The h Bar

9:10 AM

Are questions related to practical stuff like windows ok? I was told that double glazed windows vs suitably thick regular glass don't make much difference from the pov of sound insulation. Is that a suitable question?

Danu

9:22 AM

Perhaps it's more of an engineering question, which is off-topic here.

Faheem Mitha

9:56 AM

@Danu Perhaps. Any more suitable site on SE?

Physics Meta

12:47 PM

0

Q: Reopen the «How is angular momentum measured in experiments/in practice?» topic

Moderators @Qmechanic and @dmckee marked it as a duplicate, but it is not so (see How is angular momentum measured in experiments/in practice? ). Linked questions are restricted to fundamental particles, whereas angular momentum is a concept applicable to any system. I now can’t post an answer ab...

discussion

user54412

1:13 PM

@FaheemMitha That might be okay here. There is a pure physics issue of reflection vs. transmission as waves traverse boundaries between media with different impedances, and possibly also of attenuation lengths.

user54412

For instance, telescope construction worries very much about having glass-air-glass segments, because light bounces around in there. It's necessary to have glass-coating-air-coating-glass in most cases.

Phonon

2:02 PM

hi

Danu

hello! Chat is a little dead at the moment it seems!

...it has been for a couple of days

I guess it's a positive feedback loop

Phonon

ah

ACuriousMind

@Danu How so?

Phonon

yeah, noticed it as well

Danu

@ACuriousMind I am reluctant to start talking when there is no ongoing converatation to rudely interrupt :D

Phonon

2:06 PM

haha

ACuriousMind

Hahaha...hecklers have it rough

Phonon

@ACuriousMind sigh man, you always force me to open up the dictionary everytime you open your mouth :pp

aha A heckler is a person who harasses and tries to disconcert others with questions, challenges, or gibes

sometimes I wonder where you've learnt these words :)

ACuriousMind

@Phonon This one from youtube videos "Comedian demolishes heckler" or somesuch, I believe :D

Phonon

hah ok :)

ACuriousMind

Sometimes I'm talking gibberish though, do tell me when that happens ;)

Phonon

2:09 PM

okis ;)

Danu

hah

Where are you from, Phonon?

Amsterdam

Phonon

ah

nice nice

which univ did you go to?

let me guess, Delft? :)

Danu

hahahhaa, nopes

I'm not an experimentalist

Phonon

:) fair enough

Danu

A new program jointly offered by the two universities of Amsterdam

Univ. of Amsterdam & Free Univ. Amsterdam

Phonon

2:15 PM

ah I see, what is its main focus?

Danu

it's an American-style program, Liberal Arts & Sciences

Phonon

and you're happy with the program?

Danu

I'm done, and happy about it :_

Phonon

Cool!

Danu

It wasn't perfect, but I managed to complement the program with a lot of physics from UvA

and got into very nice programs in Europe

so I'm content

Phonon

2:18 PM

wow, yeah indeed can imagine, at least it wasn't the same routine program that most EU univs adopt...

Danu

but I wouldn't recommend this particular program to a physics student, per se. For me, it made sense because I didn't discover physics until after I got into uni

Phonon

sure, but at least it's a good example of "diversity in education" paying off

Danu

yes

Phonon

most univs I've heard of, are so attached to their old school principles, and obviously they're convinced they're offering the best programs...

so it's good to hear that for a change, like in your case, a different approach has been taken and paid off!

As Feynman used to say, education has to be adaptive...always...

Danu

Yes, that's true. At least I learned to do a lot of self-study and pick my own topics of interest at an early stage :P

Phonon

2:21 PM

perfect,

@ACuriousMind doorbell for you mate: physics.stackexchange.com/questions/131811/…

hahahah just kidding :p

Danu

gauge, gauge, ACuriousMind!

Phonon

:)))))

Danu

Condensed Matter QFT has always seemed quite the nasty topic to me

Phonon

yeah I agree

I'm in enough trouble just dealing with Condensed matter physics alone, can certainly do without the QFT :D

ACuriousMind

Weird, just as you began talking about me, I was getting server not found for physics.SE and chat.SE, but no other SE site. Clearing the cache didn't help, but it suddenly started working again

Danu

2:41 PM

I get that sometimes, for a few seconds only though.

ACuriousMind

Well, it's at least not as annoying as the immortal notifications from a few days ago

John Rennie

Hi LIUFA, are you there?

