The h Bar

Anonymous

14:01

@Sumant Hi. I see you're from Bangalore :-)

Sumant

@blue Yeah hi, where are you from?

Anonymous

Grade 12 if am not wrong (?)

Sumant

11

Slereah

0

Q: Does any non-Hausdorff manifold admit a metric tensor of signature $(p,q)$?

Hicks in his book, "Notes on differential geometry", works with manifolds by specifically stating that they are not required to be Hausdorff unless otherwise stated. He then goes on to define the usual manifold structures, vector fields, connections, metric tensors, etc. In chapter 6, he defines...

plz help

Anonymous

@Sumant Assam

Anonymous

14:03

@0celouvsky Another JEE'r Indian :P You're screwed...the next batch is coming!

0celouvsky

@Slereah I have the papers that talk about what I'm working on this summer

do you want to check them out?

Slereah

Sure

0celouvsky

do I have your email?

Slereah

I have too many pdfs open

I should close a few

Dunno

it's [email protected]

0celouvsky

lol yahoo

Slereah

14:08

Same email since 2001 baby

0celouvsky

I wasn't even alive then

Slereah

Ahah

0celouvsky

check your email

Slereah

Wait you were

just

a little baby

I wonder up until what point in a GR book you could drop the assumption of Hausdorfness

probably when you start talking about curves

unless you're O'neill and do the partition of unity in the first chapter

Balarka Sen

@blue jesus no

0celouvsky

14:11

drop the assumption?

spacetimes are hausdorff dammit

Slereah

says u

Have you seen a spacetime in the sky

Anonymous

@BalarkaSen Prepare to do the march with Ocelouvsky :-D Naked is preferable.

Balarka Sen

i have nothing against jee

Slereah

Balarka Sen

also, naked lunch, not naked march

Anonymous

14:13

@BalarkaSen You told me something else in the Maths chat room :P

ACuriousMind

@Slereah what book is that?

Balarka Sen

when i say i have nothing against jee, i meant i have nothing against jee in this room

Anonymous

@BalarkaSen Oh, that's clever ;-) You hardly visit this room. I like that attitude =P

Anonymous

But don't worry. The JEE squad will soon attack the maths chat room too, in the near future =P

Slereah

@ACuriousMind Hawking and Israel

0celouvsky

14:15

Why don't JEE people go to their own room

Why do you enjoy torturing us

Balarka Sen

nah. people have tried before; the only hot topic in the math chat is geometric topology

Anonymous

@0celouvsky See, I'm the nice one. I've stopped discussing JEE questions here. Not everyone is as nice as me ;)

Anonymous

@BalarkaSen That's the calm before the storm :D

ACuriousMind

@Slereah Heh

Slereah

Penrose has a brief aside about non-Hausdorff manifolds

Fairly brief though

overall I think Geroch was the first guy to seriously propose them

Balarka Sen

14:18

why do you want to do non-hausdorff spacetime

Slereah

Before that non-Hausdorff manifolds were like

Balarka Sen

what have you been doing to your life man

Slereah

"Oops I took the wrong quotient and my manifold isn't Hausdorff"

@BalarkaSen it has been proposed by some as a model for QM stuff

basically a geometric version of Everrett

allthough from the papers you wouldn't guess it

None of them even attempt to do a single particle

I don't think it's a very good model for that

mostly they just do topology

the popular model is that the spacetime would split at points along the light cone of that point

@0celouvsky got the mail

"To all the women I have loved"

Slow down, Casanova

"Don’t try to be a good man, just be a man.
-Zefram Cochrane"

Good quote, though

0celouvsky

Haha

That dedication is pretty goofy

Slereah

quite

ACuriousMind

14:27

Agh, my brain. Apparently one can glue two solid tori into a 3-sphere

Slereah

How

Doesn't gluing preserve genus?

Oh wait, nevermind

0celouvsky

@ACuriousMind how?

Wait, three sphere? Wtf

I saw this in knot theory a while ago

It made sense at the time!

Balarka Sen

Glue them by the map $T^2 \to T^2$ sending meridian to longitude.

