The h Bar

imbAF

00:50

Would it be incorrect to conceptualize a n particle state of different types of particles $|n_1,n_2,....n_N\rangle$ of some arbitrary system as excitations of different types of fields in some region of spacetime where $x_1^0=x_2^0=...x_N^0$ ?

Relativisticcucumber

03:27

in my cm lectures, we show that if we have free electron plane waves and look at energies from the hartree fock equations, we get a sizeable correction to naive free electron energies. then we go into a lecture on screening to explain why the correction might not actually be so sizeable. the problem is, to me screening only makes sense to wash out fields of different charges. e.g. electrons can shield attraction to the nucleus. how can electrons screen out other electrons tho?

naturallyInconsistent

03:53

@Relativisticcucumber I recently wrote somewhere about this issue. Maybe trying to call it screening is just wrong. Instead, the exchange interaction comes from Coulomb interaction and is way too strong when implemented as a Slater determinant. A Slater determinant, by being a determinant, guarantees that the probability density of an electron to be somewhere, is independent of all the other electron's positions. But this is nonsense: if an electron is known to be somewhere, then Coulomb potential would

push other electrons far away from that point, resulting in a Coulomb hole in configuration space. That is why it is called correlation, and is not at all captured by a Slater determinant, by definition of correlation under Hartree-Fock. This means that the exchange interaction as computed from a Slater determinant is guaranteed to be an overestimate of the actual residual Coulomb interaction coming from fermion statistics. This way, I avoided the use of screening to explain this important fact.

@SillyGoose miao miao gave some...

@SillyGoose shortcomings? You aren't likely to get it in a textbook... Alternatives and various forms? Ah, I see you are looking for MTW lol

@SillyGoose That's because when you are good at tensor indices manipulations, the whole requirement to deal with transposes disappear. The index notation sweeps away all these unnecessary noise when trying to get to correct equations, and only when you are required to implement the tensor equations as matrices, do you actually need to figure out the transposing. A notation that eliminates noise and clutter is appreciated.

Relativisticcucumber

@naturallyInconsistent hm u mean this is what Lindhard theory does?

tmu what happens in hartree fock is if you go with it, you are bogged down by the long range nature of the coulomb potential

so if we magically come up w a 'screened potential' this would be good.

but i dont even see how Lindhard screening does this

idk im just lost on this whole thing

naturallyInconsistent

@SillyGoose This is because physics textbook authors are 1) lazy, 2) under immense time constraints to teach horribly complicated physics and don't have time to cover, at time of instruction, mathematical details irrelevant to the difficult physics being taught. Of course the details matter, but you cannot see the details from Cartesian coördinates in Euclidean or Minkowski metric. You will at least require curvilinear coördinates in order to realise that the difference matters. Now, after

generations of physicists doing these "blind leading the blind" kind of dance, it is no wonder that even lecturers themselves, who may have absolutely no difficulty solving problems and getting correct answers, are confused about which entities are a (1,1) tensors and which are (0,2) tensors.

@Relativisticcucumber This is not what miao miao meant, since miao miao had expressedly avoided using screening as the actual physical mechanism to discuss the matter, but yes, in a condensed matter system, it will also be necessary to discuss screening. You can learn about screening quite understandably in plasma physics, where they discuss what happens if you have ionised plasma and you introduce a charge into the plasma. The physical situation is cleaner and clearer there, and then we reuse the concept

@SillyGoose Your suggestion is bad! At least by using the correct word "tensor", an unsuspecting mathematician might be able to search for the correct term in the mathematical literature and decipher what the physicist is saying. Those stuff are not mere matrices; they obey the correct tensor transformation laws, which matrices are not required to obey.

Silly Goose

04:15

@naturallyInconsistent hm i will take a look at MTW during the coming break

@naturallyInconsistent but that is not the mathematician's definition of tensor

Separately, going back to Leinaas & Myrheim, so is part of the idea that a quantum state can be thought of as a classical field $\Phi: X \to V$ that transforms under a choice of a (restricted subset of) irreducible representation $\pi: \pi_1(X) \to U(V)$?

Classical field since the field is not operator-valued.

I was trying to think concretely. Consider the vector bundle $(X, \mathbb{C}^2 \otimes \mathbb{C}^2, E, \pi)$ where $\pi$ here is the projection as describing two identical particles. Then we describe quantum states as sections of this vector bundle. A simple example might be $\Psi(x) := \alpha(x) \psi_1 \otimes \psi_2$.

