The h Bar

Cows

00:18

hey

hmm will stream later . . . . need to do some dirty work first to prep the data graph

*** Everyone I need a time auto correlation function 101 . I have to implement this tonight hehe

:D

Keeping it hardcore, getting motivated to code. . . . youtube.com/watch?v=L_u97PqWX6g

Got to get this done

N.E.R.D & Rihanna - Lemon

►

Fawad

01:00

> I do not participate to this site any longer. I do not accept a situation in which, a scientific answer not understood by some users, is downvoted repeatedly instead of asking clarifications from the poster of the answer. And such a situation is considered normal, instead of being avoided. And when the poster of the answer protests, he/she is considered not O.K. Given this situation, I don't see any reason why offering my knowledge at all.

Sofia

5k 2 10 30

DanielSank

01:15

@Fawad what about it?

heather

01:43

curse my chromebook!

it automatically updated which for some reason broke linux =/

dmckee

@DanielSank I seem to recall that this user held a forcefully opinion on matters related to entanglement.

For instance:

3

Q: Faster than light signals and the price to be paid if we accept them : a very simple protocol

Some physicists currently understand entanglement as transferring information instantaneously, yet not violating causality. Is this really a satisfactory explanation, or should be look for something better? In particular, some people try to be explicit about a signalling between particles, but t...

quantum-mechanics special-relativity quantum-entanglement faster-than-light

@DanielSank Did you get an email from the person responsible for that site, too?

::Pokes around a little to see what it is (as opposed to what the email days it might be)::

Oh.

Cows

02:00

ok i am back from my walk. I think I can code now

@dmckee hey dude. . . I said hi to you the other day, and you were acting all upidy upidy. What's up with that? You feel better than me? lol

dmckee

@Cows Don't recall the incident, but in all likelihood I considered the demands of my infant child more important than chat (that's been happening a lot recently), and by the time I noticed your greeting it was hours later and your avatar didn't even appear in the sidebar.

But let me make it up to you.

Hey, @Cows. Nice to see you. How've you been?

Cows

@dmckee oh just been hanging out and so forth.

dmckee

I just got my grades turned in late last night, and I have to board a plane tomorrow, so it's nearly straight from school stress to packing stress. But I am determined to chill while I'm on the west coast. Assuming we don't have to evacuate.

::raps firmly on his own head:: Knock on wood.

Cows

Wow, that's quite a busy schedule

dmckee

My in-laws badly wanted this trip to happen, but it had to be arranged around multiple constraints meaning that it ended up being less convenient that is desirable.

enumaris

02:13

kaggle forcing me to use their kernel is gonna drive me insane

Cows

I can imagine.

@enumaris I have been hoping to see you

Can you help me connect through basic auth

enumaris

connect where?

Cows

It is to an API end point out of south America. I can't connect

I have the secret and key, and have tried to do this via node and get wierd messages

the API documentation is in spanish

enumaris

o.o

Cows

Can I share more details with you about this?

enumaris

02:15

not sure I can help...I'm not all that great with stuff like that lol

Cows

oh lolz

enumaris

I think Bernardo or David Z would know better than me

Cows

I need to get POS data and make some correlation functions

with that data and facebook data

enumaris

POS?

Cows

Point of sale

enumaris

02:17

oh

Cows

I am building "God Mode" for my client

enumaris

o.o

Cows

@enumaris I also have some phone location API i need to integrate, but it seems I need to do some proxy conx

enumaris

uhhhh

I'm working on a kaggle competition lol

cus I don't have a job..=/

Cows

oh nice

whaaaaa . . .

I am sure you will get a job

ACuriousMind

02:20

@enumaris Use your time to write some more physics.SE answers, then ;)

enumaris

I find that when I go to write answers, unless the questions are extremely straight forward (e.g. homework questions) I start going into caveat after caveat until I'm too lazy to finish the answer...

