« first day (2043 days earlier)      last day (2060 days later) » 

12:12 AM
best title
 
12:24 AM
@Slereah don't various quantities in QFTCS depend on $1/\sigma(p,q)$
 
12:41 AM
yes
It's the equivalent of $1/r$ after all
Hm
If I have a spacetime with a thin shell wormhole in it
That is, I remove two shapes out of the spacetime and I identify the inside of one with the outside of the other
To compute any differential equation, do I just check the equation on the original spacetime and force the solution to be identical around the identified parts?
That is, if $A,B$ is the area of the two mouthes, $f(A) = f(B)$
Or do I need a bit more
Ah, I think Friedmann discusses the problem
Ah, he requires both continuity of the solution and its derivatives
$\Phi(A) = \Phi(B)$ and $\vec{n}_A \cdot \vec \nabla \Phi(A) = -\vec{n}_B \cdot \vec \nabla \Phi(B) $
 
1:43 AM
Mass has dimensions of mass, instead of dimensions of energy.
Hooray!
 
@DanielSank huh?
oh you hate natural units
why is that again?
 
user54412
I'm about to send a rage email to my department, hoping to spark an insurrection against the oppression inflicted on us in the name of IT security.
 
user54412
When you know you'll be gone from a place in 2 months, leading rebellions becomes much more attractive than actually getting work done.
 
@ChrisWhite oh?
what did they do
 
user54412
they're making us use those portable cryptocard things to access everything, including email
 
1:57 AM
@ChrisWhite that's what they do in the government for people with TS clearance
clearly Princeton academics is sensitive fucking information
 
user54412
I'm starting to sympathize with Hillary. Just wait til I send my advisor some data through gmail.
 
2:13 AM
@ChrisWhite what happens if you do that
 
To actually get things to change on that front you would want to get the faculty and staff senates (or local equivalents) to weigh in on your side. You need to know how much this is annoying the department secretaries and other people with real power. And a few professors.
But the simple fact is that really tight data security is inconvenient.
 
user54412
One of our very active, very respected emeritus actually beat me to sending out a rage email, so there's one ally to start.
 
2:29 AM
Emeriti have no formal power in most places, but they often have a lot of swing even so.
 
3:22 AM
@ACuriousMind Just read the proof of the Hairy Ball theorem, blew my mind
@ACuriousMind So how do we know that a noncompact manifold admits a nonzero vector field
 
@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ I have finally proved the Hairy Ball Theorem
 
 
1 hour later…
4:34 AM
@0celo7 cool
 
user116211
4:45 AM
Soo many people!!!!
 
5:05 AM
Wow, special speaker @Slereah !! I've always wanted to talk to him!!!
6
 
@MAFIA36790 Yes, anything special today? I've never seen 4 rows of names on the right hand pane!
 
user116211
I really don't know why it happened; probably due to the announcement of physics AMA at the main site.
 
5:32 AM
So many people that I thought I entered a wrong room
 
5:58 AM
I count 36 people :O
 
6:22 AM
Hey, one question to some of the high reputation guys here. I have observed, that statements of high reps. which are essentially the answer of an asked question are sometimes given as comment, not as answer. But from all I could find on the meta site, this seems to be bad etiquette.
Especially due to the temporary nature of comments this seems to be a waste :-)
 
user54412
@user_na You're right, answers shouldn't be given in the comments (though is is not unique to us -- certain other SE sites are even worse)
 
user54412
One reason is probably that some of us (especially those of us who've been here a long time and have high rep) hold ourselves to very high standards for quality answers, and it sometimes would take too long to write such an answer if we're not particularly interested or have other things to do. But then we don't want to leave the question without any answer at all.
 
user54412
This isn't really an excuse, just an explanation.
 
user54412
In any event, if you see an answer in a comment, feel free to post it as an answer and earn rep yourself. If you quote directly, you should probably mention where it comes from. If you reword things, and especially if you expand on the answer, then I would say pretend the comment doesn't exist.
 