0celouvsky

I don't know how that's supposed to explain anything

ACuriousMind

It...does make a kind of sense. You have two solid tori $D^2\times S^1$ and you glue each $\partial D^2$ to the $S^1$ factor of the other. That gives something you can't draw in $\mathbb{R}^3$, but it's fibered over $S^2$ with fiber $S^1$ so I can accept it's $S^3$

0celouvsky

14:32

@ACuriousMind that's what Elven lord did

Balarka Sen

Here's a proof. $S^3 = \partial(D^4) = \partial(D^2 \times D^2) = \partial D^2 \times D^2 \cup D^2 \times \partial D^2$

ACuriousMind

I'm not sure how to see it is the $S^3$, though

Balarka Sen

But that doesn't make the attaching map explicit unless you do it more carefully.

0celouvsky

@ACuriousMind I think he removed a point and showed the gluing is R^3, then argued adding back the point gives the compactification

Slereah

Wait, how do we get $D^2 \times D^2$ from $D^4$

ACuriousMind

14:34

@Slereah Note that all the balls are topologically the same as cubes, and that you can simply build higher-dimensional cubes from lower-dimensional ones in that fashion

Balarka Sen

They are homeomorphic. Think about $D^n$ as $[0, 1]^n$

Slereah

I suppose!

Balarka Sen

ACM beat me to it.

Slereah

Also I didn't know that the Leibniz rule applied to boundaries

Balarka Sen

It does! That's why you use $\partial$ to denote boundaries!

Well, partially at least.

Unintentional pun too

Bernardo Meurer

14:36

When you have an exam the next day

ACuriousMind

I was about to ask whether the $\partial$ly was intentional

Bernardo Meurer

and your lab mate forgets to write the lab report

so you gotta do it

but you can't even integrate

:)

Hello darkness my old friend

Slereah

The integral would be the interior, I suppose

Though that only works for immersed surfaces, I suppose

0celouvsky

What are you talking about

Slereah

Well there isn't really an inverse operation to the boundary of a manifold

Balarka Sen

14:41

I don't know what the correct notion of integral is. I'd look what the correct Kronecker product in bordism theory is.

Slereah

oh yeah i guess it could be the cobordism

integrate those circles into pants

Bort License Plates

►

the greatest Simpson joke of all time

0celouvsky

Please don't post vile things

Slereah

Oh right, @0celouvsky wasn't born when the Simpsons were good

Like, literally

ACuriousMind

@Slereah How did you go from cobordisms to Bort?

Slereah

I just have that joke stuck in my head

Although they do sound similar

Co-bort-ism

0celouvsky

14:47

@ACuriousMind I don't think the simpsons are family

friendly

ACuriousMind

@Slereah Is that a Siamese twin where both are named Bort?

Slereah

When @0celouvsky was 7, the Simpsons were on season 16

Tough

0celouvsky

@ACuriousMind -.-

🤦🏿‍♂️

ヽ(￣д￣;)ノ=3=3=3

ACuriousMind

What the hell is that?

0celouvsky

Wtf did you post

ACuriousMind

14:49

That's what you posted!

Apparently, that's what the "man facepalming" Emoji renders as for me

The wonders of unicode

0celouvsky

gyazo.com/5107381714e1c15d4195cc5405e76058

Bernardo Meurer

It renders as nothing to me

ACuriousMind

@0celouvsky I used to watch them with my family all the time

Bernardo Meurer

I guess I don't have emoji font

0celouvsky

@BernardoMeurer you probably need the newest iOS

Bernardo Meurer

14:52

Hm?

I'm on my computer

0celouvsky

@ACuriousMind what the hell. They're about sex and drugs and degeneracy!

Slereah

🤠

0celouvsky

Homer is a fat slob who represents everything wrong with the west

Bart should be shot

Slereah

aka the average american

ACuriousMind

@0celouvsky That's...kinda the point :P

0celouvsky

14:53

The girl kid should too for being a smart ass

@ACuriousMind you're cherishing degeneracy. What the hell

Slereah

Another obvious example that @0celouvsky has never seen early simpson episodes

ACuriousMind

@0celouvsky I don't really recall them being particularly about sex or drugs, except in certain episodes

0celouvsky

@Slereah says the person who's never been to America

@ACuriousMind they're yellow

ACuriousMind

Also, you do realize the show is satire, right?

