The h Bar

College street is, like, a data dump of books.

user228700

@blue Ah, well, whichever.

10:09 AM

Hey @BalarkaSen

mystical greetings

Anonymous

@BalarkaSen Ya, but very cheap prices too :D

What makes them mystical

Are you wearing a cape

and a mask

user228700

For all we know, probably!

Anonymous

I used to get Rs.500 books at only Rs.100 sometimes.

10:10 AM

"m" in the word "mystical" stands for "mystical".

that's the main reason, really

@blue Oh yeah it's a great place

So

mysticalystical

ad inf

m(ystical)*

maybe i killed the chat with mysticism

@blue over

Anonymous

10:15 AM

@Yashas You got selected ? :)

I don't get the results so soon

I am still skeptical about their program

Anonymous

Anyway, how was the interview ?

they asked one physics question

oh btw did you people do well in JEE

Anonymous

I've heard that IIITH is great for Computer Science

10:16 AM

I never gave the answer which they wanted

the guy asked me to figure out how the force acts when two wires are placed close to each other

I was doing the math part

field and everything else

at the end, he disclosed that he wanted me to tell that wires behave like magnets -_-

Anonymous

@Yashas Which program?

Anonymous

@Yashas :O

he wanted a simple answer lol

iiit.ac.in/academics/curriculum/undergraduate/cnd

I want to get into IIT Kanpur somehow

they have a double major system

I want Physics + CS :/

hello, nice :)

Anonymous

Wow, that course is like a combo of CS+maths+phy+chem+bio :P

Anonymous

10:19 AM

Not bad if you want to pursue CS in future but bad if you want to pursue physics

user228700

@Yashas They have the same thing at BITS, ya know...

I am allergic to BITS

Anonymous

Me too ^

user228700

Why?

Their admissions is a crapshoot

Anonymous

10:20 AM

After giving BITSAT I lost all interest in BITS. Haven't ever seen a more stupid exam than that

Anonymous

15 days * 3 times a day

user228700

@Yashas Will u please elaborate?

Anonymous

All separate papers

Anonymous

The most biased test ever

@Kaumudi.H different papers for different students

Anonymous

10:20 AM

Plus english and logical reasoning...meh

you'll know when your dumb classmate gets 420 and you get 360

user228700

@Yashas Well, at least there is no reservation system. JEE is more biased than BITS in this regard; besides, if ur "dumb" classmate got 420, he may not be as dumb as u think he is...

Anonymous

Also, it is too costly for me...

they also offer a seat for board toppers lol

that is the funniest thing I have heard

Anonymous

@Yashas yeah :P

10:21 AM

in the end

it only matters what you end up doing

in the end nothing matters yo

yes

sort of

it matters!

@blue well, actually they aren't that good. But, they still manage.

Anonymous

"we will die anyway" ~Balarka Sen [2017]

10:23 AM

I want the B.Sc + M.Sc Physics course at IITK with CS as second major.

Everyone dies!

but that becomes 3 degrees! -_-

which isn't allowed

@blue haha; but why not live the best life practically possible?

There is no just B.Sc course in Physics

user228700

@blue True, it's pretty costly.

10:23 AM

or at least try to

Anonymous

@Yashas Kanpur offers 4 years BS in Physics with CS as minor

I need both CS + Physics as major -_-

BITSAT is crap.

Anonymous

@Yashas Not possible other than BITs...

@blue possible in IITK!

IIT Madras offers 50% as electives :O

10:24 AM

@SBM a most consistent endeavor

Anonymous

@Yashas No, they won't give you a double major in any IIT. Where did you read that?

@blue iitk.ac.in/ee/double-major-program

@BalarkaSen doesn't mean you'd be Socrates if you enjoy studying

user228700

@Sid Why is everyone so biased toward JEE? Sure, yeah, BITSAT has several different papers but in the end, no matter what kind of paper you get, the level of the questions is going to be relatively unchanged. Besides, like I said before, it's not like JEE is oh so pure in this regard! Reservation for castes still exists.

@ACuriousMind The field $X$ in the Polyakov action is the differential of the embedding, right?

10:27 AM

@Kaumudi.H "the level of the questions is going to be relatively unchanged" is not true

JEE reservation is nonsense

@Slereah What should it be the "differential"?`The $X$ is just the embedding itself.

those who get into IITs through reservation attend coaching

the really deserving students never make it to IIT

@ACuriousMind What if it's not Minkowski space, though

Anonymous

@Yashas "Double Major is a program where you can earn a second major on your degree.
However, second major is **not equivalent to a second degree as the major**
requirements are significantly less than those of a second degree. "

You can't have a product of two spacetime points

Anonymous

10:28 AM

That's essentially a minor (with a different name :P)

@blue The degree will be B.Tech in XXXX with YYY as second major

:(

user228700

@Yashas ...what are u getting at, exactly?

