The h Bar

Lozansky

12:03 AM

Like this problem

Is hard no matter what you guys say:P

Here's the solution in case anyone's interested:

danielunderwood

I remember there being a problem in Griffiths that messed up most of our class. I think it was about overlapping spheres or something?

Emilio Pisanty

2 hours ago, by Lozansky

perhaps?

the solution uses overlapping cylinders

Lozansky

@danielunderwood There is one with overlapping spheres where you calculate the field in the overlapping region

iirc

Emilio Pisanty

@Lozansky those are reasonably ugly, yes

infinitesimally-small separation between regions held at different potentials is tricky territory

all sorts of unphysicality dragons there

Lozansky

This is the one I was thinking of

But it's pretty trivial if you use the hint so I doubt it's the one @danielunderwood is thinking of :P

Emilio Pisanty

12:13 AM

@Lozansky for some reason, that makes me think of the French group theorist Jacques T.

... which is probably a very strong sign that I should really go to bed now.

Lozansky

oO

Getting late here as well

I'm off

Thanks for all the help guys

Emilio Pisanty

1:49 AM

@DanielSank heads-up - see the link in this question.

DanielSank

2:58 AM

@EmilioPisanty Heh, the guy who answered that is interning with us :-D

Bernardo Meurer

3:19 AM

@DanielSank </3

tarit goswami

4:19 AM

@Blue Yes, I am from WB :-)

@Blue No, I think no Institute offers QI in Undergrad level in India, I am doing MOOC by Peter Shor and the Caltech, Q Tech course on Quantum Crypto

@Blue Can I know from which institute you are?

I will like to work on QI later, I heard HRI is a good place for QI in India.

Captain Bohemian

5:01 AM

isn't the center of a group G the normal subgroup of G?

Captain Bohemian

5:12 AM

ncatlab.org/nlab/show/classical+Lie+group It turns out the knowledge I have learnt about Lie group is merely about classical Lie groups. There are still exceptional Lie groups! What on earth are they?

I think I have had some rudimental touch with some of exceptional Lie groups, but I still know too little of them to get a profile of them.

@bolbteppa are exceptional Lie groups closely related to supersymmetry?

Semiclassical

5:36 AM

John Baez's page here is suggestive: math.ucr.edu/home/baez/octonions/node13.html

David Z

@JohnRennie you around?

John Rennie

@DavidZ morning :-)

Semiclassical

To wit: you get the three classical families by constructing algebras based on the reals numbers, the complex numbers, and the quaternions.

The next thing to try would be to pass from the quaternions to the octonions. but those guys are weird

David Z

@JohnRennie Hi :-) I had some questions about some homework answers you pointed out recently, could we discuss that either here or in another room? (your choice)

John Rennie

Here is fine. I'm guessing you think I'm being over zealous in criticising people for answering homework questions?

Semiclassical

5:39 AM

(octonions aren't even associative, ay yi yi). so it's maybe not surprising that it's harder to create Lie algebras based on them, and that what you get will be 'exceptional'

David Z

@JohnRennie Nah, it's not about that. It's more like a couple of the ones you pointed out didn't really seem like "complete answers" in the sense I understand it. I can post a link or two in a minute

Semiclassical

c.f. this sentence from his page on F4: "In 1951, Freudenthal embarked upon a long series of papers in which he described not only $F_4$ but also the other exceptional Lie groups using octonionic projective geometry."

David Z

I wanted to check with you so we wind up on the same page about this

Semiclassical

which...oooookay

John Rennie

@DavidZ my view is that if you give a helpful answer a homework question then you encourage the asking of homework questions. So it doesn't matter if your answer is complete or not.

The point is that I don't want people to ask HW questions here. It isn't that I don't want them answered, I don't want them asked in the first place.

Semiclassical

5:42 AM

@CaptainBohemian oh, forgot to ping you on the above

John Rennie

And note that there is a particular user who seems to make a habit of answering such questions.

David Z

@JohnRennie Well, sure, I actually agree that giving a helpful answer to a homework question encourages the asking of homework questions. And I also believe that we don't need to encourage that. But it does matter in the sense that our homework policy makes a distinction between how we mods are supposed to handle complete answers vs other answers.

Jalapeno Nachos

sup dawgs

anyone know why there's so little data-driven fluid dynamics research?

John Rennie

@DavidZ In my ideal world all answers to homework problems would be deleted, but I appreciate that's a minority view. But I wanted to bring the asnwers to the mods' attention, and in particular the user who is making a habit of answering them.

Jalapeno Nachos

I'm looking but can't find much

David Z

5:49 AM

@JohnRennie OK. Well, the way I would suggest bringing that particular issue to our attention is by casting a custom moderator flag and briefly explaining what you've observed.

Though in this case, no need to cast the flag now that you've told me. We'll look into it.

John Rennie

Noted, thanks.

Jalapeno Nachos

:(

I'm leaving bye

David Z

The answers themselves, taken individually, don't all seem to be worthy of moderator action. In general, any time there's a pattern of behavior that looks suspicious or troublesome but the individual instances of it are not flag-worthy on their own, then a custom mod flag is the way to go.

@JohnRennie and thanks for noticing.

On a somewhat separate note: if you don't want people to answer homework questions (in order to minimize the incentive for others to ask them), I think it would be a legitimate response to downvote those answers.

