The h Bar

@Semiclassical Yeah I didn't think it was tasteless as in obscene but tasteless as in a really unnecessary attempt at unsuccessful snark which ended up being not more than a cringe for me

But I don't complain about not having to see those messages anymore

Or anything of the like for the next hour

Abcd

@ACuriousMind Mind explaining enthalpy? asking you after going through the Physics.SE answers and my book.

0ßelö7

Doing unnecessary things is wrong. Increasing entropy for no reason.

Semiclassical

5:15 PM

well, I put ignore up

soooo

0ßelö7

New user shows up after someone gets banned? Interesting.

ACuriousMind

@Abcd Sure, if you can be a bit more specific about what you want to have explained about it

The Wiki article is passable, imo

Abcd

@ACuriousMind "energy required to create room for the system". Does this also include a view that initially the system didn't exist and then it came into existence because of enthalpy provision?

@ACuriousMind Went through it too.

I don't like this definition "energy required to make room for the system". the formal definition is more intuitive: " It is equal to the internal energy of the system plus the product of pressure and volume."

ACuriousMind

@Abcd Not so much "because". The idea is that you consider the hypothetical that there was no room for the system (e.g. a piston with the piston fully down) and the "energy required to create room for the system" is then the work necessary to raise the piston to the current volume at the current pressure. But there's no causality implied.

Abcd

@ACuriousMind That piston example is great! Then why do we include the "internal energy" term too?

ACuriousMind

5:22 PM

@Abcd Because enthalpy is supposed to represent the "total" energy of the system, and the internal energy belongs to that, too.

Abcd

@ACuriousMind In the piston example, how does the gas gain internal energy?

Oh, so we would have to work against the internal energy too while raising it?

ACuriousMind

@Abcd By heating it up. In the hypothetical, the gas would start at absolute zero and the internal energy is the energy required to heat it up to its current temperature

Or, well, we start with a gas at absolute zero with zero pressure and zero volume (not that such a thing actually exists), and the enthalpy is the total energy required to get that gas to its current temperature, pressure and volume

Some of the energy goes into "raising the piston" and some of it goes into the thermal motion of the gas particles

Abcd

@ACuriousMind To get there we would also have to work against the pressure of the gas?

pressure exerted* by the gas.

ACuriousMind

@Abcd We're not working against the gas - we're heating up the gas, getting it to exert pressure and thereby raise the piston.

0ßelö7

@Semiclassical Oh, he wants me to prove $(a\times b)_i=\epsilon_{ijk}a^j b^k$. That's only like the 5th time...

Abcd

5:29 PM

Could you represent this piston example mathematically @ACuriousMind. (I know the first law of thermodynamics)

ACuriousMind

@Abcd Ah, yes. We supply heat $Q$ to the gas, causing it to have non-zero pressure. This pressure pushes the piston up, doing some work $W$ in the process. The first law now tells you that the difference between this work and the heat supplied is the internal energy - if you did this experiment (starting from a very cold gas at very low pressure/volume), you'd find that the work done is much less than the ehat you supplied -

the reminder has gone into internal energy, i.e. the thermal motion of the particles.

Secret

3 hours of color sorting done

(Please ignore anything on the upper right corner, they are some random naming thingy and will be edited out later)

Semiclassical

@0ßelö7 ...ugh

that's just boring

Abcd

@ACuriousMind can you derive enthalpy's equation from this? (the one that fits its definition - "energy needed to make room for the system")

0ßelö7

@Semiclassical otoh the rest of the hw is interesting. If you take real/imag parts of a wave function the resulting equations are like a potential flow and you can develop energy conservation, etc. for it.

Abcd

5:35 PM

H= U + heat supplied to gas? @ACuriousMind?

Semiclassical

neat

Abcd

where U is internal energy of the gas. and H is enthalpy.

ACuriousMind

@Abcd Well, the definition is just that it's the sum of the internal energy and pressure times volume. The interpretation is that it's the energy needed to make room for the system at its current temperature, which comes about because it's equal to the heat you have to supply to a gas at absolute zero and zero volume to get it to the current temperature and volume, as I just argued.

