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user116211
4:03 AM
Are you done with the ideals yet @secret? I have one or two problem; if you want, you can ping me; although I have to try them myself first, hmm.
 
yeah, Acuriousmind have troubleshooted my proof logic, thus the ideal proof is done for now
 
user116211
I need to study polynomials, but I've a packed schedule; dammit ;/
 
@Skyler when we gonna play Smash Bros?
 
user116211
@DanielSank o/
 
@DanielSank I'm thinking next Friday, I head back to LA later that weekend but finish my finals Thursday, have a dinner with coworkers that night though
 
user116211
4:09 AM
@JamalS, I know; for me Qmech lives in an old European castle with big study room and lots of books; and he is the Dark Knight too.
 
@MAFIA36790 I'm Batman
 
user116211
But sometimes her enjoys watching YouTube videos and sharing them ;)
 
user116211
@Skyler Proof?
 
@DanielSank can back this up
the only other potential candidate is ACM
but he has his own special signal
so it cant be him
 
rob
I can confirm that Batman has access to @Sklyer's account, but I can't confirm the other way around.
 
user116211
4:13 AM
@Skyler ACM is an AI.
 
i kinda wish it was possible to make it so that whenever @ACuriousMind was typed this would pop up
 
4:40 AM
@MAFIA36790 \o
@MAFIA36790 He is Batman.
Trust me.
 
user116211
@DanielSank Adam West type or Christian Bale type? ;)
 
user116211
@DanielSank I trust you.
 
@MAFIA36790 Christian Bale for sure.
 
user116211
Ahh; okay.
 
5:07 AM
@Skyler It could be arranged (eventually)
4
 
"The resulting expression for $\langle T_{\mu\nu}\rangle$ are found to be everywhere regular so long as the ship does not exceed the speed of light, $v < 1$."
so sad
 
5:56 AM
Apparently there hasn't been a lot of papers on Krasnikov tubes recently
 
Hi @Slereah ! Are you a general relativist?
 
Sure
 
Cool. Do you research? I love reading your stuff ( though I don't understand it all, lol)
 
'fraid not
 
Ohk.
 
user116211
6:18 AM
@SwapnilDas He is building a time machine secretly.
 
Time machine prognostics are bleak
From Kay and Wald's paper I think basically that they can be ruled out
 
user116211
WTF ;(
 
6:47 AM
Any good book for Multivariable Calculus?
 
 
3 hours later…
9:34 AM
"In particular we argue that the theorem proved by Kay, Radzikowski, and Wald to the effect that time machines with compactly generated Cauchy horizons are incompatible with the F-locality condition actually does not support the “chronology protection conjecture”, but rather testifies that the F-locality condition must be modified or abandoned"
Krasnikov is really really into time machines
 
so all backward time travel possibilities are gone?
 
10:06 AM
@koolman Got the answer, sorry for delay.
@koolman With the general proportionality relation derived in your solution, you just needed to divide my differential form down.
 
10:44 AM
@SwapnilDas now I got the answer
Thanks a lot
 
 
1 hour later…
12:11 PM
0
Q: Physics Catapult Problem

Omer Nave I'm having touble solving this problem. I know I can find V(x) but I don't know how to find V(y). Any ideas? Thanks!

off topic and lack of research effort
 
12:30 PM
@koolman Our mission successful ;)
 
user116211
@Secret Amusing thing is why it was asked in Worldbuilding.
 
no idea
 
@MAFIA36790 Perhaps because physics helped to build the world 😛
 
12:52 PM
@SwapnilDas yup :)
 
1:05 PM
if i hang a negatively charged ball and put an alpha-source near it, how will the ball move?
 
hello everyone
@DanielSank, sorry, I had to go so I'm just reading your link now - it makes a decent amount of sense though.
@AmeyShukla, try Apostol's Calculus, Vol. 2
 
@Skyler Well, you would have to make the bot intelligent so it doesn't post it when I'm mentioned several times in quick succession, but I guess that would be possible (for people knowing how to write chat bot, i.e. not me)
@DHMO If you mean a source of alpha radiation, why do you think it would move at all?
 