Nope nope nope. You choose students based on a single exam. Not 50 different exams.

@Kaumudi.H the students who are economically backward and need the reservation system to help them out won't get help through the system

those who get in using the reservation system are smart people who could afford coaching

10:29 AM

@Slereah Then you need a more general version of the Polyakov action.

Anonymous

@Yashas Don't know how "second major" is different from "minor" as offered by some other old iits like kgp and madras and roorkee

I should wait for my rank

IIT Kanpur Physics is too hard to get

need a rank around 3k

user228700

@Yashas And how are u so sure of this?

is the JEE rank not out yet on your end

Anonymous

@Yashas branch change dude..

10:30 AM

@Kaumudi.H I have classmates who are 10x richer than me but are in the reserved category

@blue what if I fail to get branch changed?

@ACuriousMind What would that version be?

user228700

@Yashas So what? That doesn't indicate anything about the larger population of the whole country.

@Kaumudi.H The trend is somewhat similar. Those who got coaching are obviously going to outperform those who don't.

Some guy might get lucky and get questions from his strong chapters in BITSAT while some other poor chap gets questions from his not-so-strong chapters. In the end, it becomes a game of luck.

@Slereah Well, observe that the $\partial_\mu X_\nu \partial^\mu X^\mu$ could be indeed expressed in coordinate-free notation as $g(\mathrm{d}X,\mathrm{d}X)$.

Anonymous

10:31 AM

@Yashas If you take the risk you might fail, but if you don't take the risk you'll definitely not be able to reach there. Anyhow, don't stick to one specific subject at one college. Always look out for the best option.

So indeed the differential of the embedding

IIT KGP has a low cutoff for Physics

user228700

@Sid ...you do realise that this could very well be the case for people sitting the same exam as well, yes?

Where the $g$ is a mixture of norms on the source and the target, actually

My order is IIT Kanpur > IIT Madras > IIT KGP

user228700

10:32 AM

> the trend is somewhat similar

If I fail to get at least in IIT KGP, I am going to go mad.

Anonymous

Make a chart of preference for ranks like 3k,3.5k,4k,4.5k,5k,....

@yashas don't agree. I have done reasonably better than a few of my friends who rushed to coaching.

I have seen $$g_{\mu\nu} \gamma^{ab} \partial_a X^\mu \partial_b X^\nu$$ used, yeah

Hence why I suspected that it was the differential

user228700

I disagree. I'm willing to be convinced otherwise, if u have data supporting this claim...

10:32 AM

Well, that kinetic term is the differential. You asked me whether the $X$ is the differential, which it is not :P

@Sid I was talking about those in the reservation category. Those who are economically backward and cannot afford coaching or something similar are going to have a hard time beating those who get those.

@ACuriousMind $X^\mu$ would be, though, no?

user228700

@Yashas Ah, put that way, I see ur point.

@Slereah No, $X^\mu$ is just a component of the embedding in local coordinates of the target.

to put in a nutshell, the people who belong to the reserved category and make it to IIT are the rich ones

10:35 AM

But $g_{\mu\nu} X^\mu X^\nu$ doesn't make sense

user228700

@Yashas Right, but however that comes about, reservation is still there.

hm, wait a moment @Slereah

I need to think more carefully

I mean maybe there are different conventions

user228700

...even the rich kids don't have to score too much to outperform those who couldn't afford coaching.

But it seems that maybe they use $X^\mu = dX$, if you call the embedding $X$

10:36 AM

hi kids

user228700

I fail to understand this argument about luck being a bigger factor in BITSAT. Luck will be a factor in any exam, even when it's everyone writing just one exam.

Well, everyone on SE>13. So, no one's a kid here.

user228700

@Avantgarde Hey :-)

@Kaumudi.H true. But you can't complain if there is a single exam.

:)

user228700

10:38 AM

Lol, that's not a particularly sound argument against BITSAT, then.

Also using a notation that only makes sense in Minkowski space strikes me as odd for quantum gravity :p

@Slereah No, the $X^\mu$ is just the embedding. Just compare this to how a physicists writes the action for a worldline - where you have the embedding $x$ and the mathematician writes $\sqrt{g(\dot{x},\dot{x})}$, the physicist writes $\sqrt{g_{\mu\nu} \dot{x}^\mu \dot{x}^\nu}$. This is no different, just with two instead of one derivative

Anonymous

@Kaumudi.H BITSAT is biased in the sense that there is a different paper for everybody (15*3=45 papers) which are computer generated. Someone's paper might be radically easier than someone else's. I agree that IITs have reservation. But mostly those join BITs are the ones who didn't get a seat (in their desired stream) at IITs (evident from their ranks). So atleast 50 percent of the peer group at IITs will be better than the peer group you'll get at BITs.

