@dmckee Are you around

My pointers are betraying me

@BernardoMeurer upvote pls

@EmilioPisanty Somewhat to my surprise a non-trivial number of users are in the habit of favoriting their own posts.

@BernardoMeurer As with greater demons, betrayal is what they do. It is up to the sourcerer to control them.

Many powerful charms and amulets are a good idea. And a pentagram, of course.

What does a pentagram even do?

Gives the whole business the proper ritual feel, of course.

@dmckee what do you mean, you agree with me on JEE questions

@dmckee I'm pretty sure C memory errors have some quantum characteristics to them

If you inspect with GDB you tamper the results

lol

Really, it's creepy

@BernardoMeurer These are known as Heisenbugs. And they are a real phenomena, because the operating environment with the debugger is not exactly the same as that without.

@0celouvsky I mean that they are mostly awful question that probe little about physics (or chemistry or engineering or math) knowledge, and the correct answer (as opposed to the one that will get marks) is often "This problem is buggered beyond recovery, ask me one that means something."

@dmckee I literally just fixed a bug by taking my shoes off

Gotta feel for people stuck in a situation where their future prospects are governed by such an atrocity.

@dmckee Indeed

I am stuck in a dilemma

This reputable seller in eBay is selling shiny Russian Nixie valves for cheap

Doesn't seem like a dilemma to me

I don't have time to test them cause exams

Testing them takes a couple minutes at most

If I had the equipment

Oh come on, get an arduino, a transistor, a transformer, a socket, some diodes and bob's your uncle

What do you guys think about string theory?

@Bilateral dwfaf;lkhadsdfsaddnbkjvsjkbasgfhh423h23h9ue knqlc

That's what I think

About anything pretty much

Cool

but I wonder about what people and students think

@Bilateral My thoughts are very abstract

@BernardoMeurer Now I think about it, I have an Arduino I could salvage. The main problem is that Nixie tubes require around 170 volts DC

Yeah, snatch a transformer from something

Get a transistor that can handle the high vooltage

proper copper wiring

and the socket, that will save your time

@Bilateral fake news

@Bilateral 11>4

So do you have any experience with String Theory?

@0celouvsky and @JoshuaLin

@Bilateral None at all apart from everyone telling me how hard it is to find experimental evidence; how experiments getting to the energy levels that you can get predictions are going to cost way too much; and how it might not have any predictive power because its so broad it can sort of predict anything could be? but i could be misunderstanding because I'm bad

Well

I would say experimental verification was thought to be impossible

but it can become a reality sooner than expected

Never underestimate technology

Hmmm yeah i guess

do you research string theory?

Indeed

what's kind of the math background you need to go into research in that area?

hey

But usually I am in contact only with other string theorists or mathematicians, so I am curious to now about the opinion of other physicists

my algebra prof keeps randomly lapsing into talking about bosons fermions and how physicists were depressed in 1990s since all QFT's have too many infinities or something whilst talking about algebra at the same time it's kind of hard to follow lol

That depends very much on which particular thing in String Theory you want to study, @JoshuaLin

What kind of fields are there?

In the 90s? That's not correct. That was maybe in the 40s or 50s

There are many "fields" in String Theory. In any case, the background needed to actually start studying a book about String Theory

is very basic.

In math?

yeah

Yeah sure, many things going on, and some of them motivated by String Theory.

what fields are seeing like the most activity recently?

There were big developments going always ever and it's going now too.

If you want a good example partially motivated by String Theory, check out Generalized Geometry as introduced by Hitchin and Gualtieri

whenever anyone mentions anything great about math its always like "Serre, Catan, Weil, Grothendieck" all these people from the 20th century, not sure I even know of any like "legends" of the present

Generalized geometry? sounds cool

havent really learnt much about geometry

Geometry is key in physics.

hm ok guess thats the next thing I should do then

Sure there are legends from the past. The thing is that now there is many more people doing math, and it is harder to spot "lone geniuses".

