The h Bar - 2017-09-05 (page 3 of 4)

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4:00 PM

Anyway, it's time for us to get our chat session started!

What happens in those chat sessions ?

AccidentalFourierTransform

we rickroll new users, obviously

Here's the agenda for today's session:

1. Intro, welcome newcomers, site questions (5m)
2. Recent physics developments (10m)
3. Some minor meta stuff (5?m)
4. Open discussion

Please keep unrelated discussion until after we've finished with the listed topics

Why homework questions are off topic here ?

First things first, is anyone new to the site, new to chat, or new to chat sessions?

4:01 PM

Yeah, I'm new to chat sessions. (chat.stackexchange.com/transcript/message/39829096#39829096)

Welcome :-)

Cool, welcome :-) I was just going through the boilerplate there before responding to you

We do this every couple weeks as a way to get people together in the chat room. It also serves as a good opportunity to discuss things relevant to the site, when there are things to discuss.

I have a question about this chat. How can I turn off the feeds for just this room?

(Reply later iff off topic to Chat Session - What's boilerplate ?)

@AlexKChen on that note, it's not really that homework questions are off topic, but we don't want to do people's homework for them and we don't want to help people who aren't also helping themselves. Read more here if you haven't already.

Anonymous

4:04 PM

27

Q: Can I silence ticker feeds in a chat room?

A chat room can have feeds, either posted as regular messages, or appearing as an overlay at the top of the window (“into an extra area of the screen”) — ticker style. When the feed appears in messages, I can mute it by clicking on the feed user's avatar next to one of its messages and selecting ...

support chat feed

@AlexKChen That's quick enough to answer; I just meant the standard "script" of sorts that I go through at the beginning of each chat session.

Or, many of them.

@Blue good find

and fast too

Anyway, let's move on to recent physics news. Anything new and interesting?

Suppose I have no physics teacher, and I thought of a problem, and (try to) analyze it. Of coursase, I get stuck or my analysis produces nonsense things like perpetual motion is possible, and I want to see where I botched off. Is a question regarding that on topic ?(Or should I ask it on chat ?)

Anonymous

2 days ago, by John Rennie

Ooh, ooh, photon-photon scattering has been observed - well, sort of :-)

4:07 PM

Also, which physics related questions you should (and it's considered better) to ask in chat rather than on main site ?

Anonymous

I found that interesting. Though, I suppose David already has seen the news

@Blue Well, posting here is for everybody, not just me. But that is a particularly interesting result coming out of particle physics.

What did they learn during the eclipse?

@skullpatrol scientifically, not much. That eclipses are cool, I guess.

Anonymous

@DavidZ Yup :)

4:09 PM

@JohnRennie hasn't John Duffield been predicting that for years?

I was thinking of observing stars to verify Einstein's theory of relativity again, but I gotta say, that thing is looking pretty solid at this point.

What else is going on science-wise?

@DavidZ North Koreans simulated a star

2

@Blue Doesn't answer my question.

Joe Polchinski posted a memoir on arXiv, for those who are into such things

AccidentalFourierTransform

19 hours ago, by AccidentalFourierTransform

Memories of a Theoretical Physicist, by J. Polchinski

yeah, very cool

ııııııııııııııııııııııı

4:14 PM

@DavidZ already read most of it (AFT posted the link last night)

AccidentalFourierTransform

young physicist, please read them!

Why should we take your word

I only glanced through it so far but I'll have to come back to that in more detail later, to see how it is

(I suspect one guy is spamming the chat session)

@AlexKChen it isn't much of a chat session

Anonymous

4:16 PM

@user21820 Write a script for yourself then. There's no meta post on how to block feeds in one particular chat room

AccidentalFourierTransform

> I was one of those students who thought he had to learn everything before
starting research.

oh boy if that isnt me

Mithrandir24601

@AccidentalFourierTransform I discovered about 3 months ago that this is completely not at all necessary

It does seem to have been a slow couple of weeks as far as physics news. Moving on, there's one thing I want to bring to people's attention first:

16

Q: Should any check-my-work questions be made on topic?

