The h Bar

12:34 AM

@0celo7 "HE," what ref is that? does it have some fluid dynamics relations in it?

12:46 AM

hey guys, anybody have a technical term for saying that you dont need to drill holes or otherwise destructively alter a material

envision you're making a table for a technical report

@user507974 What material is it? You might want to ask on English SE

@BernardMeurer i mean basically I'm doing a research paper on nano-adhesives and in the intro I say that as we started making adhesives we started moving away from screwing in/riveting everything

@user507974 Very nice question, but I have no clue, they may help you, the people there are word wizards

I was trying to think of a technical term you might see in a paper corresponding to that type of criteria

It's where I go when I don't know the word I want at least :)

1:01 AM

@vzn el Hawking et el Ellis

4 hours ago, by 0celo7

it's the perfect fluid Lagrangian

does it have a fluid lagrangian?

yes

@0celo7 is it GR stuff?

dammit stackexchange

yes

@0celo7 can you expand on that some, what eqns are they working with? have been looking around for something like this for awhile, conjectured about it etc

1:05 AM

@vzn it's nothing you would want (it's incomprehensible)

I'm sure if I could chain up @ACuriousMind and threaten paid he could figure it out

But that's about it

ACM has said/ "admitted" he is not into fluid mechanics/ dynamics etc

that's not relevant here

@0celo7 anyway (in)comprehensibility is often in the eye of the beholder eh?

@vzn i read that as incompressability for a sec

@vzn i've read a shitload of GR and I've never seen anyone approach it like that and after a year I have no clue what it's about

1:07 AM

(or the brain, that is...)

@0celo7 ah, so you want to give up on it asap. remind you, it was you who asked

do they cite anyone? papers? etc? maybe will have to get a copy of that just to figure it out myself :|

@vzn no

HE contains a lot of original material

@vzn it doesn't keep me up at night

@0celo7 this one? cambridge.org/us/academic/subjects/physics/…

unlike the fact that I cannot prove the inverse/implicit function theorem

@0celo7 so then, what does keep you up at nite?

@vzn yes

1:12 AM

Mar 9 at 22:47, by vzn

@yuggib ahem, playing "devils advocate"... wondering what papers/ refs pursue fluid dynamic/ density analogies wrt space(time)... seems not fully fleshed out anywhere... have long wondered that myself... there is some connection to soliton theory...

@vzn it's like two pages

but getting fluid dynamics from a Lagrangian is tough

@vzn what do you think about the new Jordan 12s in black nylon

they're dropping soon

Lagrangian (field theory)

@0celo7 aha. presumably a variation of the lagrangian density? just found this. never looked into it before.

Lagrangian field theory is a formalism in classical field theory. It is the field theoretic analogue of Lagrangian mechanics. Lagrangian mechanics is used for discrete particles each with a finite number of degrees of freedom. Lagrangian field theory applies to continua and fields, which have an infinite number of degrees of freedom. This article uses L {\displaystyle {\mathcal {L}}} for the Lagrangian density, and L for the Lagrangian. The Lagrangian mechanics formalism was generalized further to handle field...

know very little about lagrangian theory but it seems to be applicable to a very wide variety of energy systems, presumably including fluids.

@0celo7 wear a pair of nikes myself. maybe did wear jordan high tops for awhile iirc (need to look up the logo. is it a figure doing a dunk shot?) they had very thin bottom soles that would wear out long before the rest of the shoe.

anyway, your attitude wrt knowledge seems somewhat nearly bipolar sometimes. you both care & dont care. reminds me of a very-near-)(-teenager around here :|

what

1:28 AM

@BernardMeurer (?!?) just saw your question. where did you see/ hear about lagrangian field theory?

@vzn me, obviously

@vzn While talking to ocelot about FLRW metric

2:01 AM

iirc lagrangians are used a lot in electronics circuits analysis... attesting further to its ubiquity in "energy systems"... not that anyone around here likes crosscutting analogies :|

4:01 AM

@ACuriousMind Is the sentence "it is defined on a dense, open subset of $N$" on the bottom of page 27 a typo?

I don't see why it should be open

it's dense by Brown's corollary

oh I'm stupid, use the implicit function theorem around each regular value

nvm

user116211

4:23 AM

I'm voting to close this question as off-topic because the subject is the history of physics. — garyp yesterday

user116211

This should definitely not be a reason to close any question at PSE; after-all history of physics is totally on-topic here.

