The h Bar

Balarka Sen

18:00

Technically energy level is the energy of the electron (according to Bohr's model anyway) needed to confine it to a specific shell, I guess.

But they come quantized, so you can "identify" it with the orbits.

ACuriousMind

I would take "energy level" to mean the actual energy eigenstate/oribtal, not merely the value of the energy eigenvalue.

Anonymous

@BalarkaSen It could also mean "vibrational" or "rotational" energy levels in molecules unless you clearly mention "principal energy level".

Abcd

@BalarkaSen Bohr's model is discarded. I want explanation in terms of the Wave Mechanical Model

0celouvskyopoulo7

@Abcd Solve $(-\frac{1}{2m}\Delta -\frac{eZ}{r})\psi=E_{nlm}\psi$

Emilio Pisanty

@Mostafa yeah, I saw it

I think you're overthinking it

Abcd

18:02

@ACuriousMind 'Why so many contradictions?

@0celouvskyopoulo7 I can't.

Balarka Sen

@Abcd If you don't understand the answers to the basic terminology questions you are asking, good luck with that.

ACuriousMind

@Abcd Where is there a contradiction?

Emilio Pisanty

"light propagation direction" only makes sense in the paraxial regime, so you can just assume that you're there

Balarka Sen

Bohr's model is the simplest model in which you'd want to understand the answers to the questions you are asking.

ACuriousMind

5 mins ago, by ACuriousMind

@Abcd The orbitals (not orbits!) are just the energy levels. Every orbital/energy level has a specific value of the principal quantum number, and a "shell" is the set of all levels with the same principal quantum number.

0celouvskyopoulo7

18:03

Imprecise terminology does not mean a contradiction

It means absence of pedantry

ACuriousMind

My answer answers your question fully and does not contain a contradiction - where do you think there is a problem?

Emilio Pisanty

then if there's no OAM to begin with in the source's frame there's no OAM in inertial frames

Abcd

@ACuriousMind Does this apply to the new model of the atom as well?

Emilio Pisanty

wavefronts are just planes orthogonal to the rotation axis

ACuriousMind

@Abcd what "new model"?

Emilio Pisanty

18:04

I'm not sure what happens with a corkscrew beam, though

ACuriousMind

I'm not talking about the Bohr model, if you think that.

Emilio Pisanty

presumably nothing

Abcd

@ACuriousMind Wave mechanical model instead of Bohr's model with circular orbits

0celouvskyopoulo7

@BalarkaSen Here's a pedantic question. How would I write a vector field along a curve in the $f:X\to Y$ notation?

Emilio Pisanty

or maybe not

ACuriousMind

18:04

@Abcd That one hasn't been "new" for quite a long time, and yes, what I said holds for that model.

Emilio Pisanty

actually, no, it probably does change

0celouvskyopoulo7

It's a map $\gamma(t)\mapsto T_{\gamma(t)}M$...but not a map into $TM$

Abcd

@ACuriousMind I thought orbitals were s,p,d,f... not 1(K),2(L),3....

Cryolune

lol this conversation is confusing to follow.

Emilio Pisanty

if the light has OAM then that component will get red- or blue-shifted

same as circularly polarized light

0celouvskyopoulo7

18:05

The value of the map is not (point,vector), it is just (vector). But the tangent space changes

Emilio Pisanty

but I'm not sure what that means for the angular momentum content

ACuriousMind

@Abcd I'm sorry, but I don't understand what you're trying to say.

Abcd

@ACuriousMind Alright. How do you denote an orbital? Please give me an example.

@BalarkaSen That literally scared me.

ACuriousMind

You usually denote them by their principal quantum number and the angular momentum (which historically has s,p,d,f corresponding to values of 0,1,2,3), so e.g. the orbital with the lowest energy would be denoted '1s'.

Balarka Sen

@Abcd s, p, d, f etc are subshells of 1(K), 2(L), 3(M), ... corresponding to the azimuthal quantum numbers. We are talking about the principal quantum numbers, how does that apply?

@0celouvskyopoulo7 Um, sure it's a map to $TM$? $X : [0, 1] \to TM$ given by $X(t) := X(\gamma(t))$?