It's long overdue that I make this post revisiting our policy on "check-my-work" questions. These are questions, often (but not necessarily) homework-like, that present a complete mathematical or logical derivation and ask whether it's correct. Historically our homework policy has rendered check...

discussion scope policy faq-proposed

AccidentalFourierTransform

@Mithrandir24601 same here :-)

This is now faq-proposed, so we'll be considering it for tagging as faq.

AccidentalFourierTransform

4:17 PM

not really unnecessary, but impossible instead

If anyone has thoughts about whether it should or shouldn't be an FAQ post, or edits needed before it becomes one, please comment on the post.

That's all I've got for today.

Anonymous

I have a question. Do questions based on physical electronics belong here or on the EE site ?

AccidentalFourierTransform

here we only want QFT questions.

@Blue What made you think I could write a script for myself? I can, but I would have thought there is some simple setting somewhere...

Userscripts often break when the site is changed.

Anonymous

@user21820 Then learn to write it. I don't know any simple setting. Sorry

4:19 PM

@Blue Depends on the question, I think.

Anonymous

0

Q: What would an intuitive explanation for the $E$-$k$ diagram?

In all of my solid state books they seem to plot the $E-k$ diagram. But I don't understand why ? What is the physical significance of the $E$-$k$ diagram? Please don't give answers like it shows the forbidden and allowed bands. For that we should have been better off plotting $E$-$r$ (wher...

condensed-matter semiconductor-physics fourier-transform crystals dispersion

Anonymous

Like this one ^

Anonymous

Solid State/Semiconductor/Physical Electronics

Oh I would not have classified that as a "physical electronics" question. In any case, it seems totally on topic. (Though FWIW that's out of my area of expertise)

Anonymous

@DavidZ Okay, thanks!

Mithrandir24601

4:21 PM

@Blue That's a condensed matter physics question :P

Anonymous

@Mithrandir24601 Well, that too :P

AccidentalFourierTransform

so... that's it for today?

ııııııııııııııııııııııı

@AccidentalFourierTransform It may not be very interesting to most of you but this paper (at least its abstract!) caught my eye when published a few days ago

@AccidentalFourierTransform Well officially the chat session lasts for another half hour, but if people don't have any more discussion, that's effectively it.

Wikipedia is great

user image

AccidentalFourierTransform

4:31 PM

@ııııııııııııııııııııııı BUT WHY IS THE ABSTRACT BOLD!?

ııııııııııııııııııııııı

@Phase Yes I think in that case citation is needed. Otherwise it's considered original research

user image

@ııııııııııııııııııııııı honestly I don't think there's a measuring apparatus sensitive enough to accurately detect the number of fingers on the standard human hand

5 +- 0.00005

AccidentalFourierTransform

user image

look at her

just look at her!

poor soul

The real cringe happens when the victim tries to high 5 but ends up getting a handshake instead but misses that too

Anonymous

Interesting. Many of the recent condensed matter questions haven't received answers. physics.stackexchange.com/questions/tagged/condensed-matter . Can something be done to improve this situation? :P

2

ııııııııııııııııııııııı

4:35 PM

Are this guy's claims true (about sun and Earth)?! youtu.be/ZRmz1pWV31I

AccidentalFourierTransform

@ııııııııııııııııııııııı I was trying to read that article (yes, the abstract seems interesting) but then they used the $\int\!\!\!\!\int\!\!\!\!\!\circ$ symbol and I gave up

\ointt, whatever

$$\int\!\!\!\!\int\!\!\!\!\!\circ$$

@Blue Interesting indeed. I guess we could try to publicize them to condensed matter subject experts.

I'll tweet about it

AccidentalFourierTransform

but why? it's condensed matter physics after all...

(who knows if that will do any good, but couldn't hurt)

@Phase that is a hard question

I'm never sure how much to cite

Anonymous

4:38 PM

It's strange. Every alternate physicist I come across in real life seems to be working on condensed matter. Here, it's opposite

"it is well known that 1+1=2 [3]" [3] Babylonian tablet

Anonymous

QM questions are usually answered quite quickly

@Blue the people in here are not normal

seriously, we have no one doing stuff that the majority of physicists do

@Blue Yeah, it does seem that the online activity of physicists is dominated by high-energy and QM-type fields

AccidentalFourierTransform

@Danu hi there

Aug 23 at 21:37, by AccidentalFourierTransform

user image

did you see this?

you are nothing but a young Gauss, congrats!