@MAFIA36790 @0celo7 o/ o/

user116211

hello.

wazzup?

user116211

clearing the review queue.

5:34 AM

have fun :)

user116211

7:48 AM

> I can derive in about 10 minutes work it took Einstein 10 years to work out.

Am I smarter than Einstein? Clearly not - I just know what the answer I’m trying to get to is. Einstein didn’t know what the right answer was - he was an explorer, hacking his way through a jungle trying to find a lost civilization. I’m a tourist wandering down a paved road with a map.

user116211

cool; definitely in my profile quote list.

8:00 AM

anybody alive

user116211

full alive

what are you up to

im trying to decide if its worth killing a few lines of text to reposition my graphic on a tex report

user116211

I'm currently reading Kreyszig.

ever write something and wish you just never wrote it that first time since you could do so much better

is his work crazy(g)?

user116211

@user507974 o.O

8:08 AM

its just not a normal day for me if i havent at least once stretched the meaning of the word pun to its absolute limit

user116211

hmm...

i mean, you basically phoenetically spelled out crazyg

Kreyszig sounds like crazyg

user116211

His name is sounding German.

true dat

8:10 AM

Ja

Ja ja

mein Deutsch ist so schlecht

O.o

user116211

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ my German is so bad

thnx

8:15 AM

Sprichst du Deutsch mafia?

user116211

@user507974 Es gibt eine Sache, die wir nennen Google Übersetzen ;P

out of curiousity, what did you input to translate mafia

what i get back out putting that phrase in is "There is one thing that we call Google Translation"

I'm sad, I thought I would at least remember how to say "I have no idea what you are saying" in German

I made a mental note to memorize that

man, im getting some stupid tex

hey guys, how did i force a graphic to the top of a page

user116211

@user507974 Sorry, ;_;

for some reason I have a graphic that even though it is place at the end of a section decides to jum pto the middle of the page, in the middle of a paragraph

user116211

@user507974 Why not give a shot at TeX?

8:26 AM

I'm making a manuscript atm

i guess manuscript is the wrong word

that means hand made

but yea, im doing tex atm

but getting some stupid results

now its working for some god forsaken reason

Secret

9:22 AM

[what is reality]
We all came from different places
Religion, Science, Esoterics, Magic, Ideals, Art, Business and so on
We each have different jargon
God, electricity, soul, arcane symbols, postmordernism, Piccaso, Capital and so on
But looking closely, you will find
Order, Chaos, chains, morphisms, networks, complexity etc.
They are so different
But their structures are so similar
Perhaps that means there exists a universal structure
The same elephant described in different ways by the blindfolded

FrancescoS

9:33 AM

Hi guys! We know that $m_ u < m_d < m_s < m_c < m_b < m_t$ where $m_q$ is the mass of the $q-$quark. Is there any reason for this hierarchy? I mean, it should be more symmetric if the isospin 1/2 quark would have larger or smaller mass than the isospin -1/2 quark of the same doublet. This is not always true. I think this is due to the yukawa coupling.. but there is any more detailed explication?

10:12 AM

Hello

The quark masses depend on the Higgs coupling

For reasons which are currently not clear

so far it seems to be arbitrary

10:45 AM

I wonder if there's an easy measure for CTC production

Like an energy scale to tip the light cone enough

FrancescoS

Ok, so there is no symmetry reason or other things... it seems to be causal... probably there is an unclear reason ;)

we wait for the new resonance at LHC

Well there might be a better theory where the Higgs coupling matrix isn't random

11:14 AM

Hm

thinking about it

The fact that free fields diverge on CTCs if there are closed null geodesics might be because they are free

Perhaps interacting fields can do it in a more general context

12:50 PM

It's hard to know though because to really understand that bit, I'd have to read the bloody Hadamard book

Well, the virus is doing something

My internet is 50% slower on the infected partition

I think it's uploading stuff

How do I check this

Gotta go out of town for two days

Let's see if my science folder fits in my laptop

33 GB

Should be fine

Secret

https://en.wikipedia.org/wiki/Maxwell%E2%80%93Boltzmann_distribution

Solved!
Physical chemist will get a E dependence instead of a $\sqrt{E}$

This is because they deal with the distribution when there is only one molecule while physicists handle the distribution for molecules in the interval dE

