The h Bar - 2015-07-24 (page 5 of 5)

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8:00 PM

@0celo7 in $S^3/\mathbb{Z}_2$ it closed. In $S^3$ it's not.

@ACuriousMind what

how

Because there it starts at the identity and ends at the antipodal point!

D:

that's BS

2pi is a full fucking rotation

Yes, in $\mathrm{SO}(3)$. But a closed curve need not lift to a closed curve in the cover.

The rotation all around SO(3) corresponds to a half rotation in SU(2)

8:02 PM

I'm getting yogurt

this is not over

does anyone else have major problems with the way the site looks now?

It's fine

also I got a 1.7 for Riemannian geometry awwwwyis

@Danu It looks normal to me

@Danu congrats

user image

the thing on the right

it makes me angry

8:04 PM

Do not see that

@ACuriousMind Thanks :) How did alg. geo. go for you?

@Danu Ah, well...f**k ample sheaves. I passed. Barely. :D

It's only there when I got to a particular question (not in the "questions" list)

@ACuriousMind close enough ^^

@Danu Which browser?

Chrome

8:05 PM

Functional analysis and the talk went far better, fortunately.

:)

Can I get rid of the notifications on the chat

@Slereah The sound? Click on the loud speaker icon in the top right.

not the sound

The notifications when there's a new thread on SE

Ah, that!

No, you cannot, I think.

Be content that we don't have a bot posting every new question here like some other sites.

8:08 PM

Dang

@Danu: Exams over now?

Yush, since last night

'twas a good night

"I ain't coming down tonight" ;D

@0celo7 Shankar is boring.

QM is boring

Can I read Gottfried please?

8:11 PM

Read Mukhanov's QFT in curved spacetime book for fun times

@obe I really don't give a shit what you do tbh

you're started a dozen books

@ACuriousMind where were we

oh yeah, I was debunking group theory

don't be such a meany, ocelot

He's being aggro the whole day already. Wrong food or something, I guess.

umad bro? :D

NO

GRR

8:14 PM

hemad

seriously, where were we

@0celo7 You were confused how a loop can be closed in $\mathrm{SO}(3)$, but not in $S^3$.

I think.

yes

@obe what are you trying to learn?

what is your level right now? etc

(also don't take ocelot's advice on studying lol ;) )

so when we say 2pi rotation, we mean a 2pi rotation in the rotation group, not in the sphere

@Danu he's not

8:15 PM

@0celo7 Yes!

@Danu Introductory QM, though I want to use an advanced book.

well why the fuck didn't you say that 20 minutes ago

@obe Use Sakurai's Modern QM

here I am drawing equators on circles and you're yelling at me they're not closed

it's good, deeper than introductory but not incomprehensible

8:16 PM

@0celo7 ...I guess I got carried away by the topology. Sorry

if it's too hard, switch to maybe Griffiths

oh

I SEE IT

the curve around half of S^3 is closed in S^3/Z_2

I SEE IT

Yes

:)

Is there a 2D manifold that has a double cover?

8:18 PM

@Danu sakurai = advanced, griffiths = easy. I think gottfried is similar to shankar though a bit more difficult.

Might be easier to visualize

@obe You said you wanted "advanced"

The moebius strip, maybe?

so then the 4 pi rotation is a 2pi rotation in S^3

??

@0celo7 Yes

8:18 PM

@Danu I am trying gottfried for now because it is advanced and bridges the introductory gap.

::angels sing::

Isn't the double cover of the moebius strip the cylinder

I GET IT

@obe Never heard of it (and I know a bunch about textbooks :P)

stop shouting pliz

@Danu shouldn't smoke so much weed then

8:19 PM

@Danu In my university sakurai is used before gottfried, therefore I'm assuming it's similar in difficulty.

Whoa...John Rennie's a vote away from getting the shiny gold tag badge for newtonian-mechanics

@Slereah Perhaps, but the cylinder is not simply connected.

@ACuriousMind I knew this

So it doesn't work for our purposes here.

@0celo7 I never smoke weed

8:20 PM

It's used in T-duality :D

10 mins ago, by Danu

"I ain't coming down tonight" ;D

Well yeah, but it's a decent example of a double cover

@0celo7 There are other things than weed :P

I thought that meant you were high as shit

The fancy Dutchman only smokes hash :P

^^ he knows what's up

8:21 PM

there's probably a crackhouse within walking distance

So... I've got a dilemma guise

this is DC, after all

I read this girl to sleep over skype

and now she' sleeping

but I"m afraid if I end the call, she'll wake up

oh fuck not this again

wat do

No, this is a different girl and there's no romance involved

@0celo7 and screw you, y'all love my stories

8:22 PM

"read to sleep"

Is she 5?

@Danu ...does ending a call make a sound? I can't remember

@0celo7 You don't know nuttin'

@ACuriousMind very loud

@Danu Yes uncle Danu, we love your stories!

@ACuriousMind ::SHFLUPLU::

@ACuriousMind I know you do, little curious mind

I haven't even been keeping you up to date either

TL;DR: Everything went BETTER THAN EXPECTED

8:24 PM

speaking of little, @ACuriousMind how tall are you (in God-given units)

@0celo7 How am I supposed to know how tall I am in your weird units? I'm 1.75m.

