The h Bar

Balarka Sen

15:00

I think so. It should be the surface area of the unit sphere.

0celo7

correct

Balarka Sen

Hm, that's the integral $\int_{x^2 + y^2 + z^2 = 1} dx dy dz$

And if I convert it to spherical coordinates I do get that it's $\iint \sin(\varphi) d\theta d\varphi$

So I don't even have to evaluate the integral by hand. OK

So everything boils down to $4\pi \int r^2 f(r) dr$

That's all.

Anonymous

Ya, it's just that weird shaped area of the element $rd\phi$ and $r\sin(\phi)d\theta$. We sum all those weird shaped areas to get surface area of the surface which is $4\pi r^2$

Anonymous

So, yes, it makes sense now!

Anonymous

Anonymous

15:05

Balarka Sen

Weird shaped area? No it's not, you just pull a tiny piece of the surface of the unit sphere back to standard coordinates using spherical parametrization

Anonymous

@BalarkaSen Yeah, that's what I called "weird shaped" :P

Anonymous

I think I get it now

Anonymous

Thanks a lot

Balarka Sen

You made me recall spherical parametrization and compute it's Jacobian. I hope you have those $5000 prepared to be paypal-ed

Anonymous

15:09

@BalarkaSen You can come one night and rob our house. I give you permission

Anonymous

You won't find anything expensive here though =P

Balarka Sen

I live in Stalingrad. I am a Russian thug

Anonymous

Uh oh. Then you need to buy the plane tickets yourself :P

0celo7

just drive

it's not that far

Anonymous

Or just swim

Anonymous

15:11

and walk

0celo7

swim?

do you need a geography lesson?

Balarka Sen

Can't, I'm in 1950's. That's why I called Volgograd as Stalingrad.

Anonymous

I never mentioned "shortest route" ;)

Balarka Sen

India is barely Independent

Leaky Nun

Come on, flagging political statements?

where is the freedom of speech

Balarka Sen

15:14

What was flagged?

Leaky Nun

@BalarkaSen "India is barely Independent"

Balarka Sen

lmao

that was a time machine joke

Anonymous

Freedom of speech is not a part of SE culture XD

Balarka Sen

India achieved independence in 1947

I am in 1950

Anonymous

Even that will be flagged now ^

0celo7

15:16

what was flagged?

John Rennie

→ 1 message moved to trash

Leaky Nun

@Blue that is flagged now

John Rennie

That was unnecessarily provocative

0celo7

lol Balarka

Anonymous

I will convert my messages to a combination of binary, octal and hexadecimal to avoid it getting flagged from now on.

Anonymous

15:18

Perhaps even then...

heather

let us move on.

Mithrandir24601

@Blue 01001001 01110011 00100000 01101001 01110100 00100000 01110010 01100101 01100001 01101100 01101100 01111001 00100000 01110111 01101111 01110010 01110100 01101000 00100000 01100100 01101111 01101001 01101110 01100111 00100000 01110100 01101000 01100001 01110100 00111111

Captain Bohemian

is renormalization group a good technique?

John Rennie

@Mithrandir24601 the temptation to convert that to ascii is strong, but ... well ... not that strong :-)

Mithrandir24601

15:33

@JohnRennie That is ASCII, or do you mean 'convert from ASCII'?

Or am I totally missing the point of what you just said?

0celo7

@Mithrandir24601 Not really

John Rennie

@Mithrandir24601 01000100 01101111 01101110 00100111 01110100 00100000 01100010 01100101 00100000 01110000 01100101 01100100 01100001 01101110 01110100 01101001 01100011

Anonymous

@Mithrandir24601 01011001 01100101 01100001 01101000 00101100 00100000 01110111 01100101 00100111 01110010 01100101 00100000 01100011 01100101 01110010 01110100 01101001 01100110 01101001 01100101 01100100 00100000 01101110 01110101 01110100 01110011 00100000 01101110 01101111 01110111 00101110

