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6:00 PM
@Sid It really depends. There have been posts that personally attack other users. Don't you think it's ok for a mod to nuke that?
@DavidZ Interesting. I tend to prefer less information about the OP's state of mind and more just getting to the physics.
Everyone has their own style.
 
Sid
Absolutely. There isn't much of a second opinion in that case. My point is, closure of border-line questions should be left to the community rather than mods.
 
I would agree.
Obviously, the issue remains that what is "borderline" to you or to me may not be to a particular moderator.
It is of interest to discuss with the moderators how they view certain issues. They all have different opinions.
 
@DanielSank Yeah, I mean, that's just my off-the-cuff attempt to come up with an introduction that links the previous question in line. You could just as well do "[ask the question]? This came up [in previous question](link) because..."
 
@DavidZ Yup. So many ways to ask a thing.
 
Sid
Exactly. Having 5 community members chipping in with close votes is much better than a single mod hammering it for closure.
 
6:03 PM
It's not the stuff about the user's state of mind that I really care about, it's about having descriptive link text and also about having the question written in a way that makes sense even if the link weren't there
 
The fraction of {possible ways to word a question} that are {not terrible} is pretty low...
@Sid It depends on the question.
In general, I agree.
That was actually one of the reasons I didn't want to run for moderator some time ago. The ironic thing in my case is that I've stopped working on the close queue anyway, lol.
It's weird that mods can't cast non-binding close votes.
 
Sid
Their close votes being binding, if they close too much, it makes them look dictatorial IMO.
But, Physics SE has much sterner rules.
So, I guess it is fine if mods close questions which violate policy.
 
So, my personal take on this is that it's much, much better to edit a question to make it better rather than close it.
 
@Sid The advantage of mods unilaterally closing questions is that they get closed more quickly - that is, quicker feedback for the asker and a more effective disincentive to ask off-topic/unclear/etc questions. Our view is that, if a question would definitely get closed anyway, it might as well happen quickly rather than slowly. (Plus, if we do make a mistake the question can be reopened by the community, it's not like it's irreversible)
@DanielSank Of course those aren't mutually exclusive options - it's supposed to be close, then edit, then reopen.
Although I guess if you can immediately see how to edit the question into shape, it is best to just do that.
 
@DavidZ That's interesting. One effect that could be in play there is that if a n00b's question is closed by a mod, they see that as one jerk closing their question instead of a whole community.
@DavidZ Yeah I sometimes wonder whether newish users get that.
 
6:08 PM
@DanielSank Hm, good point
 
Having a question closed feels crappy.
@DavidZ Yup.
That's how I'd feel, anyway.
If a community closes a question I am waaaaay more likely to think "oh, I should learn the rules here".
If a mod closes it, I'm focused on that one name. That one guy who ruined my day and is keeping me from doing my homework or whatever.
 
@DanielSank Probably not. It's an unusual system. Clearing that up was the point of calling it "on hold" for the first seven days; I would assume that helps a bit, but I'm not sure how much.
 
@DavidZ Yeah, hard to know.
This, by the way, is why I think the right way to think about close reasons is "what do I want to convey to newer users about how they can write better questions", rather than "how do I logically explain the criteria by which this question is unacceptable".
It's like, if your math homework is wrong, and the teacher writes "Wrong, matrices are commutative" that's less useful than "Matrices aren't commutative. Take a look at the commutator to make this work out".
I think we do a reasonably good job at this in the homework close reason, actually!
 
Can some please explain why the retarded green's function has a commutator as in this question? physics.stackexchange.com/questions/333844/…
 
@Anonjohn Ugh, seven years ago I could have helped you there. I've forgotten everything now :-(
 
6:13 PM
@DanielSank Thank you :) atleast you responded. :|
 
@Anonjohn Pffft fat lot of good it did you.
All I remember is that you have to work through things from the very beginning and make sure you understand all the steps in order to understand this stuff.
I was too slow at it and eventually stopped that line of study.
I do easier stuff now.
 
Thats alright! I am sure i will figure it out eventually :) Its just nicer when people respond, to a request, even if in the negative.
@DanielSank What do you work on now?
Oh wait, just read your page.
This forum can be quite intimidating for new comers, to be quite honest.
 
