The h Bar - 2018-10-19

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2:31 AM

...lol like the plague™ o_O rjlipton.wordpress.com/2009/11/04/on-mathematical-diseases

e^e is my MD

3 hours later…

6:08 AM

-1

Q: Are there certain physical theories that would inevitably imply fascism

The boltzmann brain hypothesis seems to refute egalitarianism. If all brains existed then the universe would be overwhelmed with Boltzmann proletarians. It appears our universe is fascist.

electromagnetism

Kill it with fire.

Oh come on, we all know that the aether implies fascism

3

he's not even trying

2 hours later…

user351417

8:40 AM

@EmilioPisanty You seen this one?

user351417

8:51 AM

Also, for any 10k users, are there presently delete votes here? I'm surprised if there aren't any; I was trying out a userscript to display vote counts just now.

@Chair there are currently no delete votes on that question. I can add a delete vote if you want to test your script. I normally wouldn't bother because the system will automatically delete the question anyway.

user351417

@JohnRennie No thanks! I'll test the script on Meta SE. There are a frequent off-topic programming questions there, and those get closed/deleted very quickly.

user351417

9:12 AM

user image

user351417

Perhaps this is slight cherry-picking, but 7 people getting the Famous-Question badge in 1 minute is quite something (actually it's probably a 15 minute span since other badges were awarded 16 minutes and 31 minutes ago)

user351417

I never cease to be amazed by the scale at which SO operates.

user351417

235

Q: Has Stack Overflow saved billions of dollars in programmer productivity?

John Carmack is a renowned developer and CTO. His Twitter account has over 100,000 followers. On the occasion of Stack Exchange's 5th anniversary, he quipped on Twitter: [... Stack Overflow] has probably added billions of dollars of value to the world in increased programmer productivity. ...

economics programming-productivity

9:45 AM

just billions?

user351417

10:44 AM

@AlNejati SO was turning 5 at the time. Now, they're celebrating the 10th anniversary.

12:07 PM

user image

2

I just boarded my ferry 🚢

12:53 PM

Is it obvious that the dipole magnetic field is irrotational?

I would think the current density is localized to a point (delta function)

1:09 PM

@Lozansky it's a bit more subtle than that, I think, because an ideal magnetic dipole is an infinitesimal loop of current. so saying that the current density is a delta function seems wrong. but that's not really an issue regardless: the magnetic field of a current loop is also irrotational away from the loop itself, and that remains the case no matter how small you make the loop

@Semiclassical Hmm, but only far away from the loop?

I need an exact result

Say we have a dipole in some direction $\hat{n}$ and some distance from it (in the same direction) we have a circular current loop

away from the loop just means "not literally at the loop"

Ah

But can we say then

That the force on the dipole from the magnetic field of the current loop is $\nabla(\mathbf{m} \cdot \mathbf{B}) = (\mathbf{m}\cdot \nabla) \mathbf{B}$?

for simplicity, take a loop of radius $r$ and a sphere of radius $1.1r$ which encloses it. every point outside the sphere lies away from the loop, so the field outside the sphere will be irrotational. now take the limit $r\to 0^+$ with $Ir^2$ held fixed.

@Lozansky this is something I forget tbh

I mean, what's $\nabla(\vec{m}\cdot\vec{B})?$

as a product rule

You got $4$ terms

1:21 PM

ugh

:P

though, two of them should be derivatives on $\vec{m}$ and therefore zero

Well not div but

curl

:P

That's the one

Yeah

1:22 PM

i'd call it "rot" but that always looks weird to me

The one I was worried about is $\mathbf{m} \times (\nabla \times \mathbf{B})$

gotcha

i mean, there's definitely possibility for something weird at zero

but everywhere else it's fine to say that the curl vanishes since there's no other current density

Yeah... that's why I wanted to bring in the delta

sure.

what i'd say is that the current density is localized at the origin

but I'm not sure it's literally a delta function

probably the thing to do would be to use Stokes' theorem in some way

oops

The original question was posed as: find the force of attraction between the magnetic dipoles in the figure

user image

1:27 PM

gotcha

So one way is to use $F = 2 \pi I R B \cos \theta$

Where let's say $m_2$ is approximated as a circular loop

And $\cos \theta$ is the angle between $\mathbf{B}$ and the normal to the loop

i'm not awake enough to give much help here, mind

Ah that's alright

The other way is to use $\mathbf{F} = \nabla(\mathbf{m} \cdot \mathbf{B})$ but yeah I just wasn't sure if I could justify $\nabla(\mathbf{m} \cdot \mathbf{B}) = (\mathbf{m} \cdot \nabla) \mathbf{B}$

you could probably pull off an energy approach as well

e.g. find the energy of that configuration and see how it changes when you increase the separation

isn't that a problem in Griffiths as well, come to think of it?

