The h Bar

user228700

13:00

@JohnRennie Just calculus. Hopefully, it won't be that bad.

John Rennie

@Kaumudi.H the Indian system does seem very hard on students. As I recall, doing A levels was hard work but it felt as if we wre doing things because we wanted to. I get the impression Indian students study things because they have to.

Balarka Sen

@JR Exactly right.

John Rennie

@Kaumudi.H electrodynamics isn't hard. It's just that the questiosn seem silly. They set up some silly, unrealistic geometry and ask you to calculate the field/potential/whatever just to prove you can rather than because it has great physical relevance.

user228700

@JohnRennie I was thinking about this just this afternoon, actually. Some of us really do want to learn this stuff but the trouble is that we've got 1.2 million people to compete with.

user228700

So the benchmark (and the number of work hours with it) keeps on rising and it gets hard, till the point where we're like "Please let it end, oh God".

John Rennie

13:03

I guess you just have to put up with the pain until you've made it to college, then you can start doing physics for fun rather than as a chore.

user228700

Exactly. Most of the problems arise from the facts that a) We have way too much crap to study in very less time (relatively) and b) Like I said, we've got to outsmart 1.2 million others.

user228700

Dyou know that some kids start preparing for this exam from their...6th grades? That's like, 11/12 years old.

Balarka Sen

I really think this sort of educational system does more harm than good.

heather

::shakes head sadly:: now I almost feel bad going to school and just chilling with my friends =P

Balarka Sen

That's never a bad thing

user228700

13:08

@BalarkaSen Why dyou think so? (I'm not procrastinating; I genuinely feel the need to discuss this :-P)

heather

ack, lost track of the time, good day all.

::sprints to my backpack::

user228700

@heather :-) Have a good day.

heather

you too =)

user228700

@JohnRennie Then again, you know the CEO of Google? That guy's home is like 1 Km away from mine. And he made it...because of the screwed up system. The thing is, this system is too accessible...it increases the competition. It takes 6 years of hard work to make it, but once you do, the promise is that you're settled for life, which, of course, is not true but I mean, it kind of is, to a large extent. So, yeah, the system works...for some people.

user228700

But then again, there are the children who commit suicide. OK, this is getting way too depressing and nobody seems eager to have a productive discussion about this so aaanyhooo.

Balarka Sen

13:12

@Kaumudi.H Ok, there are several bunch of reasons which come to mind. Firstly, there are a whole lot of students who are actually good at competitive stuff which understanding what they do too (I secretly envy them because I am not, and have never been). But there are also a handful like me, who can never cope with this system.

Let's fix something I actually know about. Eg, math.

user228700

@BalarkaSen What dyou mean by "good at competitive stuff"?

Balarka Sen

I, personally, like math. But I can never do complicated mathematical problems in my high school exams in the given time limit - I can do them if I think for long and hard enough, but never in the exams.

The fundamental thing is, and I can say this because I think I know quite a bit of math beyond high school, being able to do IIT-ian complicated mathematical problems is not a necessity for studying math contrary to popular belief.

@Kaumudi.H I don't understand the question. Being good at the competitive structure of the system, I meant.

user228700

@BalarkaSen What does "being good at the competitive structure of the system" really entail?

user228700

@BalarkaSen Oh, so you are in high school?! (;-)

Secret

I recall back in one of my uni exams, I feel joy at doing a question that is not directly covered by the syllabus by using first principle arguements and abstract definitions of linear functions

user228700

13:20

@Balarka: Hello..?

Balarka Sen

@Kaumudi.H Able to do the problems given in the exam in an appropriate time limit, writing the descriptive and explanatory answers in a near-perfect way, etc.

My internet's a bit down, sorry about that.

Secret

1st principle do sometimes help when a question look unrecognisable. I often resort to that when a question look alien

Sir Cumference

Howdy again

@AlfredCentauri Huh, can I see what's in your script?

Balarka Sen

There are students who can do well in the system, as well as knowing the "actual math". But there exist students who can do the former, but not the latter, and vice versa.

Sir Cumference

@BalarkaSen That's me exactly

I can solve problems and enjoy doing them so long as I have enough time

user228700

13:23

@BalarkaSen I realise that your brain is different from mine but I must admit that at the beginning, I used to think that I'm not cut out for this competitive stuff. I faced the same problems as you--it was almost impossible for me to complete the problems on time, etc. But the more I practised, the more I was able to do the problems within the allotted time frame.(Please bear in mind that I fully understand that this may not work for everybody.)

