The h Bar

Stan Shunpike

12:09 AM

@ACuriousMind yay! you were elected! super, i am sure this will make the community better of :)

Ramanujan

12:20 AM

@StanShunpike I don't think so

0celo7

12:43 AM

@Ramanujan Explain

Sir Cumference

Howdy

0celo7

why is Chick Fil A so good

Sir Cumference

I think I'm dehydrating

0celo7

I want to play a violent video game

what is wrong with me

Sir Cumference

12:59 AM

Er, any Jews here?

yes

Who?

you

...

so really that was a stupid question

rob

1:05 AM

@SirCumference What possible purpose could that question serve?

Sir Cumference

@rob I was gonna ask a question

ACuriousMind

You might try Mi Yodeya if it's a question about the religion itself.

user218912

jew.se xD

0celo7

oh my god

Sir Cumference

Yeah, no one's there

0celo7

1:07 AM

@ACuriousMind how do you know about that?

Sir Cumference

@0celo7 Because it's a graduated site?

Kinda popular

Ramanujan

@0celo7 see Acuriousmind total downvotes

ACuriousMind

@0celo7 It pops up from time to time in the HNQs

user218912

@Ramanujan so?

Sir Cumference

By the way

9

Q: Animated profile picture on stackexchange.com homepage

There's a user on Programming Puzzles and Code Golf named Oliver Ni who has a little almost-white dot on an almost-black background as their profile image. Or so I thought, until glancing at the Stack Exchange homepage (on desktop) and seeing a lively geometrical animation in the sidebar. It woul...

user218912

1:08 AM

how is it his fault people ask bad questions?

Sir Cumference

This is actually really cool

rob

@SirCumference If the question is relevant for the physics chat, ask it.

Sir Cumference

@rob Half of the questions here aren't

Ramanujan

@bl00 possible hate towards OP

user218912

@Ramanujan what?

ACuriousMind

1:09 AM

@Ramanujan You're not the first to have brought that up, yet I still fail to see what my up- or downvoting habits have to do with my ability to moderate.

Ramanujan

@ACuriousMind congratulations

rob

So ... I know I haven't spent a lot of time in this chat room

Sir Cumference

@rob Be sure to read the chat rules

rob

But internet chat rooms in general are places that sometimes attract bad actors

And asking whether anyone would like to identify by religion or ethnicity seems like the kind of thing that could go sour quickly.

ACuriousMind

@SirCumference In this case, the guide to moderating chat might be more helpful.

Sir Cumference

1:12 AM

@rob Eh, people here are pretty open

user218912

@0celo7 I've been so tired and feeling foggy lately, what's wrong with me?

0celo7

toxoplasmosis

@ACuriousMind Should I play a video game tonight?

rob

Yes, but "none of the regulars here mind" is an exclusionary attitude.

user218912

@0celo7 well the symptoms do fit.

Ramanujan

@0celo7 how about "8 ball pool "

0celo7

1:14 AM

never heard of it

Ramanujan

It's good multiplayer online game(snooker type)

user218912

@0celo7 do you have a console?

0celo7

no

user218912

:(

Sir Cumference

@bl00 I see a :( on your gravatar

What's wrong? Feeling blue?

...Ehh?

0celo7

1:18 AM

stop

Sir Cumference

._.

user218912

I am always feeling blue.

0celo7

do you know calculus yet

user218912

but that's a good thing.

Sir Cumference

@0celo7 How much?

I can differentiate and integrate

0celo7

1:19 AM

@ACuriousMind I'll just read algebraic topology unless you tell me to play something

user218912

@SirCumference then read tong's notes and watch mit ocw calc 3.

Sir Cumference

@bl00 Oh god...

ACuriousMind

@0celo7 I have no preference for how you spend your spare time

user218912

what?

Sir Cumference

Anyway...

0celo7

1:20 AM

dammit

user218912

don't you want to get good? @SirCumference

0celo7

@ACuriousMind I knew becoming a mod would change you

Ramanujan

Haha

Sir Cumference

@bl00 I haven't the time

@0celo7 He isn't the curious mind you once knew

user218912

@SirCumference make time for it, it should be your top priority.

