The h Bar

AccidentalFourierTransform

4:00 PM

::ahem::

0celo7

@ACuriousMind implying Germans know how to BBQ

ACuriousMind

@AccidentalFourierTransform ::hands over lozenge::

AccidentalFourierTransform

Dec 17 '16 at 17:10, by AccidentalFourierTransform

t̥̥͇ḫa͓̘̣͜ṋ̖͔͝ͅͅk̳̻̺͉̝̯͙s̝̦͕̯ͅ

ACuriousMind

@0celo7 I have a pet Texan who does it for me

@AccidentalFourierTransform Touchè

Yashas Samaga

0

A: Which body has high moment of inertia (rigid body or soft body)

The moment of inertia of a substance is given by $$I = \int r^2 dm \tag{1}$$ The immediate conclusion you can infer from the above formula is that moment of inertia does not depend on the elasticity of the object, it only depends on the mass distribution. Intuitively, the yolk (yellow part) is...

What's wrong with the answer?

AccidentalFourierTransform

4:02 PM

the thing about the moment of inertia

Yashas Samaga

@AccidentalFourierTransform ?

0celo7

@ACuriousMind Implying they know how to either

You want a Memphian

AccidentalFourierTransform

@YashasSamaga I was kidding. I did not, and will not, read that post. As you can see, Im very busy with my businesses (i.e., Im watching a youtube video :-P )

Mostafa

@YashasSamaga Maybe because people find answers that say there's no answer boring. Just like proofs that prove there are no solutions.

2

0celo7

@ACuriousMind you know, I'm a cat

Slereah

4:07 PM

Jost came in the mail

Hurray

0celo7

Would you BBQ me?

@Slereah pic?

Yashas Samaga

@anonymous physics.stackexchange.com/questions/51281/…

ACuriousMind

@0celo7 That's a weird question

AccidentalFourierTransform

@0celo7 ACM is a vegetarian. We discussed that already...

Slereah

0celo7

4:10 PM

@ACuriousMind You're avoiding answering it

ACuriousMind

@0celo7 That's an astute observation

0celo7

@ACuriousMind jesus, you'd actually eat me?

@Slereah don't you dare keep it next to those physics books

Slereah

Well math books are two shelves down

But GR is the shelf at arm level

0celo7

Ok, just GR books?

no QFT garbage?

i.e. lies?

anonymous

@YashasSamaga What?

Slereah

4:12 PM

QFT is the shelf below

0celo7

I can see Birrel and Davies right there

Yashas Samaga

@anonymous I was trying to explain that earlier.

Slereah

Birrel and Davies is GR enough

It is the baby of GR and QFT

Yashas Samaga

@anonymous that liquids which are inside a sphere are not counted while calculating moment of inertia

0celo7

So it should have been euthanized

AccidentalFourierTransform

4:13 PM

@Slereah I think I read Carlip's 2+1 QG. Is this book the one that ends with "we leave it to the reader to generalise this to 3+1."?

Slereah

Lemme check

anonymous

@YashasSamaga -_- That is for low viscosity fluids. Yolk has high viscosity.

0celo7

@AccidentalFourierTransform you read all of it?

Yashas Samaga

@anonymous If you count it completely, you are cheating as well.

Slereah

"I leave this as an exercize to the reader"

yep

Mostafa

4:14 PM

@0celo7 String Theory....Quantum Gravity....Are these really Physics books? ;)

Slereah

Last exercize of Visser was "quanticize gravity"

anonymous

@YashasSamaga How ?

0celo7

@Mostafa yes.

Yashas Samaga

@anonymous To explain that, I took another case where there is no frictional force b/w the liquid and the shell. You still kept saying the same.

AccidentalFourierTransform

@0celo7 no, some of it, for the lulz

0celo7

4:15 PM

They are most certainly not mathematics

Physicists who say string theory is math do not know what math is

Yashas Samaga

@anonymous Write the moment of inertia equation in the vector form. Tell me how you'd include the MoI of the liquid.

anonymous

@YashasSamaga Doesn't matter whether you take the yolk as friction-less or not the fact remains the same that boiled rotates faster.