@user_na See Chris' answer. I won't write an answer unless I'm confident I can give a complete and accurate response to the question. There are times when I only think I know the answer or I only know part of the answer and then I'll leave a comment.
 
6:30 AM
So, I see this as a chance for low rep'ed underlings like me to rise :-)
 
I agree that if you see a comment and it prompts you to extend that comment into a full answer then you should go for it. I've done this many times, though I usually credit the original comment in my answer. Part of my motivation for leaving a partial answer as a comment is the hope that someone more knowledgable will pick it up and run with it.
 
Good to know
 
user54412
@user_na Indeed. Actually there are times when I know the answer to a question but I feel many others would too, so I leave it for someone else to get rep from.
 
user54412
These days I mostly stick to my niche field.
 
We do have a few (mainly just one :-) members who specialise in answering in comments, but that's life - just ignore them and move on.
 
user54412
6:33 AM
On another note, I watched this room from a private browser, and when I logged off rather than my icon disappearing from the top right, it moved to the front, as though I had just said something. I'm guessing some sort of recent chat bug.
 
user54412
@MAFIA36790 see above comment
 
@ChrisWhite but how do you know know that you are moving to the front if you are logging off?
 
user54412
from my other browser -- you can watch this room anonymously
 
@ChrisWhite I see
 
user116211
6:49 AM
That would be a great coincidence that everyone is using incognito mode.
 
user116211
@AnkitSharma: Hallo!
 
@MAFIA36790 someone tricked me again
in Mos Eisley, 12 mins ago, by Chris White
Is your room always this crowded, or are icons not being removed as people log off (as I suspect is happening in physics)?
:D
 
user116211
@AnkitSharma Our room is quite less populated unlike Eisely; but today was quite weird as so many people gathered today; that's why.
 
My fav chat place is

 The Screening Room

“We are all the pieces of what we remember. We hold in ourselv...
 
user116211
@AnkitSharma yeh, yeh; I know ;P
 
6:56 AM
Rest i can be found in agent of nothing, Hinduism chat room and occasionally in mos or maid cafe
 
@ChrisWhite I am experiencing the same.
 
user116211
I always wondered btw, why the icons didn't disappear even if the user is not available or present there.
 
It's just a bug.
 
7:19 AM
It looks as if the icon does disappear if you click the leave link, but it doesn't disappear if you just close the browser.
 
user54412
Speaking of bugs, I just wandered into the greatest list of abuses you can do to SE questions and answers.
2
 
user116211
@JohnRennie Hmm... at least I thought so but actually it doesn't happen so; I checked through the incognito mode after I closed the chat tab after an hour; my icon was not there. So, yeh.
 
speaking of bugs
 
 
2 hours later…
9:06 AM
Don't know if this is a bug or something else, but I seem to have lost the ability to access certain things on PSE. For example, I wanted to VTC a copy-paste homework question, but the "close" option was unresponsive. Same for all the other options as well as the downvote button. The only option that worked was the "edit" option. Trying to ask about this I wanted to come here, to the chat rooms, but the dropdown in the top left (the one with the SE logo) didn't drop down.
Instead, I was taken to the SE site. I was lucky there was a link here in de sidebar on the right hand side of the homepage. Any ideas? (I guess I should tag a mod or something, @Qmechanic)
 
@Wouter I've just been working through the review queues and everything seemed to be working normally. I wonder if it's some problem on your computer.
 
@JohnRennie Damn, I was hoping I wouldn't have to close my browser. I have the bad habit of keeping loads of tabs open. I'll give it a try and report back ;)
Okay, closing and opening the browser hasn't worked. But I've just noticed Matlab gave an error about low-level graphics.
That sometimes messes with other stuff as well, so let me close Matlab for a sec.
Still nothing.
Last resort: rebooting. See you in a few minutes.
It's still not working... :(
 
user116211
Work with another browser.
 
user116211
Sometimes it is due to the RAM as you mentioned you opened many tabs; but even in that case also it would work.
 