@Anonjohn I'm happy to hear that.
 
Sid
SE is pretty intimidating anyway. Once you get used to it, it's extremely addictive
 
Yes it is.
And you are a student?
 
6:17 PM
Yea.
 
I would ask where, if you don't mind answering.
 
Ambitiously self learning QFT and conformal field theory.
 
I know some users prefer to remain anonymous.
 
Currently at TIFR, Mumbai, India.
I like the anonymity, but you're a nice guy :)
 
I haven't been in Mubai.
Is it good for tourists?
 
Sid
6:19 PM
You should. @DanielSank
And try the food.
 
Its better than the rest of india. But india is not really tourist friendly.
 
I love Indian food.
 
When i travel abroad, I experience a huge culture shock. Especially with how nice people are.
 
Actually, as you are Indian I will share something with you.
 
Sure :)
 
6:22 PM
Here is a vegetarian chili recipe. A friend of mine from India said it was good and made it for her husband, who also liked it and requested that she make it again.
So I think it is suitable for Indian tastes.
 
@DanielSank That's a good point, and I'm not trying to dismiss it by saying this, but I think we should also keep in mind that the fundamental reason we have question closures in the first place is to protect the site from bad questions. Helping people who have asked bad (I mean, off-topic/unclear/whatever) questions to ask better questions is an admirable goal, but it is not the reason the closing functionality exists, and I would argue, not the primary goal of the feature.
 
@DanielSank Thanks. Not much of cook, but will try it this weekend.
 
I would point out that helping would-be users improve their asking-fu is a pretty direct way to protect the site from bad questions.
...and it means less work for you.
 
@Anonjohn Funny how I often hear people say that (i.e. that the forum is intimidating at first). I honestly felt "at home" the moment I opened an account:P and it's still the only place in the entire world where I truly feel at home.
 
@ShaVuklia I have grown to like it over the last week, but to be honest, some i have always been afraid of saying something wrong or stupid here.
 
6:29 PM
Yea I have that fear too in real life, but never online, as I can take my time to type out my questions/thoughts @Anonjohn
 
@DanielSank Why can't there be a compulsory walk through through what a good question is once someone makes an account. Giving a good example and all with the most rudimentary concepts. As of now it's not compulsory. Though there is something like that when one visits Meta for the first time. Though making it compulsory doesn't mean one will actually go through all of it. But at least he/she would remember something.
 
Its probably a function of the kind of person you are. Its probably fun when you approach the forum with an open mind and the intention to talk and discuss physics.
 
yea, definitely the latter:P it's amazing that the overall theme is physics (or maths, I love the math chat)
 
@ShaVuklia I think, in the few run ins we had had over the last couple of days, you have been one individual, who has been quite prolific with questions
 
your answer to my question about Biot-Savart was really nicely written, btw
 
6:32 PM
Thank you:) I think thats the way to get the most out of the forum
 
hahaha:P yes, that is true. I used to post them on the forum, but when I discovered the chat, I usually try there first.
 
and transform it to a learning experience
Are you a student as well?
 
yes, first-year student maths&physics
 
@DanielSank I don't think so. (Depends on our definitions of "pretty direct", I guess) I definitely agree that helping people improve their asking-fu is a useful tool in our efforts to protect the site from bad questions (and encourage good questions - the two goals are intertwined), but I don't believe it will stop or even significantly reduce the influx of bad questions.
 
Sid
@ShaVuklia Interesting choice. You must be enjoying it. :)
 
6:33 PM
Yes, I guessed as much!
 
@Sid you have no idea how much I love it:P
lol, some random guy just placed a pink stress ball besides me on the table as he passed by
 
@ShaVuklia Your bio says you're dutch :) My parents lived there for many years.
 
that is the second time this year I receive a stress ball from a stranger
 
Sid
@ShaVuklia Apparently people view you as too stressful :P
 
@Anon oh cool!
@Sid Haha XD
 
6:38 PM
@ShaVuklia Don't you have a summer break or something?
 
@Anon oh gosh no. I have my finals in a week, then a project that will last a month, and then "retake finals". So I'll be done 7th of July.
How about you?
 
