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6:01 PM
@0celo7 Why are you so hung up on this, btw? Just wondering!
 
@Danu Dunno
 
Maybe it's more productive to spend most time on something else and only deal with this thing when e.g. talking to supervisor so you can actually make progress ;)
 
well now I'm stuck on some other GR and will be for hours and hours
I hate life
 
The AI took my shiny points on stackoverflow away ;-;
 
That pricks heart!
 
6:11 PM
@ACuriousMind I'd like to see you answer this question without indices.
0
Q: Identity $ \epsilon_{abcd} R^{cd}_{\phantom{cd}mn} = \epsilon_{mncd} R^{cd}_{\phantom{cd}ab}$ in vacuum

phy_mathstarting from \begin{align} \epsilon_{\rho\lambda\xi \kappa} R^{\xi \kappa}_{\phantom{ab} \sigma\tau} + \epsilon_{\rho\sigma \xi \kappa} R^{\xi \kappa}_{\phantom{ab} \tau \lambda} + \epsilon_{\rho \tau \xi \kappa} R^{\xi \kappa}_{\phantom{\xi \kappa} \lambda \sigma}=0 \end{align} The paper say...

^ such things give me cancer.
 
6:29 PM
@0celo7 Ehh? :P
It ain't so bad.
 
Greetings all.
I wish to rant about special relativity, is this the correct place to do so?
 
Probably?
 
@barrycarter It's definitely the place to rant, not sure if to rant about SR
 
Wait, wouldn't the general case include the specific case?
(For all x rant(x)) -> rant(SR)
 
That'd be true if I had any pretension to make sense
 
6:33 PM
If someone is traveling .99c with respect to me, when 10 seconds have passed on my clock, their clock reads about 71 seconds and I'm about 70 light seconds behind them.
 
@Danu let me find the worst one or not, too lazt
 
well this maybe quite awkward question but which book i good for GR
 
However, if there is an object 10 light seconds ahead of me (but traveling at my velocity), they will see it at time 0.708881 as being 0.708881 light seconds ahead of them.
OK, wait, that's not quite my rant. Let me find a case where it gets worse.
OK, here's the crux of my rant. The Lorentz contraction and time dilation are NOT transitive, even though the Lorentz MATRIX of transformation is transitive (since matrix multiplication is transitive).
 
"transitive" is a property of relations, not of operations.
 
@BernardMeurer have you still kept funny man blocked?
 
6:40 PM
@DeNiSkA Why do you ask?
@ACuriousMind Have you had lessons on formal logic?
 
@ACuriousMind You're right, let me rephrase that.
 
@BernardMeurer No, but it is kind of hard to do math and not learn at least the basics
 
@ACuriousMind Yeah I figured, I was asking more because I wanted a reference for a good starter's book
 
Associative, I meant associative.
If L(b,c) is Lorentz contraction between reference frames b and c, then L(b,d) = L(L(b,c),d) does NOT hold.
If b*c is the Lorentz contraction between two reference frames, then (b*c) x (c*d) does not equal (b*d)
I have no idea what I'm trying to say, never mind.
Does anyone know what I'm trying to say?
 
6:58 PM
Stackoverflow will make me have a stroke
 
7:13 PM
@ACuriousMind Seriously, how do you write $t^a{}_bt^b{}_cX^c$ abstractly
 
@0celo7 Why would I?
 
@ACuriousMind Uh, why does that matter?
it shows up in GR so it might show up in Riem geom somewhere
0
A: Extrinsic curvature components

Uldreth1) On first glance it seems to be correct. If your hypersurface is given by $r=R$, then it is the level set of the coordinate function $r$, thus $\mathrm{d}r\sim n$. 2) The covariant derivative is calculated with respect to the original metric. The connection induced on $\Sigma$ by the induced...

How did he come up with this in at most 32 minutes?
 
By being smart? :P
 
@ACuriousMind :(
@ACuriousMind That post just pisses me off because of physics math
Extrinsic curvature is not hard when you don't bother with coordinates :)
 
You know
I think it is best to teach GR starting with extrinsic curvature
It's a lot more visual
 
7:26 PM
@ACuriousMind Would it be uncouth to email an author and ask when there's gonna be a second edition if he's said previously that there will be one?
 