Then, we define interchanging the two particles by acting with a non-trivial element of the image of a non-trivial unitary irrep, let's call the element $P_{[\gamma]}$, in the same way that we do in usual field theory: pointwise. I.e., $\Psi(x) \mapsto \alpha(x) P_{[\gamma]} \psi_1 \otimes \psi_2$.

Is this a fair assessment of what is being done in Leinaas & myrheim?

naturallyInconsistent

04:54

@SillyGoose so what? The physicist would care that it takes on the transformation properties; the mathematician would define something else, but it would still map cleanly onto the same entity. The two sides would not choose for totally incompatible things to be called the same thing.

at least, we are not at that level of antagonistic relationship

naturallyInconsistent

05:07

@TobiasFünke South Korea just had declared an emergency martial law that the president could only push through for 6 hours and then got struck down as unnecessary by the parliament. Yet, the deposal of the president also took quite a lot of effort, and it was only after many days that it finally got through. It is not just Europe that is going through hard times.

Ryder Rude

07:03

i am thinking that there is nothing u can do with truly random algorithms that u can't do with pseudo random algorithms

so quantum mechanics does not offer any update to the Church Turing thesis

@DIRAC1930 i think $A^{\mu}$ does transform like a contravariant vector under general co ordinate transforms

$A^{\mu}$ is $g^{\mu \nu} A_{\nu}$. And $A_{\nu}$ is a dual vector by definition

Ryder Rude

07:21

30

Q: Physics and Church–Turing Thesis

Is there constructed some set of physical laws from which we can logically obtain that any function that can be implemented in some device is Turing computable? EDIT I believe that if we restrict ourselves to classical mechanics (I mean if we suppose that any device obey just classical mechanic...

Shor says quantum mechanics "appears to be Turing computable"

but wavefunctions can be non computable as it uses real numbers

i think the idea is that it can be approximated by Turing computation to arbitrary precision

Growing Mind

07:36

Hello Everyone...

qwerty

@bolbteppa I feel a bit sad about this and other things sabine puts out these days. i used to be a casual reader of sabine's blog 10 years ago and now it feels like all she does is just clickbait/ragebait videos.

Slereah

That is what computable means

John Rennie

@qwerty I agree, but it's making her a lot of money. If I was offered the chance of compromising my principles for a million subscriber YouTube channel I would be sorely tempted.

Slereah

@JohnRennie Damn capitalist

John Rennie

Possibly ... fortunately it doesn't seem likely I will ever have to make that decision :-)

Ryder Rude

07:42

@Slereah oh

qwerty

@JohnRennie I don't even think she thinks she's compromising her principles. she has beef with academia (and fair enough) and I think she thinks she's taking it to "its logical conclusions", if that makes sense.

Ryder Rude

do u think physics's use of real numbers could be overkill if all of physics can be formulated using Turing computations?

maybe physics is not about finding minimalist models to describe experiments, but is about finding any model at all

also, physics is open to using any kind of math, computable or non computable

John Rennie

@qwerty I suspect it's a gradual transition. Even after she was forced to quit academia her blog and channel remained fairly optimistic at first, but it's gradually veered down an overtly anti-establishment path.

Ryder Rude

i think it is okay to not restrict oneself to computable math

because there already r hints of non computable processes in spacetimes

so one should not restrict physics prematurely

@qwerty Sabine is contrarian

qwerty

her original contrarianism was over things like funding particle accelerators like the LHC. i think that's a defensible view that can be carefully debated, and I seem to recall there was at least attempts to do so on her blog.

it seems to have now spun something broader like "what kind of and quality of academic research should be taxpayer funded?" which is what the linked video was "really" about if you remove the appeal-to-emotion she weaves through it

Ryder Rude

08:05

she would recommend funding superdeterminism research, which is strange

Tobias Fünke

08:57

good morning :)

I think it is a well-known condition of "retired" physicists to think one understands all topics and that one's opinion is so worth to hear, lol

Tobias Fünke

09:09

@HerrFeinmann nooo, stay with CM ;)

antimony

@JohnRennie my thought exactly. we'd all be tempted in one way or another to find a way to bs ourselves that it's justified

Herr Feinmann

@TobiasFünke CM is the nest of the devil

Tobias Fünke

haha yes I would not disagree

Herr Feinmann

But I guess there is something more scary in the theoretical realm

Tobias Fünke

what is it?