4:40 PM

Danu is only 22?

1995?

maybe he writes unpublished papers with fantastic results to prank people later in life

I wasn't born in '95

Hii

I'm from '93

4:41 PM

@Danu You've got one year left. It is known.

Pull a Galois

@Phase In my house the average is 4.75 ... among my friends, colleagues, and acquaintances I estimate 4.99 ... I think you've underestimated your uncertainty here.

@0ßelö7 ? I think Galois died at like 20.

Do anyone knows which is best place to learn C

@Danu Hmm. How long did Abel live?

Danu doesn't have girl problems anyway (I hope)

so not gonna work

4:42 PM

@Blue the rain has completely stopped

I had to turn my backpack upside down to get water out

my calculator was in standing water and somehow is alive

@BalarkaSen Confirmed

ııııııııııııııııııııııı

@Blue Yes, exactly. we don't have a condensed matter expert on the site while in real life they constitute the greatest community compared to the physicists of other fields. Here we mostly have particle physicists, string theorists and mathematical physicists.

@ııııııııııııııııııııııı Where are you?

Anonymous

@ııııııııııııııııııııııı Maybe they are busy doing experiments in the lab :P

Pretty sure he is talking about PSE

4:44 PM

@ııııııııııııııııııııııı and a colloid scientist ...

@0ßelö7 Right.

@ııııııııııııııııııııııı Maybe we should make a concerted effort to get people from other fields like condensed matter more involved in the site

Anonymous

I think we need to publicize some particular tags

Anonymous

Via social networks and ads

@ııııııııııııııııııııııı Counterpoint. But you're right that our condensed-matter community is weaker than it could be.

4:44 PM

I think getting theoretical condensed matter peeps would be great, too.

(maybe condensed matter people are too busy doing work and don't go on the internet)

Anonymous

@rob He seems to be the only one answering those type of questions

Anonymous

That too he rarely gives detailed answers :P

I have this theory that the more "useful"/applied/funded areas of research will always be underrepresented on free knowledge-giveaway websites.

AccidentalFourierTransform

physics.stackexchange.com/tags/condensed-matter/topusers

4:46 PM

This is my theory of why MO works so great while something like that in physics somehow doesn't seem possible.

@0ßelö7 The professor who told me "theorists write books because experimentalists are busy" was a condensed-matter experimentalist.

@rob do I know him?

@rob Theorists write books cause experimentalists have nothing new to add ;D

user image

"600 is good enough"

@0ßelö7 Don't think so.

4:49 PM

More seriously, I think that probably experimentalists write less books because their knowledge is less broadly applicable. Experiments require very specific knowledge which doesn't carry over well to others, or so I like to think.

@Danu Agreed. It's hard to read or write a book on a specific technique.

Anonymous

12

Q: Community Promotion Ads - 2017

It is a bit late into this new year, being that we're already in the second month, but we are now cycling the Community Promotion Ads for 2017! What are Community Promotion Ads? Community Promotion Ads are community-vetted advertisements that will show up on the main site, in the right sidebar....

discussion community-ads

Anonymous

Perhaps we can make some posters for this ^

@Blue what for?

Posters on our site won't attract new people much :P

Anonymous

4:51 PM

@EmilioPisanty Read the discussion a bit ^ We were thinking about how to publicize certain tags (related to experimental physics) like condensed matter

Those posters probably work for the more.... non-conventional sites, I think

@Blue who do you want to funnel into those tags?

and, if they're seeing community ads, why are they not already paying special attention to them?

Anonymous

@EmilioPisanty Experimental physicists obviously

@Blue that wasn't the question

what population, internet-wise?

Anonymous

@EmilioPisanty What? I don't think we have "tag" advertisements as such

ııııııııııııııııııııııı

4:54 PM

@Blue condensed matter (both theoretical or experimental)

@Blue are they already using the site? are they using SE but not PSE? are they not on SE at all yet?

only the first population will see that advert

... in which case, they're most likely already aware that tags exist and would have looked for the ones that interest them

Anonymous

@EmilioPisanty There are so many people (like me) who have questions related to condensed matter and experimental physics. But they mostly go unanswered.

