The h Bar

4:00 PM

oooooh, this is a nice answer

7

A: The scope of \newcommand is the entire page

This answer will serve as a demonstration: $$\sin \pi = 0$$ What I typed was true (edit or view source), but what you see is false.

0celo7

@ACuriousMind that doesn't make sense, hence the what

How are they numbered the same if it jumps around

ACuriousMind

There are equations 2.3a,2.3b, then theorem 2.4, then equations numbered 2.5a,2.5b, then an equation numbered 2.6, then theorem 2.7, etc.

It's very weird

0celo7

Ohhhh

ACuriousMind

I also don't see anything numbered 2.1 or 2.2

0celo7

@ACuriousMind that's standard

Slereah

4:03 PM

I forget the exact chapter numbering of the PM but it's a mess

0celo7

It's so standard that I know there's a book that does that

ACuriousMind

Ohhh, the second number does not count the n-th thing in the chapter, but the n-th numbered thing in the entire paper

0celo7

But I can't remember which :P

ACuriousMind

I find this really weird

0celo7

@ACuriousMind ok now that is stupid

Slereah

4:04 PM

ah, found it

The chapters are

1,2,3,4,5,9,10,11,12,13,14,20,21,22,23,24,25

Emilio Pisanty

from an approved, archived PhD thesis

ACuriousMind

@Slereah But...why?

Slereah

I suspect that he had to do some structure changes and he didn't bother changing the numbers?

ACuriousMind

@EmilioPisanty Beautiful.

The randomly appearing y is a nice touch

Emilio Pisanty

@ACuriousMind hah

would you believe, I hadn't noticed that

but it makes sense as part of a larger figure

ACuriousMind

4:11 PM

Ah, so it's not that random

Emilio Pisanty

those axes, though...

ACuriousMind

Lol, why does energy go from 1 to 23?

And then from 29 to...20?

Did no one ever look at these graphs after they were made?

0celo7

Turns out poincare recurrence is false for nonfinite measure spaces

So maybe the old thought experiment paradox is indeed false

ACuriousMind

@0celo7 Which one?

0celo7

@ACuriousMind two boxes connected by a tube

Put gas in one box, open up the tube

Eventually the gas will be back in the first box

Well...I guess the allowable phase space of the particles will be bounded by the total intial energy or something

So it's in some large ball

ACuriousMind

4:19 PM

@0celo7 The standard resolution is that "eventually" potentially lies after the heat death of the universe, so I'm not really bothered by that paradox to begin with

0celo7

@ACuriousMind but unless the region of phase space you're working in is finite, "eventually" will never happen

ACuriousMind

Yeah, but as you said, the accessible phase space volume is typically finite - bounded by energy in the momenta and the box itself in the positions

Emilio Pisanty

@ACuriousMind the associated postdoc did, but it was too late

PhD student was on a gtfo asap kinda plan

supervisor obviously did not look into the details closely enough

AccidentalFourierTransform

5:23 PM

So I have this second order differential operator $\mathscr D=\alpha(x)\frac{\mathrm d^2}{\mathrm dx^2}+\beta(x)\frac{\mathrm d}{\mathrm dx}+\gamma(x)$ which I want to diagonalise

the coefficients are singular at $x=0$ and $x=\infty$

So I solved $(\mathscr D+\lambda)f=0$, and the solutions are regular both at $x=0$ and $x=\infty$ for all $\lambda>0$

does this make sense? the spectrum of $\mathscr D$ is continuous, is that possible?

I was expecting $\lambda$ to be quantised

0celo7

@EmilioPisanty haha

@ACuriousMind ok, so it's all fine

Epistemological crisis averted

@EmilioPisanty what is that plan?

John Rennie

This kind of got away from me a bit. I'm unconvinced it was really worth it.

0celo7

5:40 PM

@AccidentalFourierTransform impressive...can one solve a general second order linear system?

I don't remember much about ODEs

AccidentalFourierTransform

@0celo7 lol no, $\alpha,\beta,\gamma$ are some specific functions

rational functions, so that the solution is a combination of $_2F_1$ functions

@0celo7 neither do I, that's the problem :-P

0celo7

@AccidentalFourierTransform ...hypergeometric?

AccidentalFourierTransform

yep

Emilio Pisanty

@0celo7 the kind where you hate your phd project and your supervisor with all your guts, but you've invested too much time into it and it's too late in the game to change projects, so you just need to submit some form of thesis to graduate and move on

@ACuriousMind that was some pretty fast action on the gauss-bonnet one

even if it was seconds shy of the three minute mark

a.k.a. you're slipping ;-)

ACuriousMind

2 min 55 secs, not one of my fastest :)

0celo7

5:55 PM

Gauss Bonnet?