LIUFA

Hello gentlemen

John Rennie

You were asking why time only flows forward, is that correct?

Danu

Hey! John Rennie in chat!!! :D

LIUFA

2:49 PM

Not really

I was asking what made time go

John Rennie

Hi Danu, if you want to talk about the flow time please join us :-)

Jim

@LIUFA the more important question is how do you know it goes at all?

John Rennie

LIUFA: the thing is that time doesn't go.

Danu

Ah, the flow of time. One of the immortal themes plaguing the human spirit

John Rennie

There is nothing in physics to imply time moves at all.

LIUFA

2:49 PM

Ok :)

John Rennie

This idea is known as the block universe

LIUFA

So how come it's not moving back?

John Rennie

See en.wikipedia.org/wiki/Eternalism_(philosophy_of_time) for details

You ask "how come it's not moving back", but the point is that it doesn't move at all.

Jim

because causality preservation means your memories don't contain info about the you that exists at future moments

LIUFA

What about inanimate objects?

like rocks in space

Jim

2:51 PM

what about them?

LIUFA

Well have you seen meteor shoot out of planet and fly into the space?

John Rennie

We nornmally think of rocks as moving i.e. their position changes with time.

Danu

I think you are talking past each other

John Rennie

But a general relativist would say that the rocks position in space and time is parameterised by an affine parameter

Danu

honestly, I think LIUFA is asking about how the arrow of time arises

so an answer about entropy etc etc etc may be more useful

LIUFA

2:53 PM

yeah

ACuriousMind

@LIUFA They "move forward in time" because you can only remember things in that direction. Nothing really says "things move in that direction in time", you can always invert the trajectory.

John Rennie

We write the position as r(\tau) and the time as t(\tau) where \tau is the affine parameter.

LIUFA

I think I do ask about arrow of time

ACuriousMind

But we human beings do not remember the future and live into the past, so you do not perceive anything going "backwards"

John Rennie

Ah OK. Have you searched the site for "arrow of time"?

LIUFA

2:54 PM

no @Danu said it and it sounds like what I am failing to understand

Danu

Guys, I'm sure this question has already been covered. Does anyone know the canonical reference (hah! We need them! :D)

John Rennie

Try physics.stackexchange.com/search?q=arrow+of+time

Jim

If you imagine your whole life as a world line, it all exists in spacetime. No moment is more real than any other moment. Your reading this now is really just the memory that the you from 15 seconds from now is recalling. And they're thinking back saying "I exist now and then and 10 seconds from now too. It's just my memories that make me think there's an arrow of time"

Danu

@LIUFA en.wikipedia.org/wiki/Entropy_(arrow_of_time)

Always start with Wikipedia

LIUFA

@Danu Sorry this is first time I have heard of concept 'arrow of time' I am amateur in physics at best

Jim

2:57 PM

arrow meaning direction or general flow

LIUFA

Thanks guys I will go have a read of those articles

John Rennie

@LIUFA: don't apologise! We were all normal once - geekdom takes some time to set in

Jim

@JohnRennie woah! geekdom? I mean, I'm a huge nerd, no doubt. But I'd never call myself a geek

I don't have the level of commitment required to be a geek

John Rennie

@Jim: I lose track of the modern terminology. Personally I've always thought we were the normal ones and it's the rest of the human race that has the problem :-)

2

Danu

Hah

geek has a somewhat negative connotation

while 'nerd' has become a term that many use with pride and all the time - to my disgust

Jim

3:01 PM

@JohnRennie Of course, the old "I'm not crazy, everyone else is" argument

@Danu I have my own definitions that most agree with when fully explained. I don't consider geek negative

But not enough time to explain

ACuriousMind

@Jim Obligatory reference: xkcd/747

@ACuriousMind: :-)

Damnit :P

hahaha

so many people here

3:06 PM

Scary, isn't it? Almost as if we were a lively community :P

Danu

I love it like this

ACuriousMind

Annnnnd...*crickets* This SE is almost as bad at small talk as we Germans in general :P

Danu

pfft

Too sensitive ;)

Also - I might have found an apartment in Munich

There's a girl who's looking for WG-Mitbewohner that I gotta talk to now, If she likes me, I'm in

Any tips for a non-German?