Depends
How many time will you employ the word "bitch"
 
Huh?
 
Bitch is pretty uncouth
 
I'll use it 0 times.
 
Should be fine then
I should try to get enough rep for 3000
I want to cast close votes
Such power
In my hands
 
7:31 PM
@ACuriousMind Ok, here's my problem with Ellis' proof
If you take a general hypersurface and closed curve, it could intersect the hypersurface once.
Now that's a huge problem.
There's no reason for it to intersect more than once, is there?
 
I don't see a problem, and no, there is no reason.
 
@ACuriousMind Ok, apply the rest of the proof.
The curve is homotopic to zero.
But the intersection number is invariant mod 2.
 
"zero"? Do you mean "a point"?
 
So there are no hypersurfaces, period.
@ACuriousMind Yes.
Now you can claim that there are absolutely no hypersurfaces, anywhere, in any space with trivial topology.
But that's obviously wrong.
(does that make sense?)
 
7:37 PM
@ACuriousMind I have to go, but Ellis' proof to show that there are no hypersurfaces in Godel can be used to show there are no hypersurfaces in any $\mathbb{R}^n$.
 
@0celo7 Not to me because I have no idea what the "rest of the proof" is. Also, I'm pretty sure the intersection number is not invariant under homotopy in the way you claim. Take any line through a surface. It's homotopic to a point, and that clearly changes the intersection number from 1 to 0 along the way.
 
@ACuriousMind For a closed curve it's invariant mod 2.
Danu knows the proof.
 
Not if things like the open disk are admissible surfaces.
 
Ok, so the rest of Ellis' proof is wrong.
 
@0celo7 It's a bit more complicated than that
 
7:38 PM
@Danu How so?
I'm not reading GP until the summer
@ACuriousMind See the part "this would mean"
 
@0celo7 Can you
 
Well, whether that is right or wrong depends on what exactly counts as a "surface without boundary". If it means "closed manifold", I'm willing to believe the statement.
 
I mean you can contract closed spacelike curves just fine
 
@ACuriousMind I know the statement is true if $\mathscr{M}-\Sigma$ has two connected components.
Btw, it is it $-$ or $\setminus$?
 
Either
 
7:44 PM
I prefer $\setminus$
 
I've seen both used
 
I like $-$ because $\setminus$ looks strange in TeX.
It's too schief. Whatever the English word for that is.
 
$\setminus$ looks a bit too harsh for me
For me, set substraction should be like
Almost -
But very slightly slanted
 
It should be $-$ at a 45$^\circ$ angle.
 
I don't congratulate you, Knuth
Not even 45°
Maybe more
20°
 
7:46 PM
Eww, no that's so wrong
The $-$ is just too bad because it's already used in algebra.
 
What?
 
But we use the same symbol for multiplication and cartesian product
 
@Slereah I never use $\times$ for multiplication.
 
We use $\star$ for the Hodge and Moyal
 
We use $0$ for all kinds of things
 
7:47 PM
@0celo7 I've never seen both used in one text.
@Slereah Such as?
 
The natural number 0
The null vector
the null element of an algebra
etc etc
All kinds of null things
 
@Danu It should be clear from context that $\mathscr{M}-\{p\}$ or something like that is not the same as $3-5$
 
For false in a boolean algebra
 
@0celo7 Yeah, that's clear but at some point most people cut out the $\{\}$'s
Or for instance $M-\text{pt}$
is already less clear.
 
Ok, I don't do that.
 
7:49 PM
Always use mathcal for the spacetime
It just looks prettier
 
eww no
 
If you want me to use $\setminus$, please find a font in which the angle isn't so large.
@Slereah Agreed.
By advisor does too, but he doesn't use $\mathrm{d}$.
 
Hahaha
physicist/10
 
One thing I found odd in HE is that he defines the connection before the metric
 
@Danu Lol
 
7:50 PM
Until then, I never thought about the fact that you can totally do that
 
He got his PhD from Princeton in math, totally a physicist.
 
Define a connection with no metric
 
@Slereah Really really easy
 
@0celo7 :3
 
@Slereah who did?
 