@ACuriousMind because it's positive?
 
negative charges attract
 
1:11 PM
A "ball" is a macroscropic "heavy" object presumably charged with a rather large charge. An alpha particle is a light particle charged with +2 elementary charges. The particle's path might be influenced if the charge on the ball is really large, but the ball will not move perceptibly.
 
@ACuriousMind then what's the point?
 
The point of what?
 
@DanielSank, hmm, it gives errors when I try to install numpy within the virtualenv
 
the point of the question
 
@DHMO Uh, you asked the question, you tell me!
 
1:13 PM
@ACuriousMind well it's from my textbook
 
for example, "cannot compile Python.h. Perhaps you need to install python-dev|python-devel."
 
@DHMO In that case, I think your textbook asked a stupid question :P
 
@ACuriousMind I agree
 
hmm...is there a way to call a python file within a python file?
 
@heather import
but why do you need to?
@heather just type python -m pip install numpy
 
1:23 PM
so I could create "functions.py" and then "import functions.py" in the main file I'm working with?
 
you don't need .py
 
@DHMO still gave the same errors
@DHMO I just think it'll help neaten up my code.
 
@heather then install them?
 
gave an error for python-dev; trying python-devel
gave an error for python-devel too @DHMO
 
@heather try python -m pip install dev
how are you installing python-dev?
 
1:32 PM
You walk on the subway it moves around
 
13
A: How can I install python-dev off apt-get?

Zeus77Are you sure you are doing it right? This is my output for # apt-get install python2.7-dev root@olympus:/home/zeus# apt-get install python2.7-dev Reading package lists... Done Building dependency tree Reading state information... Done The following extra packages will be installed: libexpat1-...

@heather ^
 
@heather Virtualenv?
 
@BernardMeurer, yep, its being a pain
@DHMO didn't work
@DHMO pip install python-dev
I don't know if I have the universe repository enabled, let me see
@DHMO, tried to enable universe repository; gives an error "sudo: add-apt-repository: comand not found"
 
@heather What are you trying to do?
 
1:38 PM
@BernardMeurer, install numpy in my newly-created virtual-env
 
pip install scipy?
 
@BernardMeurer, didn't work
 
[Division by zero] Caption: It will be cool if I can somehow automate this:
 
gave errors
 
1:41 PM
@heather "Gave errors" is about as useful as "potato"
7
 
in a nutshell: first iteration of the algorithm, showing what 30 be and cannot be to obey associativity
 
@BernardMeurer, sorry, yeah, "Command python setup.py egg_info failed with error code 1 in /home/heather/.virtualenvs/quantum/build/scipy" also "Cannot compile 'Python.h'. Perhaps you need to install python-dev|python-devel."
@DHMO, I added that package, now add-apt-repository ran; universe was already activated.
 
@heather then u can install python-dev?
 
sudo apt-get install python3-dev
you're using a py3 venv after all
 
@BernardMeurer potato
 
1:46 PM
@DHMO Pesky chemist
 
@BernardMeurer, phew, that worked
 
@heather Yeah, now do pip install scipy
 
gave the same errors as before @BernardMeurer
 
python -V
 
2.7.6
 
1:48 PM
Aha
You screwed up setting the venv
You're running Python 2
 
should I delete the virtualenv and create a new one?
 
Uhum, make sure you make a Py3 one
 
right, that would be preferable =)
 
2:01 PM
would I download one of the two "source release" ones on this page?
 
What? Why would you download Python's source file?
just sudo apt-get install python3
 
the instructions danielsank gave to me had me downloading python from that page
okay that sounds a lot easier
 
@heather Ye, that's because @DanielSank is getting senile :P
 
so, I can just mkvirtualenv now that python3 is installed?
 
Idk, I don't use virtualenvwrapper, I do it manually because I'm an old man
 
2:08 PM
you aren't old, geesh
 
python in Ubuntu defaults to python 2 (RRRGRGRJKMgJGDFIUDGY) so maybe you have to specify you want Python 3
I'm ancient
I have 3 white hairs
 
yep, you're right, I have to specify python3 somehow
 
@BernardMeurer Be thankful you're not down to 3 hairs total :P
 
i could swear right now
147
Q: Using Python 3 in virtualenv

PrometheusUsing virtualenv, I run my projects with the default version of Python (2.7). On one project, I need to use Python 3.4. I used brew install python3 to install it on my Mac. Now, how do I create a virtualenv that uses the new version? e.g. sudo virtualenv envPython3 If I try: virtualenv -p py...