Slereah

I've been to America

0celouvsky

14:54

The whole show is about being on so many drugs that the people become yellow

Slereah

Drugs don't turn you yellow

You're thinking of hepatitis

Balarka Sen

@ACuriousMind that stirred some unpleasant Dead Ringers memories

Bernardo Meurer

@BalarkaSen I'll beat you up

ACuriousMind

"Oh, the walls are melting again"

Balarka Sen

go see a psychiatrist

or be a cenobite for that matter

ACuriousMind

14:56

@BernardoMeurer Hmmm? Why would you say that?

Bernardo Meurer

@ACuriousMind He called my gender dumb yesterday

0celouvsky

@ACuriousMind no

I don't know what it is

It's like that Kardashian documentary

Balarka Sen

@Bernardo If you become a Cenobite I would definitely stop calling that

Bernardo Meurer

I am not becoming a cenobite

I am a non-Hausdorff manifold

Balarka Sen

(Explanation for kids: Cenobites are extradimensional sexually ambivalent sadomasochistic maniac demons. They're also pretty cool.)

0celouvsky

14:58

What the HELL

ACuriousMind

I'm...not sure I'd call that an "explanation"

Bernardo Meurer

I'm not a masochist

0celouvsky

@BalarkaSen you're just a kid why do you know about those things

Bernardo Meurer

I am a sadist though

Balarka Sen

@ACuriousMind That's the best Clive Barker gives you

0celouvsky

14:59

Am I the only one who strives for Christian goodness and wholesomeness in my life?

Slereah

Yes.

I'm more of a Moloch fellow

that's where it's at

Balarka Sen

@0celouvsky they used to sell cenobite toy models to 8 year olds

when the movie got out in the 90's

Slereah

They did that for everything, really

0celouvsky

The intergalactic demons are SO EVIL

They are poisoning our children

Slereah

There were alien toys, predator toys, robocop toys

Robocop was pretty brutal a movie

Balarka Sen

15:03

it's pretty good tho

Slereah

Also a lot of people get thrown through glass

RoboCop Can't Stop Throwing People Through Windows

►

Balarka Sen

the robocob dude, peter weller, also acts in naked lunch

hence my favorite actor

Slereah

Have you seen Robocop 2

It is great

Robocop 2's title isn't just to indicate that it is a sequel

Balarka Sen

Ya I have

Slereah

The movie is literaly about robocop 2

0celouvsky

15:04

It's curious

Kids nowadays genocide entire races in their video games, but are upset over some wars in the middle east

Slereah

Well, u know

The issue of reality and all

Balarka Sen

fantastique and reality and etc

0celouvsky

@Slereah what happens 10,000 miles away isn't any more or less real than a video game

Slereah

Damn you and your local realism

0celouvsky

reality is only real in sufficiently small balls

ACuriousMind

15:07

@Slereah heh

Balarka Sen

it's a good argument tho

ACuriousMind

Where "good" means "completely bonkers" :P

0celouvsky

How could you tell that some war in syria is real

Balarka Sen

exactly right

0celouvsky

By going there

hence you need locality

well?

no argument?

Slereah

15:09

smbc-comics.com/comic/moral-relativity

Is this also a good argument

0celouvsky

no

ACuriousMind

@0celouvsky I'm not in the mood to take your bait :P

0celouvsky

they're forgetting the luminoferous ether

Slereah

I wonder if there's an ether version of GR

After all the Lorentz ether theory is the same as SR

0celouvsky

ok that's messed up

Slereah

15:11

I'm guessing ether GR would have to be Pauli-Fierz GR

ACuriousMind

@Slereah I was just about to propose that

Balarka Sen

after a loop we come back to physics, and time for me to duck out

0celouvsky

This second paper my prof sent me has a shitload of typos

who the hell proofread this

pretty embarrassing

idk how to tell him

missing ", missing spaces

on every page

There it is

The holy grail

Slereah

Is it

0celouvsky

almost

it's for closed manifolds

for boundaries, who knows

It's funny. PDE on closed manifolds is quite easy actually

It's boundary conditions that make everything hard

Slereah

15:22

If it's so easy try solving a nonlinear hyperbolic PDE on the torus

Bernardo Meurer

@JaimeGallego What cruise trip?