It is this dE term that result in the $\sqrt{E}$ dependence to convert from physical chemit to physicist maxwell boltzmann distribution in energy

The Hadamard solution is totally only for free fields

My guess would be that for interacting fields things are much worse

"Natural octonionic generalization of general relativity"

ew

1:15 PM

@Slereah I don't think there's anything natural about octonions :P

what about onions

Do you think asking a question "can you prove this formula because I'm too lazy to comb an entire book about it" would go well

@Slereah Those are fine

@Slereah Not if phrased like that :P

I'd really like to see a proof of the Hadamard form

But nobody proves it and they all refer to the Hadamard book

Which doesn't have the formula explicitely written somewhere

I love "references" like that

yeah I think you kind of have to read a few chapters of the book if you actually want to prove it

btw it's public domain so I can totally post it here

ia801400.us.archive.org/20/items/lecturesoncauchy00hadauoft/…

1:23 PM

Well, I'm not going to read the book for you!

Maybe I'll try reading it while out of town

What are you doing "out of town"?

Visit my dad

@Slereah link?

@ACuriousMind how do I check if my computer is uploading something

arxiv.org/abs/0707.0554

1:25 PM

why link the abs

@0celo7 First rule: If your computer is infected you can't trust anything it displays to begin with

I don't know if my computer is infected

I've run two different antivirus programs that say no

and I haven't downloaded anything

but I still get those ads

back up your data and reinstall everything

Wipe out that shit

and speedtest says my internet is waaaaay slow

@Slereah I've got a TB of shit and am in school

I can't rek my computer now

1:41 PM

@ACuriousMind Ofter closing about 50 tabs my internet speed has gone back up

...and that surprises you? :P

@ACuriousMind Yes.

let's try reinstalling chrome

@DavidZ I'm a bit confused about this one

physics.stackexchange.com/questions/253062/…

how do I actually do that

How did it get in that state?

What got deleted when?

@ACuriousMind you may also find it... curious

1:45 PM

@EmilioPisanty spittin fiyah over here

@ACuriousMind let's hope I can remember my google account :P

@0celo7 Beg your pardon?

@EmilioPisanty no time to explain, virus killing time

Secret

>Heuristically, this has to do with the Pauli exclusion principle and the fermionic creation operators anticommuting instead of commuting, formally you have to step through the LSZ or interaction picture derivation of the Feynman rules in order to see the origin of this rule.

Checking LSZ now

@EmilioPisanty You're right, the timeline on that one doesn't seem to make much sense.

nope, fuck

1:47 PM

Also...am I inspecting a post closed by CuriousOne and answered by TheCuriousOne? I need a new name... :P

@ACuriousMind And also the RemovedAbandonedClosed claim is confusing, because the answer is upvoted

@EmilioPisanty DZ deleted the answer before the roomba got the question, I think

@ACuriousMind But the timestamps are the wrong way around

It would explain the auto-delete

@EmilioPisanty Yeah, something is wrong with them, but the timeline makes sense, except for the "undelete" at Jun 1.

Is your iPad infected? @0celo7

1:49 PM

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ laptop

I think

No one will tell me if it's actually infected

Take it to a shop

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ yeah I guess

@ACuriousMind Yeah, that timeline makes no sense

there's one in the student union, I should probably go there

Or it does, except the answer is marked as deleted

Anyways, hopefully @DavidZ can clarify :).

1:52 PM

This might be a case for Meta Stack Exchange, this looks as if something in the documentation isn't working as if it should

In particular, I see a "deleted by David Z at Jun 1" below the answer when the timeline is showing an undelete?

@ACuriousMind Yeah, whatever weird circumstances got it there, the timeline makes no sense and it ought to.

@ACuriousMind That's one undelete vote cast by someone, I think

@EmilioPisanty There's one undelete vote registered at Jun 1 0:00, and then at 8:38 DZ allegedly undeleted it, unless I am misunderstand what an entry "undeleted by David Z" means.

You could try and hunt around on YouTube for anybody who had a similar problem too @0celo7

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ Why on earth would you look on YouTube for that? :P

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ I found one person who had the exact same problem

A Google tech person said to delete the cache and that was it

1:55 PM

@ACuriousMind In the timeline? Yeah, it's a bit confusing.