Yashas Samaga

@anonymous It wasn't related to the boiled egg. Somewhere you started claiming that frictionless liquid would have to be counted in MoI calculation. That changed the topic and I started complaining about it.

Mostafa

@0celo7 And mathematicians who say String Theory is physics don't know what physics is.

0celo7

@Mostafa except for the fact that mathematics > physics (clear), so mathematicians get to decide what is physics or not.

anonymous

4:17 PM

@YashasSamaga No, I said liquid has to be counted for its degrees of freedom and energy dissipation.

0celo7

Now, you can say that it's neither.

I could be convinced of that.

Yashas Samaga

@anonymous for that I said, you shouldn't incldue it in MoI calculation because you'd double count the effects. You argued no, it had to be included.

anonymous

@YashasSamaga If you want to do it accurately then you have to take moment of inertia of the liquid also. And no, it would not double count the effect.

Yashas Samaga

I said "If you assume that only the shell rotates and the liquid slowly starts and tries to damp the shell's rotation. You shouldn't include the liquid in the moment of inertia."

You said "The liquid MI matters a lot."

0celo7

@Slereah are you gonna start reading?

Sir Cumference

4:19 PM

howdy

Yashas Samaga

@anonymous Firstly, the liquid is not rigid. You cannot calculate the moment of inertia.

Slereah

Fugg I'm sick and I woke up at 6 AM

user228700

@JohnR: What is uup?

Slereah

Ain't got head for analysis today

Sir Cumference

@Slereah Cold?

Yashas Samaga

4:20 PM

Either you have to assume that the liquid moves in sync with the shell or it doesn't.

Slereah

yeah

Yashas Samaga

If it doesn't, then you cannot calculate the moment of inertia.

Sir Cumference

Dang, same

Slereah

That will teach me to go and meet people

anonymous

@YashasSamaga You can, experimentally with some error.

Slereah

4:20 PM

People are full of germs

Yashas Samaga

@anonymous huh, you added the experimentally term now...

0celo7

some guy is doing online gambling in physics lecture

seems like a good idea

Slereah

He's getting a physics degree, isn't that a thrilling enough gamble of his future for him

John Rennie

@Kaumudi.H the brother's mother in law (my aunt in law?) has just phoned to say her computer is bust. So as the family computer nerd I now get to drive 200 miles to Somerset to fix it!

0celo7

@Slereah this is engineering physics

@JohnRennie what? can't you say that you can't take off from work?

John Rennie

4:22 PM

Literally just phoned, she phoned about ten minutes ago.

user228700

@JohnRennie Oh, that sucks :-( (If it does, I mean. Are u going to enjoy it?)

0celo7

that's what my parents do when I ask them to visit (I cri evrytime)

anonymous

@YashasSamaga I thought you are intelligent enough to understand that. Obviously I don't expect you to calculate MI sitting on your couch with just pen and paper without knowing the physical properties of the yolk.

John Rennie

@0celo7 she knows I can work from anywhere there's an Internet connection :-)

0celo7

@JohnRennie dammit man why did you reveal that!?

John Rennie

4:23 PM

@Kaumudi.H I'll use it as an excuse to visit family. My niece has been nagging me to install a bluray drive in her laptop so I'll do that at the same time.

0celo7

huh?

how does a blu-ray drive fit in a laptop

user228700

@JohnRennie Cool :-)

John Rennie

@0celo7 ??? you can get laptop bluray drives

0celo7

@JohnRennie how thick are they?

how is there room in the laptop

John Rennie

For example this one.

0celo7

4:25 PM

god, ebay

Mostafa

@0celo7 Maybe in the future popular-scientists can take care of it.

John Rennie

You have to be careful though as laptop optical drives come in thicker and thinner forms. A lot of the cheaper laptop blurays are the thicker version that won't fit all laptops.

@0celo7 that's the one I bought for my niece

0celo7

@JohnRennie my laptop doesn't even have a CD drive

how should it fit in there?

