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12:19 AM
Anybody have the latex code for the list of Dynkin diagrams mathworld.wolfram.com/images/eps-gif/DynkinDiagrams_701.gif
 
12:40 AM
@bolbteppa email Brian Hall and ask for them
 
12:53 AM
@heather are you still there?
 
yes, but i'll be leaving soon, sorry
 
I've tried to make a digest of the paper.
we can pick it up at some other time.
 
thank you, i'll read through that!
thank you so much =D
 
no worries. You can also add text on the left panel and it will typeset (in LaTeX) on the right.
 
okay.
 
12:54 AM
this is simpler for long technical discussions.
all right... we'll be in touch. Best!
 
"the answer" -> the answer ACM linked here physics.stackexchange.com/questions/279263/…?
 
yes its looks like a trick to use SPDC type I to generate entangled pairs... I'll read through this... thanks.
 
that's what i'm using, yeah.
@Mithrandir24601 said it was incomplete though.
 
this is closely related to what's in the paper I showed you...
ok... go. we'll come back to this later.
 
okay, have a good night!
 
 
1 hour later…
2:05 AM
Hi, everybody.
 
@DanielSank Hey!
 
@Blue Ah yes, that could be possible. Try googling "angular momentum eigenvalues for valence band electrons"
 
@DanielSank I was informally invited to give a talk, should I mention it to those people again or drop it unless they bring it up
 
2:43 AM
@0ßelö7 Impossible answer.
That's like asking "I have a can of Coke. Should I drink it?"
 
what more information do you need to give advice?
 
Well, weather or not you want to go would seem relevant.
 
@DanielSank very much
 
@0ßelö7 Well then yes, mention it.
 
3:01 AM
@DanielSank ok, thanks
 
3:39 AM
i'm a noob in physics and i want to not be a noob, any suggestions?
 
how much math do you know?
 
4:00 AM
a fair bit, up to a typical graduate level
@0ßelö7
 
@frogeyedpeas then why are you a noob
 
well because in the physics world i honestly don't think i know more than basic classical mechanics
and i'd like to get out being hand wavy to having a concrete understandign of what i'm doing, ideally doing my own math (i.e. checking equations myself, writing simulations myself)
@0ßelö7
Maybe, now this is a tall order, it would be cool too if the stuff i read in pop science websites, I could actually then read in their original research paper form, and verify up to the math
 
4:16 AM
@frogeyedpeas ok, read Hall's "Quantum Theory for Mathematicians"
@JohnRennie morning?
time for a benchmark?
 
It's a bit early in the morning for benchmarks. Give me a chance to drink my coffee first :-)
 
4:49 AM
@Kaumudi.H morning :-)
 
user228700
Morning! :-) How's ur coffee?
 
Anonymous
@Kaumudi.H Hi, no class today?
 
user228700
@Blue Hey :-) No, I'm on Onam vacations till the 10th.
 
user228700
And you? What are you doing here?
 
Anonymous
@Kaumudi.H Ooo...nice. I have class in 30 mins :P
 
4:51 AM
Coffee is good. Mum buys this posh coffee so I'm drinking that :-)
 
user228700
@Blue Ah :-P Have a good day! :-)
 
user228700
@JohnRennie Ah, haha, I see :-)
 
user228700
You drink instant coffee, don't you?
 
Normally yes.
But my Mum buys this coffee that is a mixture of instant coffee and ground coffee.
 
user228700
I've heard that coffee connoisseurs look down quite harshly upon instant coffee drinkers! (And that would include even me for we don't have a coffee machine!)
 
4:58 AM
So it has the convenience of instant coffee but has some of the flavour of freshly ground coffee.
 
user228700
Ah, nice. Hence posh, eh? :-)
 
I'm not a coffee connoisseur :-) It's just something I drink first thing in the morning to get me started.
 
user228700
Yep, yep, I know :-)
 
@Kaumudi.H posh = expensive !
 
user228700
Well, right, but I assume that blending in some of that ground coffee is, by definition, going to be more expensive than instant coffee!
 
5:01 AM
Yes, and I guess that's fair enough. It must cost the manufacturer more to make.
 
By definition? What if you grow your own coffee? =P
 
user228700
^ Ah, I hadn't considered that!
 
