By feeding it the coordinate vector $\partial/\partial x$ on the $X$ component

@BalarkaSen Tale of Tales?

@0celo7 index notation is just busywork

@Semiclassical it is $\nabla_1$

@TerryE Indeed, Tale of Tales.

@0celo7 yeah, that's what I figured.

Balarka is just showing off.

Like I said earlier

the only thing worse than having to use indices is not being able to use them

Nah

I genuinely find it impossible to read and understand literally anything in indices

So I am not going to use it. I haven't needed it, either, so far in my life.

#noregrets

depends on what you're doing, to be fair

What I found funny was that there's one place in physics where we avoid using index notation

and that's in quantum mechanics.

@BalarkaSen avoid any kind of geometric analysis

@0celo7 I would

I have 0 wish to do geometric analysis

I mean, we'll use it for stuff like $[L_i,L_j]=i\epsilon_{ijk}L_k$

(there's probably an hbar in there)

@Semiclassical hbar = 1

there we go

@BalarkaSen Geometrization of 3-folds is geometric analysis...

@0celo7 Doesn't mean I have to learn it!

but we write stuff like $\sum_n |n\rangle \langle n |=\mathbf{1}$

and we always include the sum in there

@Semiclassical In this case, n isn't an index

uh

(also, convention)

not sure what you mean by that.

I guess maybe the point is that bra-ket notation doesn't really lend itself to index notation as such.

in the sense of $x_n$ or $x^n$

well, sure

it's a summation index

I think if you wanted to use index notation you'd instead understand that as $|n\rangle = \psi^n$ and $\langle n | =\psi_n$

(or maybe the other way around? i can never remember the convention)

@Semiclassical people use indices for QFT. Spacetime and Hilbert indices

and then that'd be $\psi_n \psi^n = \mathbf{1}$

The worst kind of mathematics is to fiddle with notational conventions

Penrose's index philosophy is so powerful that it makes sense on any Hilbert space

but that doesn't seem right either, since it's not clear to me how one distinguishes between the inner and outer products of $\psi_n,\psi^n$

I'm sure I'm forgetting something

Outer product should be $\psi_n \psi^m$, actually

and then the inner product is just $\psi_n \psi^n$

so I guess it works.

@Semiclassical At this point, convention starts to get in the way... I've no idea how valid or not this is...

well, I think the correct statement is that $\psi_n\psi^m = \delta_n^m$ and $\psi_n \psi^n = 1$... that doesn't seem right

Are you trying to write orthonormality in index notation or what

pretty much

and I'm sure i'm making it too complicated

Oh, about the red sky I mentioned earlier: bbc.co.uk/news/uk-england-41635906

@dmckee In my absence these past weeks I apparently missed that you have since become a father! Congratulations!!

hmm. $\psi_n \psi^m = \delta_n^m\implies \psi_n \psi^n = \sum_m \delta_n^m = 1$

so maybe that does work

@DanielSank Go away

I sorta doubt I'll start using it, though

You left me

@BernardoMeurer wtf

@BernardoMeurer And you want to fix that by pushing me away.

YOU NEVER LOVED ME

I WANT YOU TO WANT ME

I ALWAYS LOVED YOU

<3

save it for the therapist, you two

<3

@Semiclassical He's upset because I didn't have dinner with him last night.

Even though I read his essay and offered corrections.

He's too needy.

@Semiclassical He hasn't seen me in A WHOLE WEEK

That is such a good song.

And the other day he didn't have dinner with me because of WORK

I'd link "I want you to want me" but that doesn't have quite the right tone for this

How is WORK more important than ME

there we go

lmao

i like that

@DanielSank I haven't complained about my love life to you in waaaay too long

Now it's all building up

And if I don't go on a rant soon I will asplode

gonna go full Wiseau on us

There's actually a movie about the making of The Room coming out

should open in the US in December

fucking hell

@BernardoMeurer Thanks. The baby is a bit over three months old now, and thriving.

can somebody tell this person that this is not OK?