ACuriousMind

Ah, perfectionism coupled with laziness is a terrible curse ;P

enumaris

XD

vzn

02:47

@Cows what ML problem are you working on? "this video has been removed by the user, sorry about that :\"

...

> “The train accident that just occurred in DuPont, WA shows more than ever why our soon to be submitted infrastructure plan must be approved quickly. Seven trillion dollars spent in the Middle East while our roads, bridges, tunnels, railways (and more) crumble! Not for long!” --Trump foxnews.com/us/2017/12/18/… o_O

DanielSank

@dmckee yes I did. I responded that is a very good idea and that I will help if certain conditions are in place to ensure longevity

dmckee

03:04

That kind of thing could be hugely valuable, but everyone involved has to understand going in just how enormous a project it really is.

vzn

03:17

@DanielSank yeah interesting, has potential, defn like the concept of "andragogy vs pedagogy," sometimes wish wikipedia allowed writing on same subj from different povs and think it sometimes tries too hard to shoehorn topics into "only one [authoritative] entry" :( ... iirc maybe this has already been pointed out by some somewhere... physicstravelguide.com

DanielSank

04:08

@dmckee yes, the structure must be such as to support unplanned growth directions.

ooolb

05:02

that's actually non trivial @DanielSank

if it's not thought through properly it will end up like wikipedia

like i said the idea of the site itself is nothing special, it's all in the work

it needs to be designed so that it doesn't reference in on itself and always has a linear structure from one topic to a different topic

doesn't reference in on itself in a loop*

user228700

Hi, everyone :-)

user228700

@JohnRennie Niiice! :-)

user228700

@JohnRennie Dang! <3

vzn

05:18

@Kaumudi.H hey hows CSE going are you learning coding/ python? :)

DanielSank

@ooolb I didn't say it was trivial.

@ooolb I completely disagree with that.

user228700

05:44

@JohnR: Do ping me when you're free!

user228700

@vzn Python, yep!

John Rennie

@Kaumudi.H Morning :-)

user228700

Hi! :-) I'm back home!

John Rennie

Good to be home? (silly question :-)

user228700

:-) Silly question indeed!

user228700

05:47

Actually, I think I will text you on Hangouts, instead...

John Rennie

Ok, I'll jump over to Hangouts ...

DanielSank

06:10

@Kaumudi.H Yay!

user228700

:-D

John Rennie

06:31

@Kaumudi.H Ten dosas???!!!

user228700

:-D That's right!

Sid

@JohnRennie What??!

user228700

@Sid I had ten dosas this morning!

Sid

...what???!

user228700

Believe it or not!

John Rennie

06:34

@Kaumudi.H a noble feat. One that I would be proud of myself!

user228700

:-) Thank you, thank you.

Sid

You will fall sick. That is overeating.

John Rennie

@Sid Nonsense. If you can still stand up and walk then you haven't eaten enough.

user228700

@Sid Well, I feel completely OK!

user228700

It has only been two hours, actually, and I think I could eat more now...

Sir Cumference

06:58

Oh god I'm 19

enumaris

07:10

ugh

I got a comment on my answer by someone claiming that photons have both an electric and magnetic dipole...-.-

ooolb

@DanielSank cool definitely don't provide any reasoning to back up your disagreement

John Rennie

@enumaris That's Holger Fiedler for you. He has some ... err ... curious views about physics.

enumaris

hmm...

John Rennie

I must confess I wish I understood the relationship between photons and classical light waves better. But whenever I look into the subject it seems formidably complicated.

enumaris

yeah...that's..."quantum weirdness" I guess

enumaris

07:31

0

Q: How can i prove EFE in general theory of relativity

I now how to prove einstein field eqation in special telativity,i was wondering how can i prove it in general relativity(by using tansors) Please help me solving it

general-relativity

uhhhhh........

this guy can "prove" the EFE's in special relativity...wat...