Mithrandir24601

@JohnRennie But how can you not be pedantic when working in binary? :P

@Blue 01001001 00100000 01110100 01101000 01101111 01110101 01100111 01101000 01110100 00100000 01110100 01101000 01100001 01110100 00100000 01110111 01100001 01110011 00100000 01101111 01100010 01110110 01101001 01101111 01110101 01110011 00100000 01111001 01100101 01100001 01110010 01110011 00100000 01100001 01100111 01101111 00111111

0celo7

oh crap I forgot about the Teriyaki

I have to go buy the sauce

lılostafa

15:43

----- .---- ----- .---- ----- .---- .---- .---- ----- .---- ----- .---- ----- .---- ----- ----- ----- .---- ----- ----- ----- .---- .---- -----

Anonymous

@lılostafa !^^^^#@##!22332!!%

Slereah

So I just realized that I have a Klein bottle shaped mug and that I haven't used it in years

Non-orientable goodness

heather

@Mithrandir24601 01010100 01101000 01101001 01110011 00100000 01100011 01101111 01101110 01110110 01100101 01110010 01110011 01100001 01110100 01101001 01101111 01101110 00100000 01101001 01110011 00100000 01101000 01101001 01101100 01100001 01110010 01101001 01101111 01110101 01110011

Slereah

@CaptainBohemian a good technique for what

Anonymous

@Slereah 01100011 01110101 01110100 01100101 00100000 00111101 01010000

Balarka Sen

15:51

@JohnRennie Well, I think it was unintelligent on part of the flagger - if the flag was genuine - to get hashtag triggered at the statement, especially because it was not a political statement, but just a joke (I feel it is in part because of historical illiteracy). I was dwindling between lack of intelligence and simply troll-flagging, but since my message got flagged even after it was sent to the trash, I am thereby forced to conclude that it is troll.

Captain Bohemian

for quantum gravity, which is my biggest interest, and also for quantum field theory, some parts of which interest me.

Slereah

Well yes, you are gonna need renormalization groups for that

Balarka Sen

Notice that my message was not directly meant to be publicly offensive at anyone, since the flag system keeps the flagger anonymous. But I wrote what I believed, not to provoke anyone. That's an unfortunate side effect.

Slereah

Well

Mithrandir24601

@heather 00111010 01000100

Slereah

15:53

You don't necessarily need renormalization for quantum gravity

it depends on what quantum gravity you're doing

but as Motl will tell you only losers do quantum gravity with a discrete spacetime

Captain Bohemian

@Slereah my original interest is for asymptotically safe gravity, but if I can't find a position for it, I may consider quantum field theory.

0celo7

@BalarkaSen calling someone a troll is grounds for flagging

Anonymous

So, there's some good news. A professor at my uni (physics department) has agreed to teach me mathematical physics. I'm excited.

Anonymous

It's a bit difficult to self-learn these stuff. So atleast that'll keep me focused

Slereah

I'm sure @0celo7 will have strong opinions on the mathematics dispensed

heather

15:55

@Mithrandir24601 01101000 01101111 01110111 00100000 01101000 01100001 01110110 01100101 00100000 01111001 01101111 01110101 00100000 01100010 01100101 01100101 01101110 00111111

Balarka Sen

@0celo7 Unfortunate, because I am going to call trolls out if I feel they are so.

@Blue That's pretty cool

Captain Bohemian

@Slereah I worked on general relativity in my MSc, but there are not many research groups in classical gravity.

Slereah

yeah it's pretty rare

Anonymous

@BalarkaSen I was quite surprised to know that he has a PhD (in particle physics) from Cambridge but is teaching in JU. Weird guy

Slereah

especially if you're not doing experimental stuff

Balarka Sen

15:57

@Blue Oh wow

Slereah

These days people only want GR for gravitational waves and cosmology

0celo7

@Blue Mathematicians and physicists use the term "mathematical physics" differently

What is he teaching you?