Sir Cumference

1:21 AM

@bl00 My top priority is school

Ramanujan

School?

@SirCumference are you still in school?

user218912

@SirCumference in the time you spend on this chat you could have watched 1-3 lectures and read 3-7 pages in tong.

user218912

just sayin.

Sir Cumference

@Ramanujan Uh, yes? I'm 18

0celo7

@bl00 and you could have read Zee twice

user218912

1:23 AM

@0celo7 why would I read it twice? but that's true.

Ramanujan

@SirCumference you are 1 yr ahead of me, oh we say college in India

Sir Cumference

@Ramanujan Same thing, basically

0celo7

@bl00 I've read it 5 times.

user218912

@0celo7 front to back?

0celo7

yes

user218912

1:24 AM

lies.

ACuriousMind

@0celo7 I'm changed because I didn't tell you to go play a game? :P Just...do what you want, you played 1000 hours of Battlefield without my approval, remember?

0celo7

proof?

Sir Cumference

@0celo7 proof?

0celo7

@ACuriousMind Your attitude is indeed different :(

I played that many years ago

I haven't touched a video game in months

ACuriousMind

oO

user218912

1:25 AM

@ACuriousMind yes your attitude has changed, you were mean to me the other day. before you were always nice.

0celo7

What part is surprising/confusing @ACuriousMind?

ACuriousMind

@0celo7 I guess it's not actually surprising but I still can't imagine just...stopping to play at least occasionally.

Sir Cumference

@bl00 Hurry up and reach 200 rep on some site

0celo7

@ACuriousMind I haven't had a reason to play games

user218912

@SirCumference why?

Sir Cumference

1:27 AM

@bl00 You're missing out on all the benefits

It makes you seem like more of an established user

0celo7

I want to continue my second run of Mass Effect

Sir Cumference

Than a noob

0celo7

but I'm too lazy @ACuriousMind

That's the sad thing

Playing games is too much effort

user218912

@SirCumference but I am a noob.

Sir Cumference

@bl00 Then stop being a noob

Get 200 rep

user218912

1:30 AM

I will start answering questions when I feel comfortable with my knowledge.

0celo7

@ACuriousMind Should I play Fallout NV?

user218912

which will probably be in 1 year from now.

Sir Cumference

@bl00 Then ask questions instead

user218912

@Obliv like my profile image? :D

user218912

@SirCumference I ask my questions here.

Sir Cumference

1:31 AM

@bl00 But you'll still be a noob that way

ACuriousMind

@bl00 I was? If you mean this, then I guess the last sentence might sound a little harsh, but I really wasn't up for doing calculations at that time (With you or anyone else)

0celo7

@SirCumference we would vtc them as homework?

ACuriousMind

@0celo7 It is the best of the modern Fallout games.

Sir Cumference

@0celo7 Well, if he answers more general questions, not really

0celo7

@ACuriousMind I played about 2 hours and got bored.

user218912

1:32 AM

@ACuriousMind it's alright. :D

ACuriousMind

@0celo7 It does have kind of a slow start, I'll admit

Ramanujan

@0celo7 do you want to play more than 2 hours?

user218912

@0celo7 not all of them but yeah.

0celo7

@ACuriousMind So should I give it another try or nah?

ACuriousMind

I'm not sure, since I think you also disliked/got bored with some other RPG I recommended. You might just have a different taste

0celo7

1:37 AM

But I really liked Mass Effect

i thought it was terrible at first

I think the first one is terrible in general actually

ACuriousMind

The gameplay of the first is rather bad actually, yes

0celo7

actually

the whole ME series is garbage

I didn't like it

the second had good gameplay but bad story

the third was just bad

amazing games, but somehow also terrible.

screw it I want to play fallout

ACuriousMind

Perhaps I shouldn't have given you the link to that essay series deconstructing ME :D

0celo7

yeah that did kind of ruin it for me :P

please don't give me one for Skyrim

hmm

do I still own a mousepad?