Help, where is this GB question

I can't find it

ACuriousMind

Here: physics.stackexchange.com/q/315248/50583

0celo7

What did you do to it?

ACuriousMind

I deleted a non-answer.

John Rennie

@ACuriousMind if you're in a moderatorial frame of mind I've just flagged a comment ...

ACuriousMind

I noticed ;)

John Rennie

6:00 PM

Does anyone mind if I cancel the stars on the post of mine that is on the star board? I'm not sure we want political commentaries on the star board. Actually I probably shouldn't have posted it at all ...

Emilio Pisanty

I do love this, though

@JohnRennie I may or may not have starred that in a trolling spirit given your later comments

0celo7

What does the starred post say?

John Rennie

Flipping heck! Who just starred it a second time? When I catch you ...

ACuriousMind

@EmilioPisanty I actually consider that a bug - it means that trolls can flood the frontpage with old stuff even if we delete everything immediately.

AccidentalFourierTransform

@0celo7 ring-ding-ding-ding-dingeringeding

Emilio Pisanty

6:04 PM

@ACuriousMind yeah, well, abuse gets caught pretty efficiently round here

user228700

@JohnRennie I'm pretty sure that ur political comment is not the C&H comic I starred just now :-P

Emilio Pisanty

if and when it becomes a problem we can complain about it

0celo7

@ACuriousMind What did it say?

John Rennie

@Kaumudi.H Calvin and Hobbs?

ACuriousMind

@0celo7 Get 10k and see for yourself

Emilio Pisanty

6:05 PM

@0celo7 nothing

> How do you know the gauss bonnet term is a total derivative?

that was all

user228700

@JohnRennie Calvin and Hobbes, yep.

0celo7

@ACuriousMind expletive

@EmilioPisanty aha

AccidentalFourierTransform

Emilio Pisanty

@AccidentalFourierTransform username is public

from the front-page entry

AccidentalFourierTransform

I know, the username was actually a blue scribble

John Rennie

6:07 PM

@Kaumudi.H I think Calvin and Hobbes is the best comic strip there has ever been. Bill Watterson had the good sense to stop before he ran out of ideas.

user228700

@JohnRennie And I agree with u 100% :-) (BTW, Accidental Fourier Transform posted a C&H comic here, which is what I starred before, which is how I brought up C&H in the first place)

John Rennie

My younger brother was a bit like Calvin :-)

user228700

Aww, I see :-) Boy, that kid is smart.

AccidentalFourierTransform

ah yeah, please post C&H comics!!

post your favourite comics, all of them :D

John Rennie

@Kaumudi.H Smart, but his own worst enemy. Which ... is kind of like my younger brother :-)

user228700

6:10 PM

user228700

@JohnRennie :-) I know. Lol, I see.

0celo7

imgur.com/gallery/Umnns

user228700

AccidentalFourierTransform

Harambe did nothing wrong

nazi monkey

►

John Rennie

@AccidentalFourierTransform Sadly, you can't shoot the kid instead.

user228700

6:16 PM

Ah, kids:

user228700

John Rennie

I once ate a spider because someone dared me 10p that I wouldn't.

user228700

@JohnRennie Did u really?! x'D A live spider?

John Rennie

Yes.

user228700

Omg. How old were you?

ACuriousMind

6:17 PM

It probably was last year or so :P

John Rennie

I forget. In my 30s I think.

AccidentalFourierTransform

what would you eat for £10?

John Rennie

100 spiders?

user228700

@JohnRennie o_O I'm unable to figure out if u're kidding or not.

AccidentalFourierTransform

you would? I would definitely pay £10 to see that!!

anyone else is willing to collaborate?

user228700

6:19 PM

Cut it out, guys. 100 spiders is a bit much.

John Rennie

I'm not kidding. It's absolutely true. bearing in mind I had a had a high paying job as a computer nerd at the time I didn't need the 10p, I just wanted to freak my friend out. Which I did! :-)

user228700

@JohnRennie Holy crap! x'D Dyou remember what it tasted like? Uuugh, how did u go through with it?!

ACuriousMind

@AccidentalFourierTransform Hm, I find 100 spiders a bit boring. Let's go for a bit more variety

John Rennie

Eating spiders is fine, though you should probably avoid the ones that bite. However I wouldn't eat anything that lives on rotted food like flies or cockroaches.

