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12:09 AM
The rest energy of an electron is tiny!
How come we can't make electrons by plugging an electron-maker into the wall outlet?
yesterday, by Abcd
3 mins ago, by Abcd
You dont like her?
Dammit, Rennie, answer the question.
4
@JohnRennie
 
 
2 hours later…
1:48 AM
Of course since the rise of computers as useful tools for physics mean-field shell models have more or less completely displaced liquid-drop models which are interesting and tractable with pencil and paper but have trouble providing a lot of details which can be obtained from shell-models.
 
 
4 hours later…
5:48 AM
@DanielSank I've never met her ...
 
6:11 AM
sorry, can't type today
 
6:37 AM
Do series ever really come up in physics, other than Taylor and Fourier?
Kind of seems bizarre that engineering/science students spend time figuring out which series converge and which don't
 
yeah, the real numbers need them as approximations
 
7:02 AM
@SirCumference There's a bunch of function basis for Hilbert spaces
like Laguerre polynomials
also I think you need some weird series for some things in antenna theory
Like Bessel series
or spheroidal wavefunctions
 
I guess, but is there ever a use to knowing whether a series convergences or diverges?
And memorizing the fifty different tests of convergence
 
@SirCumference You generally want your physical quantities to be convergent
 
^
 
Ok, I'll take your word for it
 
you can't escape memorization in math
 
7:07 AM
@skull Meh, anything that doesn't have a geometric intuition is dull
 
Also it can be a symptom that something is wrong in your theory
ie
perturbative QFT isn't convergent
@SirCumference Geometric intuition of convergence is one of the oldest analysis thing!
 
lol
 
@Slereah Yeah I know that one, but there's no geometric intuition on why many of the tests work, for example
At least none that I can come up with
 
Well tough titty
 
Geometry is what makes math good
 
7:09 AM
opinion
 
Yeah :P
 
If geometry is so good why did we drop using geometry for everything in the 16th century
Thank u Descartes
 
16th century dropped a lot of stuff. Witch trials, etc, some of the good things like geometry died too
I don't know what I'm saying at this point, it's 3:00am
 
If you love geometry so much buy this book :
It's classical mechanics entirely made with synthetic geometry
@skull No
 
kk
 
7:12 AM
That's a bit extreme :P I just think geometry makes math much more inuitive
 
If math was intuitive we wouldn't need mathematicians
 
2 + 2 = 4 need not be geometric
:P
 
@skull Dude cmon
@Slereah :44879178 :44879178 Math can be intuitive, mathematicians are the only ones who care enough to get the intuition though
 
if it's so intuitive why are you always asking questions :V
 
To build the intuition :P
 
7:15 AM
You don't want to end up like Secret, drawing awful nonsense diagrams
 
Define: intuition
 
Not a formal definition, but confidence that something works. Ya know, when you get that "aha!" feeling
 
"Young man, in mathematics you don't understand things. You just get used to them."
 
Making something feel natural
 
(von Neumann)
 
7:18 AM
@Slereah Pessimism :V
OK here's a good example. Anyone remember the difference between Calc II and multivariable calculus? One is a lot of memorizing techniques and the other can have a strong geometric intuition
Which did you end up enjoying more
 
I enjoy bike rides in the park, but I don't know how useful it is for physics
 
to each their own
 
Well, having an intuition on the concepts lets you know when they are relevant in physical scenarios :P
@skull Fair
 
the geometric intuition of series doesn't help you using them in physics
 
I guess so. But it does make it more satisfying imo. Being able to intuit basic things like FTC geometrically just feels nice when you use them, even if the intuition isn't entirely necessary
 
7:28 AM
It is nice, just
don't get stuck on a thing because you can't find the intuitive explanation
Sometimes you just have to practice abstract rules to get used to them
otherwise you'll just be stuck
 
@Slereah Eh, I mean in general the better an intuition I've had in math, the better I can understand their applications in physics
That math intuition often turns into a physical intuition
E.g. being able to compute a bizarre integral is nice and all, but truly grasping integration conceptually lets you know when it is relevant to a physical situation
 
8:28 AM
Somebody please suggest me useful videos for vector calculus.
 
Sid
@user187604 Read books. Forget videos
 
^go to vids after
(if at all)
 
Sid
If you want book recommendations, read Thomas Calculus, Kreyszig, Tom Apostol for starters.
 
@Sid @skull thanks a lot...
 