What's the protein and its structure which is found in the wool of a sheep? Come back when even NEET asks such type of awful questions.

To the physicst, the $x^\mu$ is the embedding, although of course $\dot{x}^\mu$ is a tangent vector.

So in this case, you have two different tangent vectors, $\partial_1 X^\mu$ and $\partial_2 X^\mu$

10:41 AM

My issue is this: " Students pursuing a Dual Major will not be allowed to pursue a minor or dual degree. "

I can't do Integrated M.Sc Physics with CS becaz that wud become 3 degrees

Anonymous

Personally none of the above matters to me. I just don't want to cough up a ridiculously large amount for my undergraduate studies.

But the $X^\mu$ itself would still be the embedding in local coordinates. The notation is somewhat confusing, but that is not special to string theory, it's how physicsts do diff. geo. :P

user228700

@blue I'm not arguing that the BITS as an institution is better than any IIT; that would be an unreasonable argument. I am only advocating for the fact that BITSAT, the examination is only as randomised as JEE.

@blue I don't understand the terminology "biased" for this. Biased, in probability, means a random variable has more probability to take certain a value than another. Did you mean it's too randomized, instead? :P

Soooo what would the the Polyakov action in curved space then?

Anonymous

10:43 AM

@BalarkaSen Biased in the sense that some people get very easy papers while some get much tougher papers. But the marks cut offs remain the same for all.

@blue Nobody knows how hard or easy their paper is before getting it on the test.

I don't understand how biased applies.

user228700

@BalarkaSen Edited, thanks :-)

random exams; scary

I agree with the randomization point and the scare factor.

But I'll be a pedant on terminologies.

@Slereah Perhaps the clearest way to think about this is this: You have the map $X : \Sigma \to M$ and its derivative $\mathrm{d}X : TX \to TM$. The Polyakov action is $\int_\Sigma \lvert \mathrm{d}X\rvert^2$. In local coordinates, $\mathrm{d}X$ is a $2\times 10$ matrix whose components we write as $(\mathrm{d}X)_{a\mu} = \partial_a X_\mu$

The r.h.s. is here just notation - do not try to interpret the $X_\mu$ alone.

10:45 AM

@ACuriousMind Polyakov action?

@blue tbh, I want a degree in physics, math, CS and EE :v

@SBM Polyakov action.

Polyakov action

(If you meant to ask a more specific question about it, please actually ask a more specific question :P)

lol

10:46 AM

@Yashas I doubt if that's sufficient

user228700

@Yashas What...what are u going to specialize in, then?

Anonymous

@BalarkaSen Suppose the cut off for Physics stream at BITs Pilani is 50 marks out of 100. Now, in my physics paper for example there were 10 questions (out of 40) only on current electricity! We have around 30 chapters in syllabus. Suppose I didn't prepare well for current electricity, but prepared well for most other chapters. On the other hand someone gets 30 percent of the total questions from their strong topic, they will obviously perform better.

:379647 CS & Physics

Anonymous

The paper is biased in the sense that equal or nearly equal weightage is not given to all topics and also one paper is not common for all

JEE pattern is predictable whereas BITSAT gives random Q.

Anonymous

10:48 AM

Perhaps I should some other word in place of "biased" to convey the message better

user228700

@blue In which exam is nearly equal weightage given to all the chapters?!

There are so called 'important' topics in JEE

Anonymous

@Kaumudi.H In all engineering exams other than BITSAT

Anonymous

I got 10 questions only from current electricity

Anonymous

Out of 40

10:48 AM

@blue I understand the situation, but this is not what "biased" means. Does it announce beforehand that they will contain more questions from a specific chapter instead of others? Does it announce beforehand that they will give more marks to the dumb people? No. So it's not biased :P

It's much too randomized, that's all.

user228700

@blue That's just...not a true statement.

Anonymous

@BalarkaSen Yeah, I think that is a better word to use

You just don't know the proportion of questions coming from the various chapters. That... can be a bit hard.

user228700

Does JEE really give equal importance to semiconductors and say, rotational dynamics?

For preparation, mostly. And then the student-to-student variation has a hate factor, which is bad for health (TM)

Anonymous

10:50 AM

@Kaumudi.H focus on the word "nearly"

Anonymous

BITSAT has more than 50 percent deviations in chapter wise weightages

Anonymous

JEE has less than 10 percent deviation

@Kaumudi.H I had ZERO questions from Modern Physics. I understand if the chapter was laws of motion or units, dimensions. But, zero from modern physics makes no sense.

user228700

Nearly?! The number of questions from those two chapters aren't even nearly the same!

user228700

@Sid Wut? Did u really? That's unsettling...