Sir Cumference

07:46

@enumaris *telativity

enumaris

right...

hmmm

John Rennie

The troll is strong with this one

skullpatrol

08:06

the best way to weaken a troll is to take away its food

enumaris

By using lorentz transformation we can simply get to E=mc^2 — shadi 14 mins ago

he can still comment on my answer?

He thinks $E=mc^2$ is the Einstein field equations???

Slereah

08:29

Also your answer is wrong :p

You can derive the EFE

Although I love the word "tansor" now

enumaris

You can't derive it tho, it's a postulated set of equations

Slereah

Well you can postulate it, yes

But you can also derive it from Lovelock's theorem

You can also derive it as the proper gauge invariant limit of the Pauli-Fierz equation

enumaris

those are not derivations =/

Mithrandir24601

@JohnRennie so... You need to have 3 pizzas next time?

John Rennie

@Mithrandir24601 It's a long term goal, but the two sausage pizzas were right at my current limit :-)

Slereah

08:35

@enumaris Why not

enumaris

You can also "derive" it from the Hilbert action but I don't see any of these as being more fundamental

Slereah

You start with some assumptions and end up with the EFE

Lovelock's theorem is a bit more fundamental I'd say

enumaris

It's like saying you can derive Newtonian theory from Lagrangian mechanics

Slereah

Just requiring second derivatives and a divergence free stress energy tensor

that's a pretty simple set of requirements

enumaris

I mean, I guess it's a matter of taste at that point

You could also argue that extremizing an action is somehow more "fundamental" than some f=ma stuff.

Slereah

08:39

Well because it is, yes :p

I haven't used $F = ma$ in quite a while

But extremizing the action is always great

enumaris

so you would argue that F=ma is derived?

Slereah

I would, yes

I mean what does "derived" mean, according to you?

enumaris

lol are we gonna go into a semantic argument now

Slereah

that's what it all boils down to, I suppose!

enumaris

I have no interest in making semantic arguments :)

Note also that the question uses "prove"

Slereah

08:43

It also uses "special telativity"

I don't know what telativity is

enumaris

If your point is my answer is wrong because my english is bad and I got prove and derive mixed up, then sure. Cool beans.

John Rennie

@Slereah that's not true

Slereah

Is it not

John Rennie

GR is one of a set of theories that can be derived from the Lovelock assumptions

Slereah

It's only one in four dimensions

I mean I guess you also have to assume that it's a metric theory of gravity

John Rennie

08:51

And restricted to second derivatives and local

Slereah

yes, that is what I said

which sounds like a fairly simple set of assumptions

John Rennie

So what you're saying is that if you start with a description of GR you can derive GR

Slereah

I'm saying with those few conditions you can derive the Einstein Field Equations

enumaris

just like if you start with an action that can reproduce F=ma you can derive F=ma :D

Slereah

Well what would you consider to be a true derivation then

enumaris

08:58

given F=ma, if F=2N, M=1kg, then a=2m/s^2 general case --> specific case. But again, I'm not really interested in having a semantic argument =/

Maybe if Lovelock's theory makes a bunch of (tested) predictions that GR doesn't and then shows that GR is only a subset of the larger overall theory, then I would buy that the EFEs are "derived".

Slereah

Well Lovelock's theorem predicts the EFE, and not any of the alternative theories of gravity

It does predict more things in different dimensions but alas not too interesting

enumaris

cool beans

Slereah

Except for string theory

I don't know if string theory links to Lovelock's theorem, though

Maybe GR on the full target space is Lovelock gravity?

I dunno

Balarka Sen

Pendulum Music Steve Reich 1968

►

Fantastic hip hop beat there

tfw Steve Reich discovered lo fi beats

Slereah

everyone looks so serious

Balarka Sen

09:13

because it's SERIOUS MUSIC

Slereah

It sounds like Mario could play to this music

Balarka Sen

Good call

I just feel like throwing a freestyle to that tune man

Slereah

will you freestyle to this

Super Mario Brothers Super Show Credits - Do the Mario!

