The h Bar

Sanya

00:02

@ACuriousMind one party is fun, five parties in three days are stress ;) and well, the kids will come in due time :p

heather

unless you are a kid =D

::throws wrapping paper ball at ACuriousMind::

=P

then all is fun and presents and sugar

and bothering your parents

and waking up way too early Christmas morning

and singing Christmas carols over and over and over and over and over and over and over and over and over and over

ACuriousMind

@Sanya five parties in three days! That is stress, but my Christmas isn't that busy :P

@heather :P

heather

@Sanya, I don't have that many friends, so =P

@ACuriousMind, ::throws snowball afterwards::

it snowed yesterday

and today =D =D

ACuriousMind

Yay! No snow here yet, sadly :(

heather

::starts singing Let It Snow::

ACuriousMind

00:07

Ugh, I need at least a cup of mulled wine before I can tolerate Christmas songs ;P

heather

hmm, maybe I should make a python program that sings christmas carols every time someone enters the hbar =P

and throws snowballs at people

well, virtual snowballs

::evil programmer laugh::

Sanya

@ACuriousMind @heather it was more a proof of principle statement than anything else

heather

0

Q: Confusion on the concept of Boltzmann brain

I heard that a Boltzmann brain is a brain-like object that materialized from random fluctuations of particle fields, where particles randomly "pop into existence" and just so happened to form a brain. Is there some special conditions required for this proposed phenomenon? If not, why isn't ther...

^the agony of this question

Slereah

Christmas isn't that interesting for me these days

I'm a grown up so I can basically buy most of the stuff I want during the year

And the stuff I want but can't buy is too expensive for a present

heather

@Slereah, but, but, the sweets and the tree and the carols and the wrapping paper fights and the absence of school...

Slereah

00:11

Well you see, i don't have school anymore

heather

ooh, you're a full-on adult? For some reason I thought you were a college student

Slereah

I wish

Sanya

@Slereah it becomes such a chore to pick christmas presents for the other adults in the same situation too, in addition to that

ACuriousMind

I like Christmas mostly because it's the time of the year I can see most of my old friends in one place since most people are visiting their parents.

Slereah

Friends is for new years

Christmas I have to visit the family

Sanya

00:12

@heather O_o~

heather

@ACuriousMind, new profile picture...

Slereah

I did ask for a physics book for christmas

I forget which one

Let me see

ACuriousMind

@heather Indeed. We are legion.

Slereah

"Linear Operators in Hilbert Spaces"

heather

@ACuriousMind, I have no idea what that means. legion = ancient roman dudes

Slereah

00:14

Very Christmassy

heather

ooh, yes

I asked for Shankar's Quantum Mechanics and Kleppner and Kolenkow's Classical Mechanics and Menkre's Topology and a whole bunch of other math-y science-y books

I'm very excited

ACuriousMind

@heather Like all my profile pictures, it's a video game character. This one is Legion.

Slereah

Last year I got Glimm and Jaffe for Christmas

ACuriousMind

@Slereah Hey, I think I got that one as a present, too. Might not have been Christmas, though

heather

oh, and Apostol's Calculus Vol 2

Slereah

00:18

Maybe I should ask for the handbook of physics and chemistry next year

ACuriousMind

@Slereah What for?

Do you have a table with one leg that's much shorter? :P

Slereah

I like to have big reference books

And if I don't ask for specific things for christmas I always get garbage

ACuriousMind

I mostly get socks.

Slereah

Well as you know

I worked in robotics for a bit

I got a lot of toy robots last year

ACuriousMind

Heh

heather

00:32

lol

ACuriousMind

I'm guessing you didn't really want any, but it's the thought that counts ;)

Slereah

So it turns out the thought didn't count

They just clutter my shelves now

Emilio Pisanty

00:49

@ACuriousMind dammit, look at this

-2

Q: Can Quantum Key Distribution be incorporated in public key cryptography? How?

Quantum Key distribution to be used to make public key cryptography more secure

quantum-mechanics mathematical-physics quantum-information teleportation

saved by the bell by about two seconds

though admittedly I was going to downvote after answering

ACuriousMind

Hmm?

What do you mean by "saved by the bell by about two seconds"?

Emilio Pisanty

@ACuriousMind check the timestamps of the answer and the deletion

wait, what?

ACuriousMind

lol

The question was deleted, then immediately undeleted

Emilio Pisanty

I mean, check the timeline

Slereah

01:26

Hm

If a metric is conformal to Minkowski space, will the Klein Gordon solution always just be the usual flat space solution?