Semiclassical

@0ßelö7 that sounds like it could also lead to kramers-kronig stuff, though perhaps what's what you mean

0ßelö7

@Semiclassical You'd have to remind me what that is. I've heard the term.

Abcd

5:39 PM

@ACuriousMind Yes. Perfect. I just want you to write these words mathematically.

ACuriousMind

@Abcd Uh. Mathematically it's just $H = U + pV$, no?

Semiclassical

@0ßelö7 it's something annoying, tbh. I remember the words but not the content

@ACuriousMind as ever in thermo, i always like to think in terms of processes. so $\Delta H = \Delta U+ \Delta (pV)$.

If pressure is held fixed but volume is varied, the last term is just the usual $p\Delta V$ work.

Abcd

@ACuriousMind My interpretation as per that piston example. Heat supplied by us is the enthalpy = current internal energy of the system + the work done by the system.

Please verify^

@Semiclassical I saw wiki use this notation for first law: $dU = \delta Q + \delta W$

Semiclassical

but $\Delta U=Q-W=Q-p \Delta V$

ACuriousMind

@Abcd Yes, exactly

Abcd

5:43 PM

Anyone knows why opposite sign conventions in physics and chemistry?

I have to study thermodynamics in both subjects.

And I might often mess up the +ves and -ves!

ACuriousMind

The sign of work is an annoying convention indeed

Semiclassical

so $\Delta H = Q$ if the pressure is held fixed. But if the volume is held fixed and the pressure is varied, then $\Delta U = Q$ and $\Delta H = Q+V \Delta p$.

that last term doesn't have a nice interpretation in terms of pressure-volume work.

Abcd

@ACuriousMind Thankss a lot seriously! Understood very well!! Now, last question: why is change in enthalpy of endothermic reactions +ve and that of exothermic reactions -ve?

ACuriousMind

@Semiclassical Yeah, sure. I didn't want to spawn a different discussion about different kinds of processes where differnt things vary, but maybe that would have been good to say

Semiclassical

i should probably stop talking, my brain isn't work-ing right now

Balarka Sen

5:46 PM

i see what you did there

i wish i hadn't

Abcd

20

Q: Why do chemistry and physics have different sign convention in thermodynamics?

In physics class, we write the first law of thermodynamics as $\mathrm dU =\mathrm dQ - \mathrm dW$ and in the physical chemistry class, we write the same law as $\mathrm dU =\mathrm dQ + \mathrm dW$. The reason being the sign convention is different in both the cases. In physics we take work...

Semiclassical

Abcd

I personally feel that the physics convention is more intuitive.

Semiclassical

the sign conventions are more merciful when you start writing in terms of T,S, p,V

ACuriousMind

@Abcd "endothermic" means you have to supply energy to get the reaction, "exothermic" means the system releases energy when it undergoes the reaction. Since enthalpy is the total energy of the system, the sign of its change tells you of which kind the reaction is.

Semiclassical

5:48 PM

then you just have $dU=TdS-pdV$

Abcd

@Semiclassical in both physics and chemistry?

@ACuriousMind Nice, understood.

CooperCape

6:09 PM

If I have a bucket of water and stick a hole in the side of it of area, $A$, the rate of flow, Q is calculated by $Q=A\sqrt{2hg}$, right? Where $h$ is the height of water above the hole? Just from $Q=Av$ and $v^2=2gs$.

dmckee

I haven't read a recent physics thermo book that uses the "-" version (well, Reif actually defines two symbols so that whe and his readers can have it both ways).

(I've read several introductory tomes that use the "-" version, but I figure that's because more engineers take that course than physics majors).

In short the "-" version is not the 'physics' convention at all: it is the engineering convention and in at least some engineering contexts it is the obvious one.

vzn

← nonlinear, succumbed to wiped off blackboard by strong sponge(s) :(

dmckee

Nov 5 '16 at 2:17, by dmckee

Avantgarde

@BalarkaSen About 35% of it. I'm not in the mood to listen to GY!BE post rock. Did you like it?