Works for me sometimes :)

anyway, who the hell cast an undelete vote in that case? oO

It wasn't the owner, because they haven't logged in since May

How did a 10k user stumble across a question deleted for 20 days and decide to cast an undelete vote on the answer, but not the question?

I'm guessing you found this via pending undelete votes, @EmilioPisanty?

user116211

@0celo7 err? What is your RAM, btw?

@ACuriousMind Yeah, exactly

I rarely go there, and when I do there's this sort of crazy stuff

16GB

1:58 PM

@0celo7 let a pro at the shop look at it

user116211

That would be good.... why not work with another browser? Opera or Firefox?

@JohnRennie o/

@PhysicsGuy: do you still want to know how strings manage to look like particles?

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ Hi

is the group table of an n-element group an $n\times n$ matrix?

@ACuriousMind Maybe something like (1) David deletes the answer because of homework reasons, (2) question gets closed and then autodeleted, (3) David comes back and undoes the delete vote on the answer

... because reasons?

No effect on the post, but lessens the prejudice on the answer's poster?

2:07 PM

@Obliv speaking as a humble physical chemist I'd say yes. Why would it be otherwise? With $n$ elements you have $n^2$ combinations.

thats what i thought too just making sure :p

can I use cycle notation inside of matrices?

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ well it seems to be fixed now

@EmilioPisanty Maybe? But how/why did DZ remember to go back to a deleted question and undelete the answer?

@ACuriousMind Maybe reminded by the undelete vote?

That still leaves the mystery of who found that question and voted to undelete

2:13 PM

But why is there even an undelete action on the answer in the first place, if it's the question that needs to be brought back?

@ACuriousMind ok, the problem seems to be fixed

give me something to google to test

@EmilioPisanty I have no idea

oh wow @johnR i don't think it's an $n\times n$ matrix anymore.. like take the set $\{1,2,3,4\}$ under the operation +. You can have $1+1$,$1+2$,$1+3$, etc then $2+2$,$2+3$, ... $3+3$,$3+4$,...$4+4$. Leading to $n!$ combinations? Then $4\times 4 = 16 \ne 4!$

@Obliv what. You have $n$ choices for the first summand and $n$ choices for the second summand. How did you arrive at $n!$?

That's only half a matrix

1 x 4 \nne 4 x 1

2:19 PM

@acuriousmind isn't 1+2 and 2+1 the same thing? I thought there were n-1 choices for the second summand

"\nne" = not necessarily equal. John's notation :-)

@Obliv That still doesn't explain how you arrived at $n!$, and not every group is commutative, so no, 1+2 and 2+1 are not necessarily equal.

The group might be non-abelian

Although one usually does not use the additive notation for non-commutative groups.

And even if it wasn't, you still need all n^2 entries but the matrix will be symmetric about the leading diagonal

2:21 PM

well if it was it'd be symmetric, no?

Yes, but the fact the matrix is symmetric doesn't mean you can just throw away half of it

That doesn't change the group table being an $n\times n$-matrix. It's now a symmetric matrix, but it's still a matrix.

Q: What is going on with this deleted answer?

0

I'm a bit confused by this Q&A pair: http://physics.stackexchange.com/questions/253062/dimensional-analysis-problem (10k on Physics, or dev team.) The question looks like this: Of note: The answer was posted 10 minutes after the answer. The question was closed about an hour afterwards. The...

@acuriousmind well if you only chose distinct sums I think you'd have $n!$ but assuming you don't care about distinctness then okay it'll be $n^2$

@Obliv $n!$ is the number of ways to arrange $n$ objects in order. I have no idea how you think the combination of two things from $n$ objects gives you $n!$ possibilities.

2:24 PM

Ah, I was wondering why a really simple answer has attracted 7 upvotes (even though someone else wrote a better answer). The HNQ again.

i'll write it out if you don't believe me. $\{1,2,3\}$ (assuming you only care about distinct values) gives the group table $\begin{bmatrix} 1+1 & 1+2 & 1+3\\ 2+2 & 2+3 \\ 3+3 \end{bmatrix}$ there, isn't that only $n!$ entries? @acuriousmind

@JohnRennie oh

:P

@Obliv No, that's $\frac{n(n+1)}{2}$ entries, not $n!$.

@ACuriousMind that's a symmetric matrix

what

2:27 PM

@0celo7 Yes it is.

what about $\{1,2,3,4\}$ that would give you $n!$ entries..

fuck dude the IT people reset chrome completely and that damn chat noise came back

too loud

@Obliv I'm telling you that the number of distinct entries in a symmetric matrix is $\frac{n(n+1)}{2}$, not $n!$.

