The h Bar - 2017-04-10 (page 2 of 5)

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10:00 AM

plus it's one of those papers that assume that you know all about the current state of the theory

Which for time symmetric theories is I think fairly cocky

Anonymous

@skullpetrol The problem is not with the exam. The problem is every child being forced to be an engineer or doctor. Most suicides are due to the family pressure and peer pressure. As far the jee is concerned, it is a necessary evil. I agree with that.

Why is it "necessary" to make the exam impossibly difficult? @blue

Anonymous

@skillpatrol India just doesn't have enough funds to provide quality education to all.

Anonymous

And same is the case with China

what do they do?

user228700

10:09 AM

Oh my God I wonder if this chat will see a day in which we don't mention India's screwed up system of education.

Anonymous

@Kaumudi.H Maybe when you fix the system =P

Anonymous

@skillpatrol What?

Now that would be a glorious day @Kaumudi.H

user228700

@blue There are so many other systems that are working under a less than perfect set of conditions, can we please talk about some of those please?

What kind of examination does China do? @blue

Anonymous

10:12 AM

@Kaumudi.H Like?

Well the UK is one example.

Anonymous

Every system has its flaws

user228700

Exactly. So let's talk about literally anything else.

Anonymous

@JohnRennie UK has a much larger funding for education.

Per capita

Anonymous

10:13 AM

Yes ^

@blue when I was an undergraduate students could get a full grant (unless their parents were rich). The grant paid all the fees and basic living expenses - though you wouldn't be living in luxury.

@JohnRennie lol

But there weren't that many grants available so the number of people able to go to university was quite small.

how about: "what is your love part and hate part about your research team?"

Anonymous

@Kaumudi.H You start. I'm not really the type of person who keeps whining about the education system. This topic came up and so I was just giving my views.

10:16 AM

The government decided that they needed to get more students going to university, but there simply wasn't the money avaliable to pay them all grants. So the government encouraged many more universities to open and offer places, but they withdrew the grant system.

user228700

@JohnRennie Lol. Even after all this preparation, the quality of living and all is exceedingly poor in these colleges here. Last year, the students of IITM held a protest against the canteen for serving them terrible food.

user228700

Yes, a protest.

So now students have to pay £9,000 per year, for four years if you go to Cambridge, and pay all their living expenses. Students face leaving university with a debt of £60,000 or thereabouts.

Thank goodness exams aren't terribly hard or education horribly expensive here

I mean you still don't find a job after

but the school part ain't too bad

@Kaumudi.H I struggle to raise much sympathy I'm afraid. If the food is cheap then eat it and shut up. If the food is poor value compared to street food then buy street food instead.

10:20 AM

Yeah^

user228700

Hmm. I don't know the exact circumstances that lead to the protest but I suspect that it was something truly terrible. For some context, let me submit that one time, they found a dead snake in our water cooling system at school after several people noticed that the water tasted and smelled weird.

Anonymous

@JohnRennie Well, see in the UK atleast all the universities have a basic standard. Right? Over here the private colleges are so ridiculously bad that 60 percent or more engineers who graduate out are jobless and underqualified. In UK everyone isn't forced to become a doctor or engineer, right?

Anonymous

In private colleges the professors know almost nothing about the subject they are teaching. The students are more knowledgeable than the teachers =P

user228700

(My school is inside the IIT campus, which is close to 620 acres of forest, which explains the snake)

@blue I have a sneaking suspicion that in the UK lots of students go to university just because they think it will be fun, and without any real career plan. So they end up with a large debt and no special qualification for paying it off.

Anonymous

10:22 AM

@Kaumudi.H Yuck!

Anonymous

@JohnRennie "lots of students go to university just because they think it will be fun"....NO..they are forced by their family to become engineers or doctors! Debt is not a problem here...education is cheap...here the problem is....stupid professors in private colleges

@Kaumudi.H It's a bit harsh to criticise the school for that. The school didn't put the snake in th water tank!

620 acres of forest?