Except for normalization, maybe

In some coordinate system, anyway

Oh wait, KG is only conformally invariant if you add the conformal coupling term, right

$\approx \phi R$

David Z

02:04

@EmilioPisanty I'm a little surprised you thought that was on topic, but whatever

DanielSank

Hi, everybody...

Emilio Pisanty

@DavidZ original plan was answer and downvote

I mighta gone soft-hearted on the downvote

might still do it though

DanielSank

@EmilioPisanty If you can answer, but want to downvote, shouldn't that suggest an edit?

Emilio Pisanty

@DanielSank no, question was fundamentally bad

but I thought it might be for the best to just get it out of the way

@DavidZ OP has re-deleted anyways

David Z

Yeah, it doesn't really matter that much in that case

Slereah

03:00

Is there a transformation to the solution of the KG equation for a conformal transformation

Like if I have $\eta \to \Omega(x) \eta$, is there a specific form for $\phi$

ACuriousMind

Well, if you are requiring the conformal transformation to be global then you really don't have all that much choice in conformal transformation - they're just the Möbius transformations.

Slereah

wot

ACuriousMind

The conformal group in 2D is just the group of Möbius transformations $\mathrm{PSL}(2,\mathbb{C})$, or equivalently the Lorentz group.

You only get "more" conformal transformations if you allow them to be singular at some point

Slereah

Good to know

ACuriousMind

In general, the conformal group is rather boring, it's $\mathrm{SO}(p+1,q+1)$ for signature $(p,q)$. 2D conformal transformations are only interesting when you look at them locally/infinitesimally, because then you get the infinite-dimensional Virasoro algebra as the possible transformations.

So if you want to know whether there's a global conformal transformation that transforms something into something else, you could just write down a general Möbius trafo and try to solve for it - should be easier than solving all those PDEs you usually deal with ;)

If you're allowing for the infinitesimal transformations your question becomes harder to answer, though

Slereah

03:20

Well I need a specific conformal transformation

Not sure which one yet

I need to work out how to convert the metric into Minkowski

ACuriousMind

I think to convert 2D gravity into Minkowski you don't actually use a conformal transformation, you use a Weyl transformation

I.e. you don't do a coordinate transformation, you really just transform $g\mapsto \Omega(x) g$

This is allowed because the E-H action in 2D is Weyl-invariant.

Slereah

But @ACuriousMind

I don't want to sound too much like a physicist

But that's what I mean by a conformal transformation

ACuriousMind

Arrrrgh

This is a point of large confusion all over the literature

Slereah

that it is

Although I guess that technically I need both

Coordinate change and Weyl transformation

ACuriousMind

But a conformal transformation and a Weyl transformation are two different things and sometimes you do both at the same time and it becomes actually important which is which

And yes, it might be that for 2D gravity, you use a coordinate change to bring the metric into the form $\Omega(x) \eta$ for $\eta$ the Minkwoski metric and then use the Weyl transformation to get rid of the $\Omega(x)$.

I did that on an exercise sheet somewhere, I think

Slereah

03:28

Well I mean

For a start

The metric I have isn't diagonal

So I'm pretty sure no amount of Weyl transformation will help

ACuriousMind

Well, you use a diffeomorphism/coordinate change to make it diagonal

Then you use Weyl rescaling to make it constant.

And ta-da, you have the Minkowski metric :P

Slereah

That's the plan

Though more than diagonal I need to make both components the same

Which sounds slightly challenging

We'll see how things turn out

I suspect this will involve intractable PDE systems again

user228700

03:46

Yello everyone :-)

user228700

I have a quick question (Sir @JohnRennie, halp!)

user228700

As an explanation for why azeotropic mixtures form, Wiki has this to offer:

user228700

> "When the deviation is great enough to cause a maximum or minimum in the vapor pressure versus composition function, it is a mathematical consequence that at that point, the vapor will have the same composition as the liquid, and so an azeotrope is the result"

user228700

"Mathematical consequence"? O.o

Secret

04:37

[Last night dream inspired question] Ground state of a black hole...?, quantum transition pathway that allow absorption of photons but not emission (thus relaxation is not radiative)...? dark matter with a ground state much lower than all known ground state...?

* [Abstract algebra project inspired search] Discrete chaos...? https://www.amazon.com/Discrete-Chaos-Second-Applications-Engineering/dp/1584885920

[* inspired question] a continous operation that has no discrete analogue, or vise versa...?