By the way, is anyone here a postgraduate or higher? I need some advice on finding time to self study (defining self-study to be study you do for enjoyment, as opposed to study along the lines of your course).
not that I don't enjoy my course. Its just that I like a change of topic every now and then.
 
I was a postgraduate student several decades ago ...
 
Then you would know all about it :)
presumably
 
5:09 AM
0
Q: The Bohm interpretation and Schrodinger's cat

blueblastI was wondering how the Bohm interpretation of quantum mechanics would affect the Schrodinger's cat experiment. Would it imply that the cat would be in one state and never in superposition, so the cat would always be dead or alive whether or not the observer looks or not?

possibly will fail if you don't have an ensemble of cats
 
@user400188 I'm not sure what you're asking. Are you doing a PhD now and finding you want to study something else in your spare time?
 
No, I'm an undergraduate.
 
What degree are you doing?
 
The problem I am facing, is that there are a lot of interesting topics like General relativity, that are not part of my course. As such to learn them I'm either going to have to wait or do my own study.
A double in Robotics and Physics
 
My instinctive reaction is that your priority should be getting a good result in your finals, and you should be cautious about anything that risks taking too much time from that.
As I recall (and it was a long time ago) I and my friends used to use what free time we had doing something completely different e.g. sport (and drinking :-)
I didn't start learning about GR until a few years ago, and I found it enormously enjoyable. But it takes a lot of time and effort.
 
5:21 AM
Hmmm. I think I'll take that advice to heart. I have found myself taking some time from my own course to study this particular way. Perhaps I should tone it down.
Thanks @JohnRennie
That said, I do have a Colleague that is teaching myself and another about GR at the moment. We have just begun (currently only up to the maths aspect) , but we plan to tackle the physics eventually.
Its a slow pace, only 1 session together a week. But I think that by the start of next semester (holidays are in between) we will have finished.
I think I'll drop my other topics in favor of my course, but keep this one.
 
There is a balance to be struck. It's always interesting to learn stuff that isn't part of your course as long as it doesn't detract from your course work. One meeting a week on GR doesn't sound excessive :-)
 
@user400188 Which year are you in at the moment, if you don't mind telling us here?
+1, agreed with @John. It's best to first focus on your coursework and finish well enough. 1 day per week on exploring new topics seems alright
 
Technically 3rd year. But because the science aspect of my course started late, I'm only taking 1 3rd year physics unit at the moment.
 
Anonymous
@user400188 GR should be taught in a Physics degree, isn't it ?
 
Not in ours. I don't think anyone at our particular university is both knowlageable enough and feels like teaching. Its the same for particle physics.

For those two subjects the uni advises us to go to other universities. For instance, there is one close by that is leading in particle physics.
 
5:40 AM
@Blue GR isn't normally taught at undergrad level in the UK, though the more able students may do some GR work.
Though maths students may study GR at undergrad level. I think that's possible at Cambridge.
 
6:09 AM
@Mithrandir24601 what is the name of your institution?
 
Anonymous
6:41 AM
@JohnRennie Oh...that must be a BSc (3 year) course I guess. Over here most of the good universities do not offer a 3 year UG course in physics. They are mostly 5 year BS+MS.
 
Anonymous
So they include GR
 
user228700
6:56 AM
@JohnR: Did I tell you that my driving test is tomorrow?
 
@Kaumudi.H no, you didn't say. I didn't tell anyone when my driving test was in case I failed :-)
Anyhow, good luck! :-)
 
user228700
Ah, well, there is a fair chance that I really am going to fail; I haven't been in the driver's seat of a car in over a month.
 
@user400188 2Okay
 
@Kaumudi.H I have to confess it took me a couple of goes to pass.
 
user228700
Oh, wow, I see. That explains why you stopped telling other people about the date, haha.
 
7:01 AM
In the end I bought a motorcycle and passed the test on that. Then I spent a year riding the motorcycle before I came back to the car. After a year on the bike I found the car test really easy.
I think a large part of the test is just confidence, and you only really get that with experience.
 
user228700
Ah, right, that makes sense.
 
user228700
Since my parents have paid an exorbitant amount of money to the driving school, they will make me pass even if I do technically fail the test, I think.
 