Emilio Pisanty

6:25 PM

@dmckee that's horrifying

Balarka Sen

@Avantgarde I have it on my to-hear list

I'm still recovering from Bish Bosch to listen to even slightly upbeat anything lol

Need more dark shit like that

Avantgarde

haha okay

Semiclassical

@dmckee maybe it's a matter of what texts they were surveying, but

Avantgarde

@BalarkaSen Try this. youtu.be/aiDNf8trWn8

Semiclassical

No Kittel, Schroeder, Huang, or Landau-Lifshitz

Reif is the only one of those I recognize

Balarka Sen

6:40 PM

@Avantgarde So this band is also from 4AD I see

Not the record though

I'll bookmark this. I hope the lyrics are not corny

Avantgarde

I just got reminded of this. Listened to it a couple of months ago. Was nice.

dmckee

6:58 PM

@Semiclassical I actually improved that table after posting that previous image. The new version includes Kittel, but not any of your other suggests (it's what I could lay hands on that week).

@EmilioPisanty I actually put it together to prepare my students for just how bad the stat-thermal notational landscape can be.

I adopted Reif's notation for my prepared notes and usually show the 1st law in both forms when I reference it.

Semiclassical

7:13 PM

@dmckee ah, kk

@dmckee lol at Kittel using Z for all three partition functions

dmckee

@Semiclassical Yeah. I guess he figures it's clear from the context.

Semiclassical

It usually is tbh

Though, I think there's one context where he would write the differently: the grand partition function can be written as a sum of N-particle canonical partition functions

I think he had that as a problem and denotes the latter as Z_N

though what always made me crazy was stuff like activity / fugacity / chemical potential

dmckee

The table is full of interest. I mean look at Goodstein (good book, BTW). Why $R$ for the work? Why $W$ for the enthalpy? Seriously, David? What were you thinking?

Semiclassical

using A for the Helmholtz free energy has always seemed weird to me. but I chalk that up to all the sources I was educated with using F

but using $\Phi$ for the Gibbs free energy is just weird (another Goodstein idiosyncrasy)

dmckee

@Semiclassical I've never understood that choice, but it is surprisingly common.

Semiclassical

7:28 PM

yeah.

I think Schroeder uses $\Phi=PV$ in one problem, which seemed reasonable enough

0ßelö7

@Semiclassical F and Phi are the same letter.

@BalarkaSen "we let g denote its positive definite fundamental tensor"

Oooooooold paper

Semiclassical

eh, I guess Phi does preserve the F sound you have for F as the Helmholtz free energy

0ßelö7

@Semiclassical that's why we say Phield

Semiclassical

I still don't like it, though. If U,H,F are all latin then it's weird to me to have Gibbs be greek

vzn

8:13 PM

shrug

0ßelö7

$N|(q-2)$?

Semiclassical

huh

0ßelö7

Is that supposed to be just a quotient? :/

Balarka Sen

lol what notation is this

0ßelö7

@BalarkaSen I don't know

elliptic regularity notation I guess

@Semiclassical There's a classic book in my field that doesn't have a PDF online. I have a library copy but would like to have a digital copy on my laptop. Can/should I use a library scanner to scan the whole thing? Will a librarian do that for me?

Semiclassical

8:25 PM

no idea

vzn

@0ßelö7 what are you reading? d | n is used in number theory to signify d is a divisor of n.

0ßelö7

@vzn Reading math, and I know what it means in number theory

Semiclassical

context, as ever, matters

0ßelö7

old PDE paper, clearly

Balarka Sen

@vzn point being that interpretation doesn't make sense here

vzn

8:27 PM

@BalarkaSen most authors will intro/ descr their notation at beginning...

Balarka Sen

old paper

0ßelö7

In any case, I hope to not need the lemma. It's not clear to me what $r$ is supposed to actually be because there's a Sobolev embedding and Holder inequality involved.

Balarka Sen

so likely not

0ßelö7

So it could be any old nasty thing

Nonlinear PDE is bad. I need a nap.

vzn

Aug 25 at 17:31, by 0celo7

Number theory is pretty boring

Apr 11 at 23:25, by 0celouvsky

I'm not, although number theory is on my list of things to learn

ACuriousMind

8:35 PM

@0ßelö7 That looks pretty weird, where is it from?

I've never seen the | used for something other than "divided by" or set-builder notation.