@ACuriousMind Switching to Windows

@ACuriousMind installing!!!!

35 minutes

damn

user218912

once I wanted to show my class a powerpoint presentation on my computer but when I restarted it right before the presentation it went into like a 30 minute windows update. ._.

0celo7

1:50 AM

@ACuriousMind Are you hyped???

ACuriousMind

I shiver with anticipation

0celo7

...wow

I didn't know you liked FNV that much

ACuriousMind

It is the best of the modern Fallout games

0celo7

Ok, it is decided

ACuriousMind

And it's made by Obsidian. They made some of my favourite games, like KoToR and Baldur's Gate (as black Isle back then)

0celo7

1:53 AM

I will learn some stuff about covering spaces

Then I will tackle constant curvature spaces

And learn representation theory to do it

then I will read BBS again

user218912

are those requirements for reading BBS?

0celo7

a PhD in string theory is sufficient

user218912

I think I will stick to my condensed matter then.

0celo7

@ACuriousMind Is Stone-Cech compactification useful?

@bl00 no

I want to learn some "classical" geometry

Constant curvature spaces are very very geometric

But very algebraic too

and I want to learn some algebra

so it's a nice compromise

ACuriousMind

@0celo7 I couldn't tell you off the top of my head what it#s useful for

0celo7

1:59 AM

But you have heard of it?

ACuriousMind

Yes

0celo7

Oh my god

I read topology in my topology prof's voice

@ACuriousMind apparently it's a functor on the completely regular spaces

ACuriousMind

2:14 AM

@0celo7 Everything's a functor (okay, not everything, but many such constructions are)

0celo7

oh god

the SE chat noise

@ACuriousMind It crashed my computer

DanielSank

2:52 AM

Hi, everybody.

0celo7

@DanielSank hi

Aaron Abraham

3:35 AM

Anyone comfortable clearing a doubt I have on electromagnetism?

David Z

Well, you can certainly post it and we'll see what we can do

Aaron Abraham

It's a minor issue (looks like it) Probably not worth posting as a question....but okay.

David Z

Oh, I mean you could post it here in chat

It might make a perfectly good question for the main site too, in which case I'll let you know

Aaron Abraham

Okay, gimme a minute...

@DavidZ If I've got this right, Ampere's Circuital Law is applied to currents through closed (imaginary) loops right?

David Z

Yeah, where the current flows across a surface bounded by the loop

Aaron Abraham

3:48 AM

Now 'loop' as in a 2 dimensional figure, right?

Whoa wait....@DavidZ the surface bound by the loop?

The 'surface' bit got me...

David Z

Yeah, a (closed) loop can always be considered the edge of a surface

rob

Ampere's Law and Gauss's Law are both boundary-value problems.

Gauss's Law relates the field on a surface to the charges in the volume enclosed by the surface.

3d -> 2d

Aaron Abraham

Wait a bit....There's this diagram from Sears and Zemansky's that's confusing me...

rob

Ampere's Law relates the field on a closed loop to the currents that penetrate a surface bounded by that loop

2d surface -> 1d loop boundary

Aaron Abraham

I thought by 'surface' one'd mean the plane enclosed by the loop....but the paraboloid stemming from the loop is well...

unexpected...

rob

3:54 AM

Right ... in 3d space, a particular loop defines more than one 2d surface.

David Z

I guess the key point is that the surface does not have to be flat.

rob

The plane is implied in that diagram, but imagine you had an Ampere integration path that followed the edges of a six-sided die, a cube.

David Z

And the loop doesn't have to be "flat" either - in other words, it doesn't have to be embeddable in a 2D plane. You can have wacky paths that go all over the place too, like what rob just said.

Aaron Abraham

(why is life so complicated? rhetorical, don't have to answer it.) Wait @rob and @DavidZ, so I could possibly create a circular loop on a very long wire, and produce an infinitely long depression?

rob

The point is that you have to get the same physical result no matter which wacky surface you happen to choose --- physics doesn't care about your coordinate system.