 
@ACuriousMind Indeed
 
2:12 PM
ran the command in the answer, and it seemed like it was working, but then I did python -V and it gave 2.7.4
 
YOU WALK ON THE SUBWAY
IT MOVES AROUND
 
?
 
@heather lel
 
lel?
 
Senility, on the other hand, seems to have you firmly in its grasp :P
 
2:15 PM
Idk how too virtualenvwrapper
I just use the normal venv
@ACuriousMind You walk on the subway it moves around
Dude this is such a good song
 
i long for the day when linux errors are "too easy" like they are for @BernardMeurer...
 
It's just practice, every once in a while I still find some Linux error that makes me want to pluck my eyeballs out
 
@BernardMeurer Whatever drugs you're taking, you need to either increase or decrease the dosage. Which of those I can't tell :P
 
@ACuriousMind I'd post a link to the song, but the clip is R rated
 
Uh...I think I found it already
 
2:19 PM
Search for "Subways" by "The Avalanches", watch the clip it's amazing
@ACuriousMind All I've been having is beer
 
@Danu "The string theoretic cohomology groups of $X$ are isomorphic to the usual cohomology groups of $Y$", where $Y$ is a desingularization of $X$. Any idea what a "string theoretic cohomology" is?
A following sentence says "The string theoretic cohomology groups count the massless string states in the CFT", which doesn't enlighten me as to whether that's supposed to be a definition or a consequence.
 
@ACuriousMind Did you like the clip?
 
@BernardMeurer Nah, I don't like trippy things
 
@ACuriousMind What the heck. You're a shame to your hairstyle
 
instead of actually trying something to fix my python 3 woes I've been glaring at the computer screen and going through the new questions on physics problems q&a =/
 
2:33 PM
@BernardMeurer Well, more precisely, I don't like trippy things when I'm of a sober state of mind :P
 
writing mathjax for equations is soothing
 
@ACuriousMind There we go :)
I'm going to go buy more beer and some chicken, brb
 
@ACuriousMind Oh, I think I know what this is.
This might be the chiral ring from CFT
Yeah, I think so this seems to confirm it
Never knew that had an interpretation as a cohomology ring.
 
2:51 PM
Hm, not exactly sure how to translate that to my setting, but thanks, anyway :)
Any chance you know what's going on with my newest question?
5
Q: Why is full M-theory needed for compactification on singular 7-folds and what does that even mean?

ACuriousMindIn "M-theory on manifolds of $G_2$ holonomy: the first twenty years" by Duff, it is claimed (e.g. in section 8) that for compactification on singular 7-folds to be possible, we need to consider not the 11D supergravity (SUGRA) approximation to M-theory but "full M-theory". Such singular compactif...

 
@ACuriousMind Chiral ring? That's in Blumenhagen's CFT book.
Somethingsomething monodromy somethingsomething
Some fields yield a ring under OPE
Oh, translating to your setting. No idea :)
Idem regarding your question---I don't even know what 11d SUGRA really is.
 
Well, it's just the only consistent SUGRA action you can write down in 11D
 
SUGRA is tjhe problematic part ;)
 
0
Q: Calculate Gaussian wave

ChillingKI'm told that $\Psi(x,0)$ is built out of plane waves according to the amplitude distribution function $$a(k) = (C\alpha/\pi^.5)e^{-\alpha^2k^2}$$ How do I calculate $\psi(x,t)$?

^homework, math.se...?
nvm, i think that's just homework
 
I wouldn't vote to migrate (that'd be migrating crap, which I don't think is intended)
 
3:02 PM
yeah; i vtc'd as homework
 
@Danu Well, presumably you know what a supersymmetric field theory is, right? It's just a supersymmetric field theory with a spin-2 field, basically
 
@ACuriousMind I can get as far as "it should be one of those easy-looking SUSY actions, this time for a multiplet containing spin-2,3/2 and 1, that are terrible in components
 
@heather I guess so. It kind of has that feel. (If not homework, where would the OP have gotten the expression $(C\alpha/\pi^5)e^{-\alpha^2 k^2}$?)
 