@Blue you mean, they go unanswered at a higher rate than other subjects?

Anonymous

@EmilioPisanty Yes. That's what we people have been discussing all this while ^

if so, that's a plausible, testable assertion about the Q&A corpus

Anonymous

4:55 PM

We lack experimental physicists

Anonymous

That's a fact

AccidentalFourierTransform

compare physics.stackexchange.com/tags/condensed-matter/topusers and e.g. physics.stackexchange.com/tags/quantum-mechanics/topusers

80% vs 40% in the last seven days

@Blue Define "lack".

@AccidentalFourierTransform so?

physics.stackexchange.com/tags/optics/topusers

physics.stackexchange.com/tags/atomic-physics/topusers

physics.stackexchange.com/tags/quantum-field-theory/topusers

condensed-matter vs quantum-mechanics is simply not a fair comparison

ııııııııııııııııııııııı

@AccidentalFourierTransform Now that you have finished your masters, please study a couple of books on condensed matter theory and start answering the related questions.

4:57 PM

^ that. particularly the optics ones.

and the atomic-physics ones.

AccidentalFourierTransform

@EmilioPisanty so nothing. I don't have a point.

I was posting what I thought was useful information

@ııııııııııııııııııııııı lmao

Anonymous

@EmilioPisanty That's what I am saying. Certain tags need to be publicized. We could atleast try even if it doesn't help much. Better than not trying at all

@Blue I don't think you understood the point.

Anonymous

Let's say tags for which >60% questions go unanswered

quantum-mechanics is simply not a good benchmark

Anonymous

5:00 PM

@EmilioPisanty Okay?

stop using it

it's huge

it's by far our largest tag

The official time for the chat session is up and I have to run, but I do hope this discussion about attracting new answerers to certain tags continues. It's definitely something we could benefit from.

it includes, among other things, a large chunk of the condensed-matter corpus

Anonymous

@EmilioPisanty Alright. Understood

if you want to argue that certain tags deserve special attention (e.g. they have high unanswered rates when compared to tags of similar size and activity) then by all means provide evidence for it.

if you want to propose community ads funnelling traffic to some specific tags, by all means do

but if the argument is that "X, Y and Z tags are under-answered", then I would ask you to back that up with credible data

@DavidZ ok, I'll shut up & get out of the way, now

5:06 PM

Oh..this was a chat session...

Anonymous

@EmilioPisanty We could just sort tags by their unanswered rate. Perhaps Data Explorer could help. Greater than 60% (in last 30 days) would look unhealthy to me

@Blue Sure. so do.

oh thank god

Anonymous

Okay...I'll do

the lecture slides have the formulas

tfw homework is due in 2 hours and they want $O(x^7)$ integrals by hand

5:07 PM

Higher coffee consumption associated with lower risk of early death.

I should live to over a hundred then :-)

@JohnRennie I coffeed up this morning and had to shake my way through fluid mechanics

@0ßelö7 if you're hands aren't shaking too badly to write you haven't drunk enough coffee :-)

@JohnRennie I didn't write for the first 15 minutes

I tried and then erased

it was bad

@0ßelö7 good man :-)

@JohnRennie I also went through a monsoon

somehow the electronics survived

waterproof backpack is so waterproof that if water gets in, it can't drain out

calculator was in a pool of water

5:10 PM

Wow. Did it survive the experience?

yup

Cool :-)

Anonymous

@0ßelö7 That's one awesome bagpack ;P

@0ßelö7 You have a wonderful backpack. :P

@JohnRennie this calculator is a beast. It needs a new battery because it won't charge past 25% lol

5:19 PM

@EmilioPisanty oh, no you weren't in the way, I was kind of handing off the baton to you in a sense

sorry

@DavidZ no, I misunderstood

I thought the chat session was about to start

oh, I see. Guess I should have said "over" or something to avoid any confusion.

5:34 PM

it's gonna rain until 5am

Hi, everybody.

AccidentalFourierTransform

sup

Mithrandir24601

@Blue According to Area 51, "80% answered needs some work", so all of PSE is under-answered...

