky ...named after the famous Aristotil?

0celouvsky

We can get Michelle to buy a whiteboard

Slereah

Harris Turtle

0celouvsky

@ACuriousMind What?

ACuriousMind

I'm poking fun at your misspelling, nevermind

0celouvsky

Aristotle -> Aristotelian

Balarka Sen

4:01 PM

You said Aristotilean

0celouvsky

Whatever.

Like you've never misspelled anything

John Rennie

I don't recall ACM ever mis-spelling the word anything

ACuriousMind

Also, the proper name of that guy is Aristoteles, not Aristotle, but by now I know it's futile to expect English to not do violence to foreign names :P

Slereah

I think you mean Ἀριστοτέλης

0celouvsky

@ACuriousMind correct, Bajoran

ACuriousMind

4:03 PM

@Slereah Transliteration is a necessary evil

Slereah

@ACuriousMind doesn't know that languages change the spelling of names to make them fit the structure of languages

Aristotle is fairly mild, compared to Confucius

Bernardo Meurer

@JohnRennie Yes, more refactoring :)

Balarka Sen

Confusius

Bernardo Meurer

If I'm doing structs I'm going all-in

Slereah

Kǒng Qiū

Bernardo Meurer

4:04 PM

*Confucius

Balarka Sen

Also Mao Tse Tung

@BernardoMeurer was making a pun

Bernardo Meurer

@BalarkaSen I have no humour

ACuriousMind

@Slereah Languages without much declension don't really have a reason for that, though. There's a difference between a transliteration and actually changing the name.

Slereah

Eh, it happens

Otherwise the name sounds weird to people

Basically all egyptian names you know are bullshit

0celouvsky

I don't think Bajoran is exactly right but it's how we say it in Nelgoush

Slereah

4:06 PM

Weird greek versions of them

although it happens less these days, what with globalism

Hell even Jesus is an example

Yeshua Ha-Meshiakh

John Rennie

@ACuriousMind: feel free to ignore this question, but is Bajoran really your first name? It seems an unusual name to find outside of the Star Trek universe.

2

Slereah

Doesn't roll off the tongue quite as well

It is not

user228700

@JohnRennie Holy crap, that looks delicious! How was it?

ACuriousMind

@JohnRennie lol, it's ocelot's rendering of my real name, which is Björn. I've tried to explain that I'm not a race from Trek several times, but to no avail ;)

John Rennie

@Kaumudi.H really good :-) The Polish smoked sausage has a very strong taste and that had nicely flavoured the beef mince.

Physics Guy

4:11 PM

What sound does the greek cow make?

µ

user228700

@JohnRennie Nice! :-)

user228700

I've decided, BTW, that I'll tackle those questions on my own. If I'm not able to, I'll ask you tomorrow. Is that OK?

John Rennie

@ACuriousMind ah :-) I was aware of a Björn Juliger working in the theoretical physics area and I had wondered if that was you.

@Kaumudi.H no problem. I'll be here from about 06:00 BST tomorrow.

user228700

Wokay, thanks! :-) BTW, I don't think that I am getting anything after all :'-(

ACuriousMind

@JohnRennie ...how did you become aware of him? Pretty sure that was a faint recollection of me having disclosed by name here before

John Rennie

4:14 PM

I honestly can't remember. Someone here must have given away your secret identity :-)

Bernardo Meurer

@JohnRennie What do you think about Google's C++ code style guidelines

ACuriousMind

Mar 3 '16 at 22:04, by ACuriousMind

@Danu My name is not a secret, you can find it by searching the transcript

user228700

@JohnR: What I'm Googling:

John Rennie

@Kaumudi.H Boo :-( That seems a bit mean of your sister to lead you on.

user228700

Slereah

4:15 PM

His name is Pootenmeyer Hoobastank

user228700

x'D

ACuriousMind

@Slereah If that was my name I'd use that as my handle everywhere :D

user228700

@JohnRennie Eh. She wasn't completely lying. But my mum sort of was. Idk, it's only 10.

John Rennie

@Kaumudi.H It's sad to see such cynicism in one so young :-)

user228700

:-(

John Rennie

4:18 PM

You can have another laptop if you want :-)

user228700

Lol, thanks but no thanks :-P I cannot deal with...heh, what was the name of the company again?