It worked perfectly fine until now. And atm I don't have any other tabs open. Not even any other software is running.
Weirdly though, it seems to be working on Chrome
 
user116211
9:22 AM
@Wouter Sometimes Opera gives a shit; but Chrome is always reliable.
 
I'm on Firefox :)
 
user116211
ah! I hardly use that ;P
 
But I get the point. Firefox has been acting up more than it used to these past months.
Chrome it is :P
Thanks for the help ;)
 
user116211
9:44 AM
oooooooooo......
 
user116211
All gone O.O
 
user116211
@JohnRennie: It's the normal room now ;P
 
user116211
@EmilioPisanty: It's quite good that you are now frequent here :)
 
@MAFIA36790 No, it's a bad sign in fact
A sign of desperation in the face of The Thesis
 
user116211
Wait, what is going on? Why a sudden flood of feeds ;/
 
user116211
9:53 AM
 
@ChrisWhite That's a great find
loving this one
113
A: Formatting Sandbox

Alex CoplanFATAL ERROR: <kbd> overflow

Also this one
2
A: Formatting Sandbox

Shadow Wizard hello world how are you? oh my... that is weird.

 
user116211
I liked the glowing red eye.
 
@MAFIA36790 boo, we've halved the room membership!
 
user116211
@EmilioPisanty once said by @JohnRennie:
 
user116211
> the amount of time I spend in the chat room is directly proportional to the amount of work I'm trying to avoid doing.
 
9:56 AM
Too true, too true :-)
 
hi all
@JohnRennie Could I ask you a quick linear algebra question
 
@JohnDoe I'm one of the less mathematically accomplished members of the site so I may not be able to help. However you can certainly ask.
 
after that ill pose a question that is almost more philosophical
and hi there John
 
@user507974 Hi :-)
 
So this is a question that a 5 year old would ask but we as physicist dont really have the full answer: What is an electron?
 
10:03 AM
@MAFIA36790 :
7
A: Chat rooms are not receiving question feeds

OdedThe scheduler was not running properly for chat.se - we gave it a kick, so it should be fine now.

 
hey hey
 
user116211
Hallo!
 
With what we've confirmed, what is the most fundamental description of what exactly an electron is
 
user116211
@Loong Ah! Thanks reading
 
Greetz, I think this question of atrts and crafts site is related to Physics. Please consider having a look and see if you can answer that w.r.t physics: crafts.stackexchange.com/questions/77/…
 
10:04 AM
@JohnRennie Thanks. If you have a linear transformation given by say a 5x3 matrix and you want to find the image of the transformation. Then as I understand you can take any two columns of the matrix. Is this correct so far?
 
My attempt: The closest thing to a fundamental answer of the electron we have is that it is an excitation in a quantum field in a vacuum that observes a special family of symmetries in space and time, some of those heavily perturbed by their neighbors and others that are very difficult to change.
 
@JohnDoe Can you have a linear transformation that isn't a square matrix? I would have thought not, unless I'm misunderstanding what you mean.
 
what would you say @Slereah?
@JohnRennie did linear imply invertibility
 
@user507974 it isn't possible to say what an electron is because no-one knows. The best we can do is say how QFT describes an electron.
 
i thought that is why we have right inverse and left inverse, cuz you are still linear
 
user116211
10:07 AM
I admire your kicks. — Shadow Wizard 13 mins ago
 
user116211
@Loong: ^^^
 
@user507974 so I guess you're trying to come up with a succinct way to explain how QFT describes an electron.
 
An electron is a soliton in the associated bundle of the principal bundles of the standard model corresponding to the electron's charge
 
@JohnRennie QFT is our most fundamental definition we've confirmed (with string theory possibly more fundamental). But if we took QFT, GR, particle physics, and the rest of physics and tried to precisely define it what would that be
 
@user507974 I don't understand the question ...
 