Though I don't always do that myself in recognition of the fact that a non-negligible portion of our community does like having homework-based questions on the site.

John Rennie

6:12 AM

@DavidZ OK. Sorry I guess I was bugging the mods unnecessarily with all the flags. I'm obviously grumpy this morning :-)

David Z

Eh, don't worry about it, when in doubt I'd still rather have you flag things to get eyes on it.

And a fair number of those flags were perfectly good ones anyway.

user7777777

Hi @DavidZ please look at this answer again physics.stackexchange.com/questions/430051/…, it is not a complete answer, the OP has already posted the correct solution and was asking for the error in his own solution. Thanks.

David Z

Hm OK let me recheck it

John Rennie

@user7777777 since you're here, I wish you would stop encouraging homework questions by answering them.

David Z

@user7777777 So, I think the key thing there is that the question asks, in part, "What average force does the juggler exert on one ball while he is touching it?" and your answer includes $F_J = 5F_g$, which apparently answers that part of the question.

Anonymous

6:27 AM

@taritgoswami JU, 2nd year (electronics)

user7777777

@JohnRennie I do only answer homework questions if they ask about a concept and show the OP's original effort.

I do not answer questions that are just blatantly pasted onto a post

Anonymous

@taritgoswami HRI takes very few people for their summer program. You could try though. There's a very nice QC group at IISERK under Panigrahi btw.

user7777777

@DavidZ Alright I see. So is there anything I can do about it (such as editing that part out)?

DanielSank

@BernardoMeurer Why?

Anonymous

@taritgoswami And which institute are you from?

John Rennie

6:30 AM

@user7777777 it's obviously a judgement call about where the boundary is, but I feel you're being a bit generous.

David Z

@user7777777 well, since it's still easily accessible in the revision history, we've taken an approach of not undeleting these answers just because they get edited. So... if you're really attached to this answer, we can try to work something out, but I'd suggest just letting this one go.

user7777777

@DavidZ Alright, it's fine. Thanks for your time.

David Z

No problem!

In the future, if you do find yourself answering a homework question, I'd say take a close look to see what the original problem is asking, and double-check the answer you post to make sure it doesn't give that away.

(For what it's worth, I kind of agree with John, but that's just my personal opinion as a contributor. There isn't a site rule that forbids answering homework questions or anything like that.)

user7777777

Thanks

@JohnRennie I'll take note

Anonymous

@taritgoswami And as for actual "quantum information theory" and "foundations of QM" there are not many people in India who are involved in it right now. The only guy I know of and who works significantly on foundations is Subir Ghosh from ISI, but he isn't really a pleasant guy to talk to (as far as my own experience goes). :P If you really want to work in QI, you're better off going abroad.

Anonymous

6:55 AM

Oops, I actually meant Guruprasad Kar ^. Subir Ghosh is the GR math guy used to stay in the same locality as me. (I'm terrible at remembering names!)

tarit goswami

@Blue Where you have learnt QI then? I think you have 2nd highest score in quantumcomputing.SE O_o

@Blue Is it online? or, in their campus?

Anonymous

@taritgoswami I had to dig up some books and papers for my summer project at IISER. Vazirani's lectures are a good start followed by Nielsen and Chuang (that's the gold standard)

tarit goswami

@Blue I have appeared for ISI this year, just for 3 marks they I haven't qualified, now in Christian College

Anonymous

@taritgoswami Eeeeh...3 marks :/

tarit goswami

@Blue Yeah, :-(

Anonymous

7:07 AM

Which department btw?

tarit goswami

Physics

Yeah

Anonymous

Nice :)

tarit goswami

@Blue I am following Nilsen and Chuang, can u share ur personal contact ? so that I can contact u?

Anonymous

@taritgoswami I was talking about their summer interns program. HRI, RRI, ISI and IISER all accept QC summer students. But you have better chances of getting in if you talk to the professors directly. Of course, they're offline!

tarit goswami

@Blue Yeah I also think so, but this winter I got selected for BARC research intern under Dr. Zafar Ahmed

Anonymous

7:10 AM

The nuclear physics guy?

tarit goswami

@Blue Yeah, but,I will work on Mathematical Physics

Anonymous

Awesome :)

Anonymous

BARC is a great place indeed

tarit goswami

Thanks :-)

Yeah

How you know him?

Anonymous

@taritgoswami blue.stackexchange98@gmail.com

Anonymous

7:14 AM

@taritgoswami Had browsed through the BARC pages last year and contacted a few people there. That time I was more into physics :P

tarit goswami

@Blue Ooh, I will contact you

John Rennie

@Blue you created a gmail account just to handle the SE mail. That's a good idea! I'll put that on my list of things to think about doing.

Anonymous

@JohnRennie Yeah, I had a few people on QSE who wanted to talk to me privately but I didn't want to give out my real email (at least not immediately). It's quite helpful, yes :)

Anonymous

@taritgoswami Sure, no worries

John Rennie

@Blue yes indeed. These days I guard my main e-mail account!

Slereah

10:21 AM

"It swiftly becomes apparent that Quantum Mechanics and Relativity are merely mind games that have zero basis in actual reality. They are repackaged Kabbalistic Occult ideas being hammered together with spurious and incomprehensibly obtuse and speculative mathematics."

He's onto us

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