►

John Rennie

God help me, but I'm liking this at the moment

Balarka Sen

@Slereah This is beautiful

Slereah

09:20

Me I just keep thinking about Disco Inferno

The Trammps - Disco Inferno

►

Balarka Sen

@JohnRennie Charlotte Gainsbourg makes semi pop music after acting on semi flop movies?

That's news

Slereah

I prefer the original Gainsbourg!

Serge Gainsbourg - Le poinçonneur des Lilas (1959)

►

Balarka Sen

Same

John Rennie

@BalarkaSen I didn't claim she was any kind of artistic genius, I just said I liked that track.

Balarka Sen

Ah, sure, I was cracking a semi joke

I thought all of her movies with Lars von Frying Pan was bad

not a popular opinion but yeah

John Rennie

09:25

Frying pan? Am I missing a meme or a pun on Trier?

Balarka Sen

yeah it's a bad pun on Trier

Slereah

plz explain the pun

Balarka Sen

frier, trier, geddit? GEDDIT?

John Rennie

Based on a mispronunciation of Trier?

Slereah

The Fox Scene from Antichrist (Chaos Reigns)

►

look at this cute doggo though

Balarka Sen

09:29

Antichrist is one of the worst movies of his

it has an interesting idea but he makes 0 effort at panning it out

just because you can make good camera movements in the woods with a lot of ambient noise doesn't mean you're Tarkovsky

like jesus

Slereah

What was Jesus's best moviee

Balarka Sen

The Room

Slereah

I actually saw the Room two days ago

It was fun enough but mostly boring

Balarka Sen

it's a piece of art though

Slereah

It's a piece of something certainly

Balarka Sen

09:32

loool

John Rennie

@Slereah art is in the (brown) eye of the beholder?

Slereah

badum tish

So there's two methods for path integrals of fermions

The classic way with Grassmann variables

And some weird ways from the 60's, where you do some integration over $SO(3)$

I have no idea how they relate

Balarka Sen

SONGIFY THE ROOM (You're Tearing Me Apart)

►

Slereah

You know what the room and antichrist have in common?

A cute doggo

The Room - Flower Shop scene.

►

Balarka Sen

good observation!

Slereah

10:12

Hey stackexchange peeps

Is there a way to filter posts

To not see all the [duplicate] and [closed] questions

because who cares for those

John Rennie

In a search yes ...

Slereah

Can't I just do it for everything to not see all that trash

John Rennie

It would be nice to have some setting in the preferences akin to the ignored tags, but I don't think any such setting exists.

You could ask on the Meta but I wouldn't hold your breath.

Emilio Pisanty

10:29

huh

this is really nice

Kramers-Kronig in the time domain

Slereah

10:45

Balarka Sen

<3

@ACuriousMind What's more disturbing is that you could bijectively rate each integer with a rational :3

A $\aleph_0$'s worth of work for Siskel and Ebert

bolbteppa

The EFE in special relativity are just the extremum of the Einstein-Hilbert action for the motion of a particle in a fixed Minkowski (flat/empty) gravitational field right

Slereah

wot

Special relativity (or telativity) doesn't have an EFE

it's just some poorly worded question

bolbteppa

11:00

The EFE are the Euler-Lagrange equations you get extremizing the EH action for the metric, $\delta S = \delta _g S(x^{\mu},A_{\nu},g_{\rho \sigma})$ where $x$ and $A$ are fixed, and the motion of a particle in a fixed $g$ field is found by varying w.r.t. $x$, $\delta_x S$ etc... Qogito Ergo D

The poorly worded question was probably unintentionally right :p

CooperCape

Isn't it Quod Erat D...

bolbteppa

Portmanteau of QED and Cogito Ergo Sum in praise of/inspired by tansors and EFE for special relativity tbh

CooperCape

Ahhhh right

John Rennie

@Blue you around?

CooperCape

tansors though...