Anonymous

@BalarkaSen This prof

Anonymous

@0celo7 He said he'll teach QM,GR, QFT etc

Anonymous

Whatever I want to learn

Anonymous

15:59

But he is very busy

Anonymous

So he won't give me much time

Anonymous

But that's okay

Anonymous

I just need some guidance

Mithrandir24601

@heather Not too great, unfortunately :/ I've currently got what I'm hoping is an infection and have just started on a course of antibiotics, so I'm coughing quite a bit, have a sore throat (especially when swallowing), am short of breath in the evening, keep wakening up at night (fortunately not short of breath, otherwise I'd have to go to hospital), had a massive rash the whole of yesterday and so, haven't been that great for the past few days, but am hopefully improving

(I'm not as bad today as I was yesterday)

Slereah

@Blue That's not math, that's all physics!

heather

16:01

@Mithrandir24601 ick, I'm sorry! hope you start to feel better.

Captain Bohemian

@Slereah but my MSc isn't regarding gravitational waves and cosmology. It's some formaulations. I am actually only intetested in the formulations in gravitational wave, not the way of actually detecting it.

Slereah

What's your master on?

Anonymous

@Slereah Well, that's what I need :P He also said he'll help with the necessary math. I'll visit him on Monday. Let's see how it turns out

Balarka Sen

@Blue lmao he's a coauthor of Indranil Biswas

Slereah

You can also ask here

Mithrandir24601

16:01

@heather Yeah, hopefully should be at least a bit better by Monday, thanks :) If not, then the GP's going to have to figure out what to do with me...

Anonymous

@BalarkaSen Who's that?

Slereah

There's enough GR and QFT people to help

Anonymous

Anyone famous?

Balarka Sen

@Mithrandir24601 This sucks

Anonymous

Indranil Biswas

Indranil Biswas (born 19 October 1964) is an Indian mathematician. He is professor of mathematics at the Tata Institute of Fundamental Research, Mumbai. He is known for his work in the areas of algebraic geometry, differential geometry, and deformation quantization. In 2006, the Government of India awarded him the Shanti Swarup Bhatnagar Prize in mathematical sciences for his contributions to "algebraic geometry, centering around moduli problems of vector bundles." == Biography == Biswas is an Indian citizen. He received a Ph.D. in mathematics from the University of Mumbai. == Selected ...

Mithrandir24601

16:02

@BalarkaSen Welcome to my life :P

Anonymous

Oh

Anonymous

Nice

Balarka Sen

@Blue Oh man he's an algebraic geometer in TIFR

that guy writes a million papers a week

just look up his name in arxiv

Anonymous

@BalarkaSen Woah. Lol

Slereah

@BalarkaSen PUBLISH OR PERISH

Anonymous

16:03

I'm lucky then =P

Slereah

I'm guessing the university dean holds him at gunpoint in his office

Anonymous

I basically wrote to him the woes of an engineering student who wants to study physics XD. He melted and gave in :P

Balarka Sen

@Slereah I dunno man but he writes so fucking much

HsMjstyMstdn

@Slereah Kaczynski reference ?

Slereah

No, that's just a common academical saying

My Kaczynski joke is the usual

Captain Bohemian

16:06

@Slereah I just saw an open position in PhD in strong coupled quantum field theory by renormalization group and Monte-Carlo simulations. I am not sure if that's position suitable for me. That's why I asked if renormalization group is a good technique.

Slereah

The usual Kaczynski joke

Balarka Sen

@Blue arxiv.org:443/find/grp_math/1/au:+Biswas_Indranil/0/1/0/all/0/1

@Slereah lmao

Slereah

that is what the humanities people refer to as a euphemism

HsMjstyMstdn

Hahaha

Anonymous

@BalarkaSen Soooo many papers XD

Slereah

16:07

@CaptainBohemian Sounds interesting enough

Balarka Sen

@Blue I clicked "Next 25" five times now

I give up

Anonymous

Me too

Anonymous

Klelk

Slereah

I tried reading Kaczynski's papers but it was in a field I really didn't care for

Balarka Sen

its in complex analysis right

Captain Bohemian

16:08

@Slereah what? but I feel they want to recruit someone to do nonanalytical work.