Really? I guess it's good if you get to pass the test, but it doesn't fill me with confidence about driving on Indian roads :-)
 
user228700
@JohnRennie You would be right to feel that way! Some of them didn't even need to drive at their tests!
 
Eek :-)
I guess my advice, for the little that's worth, would be to try relax and enjoy the driving. Probably easier said than done though.
 
user228700
7:07 AM
Hmm, thanks :-) I might ask the driving school if it's possible to practice once before the test.
 
user228700
Today evening, perhaps.
 
Actually that's not a bad idea.
 
user228700
Yeah?
 
Though they may charge extra of course.
 
user228700
They will :-/
 
7:09 AM
Yes, maybe get the instructor to give you a mock test?
Or at least take you round the usual test routes.
 
user228700
Yes, I will ask if this can be arranged.
 
Windows 10 all still working fine?
 
user228700
Right, so I've called and they told me that there will be a trial at the test center at 9 AM.
 
user228700
@JohnRennie Yes :-) Time to activate it, don't you think?
 
@Kaumudi.H yes, if you're happy it's all fine then activate it.
 
user228700
7:16 AM
OK (Y) The code is in the case containing the battery, isn't that what you said?
 
Yes. Take the battery out and you'll see a blue green label with the key written on it.
The key is five groups of five letters.
 
user228700
OK. Will do now and update you.
 
user228700
Yes, done :-)
 
@Kaumudi.H It activated OK?
 
user228700
Yep!
 
7:28 AM
Good. All set then! That was fairly painless all things considered.
It's a shame you don't know more about what your programming courses are going to cover or you could download the software for them now.
 
user228700
@JohnRennie Not really but it is done and over with now!
 
user228700
@JohnRennie For now, I am meant to learn Python, familiarize myself with Git/Github and solve those exercises.
 
You could install Python ...
 
user228700
Yes, that I must do.
 
It's a small download and a quick install.
You can also install GIT for Windows. You don't have to use unix/linux to run GIT.
Let me have a quick look to see what version of GIT I use on Windows.
 
user228700
7:32 AM
@JohnRennie Ah, but I think I am meant to.
 
I'm pretty certain I installed this one:
NB that link will autostart the download.
 
user228700
@JohnRennie Ah, too late! :-)
 
user228700
I'll do it a bit. Thank you :-)
 
It won't hurt to have GIT available on Windows. It's a small program and installs quickly. And it works in exactly the same way as on unix.
@Kaumudi.H do it now!! :-)
 
user228700
:-) I'm about to go make lunch, you see.
 
7:34 AM
Ah, yes, food always takes priority :-)
 
user228700
:-) Sandwiches again!
 
Q. why is there always lots to eat on the beach?
 
user228700
Uhh, no idea. You tell me.
 
A. because of the sand which is there
(c) Dad Jokes Ltd
3
 
user228700
@JohnRennie x'D I cracked up because of the copyright statement more than the joke itself!
 
7:38 AM
I aim to please
(though I usually miss)
 
user228700
:-)
 
It's hours till lunch
 
user228700
:-( More coffee?
 
Yes, in a moment I shall make another pint of (posh) coffee
 
user228700
And I'm off to make lunch! I'll be back to ask desperately for help regarding Git etc. :-P
 
7:41 AM
Actually I have to go out soon to fix a laptop for one of my mother's friends.
I'll be back about 11:00 BST
 
user228700
@JohnRennie Ah, this again! :-) Have fun!
 
Enjoy lunch. See you later.
 
user228700
OK, bye! :-)
 
Anonymous
@Kaumudi.H Are you sure your uni has Git in syllabus? For using Github you don't really need to know Git :P The coding club might expect you to know it, though :)
 
Ok, this is unironically my favorite rap song of all time.
 
8:09 AM
@ACuriousMind this is theoretically true but in practice has never happened to me in years of using BitTorrent. If you're just a little careful you can be sure you'll be safe.
 
 
1 hour later…
9:11 AM
@JohnRennie they also do GR in part II physics :)
 
user228700
@BalarkaSen Unironically? Really?
 
user228700
Ah, Memelous again, I see.
 
user228700
@Blue Yep, the coding club does :-)
 
@DanielSank the Uni is University of Bristol, the school is school of physics, the department is either physics or centre for nanosciece and quantum information (NSQI) and the group is centre for quantum photonics (CQP)
 
user228700
@Balarka: Have you watched/read/listened to anything created by Bo Burnham?
 
