The h Bar

user54412

12:22 AM

"Since in quantum mechanics there is one quantum state per unit volume in classical phase space" - Ed Witten, Quantum Field Theory and the Jones Polynomial, pdf here

user54412

@ArnavTripathy I think the above quote is sufficient to ask on the main site something like "what is the proof of this off-hand statment?"

user54412

Also your other question was good - you really should ask it - don't worry about making it perfect

ManishEarth

@ChrisWhite Yeah, it seems like a question many people will have.

The two books I was reading just mentioned that you can allocate a chunk of k space to each state. They didn't mention why in the world they liked doing that

(and then later strange conclusions were drawn)

user54412

@ManishEarth Perhaps you can read more Witten: "The topology of M is rather intricate (and this was in fact the main subject of interest in [33]). On general grounds M inherits a symplectic structure (that is, a structure of Poisson brackets) from the symplectic structure present on M_0 before imposing the constraints, M is a compact space (with some singularities), and in particular its volume with the natural symptectic volume element is finite."

user54412

... or maybe not....

ManishEarth

12:29 AM

symplawha? :P

I had understood the need of it finally

But I never needed that later so I sort of forgot

If I have a glimpse at the relevant pages of the book I'll get it again

ManishEarth

1:33 AM

O_0

I'm varying the unit cell size of diamond, and I get two points of convergence

Go home physics, you're drunk

2

user54412

@ManishEarth Should I (you) be worried that the points show a lot of scatter? Is that roundoff/instability/something bad?

ManishEarth

@ChrisWhite I'm generating a better resolution plot, we'll see

that may or may not be scatter

user54412

Out of curiosity, how are you calculating this? Summing pairwise interaction energies?

ManishEarth

I'm using abinit. First-principles calculation

Take the Schrodinger equation, apply the Bloch condition, and do some numerical method magic

And, now I see my problem

I need to take more k points

(I forgot to change the default value)

Set it to a 6x6x6 grid, hopefully it won't take an hour to calculate :P

goes back to watching Pink Panther/Tom&Jerry cartoons

(doing anything else would mean that I won't be able to immediately act on it if I get output)

ooh, done

Still lots of scatter

(Also, I realized that I spelled "convergence" as "conversions". Go home Manish, you're drunk too)

ManishEarth

1:58 AM

Strangely enough, I got pretty good convergence for crystalline silicon

That's diamond with a 10x10x10 k point grid. Still iffy.

user54412

@ManishEarth if you had to explain what this k grid is in one sentence...?

ManishEarth

@ChrisWhite You probably know what the trapezoidal method is, right?

That integration thingy

user54412

ummm yes :)

ManishEarth

Well, k points are "special points" which work very well for integration by that and similar methods. Instead of summing over an incremental set of points, you sum over these special points I can either specify how many k points total I want (it will automatically choose the best n points), or I can choose a grid of points where it chooses the best point per region

(and does a bunch of symmetry magic)

tpg2114

@ManishEarth Pink Panther >> Tom & Jerry

ManishEarth

2:13 AM

@tpg2114 you want to bit shift pink panther into T&J? :P

user54412

^ someone's been coding too much C lately...

ManishEarth

I've always loved Tom&Jerry, but atm the former is funnier for me :P

@ChrisWhite Actually, I haven't touched C :P

Or C++

tpg2114

I like(d) Tom & Jerry too, but Pink Panther was one of my hands down favorites

And Rocky and Bullwinkle

ManishEarth

except for the compilation, which was done by the configure&&make

@tpg2114 Never heard of that

tpg2114

No Rocky and Bullwinkle? Man! You're missing out...

