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00:00 - 17:0017:00 - 00:00

5:03 PM
@0celo7 Didn't you say Einstein didn't understand GR better than physicists do today?
 
@SirCumference yes
 
@0celo7 So why you asking for a quote from Einstein?
 
shrug
 
@ACuriousMind HALP
 
@BernardMeurer he's not here.
 
5:16 PM
Dammit
 
5:28 PM
hey guys what does this question mean? Write three fundamental formulae of hyperbolic functions
 
@HariPrasad I guess sinh, cosh and tanh?
And the way you derive them using Euler's identity?
 
ah yes but another question specifically asked for that and the next one is this. what to do now?
 
@HariPrasad "What to do now"?
Just rearrange Euler's identity using algebra, and get rid of the imaginary numbers
 
i mean i did what said for another question from the same set. which means this question is asking for something else
 
Email your teacher for clarification
 
5:35 PM
@SirCumference haha thanks but not going to happen since i need to submit this thing within 9 hours and its like 11:30 pm now
 
@HariPrasad Welp, anyone in your class still awake?
 
none knows what to do
 
Ya tried looking up the question online, word for word?
Might be a textbook question
Which would have an answer's section
 
yes could be.
 
What was the other question?
 
5:39 PM
For the third, they probably mean sinh, cosh, tanh, and then csch, sech, coth
 
Just write out the Taylor series of each or something
That might be close enough
 
@SirCumference sounds good
 
What class is this?
 
semester 1 - Electrical and Electronics Engineering
 
5:41 PM
Huh...that's unexpected
 
@SirCumference why?
 
I expected it to be a pure math course
 
@SirCumference things are different in India
 
Didn't know hyperbolic functions were used in electrical engineering
Well, I'm probably wrong
 
you are
 
5:42 PM
Cool
I guess
 
Can i bother you guys for a minute?
 
Yeah, sure.
 
I am thinkning the quantum physics interpretation
 
Just ask
If we don't know, we won't answer
 
I don't understand how von Neumann interpretation can ever start...
since I can choose the detector to randomly emit photons.
 
5:44 PM
I want a hint to how i could calculate the final velocity of an object in freefall assuming a changing acceleration
 
What variables you have?
 
@SirCumference Thanks and bye
 
@HariPrasad Np
@ArmendVeseli $v_f = v_i + at$
 
No, variable acceleration
 
Oh, is this Newtonian physics?
 
5:45 PM
With newtons law solved for a
Integrating as a function of r makes no sense
 
Do you have a function for the acceleration?
 
GM/r^2
 
Yeah, I realize I need to recall two years ago
Welp, crud. I don't remember...
 
It's a tricky one
Maybe it has something to do with substituting GM/r^2 into the jerk equations of motion
 
Has anyone given any thought on the von Neumann interpretation in quantum mechanics?
I wonder if we can just make a detector randomly emit photons in the traditional double slits experiment to silent it?
(von Neumann interpretation = consciousness causes collapse )
 
6:06 PM
Tooday was a bad day, I had to vote to close in nearly 50% of the reviews :-(
 
6:21 PM
Is there a name for the PDE that looks like the heat equation, except the Laplacian is replaced with the standard spin-1/2 Dirac operator in the plane? That is: is there a name for this equation du(x,t)/dt=Du(x,t) where $D=-i(\sigma_x\partial_x + \sigma_y\partial_y)$ is the Dirac operator.
Similarly, does any have any references where I could learn about the fundamental solutions to this differential equation?
 
6:35 PM
Ha! Cited myself in an answer
2
 
@DanielSank Smartass
 
6:55 PM
@ArmendVeseli It can't always be solved exactly! If $x''(t)=-\frac{1}{x(t)^2}$, you're not going to have a simple answer , and you'll have to resort to special functions or numerics
 
7:13 PM
@DanielSank Isn't citing yourself in your own answer just redundant?
You're not getting confirmation from another source
 
@Shing Your this sentence is unclear to me, give more details.
 
@SirCumference well, citing a paper gives the reader a lot more information than I'm willing to type into the answer box.
 
@DanielSank True
 
7:53 PM
'lo again. Just dropping in to see if I've got the right books from the authors recommended last week
 
@DanielSank Always a lot of fun.
 