You are giving examples from algebraic geometry, the major development of which happened in 20th century. But algebraic geometry does not classify as all of math.

If you are into algebraic topology you may like differential topology. That's the math area that I like most.

There are still a lot of work going on in homotopical algebraic geometry. Lurie et al

That's in fact the fashion nowadays I think

Well that is a very abstract area

Most mathematicians don't know about that

But it has become widely known

@Bilateral This is not true. Where did you get that information?

yeah im reading "Introduction to Manifolds" by Tu now so that I can later go read Bott and Tu's stuff

By experience. I work at a mathematics department.

And I am familiar with the community

Well, that's false. People who do not work with algebraic geometry do not know algebraic geometry, obviously. But people who do does :P

Lurie's theory is very popular but there are very few experts work on that.

I didn't say that. You didn't understand what I said.

The experts are rare, yes. But a lot of people understand that!

Of course there are many algebraic geometers. And algebraic geometers of course know algebraic geometry.

But Lurie's work is a very specific topic

which is not even algebraic geometry properlyu

is algebraic geometry/algebraic topology/category theory

It's algebraic geometry of spectra.

Many people have an "idea" of what is it about, like me. But not so many experts actually working on that.

Most of actual homotopy theorists are aware of the field and frequently use it. I don't know what you are talking about. It's hugely popular (not just "pop-science popular") nowadays.

I am talking about Lurie's work

Me too.

on the classification of QFTs

and

on derived algebraic geometry

compared to other fields in mathematics

Oh, I am not talking about TQFT's! That has nothing to do with spectral algebraic geometry.

it is minuscule

compared to mathematicians working in computation or numerics

it is ridiculously small

@Bilateral which is blatantly obvious :P but it is a huge field of interest in algebraic geometry and homotopy theory

comparing a field of mathematics to all of mathematics is a useless endeavor

well, you have to broaden your point of view.

I know many algebraic geometers

who have no idea about Lurie's theory

and many that consider it abstract nonsense

so it is not so easy

can you mention 10 departments in Europe specialized in that?

Maybe you have been talking to the wrong kind of algebraic geometers. The complex algebraic geometers are not into these.

well maybe so

but that shows that is not so "widely known", if there is people that even consider it abstract nonsense

Every modern scheme theoretic algebraic geometer I have talked to is aware of this stuff. I find homotopy theory-inclined algebraic geometers are more into it.

"aware of this stuff"

Yeah sure

a different thing is people PUBLISHING new papers on that

@Bilateral There are a wide community of people who consider 20th century scheme theoretic algebraic geometers as abstract nonsense. :P

@BernardoMeurer One of these traveller's 240 to 120 transformers works out to 170 DC when rectified. I'll search for one of those.

which is what I have been meaning from the begining

@Bilateral But it is not! Schemes are very, very popular.

But I am not talking about schemes

@JaimeGallego Sounds good, get a good rectifier. Don't cheap out when dealing with high voltages

OF course schemes are very popular

I have almost died twice because of that

well it is pointless discussing with you

Ciao

You are giving a wrong-headed logic about if people outside the field consider it to be abstract nonsense then it is a minuscule branch. Hence why I brought up the example of schemes.

lol

@JoshuaLin Right, any codimension 1 submanifold of R^k is orientable.

(Compact closed)

right; I was thinking I could use some sort of argument that if it gets embedded; then surely it encloses some hole so its top homology is Z and its orientable or something? actually im not sure how to prove it

still learning

but I think I constructed closed compact nonorientable n-manifolds that fit into n+2 space

@BernardoMeurer Noted.

@JaimeGallego Really, treat HV circuits with respect. They will fuck you up if you don't

If you work with smooth embeddings, then a smoothly embedded n-dimensional manifold in R^(n+1) has trivial normal bundle.

That, along with the orientability of R^(n+1) gives an orientation on the manifold.