Slereah

The beamsplitters have arrived

Hurray

now I just need thems lasers

I hope they send it

it feels pretty fishy

Balarka Sen

For a moment I read it as "The unabombs have arrived"

Slereah

Sorry, my terrorism is laser based

I'm gonna blow up the white house with a giant laser, Independance Day style

3

Anonymous

Flags incoming

Balarka Sen

lololol

Slereah

16:13

It's a 250 mW laser so it might take a while

One thing I need to do is to build some metal arms for the interferometer

There's some metal arms at the local hardware store but they don't seem to have like metal things to hold onto it

Not sure of the name

Like you have a square metal beam and then a little square metal thing to slide onto it

with a screw to hold in place

I am not great at english words for hardware

HsMjstyMstdn

...

Do you mean a long, thin metal rectangle that has a sleeve it can slide into and a screw to lock the sleeve in place ?

Slereah

yes

Anonymous

16:30

@0celo7 I found his RG profile just now. Looks more of a math guy

Anonymous

So, I hope he'll be rigorous :)

Slereah

Don't hope for rigor

Rigorous math is awful for physics

Do you really want to have to worry about the domain definition of the Hilbert space operators

0celo7

He's an algebraic geometer

Anonymous

@Slereah I do want to. I don't want to be illiterate

Anonymous

Just that life is too short to learn everything :P

0celo7

16:32

Life is too short to be an analyst @Blue. Learn from my mistakes

Anonymous

I will have an engineering degree anyway =P I can fall back on that. You too can make bombs and earn money

Anonymous

You're a nuclear engineer

Anonymous

Rest of the time I'll spend learning those math stuff

Anonymous

Lol

Slereah

nerd

0celo7

16:34

@BalarkaSen Jesus. Are these meme papers?

Slereah

Some researchers just do minimal variations on the same paper

2

0celo7

He isn't single author on any of those

Does he just slap his name on everything?

Balarka Sen

@0celo7 hehehe

Slereah

So that they can show that they published a whole bunch of papers for more money

Look at me

i'm a valuable asset of your university

Balarka Sen

No, not really. He actually spends 24/7 thinking math.

I have seen that guy. He's crazy

Anonymous

16:36

@BalarkaSen Where? Workshop?

Balarka Sen

I was in TIFR for a month or so

HsMjstyMstdn

@Slereah YES

Anonymous

@BalarkaSen For what? Research?

Balarka Sen

Nah, learning algebraic geometry

TIFR is a fort of algebraic geometers

Anonymous

I mean how did you get a call? Personal contacts?

Anonymous

16:38

Strange that they called a high schooler at TIFR. It's RARE

Balarka Sen

@Blue Well no someone whom I knew invited me after becoming a faculty there

Anonymous

@BalarkaSen I see. Awesome contacts you have =P

Balarka Sen

meh tbh i didn't enjoy my time there

it was all algebra

0celo7

@BalarkaSen teach me algebraic geometry

Anonymous

@BalarkaSen Umm, didn't you say you want to do your PhD there?

Balarka Sen

16:51

@0celo7 So, suppose you have a ring $R$ and look at $\text{Spec} R$ with the structure sheaf

That's an affine scheme

0celo7

what is Spec R?

brb gotta eat

Balarka Sen

you don't want to know

you just want to know it's an affine scheme

that's all

@Blue I do

0celo7

@BalarkaSen I am currently worrying about decay rates in weighted Sobolev spaces. I can handle whatever mess you throw at me

Balarka Sen

It's a nice place; you get nice food there.

Anonymous

@BalarkaSen Lol. Food is a good reason to join that place

Anonymous

16:53

Plus it's Mumbai

Balarka Sen

I don't like Mumbai

Anonymous

You can direct some Math-based Bollywood movies

2

Balarka Sen

lmao

Anonymous

Actually someone should do that

Anonymous

Mainstream movies are meh

Balarka Sen

16:56

dude i need to watch the movies this math major shane carruth made

apparently they are hippie as hell

he directs, produces, writes, composes and acts on all his movies

Anonymous

@BalarkaSen 0o

Balarka Sen

@Blue I can recommend you some Bengali hipster films but maybe I shouldn't

well, at least, directed and acted by Bengalis

Anonymous

I'm procrastinating a lot nowadays...so maybe you shouldn't X'D

Balarka Sen

procrastination is good, but that was not my concern

google "director Q"

Anonymous

17:05

Hippie...I don't even doubt that

Balarka Sen

lol

a lot of the people who are into underground films love him but i kinda think he's boring

he's just making Indian movies based off of the schlocky 60's American movies

Tarantinoesque, I guess

Semiclassical

bolly-sploitation?

