The h Bar

Cows

00:01

Hi heather. How are you

@hea

@heather

heather

good @Cows how about you?

oh, day just got better

Cows

I am doing pretty well. Just stopped at a coffee shop. Figured I'd hang out on here for a bit

heather

months copy of physics today came =D

@Cows nice.

Cows

00:29

At the beach now. Going to listen to some music and walk on the beach woohooooo. Happy times

Mockingbird

01:00

Hey, everyone. Do self-similar manifolds show up in string theory?

ACuriousMind

@Mockingbird What's a "self-similar manifold"?

Mockingbird

@ACuriousMind Fractal manifold?

ACuriousMind

@Mockingbird I know what a fractal is and what a manifold is, but fractals are not manifolds.

Cows

01:26

Walking aroubg Hermosa beach. Oh the memories. Oh life i can't say how i feel right now. I can smell the air. I feel like there is greatness to come. Something amazing.

I know i will be better than anyone who has everblaughed at me or not taken me seriously.

Lolz i've been sized up by all sorts of people and laighed at openly to my face and been made clear i don't belong a few times. It's ok i really don't I'm better.

I can feel the breeze.

I was going to bring a complex analysis text to the ocean but i figured i'd just hang out alone.

I don't drink alcohol anymore and have significantly curtailed companionship to improve my life

Money is quite important. It allows you to be able to sleep and think. And everything else

I love math. I swear. And I can do ad code it. Atnleast if i am getting paid.

Eh running out my mind on here.

I will be driving back home soon. Can't be out late. Have a conference call in a few hours , then will code all night sleep and repeat as long as i am getting paid

Any camels or donkeys in hermosa? Come hang out. I might even buy you a soda

ACuriousMind

01:57

@davidphysics I see your neurons aren't fuzzy anymore? ;)

0celo7

02:22

what's up

Semiclassical

evening

0celo7

me trying to explain elliptic regularity:

Cows

03:00

Stopping in el segundo for food

Buying some Mediterranean food

Cows

03:22

Ok have my Mediterranean food, bought some frozen fruits, healthy juice for the night(el codito hehe) and yeah heading home.

Cows

04:01

ok just ate! Elated!

0celo7

04:58

this should probably be "subconverges", right?

I can't read.

Lagranian

05:11

@user685252 Hi bro =)

0celo7

05:47

@JohnRennie have you done jury duty?

John Rennie

@0celo7 Yes, it was ... eye opening

0celo7

is youtube.com/watch?v=94zkBGm1IoU a good way to get out of it?

Secret

There exists things in itself, and these are the nomenon

John Rennie

@0celo7 Jury service is worth doing for the experience.

I learned a lot about my fellow humans.

If I was asked again I would do it in a flash.

0celo7

@JohnRennie the more I learn, the more I develop my plans for mass extinction

Secret

05:50

I used to have jury offers, but probably because everytime I am full time, I never get the chance to attend it

0celo: Your plans of mass extinction will never be grander than mine :P

John Rennie

Yes, I'm reluctantly being pushed to the conclusion that the extinction of mankind would be no great loss to the universe. The best approach is to stop thinking about it and get on with having a good time.

The sociological equivalent of shut up and compute

Secret

I don't just want humans to go extinct, I want the whole universe to be stuck at the true vacuum forever and ever. This is because the essence of shutting up someone forever is to erase them from existence so they cannot even scream

(Bullying memories can turn anyone into psychopaths)

Never let perfectionism to mix with obstination, for this unholy combination will create and destroy all

[End Godmodding]

0celo7

grr

I hate engineers

$k_f$ means FIN not FLUID

USE BETTER NOTATION

davidphysics

07:57

@ACuriousMind Nope! I don't think I like the username though...

Mithrandir24601

@0celo7 Hmm... Or maybe the problem isn't the engineers deciding to do this but the people doing fluid dynamics deciding to do this? :P

Cows

08:23

@davidphysics checked out your code. good stuff. I also snooped around your website. Great presentation.

@da

Phase

@JohnRennie I mean being realistic, what would be a great loss to the something enormous, unfeeling and unthinking. I think wiping out the humans could lead to a potentially very boring universe though :(

Cows

@davidphysics someday I hope to populate a personal page with good content.

John Rennie

@Phase I'm not sure the word boring has much meaning if there isn't anyone around to be bored :-)

Phase

Well if there's a higher power he'll probably just boot down the universe and load solitaire instead

John Rennie

I know we're physicists not engineers, but just take a look at this! Not that I will ever be able to afford one ...

Mr. Xcoder

08:27

ಠ_ಠ That looks quite expensive

Cows

It looks like a great car.

@davidphysics sometime may be you can teach me how to do black hole sims with ray tracing. I've seen videos of this and have never done it

@davidphysics is it Newton - laplace or Einstein equations you are starting from?