Jaime Gallego

Apr 11 at 20:52, by Jaime Gallego

Some of my friends are going on a cruise next week

Bernardo Meurer

Ah

Ah yes

The ones that made the mistake of going to Slovakia

0celouvsky

They have money for a cruise?

Jaime Gallego

I ain't shelling out 1200 bucks for that

It is supposed to be a school trip

Bernardo Meurer

15:26

1200€ for a cruise with kids?

Why don't you tie me up to a rock and put me to swim

0celouvsky

What kids have 1200???

John Rennie

@BernardoMeurer Tie you to a rock and throw you into the sea? Have you been going out with a mafioso's girlfriend again?

Bernardo Meurer

@JohnRennie Sadly no

Honestly that was better than the stuff going on currently

Jaime Gallego

@0celouvsky Their parents do. They believe it will be an educational experience because they'll be two hours in Pompeii

0celouvsky

1200 for two hours

John Rennie

15:28

@JaimeGallego I believe there are some educational wall paintings there ...

0celouvsky

Scratch that. People flag for prostitute jokes.

Bernardo Meurer

Date women whose boyfriends can, and will, try to kill you. That's my advice for the day folks

Jaime Gallego

Ah, and Malta. But you know what kind of destination is that.

0celouvsky

@ACuriousMind does dim_c mean anything to you?

Context of Hilbert spaces

Small c

Bernardo Meurer

@0celouvsky It's a variable declarator in VB.NET

0celouvsky

15:30

Not complex numbers C

Bernardo Meurer

What a shitty language

Slereah

Wait

Does Steenrod even assume manifolds to be Hausdorff?

"We shall restrict attention to manifolds which are separable, metric and connected"

I suppose he does!

Man there's almost nothing on non-hausdorff manifolds

There's like 3 good sources, and they don't amount to much

0celouvsky

Why exactly do you care?

Slereah

Well there are some causality-related theorems with respect to non-Hausdorff spacetimes

hindawi.com/journals/ijmms/2009/891785/abs

let's investigate this paper

All topology

Where are the differential geometry papers on non-Hausdorff manifolds

Bernardo Meurer

@0celouvsky He's studying my sexual behavior

Slereah

15:47

Do the foliation sheaf manifold things have bundle structures on them?

0celouvsky

I don't know what you're talking about

DanielSank

Hi, everybody.

@BernardoMeurer do you still need calculus halp?

0celouvsky

Wtf he asked you before me?

DanielSank

@0celouvsky Uh, yeah. Are you surprised by this?

Slereah

Foliation of manifolds are one of the rare fields where people commonly use non-hausdorff manifolds

DanielSank

15:51

Everything is measure theory to you.

Slereah

Do people define common bundle structures on them?

0celouvsky

It is not

Slereah

Tangent bundles and such

Bernardo Meurer

@DanielSank Later today

DanielSank

@0celouvsky Should I flag that?

What do you think?

0celouvsky

15:51

Go for it

I don't care

DanielSank

Hmmm

ACuriousMind

@0celouvsky Be Nice.

DanielSank

@0celouvsky y u jealous? I can explain stuff pretty well. Ask @heather.

Slereah

I don't know why but non-hausdorff manifold papers are always about random boring stuff

Homogeneity and whatnot

rob

Papers about homogeneity seem to be all alike.

Slereah

15:58

heyooo

ACuriousMind

@rob Do you just watch the chat and wait for a chance to make a pun? :D

rob

@ACuriousMind I live my life waiting for chances to make puns.

ACuriousMind

Fair enough

Slereah

how does Steenrod prove the existence of a Riemannian metric, anyway

Let's check

rob

Once I sent a list of a dozen puns off to some magazine for a contest. At the last minute I removed the two silliest ones from the list. I thought for sure they were good enough to win, but unfortunately no pun in ten did.

Slereah

16:01

he proves it by the use of other theorems I don't know

;w;

@rob old one

rob

@Slereah Guilty.