7:51 PM
It's the way all math books do it
 
I know
It's just a thing I never thought about
 
It's called the Koszul connection
 
Because all physics books define the metric first
 
And the Levi-Civita connection is the unique metric, torsion free Koszul connection.
@Slereah Because physics books are shit
 
Koszul sounds like a name from LoTR
 
7:52 PM
Isn't Levi Civita also a metric connection?
 
@Slereah slight typo
 
If we go by silly names, "Klinkhammer" sounds like a whacky nazi in Hogan's Heroes
 
best show ever
 
Did you guys know there used to be a guy pre WW2 whose name was Gay Hitler?
 
@FenderLesPaul lol
 
@Slereah Isn't the guy called Klinkhamer?
That's a Dutch word.
 
Colonel Klink
But there's a physicist called Klinkhammer
 
At least one called Klinkhamer, too.
 
Richard Klinkhamer (Dutch pronunciation: [ˈriʃɑrt ˈklɪnkɦaːmər]; 15 March 1937 – January 2016) was a Dutch murderer, who went on to write a book about how he could have committed the crime. In 2000, he was sentenced to six years in prison for manslaughter after killing his wife and hiding her body. == Murder conviction == In 1991 Klinkhamer's wife, Hannelore (née Godfrinon), went missing from their home in Hongerige Wolf. A year later Klinkhamer went to his publisher with the manuscript for Woensdag Gehaktdag, which detailed seven ways in which he could have killed his wife. The manuscript in...
 
8:01 PM
Oh yeah, Woensdag Gehaktdag
funny title for a book
 
8:24 PM
-3
Q: How would I do this

micheal aresI want to make a program in nim that would close all browsing process when I try to watch porn to stop me. Or in python please help me this could help a lt and bring them to the lord

Oh my god
 
@BernardMeurer lol...that's great....
 
I gave a proper answer even
 
there was no need to answer it...hahh...let him watch porn
 
8:39 PM
I treat PSE like porn because I don't want people to find out about this place.
 
@Keepthesemind Different Klinkhamer
Actually
There is another guy
Poplawski
There is a physicist named Poplawski
And a murderer named Poplawski
Hopefully not the same
 
9:21 PM
Is actually extremely interesting, though rather macabre.
 
 
1 hour later…
10:50 PM
@0celo7 ...why?
 
Why what?
 
Why do you not want people to find out about this place?
 
Because, perhaps to contrary belief, I do/say things here that I don't in real life.
I'm not this weird IRL, basically.
 
You should not be ashamed of liking index porn (=GR).
 
He only likes GDP porn
 
10:56 PM
@ACuriousMind you know I prefer index free porn
 
Also nothing to be ashamed of
 
Ah, but I've declared my love for a man (you) in here.
That would be awkward if a certain person found out.
 
I think @FenderLesPaul knows
 
He's my side bitch
He's not like you
 
11:25 PM
@ACuriousMind oh, I'm stupid
I meant a certain girl, not FLP :P
 
@0celo7 You don't say :P
 
On mobile, don't know which part you're referencing.
That I'm stupid or it would be awkward if she read this chat?
 
You really think I'd flat-out say you're stupid? oO
 
Yes.
 
I'm not that mean :/
 
11:30 PM
Sounds more like my kinda thing, eh? ;D
 
@Danu That would not be evil enough for you
I already know I'm stupid
You tend to crush my soul.
 
I must have missed that oO
 
Which part?
 
Danu crushing someone's soul
That sounds entertaining
 
I called him a dementor the other day
 
11:34 PM
You missed it... all those times? :P
 
Danu is just mean
 
But that hurt his little feelings
 
Hahaha
I love how I'm like the antichrist to these people
And you're Yeezuz (@ACM)
 
ACM isn't jesus, I just like to have fun with how much a jesus he is
wait, I just ruined my case
 
uhuh
 
11:36 PM
@Danu Where you doing your PhD?
I need to look at places for foreign study soon.
 
@Danu I actually have sometimes people holler "Hey, Jesus!" at me because of my hair and beard
And yes, I missed your soul-crushing :D
 
@0celo7 So you can avoid me? :P
@ACuriousMind It'll come again, don't worry.
 
@Danu I think we would be friends in real life
Where you don't have power to abuse me
 
@0celo7 Riiight ;)
 
@ACuriousMind Soul crushing ^
 
11:39 PM
@ACuriousMind You should get snapchat
 
@Danu :(
@BernardMeurer YES
 
@0celo7 @ACuriousMind Skypz?
 