0celouvskyopoulo7

18:10

@BalarkaSen a point in $TM$ is an ordered pair $(p,v)$, $v\in T_pM$

Balarka Sen

Fine, $X(t) := (\gamma(t), X(\gamma(t))$ you pedant

0celouvskyopoulo7

But I only want the $X(\gamma(t))$

Balarka Sen

I don't get it. What is that you are looking for?

I described a vector field over $\gamma$ as a path in $TM$. Is that not what you are asking for?

0celouvskyopoulo7

Not quite

the pedantry might cause a singularity

I have a path $W$ in $TM$

This projects to a path $\gamma$ in $M$

But now there's a vector field along $\gamma$.

With 100% pedantry, I don't think it's quite right to say that vector field is $W$.

Balarka Sen

jesus man. hm.

0celouvskyopoulo7

18:14

I bet one has to talk about the pullback bundle

Anyway, it's not important.

Balarka Sen

Well, I can say that if you want. A vector field along $\gamma$ is a section of $TM$ pulled back to $\gamma([0, 1]) \subset M$.

0celouvskyopoulo7

That's probably better.

Oh, that reminds me

Did you understand the comment in do Carmo about angles around corners when he defined a parametrized surface?

Abcd

Sorry. Power cut.

@ACuriousMind So 2p and 2d have same energy?

@ACuriousMind Are energy levels 3 dimensional?

Balarka Sen

@0celo I don't have doCarmo with me. Do you have a snapshot?

0celouvskyopoulo7

@BalarkaSen Not on this operating system, no.

Balarka Sen

18:18

I'll check it out later

0celouvskyopoulo7

thanks

Anonymous

@Abcd There's nothing like 2d orbital....

0celouvskyopoulo7

I always thought it was a strange comment because I always assumed I was working away from the boundary. I think one can do that

The variations are supposed to be small, after all

Anonymous

You have 1s; 2s,2p; 3s,3p,3d; ....so on @Abcd

Anonymous

I think the second paragraph of this Wiki article answers your question:

Anonymous

18:20

Energy level

A quantum mechanical system or particle that is bound—that is, confined spatially—can only take on certain discrete values of energy. This contrasts with classical particles, which can have any energy. These discrete values are called energy levels. The term is commonly used for the energy levels of electrons in atoms, ions, or molecules, which are bound by the electric field of the nucleus, but can also refer to energy levels of nuclei or vibrational or rotational energy levels in molecules. The energy spectrum of a system with such discrete energy levels is said to be quantized. In chemistry...

Slereah

Jesus

The internet is bad tonighty

0celouvskyopoulo7

@Slereah I just got GitHub for PC, why aren't my respositories showing up?

They seem to show up on github.com

Slereah

Did you add the repository?

0celouvskyopoulo7

I guess I have to add it manually

Yeah I just did

Abcd

Is something wrong with the SE chat today?Any bugs? i am unable to send messages properly...

Slereah

18:25

there's only losers on it

Abcd

@Blue Sorry, my bad

0celouvskyopoulo7

Windows
Platform Version Type Size How to install
XP/Vista/7/8/10 2.12.4 Installer 32.4 MB download and double click on the installer exe
XP/Vista/7/8/10 2.12.4 Portable (.zip) 42.5 MB download and unzip the zip

wot

why is the portable larger than the .exe

Emilio Pisanty

@0celouvskyopoulo7 possibly the exe radios in for even more data?

Abcd

@Blue Alright. Checking...

0celouvskyopoulo7

"no latex distribution was found on your computer"

Anonymous

18:27

@Abcd Umm, try refreshing the page...

0celouvskyopoulo7

@Slereah halp

Emilio Pisanty

@Abcd what do you mean by three-dimensional?

Abcd

@Blue It does not. It compares energy level to an "orbit"

Slereah

@0celouvskyopoulo7 Install a tex distribution

Anonymous

@Abcd Principal Energy Level=Orbit=Shell.

0celouvskyopoulo7

18:28

@Slereah I don't know what that means

Abcd

@EmilioPisanty Here, non circular like in orbits i.e. having 3 dimensions

Emilio Pisanty

@Abcd what?

Abcd

@Blue But orbitals are 3 dimensional so how can orbits be 2 d.

Sorry.

Typos.

Anonymous

I can't understand what your question is. Are you asking what orbitals are?