Sir Cumference

Exams trip me up

Balarka Sen

@SirCumference Yep. Also, there exists some specific kind of problems I do not actually enjoy.

Sir Cumference

@BalarkaSen Well yeah

In high school it was writing proofs in geometry or doing huge things involving matrices

Balarka Sen

@Kaumudi.H Agreed, but I don't really want to practice. That's the difference.

Sir Cumference

Nowadays it's just everything I'm not very good at

Balarka Sen

13:25

I do not feel like qualifying for the competition is a good motivation for learning.

user228700

@BalarkaSen Ah, then what can I say? Practice is key.

Balarka Sen

We disagree fundamentally, then.

If I learn, and that automatically makes me cope up with the system, I'm fine. I don't believe the latter helps learning.

user228700

@BalarkaSen No, it is definitely not in good spirits to focus on the exam rather than the aspect of learning itself but as I have learned--especially if one is interested in pursuing a career in the sciences/engineering/medicine--getting into a good college is fundamental.

Balarka Sen

By which I also mean to say that the exam structures we have at the moment - the kind of problems we are asked to solve etc - is not even a bit useful in learning the actual mathematics.

@Kaumudi.H Well, I disagree! Learning is fundamental, not getting a career.

Which, I think, concludes the discussion - there is no basis we agree on that lets us continue the discussion further.

user228700

@BalarkaSen Ah, this is where we disagree, then.

Secret

13:29

the issue of the system is that they sometimes don't explain the why. I recall I hav to discuss with my peers alot to learn some of the whys from them

Sir Cumference

I think @BalarkaSen should be right, but sadly in our world learning is less important than having a job

user228700

For many many people like me, the prospect of building a great career is more important than learning now; learning should always be the priority but a career is equally important.

Secret

and I do share what sircumference said in exams, I am never known to do any physics problems properly under any time limit

which is quite ironic given I am a physics major

Sir Cumference

Even though learning should ideally be prioritized

Balarka Sen

@SirCumference I know some actual mathematicians (in real life, yes) who think the math we are taught in the system is garbage, and prefers learning over doing that.

I don't know the story in other branches of science.

Sir Cumference

13:31

@BalarkaSen Of course, and I hate the system. But unfortunately, the system is here and it's essential to our lives

user228700

@SirCumference While I agree that learning is key, and really, it is the motivation to go on, I find your statement that "having a job is less important" plainly absurd; we all don't have the luxury to think like that.

Balarka Sen

The luxury etc seems like irrelevant

ACuriousMind

@Kaumudi.H If you read him carefully, he's complaining that the opposite of that is true.

Sir Cumference

@Kaumudi.H Uh, I never said that :P

Quite the contrary

user228700

Oh :-P I'm sorry...I did read it correctly but misunderstood because u prefaced it with "sadly".

Sir Cumference

13:34

Regardless, learning and having a career go hand in hand. It's the reason why the people who excel in a field are usually the ones who love it

Balarka Sen

I do want to pursue studying mathematics, and for that indeed I need to try to strike a balance between the system and my own personal studies. But that doesn't make the fact that I think the system is garbage false.

user228700

@BalarkaSen I have to agree that if you desire to pursue a career in mathematics, then the system will not work for you. However, this isn't the case for every other branch of science, you know.

Sir Cumference

@BalarkaSen The system is garbage, but it's designed in such a way that people who love a subject will naturally do better in it

user228700

@SirCumference Agreed. Sorry about before :-P

ACuriousMind

@SirCumference They do? There's heavy bias in the sense that those that don't love it usually don't go around announcing that.

Balarka Sen

13:35

@Kaumudi.H Ah, true enough. Yes, I don't plan to take JEE or IIT or anything.

user228700

@BalarkaSen So hang on, you're not even in 12th yet? That's crazy.

Balarka Sen

I also don't really identify mathematics as a branch of science (neither do I think the majority of mathematicians/mathematics students/etc does per se), but that's different story.

Sir Cumference

@ACuriousMind Let me give an example. I loved physics in high school, so I studied my ass off to make it intuitive to me

Balarka Sen

I'm in 11th.

user228700

Whoa. That is crazy. From where have u learnt such advanced stuff?

Sir Cumference

13:37

That's why I did better on tests. My interest was my drive to do better in physics

Secret

Balerka, you really don't sound like a 11th grader when you talk about all that topology stuff

3

I am suprised

Sir Cumference

An 11th grade has a better grasp on Riemannian geometry than I do...