It's a classic

user54412

2:16 AM

@tpg2114 agreed about Rocky and Bullwinkle :)

tpg2114

And it was on Netflix streaming for awhile, it may still be

ManishEarth

@tpg2114 Never was aired when I was a child, so never really got to know of it :)

I'll try it out

user54412

@ManishEarth it's the best collection of cold war stereotypes of the USSR ever assembled :P

tpg2114

It's from the 60's, but Nickelodeon had it on at like 6am when I was growing up

ManishEarth

lol

tpg2114

2:18 AM

@ChrisWhite That's the best part! It's almost 100% propaganda

ManishEarth

Tom&Jerry used to be on right after school. I used to watch it every day

user54412

I wonder if Soviets had a similar version about Americans...

tpg2114

Then all the shorts... I loved Mr Peabody and Sherman, and Asop's Fables

ManishEarth

@tpg2114 Which makes it probably 5 times funnier in retrospect, no?

tpg2114

Definitely. It's awesome

It used to be an hour of Mr. Wizard and an hour of Rocky and Bullwinkle from 5am to 7am. I would get up early when I was young, like age 5-8, to watch it

Mr. Wizard was great cause it was this creepy old guy trying to teach science to kids in his basement but just making fun of how stupid they were

ManishEarth

2:20 AM

Ah. My sciency show was Bill Nye

tpg2114

Bill Nye was entertaining

Beakman's World was funnier

Same era, different style though

ManishEarth

never heard of it :P

Shoulda watched more TV as a kid :P

tpg2114

That's on Netflix too I think... at least it used to be

Had a guy in a big rat costume...

Similar production quality as Mystery Science Theater 3000

Which is also an amazing program

ManishEarth

I don't think they have Netflix here.

@tpg2114 I think I remember that, but I don't recall watching too much of it

tpg2114

If you ever get a VPN into the US, I'll give you my login so you can watch some classic shows

ManishEarth

2:23 AM

thanks :)

tpg2114

MST3K is the guy with 2 robots watching really bad horror/sci-fy movies and making fun of them

ManishEarth

I do have an ssh tunnel to the US, but that's a web host and I can't use bandwidth watching TV

(and to France)

tpg2114

I think we lost @ChrisWhite to some classic TV on Netflix...

ManishEarth

lol

tpg2114

MST3K is actually on Amazon Prime now. They pulled off of Netflix

ManishEarth

2:25 AM

hmm

Some of these are on youtube too :P

tpg2114

I'm sure they are, but they are mirrored and weird sometimes

ManishEarth

But the more recent ones, less so

tpg2114

To avoid copyright

ManishEarth

IIRC copyright expires in ~50 years or something

Though there may be caveats to that

tpg2114

I think holders can request an extension when it's about to expire

ManishEarth

2:27 AM

yeah.

tpg2114

►

This is one of my favorite skits in the show

From the early 90's

ManishEarth

lol

That still happens

tpg2114

I know, that's what makes it so funny

ManishEarth

You probably have seen those "I'm a PC, and I'm a Mac" videos, right?

tpg2114

Yeah, for sure. I remember those when they were commercials on TV

ManishEarth

2:31 AM

ah

yay, long calculation done

tpg2114

What do you define to be a long calculation?

ManishEarth

This one took 20 minutes

OK, not that long

But still, long

tpg2114

:) I've been running things that take a week to run on 5000 processors... And I have to wait a week to get the computer time to do it

ManishEarth

@tpg2114 That's different, you probably batch all the calculations together or something. And you can go on with life while you wait :P

tpg2114

It's only a single run... each run takes that long

And that many processors

ManishEarth

2:35 AM

But yeah, I bet the same goes for @ChrisWhite and telescope time

wow

tpg2114

Detonation in a high explosive in 3D... 50 million cells

End up with 10 TB of data

ManishEarth

oh

that makes sense

tpg2114

top500.org/system/177935

ManishEarth

New graph (zoomed in x axis) is much better.

tpg2114

top500.org/system/177833

On those machines

ManishEarth

2:37 AM

wow

tpg2114

Can I nitpick your graph?

ManishEarth

I need to check the capacity of my institute's supercomputers.

@tpg2114 sure

I know, it's still pretty scattered

tpg2114

You need axis labels and to drop the text from the picture itself... That would be a caption under the figure

ManishEarth

@tpg2114 ?

ah

tpg2114

So your "Carbon Energy vs..." would become axis labels instead

ManishEarth

2:39 AM

Yep

tpg2114

And your 14^3 thing would be the caption

Unless you were plotting multiple resolutions, then it would be a legend

I can't comment on scatter since I don't know what it's supposed to look like... :)

ManishEarth

@tpg2114 Yeah, this isn't for presentation though so I was more concerned with getting convergence than with prettifying graphs (for that matter, the previous graph, labelled 10x10x10 is actually 14x14x14)

tpg2114

What should it converge to?