0celouvskyopoulo7

windows defender doesn't like TeXLive

what is going on

this is so easy on OSX

Mostafa

18:30

Yeah I was thinking about the rotational Doppler effect
(a light beam with helical phase fronts when reflected off a rotating surface will be red or blue shifted, as in http://science.sciencemag.org/content/341/6145/537?iss=6145)

Jaime Gallego

@0celouvskyopoulo7 ::makes malware joke::

Mostafa

@EmilioPisanty But I don't think (temporal) frequency affects the angular momentum

Anonymous

@Abcd I never said "orbits can be 2d". What are you even saying? I just said that "2d" orbital doesn't exist. For n=2 only 2s and 2p orbitals exist.

Abcd

@Blue I want to get a concrete explanation of these 3- energy level(aka orbit aka shell), orbital (aka subshell) and principal quantum number(n)

@Blue I know. I am sorry for my mistake.

Mostafa

For example, intrinsic OAM simply $l\hbar$ for a Laguerre-Gaussian beam independent of $\omega$

Emilio Pisanty

18:31

@Abcd that's some misidentifications there

Slereah

@0celouvskyopoulo7 get miktex

Texstudio or texworks are only text editors

the latex to pdf compiler you have to get independantly

Abcd

@Blue SE chat is malfunctioning so I am making such errors...

@EmilioPisanty I need help. Can you explain the necessary stuff?

0celouvskyopoulo7

ok getting miktex

Emilio Pisanty

@Abcd An orbital is a complex-valued function of position $\psi:\mathbb R^3\to\mathbb C$, which is often (but not always) visualized through the contours of constant $|\psi(\mathbf r)|^2$ (which then form 2D surfaces in 3D space).

Anonymous

@Abcd Ok so you basically want to know what "orbit" is, and what an"orbital" is ? (I already said that principal quatum number essentially denotes the principal energy level in which the electron exists.)

Emilio Pisanty

18:33

Orbitals have well-defined energies.

0celouvskyopoulo7

@EmilioPisanty what are the chances of an 11th grader knowing what $\psi:\Bbb R^3\to\Bbb C$ means...

Emilio Pisanty

@0celouvskyopoulo7 well, @Abcd can give a shout if that is confusing

Jaime Gallego

@0celouvskyopoulo7 Beware that installing MikTeX and all the packages takes ages.

0celouvskyopoulo7

@JaimeGallego I have a fast computer.

Abcd

@EmilioPisanty It's confusing. Hope you don't mind.

Cryolune

18:34

same it took like 3-5 mins to install.

0celouvskyopoulo7

@Slereah What is this missing packages on the fly thing? Presumably I should let it do that silently, no?

Emilio Pisanty

@Abcd I don't, so long as you're honest about what you do and don't get

Slereah

@0celouvskyopoulo7 yeah that's best

Especially if you need a lot of packages

Emilio Pisanty

@Abcd orbitals are the 'wave' aspect of matter

it's just a function that takes in positions and spits out complex numbers

Slereah

Installing packages by hand is a pain

Emilio Pisanty

18:36

these are diagrams of orbitals

each orbital describes the probability distribution of the electron in a given state

0celouvskyopoulo7

@JaimeGallego that took two minutes

you're impatient

Jaime Gallego

"and all the packages"

Secret

riemmann curvature tensor: Is the part $\nabla_u \nabla_v-\nabla_v \nabla_u = [\nabla_u,\nabla_v]$?

0celouvskyopoulo7

@JaimeGallego I think it did everything?

Slereah

that is what $[,]$ means, yes

Secret

18:38

ok

Mostafa

Guys
MikTeX or TeXLive?

0celouvskyopoulo7

Ok, now how do I get TeXStudio to work @Slereah

Slereah

Define "to work"

0celouvskyopoulo7

How do I get my .tex into it and start editing?

Slereah

It's F5 to compile

Emilio Pisanty

18:39

@Mostafa yeah, but if the beam power is constant then the photon number changes, no?

