^ Science

ist^

@ChrisWhite Oooooh, congrats on having a set date.

@ChrisWhite :D

@BernardMeurer @ChrisWhite I'm getting married in July. If you want to come by we could probably split the cost of stuff.

@DanielSank Nice!

She's an astrophysicist :-)

Ehm, I have no news guys ;-;

I tried a bad pickup line yesterday and it went well

that's it

@DanielSank That's proof that opposites attract each other you being quantum physicist

Unification is near

:-)

Congratulations

@skillpatrol Oh man, that's a really good one.

@BernardMeurer FFS details.

FFS? Your young acronyms are too sly for me

@BernardMeurer "For fu--s sake"

Ah!

I hope I don't get banned for that.

nah, you don't have a record ;)

TL; DR: I said "Are you Crimea?" "No?" "Because I'd like to annex you"; got her number

go figure

LOLOLOLOL

I'm sort of bewildered by why an intelligent well spoken person such as yourself would even try such a thing... but I suppose you're also smart enough to respect data, so if it works...

@DanielSank Very simple: It somehow works

I think it's my latino fire

@BernardMeurer I have a really funny story for you.

@DanielSank Go for it :D

@ChrisWhite attach?

W2?

@BernardMeurer A good friend of mine has a friend named William Preux.

Will is the greatest ladies' man I've ever heard of.

He constantly bemoans his lack of a steady relationship while going through one-night-stands like grains of rice.

So one evening, Will is sitting around flipping through Tinder.

He gets a message from a woman which went something like this:

"Heyyy boi. You look gud XD If you wanna hook up texxt me, ok?

It's a guy, I can tell already

Now let me ask you something, dear friend: what would most young men do in this situation?

Most? Go drool over it and try to get laid

I'd hide

what did he do?

asl

@BernardMeurer Correct.

In fact, in this situation Will had a 100% chance of spending the night with this young lady.

Omg Dan the buildup is killing me

However, his response, which will go down in history, was as follows:

"Woah! That's pretty forward. Why don't we try it again only this time with proper spelling?"

lol

Hahahahahaha

What I learned from this is that Will is SO saturated in these opportunities, that it was actually worth it to him to trade an opportunity for sex for a quick chuckle.

He's one of mine!

Well, apart from the saturated part

The economics of that... the simple supply and demand balance displayed by this blew my mind.

Microeconomics of tinder

What was her reply?

sounds like a cool PhD thesis

@skillpatrol I don't think she replied

@skillpatrol Are you kidding? I'm sure there was no response.

Just checking :)

How can I star that more times?

This chat room is one of the best sources of humor in my life.

@ChrisWhite perfectly played :-)

Sort of like this.

@DanielSank thinfi.com/0026

The password is the name you gave the octopus at Monterey

@BernardMeurer <3

You just made me happy in so many ways.

Hahahaha

I remember my stuff man!

You remembered that I love octopuses, you remember that I named the one in Monterey, you remembered the name, and I'm happy for you :-)

@DanielSank See! The crimea line works!

@BernardMeurer is it adorabilis?

@HariPrasad Good guess, but no.

There's no way anyone is going to guess this.

@DanielSank Now they'll obsess over it

@BernardMeurer Jimi (Hendrix) ?

@BernardMeurer Have you actually gone out yet or just got the digits?

@JohnRennie Interesting guess. Where'd that come from?

Monterey Pop

@BernardMeurer ::makes popcorn::

The 70s

@DanielSank I ain't touching that until I move to the US, met her because she's the sister of my childhood friend's gf

And I bet an octopus would make a mean guitar player :-)

friend who lives in bloody houston

@JohnRennie HELL YES!

@JohnRennie I heard Liszt only composed for octopuses

@BernardMeurer flapjack?

@HariPrasad Nope

@HariPrasad Are you looking up octopus species nicknames?

Why would you call an octopus "flapjack"

@JohnRennie It was a funny cartoon

@JohnRennie Here's a reason:

:|

@BernardMeurer Guinea Pigopus?

@HariPrasad Nope

Going to Monterey caused me to stop eating Tuna

@BernardMeurer Oh?

@DanielSank Yeah, Tuna was never my favorite fish anyway, and they had this nice exposition about the damages of Tuna fishing

and I was like hell nah

Well, well, It's my time to go to sleep now folks

cya later

ciao

@Danu <3

@DanielSank Just to respond to what you said, I'd love to go to your wedding, but I'm a student (read:broke) so I'll have to see what I can do :p Maybe I can pretend to be visiting UCSD. Nighty!

yooo

oooooooooooooooooo

@BernardMeurer Opisthoteuthis sp?

