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12:17 AM
@skullpetrol You know @ChrisWhite is American
 
12:33 AM
Associate Justice Scalia is dead. Way to throw a wrench into the race.
 
 
3 hours later…
3:21 AM
Cool how many LIGO questions that we're getting. In the future, I wonder if we should prepare for these kinda events that attract many questions and views. I mean, we could post likely questions in advance, and build a collection of high quality answers
Or we could encourage an officual LIGO experts to utilize PSE to answer common queries about their experiment
I'm just brainstorming. I think we're doing pretty well. I just think we're probably not exploring the full potential of the site
@skullpetrol isn't that Einstein? The counting counts quote
 
Yup :-)
 
"Not everything that counts can be counted, and not everything that can be counted counts." (Sign hanging in Einstein's office at Princeton)
2
Very true
 
3:38 AM
0
Q: How long should I wait to get a question answered?

user93868I posted a question 2 days ago, which I think is reasonably well worded and clear to understand, but it has no response: Transformers: relation between their current, voltage and resistance Generally when I post a question, I get an answer within a few hours. If not an answer, I at least get a ...

 
Damn it's cold!
 
That's what happens when it snows :P
 
It's not snowing!
 
@innisfree The LIGO people have many channel over which to do outreach already, but that doesn't mean they won't be interested.
However, we have a non-trivial problem with the kind of questions we get after big events.
 
Well-informed, well-written questions by laymen?
 
3:44 AM
A significant fraction of them are asked by people who are unprepared for anything but the glossiest and four-colorest of popsci answers and at the same time think they understood what they've already read and are desireous of hearing the real deal.
Take physics.stackexchange.com/questions/235966/… as an example. The OP has wavelength and amplitude confused.
 
@dmckee Well I confuse space and spacetime, these things just happen!
 
I'm thankful for people like Chris W. and John R. who have the patience to field at least some of the better questions. I find the site so frustrating in the wake of a major announcement that I can't really spend any time on it.
 
@dmckee What's the most expensive textbook/monograph you've had to buy
 
Not a clue. I haven't bought many texts recently.
 
@dmckee Does the university provide any you need?
 
3:55 AM
Sometimes. Other time the publishers will simply send me a desk copy. Rank hath its privileges. Even at a second tier state university.
And as if the LIGO related question weren't enough there's this:
0
Q: Is there any property of a Neutrino that prevents it from being considered the missing monopole that will make Maxwell's equations symetric

Shayne MurrayThe zero in Gauss's magnetic law is it an approximation? Could it be in reality be a really tiny number like the magnetic field strength of a neutrino? Neurino's are members of the Lepton family that contains only the three flavored neutrino's and the electron and it's more massive forms the ...

 
@dmckee Would it be an abuse if you got that GR book for me and mailed it to me
Actually, it's not even GR
pure math
 
Obviously. It's not like we're going to be teach a GR course anytime soon, and if we did we'd need a text that our students would have some remote hope of understanding.
 
@dmckee Oh come one, there have to be some people in the math dept who would understand it
It's not a GR book
 
4:57 AM
Still GR going on huh?
 
 
5 hours later…
9:28 AM
What has been up with the review queue lately?
@dmckee PLEASE DON'T CHOOSE HARTLE---RESIST THE TEMPTATION :P
 
9:38 AM
good morning @Danu
 
hi
 
I hope I was able to cover all the basic facets of issues "peer review" questions might have in my meta question
 
 
1 hour later…
10:56 AM
aye
 
 
2 hours later…
12:46 PM
0
Q: How much mathematics is allowed to be the focus of questions?

Self-teachingDavideSince there are mathematics and mathematical-physics tags, I was convinced that it is perfectly legitimate to ask for a mathematically rigourous proof, i.e. a methematically correct, once given the assumptions made in physics on the mathematical objects used in the derivation, such as functions, ...

 
1:31 PM
I see $|\vec v \vec v\rangle$ in a physical text. What does it mean?
Why do they square the vector inside the ket?
 