10:09 AM
I'd rather not use the particle definition commonly used because it doesn't work in interacting theories or in curved spacetime
So a well localized soliton is probably best
 
@JohnRennie i think @Slereah kinda got it all down
@Slereah can we defined according to the standard model a bit more
define*
 
Probably but I dunno
Like I don't know what soliton you could define as being "one electron"
 
you have spatial symmetries, lepton, rest mass
 
I guess it should have an energy of ~511 keV
 
@JohnRennie Yes you can, say $T: \mathbb{R^5} \to \matbb{R^4}$ given as $T(x) = Ax$
 
user116211
10:12 AM
@JohnDoe \mathbb
 
@Slereah but can we basically say that you have symmetries in spacetime [what are the symmetries other than that]
would mass be a spacetime symmetry too?
 
@JohnDoe OK, you've lost me now. You need to ask some who knows more about maths.
 
You don't need spacetime symmetries to define the electron
Well, you do, but only local symmetries
and yes mass is a Casimir operator of the translation group
 
@Slereah SU2 ?
 
@MAFIA36790 The response is not visible
 
10:15 AM
SU(2) yes, kinda
 
user116211
@JohnDoe ??
 
(SL(2,C) technically)
 
@Slereah was that the difference between relativistic and not
 
user116211
@JohnDoe You cannot see the mathjax?
 
Yes
(kinda)
 
10:16 AM
@Slereah when you say kinda that only makes me more curious
 
You have SL(2,C) ~ SU(2) xSU(2)
 
what else besides relativity?
oh yea, it is locally SU(2)
is SL(2,C) still describing one electron btw
 
What do you mean by "describing"
The electron field isn't the rotation group
It's the associated vector field $\Bbb C^2 \times \Bbb C^2$
 
well, nonrelativistically we consider we treat the electron as having SU(2) symmetries right
 
yes
that's because SU(2) is the spin group of SO(3)
 
10:19 AM
yea
 
@JohnDoe I think mafia367 simply meant you misstyped "\matbb{R^4}"
 
so for SL(2,C), what is the physics encoded by SU(2) x SU(2)
im probably wrong, but it looks to describe to me the behavior of those symmetries in relation to another identical symmetry
like electrons are correctly described by considering that another partner electron exists locally
(again though im probably wrong)
 
Wow! They fixed that chat avatar bug fast :O
 
did that wild guess make any sense @Slereah?
 
The two copies of $\Bbb C^2$ correspond to the left handed and right handed electrons
Somewhat "independant" particles
That are coupled by the mass term
 
10:26 AM
"coupled"?
 
they interact
 
user116211
BTW, @vzn, who would host the AMA session of Slereah?
 
user116211
DZ?
 
user116211
Or @JohnRennie, would you like to do it?
 
@MAFIA36790 no, I always stand at the back on these occasions
 
user116211
10:35 AM
ooo.... okay.
 
oh yea, back to the other part, @Slereah, so what about other particle flavours
here we got into this discussion because we were describing mass as having a spacetime dependence
 
Same, just different charges?
 
Homework?
0
Q: How can I linearise the compound pendulum equation?

Abduljalal KuraraHelp me linearise $T=2 \pi \sqrt{h^2+2k/gh}$. Hence how do I deduce $g$ and $k$ from my graph? And what does $k$ represent physically?

 
they are also Casimir operators?
lepton number and etc
 
user116211
okay, @Slereah whom do you want as the host?
 
user116211
10:38 AM
@JohnRennie Totally.
 
@MAFIA36790 well you could regard it as a conceptual question about how to mangle your graphs into a straight line. The best I could come up with is to graph $T^2h/2\pi$ against $h^3$ in which case you should get a line of gradient unity and $y$ intercept $2k/g$.
 
user116211
@JohnRennie He didn't actually ask that; that would be otherwise if he changed the blatant HW query to that.
 