John Rennie

I can't remember. The trauma has wiped it from my brain.

user228700

Surely you're lying as to not discourage other users from using their "services".

user228700

Surely!

John Rennie

Was it UPS?

user228700

4:22 PM

UPS=TNT?

user228700

'Cause I checked and it was TNT.

John Rennie

Ah, yes, it was TNT.

To be fair they were very good right up to the point where the delivery hit the Indian customs office. Then things went downhill.

And TNT are a generally well respected carrier.

user228700

Actually, yes. It's extremely unfair of me to blame them fully. The courier boy who came home told us that it was due to the govt. of TN that it got delayed this much.

Slereah

Is the cover of the manifold for atlases and the cover of the manifold for local trivialization always the same?

Like do they share the same covers

user228700

...because they were going on about triple-checking everything etc.

John Rennie

4:25 PM

Good job they didn't find the drugs hidden inside the laptop, eh :-)

user228700

:-) Yeah.

user228700

I bought myself a present! I didn't have anything new (any younger than 3 yo) to wear today/tomorrow so I went out and bought myself yet another baggy T-shirt.

user228700

(The other T-shirt my mum wants me to wear on April 2)

John Rennie

The date of the exam?

user228700

Yep.

John Rennie

4:28 PM

Holden Caulfield thinks the JEE is a phony

2

user228700

God, yes.

user228700

BTW, how did u get the SE T-shirt?

John Rennie

Holden Caulfield thinks a little telephone is a phony

user228700

Probably. That guys thinks everything / everyone is a phony.

ACuriousMind

Who the hell is Holden Caulfield?

John Rennie

4:31 PM

@Kaumudi.H Can't remember. I got one years ago for being one of the top users on the ServerFault SE. Then I got a second when I passed 100k here - or at least I think so.

@ACuriousMind Catcher in the Rye

user228700

Holden Caulfield

Holden Caulfield is a fictional character in author J. D. Salinger's 1951 novel The Catcher in the Rye. Since the book's publication, Holden has become an icon for teenage rebellion and angst, and now stands among the most important characters of 20th-century American literature. The name Holden Caulfield was used in an unpublished short story written in 1942 and first appeared in print in 1945. Although it has been conjectured that J. D. Salinger got the name for Holden Caulfield in The Catcher in the Rye when he saw a marquee for Dear Ruth (1947), starring William Holden and Joan Caulfiel...

user228700

@JohnRennie Oh, cool!

John Rennie

Some might say we have a few Holden Caulfield-a-likes in this chat room, but I couldn't possibly comment :-)

user228700

It's a humorous book, @JohnR.

user228700

Hang on...

John Rennie

4:35 PM

@Kaumudi.H which is odd, because you wouldn't think a book about the upper arm would be that popular

user228700

One second...

user228700

Bernardo Meurer

@JohnRennie This code will be amazing

user228700

Bernardo Meurer

assuming I can ship

:P

Emilio Pisanty

4:41 PM

Stack Overflow Introduces Dance Dance Authentication

►

April Fools' is out y'all

it's pretty underpowered though

I miss unicoins =(

user228700

(Last one)

John Rennie

@BernardoMeurer in effect you're writing it in C++, using C :-)

user228700

@JohnR: Those photos of chapter 12 of the book were for ur enjoyment, BTW. Dyou plan on reading 'em?

John Rennie

Actually that's pretty much how C++ class member functions work. If you look at the assembly they get passed the address of the object as an extra hidden parameter, just as my code explicitly passes the address of the struct. When you use this in a class member function you're using that hidden parameter.

@Kaumudi.H I did read them. But teenage angst isn't really my thing. I'm not a teenager and don't have any angst.

user228700

4:47 PM

Right. I was only telling you that I think it's humorous anyway.

Slereah

C++ objects are just concatenated structs

one concatenation per inheritance

Bernardo Meurer

@JohnRennie I just pushed the new code to the struct branch

go check it out

THIS WILL BE GREAT

@JohnRennie Why did you make boardInit return a bool?