Like seriously damn

bolbteppa

11:08

tensors are hard enough

CooperCape

$\tan (v_i\otimes w_i)$

I'm on phone I don't know if that worked out

Balarka Sen

what does that even mean

you cant tan a tensor

is that a joke

CooperCape

Yes

Balarka Sen

good

it was a shit joke

CooperCape

Someone wrote tansors in a queston

user228700

11:11

@JohnR: Sorry that I didn't finish downloading the bunch! I fell asleep for three hours in between :-/

CooperCape

Chill

bolbteppa

Not a joke, it's the graded algebra of tan tensors = tansors $\tan (v_i \otimes w_i) = v_i \otimes w_i + \frac{1}{3} (v_i \otimes w_i) \otimes (v_i \otimes w_i) \otimes (v_i \otimes w_i) + \dots$

user228700

Also, @Balarka: Hey, man!

bolbteppa

haha

John Rennie

@Kaumudi.H you fell asleep at your laptop? Now that's what I call CHILLED :-)

Balarka Sen

11:12

@bolbteppa That's not an element of the tensor algebra in general

You're writing an element of $\prod T^k V$

bolbteppa

Which is why we gave it a new name of tansor

Balarka Sen

Tensor algebra is $\bigoplus T^k V$

user228700

@JohnRennie Pretty much! :-P It would seem that I didn't get very much sleep last night. I rested my head on the table to shut my eyes for a few, fell asleep soon enough, then slumped onto the bed when I woke up momentarily :-P

Balarka Sen

Hey @Kaumudi

Done with all the exams whatsoever?

John Rennie

@Kaumudi.H :-) In any case there's no urgency. I'll leave the files there for a few days.

user228700

11:13

@Balarka: Decided to participate in WinterBash, I see!

user228700

@JohnRennie OK! :-) Still, I should be done soon...

user228700

@BalarkaSen Yupp! :-D I'm home!

Balarka Sen

I'm uninspired this year

Most people have collected like over 20 hats. I have 5, and have stopped bothering

None of the hats look good

user228700

Dude, I have zero! x'D

Balarka Sen

Collect some

@Kaumudi.H Congrats

user228700

11:16

:-) After hearing you talk about Tarkovsky so much, I've decided to watch "The Mirror".

Balarka Sen

One of his least powerful movies, but worth watching anyhow

user228700

:-/

Balarka Sen

I mean it's damn good

Just not what Tarkovsky's full potential is, to me :)

He's probably the greatest director of all time (not my opinion; ask your friendly neighborhood movie critiques), so ranking his films are hard

user228700

Hmm, I see, OK.

Balarka Sen

The visual style of Mirror is unique

user228700

11:22

Hmm...

user228700

I'll let you know what I think after I watch it!

Balarka Sen

okie dokie

Slereah

12:37

Let's read Recherche Critiques sur l'électrodynamique générale

I've been wondering how much it actually discusses advanced potentials

Heheheh

The article talks about electromagnetic mass

even though it's from 1908

After special relativity

he doesn't even mention Einstein

Anonymous

@JohnRennie Hello! I just came home...

Slereah

Oh man

He still talks about the aether

Embarrassing

Was special relativity still not well known in 1908

Prathyush Poduval

12:57

@Slereah I think Einstien also mentioned the aether in his SR paper, for space-time (i'm not sure bout it)

Slereah

Well obviously

Since that was the theory of the time

Prathyush Poduval

could be he's talking about aether in the same sense Einstein meant it

Slereah

Nah

He doesn't even mention Einstein

He's 100% talking about the Lorentz aether theory

ugh

It's one of Those old papers

Without any vector notation

Prathyush Poduval

@Slereah I'm not familiar with that theory

Slereah

The Lorentz ether theory is basically special relativity

Except instead of the Lorentz group acting on the structure of space, everything is an effect of the ether

Prathyush Poduval

13:03

that doesn't make sense, what kind of effect is he talking about and how do they happen?

Slereah

Length contraction and time dilation

Einstein isn't mentionned, but you know who is?

Schwarzschild.

He apparently worked on the Lagrange equations for EM

Prathyush Poduval

is there an english version of the paper?