John Rennie

Jobs had this obsessive hatred of optical drives. I don't know why he felt that way.

0celo7

and why does one need blu ray anyway?

@JohnRennie Because one doesn't need them?

John Rennie

4:27 PM

But he managed to get the optical drives removed from almost all the Apple range.

@0celo7 because my niece has a large collection of films on bluray

0celo7

tell her to get a TV with a bluray player

user228700

..? Won't that cost significantly more than a drive?

0celo7

70 inch curved TV

John Rennie

She has a TV with a bluray player, but she wants to watch films in her room with her friends and Mum won't allow her a TV in her bedroom.

Mostafa

@0celo7 mine has a DVD drive. I have used it only once or twice (bought it in 2011)

0celo7

4:28 PM

@Kaumudi.H cost shmost

@Mostafa agreed. I bought an external one that I have used exactly once in two years

John Rennie

@Kaumudi.H bluray drive £25, TV £500 :-)

0celo7

What good TV costs 500?

user228700

@0celo7 I'm literally broke. Oh, hang on, yep, almost; I've Rs. 20 in my purse.

John Rennie

@0celo7 The better of the Samsung budget TVs cost around that

For £500 you can get a pretty good 42" or thereabouts TV

0celo7

@JohnRennie why will mum allow a laptop but not a TV?

I made that argument to my parents constantly and they never budged

Ridiculous, really

John Rennie

4:31 PM

You're asking me to explain my sister in law's logic?

0celo7

yes

you're old

rather fatherly

John Rennie

Yes, but I'm a nerd and believe that all children of any age should have large quantities of laptops, phones, etc, etc

Yashas Samaga

How viscous is egg albumin relative to honey?

0celo7

@Kaumudi.H How much is that in $$$

user228700

@0celo7 No man who buys 2 laptops a month is qualified to be known as "sane" and "fatherly" :-P

0celo7

4:32 PM

@YashasSamaga far less

John Rennie

I have been battling for the last 15 years to persuade my brother and sister in law to let me give computers to my niece.

Yashas Samaga

I am freezing a bottle of honey atm

0celo7

@JohnRennie my 5 year old nephew got an iPad

John Rennie

Good for him!

Yashas Samaga

to see if the frozen honey rolls down faster than the unfrozen one

0celo7

4:32 PM

Because he was being bullied on the bus for not having tech

user228700

@0celo7 $0.3

John Rennie

A friend of mine's daughter was using an iPad at age 1

0celo7

Back in my day we played with sticks, until I almost took out Marvin's cousin's eye

John Rennie

And was pretty good with it.

0celo7

@JohnRennie Oh, my other nephew (2 or 3) was using an iPad as an infant

I'm saying the other one has an iPad

user228700

4:34 PM

I used to be an expert at building a house using lego blocks.

John Rennie

Good - I approve whole heartedly

0celo7

like he takes it to school and stuff

Slereah

How does one use an ipad as an infant

You can't breastfeed an ipad

2

0celo7

@Kaumudi.H :(

John Rennie

@Kaumudi.H I used to build houses with Lego :-)

@Slereah eh?

@Kaumudi.H: anyhow, I'm going to set up a shiny new PC for my aunt in law rather than trying to fix her old one. I did try and persuade her to have a laptop but she was insistent she wanted a PC.

user228700

4:36 PM

x'D Awesome! Has she ordered a new one?

John Rennie

No, I'll give her one from my pile of PCs.

0celo7

ok, I never said john was sane

he is clearly not...

user228700

U have a pile of PCs as well?! What the hell...

user228700

@0celo7 Yeah, OK x'D

0celo7

@BalarkaSen Does "affine diffeo" mean anything to you?

John Rennie

4:38 PM

@Kaumudi.H no-one wants PCs these days (except aging aunt in laws) so I have a stack of unwanted ones. I sold some on ebay a while ago and got £5 each for them!

Balarka Sen

nah man. perhaps a diffeo which preserves the affine structure?

user228700

@JohnRennie £5 each?!