God
for the love of a deity, my dear Valentin
 
After the LIGO announcement last Thursday Feb 11th, we now have more than 200 posts tagged . There are more than 90 questions about gravitational waves without the tag. Is there a 3k+ user who could e.g. comb them for e.g. duplicates, outdated posts that should be closed, retag & improve appropriately, etc?
6
 
God
Qmechanic, can I ask you a rather preposterous question?
 
@God : You can ask.
 
God
In your opinion, is nature fundamentally deterministic?
ofcourse I am only trying to collect your opinion, not a fact, and even if you believe that nature has it's strings pulled on by a clown, I will not by any means ridicule you, but surely, there is a feeling in your heart which is not rational in flavor regarding this particular matter?
 
1:50 PM
Hey remember when math people tried to solve the 4 color theorem
And saying it was hard and all
And then a computer solved it
And they were all like UH IT PROBABLY WASN'T THAT IMPORTANT A THEOREM
Those little bitches
 
2:22 PM
@Danu hey mate, was wondering whether you knew of a "readable" account of the calculations showing gw's are quadrupole? (of course, just intuitively, I understand that with mass / momentum conservation, monopoles and dipoles are ruled out).
 
@yuggib you around
@Phonon Zee does it pretty well.
 
@0celo7 oh, could you ref me to it? thx
 
@Phonon Do you have Springer access?
 
sure
 
Zee isn't Springer, but I could find a Springer book that does it.
I'm 99% sure the second one does the calculation as well, I know the first one does.
 
2:27 PM
@0celo7 alright, thanks a lot, I ll try to also get hold of a copy of Zee's. I ll look into both
 
user116211
Does anyone know where I can get a pdf of Reif's Statistical Physics?
 
@user36790 There's the standard site, but we're not supposed to talk about "getting pdfs" here.
 
user116211
@0celo7: Nay! Don't want to ask it PSE!
 
The "standard site" is a Russian PDF depository.
 
user116211
@0celo7 Never heard of that! Normally get pdf from Internet Archive.
 
user116211
2:32 PM
@0celo7 Can you give the URL?
 
No.
 
@Phonon Carroll for life
 
@0celo7 I am around yes
 
@user36790 Google "libgen"
 
@yuggib does this look alright for a first course on math-oriented fluids?
before I've taken functional analysis, measure theory, etc
the class also uses Landau
 
2:42 PM
I have no springer access anymore T__T
 
math.utk.edu/~schulze/513.pdf actually, here's the book list
@yuggib what, why?
how can a mathematician function without Springer access
 
My Rennes account expired, and I had the access through it
now I have no more access to springer books, only to papers
I'm very sad
however I would use Landau
and the math one seems ok, and rather short
 
2:59 PM
@Danu I got into Berkeley!
 
:O congrats @FenderLesPaul
 
As I understand arxiv.org/pdf/1212.5214v2.pdf, |a_0 a_0> is what you call "a tensor product". It just says that I have a vector of vectors or "concatenated vector", right? Then, obviously, |a_0 a_0> + |a_1 a_1> = |00> + |11>, given |a_0> = |0> and |a_1> = |1>. I just do not get why |b_0 b_0> + |b_1 b_1> = |00> + |11> given |b_0> = 1/2 |0> + √3/2 |1> and |b_1> = √3/2 |0> - 1/2 |1>. Can you explain that?
Can you explain me basics on this example?
 
@skillpatrol thanks :3
 
@ValentinTihomirov Read any introductory quantum mechanics text.
 
user116211
3:29 PM
@Danu Thanks! But there is no Statistical Physics ;(
 
4:33 PM
@dmckee Is it abusive for one of my own profs to get a desk copy of that book and "lose" it in my backpack
 
There are two way to get a desk copy.
One is to ask for it alleging that you will either be teach a course from it or evaluating it for possible adoption. Giving you a text obtained in that way would be, IMHO, unethical. Because the request was based on a lie with material gain the aim.
 