;-;

user228700

Very. @Balarka: It was my impression that you have finished your under graduation.

Balarka Sen

I don't really feel comfortable talking about how I know a bunch of things. I liked math, so I learnt ahead. In any case, this is very off topic.

Sir Cumference

^

ACuriousMind

13:39

@BalarkaSen It depends on what, exactly, you take "science" to mean.

user228700

@SirCumference Dude, this ;_; looks more like you're crying.

Sir Cumference

@Kaumudi.H Well it's a sad text face :P

Balarka Sen

@SirCumference I really don't know any more Riemm. Geom. beyond the abstract terminology, I assure you.

ACuriousMind

For some reason, I thought for a while that ";-;" was the face of a Paras

user228700

@BalarkaSen OK. In any case, good luck :-) And thanks for all the help :-P I can't stop saying "Whoa". U know waaay more than any of my peers ever did.

Balarka Sen

13:41

@ACuriousMind I always felt like science has a general observation-explanation sort of structure. I don't think mathematics has that.

Sir Cumference

@Kaumudi.H He definitely knows more than anyone in my high school did

Most never learned calc

user228700

@SirCumference Dude, he knows more than any of my peers who studied for this effed up exam (and even got into IIT or whatever) ever did. I'm not even kidding.

Secret

Well... my chemistry root does make my recent algebra stuff more like the science as I generate a whole bunch of structures before trying to figure out their underlying rules, analogous to chemsitry and physics

Sir Cumference

@Kaumudi.H If you want to be surprised, check out Math SE's chat. There are middle schoolers far above me in terms of mathematics

Like, how the hell...

user228700

@SirCumference No, thanks. I'm having a sufficient number of existential crises as is.

3

ACuriousMind

13:44

@BalarkaSen Well, that's true for what I would call natural sciences.

Sir Cumference

@ACuriousMind Oh yeah, there are people who think computer science, creation science etc. are sciences too

user228700

@SirCumference Gosh, Ikr? Oh, BTW, you're studying cosmology, right? I'm curious--that's ur major? And u're only a freshman? (I'm asking for a friend who wants to pursue cosmology)

Sir Cumference

@Kaumudi.H Double majoring in astronomy and computer science

Balarka Sen

@ACuriousMind Ok, this is a fair point.

user228700

@SirCumference Wow, I see. And are u toward the end of ur course or are u a freshman/sophomore?

Sir Cumference

13:47

@Kaumudi.H Freshman

user228700

Dammit, aren't u way too cautious about the stuff you reveal about your life on the internet? :-| I was wondering which university offers courses like that...where, you know, you can major in cosmology. Like, right away, I mean.

Sir Cumference

@Kaumudi.H I dunno if cosmology is a major

ACuriousMind

@SirCumference It's not a matter of "thinking" so much as a matter of definition - what is "science"? Depending on what definition you choose to adopt the number of disciplines that are or are not science change. And if you go around asking people what science is you'll find that they sort-of agree on the general idea but that it is impossible to reconcile all answers into a single consistent definition

user228700

@SirCumference My friend who wants to eventually become a cosmologist? He's doing this terrible 5-year course in all the sciences, including Math. And then he gets a masters...in one subject.

Sir Cumference

@ACuriousMind Well you're asking me more of a philosophy question :P

user228700

13:50

@SirCumference :-| Oh, so it only comes in the double-major package? :-P

user228700

Sigh, I should go eat or something. Bye!

Sir Cumference

@Kaumudi.H Er, no, double majoring isn't related. You should take it if you are an astronomy major

Or physics

ACuriousMind

@SirCumference Of course - before we can do science we must do philosophy to have something to ground our science on.

That philosophy is off-topic at physics.SE does not mean it's unimportant for physics as such :P

Sir Cumference

@ACuriousMind I define science as observing, etc. to find out about a particular topic

Balarka Sen

philosophy is good.

Sir Cumference

13:53

Social science counts, for example

ACuriousMind

@SirCumference So if I sit down and observe a particular bird in my garden all day, that's science?

Sir Cumference

@BalarkaSen Philosophy is the only thing that hurts my head more than physics can

@ACuriousMind if you make hypotheses and follow the scientific method, yes

Secret

Nothing exists vs nothing exists

Sir Cumference

I should've specified, but it's hard to type much on a phone

ACuriousMind

@SirCumference Ah, but that wasn't part of your definition! What's "the scientific method"?