8:35 PM
Hmmm ... I suspect it is too early to expect anything, but I am curious to hear what, if any, progress you've made with the reviewer/editor.
 
@MonaLisaOverdrive Looks good for a course on nonrelativistic QM! Note that Sakurai died in the process of that book, so some of the later chapters aren't written by him, only based off of /incorporating his notes. I can't comment on shankar since I've never read it.
 
Shankar is amazing
One of two physics books worth reading imo
 
9:03 PM
@dmckee Have you heard of "Packback"
 
9:15 PM
Good to know @NeuroFuzzy and @Ocelo7. Thanks!
 
No.
Google seems to suggest some kind of textbook rental platform.
 
specifically "packback questions"
 
::shrug:: They want you to sign up to even look around. That always puts me off.
 
@dmckee I wonder who in our physics department decided this was a good idea.
It's basically a forced PSE for the class
you have to ask and answer questions for a grade
 
Howdy...again
@dmckee Say, you're good with astronomy right?
 
9:29 PM
@SirCumference I'm not an astronomer, but I have enough interest to know this and that.
 
@SirCumference you've asked literally everyone that
find a prof or grad student at your school to annoy
 
All right, well is the velocity dispersion of a star cluster simply the standard deviation of the stars' velocities?
@0celo7 Easier said than done
Crap
 
Easier done?
Well shit, do it then.
 
I'm tired
 
@dmckee re-submitted yesterday.
 
9:31 PM
@SirCumference That'd be my guess, but I don't know if it is the practice.
 
@dmckee All right. @HDE226868 Might you know?
I suppose Chris White is still celebrating his PhD
Congrats to him
 
@SirCumference the rumor is that he's been on a bender ever since...
 
@DanielSank So I've heard
 
@SirCumference what do Canadians know about astronomy?
 
What a weird question
 
9:35 PM
Well they can see aurorae better...
Dunno if that counts as astronomy tho
 
@DanielSank My bender was short lived but intense. I was green the next day.
Never again.
 
@dmckee What was it for?
Legends say that when we need Chris White most, he will return
 
I mean the one following my defense. That's the biggest one most academics have for something happy.
 
@0celo7 Hah! That sucks.
 
@NeuroFuzzy I asked a question about the superposition principle, i.e. why don't the various charges interact
we'll see if I get a coherent answer
 
9:41 PM
Well, it's basically like here
Except instead of rep, you get a grade
 
yeah, 10 freaking percent of the final grade is this website
 
and instead of curating content for the current and all future askers, you're curating content for your professor (or TA, more likely)
as usual!
 
@0celo7 Just ask one of the popular questions from this site
Like this
-17
Q: How can magic be explained with Physics?

Margaret RosaAssuming that, hypothetically, and for this example only, "magic" means things like magical powers. In movies, games, etc. we witness magic; however, it's never explained how it works with regards to the likeness world in which they take place in to ours. My wonderng is, how can magic be explai...

 
@SirCumference well
 
Or this
 
9:43 PM
I answered a question on "electrons with the opposite charge"
 
-18
Q: If there is no gravity on the moon why is the american flag waving?

ZaneIf there is no gravity on the moon, how could this flag be flapping in the wind? (see link) http://www.stumbleupon.com/su/2wD6eg/hea-www.harvard.edu/~fine/images/desktops/Armstrong.jpg

 
@dmckee ooof. Sounds rough.
 
someone asked what would happen if we turned off gravity
 
That's an odd question
 
@0celo7 My advisor is a much larger man than I am.
So is his favorite drinking buddy.
They were buying.
 
9:44 PM
what
wrong person?
 
Yeah.
 
Yes
Jinx
 
@0celo7 All right, I think I've got the best question
Ask this, you'll get an A for sure
 
interesting factoid: If $X\subset \Bbb R^{n+1}-\{0\}$ is compact and intersects each half-line through the origin exactly once, it is homeomorphic to the sphere $S^n$
 
Only drow elves could wield it.
 
9:46 PM
(pure evil)
 
And axion faires. But they are rare in this age of the world.
 
I love how it had 2 upvotes
 
@dmckee "They were buying", and you were still in "consume free calories" grad student mode ;)
 
I've actually seen a lot of funny-bad questions
 
Oh, I wonder who the answerer could possibly be?
 
9:49 PM
Then there are the awful answers
 
@dmckee huh?
 