to find the energy of the dipole-dipole system

oh, derp. that's all $-\vec{m}\cdot \vec{B}$ is

ignore meeee

i think your approach of approximating one dipole as a loop makes the most sense tho

that lets you, on the one hand, integrate the force over the loop

while still using the simplicity of the explicit dipole expression

2:10 PM

Hmm @Semiclassical

$\int dz \dfrac{\partial{\mathbf{B}}}{\partial y}|_{0,0,z} \approx \epsilon \dfrac{\partial{\mathbf{B}}}{\partial y}|_{0,0,0}$

This is for a square loop of side $\epsilon$

looks right

I don't see how to justify setting $z=0$

Sure, in the limit it makes sense

hmm

But we could just as well have started at $z = \epsilon$, depending on the direction of the loop

user280247

3:02 PM

Hello guys...just come with a silly question: to solve for the force in newton eq. Do we need 4 data points (2 velocities and 2 positions) or just 1 velocity and 1 position?

user280247

There are many books which say 2 data points. But I can't see how the force is determined in that case

Take the example of a ball falling through the atmosphere, subject to a drag force $\propto -v$, and assume that we move through a large enough distance that we should use Newton's law of gravitation instead of just $F_g=mg$

You'll have $F_{net}=G\frac{m M}{r^2}-b v$

so knowing the position and the velocity at a given instant will indeed be sufficient to deduce the force

user280247

hmm...

user280247

but we have the expression for the force there. should it work without it?

user280247

Suppose we see a ball at 1m/s and x=2. What can we say about the force? @Semiclassical

3:15 PM

Nothing.

user280247

So we need 2 data points and F. I mean, 3 data points...

You certainly need some knowledge about how the forces depend on position and velocity

user280247

but why books say 2N pieces of information though? @Semiclassical

N= what?

You've gone from four data points up to 2N

user280247

total coordinates @Semiclassical

user280247

3:18 PM

yes I'm sorry XD

So, 2 for each particle?

user280247

in 1D, yes

user280247

We would need 2N data points and some expression of the force.

sure.

user280247

Well so I trust you, thanks...

3:20 PM

there's nothing to trust. if the force law is a function of position/velocity, then you need to know position/velocity for each of the N particles

but you shouldn't expect to be able to know the force without knowing the force law. i mean, do you expect to get the same force 2 meters above the moon as compared with 2 meters above the surface of the earth?

user280247

Yes but they didn't say the force (law) was known...

then they're being careless.

user280247

So if I rewrite the initial problem v=1m/s, x=2 and F=5N we can solve for the motion isn't it?

sure.

user280247

I guess they take it as obvious but it is an introductory book

user280247

3:23 PM

theoretical minimum (susskind)

I think the more important point is the principle that the forces can only depend on position and velocity

user280247

Yes, I didn't know that

so once those are known, then the forces are determined (in the sense that they couldn't be different than what they are, not necessarily that you'd know them)

user280247

They suppose those forces aren't function of time, for example

yeah

which is not a good assumption sometimes

user280247

3:25 PM

Fine. Thanks a lot @Semiclassical

np

3:38 PM

Ugh I've had this cold for two weeks and it hasn't been getting better. Maybe I ought to see a doctor

hi

1 hour later…

4:49 PM

hmmm

danielunderwood

weeee

ufff

danielunderwood

@ACuriousMind the job market is opening up for you. I've seen two postings with COBOL in the past day

@danielunderwood whoa

danielunderwood

One of them also wanted 5 years of z/OS experience lol

And a bunch of technologies that I've never heard of

4:53 PM

In a few years, they'll need a necromancer to get candidates for that job :P

danielunderwood

They can apply saying they're an endangered species...."I'm one of only 22 COBOL developers left"

I made a sad realization. I think my ability to work with C/C++ build tools is a bigger accomplishment than being able to work with the actual languages

@danielunderwood Is using the build tools harder than correctly using C++ templates? :P

I've only written pure C, so I can't tell

danielunderwood

I haven't had much trouble using templates, but I haven't used them a ton or for anything especially complicated either

Certainly beats passing around a struct with some sort of type info and a void * like I've seen though

All of those are better than working with opengl though. Or maybe I'm just not familiar enough with opengl