Balarka Sen

exactly

0celo7

@b So what is Spec R?

Balarka Sen

@0 as a set, it's just the collection of prime ideals of R

but it can be given a topology

0celo7

17:14

prime ideal?

Balarka Sen

an ideal I of R is prime if ab \in I implies a \in I or b \in I

(6) is not a prime ideal of Z, but (2) is

0celo7

hm, ok

why does one care about those things?

Balarka Sen

which things

prime ideals?

0celo7

ye

Balarka Sen

if X is an algebraic variety in k^n, i.e., cut out by polynomials f_i(x_1, ..., x_n) = 0 for i = 1, ..., m, then X is called irreducible if it cannot be written as union of multiple varieties. If I is an ideal of k[x1, ..., xn] consisting of polynomials vanishing on X, then I is prime

so prime ideals are like irreducible algebraic varieties

0celo7

17:22

@BalarkaSen If I don't care about varieties, will I care about algebraic geometry?

Balarka Sen

prolly not

but it does make me question about the world if people does not care about zero sets of polynomials

0celo7

Really?

I think they're uninteresting

I imagine most analysts feel the same

Balarka Sen

i respect that but find it hard to imagine how they can be uninteresting

i understand everyone has different tastes

0celo7

I don't dislike it, I just don't like it

Balarka Sen

ah ok

That clarifies

Anonymous

17:26

@BalarkaSen The set of original movies and bollywood/tollywood movies are mutually exclusive. That's a law of nature.

0celo7

@BalarkaSen My anecdotal view is that hardcore analysts are indifferent towards abstract algebra, but hardcore algebraists genuinely dislike analysis

I am not including people who cross the line in there

Balarka Sen

@Blue Well Q is not Bollywood, he's an independent filmmaker.

But I still find him boring

@0celo7 Hm, could be true

I have only majorly interacted with the community who lie in between those extremeties

0celo7

@BalarkaSen My rep theory class is mostly hardcore algebraists

Balarka Sen

I was genuinely surprised when a person whom I knew as a dynamical analyst piped up a conversation about sheaf cohomology in the middle of a talk

Incidentally that's the same person I am learning ODEs and dynamics from now

0celo7

Like number theorists and combinatorialists

speaking of, I have more god-awful algebra homework

Balarka Sen

17:31

I think number theory is not really hardcore algebra but it's difficult to draw the line

0celo7

algebraists love examples

what is up with that

@BalarkaSen We have a dynamical systems guy who is a wizard at most things

I was talking to him about some functional analysis thing and he ended up writing heat kernel asymptotics from memory

Semiclassical

daaang

Balarka Sen

how the heck does that even work

0celo7

@BalarkaSen It was about Sobolev spaces

This was a year or so ago before I knew this stuff well

And he explained to me how i could derive what I wanted without Sobolev.

Semiclassical

I should probably know what a Sobolev space actually is

0celo7

17:37

Heat kernel asymptotics can be derived 3 ways from sunday

Semiclassical

there's usually a number of different ways to obtain asymptotics in general.

though some are easier to develop further than others.

0celo7

The cleverest way is the old Indian method

The most common anymore is the $\psi$do method because it's so general

@Semiclassical Do you want me to tell you?

Semiclassical

sure

0celo7

$H^1(\Bbb R)$ is easy enough

@Semiclassical So you start with $L^2$ (all on $\Bbb R$) and wonder what it means for an $L^2$ function to have a derivative

Semiclassical

Am I right to think this has something to do with "can i integrate by parts and ignore the boundary term?"

0celo7

17:41

Yeah. So any distribution has a derivative via the rule $$T'(\varphi)=T(\varphi')$$ for $\varphi\in C_c^\infty$

Semiclassical

What's T here?

