The h Bar

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

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

12:11 AM

Well you see, i don't have school anymore

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

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

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.

Friends is for new years

Christmas I have to visit the family

Sanya

12:12 AM

@heather O_o~

@ACuriousMind, new profile picture...

I did ask for a physics book for christmas

I forget which one

Let me see

@heather Indeed. We are legion.

"Linear Operators in Hilbert Spaces"

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

12:14 AM

Very Christmassy

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

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

Last year I got Glimm and Jaffe for Christmas

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

oh, and Apostol's Calculus Vol 2

12:18 AM

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

@Slereah What for?

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

I like to have big reference books

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

I mostly get socks.

Well as you know

I worked in robotics for a bit

I got a lot of toy robots last year

Heh

12:32 AM

lol

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

So it turns out the thought didn't count

They just clutter my shelves now

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

12:49 AM

@ACuriousMind dammit, look at this

-2

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

Hmm?

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

@ACuriousMind check the timestamps of the answer and the deletion

wait, what?

lol

The question was deleted, then immediately undeleted

I mean, check the timeline

1:26 AM

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

2:04 AM

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

DanielSank

Hi, everybody...

@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?

@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

3:00 AM

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 $\phi$

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.

wot

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

Good to know

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

3:20 AM

Well I need a specific conformal transformation

Not sure which one yet

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

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.

But @ACuriousMind

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

But that's what I mean by a conformal transformation

Arrrrgh

This is a point of large confusion all over the literature

that it is

Although I guess that technically I need both

Coordinate change and Weyl transformation

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

3:28 AM

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

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