The h Bar - 2016-10-12 (page 4 of 5)

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5:01 PM

I know my chemistry passion very early on in my childhood, ad it has stayed with me ever since. My quantum passion is mainly inspired by my high school teacher. Unlike nearly every other physics subjects, quantum does not have that scifi realisation driving factor on me and is the only physics subejct I can say I intrinsically like

But if he wasn't a physicist, who else would I ask my bullshit?

My passion on all other physic subjects are not as pure as quantum's

@MikeMiller Danu

Oh wait...

In fact, I can argue that nearly everything not chemistry and not quantum have more or less something to do with my scifi drive, as if everything is soley aimed for dealing with the scifi

@BrandonEnright I think the main problem is trying to explain too much too fast.

5:08 PM

"The answer is that both observers observe the other person's clock to be running slower. Strange but true." No. Symmetrical time dilation is an absurd, even though validly deduced, consequence of Einstein's 1905 false constant-speed-of-light postulate. Actually, in 1905, Einstein introduced ASYMMETRICAL time dilation - the moving clock is slow, the stationary one is FAST. This version of time dilation was not validly deduced but implied time travel into the future. So Einstein's "theory" became an irresistible fairy tale (Harry Potter science). — Pentcho Valev 16 mins ago

Who is Pentcho Valev and why is he attempting to pick up where JD left off?

Deal with it there are Bazillions of anti GR people

@JohnRennie I take it you haven't encountered him before, then?

@ACuriousMind You have?

What is the story?

@0celo7 Yes, he's been on the site long enough. Just another user convinced that Einstein was wrong.

5:13 PM

Not JD then.

@ACuriousMind I'm fairly sure Einstein was wrong. Have you seen the shit JD posts directly from Einstein?

Let's not talk about JD.

Oh come on.

Did they tell you to stop JD conversations?

I see nothing wrong with talking about JD, as long as we're not being disparaging.

@JohnRennie I wonder why you think that one deserved a custom flag.

user218912

I need to get everything in cahill inside my head as soon as possible.

Seems trivial

user218912

5:19 PM

for you maybe...

@bl00 haven't you had the book for like 2 years now?

flagging

seriously, wtf kind of comment is that

from a room owner

Oh OK spoilsport

thank you

user218912

@0celo7 1.5 and remember I went on a physics break for like 7 months. so I've been meaning to read it for 7 months.

It did appear to become more inappropriate the more often I read it, actually

5:20 PM

we can at least be civil

@ACuriousMind I think sticking anything in someone's testicles (against their will) is inappropriate.

also why are you assuming that person has testicles @JohnRennie

It was rather evident that John didn't mean that as an actual physical threat.

@ACuriousMind Oh, I didn't actually mean any of the stuff that got me banned

user218912

@0celo7 he assumed their gender :o

@bl00 *sex

I won't discuss the importance of subtext with you again :P

5:22 PM

you don't know basic LGBTQA+ lingo

Well, that is perhaps not the worst thing, have a look at this first:

wtf

O.O

user218912

lol secret got banned?

user218912

:o

5:24 PM

no, he's still in here, but the post got nuked.

no he's suspended

@KazWolfe 30 min auto ban for validated flag.

@ACuriousMind huh. i thought they got removed from the sidebar too?

That was definitely inappropriate content

@KazWolfe No, suspended users can appear fully normal in the sidebar, they just can't chat

5:25 PM

@ACuriousMind Ah. TIL.

user218912

for me nothing is inappropriate as long as it's in blue.

@bl00 torture is usually red

user218912

that was out of context.

For anyone who is following the war in Syria/Aleppo:
-> A reasonable comment form an US Senator on the situation
https://www.youtube.com/watch?v=VfyDgDTu0Go

your pinned post is really relevant right now.

5:29 PM

Pentcho Valev appears to be male ...

@KazWolfe which one?

We seem to have a lot of flags. Are we going to get raided by shog?

user218912

I never flagged anything before.

user218912

am I cool or what

@ACuriousMind I note Valev's comment has been deleted so my custom flag had the desired effect. What is the best way to flag up comments like that one? There is no downvoting on comments and I'm loath to leave that sort of thing as it is.

@JohnRennie I think a flag was appropriate, but a simple "not constructive" would've done the job

5:36 PM

@ACuriousMind Noted. Can we have a red hot knitting needle flag for this type of thing?

Careful...

:: John teeters on the edge ::

Spreading misinformation in comments is not constructive, and according to the current vote tally at this meta question it seems fine to me to just go ahead and delete such comments.