@DanielSank o/

@Mithrandir24601 maybe people should ask better questions

Mithrandir24601

@0ßelö7 You may or may not have a point... I rarely actually look on the main site...

5:46 PM

I always have a point

Can anyone tell me best place to learn C

6:02 PM

@Blue @AccidentalFourierTransform Some comments on the stats you showed earlier

physics.stackexchange.com/tags/electronic-band-theory/topusers

marks 2 total, 2 unanswered over the past 7 days

That can only be physics.stackexchange.com/questions/355552/fermi-energy-level and physics.stackexchange.com/questions/355534/…, with the latter at score -2

@Koolman The Cshore

@Koolman for actual advice: download GCC and screw around until you know it

... which suggests it's not a particularly trustworthy metric

@EmilioPisanty are you a stat fiend

@0ßelö7 not particularly, no

I'm in trouble. I don't think I can make it home with my backpack in this shape

6:10 PM

@0ßelö7 So bad a condition?

this rain is incredible

@Sid it's not drying at all, and is now somehow wetter

Waterproof, right? :P

@Sid almost

it was a pretty bad rain

still is a bad rain

I think I need to put it in my office, run home, then get my car. Can't risk my laptop getting soaked

Or I steal a trashbag

But in any case @Blue @AccidentalFourierTransform here's your data

wrap up everything in that

then shove it in the bag

(that's not a bad idea)

6:13 PM

I don't notice any particular qualitative trends in the tags it comes back with.

@Giskard42 what is gcc

@Koolman Gnu C Compiler

@Koolman Compiler

i am using on ubuntu

terminal

@Koolman Then you probably already have it. if not, download it, think of a project you really want to finish, then look up every question you can think of until that project is finished.

@Koolman (That's how I learn, but others might have other methods.)

6:16 PM

Can I not get set of questions after every topics

There's a pretty reasonable continuum of tags with unanswered ratios (over the past 12 months) running from 20% to 40%. Condensed-matter is the largest by total q's in that continuum, but it's not that anomalously large. The rest of the tags cover a pretty varied scatter over the site scope.

In that I have learned if else , almost array

looping

Well... you have got the basics so far...

@Koolman I don't find that method of learning useful, but you might - you can look up one of the many gcc tutorials if you think that works for you.

from where I can that

gcc tutorial

6:19 PM

@Koolman I don't know of any personally, I learned programming through embedded design, but here: stackoverflow.com/questions/1345506/…

Heh, "closed as not constructive"..

SO does have too high standards sometimes..

I would actually be curious what fraction of people learned programming in the "conventional" style, with books/tutorials/tests, vs how many just... picked it up

@Giskard42 thanks

@Giskard42 That would be an interesting survey...

"Breadth-first" vs "Depth-first learning"

university/formal learning is depth first, and real-world learning is breadth-first

I guess

6:27 PM

@Jasper have you talked to Lee recently?

when is his book coming out?

@0ßelö7 His is trying to submit the manuscript to Springer this month, so the second edition might be out next year. That is the latest news I have. Thanks for asking!

@Jasper Ah, my advisor wants to teach RG next semester and I'm looking for books for him

sounds like it won't be out in time

@0ßelö7 Lee's book doesn't cover much material, which is why Ted doesn't like it. But I like it because whatever he covers he does it very well. Other books are of course those by Petersen, Sakai, and Chavel, all with the title Riemannian Geometry. I particularly like Lee's treatment of Hopf's Umlaufsatz and the Gauss-Bonnet theorem.

I know all of the books

Sakai and Petersen are too advanced

Chavel is good only to understand his analysis book

do Carmo is the best book, period. Don't know why people don't like it

I think all three are more advanced than Lee, but I like Lee best.

I once told Lee that his writing is the epitome of mathematical exposition.

ııııııııııııııııııııııı

6:32 PM

@0ßelö7 Does that mean your backpack doesn't respect time reversal symmetry?

@ııııııııııııııııııııııı it respects PCT

@Jasper I doubt anyone can actually read Petersen. Sakai is very good

@0ßelö7 There is also the book by Cheeger and Ebin, Comparison Theorems in Riemannian Geometry, which you can look at.

In what world is that an introduction

Mithrandir24601

@AccidentalFourierTransform I've just started reading the memoirs and I already relate to them...