Sid
@ShaVuklia Retake finals?
 
I just started my break :) Which is why i have so much time to spare.
And presumably you're taking electrostatics 1?
 
@Sid yea it's to retake tests that you failed at. I skipped a couple of tests, to spread it out. I don't want to waste the retake finals (which are the first week of the summer holiday) on vacation :P
but yea, I'm taking electrodynamics I guess
 
@KunalPawar Because the SE software isn't written that way.
@DavidZ Are many of the bad questions from one-time or first-time posters?
 
6:41 PM
@ShaVuklia No wonder people are leaving stress balls on desk
 
hahahahhaha!! :P
electrodynamics is doable tho!
I also have to do quantum, starting tomorrow :P
which year are you actually?
 
@ShaVuklia I am finishing off my masters!
Hope to apply to cambridge next year.
Fingers crossed.
 
Sid
@Anonjohn For PhD?
 
oh niiice @Anonjohn
I hope they accept you! When will you know?
 
@Sid The tripos first. I have a long way to go before i can start a PhD. I know nothing!
I will apply end of this year.
And will know by Feb 2018
 
6:45 PM
oh right, I assumed your masters had already finished
 
@DanielSank I believe so - not all, but a significant fraction - although I'd want to make some attempt to look at the data before definitively claiming so
 
@ShaVuklia Oh no. I have this last year to see through!
 
haha:P
 
If things don't go well, a stay back and learn more, i guess.
@Sid Are you indian as well?
 
user228700
@JohnR: What the heck are u still doing around?! :-o
 
Sid
6:48 PM
@Anonjohn yes sir.
 
@Sid Cool! I see a lot of JEE prep people here on SE.
Infact, there was an incident involving a few yesterday.
 
user228700
(I'm in love with Aragorn, BTW. Well, was, until I learned that he's really almost 90 years old!)
 
@Sid Are you also in that boat?
 
Sid
@Anonjohn I think it is fair not to discuss what happened yesterday. What's gone is gone.
"That boat"?
 
@Sid One of the people prepping for JEE i mean.
 
Sid
6:52 PM
Well.... I don't know. I mean, I am going to appear for the exam. And I believe I would do fine.
 
@Sid I didn't mean to kick any dust. I was pointing something. I don't really mean to talk about anything of the sort.
@Sid Good luck, for it then!
 
Sid
Also, the reason I am in SE is because people here are a lot more co-operative and talk normally unlike some of my Real Life friends..
 
@Sid It can get a bit intense, the JEE thing. When is this thing anyway.
 
Sid
The Day after Tomorrow.
D-Day. :P
 
user228700
Well, tomorrow, really. It's officially the day before, 20th now.
 
Sid
6:54 PM
Oh, not in UTC, the one which SE uses.
 
user228700
Ah, well.
 
@Kaumudi.H Another person watching the clock! Appearing for JEE as well?
 
user228700
Hi :-) No, I am rid of that nonsense; not writing it.
 
@Kaumudi.H Thats a wise move :)
 
user228700
Prepared for it for three years though.
 
6:56 PM
@Kaumudi.H And dropping it now? why?
 
Sid
I am already fed up in the last 2 years.
I just want this thing to end now.
 
user228700
@Anonjohn Eh, it's too long a story :-)
 
user228700
@Sid One more day to go! You're nearly there! :-)
 
@Kaumudi.H Well, good luck, with whatever you have planned :)
 
user228700
Thank you :-) And u as well.
 
6:58 PM
@Sid I am sure you ll do very well :)
 
user228700
@Sid: Good luck, then!
 
Sid
Well, I hope to. :)
In any case, skills matter more than a tag. So, not a huge amount of pressure on me either.
 
@Kaumudi.H I was reading the Hellboy in Hell comics, but I've finished and there's only half an hour till bedtime so it hardly seems worth starting anything new.
 
@Sid Its true. And i honestly don't want to get into a philosophical discussion about "tags" etc. But, in my experience, the best way to learn anything, is to talk about it. And to find people to talk about it with. I think thats the great advantage a IIT has.
 