@HariPrasad He went to sleep.

great! I woke up

Supersymmetry lecture starts with recap of scalar field theory -___-

@Danu Oh, poor you.

At 8 AM!!

"I'm Danu and I'm so smart that I'm bored by scalar field theory."

I got out of bed for this

poooooooooooor

@DanielSank not too smart, too drilled by years spent in the machine of university QFT courses, where scalar field theory is done every semester in SOME course.

2D solitons was much more awesome (and simple!). I'm taking this course called Instantons & Black Holes; it's basically my last shot at getting interested in physics again :/ but so far it's been fun, so I have good hopes :)

So what have you been up to @DanielSank

@Danu Telling stories and setting @ChrisWhite up for an excellent joke. Scroll up.

...and writing a paper.

@DanielSank cool! I'll be starting on my thesis soon-ish

@Danu Good for you.

Title?

So maybe I'll end up writing a paper within the next 1.5 years

@Danu The trick to writing a thesis is to procrastinate and play video games.

@DanielSank no title yet, but it will be on 2D superconformal fields theories separated by domain walls

Trust me, I'm a doctor.

Or something related to it... I hope to compute some geometric invariant

It bugs me that theorists call say "theory" to mean "Lagrangian".

Why have you castrated the word "theory" like that?

No lagrangian lol

Fine, you know what I mean.

CFT doesn't need Lagrangians

Oh my god, really, dude?

CFT's are very special in the sense that they're completely algebraic

It's awesome!

Do you really not understand what I meant or are you play-acting to make fun of me?

@DanielSank I really don't understand

@Danu k, forget it.

Or rather, I know theorists often do this, but I'm not right now

So your remark doesn't make a lot of sense to me atm

In the ideal gas model, we assume that particles collide with each other, right?

@Anthony Sort of.

Not really because we model them as points

The ideal gas is a weird idea where there's enough interaction between particles to get everything into thermal, equilibrium, but not enough to affect the dynamics or give the gas any of the properties that actually exist with interacting particles, such as phase transitions.

The Van der Waals eqn/model fixes this somewhat I guess

@Danu Yeah but that gives totally different physics.

Sure

I mean, how can the answer be sort of and not really? In the definition, don't we say that collisions between particles are elastic?

We don't rule out collisions, right?

So what, is it just that because they're points collisions happen with probability zero or something.

@Anthony The ideal gas is a made up model that approximates how real things work to a good degree in some cases.

It's a mathematical model, not a physical one.

I'm 100% okay with that, I just want to be sure I understand that model.

Well, I suppose it has a sort of reasonable physical interpretation.

Again, the idea is that the particles don't interact at all, but still remain in equilibrium.

So they don't collide.

Correct.

Great.

Why does every resource I read say they collide elastically.

@DanielSank it's an extremely good model, physically, for everyday life stuff

@Danu No, it's not.

It's awful for water.

For GASes :P

It works for some things, in some temperature ranges.

Not arbitrary fluids

Like, the first line of wiki says "An ideal gas is a theoretical gas composed of many randomly moving point particles that do not interact except when they collide elastically. "

All gases in everyday life circumstances, I conjecture

@Anthony I'm not 100% sure if this is true, but I think if you have collisions you get different behavior than PV = n k T.

@Danu Ok, I made rice for dinner. Was the steam over my pot obeying the ideal gas law?

@Anthony Ok then I might be wrong. Perhaps if you have point particles with elastic collisions you actually still get the idea gas law.

@DanielSank it's not a pure gas by a long shot, but even then I think it's going to be reasonably close

If the particles have nonzero radius then that definitely won't work though.

@Anthony when we say ideal gas particles collide we really mean they exchange energy with each other to reach a statistical distribution of energies.

@Danu No way! The steam in contact with water is on the verge of condensing. Not even close to an ideal gas.

Yeah I believe that. It's just my issues then is that we seem to treat different species of ideal gases as non-colliding.

@DanielSank what letter do you use for Boltzmann's constant ;)

@skillpatrol $k_b$

Why?

Just wondering

@JohnRennie Don't they do that by colliding?

@DanielSank like I said, not even close to a gas at all, but I think certain features will still be fine

Like volume

@Danu Dude, the steam is definitely a gas.

Someone here: physics.stackexchange.com/questions/105918/… says that "A system of point-like particles which collide elastically cannot be distinguished from a system of point-like particles that don't interact at all."

@skillpatrol Is there any other commonly used symbol?

There is lots of non vaporized water in it

R @DanielSank

@Anthony I guess because they never actually touch like I said

@Danu Even so if you have any gas at the condensation temperature it's not acting at all like at ideal one.