5:15 PM

Oh

I did something in OpenGL...ugh, 8 years ago (damn, time flies). It wasn't pretty back then, no idea how it looks now

danielunderwood

Yeah it's probably been 4 or so since I've worked on it. When I did, there were a lot of things using "intermediate mode" where you would do glBegin(); ... glEnd(); and draw vertices in between or something but it was meant to use buffer objects to hold the data. It was cleaner, but conceptually more difficult I think

I don't quite remember how it went, but it took me a bit to wrap my head around

Probably some of the most fun I've had working on code, but a pain as well

Yeah, it's its own kind of fun to see the result of your code so directly

I made a small physics simulation with balls bouncing off flat surfaces

Even had a command line and a small parser to place new balls and surfaces

...and it's written in Delphi, because that's what we learned back in school :P

danielunderwood

I found it really entertaining to be able to see my mistakes. I had camera movement and completely messed up the code with how movement was calculated

I've never even seen code written in Delphi lol

Though I had a link between it and pascal in my brain and sure enough it seems to be related

5:31 PM

@danielunderwood The syntax is much like Pascal, if you've seen that

procedure TSphereCollider.ProcLnColl(S : TSphere; L : TLine);
var RL,N0,R : Vector; d,t : Real;
begin
  RL:=AddVector(AddVector(S.O,Invert(L.P1)),Invert(MultSkal(L.Q0,ProdSkal(L.Q0,AddVector(S.O,Invert(L.P1))))));
      N0:=MultSkal(RL,1/Betrag(RL)); d:=Betrag(RL);
      t:=(-1)*d/ProdSkal(S.V,N0);
      R:=AddVector(MultSkal(S.V,t),MultSkal(N0,2*d));
      S.V:=MultSkal(R,Betrag(S.V)/Betrag(R));        end;

My old code for computing if a ball and a line collide

Dear god I had forgotten about the terrible pre-fix notation for my custom Vector struct

Also, I had not yet understood that variable names are allowed to be longer than 2 characters :P

I just need to get that thread undeleted and I'll have 3k rep...

danielunderwood

Yeah I'll take python or C++ over that lol

And I still get confused about 2 character variable names when doing math stuff. Like if I'm implementing an equation, do I just use the symbols in the equation or give them names?

eta

rho

phi

6:15 PM

25 rep away~~

danielunderwood

unless another question gets deleted!

Anonymous

user image

Anonymous

@enumaris Go celebrate ;)

@enumaris unusual, have never seen someone so motivated to vote questions for re-open. seems like it rarely succeeds anyway right? wondering what is your motivation?

ayyyy

@vzn I'm power hungry

I can now be Enumaris-3000

6:24 PM

@enumaris lol ok but seems like you might still be substantially hungry even after 3K o_O :P

danielunderwood

just 3000 is pretty unsafe

would be a shame if someone downvoted one of your questions/answers

Anonymous

@enumaris Not for long

lol

lol nice rep there hope nothing happens to it :P

guess youve been assimilated o_O

blog.codinghorror.com/the-gamification

fake internet points are important yo

Anonymous

6:27 PM

> It's the damn users. They've ruined every program I've ever created.

← worked 90m on 1st new medium post this morning, now has 7 views o_O

Anonymous

7 views is pretty good

Anonymous

(for one day at least)

:| lol thx man... early day s on building the media empire/ world domination... admittedly lagging eg bezos at this pt o_O

Anonymous

Medium is not that popular yet, but I like the UI

6:33 PM

@Blue think the ui for reading is ok but boy their article editor is really crappy as far as no power user control over it, seems to have zilch ability to edit the html directly @#%* argh geez o_O

but, site has many very elite writers/ intellectuals etc & many topnotch publications...

Anonymous

Ah, that's disappointing. I never really wrote anything on Medium

Anonymous

Yes, I did see some nice posts there from time to time

Anonymous

It feels like a Quora and Wordpress hybrid

actually some very cutting edge/ timely content/ writing but its not easy to surface the great/ quality/ relevant stuff. even a lot of hackers/ coders writing on it. probably lots of excellent physics content too, but havent checked yet. very diverse crowd. was hoping there would be bigger built-in audience but guess not, its bring your own audience :| ... the editor is impressive as far as wysiwyg/ ease-of-use but really needs something for power users :(

Anonymous

@vzn It doesn't have MathJax support I presume?

Anonymous

6:42 PM

Oh, and what's the link to your medium article?