@ACuriousMind I agree

@Obliv how could it even be $n!$

Cor, nine jets have just flown over my house at low altitude in formation. I wonder if the Red Arrows are in town.

2:28 PM

that's way bigger than the amount of entries

for most $n$

@JohnRennie Cor?

$\begin{bmatrix} 1 + 1 & 1 + 2 & 1 + 3 & 1 + 4 \\ 2 + 2 & 2 + 3 & 2 + 4 \\ 3 + 3 & 3 + 4 \\ 4 + 4\end{bmatrix}$

And I still have no idea how you came up with $n!$, because your "writing out" if I don't believe you consisted of writing down the only case ($n=3$) where $\frac{n(n+1)}{2} = n!$.

wait

that's 10 LOL

@Obliv every GR person knows a 4x4 symmetric matrix has 10 entries

it's the Schlafsatz of GR

@ACuriousMind Ok, the IT people seemed to solve my problem. Should I still be worried about a virus?

@0celo7 You should be deathly afraid.

(I'm not actually qualified to give computer advice :P)

2:30 PM

n + n - 1 + n - 2 + ... n - k (k = n - 1) does that also give you the amount of entries
?

@0celo7 urbandictionary.com/define.php?term=cor

Used only facetiously these days.

@JohnRennie Papa bless

yeah that should. but the other way is easier

@Obliv I proved that formula somewhere in chat

I was having a crisis about symmetric matrices one day

@Obliv ...yes, $\sum_{i=1}^n i = \frac{n(n+1)}{2}$. It's anecdotally ascribed to Gauß, who allegedly derived it in primary school

2:32 PM

@ACuriousMind Yup, did you also know he allegedly only shat on prime numbered days

Yes, I read SMBC :P

@ACuriousMind I know

I thought it wouldn't need a proof though? @0celo7 every distinct entry matrix of a set should have rows that have 1 less entries from the previous row

@Obliv What do you mean it "wouldn't need a proof"?

@Obliv huh?

Can you prove that a symmetric $n\times n$ matrix has $n(n+1)/2$ independent components?

2:34 PM

Its proof is one of the standard first applications of induction.

@ACuriousMind I think one can do it without induction.

The diagonal has $n$ entries

The off-diagonal has $n^2-n$ entries

But these are symmetric so it's really $(n^2-n)/2$

i guess it can be proved but it'd be pretty simple. if any row had the same entries as another row then it wouldn't be distinct

But $n+(n^2-n)/2=n(n+1)/2$

so contradiction to claim that each row has 1 less entry than the preceding one

@Obliv Just use my argument

2:36 PM

@0celo7 I was talking about $\sum_{i=1}^n i = \frac{n(n+1)}{2}$. But yes, one can also do that without induction.

what's an off-diagonal @0celo7

@ACuriousMind deja vu dude

@Obliv the terms which are not on the diagonal

how do you prove that w/o induction

how do you know the off-diagonal has $n^2 - n$ entries?

because the whole matrix has $n^2$ entries

i think my way is simpler

2:37 PM

and we subtract the diagonal which has $n$

so the rest has $n^2-n$

if you have $k$ apples and remove $l$ of them you have $k-l$ apples :P

i thought the whole matrix had $n(n+1)/2$ entries

...what

@Obliv independent

ARENT WE TALKING ABOUT THE MATRIX ACM DESCRIBED

I don't know.

I'm saying random shit honestly

But nothing I say is wrong ;P

Aha, now that it has been starred it is law

2:39 PM

@0celo7 Believe me, you don't want to say that :P

@ACuriousMind Why

@0celo7 because there's a lot of self-deprecatory comments by you in the chat log that were starred

Aha, it was the Red Arrows. They're on their way to do a display at the Isle of Man TT races.

Kind of them to pop round and do a display just for me :-)

@ACuriousMind well which ass keeps starring those

I believe you call the collective behind that "the Astronomer" :P

2:42 PM

who is this person

is there any reason that I should write the group tables of $S_3, D_8$, and $Q_8$? Will I get any insight from writing $8\times 8$ matrices with 64 entries ...

yes.

well nothing you say is wrong so here we go

good.

no

you know what no

64 fucking entries. no