@EmilioPisanty Lol, now I'm going to bother you on Facebook too :P

jfc

@BernardoMeurer oh, hell no

@dmckee That is great to hear! Is it a o boy or a girl?

@BernardoMeurer A little girl. Which means I've officially had a spinectomy and am no longer allowed to say "no".

if I were feeling polite I'd tell them that I don't accept unsolicited problems over social media and indicate that if they do so again I'll block them

@dmckee you do know how to write starbait =P

if I weren't feeling polite, I'd probably just block them without a word---except, perhaps, "f*** off"

@Semiclassical nope. straight block and marked as spam.

i didn't say you were obliged to be polite :P

at that point they've lost any right to courtesy

@dmckee That is absolutely lovely! Since you can't say no anymore will you get me this for christmas?

@EmilioPisanty Check your facebook messages :P

@BernardoMeurer you could've asked for anything and you asked for an algorithms book?

here, try this

@dmckee that's fantastic! Also, since you can't say no anymore, will you get me this for Christmas?

@EmilioPisanty I need the book! And I already have that LEGO set!

@BernardoMeurer 730 pages. You'd really go and read that?!

I am looking forward to the time when she's big enough for lego.

@secret hmm, re: my integral from earlier, check out this answer of robjohn: math.stackexchange.com/a/63322/137524

@Keepthesemind Yeah? I like algorithms!

Implementing them in C is fun af

@BernardoMeurer But reading about them?!

@dmckee you should snag one of the Saturn V sets and keep it until she's ready to become a lego space nut

Specially when I have @dmckee and @JohnRennie to hold my hand as I walk through the fire

@dmckee She's going to be a C master

@EmilioPisanty my dad managed to snag one of those this year

we took our time building it

it's pretty cool :)

I was too slow =(

yeah, my dad was on the ball for that

Walmart accidentally put it up for sale online early, and he managed to snatch one up before they took it down

So I went to an interview at Manchester Uni last week - and now they've sent me an email saying "Thank you for your application to The University of Manchester, which has been forwarded to the Admissions Officer for your chosen course for consideration. Depending on the course, you may be invited to an open day or interview."

Not sure how I feel about this.

Oh okay then - they just offered me a place :)

Dunno yet - that's 2/5

Obviously the big cheese is Oxford but we'll see.

But it goes 1. Ox 2. Manch 3. Bris

@Blue 2 out of 5 I applied to

@Blue It would've been but it does Natural Sciences (Where's John...) and not straight physics whereas Oxford does straight phys.

Thanks :p

I was considering that but then I realised the modules I picked would be Phys A Phys B and physical chemistry

To much of a theme to not apply physics.

What's natural sciences?

@BernardoMeurer Hit me up in google chat.

@EmilioPisanty did you solve the problem?

If you read 'angular momentum about the vertical axis is constant' would you read that as 'angular momentum is preserved as you vary z' (where z is the vertical axis)

Suppose I have $$G = 1 - \exp \left( \int_0^\epsilon dx \ln g(x) \right)$$

How do I expand that for small $\epsilon$?

I think it's $-\epsilon \ln g(0)$.

not english native, so I don't know why about is used in such a way?

"Show that the angular momentum about the vertical axis is constant"

I didn't know the Dirac matrices can be spacetime dependent until the recent.

@Blue The ability to learn other things as well as the subject you applied for changes everything - if I went somewhere and didn't do physics, the last 5 years of my life would have been totally different

(I actually started my undergrad in CS)

@DanielSank I also think this, for whatever that's worth... Or not

Or $G\approx 1-e^{\epsilon \text{ln}g(\epsilon)}$

@DanielSank I no longer agree with this :P

@Blue Only NatSci at Cambridge contains at least as much physics as any other course I've ever heard it compared with

I did an MSc at Nottingham only to discover that I'd already done massive chunks of it

@CaptainBohemian very cool but not so obvious, e.g. physics.stackexchange.com/a/153849/25851 , mathoverflow.net/q/121620/38721 , physics.stackexchange.com/q/161744/25851

@Blue Well... Yeah...