Slereah

No

gallica.bnf.fr/ark:/12148/bpt6k96034863/f151.image

the french version

There's a lot of wanking about whether or not electric and magnetic fields are fundamental to electrodynamics

Prathyush Poduval

then what is fundamental to electrodynamics?

according to him

ACuriousMind

@Slereah Is "fundamental" ever defined? :P

Slereah

13:12

@PrathyushPoduval It's an old thing

You can define electrodynamics (classically at least) without ever refering to EM fields

Just by dynamics of point charges

For instance with the Jefimenko equations

heheh

it talks about differenciating under the integral sign

Slereah

13:35

I'm having some trouble reading the paper bc it's old but I think basically he's arguing that advanced potentials can't work because of the Cauchy problem

Otherwise you can't predict events without knowing events from past infinity

Since you get converging waves from infinity on all charges

also something about creating infinite energy from systems by having the energy go in and out via retarded and advanced waves

Slereah

13:49

Apparently it goes all the way back to Lorentz

Physics Meta

0

Q: What happened to the comments on a question?

This question on renormalisation in quantum field theory had a number of comments under the main question, including one of mine; they all seemed to have been removed without any indication that they had been so. How come?

discussion

Slereah

"This solution isn't the general integral, there will be, for instance, solutions corresponding to a wave motion towards the volume elements rather than away from them. We reject them from the theory by admitting that charges are the sole generators of perturbations. We also exclude ether states that are completely independant from charged matter."

Lorentz didn't even believe in sourceless EM waves!

Emilio Pisanty

@knzhou I'm preparing one now and I'm giving this template a whirl, it needs some changes to fix e.g. this format (particularly p.10) but it's otherwise quite nice

there's more templates here in case you haven't seen that list

(btw if you do run that first one, it's xelatex/lualatex only, pdflatex won't cut it.)

GPhys

14:09

Quantum field theory final exam in 50 minutes.

He scheduled a 3 hour exam so I think we're calculating something in QED to tree level

Slereah

Spoiler : It's a muon-electron scattering

Damn

One biblio reference in this is the number 1 of a journal

"The notion of field doesn't seem to be applicable to gravitation."

Oh how he ate those words

GPhys

14:34

I hope so - wouldn't that be just one tree level diagram?

Can't draw to check right now, in class

Slereah

Sorry you're gonna have to solve quantum gravity

Solve all worldsheet diagrams in an 11 dimensional Calabi-Yau manifold

ACuriousMind

@Slereah There are no 11d CY-folds, CY-folds are necessarily complex :P

Slereah

Doesn't string theory use 6D Calabi Yau manifolds?

ACuriousMind

@Slereah sure

Slereah

Why can you have 6D complex manifolds but not 11

ACuriousMind

14:41

..because one is even and the other is odd? :P

Slereah

Doesn't it need to be $2^n$ though?

ACuriousMind

The "nD" is the real dimension and the manifold can only be complex when $n$ is even.

Slereah

o

ACuriousMind

Since one complex dimension is two real ones

Slereah

What's the tangent space for a 6D complex manifold, then?

ACuriousMind

14:47

I don't understand the question

It's a 6d vector space, obviously :P

Slereah

But where does the complex part come in

Isn't a complex manifold where the tangent space has a complex structure

ACuriousMind

In there being a complex structure on that 6d vector space that makes it into a 3d complex vector space

Slereah

so just $\mathbb C^3$?

ACuriousMind

Yes, but I think you're asking the wrong question :P

Slereah

I just wanted to know why the requirement for even dimension :p

ACuriousMind

14:49

@Slereah Uhhh. Because $\mathbb{C}^n \cong \mathbb{R}^{2n}$? Or, more physicsy, because one complex number is two real degrees of freedom?

Slereah

Yeah I see that now :p

user228700

@JohnR: Ping me when you're around!

Slereah

are there simple examples of Calabi-Yau manifolds

Transcript for