@are you using webgl and threejs for this?

@davidphysics ^^

At any rate just curious nothing exotic going on

Phase

$\int_c 🐲 \cdot \vec {d🙉} = \int \int_s \nabla 🐲 \cdot \vec {d🙈}$ the closed 1d monkey to 2d monkey theorem

aww..

That'll have to do.

Slereah

08:43

Is the donkey the boundary of the monkey

Cows

lol

Phase

The boundary of the money is obviously 🐒

Jesus @Slereah come on

0

Q: Can I do double slit experiment with Electrons or Photons?

Young's double slit experiment. The phenomenon of interference was first observed and demonstrated by Thomas Young in 1801.

Trying to find a user with more than 1 rep

: p

Cows

Dicking around with Euler Gamma func

I must try to learn complex anal

It's time I know the basics of this

Phase

Complex anal is indeed a necessity for any student

Cows

yeah I have tried to avoid it a few times, but everytime I hear things like poles, branch cut, analytic continuation etc I usually have a dark cloud of uncertainty around my head, but I want to fix that

I meet complex analysis everywhere, I can't run

Although I had to do some assyptotic series and review taylor expansions, and optimal approx before diving in

learned some integration tricks and some techniqes for making taylor exps help with anal cont

baby steps lol

but yeah right now I am looking at some tricks with Euler Functs

and how to scale hor and vert edges

*horizontal and vertical edges.

*Euler Gamma functions

still there?

John Rennie

08:56

@Phase I'm not sure what to do about that. It's obviously insufficient effort but I'm reluctant to just close with a comment effectively saying don't be lazy when it's a new user.

Phase

Link em the policy?

Mithrandir24601

@JohnRennie Surely there's something that qualifies as a duplicate somewhere?

John Rennie

@Mithrandir24601 I'm not sure there is. There are shedloads of questions about the Young's slits - both light and electrons - but nothing quite like the question asked here.

Mithrandir24601

@JohnRennie Hmm... I'd make the argument that if other questions ask about it while referring to using either photons or electrons, that's good enough, but that maybe isn't so likely then :/

You could go along the 'not useful to the site' line...

Phase

Maybe if it was edited to

"can you do the double slit experiment with anything? Like electrons and photons?"

that could open the gate for a more conceptual question?

Mithrandir24601

09:05

It's not like I've ever seen a question on Worldbuilding that the answer could be easily found (other than duplicates) so I've never actually had to come up with a comment for this one :/

Phase

09:30

-1

Q: Speed of pendulum needed to make one revolution

I've got an exam coming up and this is one of the practice questions that I've been having trouble with Attempt All the energy of the system is located in the gravitational energy of $m_1$ at the top. $$E = m_1gh = m_1gL$$ Right before $m_1$ hits the spring, it has all the potential energy f...

homework-and-exercises newtonian-mechanics classical-mechanics energy

I dont understand the diagram (???)

I cant resolve the length of the pendulum and the apparently changing pivot point in my head

O

Oh ok, I get it.

The dot is actually intentional, and it winds around it?

Balarka Sen

09:58

What in the flick's name happened to the starboard

@0celo7 It's up again.

davidphysics

@Cows Thanks! Geodesic equations, it is much easier than the Einstein equations but much harder than Newton

@Cows you're referring to this image right? mathandcode.com/img/blackholesmaller.gif

For that one I actually used Mathematica to write out the geodesic equations in 3 dimensions... they're very ugly and unwieldy, but if you have a camera in 3-space your positions/directions are all 3-dimensional vectors.

Secret

10:18

360 cameras are pretty common now

Emilio Pisanty

10:53

@ACuriousMind yeah, fire & lightning would do the trick

Slereah

@JohnRennie arxiv.org/pdf/1205.1616.pdf

it's only for a shell though

John Rennie

@Slereah aha! thanks :-)

Slereah

I looked up the solution for classical gravity on a torus

It's ugly

mathpages.com/home/kmath402/kmath402.htm

I think it's related to the toroidal harmonic function, which is very ugly indeed

really anything with a torus is gonna be ugly because the toroidal coordinate solution of the Laplace equation is awful

It's also not separable

This paper has the Weyl metric in toroidal form, though

Which might be useful

Secret

13:47

Emergence – How Stupid Things Become Smart Together

►

parvin

hello

guys, what is energy? can some one explain this to me?

I was wondering, when we say current is flowing and each charge needs a unit of energy to move, is the charge (mass, electron) actually moving or is it the energy that they are passing to each other?

then it came in to my mind that, then what is energy?

and what's the difference between energy and force?

ACuriousMind

@parvin See physics.stackexchange.com/q/3014/50583, physics.stackexchange.com/q/138972/50583 and their linked questions.

parvin

thnks

0celo7

14:10

@ACuriousMind Sunday?