ManishEarth

@tpg2114 It should be a simple minima if I was using an infinite # of k points (read:100% accuracy)

tpg2114

Minima when? As x increases?

ManishEarth

2:43 AM

@tpg2114 Yeah

It's the total energy of diamond plotted against the size of the unit cell.

I should be able to find out the correct unit cell size by finding the minima

I'm just experimenting

tpg2114

I should be working right now... but instead I'm drinking

ManishEarth

I should be sleeping right now. Instead, I'm working :P

tpg2114

That will be later tonight for me. It's only 11pm now

The night is still young

ManishEarth

Well not working, more like playing :P

@tpg2114 It's 8AM here

tpg2114

I'm about to go through and mass-kill "thanks" from posts... I wish I could say I was playing

Although I was playing some NetHack earlier. I can't think of a more frustrating yet addictive game

ManishEarth

2:52 AM

@tpg2114 alright. Tr not to kill the main page :S

tpg2114

I know, I only do 5 at a time

ManishEarth

@tpg2114 Same here. Used to play it, have started playing it again :)

tpg2114

I wouldn't want to upset some people by bringing non-research level questions to the front page

ManishEarth

(on a screen session on one of my sshs)

ick

tpg2114

I used to play all the time, just started again like 2 weeks ago

It's so darn annoying but I can't stop playing it

Between NetHack and the Tour de France, my productivity is at all time lows

ManishEarth

2:58 AM

I keep running rm *_*. My terminal is staring at me.

@tpg2114 You're participating in Tour De France?

tpg2114

I wish! Just watching

ManishEarth

ah

tpg2114

I do manage a professional women's cycling team... but I'm not good enough to race in the Tour de France

The only racing I do these days is track racing... Getting ready for elite national championships in August and collegiate nationals in Sept

ManishEarth

nice though

tpg2114

Yeah, I look at that once in awhile

ManishEarth

3:01 AM

I don't get the logo though :S

tpg2114

I've earned some rep there, but the questions aren't usually all that interesting

"We love you SE so don't close us down for poor statistics"?

ManishEarth

never really seen anything there

@tpg2114 LOL

tpg2114

It's all super super basic stuff for the most part

Which is great. Beginners eventually become professionals. But I have enough on my plate to answer things there too

ManishEarth

yeah, there are tons of sites I could participate on but don't because of time issues

(I also have a tendency to cycle through sites -- visit all to check on but only answer on one)

tpg2114

I lurk on almost all of them...

Just to see whatever the hot questions are at the moment

ManishEarth

3:04 AM

@tpg2114 use the supercollider

tpg2114

What's that?

ManishEarth

(the thing that contains the inbox)

tpg2114

Oh, yeah, that gives site-wide hot questions

But I'm still interested in hot questions in most topics that don't make the big list

ManishEarth

It's real name is the StackExchange™ MultiCollider SuperDropdown™, but we call it the supercollider in short

@tpg2114 hmm, yeah. Certain sites (I'm looking at you, math/TeX/Unix/SO) seem to make it a lot

tpg2114

Interesting... Yeah, I check that. Then I go through sites that don't show up there to se what's hot there

ManishEarth

3:05 AM

Many times with not-so-interesting questions

tpg2114

Yup... exactly

I wasn't even checking physics that often

ManishEarth

Saw the "I shouldn't be able to see the sun" one? :)

user54412

You know, physics seems to average 1 or so hot question at all times (we have 2 currently I think)

ManishEarth

yep

user54412

@ManishEarth no, don't bring it up

tpg2114

3:07 AM

But then I saw that in 3 months of me not being around, the same people had the same issues with silly things and decided that you guys (the mods) needed some other people to chime in

ManishEarth

@ChrisWhite ha!