10:52 AM

@Kaumudi.H semiconductors isn't there for JEE Advanced and questions from rotational dynamics covers Newton's laws of motion, kinetmatics, etc.

Anonymous

Okay, let me show you a graph.

Anonymous

Anonymous

This was the 2016 mains paper ^

user228700

Wtf, my experience was completely different and I figured that it would've been the same for most people because BITS actually releases the weightage for each chapter.

Anonymous

You'll not find more than 10 percent deviation in the chapter-wise weightages

10:53 AM

@Slereah Actually, string theory in a curved background is a bit more complicated: If you take the general action in a curved background and expand the metric around the flat metric, the additional term you get in the string S-matrix looks like the insertion operator for gravitons. This motivated people to also include other massless stringy excitations into the background on the target, leading to the notion of the Kalb-Ramond field and the dilaton.

Anonymous

In BITSAT there can be more than 50 percent deviation!

Blue Oyster Cult: Monsters

►

user228700

@blue ...that's wow, I see. I was under the impression that BITSAT actually follows the weightage pattern that it releases.

user228700

@Yashas Hmm, yes, you're right.

@ACuriousMind Isn't that equivalent to $g_{\mu\nu} \partial_a dX^\mu \partial_b dX^\nu$?

10:55 AM

@Slereah What is $\mathrm{d}X^\mu$?

Components of $dX$

user228700

Anyway, I see ur point about ~~bias~~ randomization; I wasn't aware that BITSAT doesn't follow its own weightage pattern.

But $\mathrm{d}X$ is a matrix!

Ah, true

That's why I said we just "write" its components as $\partial_a X_\mu$, but you shouldn't try to isolate and interpret what the $X^\mu$ alone is.

10:57 AM

Well, I guess it would be more...

Hm

user228700

I should probably get some lunch...

Alright

So it would be something like $g_{\mu\nu} \gamma^{ab}(dX)^\mu_a(dX)^\nu_b$

I'm not sure how to write this without components

Anonymous

@Yashas EE is not very different from CS (about 60 percent of the course overlaps). You can make up for that by taking extra electives in CS. And take a minor in Physics.

leave it

3 more days

waiting for ranks is torture

@Slereah Huh? You write it as $\lvert \lvert \mathrm{d}X\rvert\rvert^2$, where of course you defined that norm to be $g_{\mu\nu}\gamma^{ab}$ in components :P

11:02 AM

need my rank first

before I can decide branch

poor state in India

Wait, why would it be a matrix

where rank dictates what branch a student takes

Anonymous

@Yashas yeah :/

Wouldn't $dX$ just be a derivative with respect to $\partial_\mu$

$dX = \partial_\mu X$

Do you even geometry? :P

11:03 AM

Do I?

Given $X : \Sigma \to M$, the derivative is a map $\mathrm{d}X : T\Sigma \to TM$, agreed?

Anonymous

@Yashas I am thinking of joining IIST actually. The course looks exciting

Lemme check O'neill for embeddings

@blue IIST :O The cutoffs are so low for IIST.

At each point in $\Sigma$, it is therefore a linear map $\mathrm{d}X_p : T_p\Sigma \to T_p M$.

11:04 AM

I'm not very good at embeddings

@Slereah Nothing to do with "embeddings", it's justa map between manifolds

Anonymous

@Yashas They will declare a rank list and take the top 100 students I think. Yeah, the cut off is low I know. But the teachers are mostly ISRO scientists. (The scary part is the 3 year bond :P)

Nowhere does it play a role that it's an embedding

Linear maps between vector spaces are matrices.

Ah yes

$d\phi : T M \to T N$

Alright then

Makes sense

But wait, if it's a map between the tangent bundles

What is the integral over?

Wouldn't $dX$ be a function on vectors

Vector fields, anyway

And the Polyakov is just an integral over $$\int_S d\mu[\gamma] \| dX\|^2$$

With $S$ the non-target space (what is it called, by the way)

11:19 AM

@Slereah It's over $\Sigma$, by viewing $\mathrm{d}X : T\Sigma \to TM$ equivalently as a function $\mathrm{d}X : \Sigma \to T^\ast \Sigma \otimes X^\ast TM$.

@Slereah ...you mean the worldsheet? :P

Well Polyakov action isn't necessarily over a worldsheet :p

The worldvolume, then

Alright

Apparently the index-free notation might be $-\int d\mu \det (X^* g)$

Or something of the type

I'd say it's more important that you know what that integral does than to figure out its "correct" notation :P

Well yes, but the two are related!

11:23 AM

You're not going to do all that much with the action itself, anyway

Knowing what exact objects are involved

I have a feeling you're going down all sorts of rabbit holes in this attempt to learn string theory. Don't worry about curved spaces yet, just see what they do on the flat one.