9:18 AM
@Kaumudi.H I am afraid not. I don't follows stand-up comedians much.
 
user228700
Ah :-/ Well, his work is truly genius.
 
I see
 
user228700
Also, he doesn't exactly fit the norms of a quintessential stand-up comedian.
 
user228700
Here, watch this when you've got the time:
 
user228700
9:24 AM
I watched the whole show and it was after this performance that it really struck me just how excellent he was.
 
I'll check it out at some point of time
 
user228700
Cool.
 
so how's college
 
user228700
@BalarkaSen Miserable :-P How's school?
 
still hanging around. :p
also that sucks
 
user228700
9:31 AM
@BalarkaSen :-) Have you finished your portions? I expect you have, no, by this point?
 
what's a portion?
 
user228700
Syllabus :-P
 
Anonymous
I came back home. Not feeling like attending classes today :P Our comp professor has a voice modulation problem. He makes me feel sleepy. lol
 
user228700
@BalarkaSen Yeah, thanks.
 
user228700
@Blue Home?
 
9:32 AM
oh not really. I have a chunk of physics I haven't done yet
and the inorganic stuff in chemistry
 
Anonymous
@Kaumudi.H Well, my second home is 5 mins away from uni. :P
 
user228700
@BalarkaSen Oh, no, not you! I meant your school.
 
user228700
@Blue You second home? Hostel, do you really mean your hostel?
 
He lives near his university, I suspect
 
Anonymous
@Kaumudi.H No. It's a flat where I stay with my mom. Sometimes alone
 
9:34 AM
it's all in kolkata after all
 
Anonymous
I earlier used to live in Guwahati
 
@Kaumudi.H Ah. Well, sort of
 
user228700
@Blue Oh, wow, that's great! None of the added misery of terrible food!
 
Anonymous
@Kaumudi.H Yep! :D I can eat home-made food along with canteen food everyday
 
user228700
@BalarkaSen Right. Have they started pressurizing you yet? :-P
 
9:35 AM
I heard CMI food sucks
 
Anonymous
@BalarkaSen How about weed?
 
yeah that's easily available
 
Anonymous
lol
 
Anonymous
You're lucky then ;)
 
user228700
@BalarkaSen Huh, my friend told me that it's manageable, actually.
 
user228700
9:36 AM
And her word can be trusted because literally everybody lives in the same building, IIRC.
 
oh really? i guess i talked to the graduate students so that's 4 years back when they were undergrads
 
user228700
Yep! Other than the fact that she is the only girl in her class, her experiences over there sounded great, man!
 
thats nice
 
user228700
@BalarkaSen Oh, speaking of CMI, have you started looking at sample papers etc. yet?
 
Anonymous
CMI is nice. One problem might be that the course is a 3 years one. I wonder how much they can cover within that time.
 
Anonymous
9:39 AM
Some people find it difficult to get a direct PhD admit after a 3 year degree course. So they have to do an MS. But well, I don't think Balarka will need that :)
 
@Kaumudi yeah I looked at the last couple year's. mostly working out problems from here and there
relearnt some number theory in the process
 
user228700
@BalarkaSen Cool :-) If you join, my neighbor might be in your class, depending on whether or not he's able to crack it...in his fourth attempt.
 
Anonymous
@Kaumudi.H 4th? :O
 
Anonymous
wauw
 
Engel has a nice book full with clever problems that i occasionally work on; there's this RMO book I have that's also nice
@Kaumudi well depending on whether or not i would be able to crack it, too
 
user228700
9:41 AM
Right, right :-P
 
Anonymous
@BalarkaSen Who's saying ;)
 
user228700
^
 
i know a guy who's in there - he's into differential geometry
 
user228700
@Blue He completed 2 years of a BSc. Math course in Amrita, Coimbatore before deciding to drop out this year and prepare wholeheartedly for the test next year.
 
