Bombay

Ah, yeah, bombay smells nice

Not sapphire though

She thinks it's too powerful

Bombay Dry?

Yeah

@ACuriousMind Yeah, but idk, i just don't like distilleds to be honest. There are only a few drinks I enjoy and I like them on weak side of things

The red one.

I don't like the taste of alcohol too much

I think it takes terrible, honestly.

Sapphire I pure alcohol dude

*is

@BernardMeurer Guess Bob's favorite whiskey and I'll do anything you want.

@0celo7 Which is why I like it mixed

@0celo7 Hint

No not with these stakes

Lower the stakes, I want Shankar hahaha

It's American

And not bourbon

It's only sold in two states

Holy fuck

Ehm

Another hint

@ACuriousMind has never had it.

Jeez isk, Defiant?

Nope. Completely wrong genre of whiskey, too

@BernardMeurer ok one more hint.

ACM has never had this kind of whiskey

Oh jeez

Hm

@0celo7 Old Overholt?

No.

Heck idk man there are a bunch os whisky brands

What is it?

Ask ACM what kind he's never had.

@ACuriousMind What kind of Whisky have you never had?

What is hiding in the last wonder of the world? Scans using 'cosmic particles' to reveal secrets of the Great Pyramid of Giza / dailymail

@0celo7 I am so tempted to star this, but then I'd have to put my room owner hat on and clear the stars :-)

RIP Mohammad Ali :'(

7 a.m. and I'm already onto my second (pint mug of) coffee. Some mornings it's hard to get going.

hey

@JohnRennie Holy cow :P

I fell on my hand yesterday

bloody wrist hurts

I might have been drunk

(I might have fallen 4 times on it)

it does sting

Maybe it is the week end

he might be drinking some breznak

or some tuzemak

@BernardMeurer I did surgery and now I can barely breath until I recover. and im on a lot of drugs.

What is the link between the exponentially decay of the propagators and on-shell states? What is the physical meaning of an exponentially decay of a field propagator?

Goodmorning everyone :)

@vzn So, should I post my meta question list for AMA, or should I wait for an official ok on the date?

@FrancescoS Do you mean that the propagator decays exponentially when leaving the light cone?

I don't think that there's a particular physical significance of this fact

The physically significant thing is that the field operators commute at spacelike separation, not what a single propagator does

ok

Hello

anyone good at statistics?

or probability?

I have a question regarding what distribution I should use to model something

@MAFIA36790 no, boarding now from london

\o

Probabioly not

I'm not interested in applying my results to real data

It's a theoretical exercise

Basically if we look at insurance claims, there are 2 independent variables of interest

the Claim frequency and the claim amount

The frequency is usually modelled with a Poisson distribution

if we assume claims occur at a particular rate

however what distributrion should be used to model the claim amount?

I'm going to run a simulation

@ACuriousMind Yes I know, but someone told me that if the states isn't on shell, then the propagator exponentially decay

@FrancescoS I have no idea what that's supposed to mean

What states?

What does a propagator have to do with states, and how can states be "off-shell"?

I'm willing to bet someone is misinterpreting Feynman diagrams here :P

@ACuriousMind Or probably I didn't understand the point of the discussion ;)

@Slereah what the hell

@JohnRennie Coffee doesn't do anything for me when I'm tired

But when I'm fully awake it sometimes makes me jittery

so you mean grammatically speaking since + means "positive" and not "positi", the correct way to abbreviate "positive direction" is "+ direction"?

@Secret Well, I'd say just writing the + is more natural if you're abbreviating. Who looks at "+ direction" and thinks "That's wrong, it should be '+ve direction'"?

I just can't figure out any reasoning to write the -ve at all.

the habit of writing -ve, +ve for most people (myself included) might have something to do with how we came up with abbreviations or notetaking symbols. We have a tendency to retain a portion of the original term in the abbreivations

@0celo7 I don't think the coffee really does anything - I drink fairly weak coffee anyway. It's more of a comfort having a mug of coffee to hand, and some mornings I need more comforting than others :-)

sneakerbardetroit.com/air-jordan-12-black-nylon-release-date

@ACuriousMind Wtf where did you see that?