Semiclassical

How old is it?

0ßelö7

@ACuriousMind One of Trudinger's old papers on the Yamabe problem, 1968.

Semiclassical

would it make sense to have $r=N/(q-2)$?

Balarka Sen

the Yamaha problem sounds interesting

Semiclassical

sounds like...a trip

0ßelö7

8:37 PM

Autocorrect

Semiclassical

YEAAAH---awww

Balarka Sen

loooool

0ßelö7

@Semiclassical Maybe. I have to work out the Sobolev embedding by hand. I'm in class and feel like death however

But I need to pretend to have done something before I see my advisor in 22 minutes

Semiclassical

@0ßelö7 ...ugh, that hits waaay too close to home

0ßelö7

I'm not even in grad school. Why do people already try to stress me out

Semiclassical

8:39 PM

Because academia convinces people that stress is normal.

...ok, now I'm a bit annoyed at the prof I'm TAing for

Mithrandir24601

@0ßelö7 Perhaps you're trying to stress yourself out and your lecturer/supervisor/whoever-deals-with-this-sort-of-thing actually would rather you be less stressed even if at the result of less work getting done?

(Yes, I'm serious)

0ßelö7

Yeah I'm stressing myself out

Usually it works but I don't feel good today

The result is misery

Semiclassical

second problem: "Find the solutions to the Schrodinger equation with the potential $V(x<0)=\infty$, $V(x\geq 0)=\frac12 m\omega^2 x^2$."

0ßelö7

I feel icky. I need to eat something healthy tonight

And drink more water. Ah, I bet I'm dehydrated

heather

i've always seen | to mean "such that", but then, I'm not in any sort of advanced study =)

Balarka Sen

8:42 PM

Perhaps you have forgotten your daily dose of memes

@heather Right, that's how it's used in set builder notation

Semiclassical

This is a nice problem, one which requires the student to remember that a solution to the Schrodinger equation on the real line is also a solution on any subset of the real line (aside from boundary conditions).

ACuriousMind

@heather That's the set-builder notation I was talking about ;)

Balarka Sen

but also not quite applicable here

@ACuriousMind you have been sniped

you ded m8

ACuriousMind

@BalarkaSen Maybe he's also consumed an unhealthy meme.

heather

@ACuriousMind totally knew that =P

Semiclassical

8:44 PM

@heather the fact that it'd read as "r=N such that (q-2)<n/2" makes that interpretation a stretch

heather

oh...actually, that kinda makes sense

set builder

defining the set = building it

ACuriousMind

Yes, exactly

heather

@Semiclassical well I guess it depends on the context; that doesn't sound dramatically weird to me.

but i know nothing =)

Balarka Sen

@ACuriousMind Lots of cancerous memes on the internet.

Semiclassical

well, (q-2)<n/2 seems to be a condition entirely seperate from r=N

not impossible, but quite strange

Getting back to the question, it's a nice problem and one can reason to the solution without much difficulty once you see the idea. But there should be some reasoning

0ßelö7

8:46 PM

If anyone wants the specific paper, the title is ~ remark deformation scalar curvature

ACuriousMind

~ is a strange symbol to begin a title with ;)

0ßelö7

That means "similar to"

Should be enough to google

Semiclassical

anyways. what the prof has in his posted solutions for that question: "The solutions are the odd harmonic oscillator solutions."

which is correct, but

no logic or anything, just "these are the solutions"

Balarka Sen

flayless lagic

Semiclassical

oh, and for some reason the solutions for next week's HW are already on the course website...gonna check with him if that was intended or not :/

Mithrandir24601

8:51 PM

@Semiclassical Maybe it's trivially obvious to him?

0ßelö7

Dang, I like my logic Bolton-style. Lots of flaying.

Semiclassical

given that he had to provide hints to the students, I don't think it should be considered obvious

0ßelö7

Maybe the students are stupid

Semiclassical

moreover, if someone gave me that as the entirety of their solution, I probably wouldn't give them credit

Mithrandir24601

@Semiclassical Is the marking scheme for the markers or the students doing the questions?

Semiclassical

8:52 PM

it's an upper-division quantum mechanics course.