Desk copy means free copy?
 
On the other hand, publishers sometime send books out blind in the hopes of bringing new choices to the community's attention so that they might be adopted. As far as I'm concerned those are fair game for anything the professor want to do with them. Because the professor didn't ask for them or make any claims about how they would be used.
@0celo7 Yes. In the old days those were sometimes special "instructors editions" with added material (extra problems, solutions, digital media), but those seem to have gone the way of the dodo.
 
@dmckee The particular prof who told me to get that book already has a copy
 
Now if the publisher want to provide extra material to professors they make it a separate product.
 
4:40 PM
I know the instructor copy of BBS's string theory book has all the problems worked out
I might be more interested in string theory if I had that copy.
 
@0celo7 But, again, my evaluation is based on how he came to have it.
 
Oh, I would never ask him to give me his copy
It's well-worn and right next to his desk
@dmckee This particular prof has hundreds of books (at least 200). Is it safe to assume he orders a desk copy of anything he thinks is interesting?
Apparently he also has more at home -- that's just nuts
 
@0celo7 He might. There is no completely uniform agreement on the ethics relating to desk copies and different people live by different rules. For myself I live by the rule `don't ask for it unless you are really thinking of using it in a class that will really run'.
 
@dmckee Hell, he used to work at a research institute for GR, he might have gotten all of his books there
@dmckee Is it unusual that there is a course in the catalogue for which I can find no evidence of it ever having been offered?
Apparently there's an applied math course on continuum mechanics and transport phenomena, but I can't find out anything about it.
 
@0celo7 Depends on the school. We just dropped a course from the catalog that hadn't been offered in circa 15 years. We also have another that never runs as a standard class but is always a special seminar even thought the catalog says nothing about that.
 
4:55 PM
yeah, looks like I'll be going to Schulze's office hours on Monday
Hopefully he knows more about the applied courses than my official advisers
(Considering he teaches them)
 
Ok. I think that I have figured out the tensors. I can compute them. But this did not help me to understand why did http://arxiv.org/pdf/1212.5214v2.pdf chosen |Φ
+> = (|00> + |11>)/√2, why did they chosen such basis vectors (a_0, a_1) , (b_0, b_1), (c_0, c_1) for properties A, B, C and why do they compute probability of obtaining 0 when measuring A and B by amplitude of |a_0 b_0>?
 
@dmckee how is one supposed to drum up interest for a class, anyway
 
@0celo7 Problem: Find a self-adjoint operator on some Hilbert space $\mathscr{H}$ whose spectrum are the prime numbers.
 
run around naked
screaming the class' name
 
@yuggib I'm not doing your homework for you
 
5:03 PM
@0celo7 We know which are the most social physics majors and we tell them that we'll be offering it.
 
@dmckee my adviser wants me to find people interested in a course on spin structures and minimal surfaces
 
Other department send-out bulk email to advisors around campus and/or flyer the school. But the details are going to depend on the size of the university/department.
 
I don't even know anyone who has heard of such things
 
That's a networking thing. Go to places where people in your major and allied subject meet and schmooze. Chat people up. Mention open problem that require the subject to examine. Talk about applications.
In other words all the people-skills stuff that I still suck at despite years of conscious effort to improve.
 
I'm a freshman, I don't know any grad students
 
5:06 PM
I loathe schmoozing.
@0celo7 Start by attending colloquia in your majors and related one. Chat up the research profs to hear about people coming in to give talks.
Once you start hanging with he grad students at least a little try not to pester them, but stay engaged.
And by "pester" I mean "keep coming back to them with a question about the next step you're stuck on" the was you treat @ACuriousMind and others in here.
 
:/
@dmckee The idea is to "pester" people here so I don't "pester" people at school.
 
@0celo7 the pesterer
 
So now I'm a troll and a pesterer.
Great.
 