@0celo7 Regularly on this site

@ACuriousMind o.o.o.o.o

link pls

@0celo7 ...it's usually (and rightfully) edited out and I don't keep a list of such things

@Danu Lee SM is such a good book

I liked it before it was cool ;D

@ACuriousMind How do I prove that the countable union of sets of measure zero has measure zero?

With math

@ACuriousMind :(

(it should follow from one of the defining properties of the measure rather directly)

@ACuriousMind Correct, it does.

@0celo7 What the heck is your question, then?

@ACuriousMind I had to reread the definition :P

@yuggib firmly regard you as the next guest for 1st available slot after jun14th. slereah had good response on his meta post, think its ok/ clear to post if you like, but the date is still TBD. did you see conversation with DZ? he just wants to have an informal evaluation after jun14th session. btw slereahs expressed response/ experience/ opinion/ feedback/ feelings etc would be a key part of that evaluation. & you can help evaluate also if you like (would likely be helpful to all).

@Danu when did it become cool

@ACuriousMind Is the "trivial group" the group with just $e$ or an empty set?

@0celo7 The empty set is not a group.

Recall the group axioms

@ACuriousMind I know

@Danu I know

@ACuriousMind I'm not sure.

Give me a minute

Think first, then ask :)

@Danu I did think

@Secret "latent variables" have a sort of nearly "schizophrenic status" in different fields & esp physics/ QM. they are a very big deal in computational linguistics aka LSA/ LSI, and actually a a key part of ratings systems theory also now (they played a very big role in the groundbreaking $1M netflix big data/ datamining contest). it would seem the concept is very fundamental/ intrinsic to big data analysis etc

the unifying/ crosscutting/ interdisciplinary concept of latent variables seems to be ubiquitous across fields...

@yuggib what are you doing in japan? how long there? DS mentioned he is visiting also soon for his honeymoon

(removed)

1 hour later...

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ Hmm?

I just asked ACM why we use the negative of the Killing form as an inner product on $\mathfrak o(n)$.

But I figured it out as soon as I typed it.

I see.

@ACuriousMind books.google.ca/…

@ACuriousMind #rekt

tfw a Pokemon game delivers a soul-crushing twist

@3075 Drugs? Sounds fun. Have a good recovery chap, glad it went alright

@MAFIA36790 He was brushing his teeth and one of his lungs collapsed so he's been at the hospital. He had surgery to get his lung back going and is now in recovery

:(

That's what you get for having good dental hygiene

A collapsed lung sounds painful.

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ When he was telling about it I don't think he mentioned any pain, but I have no clue. I'd imagine it's more of an agony feeling where you can't breath

Yup, he's probably on heavy medication @BernardMeurer

@MAFIA36790 2 times a day is non-ideal, you want at least three and if possible after every meal

Go to the dentist. @MAFIA36790

@MAFIA36790 My mom's a dentist, only reason I know that :v

And go to the dentist, a cavity can yield much worse infections if untreated

@MAFIA36790 If you don't want to loose your teeth over a cavity go to the dentist and solve that issue

@JohnRennie o/

@MAFIA36790 A year? Time to go again :)

I go to the dentist every day :v

:V

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ Hi

Do you use the abbreviations +ve and -ve @JohnRennie?

Yes, I do.

It's not something I have any strong view on, but the characters $+$ and $-$ on their own are quite small.

Useing +ve and -ve is physically bigger and I think often clearer.

@JohnRennie What does ve stand for?

Positive @Keepthesemind

it stands for the last two letters in the word :P

I suppose we could use +tive and -tive instead if we wanted to be really silly :-)

:-)

@JohnRennie That's... bad. Did you think of this yourself or are you mimicking other language criminals?

I'm not sure I see why it's bad. If I choose to use +ve as a symbol to mean positive that doesn't strike me as controversial.

@JohnRennie OK. Why not use :) for positive and :( for negative then?

@MAFIA36790 For example a really cool Einstein ring.