ACuriousMind

@0celo7 Got an RPG session there whose duration I cannot predict. This weekend is pretty full for me

Slereah

neeeerd

What system?

ACuriousMind

Either The Dark Eye or Dungeon World, depending on who shows up - we play our long-running TDE campaign if everyone is there, otherwise DW.

0celo7

14:25

@ACuriousMind Hm.

The space of Lipschitz functions is probably a Banach space

I feel like this was something I knew in Advanced Calc 1

Slereah

@0celo7 when you do some solution in GR

How do you pick the boundary conditions for the metric

Is it like

Asymptotic flatness

or is that not enough

or does the unique solution suggest itself if it's static

I dunno

Abcd

14:45

Why am I unable to reach this site:

physics.qandaexchange.com

The error shown is: "Fatal error: Call to undefined function session_start() in /home/public/qa-include/app/users.php on line 146"

Slereah

@0celo7 plz respond

Anonymous

@Abcd The site is down it seems

Anonymous

It has happened before

Slereah

Oh wait

I guess all you need is a choice of coordinate system

I think

0celo7

15:06

@Slereah idk i don’t know how to solve the global Cauchy problem

I only Know the local thing

0celo7

15:24

@Slereah asymptotically flat is good enough to get a GHMD though

Slereah

What's a GHMD

Sir Cumference

Morning

0celo7

@Slereah globally hyperbolic maximal development

Slereah

o

0celo7

The proof uses Zorn’s lemma so don’t trust it

Slereah

15:25

I'm trying to find the answer to that dude

that asks the metric of a torus

It's not pleasant because I have to use toroidal coordinates

Sir Cumference

Sigh, idiot phone

Slereah

The classical gravity of a torus is already awful

With no closed form solution

0celo7

I wish I understood the phenomenology of the Cauchy problem better

Sir Cumference

@dmckee I wonder if they also call it decimal comma instead of decimal point?

Secret

15:59

So, somewhere when I am wandering in the nether, I proposed in hsm about organising a panel discussion on the history of mathematics. Hopefully it won't get downvoted to oblivion

more details later

ACuriousMind

@SirCumference Yes.

Cf. the German Dezimalkomma.

Secret

It feels like I could separate this as Dezimal komma which basically reads like Decimal Comma, which cause me to wonder, is the German for point and fullstop "komma"?

ACuriousMind

No, Komma is German for "comma".

"point" is Punkt.

Physics Meta

16:42

-1

Q: What are the criteria for journals being "reputable"

There are a lot of journals that cover or intersect with physics. What are the criteria for reputability?

discussion reputation

Abcd

17:07

@JohnRennie How do I derive results for entropy changes of system and surrounding during irreversible processes?

John Rennie

I don't think there's a simple answer to that.

You can use dS = dq/T

Abcd

@JohnRennie It's $q_{rev}$.. That's why I didn't know how to even begin.

John Rennie

In an irreversible change the system and surrounding may have different temperatures so the entropy change for each will be different i.e. the net entropy change won't be zero.

CooperCape

boo...

Abcd

That simply follows from clausius inequality. (equality holds only for reversible processes)

CooperCape

17:10

Just a quickie ummm can I just stick a jquery command (for completeness it's $.isNumeric(num)) into my js code? Does it require any importing or anything?

Also incase there's an easier way of doing this is there an opposite function of isNaN() in js?

John Rennie

!isNaN() ?

CooperCape

I tried that but to no avail...

umm

currently looks like

John Rennie

@Abcd I don't know. I would have to Google it. It would help to have a specific example, but not now as I'm close to quitting for the day.

CooperCape

`while (!isNaN(inpt.charAt(findx - i))) {
testnum += 1;
i += 1;
}`

John Rennie

Give us an example. What is inpt i.e. what string is it?

CooperCape

17:15

Okay

var inpt = document.getElementById("inputfunction").value;

Which gets the inputted string from a html text box.

0celo7

CS chat again

3

CooperCape

Then var findx = inpt.search("x"); (as you can probably tell) finds the number value at which x is found

Sir Cumference

@ACuriousMind Neat

CooperCape

So when I have isNaN in the while loop it counts the number of letters before x... (Inputting '1abcdefgx' gives an output of 9, for example)

Sid

@CooperCape and x is another string?

CooperCape

17:18

However I want it to do that for letters not numbers

it's a character in the string

from inpt

John Rennie

This prints "3":

var inpt = "000a111";
var findx = 6;
var i = 0;

while (!isNaN(inpt.charAt(findx - i)))
{
i += 1;
}

WScript.echo(i);

CooperCape

Ahhh okay...

hmmm actually

Sid

@JohnRennie Doesn't that simply print all the characters in the string?