Aaron Abraham

3:57 AM

Hmmm...

David Z

@AaronAbraham what do you mean, infinitely long depression?

Aaron Abraham

Sorry...framed it weird,,

rob

The diagram you posted is arguing for both a $\vec J$ term and a $\partial E/\partial t$ term on the source side of Ampere's Law.

Aaron Abraham

Ah well, just chuck the depression bit...at least I've got some things cleared up. This was helpful, thanks ! @DavidZ @rob

David Z

Cool, no problem. Hopefully it makes more sense now.

Aaron Abraham

4:01 AM

Kinda does actually...

David Z

I do think it would have been possible to make a good main-site question out of that, but it might have been tricky to phrase it well.

rob

Good!

Aaron Abraham

(Trust me...being a high-schooler sucks....it limits who you can clear stuff up with....but SE helps ;) )

@DavidZ Yep, phrasing it would be tedious....

David Z

I'm sure we have some questions about loops and surfaces already. If you can find them, they might make for interesting reading.

Aaron Abraham

Will do....found this already physics.stackexchange.com/questions/264831/…

Not the same, but as you mentioned...it makes a good read....

Also @rob and @DavidZ , any of you guys into Mechanics?

David Z

4:05 AM

What kind of mechanics?

Aaron Abraham

Lagrangian ^_^

user116211

@DavidZ, @rob, you people active in this moment?

user116211

Never saw that.

David Z

I'm putting off going to work :-P

user116211

Anyways, @rob congrats for being the new room owner ;)

David Z

4:06 AM

@AaronAbraham I suppose so, considering that all of physics is based on Lagrangian mechanics

Aaron Abraham

Oooh @rob you're a Mod now! I learnt about it late (right now).

rob

Thanks. One of the comments during the moderator election was that people care about chat and I should try it. I'll see if it works or if it sucks up all my attention.

user116211

Aha! Qmech and Manish are also here ;)

user116211

@rob You'll enjoy it ;)

David Z

@rob I guess it takes up as much time as you let it. I lurk a lot but don't often actively participate.

user116211

4:08 AM

Anyways, @0celo7, I'm reading about Borel sets; any problem and I'll ping you.

David Z

Part of the moderation job is moderating chat, too.

user116211

Royden is till good now.

user116211

There is Nested Set Theorem.

user116211

And of course, Heine-Borel Theorem.

Aaron Abraham

@DavidZ Well let's see...There's already a question on this on the Main site, but it doesn't really provide a satisfying answer... Question's broad but still: Could you sum up the advantages of Lagrangian mech. over Newtonian mech. ? At least in a way a high-schooler (who's only ever dealt with Newtonian his whole life) understand. A short example would help too ._.

user116211

4:12 AM

@AaronAbraham wait...

David Z

@AaronAbraham In a nutshell, constraints

Aaron Abraham

@DavidZ Such as?

(I know I'm being tooo broad....

...but even short specific examples would help...)

David Z

At least, that is usually the first type of situation you'll encounter where Lagrangian mechanics has a big advantage over Newtonian. For something like a ball rolling on a track, or a roller coaster, where the motion is rigidly constrained to some funny-shaped path, Lagrangian mechanics allows you to ignore the constraints.

Aaron Abraham

I.AM.INTERESTED....PLEASE CONTINUE..

David Z

It works for an object sliding down the outer surface of a sphere too, where it's not constrained to stay on the sphere but obviously it can't fall through the sphere. That one you can do in Newtonian mechanics but the ability to ignore the constraint (specifically the normal force from the sphere) makes it easier in Lagrangian mechanics.

Aaron Abraham

4:17 AM

@DavidZ What would the other types be about? (Just curious).....WAIT...

@DavidZ Give me a minute....need to hunt down a question I saw a while back.....