Thomas Calculus
is he the inventor of calculus
 
8:43 AM
@Slereah :-) Missing apostrophe error!
 
Sid
Well, I should have said, "Read George B Thomas's book"
 
One of my favorite dumb science joke remains some joke article on the Erlenmeyer flask
 
@Sid you might get the books in free in b-ok.org or b-ok.xyz
 
It was something like "The Erlenmeyer flask (invented by Francis Flask)"
Or some similar name
 
@skull @sid
 
8:54 AM
Mornin'.
 
Morning :-)
 
Today I am turning 16, finally.
 
Happy birthday! :-)
 
:thumbs up:
 
Sid
@NovaliumCompany Happy Birthday!!!
 
9:02 AM
@NovaliumCompany happy birthday.
 
Sid
What do you get when you turn 16? Licence? Legal drinking?
 
Spots? :-)
 
Sid
Definitely that^ :P
 
spots. as in acne?
 
9:17 AM
no that's the name of his dog
 
Who would call their dog Acne?
 
who gets a dog at 16?
 
Getting a dog at 16 seems perfectly normal to me
 
why not earlier?
 
You can't eat a whole dog when you're younger than 16
 
9:28 AM
Eeeww
 
 
5 hours later…
2:54 PM
That escalated quickly
 
it always does
that's the one thing these mods never concider
albeit, an extremely difficult task to try and control
 
3:11 PM
-1
Q: Why doesn't the sun come up in the night when we actually need the light?

Jome SikThe sun always is there in sky during day. But at night, it's dark, we need the light, but sun not out. Why does this happens?

One of life's great mysteries.
 
Anonymous
Lol
 
Anonymous
The obvious answer is that the sun is scared to come out in the dark ;)
 
Anonymous
It's freaking hot here today, phew. Bathed thrice
 
What's the temperature?
 
Anonymous
Temperature is not that much. 32 C I guess (evening). Was 37 in the afternoon. It's the humidity which makes the temperature seem like 50
 
Anonymous
3:22 PM
You would have to spend your whole day in an air conditioned room to remain sane here. Even 5 mins outside and you start sweating like a pig
 
@user187604 Go for Khan Academy's articles, not videos
Textbooks are a thing of the past
 
Anonymous
 
@SirCumference thanks. Are you in physics honors (ie bs degree)?
 
@user187604 Well if you mean "are you a physics major", yep
 
@SirCumference yep. I was asking that. Are you from UK?
 
3:29 PM
U.S.
 
@Blue 46 here
 
Anonymous
@AvnishKabaj Lol, where do you stay?
 
@SirCumference why would you say that?
 
@Blue Delhi
 
Anonymous
XD
 
3:30 PM
@skull I'm just kidding a bit :P But in seriousness, Khan Academy's articles are amazing (written by the guy from 3Blue1Brown)
 
@SirCumference while drawing vector fields we do take a point and stretch the arrow to the field value perpendicular to the point axis. Then how would we have radial field? The arrows aren't going to be perpendicular to the point axis.
 
Anonymous
One of the reasons I don't visit Delhi
 
@Blue It's nice tho
We have
The red fort?
 
Anonymous
Who the f*** cares about 200 years old buildings
 
cULtUrE iS EveRYiThInG
 
Anonymous
3:33 PM
"12 May 1639 – 6 April 1648
(8 years 10 months & 25 days"
 
Anonymous
Lol, it's even older
 
Cyberhub
You can't beat that
 
Anonymous
What's that?
 
Anonymous
hmm
 
3:36 PM
user image
2
 
Anonymous
The only place worth visiting in India is Kashmir, but alas :P
 
coffee anyone?
 
@Blue we English do ...
 
Anonymous
Heh, I'm not surprised. You people still have queens and company :P
 
@Blue I grew up in a house that was 300 years old.
 
3:45 PM
:O
 
Anonymous
wow
 
A castle?
 
Anonymous
DidGhostsHauntYou
 
Sid
@JohnRennie that's what you were made to believe. :P
 
@Sid we had the original deeds to the house, dated some time in the 1600s - I forget exactly when.
@skull it was originally a flour mill and bakery
 
3:49 PM
cool
 
Sid
@JohnRennie Fake News Deeds! :P
 
@skull it was a really great house to grow up in. Lots of twisty corridors and spooky cellars :-)
 
Anonymous
Some of the 300-400 old buildings did use to have some solid architecture though...much better than today's standards
 
did you have your own room?
 
