@Slereah do I shoot him?

will the world be messed up forever?

@Slereah I'M GONNA FAT MAN HIM UNLESS YOU SPEAK UP

@ChrisWhite Well, I haven't looked at any of them - what do you dislike so much?

@ChrisWhite There might be something to that. I've only seen the EM one but I found it to be relatively good.

@Slereah This is all your fault.

It's not amazing and indeed it does a relatively poor job at formal relativity, but it's a good stepping stone between Purcell and Jackson.

@Slereah Crap...

Yeah, that's what happens!

@Slereah My char is pretty good now

Doing 80-90 damage at level 20

about 80 stimpacks saved up

that is good

a few rockets and a few nukes

if you find the explosive shotgun hold onto it btw

it is the best

armor is like 80

I'm using a shotgun, .45 rifle and .308 sniper now

.44 mag for a backup

can I not craft an explosive shotgun?

also did you get the alien gun?

nope

Explosive shotgun is one of those random drops, I think

ah

@Slereah it's REALLY good

80 damage without mods

Hey, how did the midterm go, @NeuroFuzzy?

Pretty good

@ACuriousMind oh hey thanks for asking! Pretty well, hopefully 100%

@Slereah how is the male voice actor for the main char?

the gril is really good

Is the girl married to the lady too

I like having a voiced protagonist

@Slereah what

Or do you have a husband

@Slereah yes

o

@NeuroFuzzy Nice!

Game of the Year confirmed

I love that that's a dialog option :D

then again

fuck him

stealing mah baby

the plot is actually good

unless they ruin it

I like how MIT is the evil organization in the game

@Slereah who is the best follower?

I think Strong is good, but I'm using Belethor_Voice

it makes sense story wise to use him

maybe Fallout 4 should be in Germany

purified water is "good beer"

and crappy beer is irradiated

@Slereah Riddle me this: why does eating mutant hound flesh cure radiation poisoning?

Does it?

Also define "best"

I like Valentine cuz he's a cool dude

@Slereah his name is Belethor

Bethesda messed up his naming in the programming

I'm sure it will get patched

how do you get followers to equip stuff

Belethor insists on using his crappy pistol

Also I would like to find a companion that is cool with me stealing shit

Strong doesn't like when you pick locks

DON'T FIDDLE, SMASH

^ subtle Skyrim propaganda

I tend to pick companions based on the quests I'm gonna do

Valentines doesn't like Brotherhood quests, etc

@Slereah really

wait, how many companions do you have?

I have dogmeat (can't find him), the reporter chick, Belethor, Strong

the Minuteman

can one recruit the mayor of goodneighbor?

he seems like a total BAMF

You can yes

how

holy god how

As far as I can tell, you have to follow the quests of the local crime lady

Bobbi no nose

@Slereah WHAT

she has quests

is she the shopkeeper?

or some other broad

Some other broad

The ghoul lady

ok

With a bad wig and no nose

will pause main quest for this

Is there a term like 'Dual' but for sets of three?

@ManishEarth triality

not kidding

thanks

I was calling them threeuals

e.g. the vector and two spinors reps of $\mathrm{Spin}(8)$ are related by triality

Came up in a programming discussion, realized a problem was similar to a nother problem with duals

but with three

well, I gave you the analog for "duality"

dunno what "dual" would be...

Are you really looking for the analog to "dual" and not "pair" or "binary"?

@ACuriousMind "dual" as used in a CS type theory sense, yes

Ah, okay.