@Blue it has an import feature but doubt it can be used for anything substantial.

@Blue thx for your interest, this is not for the fainthearted but ripped from the headlines (actually, has many ripped headlines)... medium.com/@vznuri/…

6:57 PM

Is it true that the total bound current in a magnetized material should vanish?

2 hours later…

8:37 PM

had a bulgolgi burrito for lunch...quite good

but a bit messy

danielunderwood

I had what I think was sour milk in my coffee this morning...very bad choice

8:54 PM

milk that went bad?

or is there a sour brand of milk?

danielunderwood

Milk that went bad. It was kind of on the edge and I thought it might be alright

lol

danielunderwood

I certainly hope there isn't a sour brand of milk, but who knows

don't trust that...

Black coffee solves all problems

danielunderwood

8:59 PM

Yeah I should have just went black coffee

Sometimes I do, but I usually like it with a bit of milk

I wish I just knew GSW :(

I do black coffee + 1 packet of sugar

takes away a little bitterness without bothering the taste of the coffee too much

I would put in 2

danielunderwood

GSW?

I feel like the milk mellows out the coffee a bit

Never with malk

9:08 PM

@Loong wow

user image

danielunderwood

That's like 20 miles above my head

I wish I just knew QFT

9:24 PM

So do I :p

9:36 PM

I feel like String theory should theoretically be able to be learned w/o QFT

You just won't get the historical motivation

u guys following this voter registration purge happening in Georgia rn?

Is it as serious as reddit has me believe

danielunderwood

I dunno. I've seen a bunch of stuff on reddit about it going back a couple weeks, but haven't seen it mentioned much on TV news. Though I don't really follow TV news all that much these days

now it's saying 300k voters were purged

danielunderwood

I have no idea what the intentions were, but it certainly looks pretty ugly with this timing. I don't think there's time for those people to re-register (if they're even notified)

election tampering is very serious

I guess it's not that serious anymore to a large portion of the public though...

danielunderwood

Yeah it's kind of sad when people start trying to abuse the system

9:47 PM

well "abuse the system" has been going on for a long long time

Gerrymandering is like...a national tradition now

Actively purging voters from registrations to prevent them from voting seems to be some next level stuff

danielunderwood

Yeah we had a bunch of gerrymandering controversy in my state. I think it ended up with the boundaries needing to be redrawn, but I'm not sure how that went

hmmm

danielunderwood

I did get an interesting piece in the mail yesterday about needing to protect our "God-given rights" to guns

You should see Kemp's ad's from the primary, the guy who did the purge

"God Given"...

where in the Bible are guns mentioned?

wat

Unless Founding Fathers who wrote Second Amendment = God?

9:52 PM

Brian Kemp's Badass Georgia Governor Campaign Ad

danielunderwood

lol

^ To the founders = God comment

That phrase has always annoyed me

and if that wasn't badass enough

Brian Kemp pro gun commercial!

danielunderwood

It also came with something about needing to be in congress to protect God

I don't mind arguments about "personal protection" or civil liberties...but God-given...come on...

to protect God...

danielunderwood

9:55 PM

mhm

when tf God ever needed protection from humans? U ever see that in the Bible? "And then God yell out, 'oh shit, come protect me with your guns!'"

nah nah, everyone knows that the founders were super christian and had god whisper the second amendment into their ears

Maybe an AR-15 can shoot down Lucifer?

danielunderwood

I haven't really been a fan of election mail, but this one left me quite informed of who I want to vote for

'Even by Georgia standards, the voter purge of late July 2017 was remarkable. In a single day, more than half a million people — 8 percent of Georgia’s registered voters — were cut from the voter rolls. Republican Secretary of State Brian Kemp, an avid supporter of President Donald Trump who has described himself as a “politically incorrect conservative,” oversaw the removals eight months after he’d declared himself a candidate for governor.'

9:56 PM

sounds legit

How a single person from this party is going to be re-elected is something else

I'm voting in minnesota, and there's the whole thing about the Democrat candidate for the attorney general

and tbh I'm not happy with him, and didn't vote for him in the primary

but uh

I think Ellison handled it as well as he could have

i may not totally like ellison on character, but on policy?

I got my mail-in ballot...I gotta fill that out and send it off

9:58 PM

not going to vote for a republican, so that doesn't leave a lot of options

He's got Bernie policies, I don't see a problem :p

right, that's my point

whatever issues i may have with ellison, are dwarfed by my issues with the policies that the republican candidate would go for

(though the other person we're all annoyed at is the previous democratic AG, who suddenly dropped out of the AG race in the spring to go for the governer's race...and lost)

Yeah, if the stories about him were true it would be a totally different ballgame, but the evidence seems to be in the other direction, recent stories comparing to court records etc

yeah.