@JohnRennie I'm afraid you'll have to write a client-side script to rename the flag option for that ;)

Actually I might get demoted back to a non-room owner now we have two extra mods. Then I can say what I like :-)

5:55 PM

@JohnRennie then it'll be like old times

Except for Chris :(

6:20 PM

@ACuriousMind For the life of me I cannot make sense of the join of two spaces

user image

like what even is this

@0celo7 It generalizes the notions of cone and suspension. I haven't seen much use for it

@ACuriousMind I can't figure out what's going on in that picture

The left face of the cube is collapsed to be just $X$, and the right side is collapsed to be just $Y$.

oh I'm stupid

for some reason I was expecting $X$ to be vertical

@ACuriousMind Hatcher defines simplices in terms of iterated joints of points

@ACuriousMind So I met the Elven Lord's son

@ACuriousMind the apple fell sort of far, but sort of close to the tree?

It's hard to describe

lol, what does that even mean?

6:33 PM

Well they're both full professors at my school

But the father comes to school every day in a 3 piece suit, the son looks homeless

@ACuriousMind clear?

Somewhat

@ACuriousMind one is an analyst, the other an algebraist

Brandon Enright

6:56 PM

Boy chat sure got more colorful in the ~year that I was away.

7:18 PM

@BrandonEnright meaning?

@bl00 yes it's great

@0celo7 did u finish ur lab report

Yes but I left it on my table

what was it on? I have to do the write-up for that dumb standing waves lab last week qq @0celo7

It was on calorimeter with a resistor

oh i thought you already did the write-up for that?

7:28 PM

On Monday

My lab is on Tuesday

This week I have a Helmholtz coil

The report will be 10+ pages

The TA knows me now, I get 100s

We talk about QM homework

what class is this for? I thought you were done with all the physics stuff @0celo7

also does your prof. require you to use a minimum amount of references/sources? If so, what website do you usually use?

No references

The textbook and lab manual are very complete

so are mine but for some reason this guy wants us to use like 2 other sources..

@Obliv what?

I have to take physics all 4 years

@ACuriousMind Did you learn about Hilbert spaces in FA?

Yes, although we didn't do the operator theory I hoped we would do

7:38 PM

you were able to take advanced math classes but not physics? Like, calorimeter & resistor setups to determine specific heats of objects seems pretty basic to me. In fact, that's what we did a few weeks ago.

user218912

@Obliv no i changed it.

what was it

user218912

it used to be the zankyou cd cover.

why change it? not blue enough?

user218912

guys guess what

7:39 PM

@Obliv I think physics is extremely nontrivial and difficult

My EM class is many times harder than QM

user218912

I got 100% on my first QFT problem set. (which was graded 15 mins ago)

user218912

thanks @ACuriousMind @0celo7 @DanielSank for the help

good job dude.

user218912

and I did 50% of it without any help just sayin, so I'm not that bad.

@Obliv thanks

7:42 PM

@0celo7 but isn't it a basic treatment of EM? Like, my class covered maxwell's eq. & EM waves without divergence & curl operators. It assumes we don't know calc 3

@bl00 I've been helping you for over a year

@Obliv same

pisses me off because I've already covered basic EM in high school with algebra. Why are we covering it again without formal math ><

Right now we are doing Kirchoff's laws

user218912

@0celo7 what's your point?

I went to a poor high school, we didn't have EM

user218912

7:43 PM

I said thanks and I'm buying you lee for your birthday.

@0celo7 so you're taking an EM class now? why did u do a specific heat lab then

Specific heat in EM

Connect the heat in the calorimeter to the current/voltage

user218912

yes they do specific heat in EM.

user218912

like joule heating.

Oh not us then. I took EM over the summer and I'm taking waves/thermo/QM/SR this semester even though it only covers 1% of each topic with baby maths

user218912

7:45 PM

@Obliv read tong's notes.

user218912

I'm reading them everyday.

@bl00 you mean his calc 3 ones? I'm doing my write-up right now but I will once I'm done.

user218912

what do you mean calc 3?

user218912

they're physics notes.

why are you bothering me with that stuff I haven't done calc 3 yet

user218912

7:46 PM

you don't need all of calc 3 to start...

user218912

just know what a partial derivative is, and the chain rule for multivariable calc.

user218912

and also know what a surface integral and volume integral is.

user218912

and you're good.

@bl00 can you prove the chain rule?

user218912

@0celo7 I know the chain rule, idk if I can prove it.

user218912

7:47 PM

I didn't try.

user218912

what I can do is look up a proof of the chain rule and then learn the proof from there.

user218912

idk if that counts.

You should have stayed in analysis

user218912

I don't have time for that right now. I'm learning so much physics.

user218912

I will take graduate real analysis in my 3rd year instead.

user218912

7:49 PM

they start from the beginning.

@ACuriousMind Holy crap Banach-Tarski is weaker than AoC

user218912

and by that time I'll have mathematical maturity.