@ChrisWhite We have 3

tpg2114

If only I could edit out "thanks" enough to get to 3k so I can VtC...

ManishEarth

(I have this type-to-filter userscript that filters multicollider items in any one of the 4 tabs)

@tpg2114 not possible

you can get max 1k rep from suggested edits

tpg2114

I know

ManishEarth

and you get nothing after you reach 2k, obviously

tpg2114

3:08 AM

Plus it cuts out at 2k anyway

ManishEarth

yep

tpg2114

I know... That last 1k is going to be hard to get

ManishEarth

Or you could answer multicollider questions and get easy rep :P

(The folks on IT Security call these posts "rep trains")

tpg2114

By the time they show up on there, it's usually too late to contribute anything useful

ManishEarth

Not really. My answer on the aforementioned sun question was pretty late.

user54412

3:10 AM

@tpg2114 It's never too late to be useful :) (and often it's not too late to get some rep)

ManishEarth

-1

Q: Example of bioactive molecules not containing ring

Most of the compound used in drug discovery process have rings. I have not observed any compound that do not contain rings. Some example of compounds which are are in various phases of drug discovery process (hits, lead, approved drugs) which do not contain rings would be helpful. Reference to pa...

Oy! Physics.SE! Chemistry can get 5 votes to close

tpg2114

I take the more (lazy) and altruistic route and try to help those homework people out

ManishEarth

You should be ashamed of yourself. -_- (not you, tpg)

@tpg2114 I did that initially, but then realized that a lot of it is pointless

Well, not pointless, just not overall useful

tpg2114

Well, it's pointless in terms of rep and even the OP often times. But a lot of those questions are still something I've asked or looked for myself

ManishEarth

Ah yep. Those usually aren't HW, not really :P

tpg2114

3:13 AM

So the poor guy studying for qualifying exams last minute and searching will find it, probably never vote for it, but at least it was useful

True... We need another term for HW

ManishEarth

Or are good-questions-hiding-behind-hw

@tpg2114 Bob?

tpg2114

I was thinking educational until I found out that educational existed

Illustrative?

I don't know

ManishEarth

Hmm, yeah

tpg2114

Something that says "Teach me how this works" instead of "I would like an answer"

ManishEarth

Thing is, a lot of people on this site ignore the tag (there's a feature that lets you hide tags).

Which is why any changes to the meaning of the tag will be resisted

i think

tpg2114

3:15 AM

Yeah, I had typed up a meta post

But then decided I knew what the discussion would look like

And it wasn't going to be productive

ManishEarth

It would be interesting, don't let my words scare you off.

But yeah

user54412

pedagogical? instructional? didactic? edifying?

tpg2114

If questions are broken windows, there are users who are broken records

3

ManishEarth

pedagogical is good. Broad, but good

@tpg2114 well put

tpg2114

Isn't all of that really just meta tagging though?

Including homework?

ManishEarth

3:17 AM

@tpg2114 Yes. Just meta tagging that will lead to withdrawal symptoms if removed

I personally would like to see it gone

tpg2114

That was really why I was opposed to adding another term that covered it like those Chris mentioned

ManishEarth

On Chem I've already stopped using it and have a meta post coming up

user54412

relevant question I asked once upon a time: meta.physics.stackexchange.com/q/4022/10851

tpg2114

I didn't want to add a new meta tag

ManishEarth

yeah

user54412

3:19 AM

I still maintain that much of our problems with homework only exist because of math.stackexchange

ManishEarth

and Stack Overflow. Don't forget Stack Overflow

user54412

it's bigger and much wider known than us, and it sets a policy of "well do your homeowork for you"

ManishEarth

However, SO' the reason the site exists in the first place so we can't gripe much :

@ChrisWhite yeah

One in every 5 hw question has a comment mentioning math

for that matter, that would be interesting to data.se

user54412

@ManishEarth I guess I only go to SO when I see an interesting hot question or when I search for my own (bash/python) answers - do they get homework too still?