Sir Cumference

13:56

@ACuriousMind I know, I said "etc" hoping my point was clear enough, since typing is really hard on my phone :/

Anyway, I think there's a Wikipedia article describing a specific definition for the scientific method

ACuriousMind

Well, I didn't know you were on the phone and leaving me to infer the actual things you mean to say is not a good basis for a discussion about epistemology or the nature of science

Sir Cumference

@ACuriousMind I know .-.

But my God this is tough to type

@Kaumudi.H I would recommend to your friend to study as much as he can about math and cosmology before starting college, like @BalarkaSen. It'll do him really good and he won't be in the situation I'm in.

Right now I don't have time to grasp it all, it goes crazy fast

anonymous

@SirCumference How did you take a cosmology course without a basic physics degree? Which country do you stay in ?

Sir Cumference

@ACuriousMind By the way, I've always found it amusing that there's no definition for math, yet we usually agree on what it is

ACuriousMind

@SirCumference The article takes the notion of "science" as given and basically lists things as elements of the scientific method if it is something that scientists do. That'd lead to a circular definition.

Sir Cumference

14:02

@anonymous 'Murica

anonymous

@SirCumference Which university ?

Balarka Sen

@SirCumference I think it's analogous to trying to define literature, or poetry, or painting.

ACuriousMind

@SirCumference Are you sure you're supposed to take that course? :P

Sir Cumference

@anonymous Oh God, here we go again...

@ACuriousMind I'm pretty sure. I took a lot of classes during high school so I could opt out of a lot of college ones

anonymous

@SirCumference You may not answer answer it if you wish. But I find it reaaaallllllyyyyy strange :P I never heard anyone taking a cosmology course directly after high school :) Anyway, it might be because I haven't met many astronomy students.

ACuriousMind

14:05

Any course in cosmology here would definitely require you to have taken a basic GR class at least. You took stuff in HS that let you opt out of GR yet you don't know it?

Sir Cumference

@ACuriousMind The cosmology is part of an introduction class. The GR is what I'm having to learn.

ACuriousMind

That is very strange.

Sir Cumference

@ACuriousMind :shrugs

Regardless, we haven't dealt too deep into GR besides some formulae

And some basic cosmology stuff

@ACuriousMind Why, when did you start with that stuff?

ACuriousMind

@SirCumference I took GR in my fourth semester, and could've taken an actual cosmology course after that if I actually liked it

That's considered the earliest point in the curriculum where it's really feasible to do so.

G. Bergeron

@SirCumference What?! You decide what is important...

ACuriousMind

14:17

I wonder what these authors were thinking: "Why, yes, referencing an unsearchable 300-page paper for a single formula without saying where it's in there is a wonderful idea! (cue diabolical laughter)"

G. Bergeron

@ACuriousMind Because they don't know!

Mike Miller

nonzero odds it's not in there

ACuriousMind

It goes on the list of stuff to check when I unexpectedly get several years worth of free time :P

Bernardo Meurer

I got rekd

G. Bergeron

14:35

@MikeMiller :) Sometimes, only the general idea to derive it is there...

Mike Miller

Sometimes the reference was wrong and there's nothing relevant there.

G. Bergeron

@MikeMiller Or that

ACuriousMind

On closer reading I found the relevant information quickly because the thing at least had a table of contents and intelligently chosen subsection headings.

Mike Miller

Table of contents are a godsend.

Slereah

15:03

>not remembering the location of every theorem

ACuriousMind

15:56

Hmm, Feynman slashing a $\psi$ wasn't a good idea...the slash is almost exactly on top of the middle line

I don't wanna type $\Gamma^\mu \psi_\mu$ everytime, though...

Danu

@ACuriousMind Use $\Psi$?

ACuriousMind

@Danu Hm, that works, but I dislike using capital letters for fermions :D

Danu

$\varphi$?

probably also looks bad.

ACuriousMind

@Danu Yes, very

AccidentalFourierTransform

$\theta^\mu$ looks fine for fermions

and it can be slashed

Slereah

16:08

You can also use $\xi$ for fermions

ACuriousMind

@AccidentalFourierTransform Yes, $\theta$ fits my slashing needs!

thanks ;)

G. Bergeron

@ACuriousMind I never liked the slash

AccidentalFourierTransform

well it actually took me a couple of days to find the best letter for a Rarita Schwinger field

"Im confused about this question?" lol

Slereah

Errr

I mean

$\chi$

You can also use xi, tho

AccidentalFourierTransform

but you cannot slash a $\chi$

ACuriousMind

16:12

I prefer to use $\xi$ and $\chi$ for Weyl spinors for some reason.