Herr Feinmann

09:18

hep-ph and nucl-th

Tobias Fünke

I mean, CM is a huuuge field, so it of course depends on what exactly you are doing anyway

I always found hep boring lol

Herr Feinmann

The structure functions haunt my dreams

@TobiasFünke Although I have more interest toward fundamental physics, I rarely find theoretical physics boring

Tobias Fünke

can you link to a definition? we have that too lol

Herr Feinmann

It's that, typically, hep people (mainly books) have a way of doing things that resonates with me more than CM people, if that makes any sense to you

Tobias Fünke

yes yes, I understand

antimony

09:21

what is CM?

Herr Feinmann

Here

@antimony condensed matter

antimony

ooooh

nice :)

Tobias Fünke

ah, thanks Herr Feinmann, sehr nett

I saw the Wikipage but immediately skipped it because there was no equation lol

but it says in the first sentence: analogous to structure factor in solid state, so I now have a rough idea

Herr Feinmann

I'll summarize that for you. Deep inelastic scattering

I don't like inelastic stuff

Tobias Fünke

xd

but yes, its also an important topic in condensed matter, regarding quasi particles, excitations and so on

antimony

09:24

wow

> "Deep" refers to the high energy of the lepton, which gives it a very short wavelength and hence the ability to probe distances that are small compared with the size of the target hadron, so it can probe "deep inside" the hadron

Herr Feinmann

Well, remember that while elastic scattering conserves energy, inelastic is a spectrum. It goes from no dissipation to total dissipation. That's why you have "deep"

In this context it happens by interacting with the internal structure of non-elementary particles such as hadrons

And since we don't really know that structure (which would entail deriving hadrons from elementary QCD, a big deal), we have to make guesses with these structure functions that are born combining basic hypothesis+phenomenological input

Slereah

I think I need to make like an important contribution to nlab and just make a diagram of the various kinds of topoi

because they have a lot of terms they throw around willy nilly

Herr Feinmann

09:46

@TobiasFünke what is your research area? I mean, I know it's CM but as you said it's a very broad field

Tobias Fünke

@HerrFeinmann I don't know if I can say the details without revealing my identity haha

Herr Feinmann

Ok, I considered that could be a possible answer. It's ok :P

Tobias Fünke

but broadly: (many-body) theory development, DFT, spectroscopy

but I do several things, I don't have a very narrow research area, for the better or worse

Herr Feinmann

Well, that is enough of an answer!

antimony

nice, i'd love to research in spectroscopy type topics!!

Tobias Fünke

09:52

@antimony what is your field of study/research area? are you a student?

I meant method developing btw; and of course theoretical spectroscopy ^^ I think I would destroy a lab in a few minutes due to my silliness

Arjun

@TobiasFünke I'm considering many-body theory as a prospective research area for me in the future : )

Tobias Fünke

@ACuriousMind Yes, I think I now fully understand! The slicing into $V_t$ induces a slicing of $M$ into $M_t$, after choosing an origin (at least then I am able to explicitly construct these). And the origin just leads to a shift in the time-label of these spaces. Thank you again.

@Arjun great! :)

Arjun

@TobiasFünke I had a bad feeling regarding cm initially due to material science and chemistry, but I feel many-body theory is quite theoretical and (possibly)rigorous?

Tobias Fünke

@Arjun well, condensed matter is a huuuuge field, so it really depends what exactly you mean

yes, many-body theory can be very theoretical, in fact it uses the same/very similar techniques the high energy people use (feynman diagrams and so on). There are also a few people I know of which are really rigorous (in a math sense), so yes, that is possible (at least to a certain extent) too

Arjun

@TobiasFünke I've heard some areas in cm use qft(I guess many-body theory does),but am not quite sure which and how it's used,would love to hear from you : )

Tobias Fünke

10:02

@Arjun yes, exactly.

wait

20

Q: What are Quantum Field Theories?

Every time I read about quantum field theories, I wrongly assume and associate the theory to the Standard Model, that is, our current theory of particles and interactions. However, it seems that the Standard Model is just a type of Quantum Field Theory, of many existent. Unfortunately, everywhere...

quantum-field-theory field-theory definition models

well, which semester are you? have you studied Green's functions in the context of many-body theory/relativistic QFT already at some point?

long story short: yes, QFT (and its techniques: second quantization, Green's function, perturbation theory etc.) are used in condensed matter. In particular, when you want to describe many-body systems and study its excitations, quasi particles and so on. It is a huge topic in itself, with many different applications...

