The h Bar

@DanielSank you two are confusing me

or maybe you're confused

see this is why this is shitty notation

NeuroFuzzy

1:14 AM

@DanielSank ohhh I get it. Sso like $ T^{i}_{; k }=(\nabla (T^{a} e_a))(\theta^i, e_k)$

For basis covectors theta, basis vectors e

Feynman

1:42 AM

Hi everyone, I have changed my photo, which used to be before of Feynman. And even the name has been changed from Feynman to Vinaykumar. Don't forget me :)

@NeuroFuzzy no!

the basis vectors have two indices

one is an abstract index and one is a coordinate index

the vector is $v^a$ and the components are $v^i$, and the two are related $v^i=v^a e_a{}^i$

uh, indices are jumbled, I think

this notation sucks

DanielSank

2:44 AM

@0celo7 I understand your objection, but I can't think of a better way to indicate what's contracted with what.

You could use function notation but you'd wind up with a depressing number of parentheses.

user54412

3:06 AM

Mar 20 at 0:05, by Chris White

I usually place indices inside parentheses to indicate which vector/tensorial/form object I'm using, and indices without parentheses mean the component of the object

user54412

Mar 20 at 0:32, by 0celo7

@ChrisWhite Eh, I don't like that notation. It should be clear from context if the index is a component index or a coordinate label.

user54412

And people wonder why I choose the notation I do.

@ChrisWhite example pls

user54412

$v_{(a)} = v_{(a)}^i e_{(i)}$

@ChrisWhite What the fuck?

what is $e_{(i)}$

user54412

3:18 AM

the i-th basis vector

user54412

the full thing, not a component

what the hell is $v^i_{(a)}$

user54412

the i-th component of the a-th vector in some set

user54412

change it to $v = v^i e_{(i)}$ for simplicity

ayy what

dude that notation does not make sense

are you summing?

what's going on there

user54412

3:22 AM

Einstein notation still holds -- it ignores parentheses

@ChrisWhite But that is not "I usually place indices inside parentheses to indicate which vector/tensorial/form object I'm using", if the $(a)$ really labels a family $V_{(a)}$. If it indicates "$v_{(a)}$ is a vector" it can't also label $v_{(a)}$ as the $a$-th member of a set.

user54412

@ACuriousMind now I'm confused

Your quoted statement would suggest writing $T_{(ab)}$ for a 2-tensor, but now it sounds as if you just write $T$ when there are no other tensors around.

@ACuriousMind Up late or up early? ;)

(Note that $T_{(ab)}$ used in that way would conflict with it otherwise usually denoting symmetrization of the bracketed indices.)

user54412

3:24 AM

The (a) was just an extra example on the off-chance I needed to label things -- has nothing to do with the rank of the tensor

@ChrisWhite Then I don't understand what you meant by "I usually place indices inside parentheses to indicate which vector/tensorial/form object I'm using"

ok so $e_{(i)}$ means that it's a vector, but assigned to the ith direction?

and $v^i$ has no parens because it's just a component

user54412

@ACuriousMind If I have vectors $\vec{v}_1$, $\vec{v}_2$, ... floating around, I don't want to call them $v_1$ and $v_2$ when omitting the arrows, since these look like the 1 and 2 covariant components of $v$. So I call them $v_{(1)}$ and $v_{(2)}$, where the label index can be up or down -- whichever is convenient to get it out of the way of the component indices.

user54412

And since no one ever symmetrizes on a single index, there's not really notational ambiguity

why not just put arrows on them :P

3:29 AM

@ChrisWhite Okay, I see that that's what you're doing, but I don't see how that's what you described back then because this way the bracketed index does not indicate at all which vector/tensorial/form you are using. It just indicates that it is not a component index

...how did I make "component" into "competent"? :D

user54412

@ACuriousMind Oh I think I see what you're saying. When I said "to indicate which vector/tensorial/form object" I meant "to indicate which tensor I'm using from some indexed set," not "to indicate what particular rank the object has"

Ah, yes, that was my misunderstanding indeed

@ChrisWhite does your TeX OCD prevent you from bolding?

user54412

@0celo7 I'm not a fan of bolding just because it's not really supported for non-Latin characters, and it also looks like I'm highlighting something important.

I don't like bolding in computer modern

but it's quite nice in the font that Hawking-Ellis uses, for example

user54412

3:34 AM

But I'm not so against it as to complain to copyeditors that my precious formulae are being ruined by it.

copyeditors?