I need to reject the ultrafilter lemma @ACuriousMind

$f: \mathbb{R}^n \to \mathbb{R}$ then $\frac{\partial f}{\partial x_a} = \frac{\partial f}{\partial x_1}\frac{\partial x_1}{\partial a} + \frac{\partial f}{\partial x_2}\frac{\partial x_2}{\partial a} + ... +\frac{\partial f}{\partial x_n}\frac{\partial x_n}{\partial a}$ is that the general chain rule @0celo7

what is that?

@Obliv No

It's $D(f\circ g)=Df\circ Dg$ for Frechet derivatives

user218912

7:51 PM

@Obliv that's for multivariable functions

inb4 ACM comes up with Gateaux derivatives

@bl00 what else can it be for?

user218912

there are multivalued and vector functions too. @Obliv

user218912

they have similar chain rules.

I thought it'd be the same. Also aren't multi-valued & vector functions the same thing? @bl00

7:53 PM

Technically, "multi-valued" functions are not functions, and I suspect that's not what bl00 actually meant.

user218912

yes ofc

user218912

xD

what is a multi-valued function o.o

maps to multiple codomains probably

user218912

$\mathbb R^m \to \mathbb R^n$

user218912

7:54 PM

multivalued

what

user218912

I swear that's what the book I first learned vector calc from called it.

lol

just ban him

user218912

:(

nvm ban me too

7:55 PM

A multi-valued function is a "function" that has more than one value, e.g. the square root without choosing one of the two possibilities, i.e. "$4\mapsto\{2,-2\}$"

user218912

I know that.

user218912

but the book also called what I said multivalued.

user218912

well it was lecture notes not a book.

With things like the complex logarithm it becomes interesting because the "branches" of these functions are closely related to covers (in the geometric/topological sense)

@bl00 That's certainly non-standard, it's just vector-valued.

then I dont' think the chain rule would be any different for multi valued function

user218912

7:57 PM

okay TIL

user218912

@Obliv don't call it that!

what would I call it then?

user218912

vector valued.

user218912

I was wrong.

NO he said that what you wrote $\mathbb{R}^m \to \mathbb{R}^n$ was non standard vector function... right?

and a multi-valued function is different

user218912

7:59 PM

oh you're referring to the CORRECT use of multivalued?

yes

user218912

sorry :/

I meant that it is non-standard to call that multivalued.

user218912

omg so much confusion.

screw this I'm going to continue with my write-up

8:07 PM

@Obliv I'll clear things up.

Let $E,F,G$ be Banach spaces. Let $U\subset E$ and $V\subset F$ be open. Let $f:U\to F$ and $g:V\to G$. If $f(U)\subset V$, $f$ is differentiable at $x\in U$, $g$ is differentiable at $y=f(x)$, then $D(g\circ f)(x)=Dg(y)\circ Df(x)$.

Note that $D(g\circ f)(x)\in L(E,G)$.

Or $L(U,G)$, whatever.

@Obliv For $\Bbb R^n$ vector valued functions, those are just matrices

and you get partial derivatives

so it's

uh, something

there's too many indices to remember

that beginning part was probably unnecessary but I understand. I don't get why $f(U) \subset V$ has to be true.

beginning part?

@Obliv you need $f$ to map into the domain of $g$

else $Dg(y)$ makes no sense

$Df$ is the Jacobian btw

which you've probably learned about

why not just say $x \in E$ is differentiable if $f(x) \in F$

what?

oh I see.

what's $L(E,G)$ @0celo7

8:22 PM

continuous linear maps between the spaces

$\circ$ is function composition?

yes

so $Df(x)$ is a linear map

$Dg(y)$ is a linear map

@ACuriousMind do you know a discontinuous linear map?

8:39 PM

user image

Why would $\sqrt{1 + (\frac{da}{db})^2} \approx 1 + \frac{1}{2}(\frac{da}{db})^2$

@Slereah What?

@Obliv taylor series

didn't you take calc 2?

don't you know your own philosophers

@slereah that's supposed to be Confucius right?

yes

8:49 PM

@0celo7 isn't it like $f(a) \approx \frac{f'(a)}{2!}$ then? I forgot lol

jesus

go back to school

aw man

@0celo7 hold on that's not a taylor series

if it were, it'd be evaluated at some $a$

It is a Taylor series

you're probably looking at physics

physics is always wrong

im using wolfram alpha

$\sqrt{1+x^2}\sim 1+\frac{1}{2}x^2$ is correct

8:56 PM

oh maybe

just plot them

hmm, is that correct :P

yes it is

I had a typo

for $x$ close to $0$ it's a good approximation.

well $da/db$ is very small so maybe that's why.

THANKS BRO @0celo7

@Obliv ok it's not really a Taylor series

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