@Blue You don't have to do all the subjects - just the ones you want to do (one maths module is compulsory though)

So, Physics+Chemistry+Biology is possible, as is Physics+CS+[insert something else of choice]

@Blue Exactly! :D

@bolbteppa these links seem to quite cater to my needs. I will read them to see if there is something I want to know. Thank you for your information.

but actually I read in some paper there is the spinor representation of diffeomorphism group.

@CaptainBohemian Kaku and GSW (mentioned in the links) set this up in context, still don't fully get it, I believe there are only infinite dimensional spinor reps not finite dimensional reps

probably the key is infinite dimensional finite dimensional, cause I read in another paper that there is no spinor representation for the diffeomorphism group, and I am so confused.

I think that's the distinction

@DanielSank I'm now of the opinion that it's $$G\approx 1-\text{exp}\left[\epsilon\left(\text{ln}g(\epsilon) - \text{ln}g(0)\right)\right]$$

Hmm... Please forgive the awful formatting

Does that mean if I revolve the vertical axis, then any paths in this rotation have momentum conserved?

Or does it mean that vertical paths conserve momentum

Whichever way I read that, it doesn't seem to be true, there are no generalized coordinates not appearing in the lagrangian

with respect to, I think.

@TerryE It means "measures around": "Angular momentum measured around the vertical axis".

Yep I am still confused, I am not native to english

OK... I'm going to actually try solving it instead of guessing: Taylor expand $\text{ln} g(x)$ about $x=0$ to get $\text{ln} g(x)\approx \text{ln} g(0)+x\frac{g'(0)}{g(0)}$

So revolving around the z axis, conserves momentum

?

integrating gives $\epsilon\text{ln}\,g(0)+\frac{\epsilon^2 g'(0)}{2g(0)}$

@Blue Sure, cross of the position and linear momentum. But I think they here refer to generalized momentum from the Lagrangian

@DanielSank Actual Answer (obtained by Taylor expanding - see above): $$G\approx 1-e^{\epsilon\, \text{ln}\,g(0)}$$

Okay, I guess it does mean the revolution thing, reading this different source: web.mit.edu/8.01t/www/materials/InClass/IC_Sol_W10D1-3.pdf

I am not an English native speaker, either, but I have got good feeling of guessing the meaning of English.

I guess even English native speakers don't know a lot of things about English if you ask them.

(I'm aware that this is often the point where the experienced prof. jumps in and tells me how ridiculously wrong that is, but anyway, I'm hoping that's more or less right)

so hungry, too hungry to think clearly now. need to go to hunt for food now.

$$\frac{1}{2}$$

@Blue AH. I interpreted the question as being about the particular language and not about the concept in general. Evidently that was mistaken.

@CaptainBohemian Oh, there are many things about English that I knew from growing up surrounded by examples but which I could neither articulate nor explain until I studied another language.

There is a huge difference between knowing from experience that "this is the way it is always done" and knowing what the structural reason for doing it that way is.

@yuggib half for my birthday :) i.gyazo.com/278bcf9edece4ef6297ad82933c500f9.jpg

@0celo7 :o that's like 500 bucks right there

@Icemybread they're not that expensive

they are in canadia

o

@Icemybread they're probably some of the greatest books of all time

come to America and buy them

@Blue see above

i can already buy them here but the amazon price for both brand new is around 500 with prime.

but i don't need them right now lol

I don't know how much they were (gift), but it's more like 300

the publisher has free shipping and no tax, so it's cheaper to get it from them

@Icemybread I still have your book btw

how's he doing

very good reference for inequalities

use it all the time

nice

@0celo7 Wait...your birthday is not today, is it?

@ACuriousMind Early gifts

and why?

birthday assassination? :o

@ACuriousMind wtf dude

secret messages?

@0celo7 Well, I didn't want to wish you happy birthday only to be told "no, it's not yet". Germans are superstituous about early birthday wishes :P

@0celo7 wtf @Icemybread, not me!

@ACuriousMind I asked for this gift so it wasn't a surprise

@ACuriousMind You know when my birthday is?