0celo7

@BalarkaSen By "affine structure" do you mean "connection on frame bundle?"

John Rennie

@Kaumudi.H Yes, that's all anyone would pay. Though admittedly these were fairly old with slow CPUs by modern standards.

user228700

...OK, I see.

0celo7

4:40 PM

@JohnRennie Hmm.

I want a PC

I need a monitor

Something to get me started

John Rennie

@0celo7 for what application? Serious number crunching? If you just want a big screen why not just connect a screen to your Macbook?

0celo7

@JohnRennie gaming

I have to play the witcher 3

AccidentalFourierTransform

"have"

0celo7

HAVE

AccidentalFourierTransform

"HAVE"

John Rennie

4:41 PM

@0celo7 Ah OK, so you need something that you can stuff with a mofo graphics card?

Balarka Sen

@0celo7 I think it's having a flat connection. The definition I know of is a smooth manifold where the transition maps are affine maps

0celo7

$\mathfrak{HAVE}$

Balarka Sen

aka translations

user228700

@0celo7 Can't even read that.

Yashas Samaga

@Kaumudi.H do you have the extension?

0celo7

4:42 PM

@JohnRennie Yes. I have more than enough money from my job to buy one. But I don't want to commit $1500+

I don't think I'll get that much use out of it.

user228700

@YashasSamaga Oh, yep, I have MathJax, thanks :-) The font sucks is what I meant...

0celo7

@BalarkaSen By affine diffeo I mean one that preserves the connection

But if you don't know about those, never mind

Balarka Sen

I got that

0celo7

I have a claim that any two cylinders, tori, Möbius bands, or Klein bottles are affine diffeomorphic

John Rennie

@0celo7 The only PCs I know well are the Dell range. In your place I would look for an Optiplex 7010 or 9010 with a big i7 in it. Those PCs have a slot for a graphics card. You should easily get one for < $500, though you'll then need to buy the graphics card.

Balarka Sen

4:44 PM

shrug man

0celo7

@JohnRennie Yeah, I don't know if I should do the whole thing custom or get part of it premade and then insert a permium GPU

I probably don't need a $400 CPU, but I might be wrong.

user228700

@JohnR: They cleaned my tank all too well--the water now smells excessively of bleaching powder >.<

John Rennie

@0celo7 If you want it on the cheap buy a second hand PC on ebay.com and buy the card separately.

@Kaumudi.H bleach? dysentery? Bleach isn't so bad :-)

user228700

:-) Well, yeah, I suppose.

0celo7

@JohnRennie I might be getting $4,000 this summer...hopefully...I will start considering it if that happens

John Rennie

4:47 PM

@0celo7 I can look on ebay.com to see if there's anything I'd recommend ...

0celo7

@JohnRennie I've been told not to trust Russians or ebay

Balarka Sen

russians are good

John Rennie

Wow, look at this for $320

That's a serious mofo CPU in that box.

Slereah

That's pretty expensive just to look at it

0celo7

only 8GB

@JohnRennie where does it say?

John Rennie

4:50 PM

Memory is cheap

Yashas Samaga

I have a 300$ PC with i5, 8GB DDR3 RAM, 1TB

custom built

usually custom built PCs turn out to be costly

0celo7

@JohnRennie The case is tiny

AFAIK modern gaming GPUs are bricks

John Rennie

@0celo7 it says the CPU is an i7-3770

@0celo7 yes, it only takes half height cards so it wouldn't be any use for you to game on. I just couldn't believe such a powerful PC is going that cheaply.

user228700

I'm off. Bye, everyone :-)

John Rennie

You want a CPU like that in a tower case.

@Kaumudi.H Bye

Yashas Samaga

4:53 PM

imgur.com/a/K5Ibv

that's my computer

decent and simple

no dedicated GPU

anonymous

@Slereah Actually you can. However, I doubt that will be of any nutritional value to the ipad :P.

0celo7

@JohnRennie ok let's think seriously about this over the summer :)

John Rennie

@0celo7: there you go

0celo7

wtf

John Rennie

Though that will be more expensive.