I'm slightly taller :D

@ACuriousMind 5'9"

both small

6'2" master race

taller in dress shoes

Anyways, wat do now with this sleeping girl who I don't want to wake up

@Danu you could have prevented this

8:27 PM

@Danu Uh, mute the call and just let it be active till tomorrow? :D

user image

@ACuriousMind but I wanna like watch stuff on my laptop :P

...can't you mute the call and then watch stuff?

She's also in AUS, so maybe she'll wake up soon-ish

you mean like mute for her?

idt it even does that

^ I win

Well, idk either how to do that, but I imagine that must be a feature, right?

8:29 PM

user image

of course you can mute skype

like

of course

No but from her side?

Not so sure

From her side?

ok jk I can

like that she can't hear me

yes

but I arleady got it

it was easy

8:30 PM

I'm getting confused as to what the problem is here :D

thanks guize

:22996035 stop removing your offensive comments ocelot :P

@Danu multiple thousand miles are not an obstacle for a very motivated man

@0celo7 Most definitely aren't... I had a girlfriend in the US for a year, y'know

@ACuriousMind Ok, so group theory is not wrong.

what a relief.

8:31 PM

However, this does not mean heresy is truth.

I'm gonna get some ice cream

to celebrate muting of microphones

and lack of dinner

I just had some frozen yogurt

@ACuriousMind so beautiful physics.stackexchange.com/questions/195785/…

mmmm

@Danu What flavour?

My recent burps have drawn my attention to the fact that I have inadvertently managed to create a classic ol' whisky-coke mix in my stomach during the duration of the evening ^^

@ACuriousMind Schwarze Johannisbeere!

8:35 PM

Yum

Johannisbeere is very rare in US

= currant IIRC

or so it seems

ye, the "black" gives it away ;)

the black?

user image

well that explains it

blackcurrant

I think Danu was making fun of the translation not incorporating the Schwarze from the German name :P

8:38 PM

@ACuriousMind there are multiple currants

black, red and white

Alrighty then.

I was talking about Johannisbeeren in general, not limited to the black one

my point was the following: errybody knows blackcurrant, and "schwarze" plus "beere" then makes it easy

...I don't know blackcurrant

you're nobody D:

8:39 PM

But, then again, I'm not errybody.

you ain't Muricun

I believe they are called african american currant

lol

lololol

Native American currant

Racist currant

whoops

8:40 PM

^took it too far... sigh

@Danu You neither.

@Danu You surprised? :P

@Danu don

@ACuriousMind u wot m8? I'll have you know that about 8/10 people that don't know me guess I'm from the US :P

7 hours ago, by Slereah

fingers(x - vt)

@Danu don't know what you mean

@Danu Not sure that's a good thing :D

8:41 PM

@ACuriousMind It's just the accent and the loudness ;)

Leeb also thought I was American :P

I'm kinda proud of my accent being good enough to fool a significant fraction of native speakers also

tfw fellow Murricans ask me if I'm a foreigner

tfw Germans ask me if I'm a foreigner

tfw neither do that with me

well I'm gonna leave now

kthnxbai

@Danu Ah, I see.

8:50 PM

Ima go to bed too

gotta have fun tomorrow so sleep a lot tonight :D

g'night

nighty night

I got one upvote on my oneboxing support for arxiv post. Offsets my spent 50 rep just a teensy bit

Ftw ACM-senpai has never said "g'night" to me

Feelsbadman

Your nights will never be good

9:01 PM

senpai?

D:

I sleep like a baby because I reject the quantum dogma

urbandictionary.com/define.php?term=Senpai

Senpai^^

9:18 PM

oh

lol

1 hour later…

10:20 PM

Strangely, I seem to understand all this spinor stuff.

Wald makes it pretty clear.

@ACuriousMind In one sentence, what is a spinor?

@0celo7 Something transforming in a projective, but not linear representation of the Lorentz group.

@ACuriousMind Nothing intuitive?

...you really expected that my one-line summaries would be intuitive?

10:36 PM

Vector is a quantity with magnitude and direction.

Scalar is invariant under transformations.

Dr. Ikjyot Singh Kohli

Hello all

Spinor...

@Dr.IkjyotSinghKohli Hello!

Dr. Ikjyot Singh Kohli

What's up?

Not much, apparently :P

Dr. Ikjyot Singh Kohli

10:42 PM

Yeahh, I'm noticing that too.. Just saw yet another misguided/manipulated "young person" who read Krauss' "Universe from Nothing" nonsense book, and is now asking questions about it, but the post was put on hold! That book is a disservice to humanity -:)

Never read it...I think the only popsci-like book I ever read was Hawking's Brief History of Time.

Dr. Ikjyot Singh Kohli

yeah, I don't think i've ever read a popsci book!

11:22 PM

I get bored by popular accounts of physics

11:39 PM

@ACuriousMind If you wanted to read just one it should be Feynman's little itty-bitty pop-sci book on QED. Hawking's book was pretty good as these things go, but it pales in comparison to Feynman.

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