Ahahah

oh my god

I was looking for Krasnikov's email

Here it is

[email protected]

He still has a .su email

For you youngsters

@BalarkaSen oh cool

.su is the TLD of the soviet union

lol

I love him already

Hmm, alright I should get some actual work done today.

How about you don't and watch TV instead

I think I won't be watching TV for a while.

@BernardoMeurer When one approaches a project with boatloads of fear... I think that describes how much respect I have for these. It's getting late, I should sleep.

And in the Azores as well

@JaimeGallego Got a project to finish :)

@dmckee I hate this project

I just want to be done with it

Cya all later

If I have to solve one more SIGABRT I will jump off one of these Azores cliffs

System just crashed

god bless auto save

@blue The only question I've seen are the ones that appear here. I don't doubt that there are good questions on the exam, but there are some that are utterly awful as well.

Writing good multiple choice question is an art. A very, very demanding and difficult art.

A good multiple choice question can't be ambiguous, can't rely on unstated assumptions and while some mere algorthmic computations are probably OK, they can't make up the bulk of a test like that.

More over the offered answers are also hard to write.

The distracters have to be linked to common misconceptions but must be clearly wrong if you know the material. Without giving themselves away to people who don't know the material.

@blue You've missed the point. The presence of good questions no help if there are a non-trivial number of bad ones.

That statement should have been clearly restricted to the question that appear in the hbar and on the main site, and I admit that it was not.

But the question you just posted is a bad multiple choice question. Verging on very bad.

Because they offered answers address three different quantities you might want to know about the assembly. When a student gets that right or wrong you haven't learned anything about what concepts they did or did not understand. Bad form.

It's challenging. But what does it test? What do you learn from the students performance on it?

You can't even localize it to "they [do/do not] understand vector angular mometnum" because one of the distracters covers the relationship between linear and angular kinematics. Yuck.

@blue Missed that. That works better.

Issue of the ed system, not an issue of the people involved

You shouldn't feel offended by this

@blue Oh. I stand by my dislike for the test. It takes very few bad questions to ruin the utility of such a test for ordering the takers.

@BalarkaSen Hey, suppose I want a bunch of harmonic functions in $D^2$. Could I just take $u(x,y)=x$ and precompose with a rotation?

Those will all be linearly independent (probably)

Er, no

they won't

You want linearly independent harmonic functions?

@BalarkaSen I just want a quick way to show that the kernel of the Laplacian on $D^2$ is infinite dimensional

no BCs

Real part of $f(z) = z^k$ for all $k$, say.

Ah, real parts of analytic functions are harmonic

Those are linearly independent.

Right.

I can never remember how the coordinate transform of the metric goes

If it's old over new or the other way around

you keep track via the indices

that's why carroll primes the indices

@Slereah $$g_{\mu'\nu'}=\frac{\partial x^\sigma}{\partial x^{\mu'}}\frac{\partial x^\rho}{\partial x^{\nu'}}g_{\sigma\rho}$$

of course

yeah, finding it ain't hard

but it is annoying to not remember

easy enough to remember

you just put the prime indices downstairs on both sides

the rest is fixed

@Slereah what are you doing that requires the debauchery of indices?

Lorentz boost of Alcubierre metric

I still associate that one with memes in my mind

is it a legit solution?

Well it's a metric

And it does what it is purported to do

How does one create it?

It's not really a physically reasonable metric for a variety of reasons

well the basic Alcubierre metric is static

It's just a warp bubble that goes on forever

you can create one but it violates flux energy conditions

you have energy fluxes going faster than light

I see

I mean, the basic notion of the Alcubierre metric is nothing new

is that just a technicality or strictly forbidden?

The idea was based on cosmological inflation

Where you have objects being separated faster than the speed of light

I don't think there are currently any hard theorem forbidding it but it seems unlikely to be allowed

All the faster than light metrics are always the same trick, really

You just have the light cone locally widened

So that locally, you can go at speed that are "faster than light", compared to outside that region

makes sense

You can check easily that the Alcubierre metric is just Minkowski space with the light cone widened in a tiny bubble

and the bubble itself moves so that you never leave your region of wide light cone

and why are you investigating it?