5:22 PM
(Sigh) Now even I'm jumping on the gravitational wave bandwagon.
Also, for those interested, Worldbuilding has been infected: worldbuilding.stackexchange.com/questions/35942/….
 
@FenderLesPaul does rd.springer.com/book/10.1007/978-1-4684-2343-3 look like it might have some interesting stuff in it?
 
5:57 PM
@0celo7 yeah
 
@FenderLesPaul any clue what the prereqs are?
 
@FenderLesPaul thanks!
you're so helpful
 
So, my text (Serway,Jewett) says Gauss's law cannot be used for a dipole, a disk, or a triangle with a point charge at each corner. Why?
 
@0celo7 it says in the preface
 
6:04 PM
I mean, the triangle and dipole make basic sense, but why can't I just put a cyinder through the disk at angle of pi/2?
 
@FenderLesPaul where
it's not on page v or vi
 
6:19 PM
@JoeStavitsky The question to ask yourself is what is meant by "use" in this case.
I suspect they mean there is no shape for the surface that makes the flux computation trivial from symmetry grounds.
With the result that you can't obtain an expression for the electric field without having to compute it the hard way.
Because the basic result is true for all cases.
 
@0celo7 one sec lemme check again
 
6:34 PM
@0celo7 I think you're fine
 
6:46 PM
@FenderLesPaul um, ok
so it's not much harder than Wald or HE?
 
gucci
@FenderLesPaul got me some cookies here
 
dopee
:)
 
7:34 PM
holy crap
"penrose and Atiyah have confirmed a long standing conjecture [...]$^{10}$"
"10. R. Penrose, private conversation."
That should be illegal
 
At least sometimes that means that you can expect a paper by Penrose and Altyah soon, and then everyone will get to cite it.
 
soon?
this was written in the 70s
@yuggib Analysis proof time
@yuggib I conjecture that if $\sum x_n$ converges and $(y_n)$ is bounded, then $\sum x_ny_n$ converges.
Indeed, let $M$ be the real number such that $M\ge y_n$ for all $n$. Since $\sum Mx_n$ converges, and $Mx_n\ge x_ny_n$, we see that $\sum x_n y_n$ converges.
 
yes
that was pretty trivial
 
Not for me
 
it is called direct comparison test
 
7:43 PM
I know
 
What's going on with the site? It keeps giving errors and is now in read-only mode
 
same.
 
@ACuriousMind what is the squeeze theorem in German
 
@0celo7 wikipedia has a name for it, but I have never heard anyone refer to it as a "theorem". It's mostly treated as a property of limits, not a "theorem".
 
@yuggib Ok, this one seems a bit trickier. If $0\le x_n\le 1/n$, can $\sum (-1)^nx_n$ diverge? I know that $\lim x_n=0$ by the squeeze theorem, but I can't apply the alternating series test because $x_n$ need not be decreasing.
 
7:51 PM
yes it can diverge
 
Do you have a specific counterexample in mind?
 
yes, give me a couple of mins
$x_n=(-1)^n\frac{1}{n}$ converge but not absolutely
 
@yuggib $x_n$ must be greater than zero.
 
so you can rearrange the series to make it diverge
 
But can you rearrange it in such a way that $0\le x_n\le 1/n$ is preserved?
 
7:56 PM
yes I think so
I mean, of course
 
How? If you move any terms back, they violate the bound automatically.
@ACuriousMind Can you offer a hint?
 
ok, simple example
$x_{2n}=0$, $x_{2n+1}=\frac{1}{2n+1}$
 
What is meant practically by saying the size of a gaussian sphere doesnt matter? Mathematically r^2 is cancelled in numerator and denominator, but in practice the force still falls off as the square of the distance. What gives?
 