@blue ah, sorry, I meant in the UK

user228700

@JohnRennie ...which is why we didn't conduct a protest or anything :-P Still, it was proof that the tanks weren't being maintained properly or that snake wouldn't have been lying there for weeks!

10:24 AM

I feel sorry for the person who had to reach into the tank and pull out a decomposing snake. I mean Eeeeeeeeeeewwwwwwwwwwwwwwwwww!!! :-)

user228700

Indian Institute of Technology Madras

Indian Institute of Technology Madras is a public engineering institute located in Chennai, Tamil Nadu and is one of India's most prestigious universities. It is recognised as an Institute of National Importance by the Government of India. Founded in 1959 with technical and financial assistance from the former government of West Germany, it was the third Indian Institute of Technology that was established by the Government of India through an Act of Parliament, to provide education and research facilities in engineering and technology. IIT Madras is a residential institute that occupies a 2.5 km²...

ah, Madras

I mostly know it from Leprechaun 3

user228700

@Slereah Hmm?

There once was a man from Madras

Who had balls made of fine brass

Anonymous

@Slereah lol

10:25 AM

So in stormy weather, they both clanged together

And sparks came out of his ass

user228700

Lol. Madras is the old name for "Chennai".

-_-

(it is a great movie)

although I had to give up on the 4th movie

Leprechaun 4 was set in space and that was too much greatness for me

Anonymous

Leprechaun 3 (also known as Leprechaun III and Leprechaun 3: In Las Vegas) is a 1995 American slasher film and the third installment and first direct-to-video entry in the Leprechaun series. == Plot == After being pawned to a Las Vegas shop owner, Gupta, the Leprechaun (Davis) jumps on his back and bites off a part of his ear, accusing him of being a greedy thief. He then beats the Gupta's legs with his walking stick and notices that he's wearing leather shoes. He removes one and states that he "appreciates a good pair of shoes." He looks down and notices Gupta's sock has a hole in it, revealing...

Anonymous

looks funny =D

user228700

10:27 AM

@JohnRennie Oh God, I hadn't even thought about that >.<

Leprechaun is what happens when the slasher genre becomes unable to be taken seriously

Anonymous

I've many snakes around my house =)

Anonymous

We use carbolic acid

Anonymous

To keep them away

Anonymous

hehe

10:28 AM

Keep a mongoose

Anonymous

We have a few mongooses

mongeese

mongooses?

^

user228700

Our school was truly strange in that regard. Monkeys learned to turn the taps and drink water from our washrooms. They also steal our lunchboxes and fish for food in our trash cans; they'd walk right into class.

10:30 AM

how many managed to pass the JEE though

Lol

Mongooses - what did we do before Wikipedia existed?

@JohnRennie the dictionary

user228700

@Slereah x'D

Anonymous

"The word "mongoose" is likely derived from the Marathi name mungūs (मुंगूस) (pronounced as [muŋɡuːs]) or probably ultimately from Telugu name mangisu ." hehe =P

10:31 AM

In the olden days, I had CD ROMs of encyclopedias

user228700

(::Beginning to realise that nobody cares but continuing anyway::) The deer were friendlier; they'd take food right out of our hands during lunch break.

all animals are friendly if you have food

@Kaumudi.H it's when the monkeys start correcting your work you need to be worried :-)

@Kaumudi.H Mmm, venison.

user228700

@Slereah Not the monkeys! They can be cruel.

that is when you punch its monkey face

10:33 AM

And get bitten!

teach them some respect

They have rabies

Anonymous

A monkey once slapped me =P They are naughty creatures

user228700

@JohnRennie Ah, the deer; so elegant and beautiful but nope. Venison. I expected nothing less of you -_-

that is the magic of animals

they can be friends and food

10:34 AM

Little known fact, monkey muscles are intrinsically stronger than human muscle. Weight for weight they are a lot stronger than us.

truly magical

although the same is true of people

little known fact

user228700

Dude.