@Keepthesemind Is that a serious question? You think :) would be a better abbreviation for positive than +ve?

@JohnRennie I think you should try it.

Trolling?

@Keepthesemind Well I think you should try painting your buttocks green and claiming you're a watermelon. That's an equally constructive thing to do.

@JohnRennie lol

@MAFIA36790 that's a good post. He does have a sense of humour then :-)

What prevents gravitational dipoles?

@MAFIA36790 I saw all of that quite some time ago. Maybe not the same post, but another one that contained all of this one.

@StevenStewart-Gallus there is no such thing as negative mass

There is no such thing as magnetic charge at all @JohnRennie and yet magnetic dipoles exist.

@MAFIA36790 So, I think Motl makes a basic thinking mistake here.

@StevenStewart-Gallus Magnetic dipoles are only possible because electric charge comes in two opposite signs.

@JohnRennie I don't follow. Are you saying that a single electron is not a magnetic dipole?

@StevenStewart-Gallus Hmm, good point.

@JohnRennie It occurs to me that I've never heard of a fundamental particle being an electric dipole either though.

Although using an electron is a bad example because the electron isn't spinning. However a rotating charged object would generate a magnetic dipole.

@StevenStewart-Gallus the electric dipole moment of fundamental particles is of some theoretical interest.

See for example this question

Or there will be plenty more relevant articles a mere Google away

@JohnRennie Okay so it looks like this is a matter of theoretical physics that hasn't been fully answered yet then. Thanks.

Hi guys! What do you mean when you say that a symmetry protect a coefficient to be small? For example, the custodial symmetry protect $\rho$ to be 1

Where is @ACuriousMind

I have some mathematical physics question

also, not for ACM, but

My mum writes thesis about autism and describes my "talents" and my mother doesn't want to give my Stack Exchange and Github profile link in her thesis.

Morris Thorne puts the metric of a wormhole converted to a time machine as, for one mouth, $ds^2 = -(1+ glF\cos \theta)^2 e^{2\Phi} dt^2 +...$

Is the first term basically a boost (well, acceleration) in spherical coordinates

$g(t)$ is the acceleration, $l$ is the radial coordinate, $F(l)$ is some form factor

I should reread visser on wormhole time machine

It's not an easy argument to follow

@ACuriousMind I'm bored. Any quick explanation of BRST and particularly how cohomology pops up?

@Danu BRST? Brazilian Summer Time? I can tell you all about that

Bratislava quantization

Ah, less fun

BRST quantization is the "rigorous" way to quantize gauge theories

@BernardMeurer Just for reference, it's not actually Bratislava :P

@Danu Yeah I googled it before he said that hahaha

So

what is the exact link between the spinors, the clifford algebra and the grassman algebra

From what I can figure

A clifford algebra is a type of Grassman algebra

And you can describe spinors in terms of a clifford algebra

BUT

Only if they are anticommuting spinors

Otherwise not

Is that notion correct

@Slereah what are you talking about

I am talking of what I just said

grassmann algebra?

is that just $\Lambda (V)$?

A grassmann algebra is a general anticommuting algebra

@Slereah I think you should read chapter 2.4 of Jost...

A set of generators $\{\theta_i\}$ such that $\theta_i \theta_j = - \theta_j \theta_i$

@Slereah How is that different from $\Lambda(V)$

Also police cars and ambulances on campus

@BernardMeurer Dammit this is what happens when your countrymen are around

Did you beat Cho's high score

?

Exterior algebra is a type of grassman algebra

Well, the odd degree part

At least I THINK

Also I probably should wait for ACM instead of discussing it with you

savage

@Slereah You know it would be easier to talk to you if you actually asked precise questions

Well do spinors have to be elements of a Clifford algebra (or homeomorphic to them, anyway)

Or is that a specific thing to anti-commuting spinors

@0celo7 c:

@Slereah Do you mean a Grassmann algebra?

Spinors in a Clifford algebra form a Grassmann algebra, I think?

