The h Bar - 2016-07-13 (page 2 of 4)

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2:00 PM

@EmilioPisanty Sorry, I cannot get your mean. Are you talking about flags?

@lucas That was just pointing out the message to @DavidZ

@DavidZ I think it's not a great question, and I think it's a bad fit for the AMA, but I don't get why you say it's against the 'normal rules and standards' of chat, or why it was deleted.

@EmilioPisanty I didn't

@DavidZ Not sure why it was deleted, then.

It was deleted primarily because it was posted before yuggib even started introducing himself. It wasn't time for questions yet.

It was also flagged.

@DavidZ That seems pretty heavy-handed to me, to be honest.

2:04 PM

If it had been posted later in the AMA, and nobody complained about it, I might have let it go

In any case, I think it warranted a better explanation to lucas.

@EmilioPisanty yep. Chat sessions are run under much stricter moderation than usual, especially near the beginning.

@DavidZ I posted it two times. What about second time?

@DavidZ I guess I don't do those often enough to tell.

In any case, if the AMA events are going to be moderated as per the leading answer at meta.physics.stackexchange.com/q/7778, then I really don't think questions should be deleted from the h bar chat room at all.

Start the side chatroom proposed in that answer, and move all the comments you want

But don't delete stuff unless it's out of order w.r.t. normal rules.

@lucas A few things: yuggib was still introducing himself, and it was barely a few seconds after you'd posted it the first time. Besides, your question took up a lot of space in a busy chat room. And honestly, it's in bad taste, which maybe isn't a reason to delete the question on its own, but it does invite harsher scrutiny than a normal question for that reason.

@EmilioPisanty there's also the fact that people are usually well-behaved enough for it not to make a difference.

2:11 PM

@DavidZ But you could say these reasons yesterday. So that I could improve my question. You just said: It is not appropriate!

@DavidZ All of those are reasonable arguments as far as I can tell. But an explanation was due to a rookie member (e.g. "try later" instead of "isn't appropriate for the chat event"). And if it's an AMA, don't delete, move to side room instead.

Emilio has a valid point.

@lucas not during the AMA. We want to limit unrelated discussion that detracts from the main event. And I think this is the first time I've been in the chat room since then.

@EmilioPisanty yes, I said "not yet"

@DavidZ They are?

I'm here for all of them!

@DavidZ "@lucas that question isn't appropriate for the chat event"

2:16 PM

I've not been suspended during one yet, so I think that's not true

this should be a meta question :-)

@DavidZ First, I didn't know what you wanted. Second, my question (and any other question) is not unrelated with respect to the phrase "any" (Ask me anything).

@EmilioPisanty again, I'm not saying that question was inappropriate for the chat event.

user116211

@skullpatrol sockpuppet?

@DavidZ I know that. What I'm saying is that the deletion was poorly communicated at the time.

2:17 PM

@MAFIA36790 yup

user116211

ohh. o.O

@lucas the word "any" is just a advertising slogan :-)

(I'm also saying that deletion of questions runs counter to the stated format, with additional questions on a side room, which means that questions for the speaker shouldn't be deleted at all regardless of what stage the AMA is at, but that's a separate point.)

user116211

I really am not getting why you are stretching this simple act of deleting your question during the session so much @lucas.

@EmilioPisanty ok, noted. I'll keep that in mind for the future. But I would also point out that during a busy chat event there isn't time for explanations. Normally, if I delete your message, you can ask why and I'll explain. During something like an AMA, the explanation will probably have to be deferred until afterwards.

2:22 PM

@MAFIA36790 I don't stretch my friend. You came now!

I'd also point out that moving messages to a side room takes a lot longer than deleting.

user116211

Though not inappropriate, but I don't want to see such question during a session ;/

@EmilioPisanty honestly, I don't think the AMA was using the stated format anyway

user116211

And David actually did the right thing.

says you :-)

2:23 PM

@MAFIA36790 I never will ask such questions anymore, just because of you:-)

@DavidZ Sure. But I'd also like to point out that that's what you did, but your explanation at the time seems off to me and is inconsistent with your later statements. Not that that's wrong (and you were under pressure so it's not a sticking point to me), but all of the friction could have been avoided with a better explanation at the time.