There's a combination of warp bubbles you can use to turn it into an acausal metric

Similarly to how you can do a closed curve with a system of tachyons

you can't actually form a closed curve with a single (free) tachyon but with two it's not too hard

why not with one?

Well a free tachyon is just a straight line

(at least in Minkowski space)

but two are...two lines

@BalarkaSen Poincare came up with winding numbers for the gravitational 3-body problem

Well the opposite of a spacelike curve is still a spacelike curve

unlike for future-oriented timelike curves

And you can still form a closed curve with two spacelike curve and a timelike curve

if u want to allow for some response time

For your tachyonic telephone

telephone operator

you should write telephone for any linear operators in your book

I wonder if non interacting tachyons still have a well defined Cauchy problem, if you don't allow 0 energy ones

I think that's the case

they all still cross the Cauchy surface once

@BalarkaSen still around?

sort of

@BalarkaSen These guys mention that one could write the degree of a map $f:S^{n-1}\to \mathrm{GL}(N,\Bbb C)$ as $\int_{S^{n-1}}f^*\omega$ for some special differential form $\omega$

Do you know which one that might be?

I don't. Maybe there's a unique left invariant differential form of dimension $n-1$ or something.

But I am not going to guess.

A'right, gotta go now.

@dmckee The questions you see here are mostly high school board exam questions which are very bad. Most of the JEE questions are discussed in the JEE prep room. Occasionally, when it becomes too difficult for ourselves or we need some external input, we ask doubts here.

@dmckee The MCQs are not really MCQs (not all of them), they are Multiple Correct MCQs. We need to mark all the correct options to get +4 marks. If we miss at least one of them, we get -2.

Guess work or any MCQ tricks based on probability or stats is too risky.

what is he doing now

@dmckee There are two stages of the JEE test: JEE Main and JEE Advanced. JEE Main is very easy and checks the basic understanding of the subjects. Only those who score above a minimum cutoff in JEE Main are eligible for JEE Advanced. The JEE Advanced is tricky and is filled with challenging problems. Admissions are taken through both JEE Main and JEE Advanced.

The top institutions take admissions based on JEE Advanced scores and the other institutions which are really good but aren't the best take admissions based on JEE Main score.

There are exams which are even easier than JEE; State level entrance exams such as CET. These exams are very easy. There are even easier exams such as COMEDK where the questions are of AP level.

God, does this guy ever give up?

He just loves shitting on AP

@0celouvsky That wasn't the goal.

@blue my dislike of JEE has little to do with the actual questions asked

It is what it does to the students

@0celouvsky How does that hatred towards what the exam does to students translate to a phobia against a discussion on JEE in this chat?

I don't think David is around, but he were I'm sure he would want to make it clear that he is not criticising the students - he is criticising the exam.

And Ryan has also said that many times.

@JohnRennie I am criticizing the students when the chat is flooded with spectral lines and crap

@BernardoMeurer

So if anyone feels they are being personally attacked that isn't the case.

@0celouvsky If you were referring to the sodium D line chat, it was just over 10 lines. And most of the questions and discussions you see here are not about JEE questions, it is regular high school questions.

And I think you can also safely assume that we non-Indians have only a vague idea of exactly ho the system works.

@blue I haven't called anyone names

And I don't know what abstract algebra you're talking about

See, you don't have any actual knowledge of the situation

@blue If you're going to start attacking each other I will freeze this room and you can all go do something more useful.

Every question Ramanujan asks is not about JEE. It is high school exams. Almost all the JEE related discussion happens in the JEE room.

@JohnRennie whatcha up to

@blue You don't have to leave, you just have to not fight.

@Kaumudi.H hi

@JohnRennie Wouldn't it be a lot more reasonable to boot them?

Hi,@Kaumudi.H.