Slereah

Don't u mean $-T(\varphi')$

0celo7

But $T'$ might actually be some bad object. Classic example being the step function, for which $T'$ is the Dirac measure

@Semiclassical A distribution

Semiclassical

mkay

then i'll second Slereah's point re: the minus

0celo7

@Semiclassical Any $L^2$ function defines a distribution via integration

Balarka Sen

17:42

convolution right

0celo7

@Semiclassical meh, it's just a sign

Semiclassical

lol

0celo7

@BalarkaSen No, literally $$T_f(\varphi)=\int f\varphi \, dx$$

Balarka Sen

ah ok

Slereah

@0celo7 do you want me to give you -1000$

0celo7

17:43

@Semiclassical the point is that you want to generalize integration by parts somehow

Semiclassical

right.

and you want to be able to work in settings where that integration by parts doesn't generate a boundary term

0celo7

Yeah. I think that sign is a convention

I'm double checking

Semiclassical

hm

in integration by parts, it's not a convention

it's a consequence of $u\,dv = d(uv)-v\,du$

0celo7

The distributional derivative is just the negative of the usual one then

Confusing, but less signs

I might be wrong, one sec

Ok, everyone uses a minus. Whatever

@Semiclassical So back to the step function. The distributional derivative of the step function is not a function.

Semiclassical

right.

Balarka Sen

17:46

the evil within 2 came out weee

hell ya man

0celo7

@Semiclassical Well we can require that the distributional derivative is itself in $L^2$.

So that means it's a function and the derivative doesn't get too wild.

Semiclassical

actually, have to go for now

back in a bit

0celo7

k

@Slereah so did you get MTW?

Slereah

Not yet

Lemme check the package tracking

It hasn't been shipped yet

Lazy bums

0celo7

18:03

did you buy it used?

Or do you not have amazon prime

Slereah

I bought the spanking new one

It says that it should arrive between the 25th and the 11th

So I guess I can't even bitch yet

0celo7

18:47

when citing a title that doesn't capitalize stuff, should one fix the capitalization or leave it as in the source?

bolbteppa

Obviously supersymmetry in 4-D is just the Wigner-Inonu contraction of the orthosymplectic algebra's isomorphic representation as an anti-deSitter algebra

Slereah

I'd cite it as is

Urgh, the orthosymplectic group

Semiclassical

@0celo7 back

bolbteppa

Now it's Urgh, the superconformal group...

Semiclassical

"ugh, super-shit"

bolbteppa

19:02

Why would 'nature' do this to us:

Superconformal algebra

In theoretical physics, the superconformal algebra is a graded Lie algebra or superalgebra that combines the conformal algebra and supersymmetry. In two dimensions, the superconformal algebra is infinite-dimensional. In higher dimensions, superconformal algebras are finite-dimensional and generate the superconformal group (in two Euclidean dimensions, the Lie superalgebra does not generate any Lie supergroup). == Superconformal algebra in dimension greater than 2 == The conformal group of the ( p + q ) {\displaystyle (p+q)...

Semiclassical

@0celo7 hmm, this answer seems appealing: math.stackexchange.com/a/453159/137524

Physics Meta

0

Q: Ping/Reference a user in the core text of a question

One more question. Is it OK to reference a particular user in the text of a question (right at the end of the post with an @), just to be sure that that user gets to read my question (he receives an inbox message, I believe) and increase the chances to extract a thorough answer from him/her? It i...

bolbteppa

Why is $dx^2 + dy^2 + dz^2 - dt^2 + dw^2 = r^2$, with $|w| \sim r$, infinite in the time direction, and finite in the spatial directions, while $dx^2 + dy^2 + dz^2 - dt^2 - dw^2 = - r^2$ is finite in the time direction, and infinite in the spatial directions?

sbp

19:59

Hey a question asks that a mass $M$ slides along a wire defined by $z = 2(x^2 + y^2)$. The wire rotates with angular velocity $\Omega$ about the z-axis. Now it asks that for what value of gravity $g$ acting along negative z-axis does the mass maintain a constant nonzero height.

Slereah

@bolbteppa I think it's because t and w have the same sign

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