@ChrisWhite do you have any publications? I would like to read something by you

Found one. You need to practice your Google-fu :P

oh, I didn't look

Hm, maybe not, though

I did find his face, remember?

3:37 AM

I think this isn't him

right university

date makes sense

Yes, it's him

user54412

@ACuriousMind That's me. Not an article this chat would be particularly interested in.

how did you decide?

ArXiv unhelpfully lists other Chris Whites when clicking on the authors name, which is very confusing

3:38 AM

@ChrisWhite astro-ph isn't all that interesting, tbh

user54412

This is probably less interesting. Not just astro, but observations and real data ;)

Why would ArXiv display the search for White, C. and not the search for the exact author's name?

I have no problem with data!

today I applied for an internship in applied physics

wow, that's nothing but data

ok, that is pretty boring :P

user54412

I just submitted an article that's the core of my thesis. I can post a link next week when it's on arxiv. It uses all sorts of index notation :p

you're kidding, right

\mathrm on one side?

also no space between integrand and measure? were you drunk while typing this?

user54412

3:43 AM

I didn't choose the notation there -- the prof I worked with has his preferences

I should send you an email

The space between integrand and measure just...wastes space :P

@ACuriousMind you're kidding, right?

user54412

Also, I put aside my OCD until making the final revisions, since the copyeditors will usually make drastic changes anyway.

wtf is a copyeditor??

3:44 AM

Someone who copyedits stuff?

user54412

The people who work for the journal and typeset your paper.

@ACuriousMind real helpful

@ChrisWhite do you get a final check?

user54412

@0celo7 Yes. Once the article is approved by the editor (who usually defers to the referees), it's typeset by the copyeditor. Then they send you the pdf and you can make minor spelling/typesetting suggestions.

apparently engineers use...Word...for papers

::shudders::

@ACuriousMind @ChrisWhite Something I never understood about Skyrim: Dragons are immortal, but can be killed. Is the idea that Alduin has to resurrect them but can't if a Dragonborn eats the soul?

So the only way to really kill them is to devour the soul?

user54412

something like that

user54412

3:54 AM

though it's not 100% clear -- did none of the dragons who were resurrected die to previous dragonborn? seems a bit of a stretch

Q: When people say Op on this meta what does it mean

Recall all the skeletons on Solstheim. They were killed by Miraak and didn't get resurrected.

Remember, he was the first DB and probably the only during the dragon wars. Then the Akaviri hunted down the remaining ones but since Alduin was "gone" they were effectively "dead."

Physics Meta

6:00 AM

0

I have seen many posts where people refer to the op of the question. So what does OP stand for? is it the asker of the question.

discussion

Q: IS THE MOMENTUM OF AN OBJECT ALWAYS >= THE ERROR IN MOMENTUM

7:10 AM

RPfnoR 6

Physics Meta

0

IN CLASS WE TRIED TO SHOW THAT THE ELECTRON CAN,T RESIDE INSIDE THE NUCLEUS USING UNCERTAINTY PRINCIPLE . WE TOOK THE RADIUS OF NUCLEUS AS EROOR IN POSITON AND FOUND THE EROOR IN MOMENTUM , THE TEACHER REASONED THAT THE ERROR IN MOMENTA IS THE LOWEST POSSIBLE VALUE OF MOMENTUM THE ELECTRON CAN HA...

discussion

0

Q: Why was my flag on a 'link-only' answer disputed?

Recently I flagged an answer to this question citing not an answer as it was providing only a link. Now, link-only answers are not encouraged here as they may become worthless when the link becomes dead. But I was surprised when the flag was not helpful; it was disputed. Now, what is the reas...

discussion

user685252

9:10 AM

@ChrisWhite you have OCD?

10:50 AM

So eerily quiet...
RIP chat

user685252

11:10 AM

It must be the all saints day

:P

Leuchte

2:38 PM

Hello everyone

I have this question in mind:
Does having the same total momentum after a collision imply that the collision is elastic?

@Leuchte Momentum is conserved in both elastic and inelastic collisions, so no.

Leuchte

Would the answer differ if we consider the individual momentum of each of the objects?

If the individual objects have the same momentum after the collision as before, they have not collided at all ;)

Leuchte

o.O yes :)

@ACuriousMind Thank you for your time

4:05 PM

Good morning? I guess it is because the time changed.

working as usual

trying to curve fit some rotational spectroscopy stuff

4:18 PM

@ACuriousMind 's job application: Skills: Rigorous pedantry.