11:02 AM
Aha, just when I feared the chat was getting quiet, and I'd have to do some real work, the delivery man has brought my new SSD. Now I can spend a couple of hours reinstalling Windows 10 instead of working :-)
 
user116211
@JohnRennie Windows 10 is evil ;(
 
user116211
It automatically got installed in my tablet ;((( Wasting all my data ;_;
 
I'm not a huge fan of W10 because I like a clean and uncluttered user interface. I normally use Windows 7 with the classic theme and turn off all the visual effects. However W10 has basically the same kernel as W7 and it's a perfectly good operating system.
 
user116211
I have never witnessed any physicist using windows atleast.
 
@MAFIA36790 That sound as if the upgrade process went wrong. I would never upgrade an OS. I always back up all the data, install a nice clean OS then copy the data back.
 
user116211
11:07 AM
Mostly use Linux.
 
user116211
@JohnRennie ? Actually Microsoft unofficially announced that all genuine windows OS would get upgrated automatically to windows 10.
 
user116211
And they would install all essential stuffs (without any permission) until that happens.
 
Linux is fun to play with, but the reality is that I can work more productively on W7 than on Linux. For productively read money earning.
 
user116211
@JohnRennie Ah! yes, I love Windows 7; my laptop is currently running on it. But Microsoft would soon stop supporting it.
 
11:31 AM
important note guys, if your computer starts automatically updating to windows 10 you can revert back by not agreeing to the terms that pop up after first boot up of windows 10
 
@user507974 I think I'm going to update
I can't handle the constant notifications and honestly 8.1 is shit
 
windows 7 is the tip of the power curve for me
I really dont like metro and their attempts to unify with phones
basically the worst part about 8 that still kind of exists less pronounced in 10
if all phones were touch screen compatible maybe
 
user116211
@0celo7 This is the worst shit that Microsoft could give.
 
@user507974 they should have never made touch screen computers
worst idea ever
 
i think it can work ok
 
user116211
11:35 AM
i don't know you guys but actually Macbook is the best thing in the world.
 
ive had to do something like 3 years of research on mac systems
id rank it better as windows 8 if thats any consoltation
 
@user507974 I use a Mac...
It's way better than windows
in every way
 
user116211
@0celo7 very much implied.
 
egh, they drop the ball in a few big ways i think
the only MAJOR advantage id give it over windows is terminal
 
user116211
Preference: Mac> Linux>>> Windows 7>>>>>>> ......
 
11:37 AM
for me: Windows 7>>Linux>>>Windows XP>OSX
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Win‌​dows 8
 
user116211
Windows XP is expired now; so not under discussion ;/
 
user116211
My latest use is Kali Linux.
 
my lab has an XP laptop hidden away for the apocalypse
 
heh
 
user116211
How????
 
user116211
11:39 AM
No one supports XP ;/
 
they turn it on, automatically starts updating to 10
 
@user507974 not allowed to connect to the internet :P
 
@0celo7 There is no best OS. That's like asking what car is best. It's just a matter of what OS best suits you. I am a hardcore nerd - I've even done device driver development for Windows (back in the NT3.5 days) and I know my way around the Windows kernel. That's why Windows suits me best.
 
user116211
@user507974 No it won't.
 
@JohnRennie Yea, thats what I think too.
 
user116211
11:40 AM
Microsoft doesn't support XP now; it wouldn't upgrade it to 10.
 
@user507974 we keep it around for legacy programs
although someone got a program from a floppy disk onto a Win10 lab computer
 
ive had 7 since basically it came out, done 2-3 years of research on Macs, 6 months on Linux, and they kind of excel at their own things
 
pretty impressive
 
@0celo7 lol
 
@user507974 our X ray machine is from the 80s :D
 
11:42 AM
OSX was based on the Mach microkernel so it's basically unix at heart. However in everyday use it puts too many barriers in the way of what I want to do. Doubtless I could work round these if I had the years of experience with it that I do with Windows, but life is too short.
 
What barriers?
Are you a nerd constantly typing stuff in the command line
 
@JohnRennie I remember my first time using it they put an open source compiler i needed behind a paywall (i could get around that but at the time i didnt know nearly as much about computers)
@0celo7 wait, you mean you dont do that?
 