@DavidZ Yeah, the format will probably need a few iterations to find something that works.

@DavidZ In any case, I think this is the biggest worry if the stated format is to be kept to.

What's the steps for moving a message?

@EmilioPisanty well... yes, that's to be expected, since over time I changed my mind a bit about just what the problems with that message were.

@DavidZ Anyways, water under the bridge.

We take it as a lesson for how to streamline future events and we move on.

user116211

@DavidZ Well, the Interview style was never going to be rigid.

user116211

> Some allowance for on-the-spot questions during the interview would be good.

user116211

2:28 PM

But yeah

@EmilioPisanty hmm... I had to check: over on the right side, click "room" > "move/delete messages", click on the message to be moved, click the "relocate" button, type in the name of the target chat room, wait for the search to bring up the result, click on the result corresponding to the target room

user116211

> We could open a side chat room for these questions.

5 clicks plus typing plus some waiting time

Backup Room – The h Bar

A backup room for when The h Bar is busy. (chat.stackexchange....

@DavidZ Yeah, that's too clunky for what we'd want it to do.

We do have this room which can be used as a side channel during events:

as sammy and lucas did

2:29 PM

@DavidZ Yeah, that one can work.

@EmilioPisanty deleting is just two clicks

@DavidZ Maybe you could ask the mods if there's a way to automate the moving?

@EmilioPisanty we'll rename it at some point to make it clear that it's like a backup channel to this main room. Maybe I'll make a meta post

Heck, maybe there's already a userscript that does it somewhere.

@EmilioPisanty I suppose you mean the SE team? I guess I could, but I'd be surprised if there is and I hadn't heard about it

If there is a userscript, that could be useful

2:31 PM

@DavidZ worth a shot

If it can't be brought down to a more streamlined flow, though, then we'd need a standing rule that all new questions go on the side channel

That's probably easier

plus it allows for using stars to vote on questions to upgrade

@EmilioPisanty that's what they would do in the old moderator chat sessions. Could be a good idea.

The people to talk to about this would be @vzn and @DanielSank, I think - they're the ones in charge of the AMA "project". My role in this is mostly just letting them use the time slots set aside for our biweekly chat sessions.

@DavidZ Commented on the answer in the format q

Let's leave it at that.

Sure

2:48 PM

Great analysis @0celo7 ;)

@Danu Hmm?

how's the pregnancy? @Danu :P

@skullpatrol Ah, yes

The big news

I am officially a mathematics student now!

3

:O

I knew it would be a boy :D

congrats!

Today (also my birthday) it was finally confirmed that I'll be doing my thesis with professor Kotschick

Also guess what book I'll be reading, 0celo7? :P

2:52 PM

@Danu Happy Birthday

@ACuriousMind See above

user116211

@Danu \o/

@Danu Not sure whether to say "congrats!" or "traitor!" ;)

@ACuriousMind :D

user116211

@Danu You are following @yuggib ;)

2:53 PM

I'll settle for "happy birthday!", I think.

2

Good choice.

user116211

@Danu: Should I call you Mathematical Physicist or Mathematician?

Mathematician

user116211

@Danu Awwkay

Pure or Applied?

2:56 PM

:P

@skullpatrol Pure

WoW

@Danu Kobayashi-Nomizu?

@0celo7 G&P haha

@Danu How come?

I've solved many of the exercises if you're interested.

@0celo7 Maybe; we'll see :)

2:59 PM

Why are you reading it

It's certainly not MS level...

@0celo7 MS?

@0celo7 seems reasonable

@Danu graduate

We'll see.

I just need to know some basic diff top ;)

Plus I'd wanted to read G&P anyways

What is there to see? I'm a first year student reading it and doing exercises

3:02 PM

second now

@skullpatrol Rising second

@0celo7 We'll see what I get out of it.

@Danu Hmm.

If it's boring/easy then that's what we'll see. I don't think so, though.

If you want powerful diff top, read Hirsch.

The exercises are very hard so it's not good for an intro textbook.

3:04 PM

Pure mathematicians want all the powerful stuff :P

It's just to get a taste---I have about a month for that plus a book on complex geometry.