ACuriousMind

Yay! I hope the rent is only demanding the sacrifice of one of your kidneys ;)

Danu

It's <500 so I'm pretty content

Half an hour biking to the university though :\

ACuriousMind

3:14 PM

As for tips...I don't know, I never had to interview for living with someone. Be yourself, I guess? (And be prepared for stupid weed jokes when people find out you're Dutch ;) )

Danu

Oh she knows already :) And I just came back from the USA, so I'm hardened!

Phonon

hahaha

ACuriousMind

But you should be fine, most people I know (would) like to have foreign roommates

Danu

Really? I had come under the impression that it's harder for non-fluent German speakers (my German is ~B2 level and thus pretty good, but certainly not fluent)

Phonon

haha Danu you reminded me of Jeff in "coupling" the tv series

seen it?

Danu

3:16 PM

nope, what about him?

Phonon

imdb.com/title/tt0237123/?ref_=nv_sr_1

he would always come up with the weirdest thoughts when it came to talking to girls :)

not gonna spoil it, you should definitely watch it ;)

ACuriousMind

@Danu Perhaps my circle of acquaintances is not representative, but that's my personal impression. I'm not sure what the strange Bavarians in Munich think about that, though

Danu

I regret to inform you that.... I probably won't watch it, @Phonon

ACuriousMind

Beware of weird arrangements though. I recall the immortal tale of one of my friends who interviewed at a WG only to find out the shower was practically in the middle of the kitchen, and see-through at that :D

Danu

Oh, I'm a huge nudist ;)

ACuriousMind

3:21 PM

Haha...alright then

Danu

(just kidding)

In fact, my close friend who will be going to Zurich to join the ETH Physics MSc. program had an even stranger encounter

a house with four people, three girls and a guy, who insisted on living naked. As part of your application, one had to send full body shots - naked of course!

:D

ACuriousMind

What the...well, if it works for them

Phonon

:))

ACuriousMind

The postal workers must love to deliver packages there

Phonon

everytime I come back this conversation has gotten a bit more interesting

Danu

3:25 PM

That's a famous joke in Holland: A mail man arrives at the door and puts the paper through the door. He also has a package and rings the doorbell, so it can be signed.

ACuriousMind

@Danu If that's the whole joke, I don't understand Dutch humor :D

LIUFA

Where has to be the rest

Danu

The woman who lives there was just in the shower, so she quickly runs out towards the door - to peek and see who's there. In the meanwhile, the mailman is losing his patience, and he decides to shout through the mail slot. When he opens it up, he is surprised for a second, but then asks: Hey, curly head, are your parents home??

IT'S A LONG STORY ALRIGHT?! :P

Now this is a painful instance of crickets

:D

LIUFA

Heard that one

ACuriousMind

Hehe...I think I heard that somewhere before (but most Germans would not tell that joke to people they barely know :D )

At least not until everyone's had a few beers

Danu

3:30 PM

hah, bearly, that's a joke me and my girlfriend made a lot this summer (it's actually spelled barely)

LIUFA

Schroedinger cat enters the bar

and does not

ACuriousMind

@Danu Damnit, I corrected it! But not fast enough...

Danu

quite standard - but decent

@ACuriousMind I'm sorry for being on your case like that ;)

Why isn't Heisenberg any good in bed?

Whenever he's found a position, he loses the momentum!

:D

ACuriousMind

lol

Poor Heisenberg

See, I can recall countless webcomics from the top of my head, but I cannot tell a damn joke. What's wrong with my memory?

Jokes and citations from movies seem to leave my head as soon as they enter

LIUFA

Wrong time arrow i suppose

ACuriousMind

3:36 PM

@Danu: There's this charming list from an Australian that has lived in Germany for some time. It might prepare you a bit for what you'll see here ;)

hwlau

@Danu What a joke!

Danu

4:06 PM

Point 1 & 2, Dutchmen do a lot better ;D

@ACuriousMind

Same for point 3 :D

lol, the eighth is a little creepy

ACuriousMind

Haha...yeah, don't take everything there seriously - most has a grain of truth in it, though.

But I've no idea why the babies should be particularly beautiful, either :D

Danu

I guess I know most of these already from numerous visits

ACuriousMind

Now that I think about it, all the stuff about bicycles and camping there is what Germans associate with the Dutch. Perhaps Australians can't tell us apart...