Slereah

Open your .tex file with it

It will open a window for it

Where you can edit

0celouvskyopoulo7

hmm

Secret

$R(u,v)w = ([\nabla_u,\nabla_v]-\nabla_{[u,v]})w$ wow that's really compact notation

0celouvskyopoulo7

the .tex files in our repo are not .tex

they are text

Slereah

Wot

There's a Spacetime.tex

And Causal theory.tex

0celouvskyopoulo7

18:41

ah, there it is

the extension is hidden

stupid

Cryolune

lmao

0celouvskyopoulo7

it says F6 is compile

F5 is "view and build"

Jaime Gallego

F5 compiles it and lets you preview it

0celouvskyopoulo7

this is too fucking complicated

Emilio Pisanty

@0celouvskyopoulo7 you never used TeX before?

0celouvskyopoulo7

18:43

@EmilioPisanty I use it hours a day

Slereah

I prefer to use F5

I like to view the result

0celouvskyopoulo7

on a Mac

where things are 10 times easier

Emilio Pisanty

@0celouvskyopoulo7 ah

Jaime Gallego

@0celouvskyopoulo7 The interface is bloated, yeah, but you just need to know a few things

The rest is typing

0celouvskyopoulo7

Error, package missing...

Slereah

18:44

Which one

0celouvskyopoulo7

yfonts

Slereah

what do you need yfonts for

ams already has fraktur

0celouvskyopoulo7

I have no clue

I've been using it for 4 years

I must have needed it at some point

Slereah

yfonts is \textfrak

But you can just use \mathfrak from AMS

0celouvskyopoulo7

I use \mathfrak

Ok, deleting

Slereah

18:46

yeah delete and see if it compiles

0celouvskyopoulo7

package error

esint not found

Did it not install packages?

Slereah

Normally it's supposed to ask you to install missing packages

0celouvskyopoulo7

I said to just install them without asking me

Maybe I clicked the wrong thing

Slereah

anorien.csc.warwick.ac.uk/mirrors/CTAN/macros/latex/contrib/…

0celouvskyopoulo7

what do I do?

Slereah

18:47

wot

0celouvskyopoulo7

Ahhh

I wanted to do lots of integrals

Emilio Pisanty

@0celouvskyopoulo7 you've got MikTeX?

0celouvskyopoulo7

@EmilioPisanty si

Emilio Pisanty

open the admin MikTeX package manager

find the package

right click

then install

0celouvskyopoulo7

Ok, now it doesn't like tikz-cd. I definitely need that one.

Slereah

18:49

oh right the package manager

Emilio Pisanty

@0celouvskyopoulo7 You'll need to fiddle with the MikTeX settings. You can tell it to either install-on-the-fly directly, or to warn you first

0celouvskyopoulo7

@EmilioPisanty On Mac, I just installed every package. Can I not do that here?

Emilio Pisanty

that's the standard mode

@0celouvskyopoulo7 you can

it'll take a while, though

0celouvskyopoulo7

I'm doing it.

Emilio Pisanty

@0celouvskyopoulo7 installing everything?

0celouvskyopoulo7

18:50

Yes.

Emilio Pisanty

why not start with the ones you need right now and then do the rest?

to each their own, I guess

0celouvskyopoulo7

Because this is simpler?

Slereah

hard drive space isn't much of a concern these days

0celouvskyopoulo7

"downloaded bytes"

Slereah

especially for latex packages

0celouvskyopoulo7

18:51

Is that really a good unit of measurement?

Slereah

it's the fundamental unit

the best unit

0celouvskyopoulo7

don't you mean bit?

Slereah

You can't affect a single bit on a modern computer

Individual bits don't have memory addresses

Emilio Pisanty

@Slereah surely you can read the byte and rewrite it with a one-bit change

if nothing else

Slereah

Well usually you do a bitwise logical operation

With an AND mask

or OR mask

Mostafa

18:53

@EmilioPisanty so... the change in the number of the photons causes a change in the total angular momentum of the beam (not per photon)

Emilio Pisanty

@Mostafa possibly

but I'm not too sold

it's the same with linear momentum, though, and that's probably easier to think about

I think

Secret

@Mostafa Only happens if the message is deemed star worthy, otherwise, it has singular number of stars

Slereah

That exotic smooth structure GR book defines spacetimes as $\text{Riem}(M)/\text{Diff}(M)$

Emilio Pisanty

I mean, the beam state is fixed by the source, right?

0celouvskyopoulo7

spacetimes?

Emilio Pisanty

18:55

what if you start with a single-photon state?