@Danu Oh, you can definitely read it in a month. Doing exercises is what's delaying me.

user218912

@Danu will you be doing research in math related to physics?

@3750 At some point, hopefully.

Hi all, can someone answer a quick question?

user218912

3:06 PM

oh cool.

user218912

@Danu I also decided to do math for ugrad instead of physics.

user218912

except i'm bad at math, (and physics).

@Danu See faculty.franklin.uga.edu/shifrin/sites/…

@3750 Nice.

@0celo7 Lol, Shifrin complied errata? :D

@Danu ~~oh no another boring geometer~~ good for you

3:09 PM

@Danu I printed them out and stuck them in my front flap.

;-P

@yuggib lol

@Danu See if you can do Problem 2.3.5 when you get to it.

That'll be after my exams (2 weeks).

@Danu I solved it last week, I'm curious if you come up with something similar

Balarka said he did it another way than I did

3:16 PM

Anyways, I feel obliged to say that in a chat called $\hbar$ GP should stand for Gross-Pitaevskii and not for what the hell you are using it for

user116211

@3750 You wanna major at math?

user218912

@MAFIA36790 yeah

user218912

and then do physics

user116211

@3750 ah! I'm familiar to the other way and would be doing the same.

user218912

@MAFIA36790 can you rephrase that?

user116211

3:18 PM

@3750 I mean Physics and then Maths.

user218912

@MAFIA36790 oh

user116211

I would be majoring in Physics.

user218912

this year?

user116211

@3750 yep.

user218912

nice.

user218912

3:19 PM

what courses are you taking in first year?

user116211

@3750 I'm yet to know; the letters have not arrived from the University; just paid the admission fees.

user218912

ok.

@yuggib I don't even know what that thing you just mentioned is

@0celo7 Of course you don't...you are not a physicist ;-)

but the chat is physical

user218912

I remember back in the day

user218912

3:23 PM

when everyone talked about physics here

user116211

Gross–Pitaevskii equation

The Gross–Pitaevskii equation (GPE, named after Eugene P. Gross and Lev Petrovich Pitaevskii) describes the ground state of a quantum system of identical bosons using the Hartree–Fock approximation and the pseudopotential interaction model. In the Hartree–Fock approximation the total wave-function Ψ {\displaystyle \Psi } of the system of N {\displaystyle N} bosons is taken as a product of single-particle functions ψ {\displaystyle \psi } , Ψ ...

@3750 when

user218912

@0celo7 from march 2015 - july 2015. if I remember.

Idk how any theoretical physicist is not drawn to pure math

@yuggib I've actually seen that equation, I think. Once ;)

3:25 PM

It's just better

user218912

yeah

user218912

@0celo7 did you drop your engineering degree?

@3750 No?

user218912

hmm

user116211

@0celo7: You don't want to be in academia, right?

3:35 PM

@MAFIA36790 No

user218912

@0celo7 how advanced are these notes?

user218912

is this your level?

@3750 They tell you at the beginning: "Graduate core course"

Stop comparing yourself to others and seek to find something you can work with.

user218912

I know that.

user218912

@ACuriousMind I'm trying to compare course difficulties

3:36 PM

Why do you care if it's my level

can you prove $|ab|<|a||b|$ yet

@3750 Why?

user218912

idk

user218912

it's fun

@ACuriousMind Milnor in T - 1 week :DDDDDDDD

get hyped

user image

3:38 PM

@0celo7 What exactly does Milnor do at T=0? Detonate?

I have to take notes...@Danu please teach me to ticz

I must draw all the diagrams

@Slereah linkfail

@ACuriousMind you've never heard "t minus X" before??

user116211

@Slereah is there any image?

@0celo7 I've heard it

3:39 PM

I'll be reading Milnor in 1 minus one week

But I don't know what happens at T=0, Milnor is not a rocket! :D

user image

@0celo7 Ahhhhh

Hey mathman

Meeting with advisor in a few hours, will discuss chap 2 of GP, he'll give me problems for chap 3, so after our meeting in a week I'll start Milnor

3:40 PM

I thought you couldn't write operators as matrices

YOUR MOVE

@ACuriousMind So...I'm trying to prove that GL(n) has two connected components in my spare time

does the preimage of the determinant show it has AT LEAST two connected components?