@Kaumudi.H It didn't taste of anything. I swallowed it whole.

user228700

NOOOOOOOO :-o

0celo7

6:21 PM

@JohnRennie That's what...hmm. Maybe not.

AccidentalFourierTransform

do spiders eat pineapple?

John Rennie

I suspect my oesophageal contractions killed it instantly. If they didn't the stomach acid would have done.

user228700

Geeeez. See, this is exactly why I try my very best to imagine complexly. I've just found out that you are a person who has eaten an effing spider!

0celo7

Do Brits call it the oesophagus?

John Rennie

@0celo7 it's a real struggle not to respond and lower the tone of the conversation :-)

AccidentalFourierTransform

6:23 PM

well you already know JR enjoys killing animals, just for the sake of it

John Rennie

@AccidentalFourierTransform do I?

AccidentalFourierTransform

Yes you do mister

0celo7

You're a meat eater, no?

John Rennie

When did I give that impression?

user228700

Eh, I don't believe that he'd do it just for the sake of it--I'd say that he enjoys eating animals that don't taste half bad :-)

John Rennie

6:24 PM

Indeed yes. When I want some lamb I don't head out into the fields with a cleaver.

0celo7

If he doesn't need the meat to survive I'd say is indeed just for the sake of it.

@JohnRennie No, you go to the breeding farm where the animals are kept and tortured in tiny cages.

AccidentalFourierTransform

if you were in a room with a cow, Hitler and Stalin, and a gun with two bullets, you would shoot the cow twice

2

John Rennie

@Kaumudi.H it was funny though. The look on my friends face was priceless. I wish I had had a camera to hand.

AccidentalFourierTransform

What the Lamb Said to Lisa

►

John Rennie

@AccidentalFourierTransform Well the other two would take an awful lot of stewing to make them tender.

user228700

6:27 PM

@0celo7 It would interest you to follow this thread:

user228700

Feb 14 at 16:00, by John Rennie

Britain has the toughest laws in Europe on animal welfare, i.e. not treating domestic animals badly, and I support those.

user228700

@JohnRennie I believe you! x'D

0celo7

@JohnRennie Have you seen young Stalin?

John Rennie

@0celo7 is that a film?

AccidentalFourierTransform

not, that is a sex symbol

dude was hot

0celo7

6:28 PM

An adult film, maybe.

He was pretty gorgeous.

John Rennie

I feel we are wandering into dangerous waters :-)

0celo7

John Rennie

He wasn't Stalin when he was young of course, he took that title when he came to power.

0celo7

I did not know that

Stalin was not his name?

user228700

Wow, there is a tumblr page dedicated to young stalin: fuckyeahyoungstalin.tumblr.com :-o

0celo7

6:30 PM

> Iosif Vissarionovich Dzhugashvili

What a name

user228700

Jesus Christ, the things one finds on tumblr...

user228700

0celo7

Young Stalin sounds like a rapper

John Rennie

I'm feeling a bit uneasy about this. He was a violent thug responsible for the deaths of millions of people. I don't think we should be making light of this.

0celo7

Fine.

AccidentalFourierTransform

6:33 PM

animals are people too

2017

@AccidentalFourierTransform specifically spiders are people too :P

user228700

Alright, I'm off. Bye, everyone :-)

AccidentalFourierTransform

cheers

2017

goodnight :D

John Rennie

Bye

0celo7

6:41 PM

@JohnRennie can I at least teach you some measure theory

Bernardo Meurer

6:59 PM

@heather Read this now

2

0celo7

@BernardoMeurer what is this calculus problem

@BernardoMeurer ask now or forever hold your peace :/

Kat will be mad at me if I don't help

skullpetrol

7:19 PM

Kat?

Skyler

7:31 PM

hey @DanielSank, did you ever work in schematic capture when you did your work with FPGAs. I've been trying to figure out how to connect a VHDL file to the VGA port, but its embedded in a project that started off with schematic capture.

Sir Cumference

7:46 PM

Howdy

2017

@SirCumference Hi.

Sir Cumference

What's up?

2017

Nothing much, studying organic chemistry :)

Sir Cumference

Neat, programming

2017

Programming? In C ?