@ACuriousMind programmer confirmed

@0celo7 I don't actually know the technical meaning in this case, but the response convinced me he was actually looking for "dual" :P

@ACuriousMind riddle me this pls

if I have an atwood machine

do the tensions do work on the pulley?

they have to

so how do I calculate the work done

I hate questions about tension :P

@ACuriousMind I just can't figure out what the expression for their work is

@0celo7 why would they?

maybe prof @dmckee can lend a didactic hand

oh

@ManishEarth something has to move it

if the pulley has a mass, yes

if the pulley has a mass

use work = torque * deltatheta

@ManishEarth yeah, what's $\Delta \theta$

that seems really complicated

the amount the pulley spins

hmm, isn't $R\Delta\theta$ just the amount the block travels

and $\tau = TR$

yes

so $W=\tau\Delta\theta=TR$

well that's trivial!

eww and then I need el newtino to get $T$

@0celo7 except!

the pulley does equal work on the string on the other side!

so

no work done

wait

seriously

> something has to move it

then what spins the thing

nothing has to move it.

It will spin on its own

once you initiate it

why does it do equal work

the tensions are not equal

oh right

sorry

no

wait

@0celo7 sorry I was assuming steady state

my bad

@0celo7 work is done on the pulley, right

ignore me it's the morning and I have coursework on the mind

great but then I end up with accelerations

in my work equation

@0celo7 One important facet here is applying the work-energy theorem to the pulley. If it has a different amount of (rotational) kinetic energy at the end of the interaction than it had before some net work was done to the pulley.

As ManishEarth notes massless pulleys never have to worry about that.

@dmckee I figured it out

was not hard

just my usual aversion to tedium

Disliking tedium is a good thing because it drives you to learn better ways of doing stuff. But sometimes you just have to put up with a little tedium to get ahead.

what's a good place to read about AQFT

wald

Obviously not

Haag maybe?

@dmckee the tedium of rote memorization is practically the only way to initially introduce "stuff," no?

Though it can be minimized, I don't believe it can be completely eliminated.

Methods and notation, yes. Some concepts have to be stated and giving practice manipulating them at the start, too. But as much as possible should be "discovered" in the context of things already known.

That way you get a builting concept web.

Hi, everybody!

Hi pal :-)

@skullpetrol 'sup?

@dmckee Balancing time spent automating tedious tasks against actually doing science is the hardest part of my job.

Chatting with dmckee about learning "thinking skills"

@skullpetrol I want that. How to learn?

I am Sofia. I left messages in the room opened for a talk of Singh and me.

:O

You're back?!?

Welcome @Sofia

:D

chat.stackexchange.com/rooms/31732/discussion-with-sofia

or not :(

Anyone recognize this:

$\sum_{l=0}^{N-m} a^l \frac{N!}{l! (N-m-l)!}$?

@skullpetrol Wat? Naaaaaaah :P

@DanielSank There is a huge online database of this type of stuff, I think.

@DanielSank And I think it may be beneficial to rewrite it in terms of binomial coefficients.

@DanielSank That's multicombinatiorial stuff, I think?

Hey, Im wondering if someone could help me explain how moment of intertia and angluar frequency applies to a rocking motion of a suitcase?

@Qmechanic, @ACuriousMind Wondering if you guys could help me? Is it a general result that if a symplectic 2-form $\omega$ is conserved for a family of diffeomorphisms generated by a Hamiltonian vector field, then the $n$-th wedge product of that form is also conserved? e.g $\omega ^n=\omega\wedge\dots\wedge \omega$? I can prove Arnold's theorem for $n=1$ but wondering if $n>1$ is directly related or not?

Try proving it by recursion maybe?

@Slereah Induction, not recursion.

But yes, @AngusTheMan, induction seems the way to go - you proved it for $n=1$, now show that if $\omega^{n-1}$ is conserved, then $\omega^n$ is, too. (Disclaimer: Haven't actually worked out if that works)

@ACuriousMind for french people, it is called recursion ;-)

@yuggib Really? That's confusing.

@ACuriousMind Thanks, I will give it a go :)

@ACuriousMind Well, at least in Bourbaki it is called "principe de récurrence"

You are right, the Wikipedia article also indicates that

the problem is that in english, a distinction is made between induction and recursion

even if they are closely related

@AngusTheMan : At the level of vector fields, it follows because of the Leibniz rule for Lie derivatives on exterior forms wrt the wedge product. There is a similar reason for flows. Btw, this answer of mine is somewhat related.