Probably

@Slereah What kind of space does that infinite vector there belong to, and what are the $f_i$.

@ACuriousMind Shankar says $|\psi\rangle$ is like a little vector at each $x$

and $\langle x|$ measures the vector at $x$

how correct is that

@0celo7 Yes

3:43 PM

@ACuriousMind So you have to show that any matrix with negative (resp. positive) det is connected to any other with negative (resp. positive) det.

@0celo7 It has 34.53 units of correctness.

Ok, I think that can be done with homotopy theory.

@0celo7 I think it can be done with linear algebra

Wouldn't det show it has exactly two connected components?

@ACuriousMind shhhh

3:44 PM

With just a tiiiiny bit of homotopy

@0celo7 Is that a bunch of hypersurfaces intersecting thing?

@Slereah No, since det is not injective.

@BalarkaSen Deformation.

You showed $|x-i_1(x)|<\epsilon$ differently than I did.

Oh

"Operator-valued nonlinear generalized functions"

Ah, that.

3:45 PM

Help I'm getting in too deep

Fucking Colombeau, he wrote the paper I wanted to write

Where are all the good paper ideas

@0celo7 If by homotopy you mean $\pi_0$, ok.

Why not.

just wait

I will produce a proof sometime in the near future

"Distributions which are not compactly supported are embedded via a localized version of (1.5.10) using a standard sheaf theoretic construction"

Not standard enough, inspector Colombo!

The hell is this

Fugg what idea could I do instead

Semiclassical gravity with Colombo???

QFT with Colombo and GR with Colomboboth exist

That might work okay

@Slereah Maybe the winning strategy is not to find a new idea, but to take one of those ideas you've had that were already taken and see if you can do more than has thus far been done with them?

Well yes that is what the idea is

I'm just combining two things here

It's not rocket science

It's just quantum gravity

I thought I was slick doing renormalization with that, but twas too obvious!

4:00 PM

Too often we come up with things we think are profound, but at the end turn out to be quite obvious. But we move on.

Well it's pretty recent by math standards

Less than 10 years

But a bit too late for me

Now I know why you are interested in CTCs! You want to build a time machine so you can go back and use all your ideas before the others had them!

It's the perfect plan

Also, it's a relatively small field

It's possible to know all the developments in the field

@Slereah Well, I imagine those in the field who eventually develop time travel go back and eliminate their competitors ;)

And there are plenty ofobvious shadowy areas

Well remember Star Trek IV

I have noidea what kind of theory to work on for like

Standard model or cosmology

Plenty of open problems but finding the doable ones are hard

user image

The Colombo CCR :p

Ooooh he even does the renormalization of lambda via generalized numbers

All my ideas

user image

4:37 PM

user image

My goodness

What the hell, someone downvoted a perfectly good old answer of mine

I'm bleeding rep

@JohnRennie Yesterday at the makerspace some guys were talking about "This god of PSE who's always giving amazing answers and knows everything" when I moved my head to see who it was, it was you

:: blush ::

It was pretty funny hahaha

You're famous in Brazil, how do you feel?

@JohnRennie is the Kim Kardashian of PSE

@BernardMeurer as being naked with my butt coated in baby oil?

3

How did you know?

You installed Linux again on my webcam :-)

@JohnRennie Only an oiled butt could have so much physics knowledge, it was clear from the very start

5:00 PM

Hey @JohnRennie

You're a GR guy now

But what GR do you do

can anyone help me prove in general that $a \mid \frac{(a-b+1)(a-b+2)(a-b+3)...(a)}{b!}$ ?

@Obliv What is there to prove?

@acuriousmind wait

I thought the remaining fraction had to be an integer

@Obliv ...what?

I mean, the r.h.s. of what you wrote there contains the factor a already

thats what I told semiclassical but he said it's not evident that $2 \mid \frac{2}{3}$ just because $2 \mid 2$ or something

i mean

5:12 PM

@Obliv Well, $2\mid \frac{2}{3}$ doesn't make any sense to begin with.

You have to know that both x and y are integers before you can write $x\mid y$.