And the slashed $\chi$ looks just weird.

Slereah

$\slash xi$

What's the slash in latex again

I forget

AccidentalFourierTransform

\not?

ACuriousMind

You need an extra package and it would be \slashed.

@AccidentalFourierTransform Doesn't look right for most symbols

Slereah

$\slashed{p}$

I guess mathjax doesn't have it

$\not p$

AccidentalFourierTransform

can you load packages here?

$\not\not$

Slereah

16:14

$\not \xi$

Looks a bit shit yeah

ACuriousMind

@AccidentalFourierTransform no

Slereah

$\not \chi$

AccidentalFourierTransform

\usepackage{lipsum}

David Z

@AccidentalFourierTransform I believe MathJax has packages which you might be able to load. They're not the same as LaTeX packages, in general, though.

ACuriousMind

@DavidZ If it turns out we could've loaded a bra-ket package all along I'm gonna be really mad ;P

Slereah

16:16

Eh

Is it really that hard to write brakets here

David Z

@ACuriousMind I've checked, one doesn't exist for MathJax yet

well, at least not as of the last time I checked

Slereah

$\vert 🐱 \rangle$

David Z

On MathJax extensions

AccidentalFourierTransform

ill stick to \not though

John Rennie

Can anyone tell what Peter Shor is on about here:

I think your answer is on the order of Assume 0 = 1. Then 13 is not prime. Violations of the conservation of momentum are inconsistent with general relativity, so you can prove anything if you assume them. — Peter Shor yesterday

I can't understand the relevance of conservation of momentum to my answer.

David Z

16:18

Peter from the MathJax team here. There's actually a very recent attempt, see github.com/mathjax/MathJax-third-party-extensions/pull/16. I'm sure the developer would not mind additional support. From the MathJax end, the ideal process for this kind of thing is to start out as a third party extension (which are mirrored to the CDN for general use) and have it mature there. When things are stable, they can move into the core MathJax distribution. (That would still leave the Stackexchange end of course. ) — Peter Krautzberger Mar 20 '15 at 16:02

Slereah

Also you totally can have non-conservation of momentum in GR

What a hoax!

John Rennie

@Slereah well yes if the translational symmetry is broken, but I still can't see what Shor is getting at.

David Z

I'm not clear on that either

Slereah

Who knows

Maybe he should go back to making quantum computer algorithms

David Z

@Slereah that was unnecessary

Slereah

16:22

It was more of a joke

Oh wait

Is it actually that guy

Danu

Yes.

John Rennie

@Slereah I did wonder if it was thePeter Shor, but that seems unlikely :-)

ACuriousMind

@Slereah Yes, that user is the real Peter Shor, not one of the fake "Einsteins" or "Feynmans" we usually see here.

Slereah

Shocking

ACuriousMind

For evidence, see e.g.:

John Rennie

16:23

Wow, I thought the real Peter Shor would be, well, less of a bitch I suppose.

ACuriousMind

118

A: Was the reduction in Shor's algorithm originally discovered by Shor?

I have to admit (surprising as it sounds) that I don't know really the answer. I either discovered or rediscovered this reduction myself. I discovered the discrete log algorithm first, and the factoring algorithm second, so I knew from discrete log that periodicity was useful. I knew that facto...

Slereah

@JohnRennie Well THAT was unnecessary :p

David Z

@Slereah It was an ~~unnecessary~~ inappropriate joke, that's my point. (Regardless of who it really is)

@Slereah I would tend to agree with that, too.

John Rennie

It is a bitchy comment - surely that's self evident?

Slereah

heh

David Z

16:25

@JohnRennie Unless this is some special English meaning of "bitchy", no, not to me at least

John Rennie

I think your answer is on the order of Assume 0 = 1

Really?

Slereah

If you think that's bitchy never read a Motl answer

John Rennie

I'm not trying to make a point. It would never occur to me to speak to a stranger like that.

ACuriousMind

@JohnRennie It doesn't strike me as particularly confrontational; it's a paraphrase of "Your answer makes a wrong/impossible assumption".

Danu

"on the order of" suggests it's quite bad

ACuriousMind

16:28

I can't fathom what exactly he means either, though

Slereah

Hm

Who are the bitchiest PSE posters

I want to make a question that would pit them against one another

AccidentalFourierTransform

"Quack, quack, quack, crackpot" always makes me laugh

-5

Q: Why was I suspended?