Slereah

He did not think this through

0celouvskyopoulo7

Since when are spacetimes Riem

Slereah

Yeah that seems wrong

Exotic smooth structures are hard because the important part is the smooth structure but in no case do we have expressions for the smooth structure

Secret

but then, we don't have matrix valued stars, so...

$$★^{\begin{pmatrix}0 & 1 \\ 1 & 0\end{pmatrix}}$$

Slereah

what

Secret

18:57

(Carry on folks, nothing to see here...)

Mostafa

Can we?
the energy can't change in that case.

the frequency shift is (typically) not large enough to change the number of the photons

Emilio Pisanty

@Mostafa hmmmmm

this might actually be way harder than it looks

photon numbers change in non-inertial frame transformations

this is Unruh-effect territory

I'm probably out of my depth

Mithrandir24601

@JohnRennie That may be, but Cambridge was 2nd in 2015, 3rd in 2016, 4th in 2017 and 5th in 2018... So it's not really doing that well compared with the past few years :/

0celouvskyopoulo7

ok this is actually taking forever

ctan servers are shit

Emilio Pisanty

@Mostafa scholarpedia.org/article/…

Jaime Gallego

19:05

@Mithrandir24601 All of them pesky Americans are catching up

Emilio Pisanty

doi.org/10.1209/epl/i2005-10595-x

Mithrandir24601

@JaimeGallego :'(

Sid

Does anyone even care about rankings?

0celouvskyopoulo7

Indians

Sid

Ha!

@0celouvskyopoulo7 You caught me. :P

Emilio Pisanty

19:07

anybody know what this link does?

from the doi I just posted

0celouvskyopoulo7

halfway through a paper on not aluminum I realize I've been reading about aluminum

what is going on

@EmilioPisanty Could you not be bothered to make a nice circle?

Emilio Pisanty

@0celouvskyopoulo7 freehand circle is exactly as intended

Mithrandir24601

@Sid Not to the individual places extent, but if any of the universities that I've been at dropped by a scale comparable to where they are, I wouldn't be overly happy. I wouldn't be like 'oh no, this is terrible', but I wouldn't be happy about it

Emilio Pisanty

404

A: The Many Memes of Meta

Meme: Freehand Circles Originator: TheTXI Cultural Height: TBD Variation: during Winter Bash season, some members substitute the freehand circles for freehand hats. Unlike the hats, they won't disappear after Winter Bash is over. See Also: Here, and Here as answer to this post

0celouvskyopoulo7

@EmilioPisanty I know it's a meme

If there were a meme about drinking bleach, would you do that too?

Mithrandir24601

19:09

@Sid What I am more concerned about is the REF rankings as that affects things like funding

Emilio Pisanty

@0celouvskyopoulo7 meh

in any case

why does the official EPL page have a broken link to a nonexistent arXiv id?

0celouvskyopoulo7

Emilio Pisanty Labs?

Emilio Pisanty

@0celouvskyopoulo7 wish it was

Europhysics Letters

Jaime Gallego

Emerson Palmer and Lake

0celouvskyopoulo7

huh, there are nuclear engineering tex packages

Mostafa

19:11

@EmilioPisanty ಠ_ಠ

Does that mean I have to learn QFT on curved spacetime in order to do research on angular momentum of light?

Emilio Pisanty

@Mostafa apparently?

0celouvskyopoulo7

Yes

Hope you like functors

Emilio Pisanty

@Mostafa take it from the man 'imself

theses.gla.ac.uk/5849

plenty of GR there

0celouvskyopoulo7

...

is that in word with TeX equations?

and triple integrals

who actually lets that get published?

Emilio Pisanty

@0celouvskyopoulo7 don't think so

pdf marks Producer: MiKTeX pdfTeX-1.40.14

0celouvskyopoulo7

19:15

@EmilioPisanty I don't see any GR in there

am I missing something?

sarcasm?

Emilio Pisanty

@0celouvskyopoulo7 me being sloppy

anyways

John Rennie

@Mithrandir24601 have Cambridge ever been as a high as second? On a reputable ranking? In the last few hundred years? :-)

I thought the US universities had the top few places sewn up.

Anyway, all that matters is beating Oxford :-)

@Abcd ask me tomorrow. I'm going to bed now!

0celouvskyopoulo7

0.88
Mbps download
77.6
Mbps upload

Something is wrong with that

Jaime Gallego

Are you sure you didn't switch these two?