I'm kind of hanging around surfing the Internet.
 
user228700
7:01 PM
@JohnRennie Ah, OK :-) Like I said, I'm (again, was really) in love with Aragorn.
 
@Kaumudi.H He doesn't do anything for me :-)
 
user228700
:-/ What's he like in the books?
 
It's a big point in the books that he's ugly.
He's also rather gruff and brusque.
 
user228700
Hmm, really?
 
Sid
@Anonjohn "Find people to talk about it"- That's what SE chat is for, right?
 
user228700
7:03 PM
@JohnRennie gruff and brusque?! That's not the way they've portrayed him in the movies!!! :-o
 
Yes.In fact the hobbits are wary of him at first because he looks so fierce.
Let me find a quote ...
 
user228700
Well, I mean, he is sort of gruff and brusque but also quite warm...
 
@Sid Nothing can be a substitute for real life interactions, where you can argue, get emotional, love it and what not.
 
Sid
Well, Yes, agreed.
 
@Kaumudi.H Are you Reading the Lord of the Rings for the first time?
Oh wait...
@JohnRennie I don't remember that. Isn't he just poorly clothed?
 
user228700
7:05 PM
@DanielSank OK firstly, for the first time?!?! Who reads it more than once?!
 
@Kaumudi.H Uh... lotsa people.
Me.
 
user228700
Secondly, hi :-)
 
@Sid Anyway, good luck :)
 
@Kaumudi.H Hi.
 
user228700
@DanielSank Wow.
 
user228700
7:06 PM
And thirdly, nah, I'm just watching the movies.
 
@Sid Good night. I have to wake up in the morning :)
 
@Kaumudi.H They are very good.
 
Sid
Good night!
 
There was a long silence. At last Frodo spoke with hesitation. ‘I believed that you were a friend before the letter came,’ he said, ‘or at least I wished to. You have frightened me several times tonight, but never in the way that servants of the Enemy would, or so I imagine. I think one of his spies would – well, seem fairer and feel fouler, if you understand.’

‘I see,’ laughed Strider. ‘I look foul and feel fair. Is that it? All that is gold does not glitter, not all those who wander are lost.
 
user228700
@DanielSank Indeed, they are.
 
user228700
7:07 PM
@JohnRennie Thanks!
 
@JohnRennie That doesn't mean he's ugly.
He was making a joke.
"laughed Strider"
 
user228700
^ I agree. I'm still in love with him :-P Man, where are guys like Aragorn in real life?!
 
@Kaumudi.H Like Aragorn in what way?
 
user228700
non-90 y/o Aragorns, I mean.
 
King of mankind?
Blessed with long life?
 
user228700
7:08 PM
@DanielSank Lol, no. Warm.
 
Which characteristics of him are you interested in?
 
Sid
Humph. People still read LOTR? I have the most controversial opinion that the Hobbit and LOTR are overrated.
 
user228700
His warmth and loyalty, most of all.
 
Sid
Though, I haven't read the books. Just watched the movies.
 
@Sid They are both excellent, IMHO.
@Sid facepalm
@Kaumudi.H There are many such humans.
 
7:10 PM
2001: A Space Odyssey is overrated.
 
user228700
@DanielSank I've read The Hobbit and liked it very much! :-)
 
user228700
@DanielSank Well, that hope is what keeps me going in that regard.
 
user228700
 
user228700
Oh, wow. Doesn't look nearly as handsome without the beard! :-o
 
Yes yes, he's pretty.
 
user228700
7:13 PM
@DanielSank :-P Oh, give me a break!
 
user228700
Gosh, it's nearly 1 AM and I still have 2.5 hours to go! God help me...
 
Sid
@Kaumudi.H It's only 1AM
 
4
Q: Do light and sound waves have mass

espaisI have been reading Hawking's 'A Brief History of Time' and it has gotten me thinking about Einstein's theory of relativity, in that it assumes that an object must have infinite mass if it is to be traveling at the speed of light (please correct if I'm wrong in my beginner's knowledge of physics)...

any mod around?
 
user228700
@Sid I'm not really a night-owl :-)
 
user228700
Hmm, the phrase night -owl doesn't make that much sense. Owls are nocturnal by nature.
 