@yuggib so $\sum_n (-1)^nx_n=\sum_n x_{2n+1}$
 
@JoeStavitsky What's a "Gaussian sphere" and for what is its size supposed to not matter
@0celo7 No, AHungoverMind cannot do analysis today
3
 
8:03 PM
@0celo7 exactly, with an overall minus
 
@yuggib umm
you can't pull the minus out, can you?
damn, I have to prove that if $\sum a_n$ doesn't converge then neither does $\sum -a_n$
 
@0celo7 do it reversed if the minus does not convince you, $x_{2n}=\frac{1}{2n}$, $x_{2n+1}=0$
 
@yuggib ok, that's better, danke
and that series is bounded by the harmonic one, so it diverges
nice
 
;-)
 
@ACuriousMind How are you hungover at 9PM?
 
8:07 PM
@0celo7 It was almost noon when I went to bed
 
@ACuriousMind Your sleep schedule is MESSED UP
 
No one is disputing that :P
 
@ACuriousMind you sure that analysis proofs won't help you clear your mind
 
Quite sure, yes
 
That's unfortunate.
 
@JoeStavitsky ...and your question is? You use Gauß' law to calculate the charge inside the sphere, not a force.
 
@ACuriousMind, oh, ok, so gauss' law can only give charges from known forces?
 
@ACuriousMind Don't you feel a little...uppity when you use ß in English speech?
 
@0celo7 almost ßupercilouß
 
@JoeStavitsky No, you can also use it to compute the field from the charge, but then you get the correct 1/r^2 dependence, so I'm not sure what is confusing you
 
8:19 PM
@ACuriousMind so, the field strength does fall off as the square of the distance, correct?
 
@0celo7 Would you ask the same for the é in "Poincarè"?
@JoeStavitsky Yes
 
@ACuriousMind Yes.
But the ß is worse.
Am I in the minority here?
Like usual?
 
@ACuriousMind there is no è in Poincaré
but there is an é in Poincaré
 
Oh, well...
 
See, that's exactly why
 
8:29 PM
btw @0celo7 , do you use Schroedinger or Schrödinger?
 
Schroedinger.
I don't have as much of an issue with accents and umlauts as I do with ß
 
do you have issues with the ç, or the ñ?
 
Of course.
 
or the þ in Icelandic?
 
Never seen that one before.
 
8:33 PM
you clearly don't use Icelandic often then
like in Sigþorsson
 
user54412
what's your one-letter abbreviation for Thursday, then?
 
Uhhhh
@ChrisWhite Mine?
Tr
my alphabet has 27 letters
 
Is the principle of virtual works way of an investigation by the induction?
 
x, y, z, and Tr
 
Are there exercises where we must use the principle of virtual work be for thinking?
Anyway, as each other Feynman exercise is for thinking.
The procedure of solving Feynman exercises: note this problem, hardly thinking and save solution.
 
8:42 PM
@FenderLesPaul congratulations!
 
I should really jump on the LIGO bandwagon/answer enough questions that I earn the right to vote....
 
What are you think about my blog hubot.pl/?lang=en_gb? Posts has been translated. This blog is about my life.
 
8:59 PM
This blog is not completely translated but you can read some about my life.
This blog is constantly developed.
 
9:29 PM
@Danu thanks!
I'm still going with UCSB but happy nonetheless
 
 
1 hour later…
Did you know @0celo7 there was an actual "letter" that corresponded to your Tr that we now use for the symbol of "and," namely & was the 27th letter in the alphabet.
 
@skullpetrol yes
 
@skullpetrol Nonsense, the & evolved from the way scribes wrote et, the Latin word for "and".
 
@ACuriousMind I thought that was the case
but wasn't it a letter of it's own at some point?
> It was also common practice to add the "&" sign at the end of the alphabet as if it were the 27th letter, pronounced as the Latin et or later in English as and.
 
It's now a symbol of its own, but it is not a letter - technically, it is still a ligature of the letters e and t
 
10:49 PM
Yes master @ACuriousMind :P
 
11:03 PM
@skullpetrol Hungover ACM was wrong
he's not infallible
 
Nobody is perfect.
 