Don't be mistaken -- I don't plan to take the course. I'm helping him organize it

6:35 PM

After reading Lee's smooth manifolds book, I think you can handle any Riemannian geometry book.

lmao

Mithrandir24601

@ııııııııııııııııııııııı I don't respect time reversal symmetry :P

If you say so.

Most of modern Riemannian geometry has little to do with manifolds.

Oh, if not Riemannian manifolds, then what?

PDEs on Riemannian manifolds

Everything has to do with manifolds, but the difficulties lie elsewhere

6:37 PM

Oh I see, the PDE part.

Yeah, Lee's books don't do very much with PDEs.

I guess you can just suggest Lee's book to your instructor.

It is very suitable for a one term course.

I was hoping the second edition would have some PDEs in it

@Jasper advisor, not instructor

I don't know exactly what Lee would add to it though.

@Jasper Me neither.

I'm sure Lee could figure something out though

If you love PDEs on manifolds, look at Taylor's 3 volume PDE.

The third volume proves the compact case of the Nash embedding theorem.

I know that proof from elsewhere

I don't need any more books to read, thanks.

Mithrandir24601

6:41 PM

@0ßelö7 ::Piles textbooks on @0ßelö7::

I remember looking at Taylor and not everything was to my liking. Some stuff was too complicated and lacking details in other places.

@Mithrandir24601 I can write a whole essay about what that user did in the past, but I won't do that now. What you see is the tip of an iceberg only.

@Jasper Actually O'Neill is pretty great

@0ßelö7 Ah yes, I think all the books we just mentioned Lee mentions them too. I guess for physicists it is especially good because of the semi- part.

standard book for PDE people because we all like GR

@Jasper Physicists and mathematicians who like GR

6:48 PM

So to solve a differential equation of the form $\frac{d^2x}{dt^2} = -\frac{C}{x^2}$ it's apparently done by multiplying both sides by $\frac{dx}{dt}$ Is there any specific reason for this or is it just a bit of a guess or...?

@CooperCape because you want to use the chain rule, presumably?

But is there any intuitive way of seeing this?

I get what happens after that but...

Maybe I'm just a bit slow rn I dunno

→ 6 messages moved to Trashcan

@ACuriousMind Will they get my messages if it is moved there?

@ACuriousMind do you know what a Pitot tube is?

Mithrandir24601

6:51 PM

@CooperCape Maybe this isn't a good explanation, but is it maybe part of the whole "let's assume there's a solution. Oh, look, there's a solution!" set of solutions?

@ACuriousMind The trash is private now?

@CooperCape all the methods for finding solutions to ODEs are ad-hoc

@Jasper I don't actually know.

@Mithrandir24601 Quite possibly... never been good at that kind of thing... oops! :/

I'm more used to a casual linear style of relative ease.

@ACuriousMind Thanks. I just want you to know that I am not the kind who likes drama. I will take it elsewhere.

6:53 PM

I must be immune to drama, I don't see any drama

@0ßelö7 It's a little flagpole where the mechanics hang their orange flags when they aren't using them.

@Jasper seems like it's been taken elsewhere for you.

@AccidentalFourierTransform Would've been perfect to do that on April Fools

> GUYS, we've figured out [insert major unsolved problem in physics]: https://arxiv.org/abs/1405.5968v1

Mithrandir24601

@SirCumference That was just a test...

@ACuriousMind Seriously, I need advice

6:55 PM

@SirCumference There's all kinds of trash :P

@0ßelö7 no

what the hell

Mithrandir24601

Perhaps he'll do a double fool where he posts something claiming to be a major discovery, making it obvious that it's not... Only it turns out that it is? :P

@ACuriousMind what did I do do you?

@0ßelö7 what?

@ACuriousMind I asked for advice and you said no

6:57 PM

Look what that no was a reply to.

you didn't even ask what the situation is

@ACuriousMind mobile

(for reference he doesn't know what a pitot tube is)

Ok. I cleared that doubt anyway

they're pretty counterintuitive

@Mithrandir24601 Funnily enough, many researchers post joke papers onto arXiv on April Fools Day.

Example: arxiv.org/pdf/1203.6708

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