Anonymous
@Kaumudi.H Huh. Honestly I think that's waste of time. He could just focus on getting a good MS or PhD degree in Math
 
user228700
9:43 AM
I dunno, man, he seems awfully keen on joining CMI, ya know?
 
Anonymous
Repeating once might be okay. Repeating 3 times is ridiculous.
 
@Avantgarde "Before and after Science" is a nice little minimalist album you should check out. This is my favorite track from there.
 
user228700
@Blue It's actually quite sad :-/
 
@Kaumudi.H :(
 
user228700
@Mithrandir24601 :-) Hi! How's it going?
 
user228700
9:45 AM
@Balarka: Cutting class today?
 
it's teacher's day
 
user228700
Ohh, right.
 
user228700
Doesn't ur school celebrate Tr.'s day?
 
I think so; I don't participate
 
user228700
Right :-P
 
9:50 AM
@Kaumudi.H Pretty well actually, thanks :) I just finished my first year of PhD-ing a few days ago, so have a couple of weeks off to sort out my life and go on holiday before it all starts for real :D
 
user228700
Ah, wow, congratulations! :-) That sounds great!
 
@Kaumudi.H it is that :) It's quite exciting :)
 
user228700
What are you working on, may I ask?
 
You can and if you give me a couple of minutes I'll even answer
 
user228700
Please do! :-) [And excuse me if I am unable to ask thoughtful questions later because I don't understand :-P]
 
10:02 AM
Right, so, in brief, I've just finished a project on what's known as t-designs and my PhD will be on simulating non-Hermitian Hamiltonians on a quantum chip
 
user228700
Very nice! (As expected, I understood nothing at all! :-P)
 
@Kaumudi.H so, the PhD project is essentially simulating non-time symmetric processes on a quantum chip
 
@Mithrandir24601 It's all gone downhill since my day :-)
:: John angrily waves his walking stick in the air ::
 
user228700
@Mithrandir24601 I...OK! I'm just glad you're having fun, mate :-P
 
@JohnRennie Nah! GR was so good :) We had Hobson of Riley, Hobson & Bence fame!
@Kaumudi.H Oh, I am :D Thanks
 
user228700
10:06 AM
@JohnRennie See, if I didn't know you, I'd be inclined to believe that you actually do use a walking stick :-P
 
@Kaumudi.H I'm not quite that old :-)
Yet ...
 
user228700
Oh, I know that but somebody else might not is my point :-P
 
@JohnRennie You don't need to be old to have a walking stick or several (one of my Grandparents used to make walking sticks so I actually had some as a child :P )
(I never actually used them as walking sticks, but I still had some)
 
Anonymous
I used to use walking sticks to pluck mangoes
 
I had a shillelagh when I was a little lad but my Dad took it away when I started hitting things with it :-)
 
Anonymous
10:09 AM
(My grandpa's walking stick :P)
 
@JohnRennie :/
 
I was very little at the time ...
It was a well meant but unwise present from one of the family in NI.
 
Yeah, my Grandparents also had a few of those
 
*have, to be fair
 
user228700
10:13 AM
@BalarkaSen You're...you're watching Pewdiepie now?!
 
i catch up with his stuff. he's the number 1 subscribed channel on youtube; source of lots of memes
 
user228700
Ah.
 
user228700
@JohnRennie Broke a lot of vases and such things, did you? :-)
 
user228700
Or were you hitting people? :-P
 
I don't remember. It was a long time ago :-)
 
10:15 AM
The only reason I know of a pewdiepie is from this video
 
For all I know it may not even be a true story!
 
eg this. if you look carefully you'll see a pewdiepie reference in the end
(watch with subtitles btw)
 
10:35 AM
Sir I want to ask another question with images on integration but my reputation is less than 10. Kindly help me sir — user134175 2 hours ago
^^^ If you have a moment to spare, you might help OP here with creating his new question.
 
lol
 
Anonymous
I guess SE doesn't allow image upload with rep less than 10
 
Can users with less than 10 rep post links to the images (uploaded elsewhere), so another user can embed them into the post?
 
Anonymous
4
Q: "You need at least 10 reputation to post more than 2 links"

satvik.tI got this error while updating a previously asked question on Stack Overflow: Getting error when importing from sibling package When I originally asked the question (and inserted over 6-7 links in it), I didn't get the above error at that time. My reputation on stackoverflow was 6, both at the...