David Z

The real advantage of the Lagrangian approach is not just constraints, it's that it lets you use generalized coordinates. That is, in Newtonian mechanics things are simplest in Cartesian coordinates $x$ and $y$, somewhat more complicated in polar coordinates $r$ and $\theta$, but if you want to use any more sophisticated coordinate system you might be out of luck.

Not so in Lagrangian mechanics. Pretty much anything you can use to parametrize your system works as a (generalized) coordinate there.

That's what lets you use the Lagrangian approach for all more advanced kinds of physics, like quantum mechanics.

Aaron Abraham

That...is scarily amazing!

0celo7

@DavidZ Really?

Generalized coordinates are what makes Lagrangian mechanics useful for QM?

The Lagrangian really only shows up in QM in the path integral.

David Z

I guess it's more evident in QFT, but yeah

user116211

0celo7

4:22 AM

The coordinates in QFT are always rectangular though.

Aaron Abraham

@DavidZ Oh wait...I found the question.

user116211

Read the differences between two approaches above @AaronAbraham.

0celo7

The Lagrangian is useful in QFT because of the Noether theorem @DavidZ

user116211

Copyright: Lanczos.

Aaron Abraham

rob

4:23 AM

Schrodinger's equation is based on Hamiltonian mechanics, which has a lot of strengths in common with the Lagrangian approach.

0celo7

And because Lagrangians generalize to fields

I don't know how to do Newtonian mechanics with fields

David Z

@0celo7 The coordinates in QFT play a different role than coordinates in Newtonian mechanics. The QFT equivalents of coordinates are (Fourier modes of) fields, and you would never consider using fields as coordinates in Newtonian mechanics

@0celo7 which is possible because of generalized coordinates

0celo7

@DavidZ OK, we're saying exactly the same thing.

I misunderstood you.

David Z

@AaronAbraham yeah, that's the sphere problem I mentioned

Aaron Abraham

@DavidZ You mentioned the motion of a body over a sphere...you also mention it doesn't have to stay on the sphere...could I possibly use the Lagrangian here?

Oh really?

David Z

4:25 AM

You can use the Lagrangian approach up to the point the mass separates from the sphere, at least

Aaron Abraham

If you won't mind.....could you show me how one'd apply the Lagrangian here? Pretty pweese? A rough sketch would suffice.

0celo7

@AaronAbraham You could discover differential geometry by doing such problems in the Lagrangian formalism

Aaron Abraham

I'm not able to ping Ocelo for some reason...

0celo7

because it's a zero

Aaron Abraham

Fuuuuu

....

@0celo7

Ah...

@0celo7 Could you...elaborate on the differential geometry bit?

0celo7

4:28 AM

ok I have to go to bed

Aaron Abraham

Alright...

0celo7

@AaronAbraham maybe

Aaron Abraham

Sleep tight...

user116211

@0celo7 :(

David Z

@AaronAbraham ooh, it's been a while since I did that. Let's see... you'd write the Lagrangian $L = K - U$ in terms of the angle $\theta$ (say $\theta = 0$ at the top, just for convenience), find the Euler-Lagrange equation, and then there's some way to get the constraint force which I forget

0celo7

4:29 AM

constrained Lagrangian dynamics depends heavily on the geometry of the constraint surface

David Z

You can solve for the angle where the constraint force equals zero

user116211

Whatever, goodnight @0celo7 ;/

0celo7

so if you study these problems, you'll end up studying the constraint surfaces themselves

and that's basic geometry

Aaron Abraham

How basic is 'basic'?

0celo7

Euler understood this

Aaron Abraham

4:30 AM

I'm not Euler..

0celo7

get the book by Arnold for details

Aaron Abraham

But thanks anyways @0celo7

.....

user116211

He can't read Arnold, now.

Aaron Abraham

Listen to him...

0celo7

amazon.com/…

user116211

4:32 AM

You should read a text of differential geometry first.

Aaron Abraham

I'll give it a pass for now...

0celo7

I am not saying it is trivial, but it is "basic" in a sense

basic != trivial

user116211

Prescribe him some differential geometry books @0celo7.

user116211

Go with Kreyszig.