It's not like the Roy Moore situation

haha

10:02 PM

of course, conservatives are wanting to make an equivalency with the Kavanaugh hearings

I'm not feeling super optimistic

"you trusted his accuser, but not ellison's? hypocrisy!"

The details are obviously the reason why one is ok but not the other, we know it's just a game to draw comparisons

Well, if u listen to Mr. Cheeto, it doesn't even matter if Kavanaugh's accuser was telling the truth or not

quoth "It doesn't matter, we won"

He has fashioned a new line based off that too: 'R's bring Jobs, D's bring Mobs'

10:05 PM

Coal mining jobs maybe...

We are in the midst of an alternative reality

Back to the Future 2 style

my adviser was so bummed 11/2016

so was everyone else in my department

When Florida went, that was the beginning...

The casual attitude to margin of error polling in the lead up, I mean...

painful

danielunderwood

I still had hope that he wouldn't be too bad in 2016

10:11 PM

really?

They were putting out talking points like 'America is divided' in the lead up as an excuse, that should have been a major sign, I think Bernie voters at least could see how careless it was to simply not appeal to everyone and actually try pick up R's in the suburbs (to the exclusion of others) as was part of the plan at one point

I mean...the dude floated the idea of a Muslim registry during his campaign...

I wasn’t caught as off guard by him being elected

Probably because Nate silver was saying right before that he did have a solid chance, even if the polls seemingly did give Clinton the better likelihood

I was extremely dissapointed

Keith on ABC's "This Week" - 7/26/15

danielunderwood

10:15 PM

Well I didn't really think he'd get away with much

boy was I wrong

(2015) the laugh at the end is just perfect

(People gave him a lot of flak after for saying he thought Clinton would win, but he was a lot more bullish on Trump’s chances than other election prognosticators)

@danielunderwood like you thought his advisers would reign him in or something?

The fact they really had no idea how .... far gone... the base was, and how susceptible they were to a figure like this, is also unreal

or you thought other Repubs would stand up to him?

10:18 PM

Should society let uninsured die?

2012 Republican debates, cheering it on

danielunderwood

Each of those was true at some point or another. I also originally thought the Electoral College may do something, but then I realized the electors were chosen by the party

Well neither of those have really been true. I thought that each of those would be the case at some point

I also thought that repubs may willingly impeach him to have Pence, but Pence has all but disappeared

My hope wad that Trump would eventually lead the GOP to imploding

I still hope for that, but that’s not going to get rid of the people he’s appointed

Trump may lose later on, but those victories are going to last

I think one has to assume the 60 million 25% of voters are simply too far gone and appeal to the other 50% of non-voters who are far more likely to vote D

Yeah. I mean, that’s always been seen as the drawback to “playing to the base “, that it puts a ceiling on which voters will go for you

...except, he won :/

I dunno what to expect on this midterm tho

This one was so significant, it is looking like another Lochner Era will be the long-term result of this one

10:32 PM

Yeah

And not just at the Supreme Court level

If they win the Senate, then I will not have lost all faith :p

Can’t say I’m optimistic there

I’m glad the House is looking encouraging

But the Senate seems unlikely

Unfortunately

10:54 PM

sad

danielunderwood

then more sad

on an uplifting note, I just saw this on a careers page

> We are innovative problem-solvers who believe water is the key for life.

At this point I think he can do w/e the hell he wants and his base and other repubs will always be there to support the Mr. Cheeto

danielunderwood

Yep. I also know someone who doesn't like him at all but "has to vote for the republican because he's a republican"

And a lot of voters here that think they just need to vote for all the republican candidates rather than looking into the candidates

-.-

well at least he still has a ways to go before he gets to Mao levels of power

Right-wing authoritarianism

Right-wing authoritarianism (RWA) is a personality and ideological variable studied in political, social and personality psychology. Right-wing authoritarians are people who have a high degree of willingness to submit to authorities they perceive as established and legitimate, who adhere to societal conventions and norms and who are hostile and punitive in their attitudes towards people who do not adhere to them. They value uniformity and are in favour of using group authority, including coercion, to achieve it. == History == The concept of right-wing authoritarianism was introduced in 1981 by...

John Dean's discourse on Authoritarian Personalities

I know of very few ways to make sense of the insanity other than this :p

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