But if you know how to prove that the r.h.s. there is integer, you should be able to adapt the method you used for that to prove that it is still integer when you omit the a (or not)

right so how can you be so sure that $\frac{(a-b+1)(a-b+2)...(a-1)}{b!}$ is an integer?

@Obliv I'm not. I'm trying to get you to formulate your problem more clearly :P

oh

@acuriousmind is there any easier method to deducing that $1+p$ is an element of $\mathbb{Z}/p^n\mathbb{Z}$ with order $p^{n-1}$ besides writing it out using the binomial theorem and testing to see if the order divides the expression

maybe I can just use strict examples for prime numbers $p$

and with enough of them I'll see the connection or something

@Obliv Are you talking about order with respect to multiplication or addition?

multiplication

5:22 PM

@Obliv Then you write out the binomial expansion once to compute that in a ring of characteristic $p$ you have $(x+y)^p = x^p + y^p$ for general $x,y$. Then you use that "Freshman's dream" formula and never write out the binomials again.

user54412

@NoahP Deriving Friedman from Newtonian is something most intro cosmology books do, and it's completely wrong. It requires summing a non-absolutely convergent series, and as you should remember from pre-calculus, you can manipulate such a series to give any answer you want. People manipulate the Newtonian equations to give the GR answer, because they know GR is right.

@ACuriousMind I hope you help me as much with Morse theory as you help @Obliv with algebra.

@ChrisWhite You can derive FLRW from Newton???

@0celo7 Well, I know basic algebra much better than Morse theory, but I'll do my best

The only Cosmology book I read was Weimberg's newest one and it assumes full GR knowledge from the beginning.

@0celo7 "derive", not derive

user54412

5:28 PM

@0celo7 you don't read many books that aren't pure math, do you?

@ACuriousMind Everything in physics is "derive" as far as I'm concerned.

@ChrisWhite Not recently.

@0celo7 The string theory lecturer today dropped "$\mu$-polystable vector bundles with zero slope" and then skipped the entire derivation of what they have to do with what we were doing, presenting only the result. You'd have had fun ;)

What the hell is that

from what I gather, cauchy's theorem states that if theres a prime $p$ that divides the group order, there exists a subgroup of order $p$ is this correct

@ChrisWhite Weinberg is not even math.

He's far too unrigorous for my taste.

5:35 PM

if I prove cauchy's theorem can't I just apply this to the situation and say the multiplicative group $\mathbb{Z}/p^n\mathbb{Z}$ has a divisor $p^{n-1}$ so there is a subgroup that has this order? @acuriousmind

@0celo7 You don't want to know, it involves sheaves

@ACuriousMind Just tell me you didn't understand sheaves at my age

@0celo7 I absolutely did not

@Obliv And how does that tell you that 1+p belongs to that subgroup?

I meant $(\mathbb{Z}/p^n\mathbb{Z})^{\times}$

@ACuriousMind when did you

5:40 PM

@0celo7 When I started taking courses that involved them. About...two years ago, I think.

And I'm still not sure I "understand" them. I like them, though ;)

@ACuriousMind Which course would that be

@0celo7 algebraic geometry

nowadays its "topology of singular spaces" that uses them

Though I'm not sure if that's really a good title for what that lecture involves

today I learned the quantum hall effect (both fractional and integer)

I have to say that it is the less boring application of geometry/topology to physics I have encountered so far ;-P

@ACuriousMind We've established that's far out of range of my interests.

Which might now include differential topology now

I'm really enjoying GP

@yuggib broadening my horizons

user54412

@yuggib What's the status of the fractional effect now? I remember ~6 years ago being told it was a sure herald of new physics, but I could never understand why.

5:49 PM

@ChrisWhite There are still many interpretations/open questions

as far as I understood, it should be due to: 1) degeneracy of the ground state 2) non-trivial topology of the control parameters of the Hamiltonian (i.e. flux of the control fields)

not clear if that reflects experiments accurately though

does not seem to imply groundbreaking new physics as far as I can tell

but I "learned" it today ;-P

I'll have another course on it next september, and then I may be able to say more

@0celo7 here you go with the dumbed down version for the general audience:
http://scitation.aip.org/content/aip/magazine/physicstoday/article/56/8/10.1063/1.1611351

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