Hey, Im wondering if someone could help me explain how moment of intertia and angluar frequency applies to a rocking motion of a suitcase?

@Qmechanic Thank you for the hint and link! :)

@AngusTheMan Conserved in what way?

If you're talking about the pullback of the flow, just use that pullbacks distribute over wedges.

@0celo7 $\mathcal L_{X_{H}}\omega =\iota_{X_{H}}d\omega +d(\iota_{X_{H}}\omega )=\iota_{X_{H}}0+d(dH)=0$

Yeah. Use the flow definition of the Lie derivative.

:D

Then because each pulled back symplectic form doesn't depend on t, the whole thing does not depend on t.

So the time derivative kills it.

@0celo7 thanks :)

have you seen this? @0celo7

what are you thinking about? :D

@skillpatrol Huh?

@AngusTheMan Np, I did this exercise a couple weeks ago :D

@0celo7 the link

@AngusTheMan Well

You do know that $g^*\omega=\omega$, right?

This is easily verified using $\mathcal{L}_{X_H}=\mathrm{d}/\mathrm{d}t \,g^*$

Anyone here using Mendeley or a similar software?

does endnote count?

@AngusTheMan cf. the second chapter of Hawking-Ellis for a proof that $g^*\omega=\omega$ iff $\mathcal{L}_{X_H}\omega=0$

@0celo7 Thanks for your help, yes I can see that now :) I will look into that book too!

@Secret Can you tl;dr what Endnote does?

@Huy stop doing chemistry

@Huy never stop doing chemistry :)

@0celo7: Doing some functional analysis atm

you should too

@Huy no

I really suck at it

me too

trying to figure out the proof I just told @AngusTheMan to loop up lol

Hawking doing magical things

I'm basically looking for a much more lightweight tool just to organize papers, lecture notes, books etc. and to be able to read them cross-platform

do you know anything like that?

other than organizing PDFs into folders on dropbox

Cross-platform is the difficult thing right there

needs to be at least for OSX and Windows

bonus points for iOS

I've been using Mendeley so far but it sometimes is laggy and even crashes and the worst thing is that hyperrefs don't work for most of my PDFs for some unknown reason, even though it highlights the links

@ACuriousMind On the bottom of page 43 in HE, how does he switch to an s derivative? And how does he insert the flow?

@ACuriousMind At first I thought he inserted it at s=0 (identity operator), but really he's inserting it, taking the derivative and then setting s=0.

@0celo7 Can't you just use the chain rule on the expression with $s$ to see they are the same?

@ACuriousMind Huh?

I know that's what I did when I read the book the first time, but I have no clue what that does this time.

@ACuriousMind Yeah, I don't see how one uses the chain rule at all.

:(

@ACuriousMind I don't know how to use the chain rule

Haag's book has literally a ref that is "Private conversation"

Haha

@0celo7: Sorry, after trying a bit I have decided it is in fact far more trivial than the chain rule :D

Taking the derivative of $\phi_{t}$ at $t=t'$ is the same as taking the derivative of $\phi_{t+s}$ w.r.t. $s$ at $s=0$.

@ACuriousMind Yes, I know that's what the answer is. But I have no clue why.

The set of bounded linear operators is in fraktur

for shame

@0celo7 Huh? That's general, and if you want, you can get it indeed by chain rule: $\mathrm{d}_s\rvert_{s=0} f(t+s) = \mathrm{d}_s\vert_{s=0} (f\circ(t+s))$

Wtf

Me a year ago knew this

And we've used that in my classes

😥

Hence my "Huh?". I spent a few minutes to figure out that $\phi_t\circ\phi_s = \phi_{s+t}$ was the reason the proof in HE works, though :D

I knew that.

I have read this book before, and I remember using that to understand it...