ManishEarth

99% of the questions there are effectively homework problems asked by adults

user54412

3:21 AM

LOL

ManishEarth

Anyone up for writing an SQL query that counts the number of closed HW questions with the word math in the comments?

tpg2114

I could maybe

ManishEarth

i'm trying too, if I don't fall asleep before I get it :P

user54412

@ManishEarth you better not sleep through the chat event in 12.5 hours :P

ManishEarth

oh, I won't

tpg2114

3:25 AM

I might

user54412

---
@dmckee I caught your update

user54412

10

A: Are right handed neutrinos actually antineutrinos and vice versa?

Short answer: Unknown Slightly longer answer: the situation you describer would obtain if neutrinos were Majorana particles (and thus not Dirac particles). It is favored by theorists because it feeds into a nice explanation of why the neutrinos are so light by comparison to the other massive par...

user54412

only question: which happens first, a clear breakthrough or you CW-ify your own post? :P

dmckee

Yeah. There are several edits there. I misread the paper at first and got all excited. It's not a big thing, but I like to keep abreast.

@ChrisWhite Now that's funny. But I have moderator superpower. Hahahahahaha!

tpg2114

Ah broken-windows

And records

I can't escape either :)

I know better than to get sucked into that debate though

ManishEarth

3:40 AM

tpg2114

@ManishEarth Doesn't look very correlated to me

ManishEarth

remember, the final dropping off is due to insufficient data

yeah, though

tpg2114

Yeah, but it doesn't look similar anywhere else either. There is probably an increase in questions asked along with the spike in closed

ManishEarth

Here's the query

@tpg2114 Yep. The spike in closed is afaict due to de autodeletion roomba

tpg2114

Although I think it still corresponds to the close out of the semester for various academic institutions

ManishEarth

3:43 AM

in other words, there's a bunch of deleted questions fudging up the data

tpg2114

Yeah

ManishEarth

@tpg2114 Yeah, that fluctuation is always there

Sites like Phys and Chem have stats following the school year, as well as the periodic (week) fluctuation that all sites have

tpg2114

Yup, it's not that surprising really

I'm sure SO does too but it's buried under all the other questions

ManishEarth

@tpg2114 yeah, it does

Anyway, I'm off. Enjoyed the discussion though :)

@tpg2114 Hope to see you in the chat session today! :)

tpg2114

Good night

We'll see, I'll try :)

ManishEarth

3:51 AM

Good morning you mean. It's 9:20 AM :P (my sleep schedule got inverted)

Your engineering-question proposal definitely needs looking into

tpg2114

Yeah, and I still like the "Other..." option too

"Just cause it's bad" if we can call it that :)

ManishEarth

Solution: get more rep

@tpg2114 lol

in Positronium, Jun 26 at 14:29, by ManishEarth

-2

A: What should our predefined off-topic reasons be?

The answers to this question are unlikely to be useful to anyone else, or to be written here anyway. I appreciate you have a question, please appreciate that we don't care.

Damn, it was deleted

tpg2114

Haha, nice

ManishEarth

a HULK SMASH!! reason would work too

:P

Anyway, logging out

dmckee

4:12 AM

@ManishEarth "autodeletion roomba" I like that. Nice.

Dilaton

4:36 AM

@ArnavTripathy from your chat comments it seems you have a bunch of very nice and interesting questions that I and certainly others too would like to see on our main page. And there are good people that could give you a nice response. Formulatiing a good question is not difficult, you just state the problem and what you'd like to know or dont understand, as you did here in chat and that's it ;-)

Sadiq

5:55 AM

Looking for physics textbook, following criteria:

* English language
* No more than about 500 pages
* Not very densely formatted, the way most recent scientific textbooks are i.e. not with lots of side boxes and such
* Calculus-based but not exceedingly formal
* Covers fairly wide array of topics
* In particular, covers physical principles behind electronics and chemistry

Any texts that meet these criteria are acceptable and I will sort them on my own.

user54412

@Sadiq sounds like a description of Halliday, Resnick, Krane

user54412

broad survey of introductory physics at an easy level; some calculus; volume 2 has a lot on electricity and a short chapter on chemistry

user54412

that said, don't expect anything deep out of that book - it mentions many topics, but it avoids all the (imo) best part, which is the underlying connections and structure found in physics