@skull yes. My brother and I shared a room when we were young, but when I got older I cleaned up one of the unused rooms and moved into that.
 
Sid
3:55 PM
@JohnRennie ...You have a brother??
 
@Sid yes, there are just the two of us.
 
Anonymous
He's a biologist iirc :)
 
Anonymous
woo...that's some great reviews
 
high school biology was my introduction to rote memorization
 
Sid
@JohnRennie Pretty cool. Great teacher from the reviews
 
4:04 PM
@JohnRennie if we had field $x \hat{i} + y \hat{j} $ then points of projection would be same as the point orientation. So how do you plot that?
 
@user187604 please don't post the same message in multiple rooms
@Sid his reviews tend to be a bit polarised. He is prone to get, let's say, a bit irritable if he thinks you're not taking the subject seriously :-)
 
@JohnRennie OK I'm continuing to post on pss
 
Sid
@JohnRennie That's a quality of a lot of good teachers. :-)
 
I would like to understand everything about physics of solids
 
2 messages moved to Trash
 
4:17 PM
9 hours ago, by Slereah
You don't want to end up like Secret, drawing awful nonsense diagrams
heh
 
::shots fired::
 
by the way I have a question
 
what's a nonsense diagram
is it like a penrose diagram?
 
I am not gonna waste a ping with the reply button which is why I box quote respond instead
 
or more like a Feynman diagram?
 
4:21 PM
I once wrote comments to reply to comments on one of my questions but it got deleted for no apparent reason.
my question is... should I edit my questions and include all the comments in it? So that I'm sure they won't get deleted
because if someone modifies my question, there is still a way to get the original true version. while wiped out comments are forever lost
by the way my comment was something totally relevant, such as "S = k ln w
 
@ofhe_iAgDWolbuuTZO_5X1L6uuwfVP You should not include actual comments/replies in your question, but you should edit any clarifications you want to make in response to comments into your question.
Comments are not for providing additional information, that is indeed what the edit feature is for.
 
@Secret I don't get it either
 
I see @ACuriousMind, so I should not reply to comments by writing comments? I should just edit my question?
 
@ofhe_iAgDWolbuuTZO_5X1L6uuwfVP It entirely depends on what sort of reply you want to make, but if it is a clarification of your question, it should probably be an edit.
 
why'd my emoticon get moved to meta
i'm so meta even my emoticons are meta?
 
4:27 PM
@enumaris It looked very meta :P
 
:D
 
(An alternative explanation involves a fat-fingered mod)
 
@ACuriousMind I was just replying to a question someone had made. my comment was totally relevant (In fact I think I rewrote it afterwards because it was deleted by ... no idea who)
 
@ofhe_iAgDWolbuuTZO_5X1L6uuwfVP Could you give me a link to the question so we don't talk in the abstract?
 
then I realized how fragile comments are. because there is no way to get them back. unlike deleted questions or downvoted ones
@ACuriousMind I do not remember now. But let me have a quick look
@ACuriousMind I FOUND IT!!!!!!!!!!!!!!!!!!!!!! physics.stackexchange.com/questions/404091/…
here is my comment that got deleted : ShreyanshDarshan I do not have an idea on the answer to your question. If there is an E field inside a conductor in a closed circuit, I do expect a current, regardless of whether there's a battery or not.
 
4:34 PM
Actually, none of these comments should be comments, neither of you is saying anything substantial about the post you're commenting on.
 
I had posted it. got wiped out. I rewrote it a few hours afterwards, I guess almost the same words but not 100% the same since my memory is not perfect
 
Holy hell
We're already halfway through 2018
Why is time moving so fast
 
@ACuriousMind I mention that the answer is not complete. and that the previous comment is wrong.
it may not be entirely as relevant as it could have been, but was this a reason to wipe the comment out...
 
@ofhe_iAgDWolbuuTZO_5X1L6uuwfVP We're pretty tough on comments: Anything that doesn't need to stay, goes.
 