@Slereah What is your actual defintion of a spinor

an object that transforms according to the double cover of the Lorentz group

Basically what is the mathematical difference between commuting and anticommuting spinors

@Slereah are anticommuting spinors the exterior algebra of noncommuting spinors

wot wot

@Slereah how is multiplication of spinors actually defined?

what are "anticommuting spinors"

Well in spinor path integrals, the fields are defined by Grassmann fields $\psi(x)$ and $\bar \psi(x)$, such that $\{\psi(x), \bar \psi(x)\} = 0$

@Slereah Ok but isn't it that they anticommute component wise?

Which, after quantization shenanigans, becomes the CAR, \{$\psi(x), \bar \psi(y)\} = i\delta(x-y)$

I am having trouble finding a book that will just spit it out clearly, but as far as I can tell, this is the full spinor

I think it's related to the fact that a spinor can be defined by a Clifford algebra element, and those anticommute as well

@Slereah how is $\bar\psi\psi$ defined?

and how is $\psi\bar\psi$ defined?

IIRC only one of those makes sense

That is part of The Mystery

@Slereah I threw away all of my physics books, otherwise I'd help

But I thought the CAR was $\{\psi_\alpha(x),\bar\psi_\beta(y)\}=\mathrm{i}\delta_{\alpha\beta}\delta(x-y)$‌​.

And the multiplication of components makes sense.

I think this might be the spinor thing where $\psi^a \xi_a = - \psi_a \xi^a$

@Slereah No no

Because I remember that when you construct the spinors as the solutions of the Dirac equation they are not automatically anticommuting

yes, that is why I ask

I know you can build commuting spinors

They work fine, outside of that whole not causal and not bounded from below

I have this hunch that the difference might be the metric tensor

The standard metric for spinors is $\varepsilon^{ab}$

I think the commuting one might be $\delta^{ab}$

...what

Fuck where is Wald

Why do I even ask you

Oh I have Straumann, that works too?

@Slereah Because I know more than you

Apparently not!

@Slereah well one picks $\epsilon$ because it is invariant under $\mathrm{SL}(2,\mathbb C)$

is $\delta$

it is $\epsilon^{AB}\xi_A\psi_B$ that is invariant

@Slereah check it?

@Slereah you need $\epsilon$ to get determinants.

so $\delta$ will not be invariant.

Hm

Then I do not know

I guess that's an ACM question

Or a PSE

@Slereah do you understand why we need $\epsilon$?

Well the spin group is $SL$ which preserves determinants

@Slereah no it's the group which has $\det =1$

or is that what you mean?

Yes

what does the Bible say

@0celo7 Check Ezekiel 23:20

I always go there for wisdom

@Slereah I prefer 25:17

The path of the righteous man is beset on all sides by the inequities of the selfish and the tyranny of evil men. Blessed is he, who in the name of charity and good will, shepherds the weak through the valley of darkness, for he is truly his brother's keeper and the finder of lost children. And I will strike down upon thee with great vengeance and furious anger those who would attempt to poison and destroy my brothers. And you will know my name is the Lord when I lay my vengeance upon thee.

Bless up, papa bless.

@Slereah Ok how does Peskin write the CCR

for anticommuting spin stuff

$\{\psi_a(x), \bar\psi_b(y)\} = \delta(x-y) \delta_{ab}$

so exactly what I said

it's the components, not the spinors

but then the classical action has $\{\theta_i, \theta_j\} = 0$

Where $\theta_i = \psi(x)$ and $\theta_j = \bar \psi(x)$

what does that correspond to

what

Grassman algebra stuff m8

I'm going to get food

You...keep on doing whatever you're doing

@StevenStewart-Gallus It is a fundamental mistake to treat the electric and magnetic fields as being separate from one another in this way. They are the parts of a single, skew-symmetric tensor object, and are intimately related by relativity.

The gravitational field is not the mixed index parts of skew-symmetric tensor in the way that the magnetic field is so, it is unsafe to try to make a simple analogy between them.

For deeper insight than that you'd have to ask one of relativists who hang around here, though, as I am rapidly getting our of my competence.