[further inspired question] If the ground state of a black hole is well defined, then what does an excited state black hole look like and what could propel it to an excited state...?

arxiv.org/abs/1511.01279 ...?

Swapnil Das

05:54

Thanks @NeuroFuzzy

user228700

07:21

@JohnRennie: Namaste! :-)

John Rennie

Morning :-)

Re your question: do you want a mathematical treatment or just a general description?

DanielSank

Hi, everybody.

John Rennie

Let me give a general description because I only have five minutes before I have to plunge back into work.

user228700

Just a general description will do.

user228700

Oh, alright...

user228700

07:25

@DanielSank: Hi :-)

John Rennie

Suppose the vapour pressure-composition curve has a maximum at some composition.

user228700

Okay...

John Rennie

And suppose you start at some composition not at that maximum.

user228700

Right.

John Rennie

As you boil your liquid mixture the boiling point goes up as the more volatile component is preferentially evaporated.

user228700

07:27

Yes...

John Rennie

The maximum boiling point is at the maximum in the vapour pressure curve, because that's where the vapour pressure is highest.

user228700

Don't u mean minimum?

John Rennie

So once you're at that point any change in the composition would lower the boiling point not increase it.

Oops yes, I did mean minimum.

user228700

Okay...

John Rennie

So your liquid is now stuck at that composition.

And now I have to get back to work :-(

user228700

07:30

OK :-)

user228700

It doesn't make that much sense to me yet, but I think I'll be able to figure it out in a bit.

user228700

Thank you :-)

user228700

Hey @Mew :-)

Mew

07:48

hi

wat r those removed bits

user228700

Nah, never mind.

Mew

aw

John Rennie

I'm back! For a few minutes ...

@Kaumudi you still around?

user228700

@JohnRennie Yep.

John Rennie

It turns out that it is possible to post laptops to India, and in fact it's surprisingly cheap. So if you would like one of the laptops from my pile of old laptops you'd be welcome.

user228700

08:02

Whoa, what? That's new and exciting information!

John Rennie

Whether you're interested or not I don't know ...

user228700

I am, but I don't know what u're offering, exactly/what u have...

Mew

what's this?

free laptops?

user228700

@JohnRennie ..?

John Rennie

Do you mind if the screen has a vertical line on it? I've got a picture somewhere ... let me look.

user228700

08:09

😐 OK..?

Mew

yeah that's cool

John Rennie

Nov 9 at 17:23, by John Rennie

Mew

i'd prefer a horizontal line but meh

how much?

user228700

Yeah, that's okay :-) Does it work properly, otherwise? Also, which company?

John Rennie

I haven't got a spare screen in my pile of bits or I'd replace the screen, but the line isn't that obvious in everyday use. It's a Dell Latitude E6430, 3GHz i7, 4GB memory, so it's a fairly storming laptop, though it's a bit heavy because it's a business laptop.

Mew

08:11

does it come with office?

user228700

@JohnRennie Can u define "heavy"? 'Cause I want to be able to carry it around at college...

Mew

@Kaumudi why do you need a new computer?

user228700

'Cause I don't have one.

Mew

what do u use now?

like right now

user228700

My mobile phone.

Mew

08:12

oh k

John Rennie

@Kaumudi it would be fine for college. It's heavy compared to the latest MacBook, but not in absolute terms.

user228700

Oh, okay...

Mew

ar eyou getting this one for free @Kaumudi

user228700

And how much..?

John Rennie

@Kaumudi Er, well, I was going to give it to you ...

Mew

08:15

wow that's generous

user228700

Free of charge?!

Mew

WAT

John Rennie

I'm reluctant to sell the laptops I fix up because I can't give any guarantee.

A laptop that's been bolted together from a pile of bits doesn't necessarily have great long term reliability.

user228700

I see. But it works fine, right?

Mew

so don't store any valuable files on it?

John Rennie

08:17

Yes, apart from the line on the screen it works perfectly.

Mew

doies ur home have the internet @Kaumudi?

user228700

Hmm. I don't think I'll need that amazing of a laptop in college anyway. And by that time, if it dies, I can always buy one.

user228700

@Mew Yes, of course.

John Rennie

Well if you're interested we need to sort out the logistics and I don't want to do that in an open forum. Your Mum has a Facebook account doesn't she? Can you get her to mail me through Facebook?

Mew

or @Kaumudi could make a facebook?

user228700

08:20

Hang on, exactly how heavy is it? I'm definitely not going to be buying fancy macbooks even if u weren't being so generous but it's not that heavy to say, have in ur backpack and cycle around?