@ACuriousMind is it really

@ACuriousMind I'll choose to believe you

better than being confused

(before you hurt yourself, I get it)

@ACuriousMind Hmm, why does he use $\phi_*$ here? Typo?

@0celo7 What do you think there should be? If you want to know how something transforms, you push it forward.

...wait, can't one write down the lie derivative using $\phi_*$ or $\phi^*$?

@ACuriousMind but it's the pullback in other books

@0celo7 The pullback is $\phi^*$. And you have to pay attention to the signs and the points at which stuff is evaluated, you can write the Lie derivative with both the pushforward and the pullback.

and in any case $\phi^*=(\phi_*)^{-1}$ for $\phi$ a diff

Essentially, that here we have the pushforward and not the pullback is the reason that minus appears there

oh god

chat tex is broke

Also, you broke ChatJax

too many stars

Use \ast, not *

fixed it

@ACuriousMind yeah

confirming my sanity here

@ACuriousMind yes

5 people think I'm turning into duffield

my math skills certainly are degrading

::crosses:: @ACuriousMind why is the cov. deriv. of the volume element 0

;_;

I think I have a PSE answer on this somewhere, but I can't find it

Wait a moment...the covariant derivative raises the rank of the form by one, doesn't it?

on page 48, Hawking says i.gyazo.com/4e3cd9d605d7fb5924c626506b15073f.png

@ACuriousMind it does not necessarily antisym the resulting form

we're talking riem geo, not bundle geo

...the volume element is not antisymmetric? oO

@ACuriousMind ofc it is

Ah, damn Riemannian geometry :D

but antisym 4-form + other random index does not = antisym 5-form

Christoffel relations are...

uh

Well, then I don't know

I'm crap at geometry that's not forms :P

And if I hate one thing then it's Christoffels

@ACuriousMind Straumann does it directly using parallel transport

Still haven't read him because I'm a lazy fuck

but he's a good reference for GR geometry

you'd skip section three (basic geometry) anyway

you'd probably read the sections on hypersurfaces and twisted products

or not

dunno how much random Lorentz geometry you know

Gee I hope this doesn't have too much topology

you just hurt ACM

"We will need four standard topologies on the set B(H) of bounded linear operators on H"

woops

Haha

Let's see... weak, weak*, strong, standard or something like that?

weak*

that's total BS

@0celo7 it's weak but on the dual :P

@ACuriousMind why not co-weak

I...actually like that better :D

weak, ultraweak, strong and uniform

ultraweak

now that's BS

"1.5 Fact. If S is a bounded, convex subset of B(H), then the weak, ultraweak, and norm closures of S are the same"

Ahh, weak* is a topology on the space, not on the operators

He has no theorems

Only FACTS

lol

I like that, too

haha

This is not a fun introduction

It could use more physics

@ACuriousMind damn do Carmo

"take any inner product on the Lie algebra"

is there a canonical one?

@Slereah Wat are you reading?

@ACuriousMind C* algebras algebraic QFT

princeton.edu/~hhalvors/aqft.pdf

@0celo7 Negative of the Killing form if the algebra is compact

@ACuriousMind yes...I seem to recall Jost saying that

do Carmo just skims the surface

(Note that "compact" here means that its Lie group would be compact, the algebra itself is never compact in the topological sense)

Freire told me there's a whole book on the diff geo of Lie groups that I should read

but I don't want to

actually we have a class that's on the geometry of lie groups

@Slereah "Prologomena" :D

@ACuriousMind pedant

Classically eduacted, that one

@0celo7 It's Greek for "what is said before".

And it's the title of the introduction to the thingy Slereah is reading

@ACuriousMind why not just "prologue"

@0celo7 That is the proper English word that derives from it, yes.

@ACuriousMind he's just showing off then

Yes, it's pretentious

ah

exercise 7 is what you said

does $G$ have to be connected as well as compact?

That question does not make sense.

why