@Secret Chinese/Japanese data?

Well, my computer is in chinese, (which is why the google is also in chinese). But the actual data is englsh. I am comparing this boltzmann looking curve with that generate by matlab to ensure my program is on the right track

How do you tell Chinese and Japanese characters apart? I'm reasonably good at distinguishing Korean.

well, if the words is in Kanji, then in general you cannot tell them apart without knowing what the word means (because while Japanese and Chinese sometimes use the same kanji to build their words, they usually differ in meaning. It's kinda like "library" in french and english means two different things)

I am from HK, which is related to china, thus I am chinese to start with

japanese also use hiragana and katakana in their language (which functions like a,e, i ,o ,u and consonants in english), and these you cannot find them in chinese

Well unless I know what those look like I can't tell them apart

How do East Asian dictionaries work

hiragana and katakana look somethign like this

while kanji look something like this

some of these are common between chinese and japanese

while some, such as "駅" are not found in modern chinese language

example of a chiense dictionary
1. The word
2. How to pronounce it
3. Meaning and description
4. words that can be formed form it (similar to compound words in english)

4:43 PM

@Secret I think the question was more like - how do you look up a word? Is there an analogue to alphabetic order?

I am not sure for japanese, but for chinese, you look up the part that forms the word. For example:

you look for the symbol that forms part of the word
Some chinese dictionary allow you look up via the pronounciation, which will be arranged in al[habetical order

@ACuriousMind Yes, the last part is what I was going for.

Huh apparently I didn't turn off Hitman: Absolution last night and now I have 15 hours in it.

@ACuriousMind Btw I like it.

But we've already established that I'm not a big fan of very slowly paced games, so that might be it.

Unlike english and european language in general, chinese words are build by simpler words in a 2D fashion, for example, the word for "tell" is shown above

even japanese words are mainly build by syllables in a linear fashion

4:48 PM

What? Tell = words + 8 + elders??

That's bullcrap

That's a complicated word. How does it not take ages to write/type?

lol the elephant one is BS

I think that language is the product of some kind of drug

Chinese words initially start as pictures, and then progressively simplified
After some time, analogue to compound words were formed by assembling words with known meaning together to give a new word

Chinese characters

Chinese characters are logograms used in the writing of Chinese and some other Asian languages. In Standard Chinese they are called Hanzi (simplified Chinese: 汉字; traditional Chinese: 漢字). They have been adapted to write a number of other languages including: Japanese, where they are known as kanji, Korean, where they are known as hanja, and Vietnamese in a system known as chữ Nôm. Collectively, they are known as CJKV characters. In English, they are sometimes called Han characters. Chinese characters constitute the oldest continuously used system of writing in the world. By virtue of their...

more info here

bullcrap!

@0celo7 Not really, for example, if you look at the history of our alphabet, the modern shapes of latters are also completely different from their Phoenician origins.

4:52 PM

No way someone can remember that!

Evolution of language is just weird.

Maybe that's why Asians are smarter. They have to train their memories differently than we do.

@ACuriousMind 9 days

Shitbucket apparatus ready?

https://en.wikipedia.org/wiki/Logogram
Chinese are an exmaple of logograms. Most european languages are phonographic (i.e. bunch together based on pronounciation

Oh god Black Jesus starts in 9 days too :o

Egyptian hieroglyphs are another example

4:55 PM

Also a Radical Redemption album and Qlimax!

This gon be a good month brehs

@JohnDuffield Howdy

@Secret Well, if you think about it, it seems more natural to write down things by actually using symbols that signify the content, not the pronounciation.

John Duffield

@0celo7 : howdy. I've been on holiday for a week, and I promised my wife I wouldn't spend time on the internet. I read a couple of physics books instead, whilst lazing on a sunbed. And I swam, and ate too much, and drank too much. It was great!

@ACuriousMind Naw, language is spoken.

John Duffield

Oh, and now I can speak a bit of Greek.

alarge

@ACuriousMind Koreans are pretty efficient at this as their characters encode pronunciation but people learn to recognize the groups of characters in a way similar to how Chinese/Japanese read kanji.