You guys are having skype calls nowadays? :P
 
We try to but ACM never joins
so it's usually just ocelot helping me read Shankar
 
I'm at someone's house @BernardMeurer, not home
 
11:42 PM
@0celo7 Bob's house?
 
My dad's house is my home...
 
You live in too many places, it confuses me
 
@BernardMeurer Nope
 
Literally just two places.
@ACuriousMind no what
 
No snap he says
 
11:44 PM
Wtf
 
Geez, I'm not going to explain every reference just because you can't seem them right now.
 
Snapchat is ridiculous
 
Everyone has snap
 
@ACuriousMind do you want to babysit me reading Shankar? :p
 
^ guaranteed not
 
11:44 PM
I had it, but in the end it just boiled down to this one annoying girl sending me snaps
 
@Danu It's the only place you'll get me taking a selfie with trump
 
@BernardMeurer Not really
 
@ACuriousMind </3
 
@BernardMeurer I'm not interested in that.
 
@Danu You have no finesse for entertainment
 
11:45 PM
Danu is pretty coarse.
He doesn't like fine food, music or entertainment.
 
@0celo7 You don't like fine music either
your girlfriend does, but you don't
 
@0celo7 lolwat
You don't like fine food, good music or other interesting cultural stuff
 
Today I learned: Snapchat is "finesse for entertainment". You people really belong to a different generation :P
 
@Danu How do you like swedish experimental?
 
^^
@BernardMeurer No idea, never heard it.
 
11:48 PM
@ACuriousMind nono, me taking selfies with trump is finesse for entertainment
the rest of snap is shit
 
I'm definitely becoming a grumpy grandpa.
 
@Danu wtf?
 
@Danu Haha, I feel the same way
 
@Danu definitely.
 
11:49 PM
@ACuriousMind You have a golden patience, you're not grumpy
 
@BernardMeurer Seems OK-ish. Bit simple (not too much production value, so to say) and too pop-ish for my usual taste but I can listen to it.
 
Bah, production value.
 
@BernardMeurer This is not really music as much as performance art
 
One of the best albums in mid-era hardstyle was created in one month.
 
@Danu The second one you say?
@Danu Do you like classical?
 
11:51 PM
@0celo7 Just wait till ya get older
@BernardMeurer Some
 
@Danu nope.
You don't like Döner, why should I believe anything you say?
 
@Danu Keep in mind those guys are literally young, broke musicians with no big name behind them like Sony Music or whatever; demanding production value is a bit unfair :p
 
@0celo7 Again, zero production value
 
He doesn't like Döner?
 
@BernardMeurer No it's not
 
11:52 PM
Pleb
 
That's a ridiculous claim
 
How come?
And,btw, define production value
 
Danu why are you so hipster?
 
Noun: production value ‎(plural production values)
  1. (film, performing arts) A method, material, or stagecraft skill used in the production of a motion picture or artistic performance; the technical quality of such a method, material, or skill.
  2. 1969, Toby Haggith, "Face the Music," Film Quarterly, vol. 22, no. 4, p. 11,
  3. Soon the novelty of all-talking pictures wore off and incidental music began to make a comeback. It was, after all, an added production value.
  4. 1994, Mark S. Miller, "Helping Exhibitors: Pressbooks at Warner Bros. in the Late 1930s," Film History, vol. 6, no. 2, p. 189,
  5. The New York publicity people asked the studio people if the films were to be shot in colour or not so as to decide if whether to feature that production value in the promotional campaigns.
 
@Danu what, Döner?
 
11:54 PM
@0celo7 Yup
 
@Danu I thought we were talking about different things ;)
 
Yeah, the average Döner really doesn't have high production value :D
 
Anyways, I'm heading off to bed
Bye, guys.
 
Why does that matter though?
Why does everything have cause hours and hours to make
Some of the best food ever comes out of a can
 
It generally brings up the level.
 
11:56 PM
@0celo7 Sure, if you're a dog
 
@ACuriousMind what?
No, spaghetti O's are amazing
Especially cold.
 
The things you say all reflect that you're 18 years old
:)
And that's fine---but don't pretend like these things are set in stone because your perspective will change (very soon)
 
No.
 
^classic
 

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