I see, good to know, thank you
but then my last comment should be removed too, since I've tried to repost the same idea
 
4:38 PM
@ofhe_iAgDWolbuuTZO_5X1L6uuwfVP They're all gone already :P
 
ok
by the way @ACuriousMind I have started recently to downvote some answers (it takes balls because of points. Not many people do that)
I am curious on whether you downvote more questions than answers
that's my question ^^
 
@ofhe_iAgDWolbuuTZO_5X1L6uuwfVP That's actually something you can look up on any user's profile: The vote stats in the lower right have a split into up/down and "on questions"/"on answers"
 
@ACuriousMind perhaps, fast-fingered is more appropriate? :P
 
hmm I don't see that @ACuriousMind I see that you have 2,528 up , 17,906 down. voted on X questions and Y answers
i don't know how many downs were on questions or answer in particular
 
@ofhe_iAgDWolbuuTZO_5X1L6uuwfVP Yes, but my particular values for X and Y leave only one possible answer to your question ;)
 
4:46 PM
true that
thanks
 
Today I learned that wolfram alpha makes a real mess out of partial fractions...
 
hello
 
yello
I discovered yesterday that using a softmax selection algorithm for my exploratory agent leads to negligible exploration if the rewards are large compared to the initial reward estimates. mmmhm...
I suppose that would be one potential reason to demand normalization of rewards
 
5:22 PM
hey all!
 
hi
 
@skul
@skull what u working on?
 
not getting banned
again
 
best of luck?
what did u do last time?
 
Typed what I was thinking.
 
5:33 PM
Consider this: goo.gl/images/uWLi8h
Why should that phosphate group be PO4 3- and not PO4-?
 
Sid
@Curio Can you draw the structure of Phosphate?
 
@Sid What do you mean?
 
Sid
You will see that 3 out of 4 Oxygen has a formal charge of (-1)
 
Yes
 
@skull Don't be so melodramatic, the last time you were suspended at all was more than 2 years ago.
6
 
5:37 PM
But not in that phospholipid
 
@Curio coz Os are bonded
Thats why its PO4-
 
But then it isn't phosphate properly
 
so what
 
Why then is that PO4- considered phosphate?
 
Organophosphates (also known as phosphate esters) are a class of organophosphorus compounds with the general structure O=P(OR)3. They can be considered as esters of phosphoric acid. Like most functional groups organophosphates occur in a diverse range of forms, with important examples including key biomolecules such as DNA, RNA and ATP, as well as many insecticides, herbicides, and nerve agents. == Chemistry == === Synthesis === Various routes exist for the synthesis of organophosphates Esterification of phosphoric acid OP(OH)3 + ROH → OP(OH)2(OR) + H2O OP(OH)2(OR) + R'OH → OP(OH)(OR)(OR') + H2O...
 
Anonymous
5:51 PM
@ofhe_iAgDWolbuuTZO_5X1L6uuwfVP Nice name
 
@Abcd thanks
 
6:07 PM
If I have a casing and a screw (let's say with areas $A_1, A_2$ and the same Young's modulus $E$) mounted between two rigid planes and I tighten the screw a distance $\Delta$, what would be the deformation of the casing and the screw?
 
Anonymous
First step to solve a mechanics problems is to draw a picture
 
make sure you draw a really pretty picture
the prettier the picture, the easier the problem is to solve
 
Anonymous
The second step is to hunt for the relevant formulae
 
I have a figure
I know the relevant formulae
But this is structural mechanics, so nothing makes sense anyway
 
Anonymous
The third step is to tear your hairs
 
6:18 PM
That's where I'm at
 
I thought the third step is to cluck like a chicken and pace around your room
so that's what I've been doing wrong this whole time...
 
If you can catch the chicken you can catch grease lightnin'
 
what
 
Sid
@Blue Ah! That's why I got a C in mechanics. I like my hair. I never tear them. :P
 
I am so ass at mechanics.
Someone tell me I can skip mechanics at uni.
 
6:22 PM
same
@CooperCape nope
 
Shame...
Remind me to take chemistry or something then
 
if you do physics you'll first do newtonian mechanics with engineer notation.
then again with physicist notation with a few more things added.
then analytical mechanics in 3rd year that's different entirely.
 
Hurmph
 
Mmm... sweet Lagrangians
 
this is why i hate physics degrees
 
6:24 PM
If you do physics
 
can't you just learn the math in first year and then start from 3rd year, doing it the right way from the start?
 
you will learn Newtonian Mechanics in 6 different ways
how fun is that?
 
Mechanics is fun
Structural mechanics is bullshit
 
that's engineering.
 