Did you use mod tools

you already said it multiple times in the chat. a simple search would find it. lol

@0celo7 No, just chat search ;)

@ACuriousMind but why would you think it wasn't today

because he didn't remember it being this early based on before?

@0celo7 Because the messages indicating it was your birthday were from 18th/19th October

@ACuriousMind But why did you think to look it up? Just making sure?

@0celo7 Well, I looked it up because you posted that birthday gift and I wanted to know whether to congratulate you!

lol

am I overthinking this?

Is that so suspicious?

why do you have a birthday?

@BernardoMeurer fortraaaaaaan

@0celo7 Probably, yes :) I have no hidden motives here, I promise.

holy shit

someone in my fortran class got the homework moved

he started the email with "Regards Sir"

@BernardoMeurer but still, fortraaaaaaaaaaan

guys i dunno what to eat

i'm not used to this living alone thing

dog

any ideas? I already made lunch earlier today

and i don't have any more ingredients atm

except bread

Well, put some ice on it, then ;P

i didn't even remember that i set my SE name to that

i don't have an ice cube tray :p

@0celo7 Reed-Simon: always a good decision

@0celo7 what do you normally eat?

idk

or @ACuriousMind too (other than frozen pizza)

I had teriyaki chicken tonight

leftover from yesterday

did you make it yourself?

yes

how long did it take?

@yuggib it's great

@3.5 5 hours

exactly

@3.5 I like to make curries

i started off making complicated foods like i had at home for the first week but it took like 5 hours out of my day for making it, cleaning and washing the dishes

dunno how my parents do it

@ACuriousMind curries?

without anything else?

or does curries mean curry mixed with some carb

@3.5 Chop a bunch of veggies, get some meat if you like, throw it all in a pan and add (curry) spices and whatever base for the sauce (I prefer coconut milk, but cream works, too) when they're done. Usually quick (< 1 hour) and delicious.

oh

good idea

what i have been doing so far is just making rice/pasta and then throwing in whatever vegetables i have on top in the last 5 minutes

that works

put some chicken in

then some kind of sauce

i have been avoiding raw meat just because i don't have room to process it separately

like cut it or whatever without getting other stuff contaminated

Can't you just cut it and then quickly wash whatever you used for it?

get a cutting board!

get many!

what kind of meat should I buy that requires the least processing?

also is it possible to just boil meat?

it would be easy to throw in some slices of chicken or whatever into boiling water.

dunno how it would taste

@3.5 Sure, but it'll taste different from fried meat and it's different parts - you wouldn't boil a steak :P

(unless you're a Bavarian)

can you boil chicken/beef breast or fillet?

@3.5 disgusting

because they don't have bones

@0celo7 why?

what if I add oil to the water

and salt

@3.5 The question is less whether you can boil them but whether the result will taste good

@ACuriousMind that's basically what i meant

ofc you can boil them but is it enjoyable?*

no

Typically, I'd only boil meat if I'm making something like a stew and it's meat I wouldn't wanna fry anyway

If you just boil it in water and salt it'll taste very...bland

@ACuriousMind then you're boiling it in broth

wait a minute!

that's it!!!

and that's completely different

I can just make stew/soup everyday

add in everything i want into the same pot

instead of processing everything separately

You can poach delicate meats (my better half poaches salmon fairly often), but it is a process to be approached with finesse and a good sense of timing: cook it too long and you produce chewy and tasteless pap.

@3.5 maybe

i will do that

brb groceries

Get it just right and it can result in flavorful and delicate forkfulls of goodness.

oh i see

i guess if you poach the meat and add everything in it will be stew

@dmckee Yeah, if you know what you're doing I'll grant it can be great; I find frying much easier though - just stop when stuff starts to burn ;)

and if you add lots of water it will be soup

right?

I think the safe way to go would be sous vide, but you wouldn't describe that as "boil".

@ACuriousMind ::chuckles:: Yep. My kind of cooking.

@CooperCape Congrats.

I just ate food in convenience store and now feel sleepy.