December 4th 2016 - I got in a fight over fried chicken
 
what...? @BernardMeurer, it's fried chicken, what's there to fight about?
4
 
3:07 PM
The last one
 
oh.
 
@Danu Well, yes, although you also have a gauge 3-form.
 
lack of research effort will mean it is not migratable to Mew's site either
 
I don't really think that the exact form of the action is relevant here, I'd like to understand more generally what "forbids" singular compactifications in a theory
Or, conversely, what "allows" them in "full M-theory".
 
What are singular compactifications anyways? Since you're working in d=7 they're not complex algebraic varieties
 
3:11 PM
@BernardMeurer, I asked this earlier but I can't seem to get it to work. I have function.py, which contains my code for all the various functions, and I have main-file.py, which does import function. when I ran it, it gives errors like hadop undefined (where hadop is one of my functions).
 
@Danu Two main constructions: Either they're orbifolds obtained by quotienting out actions of discrete groups from the 7-torus, or they are so called "twisted sums" obtained from gluing Calabi-Yau cylinders.
 
So like mapping cylinders of CY's?
 
There's also the "boring" way like $S^1 \times Y$ where $Y$ is a singular Calabi-Yau
 
No, those would be 8d
 
@ACuriousMind, you need 20 rep to talk in the chatroom, right?
 
3:12 PM
@heather yes
 
okay
 
@Danu No, the correct notion is that of an "asymptotically cylindrical CY" $Y$ and then one glues $S^1 \times Y_1$ and $S^1\times Y_2$ in a certain way
 
@heather Where can I see the code?
gimme teh codez
 
$Y$ is asymptotically cylindric if it asymptotes to $\mathbb{R}\times S^1 \times S$ for a K3 surface $S$.
 
3:15 PM
404
 
But the specific construction of the singular 7-fold shouldn't really play a role, I can just take the simple orbifolds $T^7 / \Gamma$.
 
@heather PLEASE don't do imports mid-code
 
These already give surprisingly rich variety of examples
 
imports all at the top
Do you have a linter?
i.e. and automated thing that shows you your mistakes
 
3:17 PM
@BernardMeurer, sorry! I'll fix that. and nope, no linter
 
@ACuriousMind Only condition discrete? Not finite?
 
@BernardMeurer, okay, the import is at the top now
 
@Danu Eh, should be finite, I guess
 
If you allow discrete you get like
all fundamental groups (of things that admit regular coverings) and stuff
 
Funny thing: The twisted sum construction gives like 20 million examples but almost all of them have second Betti number zero so they don't give Coulomb branches
 
3:18 PM
@heather Get a linter, i dunno how to do it on Vim, I use Atom.
 
@ACuriousMind Iunno what Coulomb branch is
 
I think your import is probably failing
 
@Danu Yeah, I don't want that, make the group finite. A $G_2$-manifold neccessarily has finite fundamental group.
 
@BernardMeurer, yeah, it worked before I moved the functions to a new file.
 
Finite quotients of $T^7$... Hmm
 
3:20 PM
@Danu I'm not sure 100% but I think it just says that the non-aBelian symmetry one has at the singularity gets broken to a U(1) and not completely as one desingularizes the manifold.
 
@BernardMeurer, does this look alright?
 
Are you using that awesome vimrc I sent you?
 
So what the hell is "full M-theory" even? I thought they still didn't know what M-theory "is"?
 
I think it already has one
 
@BernardMeurer, yes
how do I check if it has one?
 
3:22 PM
Write some bogus python code, filled with errors
Try saving and see if it complains
 
okay
 
@Danu That is (part of) my question, too
 
@ACuriousMind It sounds like BS, basically :)
But good that you ask---though I do not have high hopes of anyone answering.
 
8 minutes till I can set a bounty ;)
 
If only these were the early days of PSE with researchers n stuff
 
3:25 PM
I wrote some of the most terrible code ever @BernardMeurer and saved it, no complaints
 
Lol, that's funky
let me try over here
 
I assume you already asked your supervisor?
 