Anonymous

@Slereah Friends, food and foes are interchangeable depending on the situation =D

user228700

@blue When I was 4, 3 monkeys climbed atop my small body to steal my packet of biscuits at a park.

though i have not eaten any monkeys so far

10:35 AM

@Kaumudi.H your Mum said, now which of these four is Kaumudi? :-)

user228700

x'D You know, she probably did.

Anonymous

@Slereah Eat my school teacher...he is a monkey.

Anonymous

@JohnRennie lol

What one monkey can do, another can.

user228700

I'm so glad I brought up monkeys x'D

10:38 AM

Better than jee

:D

Oh god

user228700

^

Feynman uses Fraktur for the EM potential

Oh wait, it's the acceleration, actually

$-(e \mathfrak{A} / r_k c^2) \sin(\mathfrak{A}, r_k)$

I don't think it should be legal to use a fancy script for functions

fancy scripts are for sets only

physicist notation is like, crap

plz

Anonymous

10:44 AM

@skillpatrol Since you were asking

don't act all innocent

I know what math people do

at least we don't use a million indices

you should

Einstein notation is great

bleh

what's the largest amount of indices a tensor is likely to have, anyway

I think Riemann tensor in spinor notation would have 8

yeah

${R_{AA'BB'CC'}}^{DD'}$

user228700

10:50 AM

Damn, I wish I could get away with something like this:

user228700

user image

i don't think there's any upper bound to the no of indices of a tensor

yeah but I mean

What's the largest you're likely to see

You can have a $(132146,48941)$ rank tensor but it's not likely to be useful

vOv

Anonymous

user image

Anonymous

10:53 AM

@Kaumudi.H

Anonymous

This would be the result ^

user228700

:-P

mind-expanding drugs aren't the good ones

(the mind-melting ones are)

Anonymous

@Kaumudi.H Just reminded me of a boy in 6th grade who wrote in his environmental science test that one of the ways of increasing soil fertility is urinating on the soil =P The answer was scientifically correct (?) but his parents were immediately called and he was suspended for a few days. Lol

To my considerable surprise I appear to have repaired the keyboard that I spilled beer over!

Bernardo Meurer

11:05 AM

@JohnRennie Do you have some spare HD space so I can have an offsite backup for my music

You can get any music you want in return :P

It's all FLAC with carefully filled metadata

Manually by me

How much space do you need?

Bernardo Meurer

Lemme see

165G

@BernardoMeurer you get 100GB online storage for 2$

access anywhere in the world at any time + high speed

Bernardo Meurer

@Yashas I have 100GB on Google Drive that I pay for, but it's filled with stuff already

Mostly documents and things like that

and 100GB isn't enough, I need 200GB

get 1TB :P

it is 10$ I think

Anonymous

11:09 AM

Make 10 google accounts 10*15=150

Bernardo Meurer

and then most plans go 100, 500 or 1TB

Bah, 10$ a month is too much, I can't afford it

You get 5TB for 5$ per month

Bernardo Meurer

@JohnRennie You may also request the addition of any given music to the library, since I LOVE tracking down FLAC versions of music and tagging it nicely

@Yashas Where?

@BernardoMeurer onedrive.live.com/about/en-in/plans

It also gives access to 5 users

Bernardo Meurer

@Yashas One drive :(

11:11 AM

you can team up with your friends

pay 1$ each :P

Bernardo Meurer

Hahahaha, you think I have friends, how cute

aw

Bernardo Meurer

My only friend is my picture of alan turing

Anonymous

Tell your girlfriends to pay

Bernardo Meurer

jk, jk I have friends

they are just cheap

@blue Never a good idea for anything

Anonymous

11:13 AM

@BernardoMeurer Learn to utilize your girlfriends...you need some tutoring =P

:O Turing fan :O

Bernardo Meurer

@blue I do utilize them, just not for their money, lol

That sounds so awfully wrong

:|

Anonymous

I am shamelessly money-minded and capitalist =P

Anonymous

lol

11:14 AM

's all the same. money is labor is people, according to Karl Marx

I am the other way round; I spend money to get fish for over 20 cats everyday!