@dmckee Yep, it was obviously the OP
 
It occurs to me that an official Stack Exchange Wall of Shame would never happen, but an unofficial one might be popular.
 
I haven't been suspended in a few months
what's up with that
 
The mods have gone soft, you've become sneakier, or you aren't hanging around with evil company anymore?
 
9:55 PM
Bah! Mods these days.
 
I think it's because David Z isn't around as much these days
 
Ya know, I had a weird dream last night.
About this chat
 
just stop
 
Where it was an actual bar and 0celo was the bartender, but he refused to serve me a drink unless I could answer his riddle
 
unless I was the God Emperor
oh that works too
 
9:58 PM
Which involved some formula with hieroglyphics
And the answer had two decimal points
 
@dmckee and a "wall of fun" could get maybe even a quasi-official approval.
 
@SirCumference I'm a $5$-dimensional connected abelian Lie group with fundamental group $\Bbb Z^3$, what am I?
 
@0celo7 driving me nuts
 
wrong.
try again
 
But really, I was trying to escape from the stackexchange network or something, along with HDE and some random guy
So yeah
 
10:00 PM
Hmm, @SirCumference I have a mission for you
 
@0celo7 Huh?
 
@SirCumference Sigidur Helgason dedicated his book to "Artie"
who is that
 
Is he choking?
 
...what
 
If so he's an artiechoke
That's all I've got
 
10:03 PM
...
it was a serious question
 
Oh my god
 
How would I know?
 
google
 
@SirCumference ?
 
@HDE226868 Is the dispersion velocity of a star cluster simply the standard deviation of the star velocities in the cluster?
*velocity dispersion
 
10:08 PM
@SirCumference No idea.
 
All right, thanks :/
 
A quick Google yields this, which says
> Dispersion should here be interpreted as the standard deviation of the velocity components along the line of sight, even though the true velocity distribution in general is not gaussian
 
Awesome, thanks
 
10:26 PM
Why didn't you google that yourself
You even gave me the LMGTFT earlier
 
10:45 PM
@BernardMeurer what do you need, my child?
 
@ACuriousMind Hey :)
 
@BernardMeurer heyhey :)
 
Is Heavy metal the main genre, with death metal, black metal, yadda yadda under it, or is Metal the main genre and heavy metal a subgenre together with black, death, prog...
 
@BernardMeurer nowadays, people tend to say just "Metal", but the overarching genre is "Heavy metal" originally
 
@ACuriousMind Okay, great, then my Genre metadata style is correct :)
 
10:53 PM
@dmckee Well, there is gems from stack exchange but it's neither popular nor very good.
@BernardMeurer Was that seriously what you wrote "HALP" for? :p
 
@ACuriousMind I'm very serious about my music metadata :p
 
I loathe people who get all hung up on what exact subcategory a certain type of music falls into :P
 
@ACuriousMind Remember the finite intersection property?
 
@0celo7 I do
 
@ACuriousMind They loathe you too
@ACuriousMind it showed up on my analysis homework and I proved it without help
I've come a long way since we first met
 
10:57 PM
Do you expect me to say I'm proud of you? :P
 
@ACuriousMind I don't, I'm just grouping all my Metal-like music into Heavy Metal
 
@ACuriousMind ...yes
 
and wanted to know which name was best :)
 
@0celo7 I'm proud of you.
3
 
You don't mean that
 
11:00 PM
Maybe I do
Maybe I don't
 
You're a quantum duck
 
Why are there so many posts in the reopen queue?
 
Schrödinger's duck!
 
@0celo7 Great moves Ethan
 
@Danu I suspect because someone who doesn't like us closing questions has discovered they can vote to reopen :P
 
11:02 PM
Keep it up
 
@DavidZ I started a Google doc keeping track of posts which look like candidates for closure under the homework reason, but which I voted to close for other more well-defined reasons. Once there are enough to comprise a data set, I'll let you know.
 
I'm proud of you
 
I'm proud of all of us.
 
@DanielSank you're not proud of me
 
@0celo7 Sure I am. Way to go you!
 
11:03 PM
...thanks
 
@ACuriousMind Is it peterh?
 
@ACuriousMind Run my kernel
 
@Danu 1. Looking at the reopen queue, it seems about half of the questions in there were edited by their authors, so it's just coincidence. 2. Since reopen votes are anonymous until the question is reopened, I could not possibly tell.
 