@ACuriousMind I need your analysis wisdom
0
Q: Why can you throw your cat off your house... and better not jump yourself?

NumrokI remember thinking about this classic problem with my friends back in school: Why do smaller animals survive falls from larger heights? Since I don't wanna end up having biology discussion let's assume the smaller animals are reasonably modeled as humans scaled by a factor k. I wanted to see ...

 
I've jumped off a house one or twice.
2
Stupid macho thing to do, but I'm sure I looked at least a little ninja rolling out of it.
At least ... that's what I tell myself.
 
@0celo7 Tough luck.
 
@FenderLesPaul Is Berkeley not good?
@dmckee lolwut
@dmckee This looks really dark, on the star-wall :D
@Qmechanic Hi Qmechanic. Has anyone responded to this yet? I may be willing to do this.
 
11:13 PM
What's the crazy ass urban running, jumping and rolling stuff called anyway?
 
Parkour
Or AssCreed
 
Parkour
 
Yeah that. Never did any, but I have (had?, probably had) some of the basic skills. Only I practice them on soft natural surfaces, 'cause I'm scared of concrete and asphalt.
 
Awwyis hahaha
@dmckee Cool!
Gotta love that music to go with it
 
We called it trail-running.
 
11:15 PM
@Danu Assassin's Creed is real
If only hidden blades actually worked!
 
I really love the "epic video style" of old youtube videos.
 
And the more skilz you had the better the short cuts you could take.
 
@Danu : No, not yet, you are more than welcome. You already know this but let me say it anyway for good measure: Remember only to do a handful or two in one go not to clog up the front page.
 
@Danu My favorite old YT video: youtube.com/watch?v=ZPaMdxC6CQI
 
@Qmechanic Oh, I would've definitely forgotten about that. Thanks.
Oh yeah hahahaha Melbourne shuffle
Crip walking for emo's
 
11:21 PM
I would kill for the song at 2:00 in HQ
 
Now I've found some youtube gold: Love the mix of cultures in this one:
The music, the super-whiteness of it all
 
I can't even handle it
 
So that is what happened to break dancing :P
 
@dmckee Four years of trail running has convinced me that it's far more dangerous than parkour.
 
11:27 PM
I've learned that human bodies may be rigid, but they can quite easily be deformed.
 
Semi related to breakdancing, pretty damn cool IMO
 
Depends how crazy you are in either environment. I tended to accumulate scratches and a few bruises but no broken bones.
 
Fun to watch.
 
@Danu Those guys can move but the martial arts guy in me wants to scream "Don't watch your feet, stupid!".
 
@dmckee "the martial arts guy in me"
Say what?
 
11:30 PM
@dmckee Is the karate kid.
 
If you watch your feet you get punched, kicked or thrown hard. Watch the other guy's center of mass.
I've actually never done any karate.
 
See here for some super hilarious stuff
The second routine is great
 
And these days I don't even have a regular workout. I'm getting fat and soft.
 
Especially how it goes into that crazy windmill afterwards
That dude is a boss
With the little kicks at the end, 10/10
 
Proving the alternating series test with nested intervals is getting very ugly
 
11:38 PM
The sequence starting at 5:40 is truly epic
 
Hmm, Steam logged me out and I have no clue what my password is. I hate when that happens.
 
user54412
@innisfree Like this person perhaps
 
user54412
that profile had no information the other day, but I suspected he had to be involved pretty directly based on the thoroughness of the answers
 
Hi @yuggib
 
Hi
 
11:48 PM
Did you watch the super bowl yet?
 
yes
it was nice
 
and...?
 
never thought I would have seen payton manning win a superbowl without scoring a passing TD
:-D
 
True dat
 
and as the old saying says
defense wins games in the end
 
11:51 PM
He now holds pretty much all the top records for qbs
 
yep, and also the record for worst shorts wore in a commercial
 
sorry but I gotta go bed...it's getting late here
 
Later pal.
 
good night / evening
 

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