Bernardo Meurer

@BalarkaSen Stop reading Marx's malware

You're talking like a pettibourgeois lumpen

@EmilioPisanty I'm confused - did they change the "after casting 300 votes, you cannot downvote non community wiki posts at more than a 2:1 ratio" at some point later? It doesn't seem to be currently active, perhaps that's only in effect on SO? Also, the original discussion on meta.SE about that is also a rather interesting read.

In unrelated news, I just logged in and am already recapped for the day - thanks HNQ, but I still hate you :P

11:32 AM

Most of the times, I feel that some silly random question becomes a HNQ.

Bernardo Meurer

@ACuriousMind Do you want to be my offsite music backup?

What would that involve?

Bernardo Meurer

@ACuriousMind Having 165GB of storage

That's it

I don't have 165 GB of free storage, actually

Bernardo Meurer

Geddammit

Guess I'll try and buy some FTP server

Anonymous

11:40 AM

@BernardoMeurer This might be useful (degoo.com)

Anonymous

Haven't tried it though.

help

I bumped my toe on a barbell

doesn't look good

Anonymous

@Slereah Apply some ice!

opposite, actually

Bernardo Meurer

@blue Seems to good to be true, I'll read their terms and conditions to check

11:42 AM

I need warm salt water

Bernardo Meurer

thanks though :)

@Slereah Lick it

@BernardoMeurer My hosting provider theoretically doesn't limit storage space, I don't use much of it

Bernardo Meurer

@JaimeGallego ::smiles::

What I don't know is if I can useradd to the server, let me check

Bernardo Meurer

What the hell is this hosting provider who doesn't limit storage? :P

You don't necessarily need to useradd, just to have FTP access

or SSH even

I guess SSH would need a user though

11:54 AM

Smell of old books and our cultural heritage, and the chemicals that is responsible for them as well the words that describe the smells

@Secret why different title in chemistry chat and physics?

That's called tailoring to the audience

@BalarkaSen It's the unit group of the Banach algebra of bounded linear operators on the Hilbert space.

user image

@BernardoMeurer :P

Bernardo Meurer

Jesus

Yes, just make me an FTP account

you can get any of my music you want in return :P

and it's a lot of music

11:58 AM

The chem folks will relate more with the VOC analysis thing than the h barers, which is why I emphasize the history aspect when sharing it here in h bar (which is more general purpose science sharing platform)

It is most likely a steamy methane water world

@BernardoMeurer Ready, email me

Bernardo Meurer

@JaimeGallego Emailed, from @meurer.xyz

@JaimeGallego Gotta go meet my mom for lunch, brb

12:22 PM

@0celouvsky does the space invader make sense

Consider a point particle with an unbounded acceleration applied to it

Let's say $1/t^2$ for $t < 0$

The particle fucks off to infinity

user image

What happens after $t^*$

Is the particle indeed gone from the space

The space invader scenario is what happens under time reversal

user image

Particle pops up from nowhere

Is this relativistic or gallelian, cause if it is relativiatic the particle cannot cross the 45 deg line at all?

Galilean

Hmm, this paper claims that if I have a manifold $X$ with a submanifold $Y$, that there is an "inclusion" $Y\to (X-Y)$, which strikes me as...unlikely

@0celouvsky Huh, fun.

Ah, lol, as usual the physicists have been a bit sloppy copying from the mathematicians :P

12:33 PM

Hmm, space invaders speed up for each row it advanced closer to the bottom of the screen...(missing thought process to complete the sentence)

@ACuriousMind um, lol?

@BalarkaSen in fact the unitary group of an infinite dimensional Hilb space is contractible.

In very stark contrast to the finite dimensional case

@ACuriousMind do you know what they actually mean?

@Slereah doesn't an acceleration have to start at a definite time, what does it mean for it to happen for t>0?