0celo7

4:54 PM

how is that so cheap?

$350?? Isn't the CPU that much

i7-4770

John Rennie

That's the starting bid. I'd guess it will sell for nearer $500.

0celo7

@JohnRennie Do people have bots that snipe bid at 0:01 ETA

Yashas Samaga

if a processor costs 1000$ on the retail market, you'll get it for 200$ at a wholesale market

Slereah

ahahah

Yashas Samaga

you'll get it for 100$ if you buy it from a manufacturing hub

Slereah

4:56 PM

@YashasSamaga was tricked by the dollar signs

John Rennie

@0celo7 Allegedly there are bots that will do that, but I always bid manually and I bid with about 5 seconds to go.

0celo7

good god

John Rennie

It's all quite exciting really :-)

You should see my ebay feedback. I must have spent £50 grand on ebay over the years.

Not all for me - I used to buy computers for my company on my own ebay account.

Emilio Pisanty

Yo folks

anyone know how to download the source for this one?

arxiv.org/abs/hep-th/9609109

I'm curious to know what "plain TEX file" means on an arXiv eprint from '96.

John Rennie

@EmilioPisanty Download the source here

Emilio Pisanty

5:03 PM

@JohnRennie yeah, but then what?

it downloads as a file without an extension

normally one adds .tar.gz and it opens right up

John Rennie

It's just a text file. Open it with any text editor.

Emilio Pisanty

this one's not working, though

John Rennie

Rename it to .txt or maybe .tex since it's TeX source code.

Emilio Pisanty

@JohnRennie ah, so it is

duh

I thought it'd be a gzipped tex file as in the description

John Rennie

+1 nerd points for me then :-)

Emilio Pisanty

5:04 PM

7zip wasn't having none of it

John Rennie

First thing I always do with an unknown file is open it ina hex editor.

Yashas Samaga

@EmilioPisanty I see TEX code in the source file.

Emilio Pisanty

@YashasSamaga yeah, I got it

and yes, it is roughly as horrifying as I thought

thank goodness for non-bare-TeX LaTeX

and yes, Leslie Lamport, by goodness I do mean you

          %BEGINNING OF PAPER


\hfuzz = 0.5in
\def\label#1{
\ifundefined{#1}
      %define new macro whose expansion is eqnumber.
\expandafter\edef\csname #1\endcsname{\the\eqnumber}
\else\message{label #1 already in use}
\fi{}}
\def\(#1){(\csname #1\endcsname)}
\def\eqn#1{(\csname #1\endcsname)}

↑ not what I would normally consider to be equivalent to \begin{document}

Danu

@EmilioPisanty Damn

0celo7

@ACuriousMind What is the moral difference between a hypothesis and a technical condition?

Danu

5:13 PM

This is what they used to have to deal with?

0celo7

I'm confused. What's the issue?

@BalarkaSen Yummy

anonymous

@JohnRennie Hello there! I had a question: In Bremsstrahlung like interaction do the high energy electrons ever collide with the nucleus ? What happens then? Does it combine with a proton or something? Is this situation even possible?

John Rennie

Remember that electrons and quarks aren't like hard spheres.

Mostafa

@JohnRennie Why not use bots?

anonymous

@JohnRennie Okay? So?

John Rennie

5:25 PM

Electrons and quarks never collide in the sense that classical particles do. The electrons interact with quarks and at low energies are simply deflected by them. This causes radiation as the electron is accelerated.

At higher energies you start getting particle production and it gets a whole lot more complicated!

Yashas Samaga

How do you smash two protons together? As two protons get closer, wouldn't their potential energy hit infinity?

John Rennie

Protons are bound states of quarks

They are not rigidly defined solid objects any more than atoms are.

At high energies the proton just behaves lie a bag of quarks and gluons, so the proton-proton collisions in the LHC are actually quark/gluon collisions.

2

Two colliding quarks never get to zero separation, so the energy is never infinite.

Yashas Samaga

The bag of quarks still have a net positive charge, right? As another bag of quarks gets closer, they should repel and increase their potential energy.