@heather Hmm
Here it did complain
 
@Danu Not yet (will do so tomorrow or the day after that)
 
3:27 PM
@ACuriousMind Mhm. I finally am starting to settle on a thesis topic myself
 
@BernardMeurer I never really understood what I'd need a linter for when most compilers already give rather helpful errors.
@Danu Which is?
 
@ACuriousMind Because you don't want to save, run, read error, fix, run again. You want to as soon as you wrote something wrong a warning shows up and says "this looks wrong". It makes things much faster
 
@ACuriousMind I don't have a precise problem yet (hopefully my supervisor will tell me within the next few weeks...) but it'll be something about the restriction(s) on characteristic classes/numbers imposed by curvature conditions.
So something about the interplay between topology and geometry.
Possibly related to this paper by my supervisor.
 
Found this on a university desk
 
@BernardMeurer "Found", sure
 
3:32 PM
You know that's not my handwriting :P
 
@Danu Riemannian curvature?
 
@ACuriousMind Yeah---the paper I just linked essentially only uses the curvature condition to quote a theorem. I hope not to get too into the Riemannian stuff since I don't know shit about it.
I'm more interested in the cohomology stuff
I'm finally (essentially) done with the book on complex geometry---it was all about cohomology.
Not sure how much of that I'll be using though :P
 
@Danu Well, but that's always the case with the stuff from textbooks, isn't it?
 
I don't know :P
 
@BernardMeurer, hmm
that's strange
 
3:45 PM
hey guys I have a music question. Is there a more descrptive name to describe the type of music using that synth like instrument in the background under all those beats?
Music in question start at begining and can be cut to 0:23
 
electronic?
 
@Secret Why on earth were you watching that video
This is called Lounge btw
I think
 
I stumble upon a facebook video which has the same type iof music. However the facebook video does not give any name for the music used thus I resort to find something simialr on loop instead
 
I recall this french group who did a lot of stuff like this, I think they were french
Ye
Kind of
 
yes, that's the type, it has the same impression
Lounge music is a type of easy listening music popular in the 1950s and 1960s. It may be meant to evoke in the listeners the feeling of being in a place, usually with a tranquil theme, such as a jungle, an island paradise or outer space. The range of lounge music encompasses beautiful music-influenced instrumentals, modern electronica (with chillout, and downtempo influences), while remaining thematically focused on its retro-space-age cultural elements. The earliest type of lounge music appeared during the 1920s and 1930s, and was known as light music. Contemporaneously, the term lounge music...
now to find a good one to put on loop
 
3:50 PM
@Secret You're welcome :P
 
is that muffled sounding instrument in all these lounge music a downtempo-ed piano?
 
Example?
 
e.g. the muffled sound right beneath the vocal in your example at 1:01
all lounge music has that instrument based on my experience, which I struggle to find its identity
 
The baseline? Or the quiet metallic sounds in the back
Or the piano
Which is actually an electronic keyboard with some fx
 
not the baseline, the metallic muffled sound. It is more clear at 1:08 as it is all by itself
 
3:57 PM
Ah, that's a Glockenspiel with some post-production I think
Or a keyboard with a weird sample
 
does not sound like a glockenspiel
the glockenspiel sound is quite sharp, crisp and high pitched
which is different to the muffled sound
 
That's why I said with post-production :P But indeed it's most likely just a keyboard
 
O wait I found the youtube video of the actual facebook video:
Underneath the drums, beats is that muffled sound. It forms the main part of the melody and can be heard throughout
 
4:03 PM
Maybe a triangle?
Or some metal percussion set
 
the sound is all by itself between 0:00 and 0:02
it also become more rich starting from 0:50
so you mean this main instrument is a keyboard with post production?
 