Well replace $1/t^2$ by some other function of compact support that is unbounded at $0$

Then it's not going to be continuous and I don't trust discontinuous physics.

yeah but does it make sense mathematically, at least

I mean obviously it's not a realistic physical scenario

even worse than Norton's dome

@0celouvsky gotcha

wait. is this not the same as $\varinjlim U(n)$?

12:40 PM

@0celouvsky The mystery is solved by $Y$ having trivial normal bundle and the original paper actually stating that the "inclusion" is only defined up to homotopy (I guess by choosing some non-vanishing normal vector field and perturbing the manifold along it)

@BalarkaSen don't think so, unless that's contractible. Is U(infty) actually a unitary group on some space?

I mean the honest to god unitary group on a separable complex Hilbert space

It's not contractible.

I guess I don't believe that result. In any case, I gotta go.

@BalarkaSen it's on nlab you nonbeliever

You haven't given a reason why your object is the same as mine

@ACuriousMind I'm with you up till the last part

@0celouvsky A vector field generates a diffeo, right? So if I choose a non-vanishing normal vector field and transform $Y$ by the diffeo it generates, I get some $Y'$ that doesn't intersect $Y$ and so lies in $X-Y$. The "inclusion" is the homotopy class of that map (and I'm only interested in the homotopy class because I really only want to know what it does on cohomology)

@ACuriousMind Isnt that vector only

fuck what is up with me hitting send too early

12:55 PM

@0celouvsky Your message could not be parsed. Please try again.

@ACuriousMind the vector field is only defined on Y but I guess you can extend it?

So it's like the gradient flow argument in Morse theory

@ACuriousMind I'm trying to picture how this works for an open disk in the plane

Ugh, take $Y$ to be a closed submanifold of at least codimension 1

I make no claim about open stuff

I mean, the open disk in the plane doesn't even have a normal bundle, does it? (Or rather, it's the zero bundle)

It doesn't

@ACuriousMind jeez

Sorry for asking

Oh, no, it's fine

1:15 PM

I just want a proof of the Maxwell Green function but people keep doing it in E + B formalism

What is that madness

When A is so much easier

Maxwell green function?

Won't that involve some functional analysis

Yes

It's just $$\Box G(x,y) = \delta(x - y)$$

if two opposite charges moving forward each other: in the free fall frame of one of them, is that charge in an inertial frame?

(like the gravity case)

1:30 PM

@Slereah isn't that the dalembert greens function?

See Cahill "physical mathematics" or Zee for the proof

yes

$\delta(r - vt)/r$ or something

Yeah...so what's the issue? You want to see a distributional proof?

a proper proof would be nice yeah

1:50 PM

does anybody know what the $\bar{c}$ in the Faddeev-Popov method means when working in U(1)
Surely it can't be $\gamma_0 c^\dagger$

@gertian It's just a second Graßmann-valued field that's suggestively called $\bar{c}$, but there's no actual relation between $c$ and $\bar{c}$.

Aha i was already suspecting something like that !
But how is one hermitian and the other antihermitian ?

I know you need this for your action to be real but what does it mean ? How do you see it from the path integral

@Slereah I'll see what I can find.

2:09 PM

Howdy

math.berkeley.edu/~sjoh/pdfs/linearWave.pdf

page 11 ff

@ACuriousMind You mean Grassmann.

thx

> By the theorem of Guido Fubini, the closed linear span of the n-fold products

That's got to be a meme

@gertian They're Lie-algebra valued, not complex-valued, so "Hermitian" doesn't really have a meaning for them. I guess the proper statement would be that $c$ transforms in the adjoint and $\bar{c}$ in the conjugate adjoint.

@0celouvsky nope :P

2:26 PM

@ACuriousMind Let $\omega$ be a $C^0$ exact 1-form defined on an open $U\subset\Bbb R^n$. Can $\omega$ be approximated by closed $C^1$ 1-forms uniformly on compact sets?