@ACuriousMind Will my QM prof know what the kernel of a linear operator is?
 
@BernardMeurer No
@0celo7 He should
 
11:06 PM
@ACuriousMind He seems pretty mathematically savvy, so I'll trust you.
 
@ACuriousMind Please
I need someone to test it
 
Don't do it
last time he had me run shit, he took over my webcam
 
now he keeps a detailed log of what I do
 
He likes midget porn
 
11:08 PM
@Danu Does it matter?
 
@BernardMeurer not true
 
@DanielSank Not really. I just thought ACM knew from the way he phrased it, so I wanted to know.
 
yes, ACM did seem to be hinting...
 
After going through the queue, I have seen that most questions were in there for edits. So it's just coincidence.
 
11:27 PM
@ACuriousMind Since unit balls are always homeomorphic for any two norms on a finite-dim vec space, is it believable that all unit tangent bundles on a manifold are homeomorphic, or even diffeomorphic?
Maybe even isomorphic as smooth bundles?
(although diffeomorphic would be best)
 
@0celo7 What do you mean by "all unit tangent bundles"?
 
@ACuriousMind $UM_g=\{(x,v)\in TM\mid g_x(v,v)=1\}$.
is $UM_g\approx UM_{g'}$
 
@0celo7 I'd call that a "sphere bundle"; are you talking pseudo-Riemannian or Riemannian metrics here?
 
Yeesh, I just reviewed three or four posts from the queue.
I'm exhausted now.
Reviewing is so much harder than everything else on this site.
 
@ACuriousMind Riemannian, I've given up on GR
Sphere bundle isn't specific enough, there are other sphere bundles not of this form
I'm thinking it shouldn't be hard to write down the diff directly?
How do you diffeomorph between two Riemannian spheres? @ACuriousMind
 
11:37 PM
@0celo7 Then I don't know
 
@ACuriousMind Then you don't know? You would know in the GR case?
 
@0celo7 In the case where we allow non-Riemannian metrics it would be obviously false since the "unit ball" of a Lorentzian metric is a hyperbola and definitely not an actual sphere.
 
@ACuriousMind Ok, sure
@ACuriousMind So, different question. $V$ is a vector space, $|\cdot|_1$ and $|\cdot|_2$ are norms
 
@DanielSank I find giving good answers to be harder than reviewing :P
@0celo7 That's not a question ;)
 
11:49 PM
@ACuriousMind got distracted by you-know-who, sorry
@ACuriousMind hmm, are norms smooth functions?
probably on $V-\{0\}$
 
@0celo7 I don't know you-know-who, unless Voldemort broke into your room
@0celo7 Smooth in what sense?
 
@ACuriousMind there's one person who can distract me away from math
@ACuriousMind $C^\infty$
a norm is a function $V\to\Bbb R$
if we view $V$ as a manifold, is the norm smooth
 
@0celo7 How are you "viewing $V$ as a (smooth) manifold"?
 
what
 
For instance, I do not know whether the standard Euclidean norm is "smooth" in the smooth structure of the exotic $\mathbb{R}^4$s
 
11:52 PM
oh god
I'm looking at the tangent space?
So the charts are just isomorphisms to standard $\Bbb R^n$s
no exotic stuff please
 
what
 
I'm so confused
 
My point is that given a norm $V\to\mathbb{R}$ you have not fixed a smooth structure on $V$, so asking whether the norm is smooth doesn't make much sense to me
 
@ACuriousMind I want to map $UM_g$ to $UM_h$ by expanding each $g$ ball to each $h$ ball
expanding/shrinking
 
Awww, my favorite player was just knocked out of a Smash Bros. tournament.
Whatever, he's a winner in my heart.
 
11:55 PM
(btw, the norm on $\mathbb{R}$ (the absolute value) is obviously not smooth)
 
I KNOW
that's why I said $V-\{0\}$
 
@DavidZ Perhaps. That's where I was going when I was writing out all the distributions. I worked out the distribution of $1/p$, but Wolfram Alpha didn't know how to do the integral I needed to get the mean.
 
@0celo7 Well, I'd say that (with or without the zero) carries no canonical smooth structure and hence the question isn't answerable
 
;_;
 
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