Aaron Abraham

@MAFIA36790 and @0celo7 would you happen to know where I can find a PDF version Of Schutz's book for diff. geometry?

user116211

4:33 AM

I hate piracy.

Aaron Abraham

I haven't heard of Kreyszig..

0celo7

Never heard of it and geometry is what I do

why do you want this book?

Aaron Abraham

To read up on differential geometry...

0celo7

oh, that book

user116211

@AaronAbraham He is the master of introductory texts.

0celo7

4:35 AM

Nothing beats Lee Smooth Manifolds for an introduction

Aaron Abraham

Or any good book on the topic for that matter...@MAFIA36790 would you happen to know if there's a PDF version of Kreyszig's ? Master you say huh? @0celo7 Would you happen to know too?

....

0celo7

But it's probably too detailed for most people interested in physics

user116211

@AaronAbraham It's DOVER!!

Aaron Abraham

I'm pretty sure my school library doesn't have any of those :(

0celo7

@AaronAbraham I know many books on geometry, what background do you have?

user116211

4:36 AM

amazon.in/gp/product/0486667219/…

Aaron Abraham

@0celo7 I'm a high schooler with an aptitude for Chemistry and Bio :P

rob

The Dover classic texts are quite affordable. Worth the investment.

user116211

@rob yes; they are messiah.

0celo7

@AaronAbraham You need to learn advanced calculus and general topology first

Aaron Abraham

@rob I'll see if I can get a hold of it....

0celo7

4:38 AM

if you want to do it properly

user116211

They publish some of the old classics.

0celo7

if you want to do it physics style...then pick up a GR book I guess

assuming you know vector calculus

Aaron Abraham

(I have a feeling @0celo7 is trying to condescend me .......:( )

0celo7

no

I am telling you there are two routes

both require a lot of hard work

Aaron Abraham

I see....

David Z

4:40 AM

@AaronAbraham he does that to everybody :-P lol

0celo7

I rather disagree

Aaron Abraham

@DavidZ I have experience......he did it to me when I was inquiring about Noether's theorem :P @0celo7

A couple of months back...

Oh? I don't remember

@0celo7 I do...

What did i say?

4:41 AM

Never mind...

pretty much what you're saying now...

0celo7

That you should learn vector calculus to understand it?

I think that's reasonable

Ok, I missed my bed time. Whoops

Hope I don't go blind

Aaron Abraham

Ah well....I'll look up Dover.....thanks @DavidZ @MAFIA36790 @rob @0celo7. Night 0celo..

DanielSank

5:42 AM

Hi, everybody.

Brody

Baryonic matter vs. chemical substances (or matter composed thereof). The latter is a subset of the former?

user116211

@DanielSank o/

user228700

5:56 AM

Hi everybody :-)

user116211

Okay, the sidebar is broken.

user116211

Ramanujan

Hi

DanielSank

@MAFIA36790 \o

@MAFIA36790 it just needs to be updated.

Also, who won?

John Rennie

@DanielSank ACM and Rob

DanielSank

6:09 AM

@JohnRennie good morning, Sir Rennie.

user116211

Rob filled in the nomination in the very last day; and he won!

user116211

I was always sure of ACM.

user116211

My first choice was always ACM.

user116211

Those who alleged nonsensical points and yelled at ACM will now be dumb and speechless.

user116211

@DanielSank It is really slow; it takes more or less 24 hrs to get updated.

David Z

6:26 AM

Yep

user116211

Hi @penta.

DanielSank

6:43 AM

@MAFIA36790 I doubt that very much.

user116211

:(

DanielSank

People who make unfounded aggressive claims on the internet do not become speechless after additional evidence proving their claims wrong comes to light.

(Although I do think some of those claims had a grain of truth)

(Still voted for ACM as mod)

3

user116211

10 hours ago, by tpg2114

No conspiracy theorist ever reforms

DanielSank

@Kaumudi hi.

@rob You can make official chat messages?

user116211

He is the room owner; he is the mod; he can do anything ;)

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