6:25 PM
Newtonian -> Lagrangian -> Hamiltonian -> Hamilton-Jacobi -> ...
 
or just scratch newtonian from the start
 
-> Schrodinger -> Dirac
 
lol
 
that's not the right order
 
no no
 
6:27 PM
Schrödinger and Dirac go hand in hand :P
 
from classical mechanics to classical qm to relativistic qm. that looked like a right order to me
 
-> Planck -> Rutherford -> Bohr -> Einstein -> Schrodinger -> Dirac -> Feynman
oh wait
I forgot Heisenberg in there somewhere
presumably after Schrodinger
 
@ofhe_iAgDWolbuuTZO_5X1L6uuwfVP you can learn qm without knowing all that class mech first
 
Schrodinger -> Heisenberg -> Dirac
 
literally every physics students learn schrodinger's equation before euler-lagrange
not literally*
 
6:27 PM
I agree @Eulb
i've learned CM first though
 
besides who cares about the learning order
 
but apparently you can't learn QM without first going through 100 years of history
 
it's how they're connected once it's all said and done that matters
 
QM textbooks care
 
only intro ones
 
6:28 PM
qm given by my prof was an advanced linear algebra course with almost 0 physics iin it
 
@ofhe_iAgDWolbuuTZO_5X1L6uuwfVP that's probably for the better
 
like I said, QM textbooks care
 
we did not see the hydrogen atom, but we did see spherical tensors
 
in an intro QM course?
 
meanwhile my qm course spends the first half of the year learning about the history of QM experiments all while learning no math.
 
6:29 PM
that's pretty hardcore lol
 
apparently that's supposed to give you intuition but i totally disagree
 
no @enumaris it was the regular QM course (1 year long, split into 2 courses)
 
@ofhe_iAgDWolbuuTZO_5X1L6uuwfVP that's standard then
the first half will be mostly math
same here
 
it was all math for me
 
I didn't have to do spherical tensors until grad school lol
and when it was presented to me, the presentation was basically, we use it to prove the Wigner-Eckhart theorem...and...just use the theorem when it's easy to apply, never actually ever resort to spherical tensors.
 
6:32 PM
we went through that too (W-E theorem and applying it to some problems) but I don' t remember much
 
what's w-e?
acronym is not clicking
 
our class
ah
wigner eckart
 
fun beans
(not really)
 
o
we didn't do that
 
my prof really harped on the usefulness of W-E
but I can't remember how to apply it anymore lol
 
Anonymous
6:36 PM
work energy
 
Anonymous
lol
 
all I remember is
for the final, one of my friends used the Wigner-Eckart theorem by actually transforming to a spherical basis...and my prof spent like 20 minutes telling him how he missed the entire point...the whole point is to never go to the spherical basis but just use the result to intuit some coefficients are 0 or some such...XD
 
fun times...
 
Anonymous
Is there anything like "GitHub for teams" for scientists/researchers (with MathJax enabled)?
 
Anonymous
6:43 PM
Maybe GitHub can somehow be tweaked for that purpose
 
Anonymous
hmm
 
isn't github for teams also for scientists/researchers? What's the restriction? o.o
 
Anonymous
LaTeX stuff
 
Anonymous
Don't know how to put in equations
 
Anonymous
Just code
 
6:45 PM
hmmm...
like a latex compiler that also does versioning for teams?
 
Anonymous
Yes
 
I've never heard of one
but I don't know too much about latex since I just used it to publish my papers and thesis then never touched it again
lol
my "team" just sent textfiles and pdfs back and forth through email
 
Anonymous
@enumaris That's very inefficient
 
worked well enough for us lol
I mean, I was the main author so I would produce the first draft, then we'd just iteratively go through the drafts and make them better.
 
Anonymous
There are a few people in my group who keep reinventing the wheel and doing duplicate effort. So I was wondering if I could somehow streamline the process so that at the end of each day everybody could update their works on the website
 
6:50 PM
there's an xkcd comic for this
 
Anonymous
@enumaris Your office allowing you to view pictures?
 
nope
I found the image on my phone
then typed the URL manually
LOL
 
Anonymous
It seems the best idea would be to just use Jupyter notebooks for LaTeX
 
Anonymous
and then upload them to GitHub
 
7:43 PM
hmmm
 
7:56 PM
@Blue Try overleaf or sharelatex
 
Anonymous
Umm, one of the problems is that not everyone in my group knows LaTeX. It would be perhaps easier to teach them basic MathJax and handling Jupyter notebooks
 
Anonymous
But thanks, I'll look into it
 
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