5:00 PM

@0celo7 Well, but when you write something down, is your primary intent to communicate with someone else or to get them to speak what you've written aloud? When you say "language is spoken" you already presuppose that the script is intended to encode the spoken language, and not merely information.

yup, korean is kinda a mix between the two. The o and _ strokes have origins from kanji

Korean used to use kanji before 200(forgot) but eventually decide to discard them completely so that they don't felt like they copy or associate everything from china

alarge

@Secret Do you mean to say that they no longer require people to study them at school? Cause you will still see kanji walking down the streets in Korea.

@ACuriousMind Communicate in such a way so that when you meet at the market to seal the deal you don't have to write down the terms on a piece of parchment for both parties to have a clue what's going on.

Really? I thought they have completely abandoned them (if by kanji you saw it forms a continuous string, then it is probably written for chinese tourist)

alarge

@Secret Again, I don't know what completely abandoned means in this case. They still did teach them at school in the early 2000s I believe, and maybe now it is no longer a required subject.

5:09 PM

I'm curious, why did two people star my "I'm not a physicist"?

Do they agree, think it was funny, or what?

Or they want people to stop thinking it because X?

@0celo7 Some simple guide to the 3 main east asian languages
http://www.wikihow.com/Tell-Chinese,-Japanese,-and-Korean-Writing-Apart

> Look for circles and ovals.

Knew that

@alarge
https://books.google.com.au/books?id=MvBFBQAAQBAJ&pg=PA88&lpg=PA88&dq=Koreans+stop+use+kanji&source=bl&ots=j-bCZBCKik&sig=aaRYxEPnnuYcdGORg1_dQvO_Awg&hl=zh-TW&sa=X&ved=0CGYQ6AEwCGoVChMI9ZbLrNzvyAIV5WGmCh0z4god#v=onepage&q=North%20Korea%20stopped%20using%20Kanji&f=false

Ok it seems they have not abandon them compeltely, but they do use them much less than kanji in japan

i.imgur.com/CrOzQ7V.gifv

aww we don't have webm oneboxing?

> So f(x) is the same as f(u) just with a different variable?

Someone just asked me this

sigh

5:27 PM

@ACuriousMind
Yesterday I have a question about degeneracy vs microstates. Slereah have helped me to clarify that for some macrostates some of the microstates are related to the degeneracy of the energy levels

I then tried to better udnerstand the difference by writing out in maths as follows:

i.e. Let's assume we have some system $S$ and it has the following degrees of freedom $(a, b, c, d \cdots)$. Therefore each state $i$ in this system is described by the ntuples $k_i=(a_i, b_i, c_i, d_i \cdots)$

@Secret The concept of micro- vs. macrostate is not an inherently quantum concept, so I'm not sure why you are writing things as if we were in the quantum case. Generically, a microstate is just a point in phase space, and a macrostate is a probability distribution over all microstates that agree on the values they have for certain macroscopic observables like energy and pressure.

@ACuriousMind so in the framework you mentioned, is degeneracy just one of the many types of microstates?, that is some of these points have coordinates related to the degeneracy and something else that is not degeneracy?

I don't understand the question. "Degeneracy" means that there is more than one state with a particular value for a particular observable. The very definition of a macrostate is that it encompasses all microstates which agree in their values for energy, pressure, etc. So they are all by definition degenerate states for these macroscopic observable.

so when we talk about one single microstate, the values cannot have degeneracy (because it is a point in phase space hence one single state)?

5:43 PM

It's a single state. I don't know what it would mean to say that "the values have degeneracy".

(Let's try another way...)
The reason I ask the question is because of some confusion on whether entropy (which in statistical mechanics, is a measure of the no. of microstates satisfying a certain macrostate) is the same as the number of degeneracy

Possibly because of too many memory errors, I don't know/forgot how to convince myself that entropy is not a measure of the number of degeneracy

Degeneracy of what?

of the whole system?

That doesn't make any sense.

or maybe in the context of molecules, the degeneracy of the energy levels

5:47 PM

You're completely mixing different things. Again, micro- and macrostates have nothing to do with quantum mechanics. There are no "energy levels"

But to answer the question you probably want to ask: No, the number of microstates with the same energy is not, in general, the number of microstates in a macrostate with that energy, since they might differ in another macroscopic observable, e.g. pressure.

ok that makes sense

Btw, In the phase space picture, is the 2nd law the same as as the system evolves with time, it explore an increasingly larger volume of phase space that is allowed by the constraints on the system?

until it explore all points in phase space that is allowed by the constraints?

JokelaTurbine

ToE seekers might found something interesting from here; physics.stackexchange.com/questions/214042/…