@user507974 for work, yes
but when I'm watching pokemon videos, etc. why would i do that?
 
sudo python robot.py -bring tissues
 
oh iTunes works WAY better on OSX than Windows
 
11:45 AM
@0celo7 dont use iTunes
so I haven't really missed that
 
@0celo7 which bit of I am a hardcore nerd did you not understand :-)
 
actually its been really funny to watch apple slowly add in features ive had on mediamonkey for years
@JohnRennie how do you poweruser with windows
id like to take notes
 
user116211
0
Q: Time involved in reflection

AlfConsider a photon bouncing back and forth between two ideal front surfaced mirrors. How long does the process of reflection (ie, absorption and re-emission take ? Thanks. Alf

 
i can get by on unix systems but for me windows feels very closed off
 
user116211
HW, right?
 
11:49 AM
@user507974 turn off user access control and stop being a pussy :-)
 
@JohnRennie well yea but after that what do you actually do
 
@user507974 Apple Music is a top 10 invention
of all time
you're missing out
 
ive done a few registry tweaks, context menu for overriding file owndership, image rescaling, open with Sublime Text 3, just basic things
oh and i added in a calculator to the start menu
or whatever its called when you pres the windows button
and a file previewer
for many other types of files (mostly text files)
 
@user507974 I don't understand what you're asking. Turning off UAC affectively gives all administrator accounts the same privileges as root. You do that then get on with doing what you want to do. Avoid any tweaks that aren't necessary.
 
@JohnRennie well yea, but what are you doing after turning UAC off
 
11:54 AM
Why would you add calculator to the Start menu? Just press Windows-R and type calc.exe
@user507974 Nothing. I just get on and use my computer.
 
paranthesis and reorganizing the equation
dont really like calc.exe personally
a while back i use to have seconds on my clock
forgot how i did that though
 
In OSX I have a trackpad finger swipe command for the periodic table
pretty useful in a solid state physics lab
 
oh yea, usually i had a periodic table gadget on the desktop
forgot about that like 3 years ago
when i reinstalled
 
You know those people who buy a car then dangle a fluffy toy from the mirror and put a Garfield sticker in the back window? Well here's a hint - neither the fluffy toy nor the Garfield sticker will make your car any faster or more reliable.
 
@JohnRennie well mine is more like putting a little bubble mirror on the side view mirrors
they are little functionality improvements that just make the workflow faster
 
12:00 PM
@JohnRennie I have my university parking pass on the mirror
so I don't get towed
 
mileage varies for the tweaks but they are nice when i need em
 
12:11 PM
@Slereah So you basically use your nonzero vector field to construct a homotopy of the antipodal map of $S^n$ to the identity
and this is not possible in even dimensions
 
12:45 PM
that sure is a solution
but a solution to what
oh, hairy balls?
 
@EmilioPisanty looks like the question was posted, then the answer was posted, then deleted, all on April 30, then on May 10 the question was automatically deleted, then on June 1 the answer was undeleted. I'm not sure why the answer currently shows up as deleted (independently of the question being deleted).
 
More importantly, what's the set of solutions for the wave equation in bipolar coordinates
Apparently might be something like $e^{i\omega t} U(\xi) V(u)\$
Where $U$ is hyperbolic functions and V is trig functions
Oh wait
Apparently the Laplace equation is not separable in bipolar coordinates
 
@Slereah what does that mean
 
That I'm gonna have to work out that equation
 
why would you use coordinates in which you can't separate one of the most basic PDE
how do you even solve a non-separable PDE
 
12:57 PM
Because on the other hand, working out a wormhole in it is trivial
Well
Laplace is separable
But Helmholtz isn't
And by extension, the wave equation
 
no, bullshit
 
Laplacian is $\approx (\cosh(\xi) - \cos(u)) (\partial^2_\xi + \partial^2_u)$
 
what the fuck
are you talking about in bipolar coordinates?
 
yes
 

« first day (2043 days earlier)      last day (2060 days later) »