@skillpatrol That's not Boltzmann's constant.

@Danu Again, that's what I was hoping, but every definition I find says they collide.

@Anthony as others have said, point particles cannot collide because they have a zero cross section. So we kind of gloss over exactly how energy is exchanged. Real gases atoms/molecules do collide of course - quite frequently actually.

That's Boltzmann's constant divided by Avogadro's number.

@JohnRennie Well fantastic. Thanks. I don't know why no one ever told me that...

@DanielSank if you put it in an infinitely large container with no dust etc to condense on I challenge you to tell me why

@Anthony I just did!!

@Danu Besides you, of course.

Actually the nearest to an ideal gas is probably dark matter

@Danu I refuse to engage in this sort of intellectual masturbation. I don't care about squabbling about mathematical models that have nothing to do with reality.

I think it's a reasonable question

Alright, thanks everyone.

Good question @Anthony :-)

@Danu ok

Hello

→ 17 messages moved to Temp. chat

→ 13 messages moved to Temp. chat

Bonjour mon ami @Slereah how are you?

The week end soon

cool

@Danu : Can we make a message pop up if a post on PSE contains the words "really exist"

Wow, those 30 messages were swept under the rug fast :P

→ 27 messages moved to Temp. chat

Make that 57

:D

What can I say, the modz do their jobz.

@skillpatrol The room is public---there is no "sweeping under rugs" going on.

It's just a common figure of speech ;)

He said, sending all the witnesses to jail

:P

@skillpatrol well, yeah, but it's a figure of speech that means something different from what you're using it for.

Indeed.

How so?

Sweeping something under the rug means hiding it.

Not necessarily

It does.

I guess it's sort of valid in the sense that the messages are no longer obviously visible, you have to actively click a link to see them, but still, the phrase implies the intent of a coverup, which is not the case here.

idioms.thefreedictionary.com/sweep+under+the+rug

Like I said it is common enough to be used in MANY contexts

Even if I'm actually sweeping the floor :P

No Fun

ALLOWED

bye

@Danu here it is ;-P

@skillpatrol o_O

@skillpatrol No idea what this is about, but never mind :P

@DanielSank I find your agreement agreeable.

Sigh

wb

i didn't think you were going to return

@skillpatrol meh

I can't leave @ACuriousMind

What would he do without me

AQFT defines states as linear functionals on the star-algebra such that among other things $\omega(A^* A ) \geq 0$

Is this always true?

@skillpatrol I like how that guy suspended me and I just went to bed

Although I have a terrible headache

And pretty sure I had a nightmare

Thanks a lot mods

Is $\langle \omega \vert A^\dagger A \vert \omega \rangle \geq 0$

I'm not sure it is

yup, just another day on the job

@Slereah Yes, that is the general definition of a state of a $C^\ast$ algebra, nothing to do with AQFT.

Oh

It seems that's how they define quantum states, though

@Slereah Yes, because it is the inner product of $A\lvert \omega\rangle$ with itself.

I suppose so

@Slereah Yes, but it's not specific to QFT - that what a quantum state for a $C^\ast$ algebra also is in the QM case.

$(\langle 0 \vert - \langle 2 \vert) a^\dagger a (\vert 0 \rangle - \vert 2 \rangle) = (\langle 0 \vert a^\dagger a \vert 0 \rangle - \langle 0 \vert a^\dagger a \vert 2 \rangle - \langle 2 \vert a^\dagger a\vert 0 \rangle - \langle 2 \vert a^\dagger a\vert 2 \rangle) = 0 - 2$

Is that not correct, tho

No, the last - should be a +

Oh right

nvm

Hm

How did they do the negative energy state in QFT then

I forget

Note, this definition does not say that $\omega(A) \geq 0$.

So it's perfectly fine for e.g. $\omega(H)$ to be negative if the square root of $H$ is not in the algebra.

Yes but it was for a free field

Although... I guess for a free field

Wait no

Still should be $a_p^\dagger a_p$

Uh...for a free field you can shift the energy of the ground state whereever you like

The vacuum energy is a renormalization parameter, not a prediction of the theory.

(We usually set it to 0 because that's what LSZ needs)

Sure but the renormalized energy is still $\approx a^\dagger a$

$+\text{vacuum energy}$ :P

Yeah

The constant that is added to $a^\dagger a$ in the Hamiltonian is precisely the vacuum energy

I'm not sure what your point is

I need to check up what was the exact thing

I forget

Hi guys, thoughts on How To Solve It by George Polya?

Ah, found it

cds.cern.ch/record/315805/files/9611064.pdf

Hm

I should redo it by hand

Make sure I understand it all

what

@ramsay Why would they?