Danu

4:26 PM

exactly

Faheem Mitha

5:27 PM

@ChrisWhite Ok, I'll conside asking it here. Thanks.

Kyle Kanos

6:04 PM

Wow...that Incnis Mrsi guy is something else

Danu

Pretty intense, no?

What happened?

Kyle Kanos

He's been pouring through old posts and complaining anywhere he can about composite boson/fermions

e.g.,

0

A: How does one experimentally determine chirality, helicity, spin and angular momentum?

By no means not a complete answer, more a criticism of @luksen’s one. It is posted here because the text is too long to fit in the comment field. First of all, the spin is not a well-defined concept for composite particles. More precisely, whether the spin of a particle is defined depends on how...

Of course, the question he answered is about elementary particles, not composites :/

Danu

Oh, that one... He made a meta post about it

Kyle Kanos

Yeah, that's how I found he was doing it more

He was commenting on a thread of mine from some time ago (about proving photons have spin of 1)

He said that my phrase "bosons have integer spin" is incorrect because bosons "follow B-E statistics"

I followed up with, "B-E statistics describe particles of integer spin." to which he brought up composite particles

Danu

6:21 PM

he really was nitpicking there - I just checked it out. I think it's still fair to say that it has integer spin

Kyle Kanos

6:36 PM

My guess is that he's a grad student who just found out this fact and is so proud of knowing it that he's blasting it wherever he can

Jim

So let him pick nits. Sounds like nobody was really wrong, and it seems to make him happy. If you think the correct meaning can be inferred from the context of your post, then don't worry about it. This is one of those no-win situations that has to be accepted

You can't avoid simplifying; sometimes it's necessary. And whenever you do, there's always going to be that special someone that will rush to point out that what you said is technically not entirely correct because you simplified

2

Danu

Anyone have anything fun to read? I'm bored

Faheem Mitha

@Danu Fun to read where? The net has zillions of things.

Danu

either physics or math SE, or a textbook?

Jim

@Danu I'm reading through several papers about linear approximations in inhomogeneous inflation. Would you consider that fun or are you looking for something else?

Danu

6:47 PM

something slightly engaging :P

ah, there we go

tell me about the field of inflation at the moment

Faheem Mitha

Interesting definition of fun.

Jim

^agreed

Danu

I did work on the beginnings of a paper with some people from princeton earlier this year - got an awesome internship there for a month somehow

yeah, this is not usually what I would call 'fun' - but I'm askin on a physics forum chat...

actually, it's fun, but I wouldn't explain it like that to a non-physicist/mathematician ;)

Anyways, about inflation, we were working on a statistical model

where the inflationary potential is randomly generated

picked from a general ensemble

anyways - what kind of inflationary models are hot at the moment?

still the good ol' m^2 phi^2?

Jim

white noise potential, or randomly generated profile for a function or randomly generated field values?

and m^2phi^2 is always a useful toy model

Danu

arxiv.org/abs/1307.3559

I was working under supervision of Enrico

he's an awesome guy - made a huge impression on me

we were working on a follow-up on this paper

Jim

6:52 PM

ah

Danu

I didn't get much done, since I wasn't/am not advanced enough

but it was a great experience

Jim

I'm doing only single-field right now and am writing a paper that provides a quantitative analysis of the linear approximation for perturbations in the scalar field

it's actually quite enlightening and showing that the approximation is usable at amplitudes much larger than usually used

Danu

some review/intro papers on that?

Jim

That's the thing, it's something that nobody outlines, everyone just uses it and assumes everyone else knows about it

Danu

urgh, hate when that happens

I guess it should be in some textbook then?

Jim

6:57 PM

No, it's an approximation. Physicists just say "And then we assumed this, and that works, so there."

Anyways, can't stay and chat. Have a department meeting in 5. Might post relevant papers afterward

Danu

okay, bye

Kyle Kanos

I've got a good book to read

amazon.com/Option-Pricing-Mathematical-Models-Computation/dp/…

Read that & write me a review sheet

so that I can pass an interview in January

:D

Or if you've got about 3 hours

there's this:

►

Danu

7:58 PM

Speedruns? Hah. I watch those every now and then

Kyle Kanos

I don't really watch them, I just listen

Danu

Also, @KyleKanos I dropped my economics courses after second semester because it truly bores me to tears - honestly I was just putting up with it to that point because there was a girl... ;)

Kyle Kanos

Haha

It's more Stochastic Calculus with reference to Financial markets

Danu

What's stochasitc calculus about (and don't tell me to start reading ;) )

Kyle Kanos

Random numbers + infinitesimal calculus

Danu

8:01 PM

calculus??