@ACuriousMind could you elaborate on this ?
Sounds like exaclty what I need but I don't fully understand it.
How does it explain the series expansion in this thread ?
http://physics.stackexchange.com/questions/44250/faddeev-popov-ghost-propagator-in-canonical-quantization

@0celouvsky I know nothing about these sorts of approximations. My stuff is always smooth, even when it isn't ;)

The whole initial value theorem of GR supposes a lot of conditions on the initial data

@gertian Ah, yes, there's a very annoying thing where physicists throw around the operation $\dagger$ without actually having defined it. I'm afraid you'll be better off looking into the reference that answer gives (Kugo) than having me guess what may be meant

Is there any paper on what happens if those are not met?

Like if a metric is insufficiently Solobev

or whatever else

2:33 PM

Note also the comment there that says that Weinberg has both fields Hermitian, so there's additionally an issue with differing conventions

Which is no surprise, really, the factors of $\mathrm{i}$ are always a mess in gauge theory :P

@ACuriousMind : let me help you with $\dagger$ for physicist

@Slereah curvature has no meaning if you

"You just take the transpose and the conjugate!"

holy fuck

Why does my thing keep sending early

@Slereah ::twitches::

2:35 PM

Yeah I saw that comment I may want to check up Weinberg notes as well...
As for the link in the link. THey don't really elaborate on it they just say Proceeding in strict analogy with the B-F oscillator

write out the operator as the infinite matrix ranging over the continuum of values ${a^i}_j$

Sadly I have to go now for half an hour :/
I'll be back asap !

Then $a^\dagger = {a^j}_i^*$

That is the explanation I always get but to identify the space the conjugate transpose lands in with the original space you need to choose an inner product - the identification is not canonical!

heheh

2:36 PM

@ACuriousMind dude just write the matrix elements

<i|A|j>

It's fine for gauge theories where the representations are unitary, I guess.

Just admit that QFT is broke

Although i'm guessing it gets harder to define operators as matrices for like

Weird operators like $T$

(It's not fine for finite-dimensional Lorentz representations, which is where the whole Majorana shenanigans begin :P)

Is it even possible to write $T$ as a matrix

2:38 PM

Sure, $T_{ij}$

(I don't know what $T$ is)

Time inversion

I don't think you can do that

Sure, it's just an anti-unitary matrix.

Wtf is that

Doesn't it do like

$T e^{iHt} = e^{-iHt}$

2:39 PM

How are you going to get an antilinear business with a matrix

Well

Not sure how you'd work it out

it's not a matrix, that's right

you can't even do it as a fake matrix like the momentum operator

I think you can write those as a matrix times the complex conjugation operator, though, since composing an anti-linear map with complex conjugation makes it linear

So...good enough? :P

2:40 PM

yeah I don't think you can break it down completely as a matrix

that's probably the easiest example of an operator where the matrix representation doesn't make sense

@ACuriousMind you can but that's cheating.

Guess I'm a cheetah then. ;) At least I can outrun ocelots.

Wald mentions a formalism of Hilbert space operators in Einstein notation

But it's "unpublished"

that swine

@BernardoMeurer Is it working okay?

@ACuriousMind you can't outrun the colt single action army.

And if you don't get the reference I don't know what to say

@Slereah it should be fairly trivial

Also rather useless

You don't get crazy GR expressions in functional analysis

2:47 PM

@0celouvsky I think I get it :)

Can we republish HE, except with modern notation

@ACuriousMind did you play MGS1?

@Slereah what's wrong now?

I mean seriously, $D/\partial t$ for the parallel transport along a curve?

It's fairly tedious to read

What else do you want it to be

Just the usual

$\nabla_{T}$

Or $\nabla_{\gamma'}$

Or something

it even uses less characters

2:52 PM

Well...the reason is that they're conceptually very different

One is a pullback covariant derivative, and the other isn't

They happen to be equal

But mostly I want to change the basis vectors

$\partial/\partial_t$ is a bit long

Yeah that does get tedious

basically i'm not that fond of having to write derivatives as fractions, if I can avoid it

especially for inline equations

they get very ugly

@0celouvsky more evidence to not believe it >:)

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