0celouvskyopoulo7

Yes.

My download for these packages is super slow all of a sudden

Did a speed test

Anonymous

19:22

That happens usually on Apple devices. Check your router settings.

0celouvskyopoulo7

@EmilioPisanty Miktex is configured to download missing packages on the fly, btw

but it's not doing it

gtg but this is annoying

Mostafa

@EmilioPisanty I think I'm gonna do it ::forehead runs with sweat::

Emilio Pisanty

@Mostafa go for it

I wish the question were better formulated

then it'd be worth plonking a substantial bounty

as it is, it just frays around the edges

dmckee

@EmilioPisanty I think it is suppose to either find the paper or search the author, but what it does (at least for me) is go to a failed search.

Presumably the webmaster at IOP is the person to notify about it.

Emilio Pisanty

@dmckee yeah

I can't be bothered at the moment though

dmckee

19:25

Not that [email protected] has been a reliable contact address for about two decades.

Mostafa

@EmilioPisanty But in the first chapter (Supporting Theory) he only mentions special relativity (no GR), and some QED

Emilio Pisanty

@Mostafa I probably misrememberd just how much GR is in there

dmckee

Any way, I dropped by to whinge and moan.

Emilio Pisanty

I was probably thinking of the sections on zilch generalizations and Noether theorems, which are about equally technical

dmckee

I have a on-line course this summer because my wife is expecting our first child in July.

Emilio Pisanty

19:27

@dmckee you were looking for kids to shout off your lawn?

dmckee

And one of my students wrote today that she is having trouble keeping up because she has two other classes this summer.

Emilio Pisanty

@dmckee congratulations

dmckee

Who the hell tries to take three classes in the summer?!?

Who lets them?

Argh!

Emilio Pisanty

this is a full-time course?

@dmckee since you're here, though

why does this work

 echo "Starting calculation. `date`" | tee -a ${logfile}

dmckee

@EmilioPisanty Five semester units. In eight weeks.

Emilio Pisanty

19:28

but not this

 echo "Finished. `date`" | tee -a ${logfile}

in the same file

dmckee

WTF? It should be none or both just on general principles.

Sid

@dmckee Maybe your student wants to shore up her CV?

dmckee

@Sid But two Ds and an F aren't going to shore up anything.

I saw two simultaneous summer courses crush one of the most promising students I've ever had the pleasure of teaching.

Emilio Pisanty

@dmckee I know

Sid

crush?

dmckee

19:31

She squeaked through with two Cs.

And ended up crying in my office.

Nothing worse than a crying student. Especially when you know they are a good, hard-working, smart person.

Sid

That sucks..

dmckee

Mind you, that was intro physics and 2nd semester o-chem, but she was hella competent.

@EmilioPisanty Both work fine when I run them from the command line in bash.

Is there some sneaky change being made to the environment between the lines?

Emilio Pisanty

@dmckee possibly

there's obviously a calculation in between

ah

duh

dmckee

^ The sound of progress.

5

Emilio Pisanty

there's a cd in between

how do I make $logfile be an absolute path?

i.e. append stuff onto pwd

dmckee

19:38

An alternative would be to use pushd and popd for directory navigation rather than cd. That way you can reliably get back to where you started.

Takes bash or some other advanced shell. I don't think it is in POSIX /bin/sh.

@EmilioPisanty I used to know that, but can't recall right now.

Emilio Pisanty

@dmckee it's good

SO to the rescue

I swear

I'm just a human version of stacksort every now and then

0celouvskyopoulo7

20:02

@EmilioPisanty ok how do I get miktex to work now?

oh, it seems to work now

but for some reason it is failing to find a package not in the document

fml

Mostafa

(not important)

David Z

@EmilioPisanty realpath, but I suppose you found that already

parvin

20:38

hi. can sb help me w my question?
is that right to say metal has positive charge in normal position?

if not, so why does electricity pass through my body when I touch the doorknob?

why does some stuff have extra electron or some others have positive charge? like when I put my foot on rug it conducts electron to my foot, and my foot gives the extra to the earth through my body, if the whole charge of the earth is neutral, why does some parts or some stuff on it are not neutral?

and in the end, why do I get electrical shock? is that a huge number of electrons pass through my body?

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