Sid
7:15 PM
Pity. Night has its own Charm. :-)
 
user228700
@Sid And so does dawn :-)
 
user228700
@JohnR: Actually, I quite like that he's burly and ragged. He wouldn't be nearly as, erm, charming (?) were he more refined, as in the photo.
 
user228700
No, not charming. Oh, what's the word?!
 
Sid
@DanielSank You tell on your profile that you have met quite a few guys from Physics SE. Do you guys conduct a meet-up or something like that?
 
@Kaumudi.H don't look at me. Galadriel is more my type.
 
user228700
7:20 PM
Oh geez, that lady is terrifying!
 
@JaimeGallego I thought I liked it but it didn't matter anymore to me after watching Solyaris.
(The one by Tarkowskij, not the american bullcrap)
 
user228700
 
user228700
No, thanks :-P
 
@Kaumudi.H There was a girl used to come to our SF reading group who looked remarkably like Arwen in the film. Sadly she has moved away from Chester now.
 
user228700
Ah, nice! :-) Arwen is preeetty.
 
7:22 PM
The most interesting characters in the whole LOTR series are unquestionably Bilbo and Gollum.
 
user228700
@BalarkaSen Gollum, yes but Bilbo?
 
Yes, even though he had nothing much to do with Fellowship. But that's where it all started.
 
user228700
Right, but how does that make him one of the most interesting characters?
 
Not scary at all :-)
 
user228700
7:24 PM
@JohnRennie :-P OK OK.
 
user228700
Still a bit creepy though, she is.
 
@AccidentalFourierTransform Mind helping me out?
 
@Kaumudi.H He's the reason the whole story exists!
 
@Anonjohn I can try.
 
user228700
So what? That doesn't make him inherently interesting!
 
7:26 PM
not to you maybe
 
user228700
No...
 
Wondering why a commutator appears in the reatrded greens function here physics.stackexchange.com/questions/333844/…
 
I don't know if you see this in the movie but he's also the first person in many many years to defy the control of the ring
other than the lord of the rings himself :P
 
i would expect to be plain and simple Tr(\rho \phi(x_1) \phi(x_2)) \theta(x_1-x_2) @AccidentalFourierTransform
 
user228700
@BalarkaSen Ah, that's true...
 
7:28 PM
omg guys, the derivation of Ampere's law was pain
I spent hours on it
 
@ShaVuklia Griffiths?
 
nobody in the fellowship accomplished this, for one @Kaumudi
not even frodo
 
yessss:( :) @Anon
 
Sid
@ShaVuklia Electrodynamics?
Or Magnetics?
Wait, that was magnetics..
 
hahahah:P
yes magnetics
 
user228700
7:30 PM
@BalarkaSen Well, yeah, but still. That doesn't make him particularly interesting to me. Perhaps my view would be different had I read the books...
 
@Anonjohn Im not entirely sure what you mean - you are asking why $\Delta_\mathrm{ret}(x-y)=[\phi(x),\phi(y)]$ is true? (assuming that equation is true, which I'm not actually sure off the top of my head)
 
@AccidentalFourierTransform yes
 
Sid
(Kicks self) - Maybe I should just calm down now..
 
@Acc
 
@Anonjohn well, you can calculate $(\partial^2+m^2)[\phi(x),\phi(y)]$
 
7:32 PM
@AccidentalFourierTransform There is a path integral over closed loops sitting there as well
In the trace
 
you should obtain zero
 
over\rho
 
Im have no idea how to calculate path integrals at finite temperature, sorry
never done that
 
@Kaumudi.H Fair enough. Have you gone through Cirith Ungol yet?
 
Its just a wick rotation away from standard QFT.
 
user228700
@BalarkaSen No...
 
@JohnRennie Bedtime is approaching, Citizen Cane :)
 
that has to be the most boring movie ever
I literally fell asleep 10 minutes in
 
@Sid Nope, no meetup.
Just happenstance.
 
user228700
I gots to finish watching before bed, dang it. Alright, bye!
 
7:34 PM
@JohnRennie Why are we posting images of actors/actresses?
 
Sid
@DanielSank So, how do you recognise each other?
 