 
Anonymous
@ACuriousMind I think so ^
 
Anonymous
10:41 AM
1 link is fine
 
Well, do we know this users wants to post only one link?
"With images" seems to suggest it would be more than one
 
Anonymous
Lol...you can tell him/her to link a page which contains the link to multiple images. A link to a google doc page or something like that
 
Anonymous
 
That seems...awfully convoluted
 
Anonymous
:P
 
10:45 AM
I just don't want to give this user instructions like "just post the links" when the system might not allow them to
 
Anonymous
@ACuriousMind I agree with that
 
Anonymous
11:02 AM
2
Q: Representation Of Linear Velocity as Cross Product

user74370Why is linear velocity represented as cross product of angular velocity of the particle and its position vector? Why not vice versa? (Consider rigid body rotation)

 
Anonymous
1
Q: How do we decide the direction of angular velocity vector?

user134175I know that the angular velocity vector $\vec{\omega}$ points towards the axis of the circular motion and there is a formula $$\vec{v}=\vec{\omega} \times \vec{r}$$ I want to know the origin of this formula which governs the direction of $\vec{\omega}$. And why only this direction, why not the...

 
Anonymous
Look like duplicates
 
user228700
11:33 AM
@JohnR: Do you remember that my sister is sending me some books from the U.S?
 
user228700
Ah, you're gone!
 
@ACuriousMind Do you know much about Jacobi fields?
I am confused about something and the usual geometry crowd doesn't seem to be around
 
@BalarkaSen nope
 
Aw. Thanks though.
 
Seriously? You ask him?
Might as well ask a hole in the ground :P
 
11:38 AM
Ah, I didn't see you in the user list.
 
I just got here
What is the doubt
 
"doubt" - cringe reacts only
So it's not obvious to me why the exponential map (assume it's defined everywhere aka the manifold is complete) is a local diffeomorphism if the conjugate locus is empty.
Should I think about the sphere picture? Conjugate locus is where a bunch of geodesics meet
So that's a singularity of $\text{exp}$
Oh, I guess I kind of see it. $q$ is in the conjugate locus of $p$ if there is a geodesic $\gamma$ from $p$ to $q$ along which there is a Jacobi field $J$ with $J(p) = J(q) = 0$
 
Conjugate locus? Do you mean cut locus?
 
But that should mean the 'spread' of $\gamma$ is trivial near $p$; nearby geodesics starting at $p$ all fall back at $q$
@0ßelö7 The conjugate locus of a point $p$ on the manifold is the set of points $q$ which are conjugate to it, ie, there is a geodesic running from $p$ to $q$ which admits Jacobi field that vanishes at the ends
I think what I said is right; the conjugate points to $p$ are exactly the critical points of $\exp_p$ now that I think about it
 
The cut locus contains the conjugate locus but I don't think you're differentiable anywhere on the cut locus. Hard to be a local diffeomorphism in that case...
 
11:49 AM
what is the cut locus
 
@BalarkaSen Yes, that's right.
You can think of it's like caustics in a flow.
When the geodesics crash into each other (roughly what conjugate points mean) you get a singularity of the exponential map. It could also be a point of nondifferentiabity.
Like on the sphere, for example.
 
right, true. I didn't think about it this way
 
@BalarkaSen there's a relevant MO post on this
 
CC @ACuriousMind
OP was even faster than you
 
11:54 AM
5
A: Distance function to a submanifold

Marco MendezI'm posting this sketch just for the sake of completeness. This question was already marked as answered by Anton. But I thought of this, more geometrical, argument after the discussion that answered the question in the first time. Notice that the fact that the $\Sigma$ are assumed to be submanifo...

See "assertion"
 
That's a cute proof
 
@BalarkaSen It is possible for two points to be conjugate without there being two geodesics that go through the second point. Don't know an example off the top of my head
 
I was wondering what saddle points of the exponential map looks like
I'll think about this. Gotta run for now. Thanks a bunch
 
bye
@ACuriousMind " We prove that, up to dimension 7, the main singularities of a complex
potential $q$ having some a priori regularity are contained in the Born
approximation $q_B$ constructed from backscattering data."
lol?
 

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