Balarka Sen

@0ßelö7 Hm?

0ßelö7

Did someone flag me

Mithrandir24601

@Semiclassical As in, final year undergrad?

Semiclassical

it's not a marking scheme. it's what he posts as solutions after the students turn in that HW set.

@Mithrandir24601 right.

0ßelö7

My chat just crashed

Semiclassical

8:53 PM

and final year physics undergrads

ACuriousMind

@0ßelö7 No, but I was about to remark that that wasn't very nice :P

Semiclassical

so definitely people who should be using calculus a lot

ACuriousMind

@Semiclassical Well, then that's simply a horrible solution to post and you're right to be annoyed

Semiclassical

right

0ßelö7

What does calc have to do with anything?

Semiclassical

8:54 PM

He also didn't post a solution to the fourth problem

Mithrandir24601

@Semiclassical In this case, I would suggest that, given the answer (not full solution), final year undergrads should know enough to be able to figure how to get there and learn something in the process, while giving the full solution would mean that they wouldn't learn anything

Balarka Sen

@0ßelö7 Did you see the paper

0ßelö7

No

Chrome crashed

Balarka Sen

lol

Gromov crashed your Chrome

Semiclassical

@0ßelö7 eh, I'm just using that as a reference point of "people who know enough math to be in their fourth year"

Balarka Sen

8:55 PM

it's too much for your little browser

0ßelö7

@BalarkaSen what about it?

Do you want me to read it?

Balarka Sen

you should

Semiclassical

@ACuriousMind what mostly bothers me about it is that we're supposed to select some of their HW problems and grade them as if they were quiz problems

ACuriousMind

What does "grade them as if they were quiz problems" mean?

Semiclassical

kinda hard to model that when the solution posted online is something I'd give a poor score on for a quiz

of the HW problems each week, we pick three of them to grade based on the correctness of the solution. the rest we just check if they did it or not.

Mithrandir24601

9:00 PM

@Semiclassical That... Does not sound like a good idea - shouldn't the markers do that for all the questions?

Semiclassical

shrug

keep in mind, though, the students don't know what problems are chosen ahead of time

and that the selected problems count as the majority of the points on the HW

it makes my job easier, tbh

even if it is a bit goofy

i like this prof, but he's been kinda frustrating this semester.

Mithrandir24601

@Semiclassical Still though - I suppose it's not as bad if it's only upper years that get that sort of treatment as I'd hope that they could go through and correct their own work, but maybe I'm being unrealistic?

Semiclassical

yeah, for the most part the students are expected to manage themselves

0ßelö7

Oh dear I'm about to get ill

Semiclassical

the test is how well they do on the quizzes

0ßelö7

9:07 PM

@BalarkaSen ok

@Semiclassical QM quizzes?

Semiclassical

ya

a few long-answer problems each time

0ßelö7

Time to play the "do I have to vomit or is it the schizophrenia" game

ACuriousMind

@0ßelö7 Make chicken soup

0ßelö7

@ACuriousMind I'm in a seminar

Balarka Sen

chicken out of there then

its either chicken soup or chickening out

ACuriousMind

9:13 PM

@0ßelö7 Order chicken soup then, I guess

Balarka Sen

go outside, breathe in some cold air, drink some water, and get un-ill

0ßelö7

It's a sauna outside

The door is by the board. I can't escape

And Ive got a meeting afterwards

Balarka Sen

can you not skip meeting

if you're seriously ill you should

ACuriousMind

Puking on your advisor might convince him you're too stressed out :P

4

0ßelö7

9:31 PM

@BalarkaSen no im fine now.

Mithrandir24601

9:53 PM

Does anyone have good example questions for the quantum computing proposal? It's a great idea, but so far, many of the questions are... Well... Let's just say that I'm very close to giving out a lot of downvotes and critical comments and I don't really want to do that :/

Cows

Going hardcore on code and smart water like a boss

Mithrandir24601

At least a third or so of the questions with 10+ upvotes feel like the OP didn't think of using Google or Wiki first :/

vzn

10:09 PM

@Mithrandir24601 hey whats new with the qbits? did you see DSs new paper? any reaction? :)

@Cows srsly interested in solitons, or was that all just for fun?