Slereah

16:13

I guess worst case scenario

I can just not care about the structures on the manifold itself and just use the ones on the Hausdorff submanifolds

Emilio Pisanty

16:41

@ACuriousMind how about Hitler Gets Angry videos?

Hitler Finds Out He was Not Accepted into Hogwarts

►

ACuriousMind

Those are fine, I guess

(Although I don't find most of them funny :P)

Emilio Pisanty

I hadn't seen that Der Untergang trailer, though, it's fantastic

@ACuriousMind I guess it's harder if the words actually make sense when you hear them

I really like this one, though

A Hitler tampoco le gusta la bachata...

►

though non-Spanish speakers will struggle with it I guess

@AccidentalFourierTransform and @DanielSank might enjoy it

ACuriousMind

@EmilioPisanty Could be

Balarka Sen

I really liked the meta-video where Bruno Ganz was angry about Hitler gets angry videos.

Emilio Pisanty

@ACuriousMind I think these started after I had learned most of my German

it wasn't enough to make the dialogue out directly

but I did at some point look it up, and I can follow it now

and they definitely became noticeably harder to enjoy

@BalarkaSen that one is good too

DanielSank

17:00

@EmilioPisanty I'll watch this when I get to a desktop

Have you seen the Wolfenstein one?

Emilio Pisanty

@DanielSank nope

what's wolfenstein

AccidentalFourierTransform

the hell is a kizomba?

Slereah

"As I'm sure you know, the category of smooth (topological?) manifolds is one of those categories where the objects are very nice but the category itself is terrible. I cannot describe the number of times I've heard the algebraic geometers curse the smooth category."

nooo

not categories :(

Emilio Pisanty

:36861931 I imagine he means this

Hitler Reacts to Wolfenstein 3D

►

John Rennie

Wolfenstein 3D

Wolfenstein 3D is a first-person shooter video game developed by id Software and published by Apogee Software and FormGen. Originally released on May 5, 1992, for MS-DOS, it was inspired by the 1981 Muse Software video game Castle Wolfenstein. In Wolfenstein 3D, the player assumes the role of Allied spy William "B.J." Blazkowicz during World War II as he escapes from the Nazi German prison Castle Wolfenstein and carries out a series of crucial missions against the Nazis. The player traverses through each of the game's levels to find an elevator to the next level or kill a final boss, fighting Nazi...

Emilio Pisanty

17:04

@AccidentalFourierTransform this and similar

John Rennie

Wolfenstein 3D was the first real time first person game I had ever seen. At the time it was astonishing. It looks, well, rather quaint now.

AccidentalFourierTransform

so... cheap electro-latino?

no wait, its from Africa

Emilio Pisanty

@AccidentalFourierTransform effectively, yes, though it's originally from Angola and if you do it right it's relatively different

but for all the fancy schmaltzy stuff, as always

AccidentalFourierTransform

cheap electro-afro then

Emilio Pisanty

How you think you look when your drunk

►

AccidentalFourierTransform

17:08

ಠ_ಠ

cant say its inaccurate

DanielSank

@EmilioPisanty yep

AccidentalFourierTransform

17:24

> Concentration made by a small thing

Mostafa

@DanielSank What sign did you eventually print on that PCB?

People here suggested those interesting hieroglyph characters

@JohnRennie I played this around 2004

Return to Castle Wolfenstein

Return to Castle Wolfenstein is a first-person shooter video game published by Activision and originally released on November 19, 2001 for Microsoft Windows and subsequently for PlayStation 2, Xbox, Linux and Macintosh. The game serves as both a remake and a reboot to the Wolfenstein series. This single player game was developed by Gray Matter Interactive and Nerve Software developed its multiplayer mode. id Software, the creators of Wolfenstein 3D, oversaw the development and were credited as executive producers. The multiplayer side eventually became the most popular part of the game, and was...

DanielSank

@Mostafa The board is not done yet.

It's really, really close.

@G.Bergeron Cheesy?

Mostafa

The mission was to destroy Hitler's paranormal division of SS.

@EmilioPisanty They don't really feel original....real speeches are another thing ;)

and I think virtually everything would be okay to post here if it's for research purposes.

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