The sound between 0:00 and 0:02 on that video is just a synth
 
I see
 
4:23 PM
Hallucinogenic drug psilocybin eases existential anxiety - honestly, the excuses some scientists come up with :-)
 
@JohnRennie One of my plants has mushrooms growing on it
Sadly they're not magic
 
Magic mushrooms grow naturally in the part of Somerset where I lived as a child. Everyone knew where to find them. We had abnormally low levels of existential anxiety :-)
 
I've been wanting to try it for a while, I'm very anxious about my existence
Supporting a potato family is stressful
 
@BernardMeurer ...what kind of plants do you have?
@EmilioPisanty Much worse HNQ bug: I was just now led to this question, which is locked since yesterday. One would expect that locked questions are removed from the hot list, right?
 
a potato family of computers - there's little Bit and Qubit, Mr. Charles P. Underwood, Mrs. Rita A. M. Underwood...
^look at the initials on the last two
 
4:59 PM
@ACuriousMind The kind they had at Ikea
@ACuriousMind See the shrooms?
 
@BernardMeurer yes
@BernardMeurer Why would I buy plants at Ikea? :P
 
I'm a computer engineering student, what did you expect?
 
I expected no plants.
 
@ACuriousMind "Why would I buy plants?"
 
@ACuriousMind Then what would I name after my fav. people?
That one is Tsiolkovsky btw
There's also Turing and Laplace
Turing stays next to my portrait of Alan Turing
 
5:04 PM
@BernardMeurer so sad when the plants die :|
 
@Sanya All my favourite people are dead
3
 
@BernardMeurer but they'll die a second time
what a tragedy
 
@Sanya Meh, they probably deserve it
 
@BernardMeurer Uhhhh
Your characters in video games? :P Dunno, never had the urge to name anything after my favourite people
 
@ACuriousMind I only play Civ and Tetris :P
 
5:07 PM
@heather @BernardMeurer there are instructions for Python 3 in the document!
 
@ACuriousMind that's a fantastic bug
 
@EmilioPisanty meta.SE post
 
did you post on meta.se?
damn train wifi
slow as a turtle
well
relative to 2015+ internet speeds
gotta love the Mother Meta, though
I disagree with your general assessment that this kind of behavior is a bug (feel free to try to change my mind) - but do you think this particular question should have been presented as hot, irrespective of its lock status? "too many comments" doesn't seem to be a pretty strong negative indicator of quality. — Jan Dvorak 24 mins ago
it seems that no amount of ridiculous behaviour by the HNQ sidebar is enough to stop people from saying "that's not a bug, it's supposed to be this crappy".
 
@heather what's the error? Almost certainly the ironmen is that you have to apt-get install some development libraries.
 
@EmilioPisanty One can certainly get that impression, yeah
 
5:16 PM
@ACuriousMind On the other hand, that's not a full historical lock on the question
it's just a lock on the comments
and only on the question itself
 
@DHMO what the...? Just run pip.
 
@DanielSank heh, windows
 
@EmilioPisanty wait, you mean the lock does not actually prevent any answers, but onyl edits to the question and comments on it?
 
@ACuriousMind I think so, yeah
 
That doesn't square with the improve this answer edit link missing from all the answers, though
 
5:18 PM
I can still comment on the answers
 
@EmilioPisanty hmmm
 
@ACuriousMind I can't answer, but I think that's only because it's protected
 
@heather @BernardMeurer yes, when you make a new virtualenv you can specify which Python interpreter to use. This is done in the doc I shared.
 
but also I can't edit any of the answers
 
In that doc, I give instructions for compiling Python 3 from source in case you want a version different from what's in the Ubuntu repositories.
If I can improve the instructions please let me know.
@ACuriousMind also consistent code style means other people can understand the code. Other people includes the author in the future.
 
5:28 PM
What has the linter to do with consistent code style?
 
@BernardMeurer because you didn't used to get 3.5, bro.
@ACuriousMind pylint, for example, finds overlong lines, unused imports, etc.
 
Any atom with more than one electron
 
@JohnRennie The space of n-particle wavefunctions is the n-fold tensor product of the space of 1-particle wavefunctions, and hence all n-particle wavefunctions are sums of products of 1-particle wavefunctions.
 
Oh OK. On a more careful reading where Sanya wroye combination I had instinctively read product.
 
@ACuriousMind well, subject to symmetries...
 
5:41 PM
@DanielSank Yes, insert (anti-)symmetrization as desired :P
 
@JohnRennie it's quoting what the post had written - I'm just not too sure what specific problematic cases OP wants to know about, thus the question. Maybe that's just me not having done QM for too much time again
 

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