... A week ago, I was suspended from the site for being “offensive”. Here is the message I got from dmckee: Hello, I'm writing in reference to your Physics Stack Exchange account: http://physics.stackexchange.com/users/23119/dimension10 We've received many flags on your p...

Slereah

Obviously Motl, so it would have to be about string theory or something involving Bohmian mechanics

G. Bergeron

@Slereah What do you mean by that?

Slereah

@G.Bergeron $\partial_t T_{ii} \neq 0$

John Rennie

16:41

@G.Bergeron e.g. in an expanding universe

Slereah

for instance, yes

errr wait

No

FRW conserves momentum

It's energy that isn't conserved

Schwarzschild doesn't conserve momentum, though

Of course you can always recast the lost energy as gravitational potential energy

Lu Bu

Any1 wanna help me with my question, it's not about expanding universes, but almost as hard. =)

So my book says:
"State of matter depends on pressure and temperature."
In my classical mental picture i can easily see how
it would be dependant upon temperature, but can the
dependency on pressure be explained such that the higher
the pressure the more the particles are pushed together.

Also i assume the pressure means external pressure.

AccidentalFourierTransform

that depends

John Rennie

@LuBu the Gibbs free energy is pressure dependent, and the pressure dependence is in general different for the different phases.

That means changing the pressure will change the free energy differently for the different phases, so it will shift the equilibrium.

Lu Bu

Oh, so it comes down to something like that.

John Rennie

16:46

Well, that's a macroscopic viewpoint ...

Lu Bu

I've watched videos/read about gibbs free energy some time ago, but i think i need to brush on the subject.

@JohnRennie "Well, that's a macroscopic viewpoint ..." What do you mean?

What's your intent in saying that.

But pressure affect Gibbs free energy and that in turn affects the equilibriums?

Sir Cumference

@JohnRennie The whole four-momentum and conservation stuff is confusing me

Lu Bu

Is that the general gist of it?

Sir Cumference

It seems to make sense to you guys

John Rennie

@LuBu Basically the Gibbs free energy has three parts. An internal energy term $+dU$, a work term $+PdV$ and an entropy term $-TdS$.

Lu Bu

16:52

I recall the energy was called enthalpy?

Or something.

John Rennie

If $dV$ is negative, i.e. that phase change involves an increase in density, then the $PdV$ term is negative and gets more negative as you increase the pressure.

@LuBu Enthalphy, $dH$, is the internal energy and work terms added together. $dG = dH - TdS$ and $dH = dU + PdV$.

AccidentalFourierTransform

^ sick reference

Lu Bu

Oh, it also has an entropy term.

This might get difficult =).

I think ima watch some video on gibbs free energy.

John Rennie

@LuBu Yes, the entropy term largely dictates the temperature dependence.

AccidentalFourierTransform

tableaux are so old

Lu Bu

17:07

@JohnRennie And the only thing that this level books tell about entropy is that it's disorder.

@JohnRennie All i understand about entropy so far, is that it has something to do with how the number of possible microstates should go to the maximum value as time passes.

G. Bergeron

@Slereah That's my point. It seems it is a bit a question of conventions in the definition, maybe the OP had a somewhat generalized definition of momentum.

Lu Bu

@JohnRennie Or something like that. It's still a bit vague to me.

John Rennie

Entropy has a very precise definition but sadly this is not always useful. In many cases we're not too fussed about the exact microscopic origin of an entropy change, we just need to know how big it is.

Slereah

Well defining momentum in GR is very complicated

G. Bergeron

@Slereah Yes and a big part of that is that since the metric is part of the dynamics a definition of momentum could be expected to take it into account and define momentum as the generator of translation on some configuration space for GR + the rest.

John Rennie

17:47

This pretty much sums up the current state of the Brexit situation. The only problem is that The Daily Mash is supposed to be a parody site.

Lu Bu

17:59

@JohnRennie Gibbs free energy is a change and not a state variable, right?

Sir Cumference

18:32

@JohnRennie That guy on the front page looks like a British Trump...

@Slereah Question

You go on Astronomy SE?

Slereah

I do not

Sir Cumference

Uh, ok, you willing to test something for me?

John Rennie

@LuBu Gibbs free energy $G$ is a state variable. $\Delta G$ is a change in the Gibbs free energy and $dG$ is an infinitesimal change in the Gibbs free energy.

@SirCumference Boris Johnson.