Are you taking the "water pipe" analogy literally?

"We also observe that the negative contribution comes from the cross term."

Ahah

That's why

"Are you taking the "water pipe" analogy literally?" No

If the electrons try to leave the wire, a force will be applied to them

Because the electrons leaving would imply a charge deficit behind

@ramsay 1. They weren't "in motion" because the proper model of electricity flowing is quantum mechanical. 2. If an electron would leave the wire, the wire would have net positive charge and hence clearly attract the electron. So there is a force keeping them in. The ion rumps of the metal attract them.

Also be aware that electrons in a wire are very slow

on the order of mm per hour

@ACuriousMind first point was not clear but second was, thank you

@Slereah if this is the case then why do we get electric shock immidiately after switch is turned ON

@ACuriousMind Wth are you telling me they lie to us in high school

Because all the electrons in the wire move at once

They just move very slowly

Hm

@Slereah Not actually correct, or rather, it depends on the model. If you model a metal with free electrons as a Fermi gas/liquid, then the only meaningful velocity is the Fermi velocity, which is rather high.

Well gee if they're free sure

but they are not very free in a wire

@Slereah What? The usual models all say the conduction electrons are free.

I think your slow speed is what comes out of Drude model, but I'm not sure.

They are free between two collisions :p

Drift velocity is dreadfully slow

@Slereah "move at once" i didn't get this :p

@Slereah Yes, but only in the Drude model. If you take the QM Fermi model instead, then you don't have a "drift velocity".

Apparently in AQFT the probability of a (discrete) observable is $p(a_k) = \frac{\omega(\prod_{i\neq k} (A - a_i))}{\prod_{i\neq k} (a_k - a_i)}$

How to show that this is true

It's too simplistic to say "electrons are moving very slowly" because that is a purely classical description

Hm

Let's see

If I have two eigenvalues a_1 and a_2, that would be...

Some models say the positive holes are moving :P

$p(a_1) = \frac{(\alpha^* \langle a_1 \vert + \beta^* \langle a_2 \vert ) (\hat A - a_2) (\alpha \vert a_1 \rangle + \beta \vert a_2 \rangle ))}{(a_1 - a_2)}$

@skillpatrol Well remember that the electrons exist as standing waves

hm, my question turned to quantum debate

Indeed.

@Slereah Is that not the Born rule in disguise?

i.e. a postulate

Yes

@Slereah Stop saying "in AQFT" for things that are true in all of QM :P

But i want to show it's equivalent to ordinary QFT

@ACuriousMind Well excuse me to not be a fancy algebra man

REAL physicists don't use that C-algebra shit

what do they use?

@Slereah Then just represent $\omega$ as a state in a Hilbert space, then expand it in eigenstates, then evaluate the numerator explicitly.

@skillpatrol hilbert spaces and linear algebra

That's what I'm doing!

So... $p(a_1) = \frac{ \alpha^* \langle a_1 \vert \hat A (\alpha \vert a_1 \rangle + \beta \vert a_2 \rangle )- a_2 + \beta^2 - \beta^2 a_2 ) }{(a_1 - a_2)}$

i think I forgot some factors along the way

It's hard to do calculations in raw tex :p

I'd better do it on paper

What do you guys do in your spare time?

Physics :V

The videoed games

Exercizing

The movies

@JesterTran math, video games, girlfriend if I'm really bored

I read the books

movies, TV shows

Partying with friends

>friends

Yes some of us have friends

Cool!

@Slereah What books do you read?

Have you guys seen a movie called The Prestige by Christopher Nolan?

Last book I read was "The clockwork rocket"

I have not

I haven't read a fiction book in years

@Slereah $p(a_1) = \frac{1}{a_1-a_2}\left(\left(\langle a_1\rvert \alpha_1 + \langle a_2\rvert \alpha_2\right) A-a_1 \left( \alpha_1\lvert a_1\rangle + \alpha_2\lvert a_2\rangle\right)\right)$. Now the only term of the four that survives is the one with $\langle a_1\rvert A-a_2\lvert a_1\rangle$ in it, and the $a_1-a_2$ cancels, leaving only the coefficient $\alpha_1^2$.

Ah yes

Thanks

Hm

A more general way to see this works is to note that $\prod_{i\neq k} A-a_i$ is a projector onto the eigenspace for $a_k$, and the denominator is just its normalization.

@Slereah Looks really interesting, the book

It's a book that has its problems

@ACuriousMind What is $A$

The author was more interested in the physics than actually making a decent story

Good worldbuilding, poor narrative

An Operator

Well

A member of the C-Algebra

@Slereah A...telephone operator?

No, that would be $☎$