@AccidentalFourierTransform Tell me how i would go about calculating non time ordered products in a path integral?
 
AFAIK, you cant
operators inside the path integrals commute
that means that whatever you calculate with it
it will be symmetrised
 
@AccidentalFourierTransform Cant you choose a path, that goes forward in time till one point operator one then backward in time to the next point insert operator 2 and so on and so forth
?
 
are you talking about QFT or point-mechanics?
because in QFT you dont integrate over paths
you integrate over field configurations
 
7:39 PM
Right, but field configurations are best understood in terms of integrations over discrete degrees of freedom no?
On a lattice or some such?
 
yep
still, no paths
you have a four dimensional grid
and one integration variable at each point in this grid
and you integrate over all those integration variables
 
So, you would integrate over configurations of the fields no?
Yea, sorry, bad language, thats what i meant by a path
So, suppose i did the integral over configurations in this 4 dimensional grid, such that i the field evolves forward in time till time t_1 insert field config \phi(X) here back ward till t_2 insert field config \phi'(X) here and finally forwards to t_f.
Does that give me non time ordered expectation value?
 
hmm that doesnt make much sense: once you introduce the grid, you dont have fields anymore
you have one integration variable per point in space
the functional integral becomes $$Z=\int\left[\prod_{i\in\mathbb Z^4}\mathrm d\xi_i\right]\ \mathrm e^{iS(\xi)}$$
where $\xi_i=\phi(x_i)$
and you cannot "evolve things back and forth in time"
you dont get to choose paths in the grid
you integrate over every point in the grid
 
these \phi(x_i) 's are functions of time as well correct?
if i stuck to one point on the grid for the time being.
*one point on the spacial grid
Actually, i think i am confused how all this is even working
But that question is attempting to do something of this sort, especially since there is no time ordered product in the integration for a retarded greens function
And i checked the book, and it seems to say this is a legitimate thing to do
Use path integrals to calculate non time ordered expectation values
 
I guess you could do that by dropping some analiticity conditions on the correlation functions
I dont really remember how it works
but IIRC, time-ordering in Lorentz signature corresponds to analiticity in Euclidean spacetime
or something like that
I dont remember how the time ordering is recovered from the Wick rotation
 
7:54 PM
Like this \langle \phi(x)_f|exp(-iH(t_f-t_1))\phi(X) exp(-iHt_1)|\phi_(x)\rangle
so if there were two insertions at t_1 and t_2 we would get
\langle \phi(x)_f|exp(-IH (t_f -t_2))\phi_2(X)exp(-iH(t_2-t_1))\phi_2(X) exp(-iHt_1)|\phi_(x)\rangle
Thats what a insertion on the path integral at $t_1$ and $t_2$ correspond to
in the schrodinger picture
@AccidentalFourierTransform Anyway, thanks for your time :)
 
that looks like point-mechanics (or CFT) lol
 
Aren't the two the same, at some level?
Fancy names for the same thing?
QFT is just QM with a large degrees of freedom no?
 
8:10 PM
yeah but $|\phi(x)_f\rangle$ is non-standard notation :-P
 
It is merely the eigenvector of the field op
isn't that a perfectly acceptable thing
 
@heather @AccidentalFourierTransform Bad news
9
A: Comment votes can be easily gamed by users with the association bonus

Adam LearAs I said in the comments, the votes are deleted, but the denormalized Score stored on the comment itself is not updated. I spent some time looking into a fix and, after further discussion with Nick Craver, I have to be the bearer of bad news here - we can't fix it at this point. Not without sp...

 
Infant this is notation learnt from peskin
*Infact
Isn't that pretty standard?
 
Maybe you just need to go down and do some footwork... the beat is ready!!!
 
8:34 PM
@SirCumference bad news indeed =/
 
8:56 PM
@heather @AccidentalFourierTransform How is that such a big deal?
 
@EmilioPisanty well, I mean, it'd be really hard to fix a decently sized problem.
unfortunate, I guess.
 
@heather no, seriously, what's the actual exploit mechanism?
someone makes a ton of accounts, earns 15 rep on each, and then uses that to upvote a comment?
 

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