Sir Cumference

7:49 PM

JavaScript :)

2017

Oh, what type of program? I don't know much programming other than basic java :P

I can only do string and array programs XD

Sir Cumference

JavaScript adds features to websites, beyond a simple read-only page

This chat uses JavaScript, for example

@2017 JS has strings and arrays :)

2017

Oh, right! I heard of javascript though I never coded anything in it

Sir Cumference

What are ya majoring in?

2017

My entrance exams will be over in about 2 months. Do you recommend any particular programming language which I should learn during my holidays to develop basic coding skills ? I hope to take up engineering at college....

Sir Cumference

7:53 PM

@2017 I hear MatLab and Python are important for engineering

Not sure if that's just hearsay though

2017

@SirCumference Ah I see, do you recommend any books? :)

What abt javascript?

Sir Cumference

@2017 Well I learned to program through a website, codecademy.com

It's free and helpful

@2017 I don't think that's related to engineering, but it's very handy to know. At least, if you use the internet often :P

You can modify websites by writing userscripts, so if there's something you don't like or want to add, you can do that.

2017

codecademy.com Looks great :D Will try for sure!

Sir Cumference

Or program your own website

2017

@SirCumference That would be handy...I should learn it :)

Sir Cumference

7:56 PM

@2017 Just know that you'll probably hate the first programming language you learn

2017

I will have 3 months of holidays anyway

Sir Cumference

It's tricky to get into the mindset needed for programming, and it takes a hell of a lot of patience. But once you get used to programming in one language, all the others are very easy to learn

2017

@SirCumference my first programming language was BASIC :P

Then I learnt basic java

Sir Cumference

@2017 In retrospect, BASIC didn't help me learn JS at all :P

2017

lol XD BASIC is too childish

but it is good as a introductory language

@SirCumference you have programming in astro courses?

Sir Cumference

7:58 PM

Sorta

@2017 Yep

Oye, gtg

Later

skullpetrol

Cya

2017

@SirCumference sure :)

bye

DanielSank

@Skyler yeah I used it, but I recall nothing XD

Skyler

@DanielSank do you do anything current with fpgas?

DanielSank

8:15 PM

@Skyler not really

DanielSank

8:31 PM

Other people in our group do.

0celo7

The concept of ergodicity is neat

skullpetrol

8:54 PM

(removed)

0celo7

9:04 PM

$\mathfrak{(removed)}$

heather

hello

0celo7

@heather So now we know what a Banach space is

@heather do you think we're ready for a big theorem about Banach spaces?

heather

i think so =)

0celo7

@heather Let $(E,||\cdot||)$ be a Banach space. Let $T:E\to E$ be a linear map (recall the concept from linear algebra).

heather

okay.

0celo7

9:13 PM

We say that $T$ is a $\lambda$-contraction if there is a constant $0<\lambda<1$ such that $||Tx-Ty||\le \lambda||x-y||$ for all $x,y\in E$.

That is, $T$ strictly shrinks distances between points.

heather

okay, that makes sense.

0celo7

So take some set $S\subset E$. What do you expect $T(S)$ to look like in comparison to $S$?

heather

sorry, i'll be back in 30 min or so - have to go on a quick errand

0celo7

ok

OBE

@physshyp blue guy finally

Physics Meta

9:28 PM

-1

Q: Should we change homework policy of physics.SE?

All possible sites given by this answer are very disappointing in dealing with question & answer and the Physics.SE is by far the best (with respect to design and with respect to active users ) so I should ask two questions. Why there is such a rigorous policy about homework questions and way t...

Student404Mus

9:43 PM

hi everyone

how could someone claim intuition in physics ?

Slereah

you write it down

"It is obvious that..."

skullpetrol

Then you say:

To justify your claim :-)

heather

10:19 PM

::sighs:: that took way longer than I thought

skullpetrol

3(Hip hip hooray)

0celo7

Back in the day populism used to be communist/socialist. Now it's reasonable and intelligent. Don't know how I feel about that.

Secret

There is not much dark matter back in the early universe

dmckee

11:07 PM

@Secret That interpretation is not supported by the text of the article which says "star-forming disc galaxies in the early Universe were less influenced by dark matter [...], as it was less concentrated."

AKA the dark matter hadn't cooled enough to collect in galactic gravity wells.

But that's not surprising: we already expect that it has much lower interaction cross-section than baryonic matter.

Secret

I see. Yeah the moment after I wrote that down, I then wondered wait where did all that dark matter came from before concluding that it must not have clumped yet. That train of thought than end on thinking about dark matter

galaxies

0celo7

11:34 PM

Making beef Wellington

@JohnRennie I will show you my attempt

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