(What does WScript.echo do?)

CooperCape

so the where '6' is found is actually the final '1' right

Which means that if 'i=1' to begin with then...

yes!

nice one thanks <3 :D

Sir Cumference

I need ideas for a userscript to write

What would be a convenient change for some website?

John Rennie

17:22

@Sid I'm running the Javascript as a standalone app using cscript. The WScript variable is an object provided by the cscript interpreter with useful mthods like echo.

Sid

@JohnRennie Yeah, what does echo do?

John Rennie

The echo method just prints the argument to the console.

Sid

@JohnRennie So, it would just print the final value of "i"?

CooperCape

John that works perfectly...

John Rennie

@Sid Yes

CooperCape

17:23

(Aside from if the input begins with numbers then x it crashes the tab but whatevs...)

minor details...

John Rennie

@CooperCape Physics, dirty jokes and Javascript advice! :-)

4

CooperCape

Wow you really are adding to your portfolio...

Just change your 'about me' to that phrase...

Sid

@CooperCape What was the objective of the code that you wanted? to find out the position of "x"?

CooperCape

Nah I wanted to get the string of all numbers before 'x'

so now if you type in say abc12345x it outputs 12345

John Rennie

@Sid Javascript is essentially a form of masochism - the IT equivalent of flagellation. So I assume CooperCape's objective is to inflict as much pain on himself as possible :-)

Sid

17:27

@JohnRennie lol

CooperCape

Possibly the weirdest phrase I've read in a while... ummm... yeah...

John Rennie

@Sid you think I'm joking :-)

CooperCape

@JohnRennie If you don't have '()' in literally every possible place and end each line with ';' are you even writing code? smh...

John Rennie

I've written pretty much every language there is, starting with OS360 assembler on an IBM mainframe.

Sid

@CooperCape if the input is, say 123xbi34, then, the output will be 123?

CooperCape

17:31

@Sid Theoretically, yes. However because 123 is at the start of the string the while loop breaks and crashes the tab

I'll just stick in a cheeky if clause and sort it out

@JohnRennie Oh wow... that's... that's a lotta languages...

Sid

if I understand correctly, then, JR's code will print 2 for that...

CooperCape

Mine's slightly different

I think

Yeah it is

because after that part I have a line that says

`xcoeff = inpt.slice(findx + 1 - testnum, findx);`
`document.getElementById("output").innerHTML = xcoeff;`

Actually two lines wowww

probably not the nicest looking slice() ever but I can reconfigure that later...

John Rennie

@Sid my code snippet was just a quick hack to test the principle. It just finds the index of the first digit preceding the "x".

CooperCape

John's code taught me that testing the while loop for !isNaN(inpt.charAt(findx - i)) when i=0 and findx returns NaN will stop the while loop before it begins...

Sid

@CooperCape meh. No one cares about "beauty" if it is working

CooperCape

17:36

Yeah true but idk... maybe if I put it in brackets it'll look prettier...

hmmm

Sir Cumference

@CooperCape Want to hear a joke?

CooperCape

Uhhhh sure

I'm intrigued

Sir Cumference

They say Newton was so good with forces, they named a unit of force after him. Why was he so good?

CooperCape

Ummm...

Slereah

he was very strong

Sir Cumference

17:44

Because he knew tons (newtons) very well

Slereah

He could benchpress 900 pounds

Sir Cumference

Ok sorry...

CooperCape

Okay I quit.

I mean

what

Oh wow I just understood it... I won't lie. It was better when I misunderstood it.

John Rennie

Does that joke really merit four mentions on the star board?

CooperCape

Newton was a star..

Sid

17:46

@CooperCape That ^

CooperCape

GMm/star^2

Sir Cumference

What is with the stars

CooperCape

idk...

How has the last 4 minutes got 9 star messages...

okay now 10

um

John Rennie

When everyone has gone to bed I will apply some detox to the star board ...

CooperCape

Personally I think we need to keep Phase's $\frac{d}{d \mathrm{dragon}}$ maths for as long as possible

0celo7

17:51

wtf happened

CooperCape

no stahp

if I delete these messages...

0celo7

what is wrong with you people

CooperCape

will starboard get cleared up?

Sir Cumference

Just came back, jesus...

CooperCape

kinda

whatever that means...

Sid

17:55

what on earth?

Gabriel Romon

yo bruvs

you been flagging ?

Sir Cumference

:41212726 wait what'd he say?

Gabriel Romon

@0celo7 your momma post got reported

CooperCape

What on earth...

Sir Cumference

How did 0celo get banned...?

CooperCape

17:59

What's wrong with that?

Sir Cumference

Did someone actually get offended by that?

CooperCape

Probably our seriel star-er

Gabriel Romon

@SirCumference someone flagged it

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