Mew

let's just say after college noone will say you have skinny arms

user228700

Huh?

Mew

wat?

user228700

What did u mean?

Mew

I was saying the laptop will build ur biceps

cos it's so heavy?

nvm

John Rennie

08:23

@Kaumudi Hang on, I'll get some scales.

user228700

@Mew :-P OK. Nice joke. Cracked me up (←Sarcasm :-P)

user228700

@JohnRennie :-P ...

Mew

why are fish easy to weigh?

cos they have their own scales

user228700

U beat me to it :-P I think I've heard this before.

John Rennie

2.4kg

Mew

08:26

wow

user228700

"wow, that's heavy"?

user228700

(I have no perception of this stuff (weight). I'm going to have to put something that's about 2.4kgs in a backpack to find out :-P)

Mew

When I put two 1 L water bottles in my back it's pretty heavy

and that's only 2kg

but the average weight of a baby is 3.

3.4kg

so it's not that bad

John Rennie

I need to get back to work for about half an hour. I'll leave you to think about it.

Mew

@JohnRennie don't worry one of us will take it of your hands at least

user228700

08:38

@Mew Hmm, okay. I used to carry about 4 kg to school everyday.

user228700

@JohnRennie: How much is the shipping charge, dyou know?

Mew

oh yeah back in the day of textbooks

user228700

*still is, for countries like India.

John Rennie

@Kaumudi low enough not to be an issue - I'll cover the shipping charge.

user228700

No way. I'm not letting u cover anything.

user228700

08:40

How much is it?

John Rennie

The quote I got was about £20, but I was guessing at the weight so I'd need to pack it up and check the weight and dimensions to get an accurate quote. However it will be something about that figure.

user228700

Okay, that's definitely way more than OK.

user228700

I asked my parents about it. They were only worried it would cost too much to ship it, but this is definitely OK. Can u like, post some more pictures please?

user228700

(@Mew: I'm sorry man :-P Why dyou need a new (well, old but new) laptop?)

Mew

@Kaumudi I don't have a laptop

just a desktop

user228700

08:50

Ohh, okay. I don't have that either.

Mew

I don't really need a laptop tho

user228700

Now Ik u're not super rich and famous, lol :-P

Mew

I prefer desktops, they'r faster

why?

user228700

Why would u not have a laptop if u're super rich and famous?

Mew

cos there's always a desktop wherever I go

user228700

08:52

And what if u need to send that super important e-mail from a plane?

Mew

people wait til i land

user228700

x'D ::Trying my best to believe u::.

Mew

lol

but yeah I don't need a laptop

I don't like em that much

but if they're free i'll take it

user228700

Okay. I really do.

Mew

(and sell it)

user228700

08:53

x'D U definitely know how to be discrete about ur intentions.

Mew

lol'

he's not going to give me one

he doesn't even respond to anything I say

user228700

Not if u're gonna sell it, no :-P He himself doesn't want to.

user228700

@Mew What? O.o

Mew

yeah he just ignores my comments

user228700

That...what? No he doesn't!

Mew

08:54

yeah like I aksed if the laptops come with office

no answer

user228700

Ohh. Yeah, dude, did u see this:

user228700

Can't find it, dammit. Basically, he's working.

Mew

yea

but he was pinging u

and not me

i'm like "free laptops?"

no answer

jus have a look girl

user228700

:-/ I...dunno. He's done that before when talking to people. For example:

user228700

Uuuugh. Can't find it. It was too long ago. Basically, he was teaching me s'thing and Bernard pinged him and then after we were done, he said "Sorry, I was caught up in teaching" to him.

Mew

09:01

lol u always get his full attention

John Rennie

@Mew I have a finite (and small) supply of spare laptops because it depends on what broken laptops I get from work and whether I can patch together a working laptop from the bits. So there is a degree of prioritisation necessary. As a salaried employee I'm afraid you're not top of the list.

Mew

@JohnRennie that's ok John I was just joking anyway

@Kaumudi this is like what happened before with Bernard lol

John Rennie

@Kaumudi what further details do you want? I can photograph the laptop if you want, but you can Google Dell Latitude E6430 for pictures and reviews.

user228700

@JohnRennie No, I was just wondering if everything else is OK..?

user228700

@Mew Yeah :-P

John Rennie

09:06

After I rebuilt the laptop I ran the Dell diagnostics and it came back with a clean bill of health. As far as I know the only problem is the line on the screen. It isn't hard to replace the screen, but you'd have to buy a new screen and that's about £50 so whether it's worth it is debatable.