Mostafa

@YashasSamaga Who's VeryCuriousMind? xD

Slereah

No particles ever go at zero separation

Yashas Samaga

5:28 PM

@Mostafa Oh! You are spying on my imgur profile?

John Rennie

@YashasSamaga Yes indeed.

Yashas Samaga

How does the collision work if they don't get to zero separation?

John Rennie

Conclusion? Is that a phone autocorrect of collision? :-)

anonymous

@JohnRennie Oh I see. They can get very close but a head on collision like classical particles is not possible. (It is difficult to visualize electrons as waves. :P)

Yashas Samaga

yes

John Rennie

5:31 PM

I answered a question on this somewhere in the PSE. Basically as the interaction strength gets large energy gets transferred into other quantum fields where it appears as new particles.

anonymous

@JohnRennie In LHC also does the same situation occur ? Do the quarks/gluons just get deflected at very close distance without head-on-collision ?

Are quarks also considered as waves or something?

Emilio Pisanty

@Danu I think that was the least of their troubles at the time

1996 sounds late enough that you'd have postscript drivers and you could see your work on screen, but for a number of years the only way to see whether your code was working was to print it

John Rennie

@anonymous At such small scales particles don't have well defined trajectories. The collision is calculated as the interaction of two plane wave excitations of the quantum fields (say John oversimplifying horrifically :-).

anonymous

@JohnRennie Interesting :) "Basically as the interaction strength gets large energy gets transferred into other quantum fields where it appears as new particles" Wow!

Emilio Pisanty

Question: this has a broken link to the old astronomy site, but it's closed. Is it worth editing?

anonymous

5:34 PM

@JohnRennie I am happy with the simplified version :D

John Rennie

@anonymous Yes, that's how Higgs bosons get created. Did you think it was magic? :-)

Yashas Samaga

Listening to all these weird physics stuff, I have concluded that people with extreme commonsense can never be physicists.

anonymous

@JohnRennie Well, I still consider it magic :P

Quantum Mechanics is magic for me !

I read about Higgs boson last year sometime. It was pretty interesting! I bought a book on it also!

John Rennie

@YashasSamaga physics.stackexchange.com/questions/233850/…

Mostafa

@EmilioPisanty The link to the astronomy site works for me :/

John Rennie

5:37 PM

@YashasSamaga also physics.stackexchange.com/questions/223092/…

Emilio Pisanty

@Mostafa and does it lead you to a question with the same title as in the url in the original post?

http://astronomy.stackexchange.com/questions/948/what-exactly-is-the-definition‌-of-motion-and-its-relation-to-machs-conjecture

leads you to

4

Q: How does a Bahtinov mask work?

For focusing the image of a telescope, one can use a Bahtinov mask. How does this mask work, and how did Mr Bahtinov get the idea to cut such a peculiar shape? Is it possible for me to design my own focusing masks?

Mostafa

@EmilioPisanty ah, no :)

Emilio Pisanty

@Mostafa ;-). See here for more details.

meh, let's just edit it.

Balarka Sen

@0celo7 The hell?

0celo7

@BalarkaSen What?

My advisor said I should read this

I'm scared to read anything by Gromov

anonymous

5:54 PM

@JohnRennie One more question: In this graph is the pinch off voltage same for all frequencies of incident light ?

(Photolectric effect)

None of my books seem to clarify this point

(Pinch off voltage=voltage at which current saturates)

John Rennie

I'd guess there will be a small effect of frequency because high frequency photons will eject electrons with a higher kinetic energy. However I'd guess this will be a very small effect and maybe immeasurable small.

0celo7

@JohnRennie can I teach you about balls please

anonymous

@JohnRennie Aha! That was what I was thinking. Thanks for the clarification :)!

John Rennie

Photoelectrons get ejected with a spread of energies and in random directions so you need a voltage high enough to make sure all the photoelectrons get to the collector.

If you have higher energy photons shooting off sideways you might need a higher voltage to collect them all. But I have no idea how big the effect would be.

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