Kyle Kanos

Maybe more accurately "discrete" calculus

Danu

oh... that sounds less exciting

are you going to be workin in financial sector?

Kyle Kanos

I'm working towards that end

Danu

have you sold your physics soul? :(

or were you never intending to work in physics in the first place?

Kyle Kanos

A few factors have contributed to my wanting to get out of academia

Danu

8:07 PM

would you care to elaborate?

Kyle Kanos

Surely

(1) Lack of enthusiasm about grading

(2) Salary (in conjunction with the already-large family)

(3) Fear that Academia will tank in the next 5-10 years due to the "college bubble" (similar to the "housing bubble" that burst in 2008)

Danu

@KyleKanos

(1) does the teaching part (and specifically the grading) take up that much time?
(2) fair enough considering comparison to economics
(3) what's the college bubble? is it an american thing?

Kyle Kanos

The labs I currently run, I'd say I spend as much time grading as I do making sure the kids are doing their work

As per 3, that's a long-winded thing

But I'll try

At the university I go to, it costs about $3,000 per student to attend

But the University, a state college, is required to take in certain financially-disadvantaged students (i.e., the poor ones)

In order to let these students in for free, the University has to increase the costs for the other $n$ students that are not getting this free education

Another set of students are given University-granted scholarships; these students also go for free but at the cost of the other $m$ students how have to pay more.

All tolled, the students who actually have to pay are shelling out about $12,000 per year to attend

Danu

okay

Kyle Kanos

It is highly unlikely a student has $12k lying around the house, so where do they get it?

From the Federal Government

Danu

8:15 PM

Ah, so you're afraid that these costs are going to get so out of hand that nobody will go to college anymore, ruining the job market?

Kyle Kanos

At some point, these students who have to pay are going to realize that there are jobs out there that don't require a BS/BA degree which would save them on the order of $40k

Danu

Point taken

Kyle Kanos

When those students stop going, schools will have to jack up costs for those that stay, which will only accelerate the rate at which students stop attending

Add into this the fact that the football team at Northwestern University successfully petitioned for Unionization, and the whole economic structure for Academia is royally f@!#ed in the next decade or so

Danu

Yes

God Bless 'Muricaaaa

Kyle Kanos

Tenure will not save anyone from the massive firings that will happen

Danu

8:19 PM

The US system is so, so broken

Kyle Kanos

I don't know that it's very broken

It's fixable, but the reality is that there will have to be some students who cannot actually attend a university

(due to grades, funding, etc.)

Kyle

But that would be elitism! Can't have that!

Danu

Hah.

I don't know - It seems very broken to me. In Europe, one can attend college for under 3000 USD a year almost everywhere

Kyle

8:39 PM

is that typically subsidised by government? e.g. here in Canada, tuition for an international student can easily reach ~30000USD/yr, but canadians in the same program pay less than a third of that, with the canadian government putting in the difference (out of people's taxes presumably)

Danu

Yes, the government helps out a lot here

In Holland, it goes up to ~15k USD for internationals, at most

but germany is a lot better even, I'll be paying ~400 dollars a year there, being from the EU helps of course

Kyle

8:56 PM

are you talking about a graduate program and does your department cover any of your costs/what is the base stipend?

Danu

Grad programs are differently structured here -

The Master's degree is separated from the PhD

Kyle

nah same as in Candaa

Danu

oh, well, I just assumed Canada ~ USA; wrong once again!

My close canadian friend John would kill me

Kyle

heh

Danu

anyhow, I'm more intimately familiar with the dutch than the german system

Kyle

8:58 PM

there are some differences - from what I gather in some parts of Europe your masters ends up being more like an extension of undergraduate studies than a separate degree (e.g. UK you do undergrad+MSc in 5 years at a single institution)

Danu

In Holland, everybody pays 1700-1900 euros a year, and a student living at home gets ~100 a month standard, while someone living somehwere else gets ~260 a month standard

Kyle

"at home" heh

Danu

The UK actually is very unique in this respect

Kyle

I live at home, by which I mean with my wife and child :P

Danu

living at parents home haha

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