Mew

@Kaumudi does anyone have a colmputer in ur family?

user228700

@JohnRennie Nah, Idc about that line :-P

user228700

@Mew Well, my parents work on the computer that have been to them by their office. If they were to change jobs, they'd have to give it back. So, no.

John Rennie

OK, well as I said I don't want to be swapping addresses etc in an open forum so I suggest we continue through Facebook.

user228700

Oh, OK. Um, Facebook. Exactly how to go about contacting u there?

user228700

09:09

(I'm not very familiar w/ it and its features)

Mew

you can use the PM system on physics.qandaexchange.com

only admin (me) has the ability to dig into those messages (which I won't)

oh wait u may need a reputation of 120 to PM

not sure what reputation u guys have ther

user228700

I have 0 reputation :-P

Mew

na u have 100 by default

2 upvotes will give u 120 points needed

user228700

Ohh. Well, I have 100 then.

Mew

tsk tsk

user228700

09:11

It's OK Mew, thanks :-) I think I'll use my mom's Fb account.

Mew

np

John Rennie

@Kaumudi You can find me here

Mew

oh the same pic

is that ur only photo JohN?

user228700

@JohnRennie Can I e-mail u or something via gmail instead?

user228700

@Mew Yeah, @JohnRennie, was wondering the same thing :-P

John Rennie

09:15

@Kaumudi yes of course. Send a message to [email protected]

user228700

With what? My address?

Mew

@Kaumudi how much do you trust John Rennie

John Rennie

Just send anything for now. That's an old address that gets too much spam to be useful, which is why I don't mind posting it in a public forum. When I get your mail I'll mail you my gmail address (which I don't want to make public!).

user228700

Okay. Mailing now! :-)

user228700

@Mew :-P With my address, I think I trust him enough :-) If he were to come here someday, I'd gladly invite him for lunch or something.

Mew

09:19

Ok just be careful

I like to see at least 2 pics before sending out an address myself

John Rennie

@Mew @Kaumudi actually I agree with Mew on this, which is why I was keen that your parents know about this. I gather that you have OK'd it with them?

user228700

:-P Sure. I do want to see some more pics...

John Rennie

Mew

lol

John Rennie

That's me :-)

user228700

09:22

34 mins ago, by Kaumudi

I asked my parents about it. They were only worried it would cost too much to ship it, but this is definitely OK. Can u like, post some more pictures please?

user228700

@JohnRennie Yep!

user228700

@JohnRennie: I sent u a mail. Did u get it?

John Rennie

@Kaumudi yes, I've just replied. And now it's back to work for an hour or so ...

koolman

10:05

Hii @Mew

Mew

hi cool man

koolman

@Mew can we not post pictures of question

physics.qandaexchange.com/?qa=427/intensity-at-same-point

Mew

of course you can

I believe I reopened the question that was closed

koolman

But as you know heather is ...

So there is no problem

Mew

yeah my belief is that pictures are ok

I find often when people type out the full question

they miss important details

koolman

10:08

Ok thanks

Mew

but that said

if you are copying from a textbook or something pleease reference

koolman

@Mew yeah

Swapnil Das

Hi.

Mew

yo

Swapnil Das

Your site is getting better day by day. Congo.

@koolman are you prepping for nsep?

koolman

10:18

@SwapnilDas actually main aim is IITJEE . NSEP is just a side aim

Swapnil Das

@koolman You are in which class?

koolman

12

And you

Swapnil Das

10th

koolman

Ohk

Swapnil Das

@koolman from where do you get tough physics probs?

koolman

10:23

@SwapnilDas irodov or physics galaxy

Swapnil Das

@koolman Cool.

Mew

is everyone as studious as you guys?

user228700

@JohnRennie: Arfgh, I'm sorry for that terrible e-mail. My phone messed up. I'll send u another :-/ I'm sorry!

Swapnil Das

"guys" : Me?

Mew

yea

Swapnil Das

10:26

I'm not at all studious.

Mew

but ur looking for hard physidcs problems no?

Swapnil Das

@Mew That's time pass and fun.

Mew

yeah true

Swapnil Das

@koolman Do you have the PG book?

user228700

@JohnRennie: U can still decipher it so never mind that, I won't send another one.

koolman

10:28

@SwapnilDas yep

Swapnil Das

It is cool no?

koolman

:)

Transcript for