Sir Cumference

@JohnRennie Pardon my ignorance

John Rennie

It wasn't meant to correct you. You have to imagine my tone of voice when I say the words Boris Johnson. Essentially the same tone as I'd use to say WTF.

Sir Cumference

18:37

@JohnRennie Sounds like he isn't well liked

Lu Bu

@JohnRennie Still trying to interpret this, but does a negative ΔG means the system lost energy to the surroundings.

@JohnRennie If this is the case, what is the significance of it as a state variable.

John Rennie

In any change, e.g. a phase change or a chemical reaction, the free energy of the system will (probably) change. So if you melt 1kg of ice the free energy of the ice is different to the free energy of the water. $\Delta G$ is just rthe final free energy minus the initial free energy.

Sir Cumference

@EmilioPisanty Sorry to ask out of the blue, but would you be willing to test something for me?

John Rennie

It's no different to e.g. pressure. $\Delta P$ is the final pressure minus the initial pressure. Both pressure and free energy are state variables.

DanielSank

PSA: Apparently, a quick way to make someone very emotional and unreasonable is to point out that they don't know what they're talking about.

Sir Cumference

18:43

@DanielSank This doesn't sound pleasant...

AccidentalFourierTransform

@DanielSank thats a lie. You know nothing about people

Sir Cumference

@DanielSank Wait, misread your message

The worst thing to tell someone is "you've lost this argument", it'll piss them off in a debate/disagreement

DanielSank

Well, in this case it was less "you lost" and more "Oh, here, let me show you the actual California law so that you can see that what I'm asking of you is quite reasonable".

Apparently, doing this with a landlord can result in thermonuclear explosion.

Sir Cumference

@DanielSank Well, I wouldn't be that matter of fact about it...

People don't like to outright be called wrong

AccidentalFourierTransform

yes they do

Lu Bu

18:47

@JohnRennie Yeah ok, but is the state variable then calculated as G=U+PV−TS. And if is, what does it signify?

AccidentalFourierTransform

youre wrong

John Rennie

Gibbs free energy

In thermodynamics, the Gibbs free energy (IUPAC recommended name: Gibbs energy or Gibbs function; also known as free enthalpy to distinguish it from Helmholtz free energy) is a thermodynamic potential that can be used to calculate the maximum or reversible work that may be performed by a thermodynamic system at a constant temperature and pressure (isothermal, isobaric). Just as in mechanics, where the decrease in potential energy is defined as maximum useful work that can be performed, similarly different potentials have different meanings. The decrease in Gibbs free energy (kJ in SI units) is...

DanielSank

@SirCumference We didn't say she was wrong. We asked for a written list of things she thought could be held against the security deposit. She refused, so I showed the law which states that this must be done.

We were trying to help her because if she didn't write the list, she can't take any money from the security deposit.

Sir Cumference

@DanielSank Well, all I'm saying is "you don't know what you're talking about" doesn't seem like a very friendly approach...

Though I don't know the details of what went on

Lu Bu

@JohnRennie So this is some sort of potential energy of a thermodynamic system that we can use to do work?

DanielSank

18:54

@SirCumference Again, nobody said anything like that. The landlady was going around the house saying things like "There's dust on that. Did your cleaner even do any work?". After a while, my friend asked for all of these things to be written in a list. The landlady resisted over and over, so eventually I showed her the written law.

She got mad.

Sir Cumference

@DanielSank Ok then

DanielSank

The raised voices started after that.

She then sent him one of the most insulting and insane emails I've seen.

It's pretty entertaining, actually.

Emilio Pisanty

19:19

@SirCumference depends on what the "something" is.

AndyD273

I have a question about heat...

I'm trying to come up with a heat negative solution for a WorldBuilding.SE question, and I think I have a way to do it, but I'm feeling kinda dumb and was hoping that there might be someone around to tell me if I'm missing something obvious

Shashaank

@EmilioPisanty Could you please help me in this physics.stackexchange.com/q/303998/113699

AndyD273

The question is about cooling a spaceship in vacuum better than a radiator system might, and I was wondering if you could do it by having a vacuum chamber on the surface of the ship where very hot liquid is released. It would instantly boil because of the low pressure, and then desublimate into ice crystals which could be collected and recycled...

Shashaank

@ACuriousMind Could you please help me in this physics.stackexchange.com/q/303998/113699

ACuriousMind

19:34

@Shashaank I find it a bit rude to ping random users to answer your question.