Mithrandir24601

@vzn He's published a new paper? Do you have a link? I actually need to sign up to some journals' mailing lists... And do some problem solving - my PhD has finally properly started :D

vzn

in theory salon, Sep 21 at 17:17, by vzn

A blueprint for demonstrating quantum supremacy with superconducting qubits / Neill et al (Google-Martinis lab)

curious what you or your colleagues think about that, also IBM supposedly now has ~17qbits open science (since may?), wonder if anyones tried that

Mithrandir24601

@vzn Ooooh, thanks :) I knew they had something like this somewhere (it's hard to not notice that they're planning to release a 49 qubit system...) but didn't know they'd uploaded the paper :)

Cows

@vzn I am serious about solitons

Mithrandir24601

@vzn Aside from the fact that they used 'supremacy', I'm extremely excited :D

vzn

10:16 PM

@Cows so are you studying physics? in school? as you may have noticed, its a very advanced topic, very little at undergrad level

Cows

@vzn

I am out of school, but hoping to get back someday. Dropped out senior year of undergrad.

I am 99% sure I will be in school next year

Mithrandir24601

I haven't tried the 17 qubit IBM one yet - I haven't been bothered to sign up to the beta, the 5 qubit one is enough to mess around on, run what I need to on an actual quantum chip and I can perform simulations of larger systems at that size anyway

vzn

@Mithrandir24601 yeah DS was saying it wasnt a great word either maybe, trying to remember

0ßelö7

@Semiclassical meeting canceled ::eye twitch::

vzn

@Mithrandir24601 are you saying youve tried the 5qbit one?

ACuriousMind

10:18 PM

Jun 13 at 21:04, by DanielSank

@Mostafa The name "quantum supremacy" is generally disliked by everyone in the group.

vzn

@ACuriousMind what group?

ACuriousMind

@vzn His group, presumably.

0ßelö7

So one paper has that strange |, another has a strange Green's function argument, and the other says it's trivial

I give up

Mithrandir24601

@vzn I've done physics on the 5 qubit one, yeah :) Just simple operations that could be used to measure a certain type of fidelity, although IBM did this ages and ages ago, so this is nothing interesting or new - it was just to demonstrate a point on my project report. If I had lots more time, I would have used it to look at the effects of noise on t-designs, but never got that far, although I still want to if I get the time some day

vzn

@ACuriousMind lol his group incl leader Martinis just released a paper with it in the title. ?!?

ACuriousMind

10:23 PM

@vzn That they dislike the standard terminology in the field does not mean that they don't use it. Nothing funny about that.

vzn

@ACuriousMind have seen complaints over the terminology (a blog, maybe will try to find that again) but havent heard anyone proposing alternatives esp in literature...

Mithrandir24601

@vzn quantum advantage

ACuriousMind

@vzn If you reread the conversation around the message I just linked, he says "We didn't invent it. Most of us really, really wish we had a better name for what we're doing.". But maybe you don't want to look too closely at that transcript.

0ßelö7

@ACuriousMind No need for sass

0ßelö7

10:43 PM

;_;

good guy libgen has it

what a beast

Mithrandir24601

@0ßelö7 That's... :o What...

I would rather have a first edition LOTR book at that kind of price

0ßelö7

who the heck writes math books in French in 1997

wow this is actually a fantastic book

how has this not been translated?

oh you dirty

@ACuriousMind what's an acceptable bad word for for french person

I don't need to look up what [214] is

3075

10:58 PM

baguette

0ßelö7

@3075 and you are?

@ACuriousMind I need help

3075

@0ßelö7 I ask myself that everyday.

0ßelö7

11:15 PM

J. Funct. Anal.

lol

Secret

11:49 PM

journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.050501

The media version: army.mil/article/194131/…

Probably one of the most illustrate version of what entangled systems look like in short range: A system where the basis of possible combinations of observable assigned to a probability distribution.

Had to read the actual paper in detail to see if the media version simplifies it correctly

Also need to revise how the correlations from non commuting observables differ from those of entanglement

0ßelö7

@BalarkaSen proud?

Transcript for