Shashaank

@ACuriousMind Ohh ok sorry . I thought I will get some help since this question was troubling a lot . But if was rude then Sorry

AccidentalFourierTransform

20:53

I accidentally rejected this edit

physics.stackexchange.com/review/suggested-edits/158761

because I didn't read the description :-S

please someone accept it!

ACuriousMind

@AccidentalFourierTransform Thy will be done!

AccidentalFourierTransform

I didnt realise that the edit suggestion was a roll-back. I thought that it was an original edit, which didn't make any sense and so I rejected it. But then I read the description and realised the edit was good and should be accepted.

@ACuriousMind thanks!

Emilio Pisanty

21:17

@Shashaank I can help you by telling you that the formatting is so poor that my eyes just glaze off immediately. There is absolutely no reason to use any of that emphasis, all you're doing is making your post harder to read.

you should also explicitly specify what you mean by "second uniqueness theorem".

FrancescoS

Hi guys! What does exactly mean that operators with same quantum numbers "mix under renormalization"?

AccidentalFourierTransform

21:33

@FrancescoS hmm sorry, that doesnt make much sense to me

I dont know what that could mean

FrancescoS

@AccidentalFourierTransform In QFT, when you compute anomalous dimension for composite operators (i.e. operators that are built from elementary fields evaluated at the same space-time point like (\partial \phi(x))^2 or also \phi(x)^2) you have to pay attention if the operators mix under renormalisation, because in this case the anomalous dimension becomes a matrix

Shashaank

@EmilioPisanty So should I edit the question with a sort of figure . How can I replace the text. That is the question. Please suggest I will surely repost the question

FrancescoS

@AccidentalFourierTransform for example here, bit.ly/2iWdVWX, eq. 4.5.6d

AccidentalFourierTransform

@FrancescoS ah, now I see what youre up to

yeah, now it makes sense :-P

FrancescoS

Unfortunately for me not ehehe :)

AccidentalFourierTransform

21:43

well, I'm not gonna pretend that I understand whats exactly going on

=P

FrancescoS

ahah ok ;)

AccidentalFourierTransform

hi @JamalS

I apologise if I was annoying =P

JamalS

@AccidentalFourierTransform The question by the OP in its original version was very unclear as to what in the article he found confusing. Thus, I thought I'd address one aspect of the article, to make it clear for an expectation value w.r.t. energy eigenstates, time-independence was only required.

AccidentalFourierTransform

yeah, my concern is that you only mentioned "energy eigenstate" at the end of your post

I think that the proper position would be at the beginning, within the assumptions

JamalS

And so what? If he (the OP) isn't smart enough to read to the end of a post, he has bigger problems...

AccidentalFourierTransform

21:49

yeah, but in general one does not need to wait till the end of the proof to find one more assumption of the theorem

JamalS

Yeah, but it's a tiny "theorem."

Emilio Pisanty

@Shashaank you should make the text clearer and easier to read; how you do so is up to you. But I would start by removing all the formatting (and certainly all the nested formatting and all formatting longer than four or five words).

JamalS

And you never mentioned in the comments that moving the assumption to the top of my answer would end your qualms.

AccidentalFourierTransform

@JamalS tiny for you, not necessarily for OP

JamalS

@AccidentalFourierTransform I mean tiny in the literal sense, not that it was trivial. If it was a 100 page proof with additional assumptions at the end, then I'd agree with you.

AccidentalFourierTransform

21:51

in any case, I want to stress that the down vote was not mine

JamalS

What I'm saying is me having the assumptions at the end of the answer was perfectly acceptable, because the answer was so small. For example, when writing an equation, you may directly after state, 'which is only true if...' and nobody would argue you should move that one line above to the top.

AccidentalFourierTransform

I guess we'll have to agree to disagree there

it is not just a matter of style

JamalS

I don't agree to disagree, but I do agree the downvote was not yours. Nevertheless, it was actually retracted by the person.

I think the question is going to get closed anyway, as it should be as I just noticed Qmechanic managed to find a duplicate essentially.

AccidentalFourierTransform

maybe it'll get closed

it just got a new answer though

and I cannot say for sure that it is a duplicate because Im not entirely sure what OP is trying to ask to be honest :P

Shashaank

@EmilioPisanty Thank you . I have reposted the question , reMoved the bold and italics and included a picture . physics.stackexchange.com/q/304059/113699

@EmilioPisanty Please suggest whether that is better else I will do the needful .

AccidentalFourierTransform

21:59

@Shashaank uh oh

please dont repost questions. Rather, edit the original one

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