Arjun

@TobiasFünke Oh,I just finished 5th semester of my undergrad education,nope not yet : (

Tobias Fünke

OK

Arjun

@TobiasFünke It also has real life applications? I guess so,since it is cm : )

Tobias Fünke

haha sure

but high energy physics too, no? scattering amplitudes etc.

it is the same thing, roughly. In condensed matter you might ask: If I shot an electron with some momentum into a solid, and some electron comes out with a certain different momentum, what happens? How is the solid excited? etc. And this leads you to scattering cross-sections too, and to the notion of band structure and so on

very real life indeed

sorry, in my band structure example above it should read: shoot a photon, and an electron comes out (that's ARPES simplified lol)

Arjun

@TobiasFünke lol,In my college most of theoretical physics is just strings and astrophysics,nice to see other stuff : )

There is only one prof who works in many body physics

Tobias Fünke

10:12

I see

I am of course biased, but I really like this (sub-)field ^^

Arjun

@TobiasFünke Well it does seem cool to me : )

Tobias Fünke

:) so I guess it is worth to try out and visit some courses if possible. then you'll see if you really like it

but again: Condensed matter is an enormous field, also on the theoretical side, and there are plenty of very interesting research areas and problems to encounter

btw: there is a classic paper: "More is different" by Anderson, which might be of interest.

Arjun

@TobiasFünke I'm planning on to build my QM knowledge now after that maybe learn some qft and then many body physics or maybe you think I should jump into many-body physics right after qm and do qft on the side?

@TobiasFünke will check that out : )

qwerty

@TobiasFünke this looks really interesting

Tobias Fünke

@Arjun I'm sorry, I cannot give you an advice, since I don't know anything about your education (system) and so on.

but having a good understanding of QM is indeed important, I'd say

Arjun

10:25

@TobiasFünke Oh that is totally fine,I suppose some level of qft is a pre-requisite for many body theory?

Tobias Fünke

@Arjun it depends on what you mean with "many-body" and "qft" exactly. some people use that more or less interchangeably. Many-body can for example just mean "treatment of many-particle systems in QM", e.g. second quantization....

Arjun

I see

Tobias Fünke

@qwerty yes it is a very nice paper

imbAF

10:50

I want to ask something about the s-matrix element for $\phi^4$ interaction

When considering all the possible combinations for $T(phi_1phi_2phi_3phi_4)$

In the following matrix element

$\langle 0|a_3a_4 \int \mathcal{L(x)}d^4x a^\dagger_1 a^\dagger_2|0\rangle$

I, from my calculation found out that fully contracted terms give zero

ACuriousMind

11:17

@SillyGoose I wouldn't call that a "classical field" - it's just the wavefunction - but otherwise yes.

@SillyGoose I don't really follow your notation here - what is $\psi_1\otimes \psi_2$ supposed to be? The crux is that the vector bundle might not be trivial when the fundamental group is not trivial, so you can't write a global section as easily like that.

imbAF

And additionally, would it be accurate to say that the order of perturbation is a deciding factor in whether all the particles at hand, incoming and outgoing, fully or partially interact?

Ryder Rude

11:41

Why is There Something Rather Than Nothing? Atheists Answer

►

naturallyInconsistent

12:17

@TobiasFünke that's so huge, that you could be one of the many rockstars making the tools we all pray to...

@Arjun there are plenty of people, both physicists and chemists, who do many-body physics only within the independent particle approximation, maybe with a bit of renormalisation. That means that they can just do everything within basic QM mathematics, nothing QFT, except for a bit of toddler renormalisation.

Ryder Rude

12:51

A (Gentle) Introduction to Quantum Computing

►

Tobias Fünke

@naturallyInconsistent xD could be...but no

naturallyInconsistent

@TobiasFünke ... doubt ...

heh

Herr Feinmann

13:08

Btw, Tobias. Are you currently a PhD student or is your bio from some years ago? @TobiasFünke

Ryder Rude

Maria is saying that the quantum correlation of $2\sqrt{2}$ is lower than the maximum correlation that can be allowed without having FTL signalling

Tobias Fünke

@HerrFeinmann xDDD I am, unfortunately, still a PhD student lol

Ryder Rude

it is a research topic what higher correlations could mean

Tobias Fünke

but I try to finish ASAP, there were some problems...

Ryder Rude

but I think the higher correlations cannot come from quantum theory

Arjun

13:18

@TobiasFünke best of luck : )

@naturallyInconsistent oh! I see..

Tobias Fünke

thanks :)

naturallyInconsistent

@TobiasFünke good luck

Arjun

@naturallyInconsistent If you don't mind me asking,what area of cm do you work in?

naturallyInconsistent

@Arjun im in nookooliar fooshun now. Was in DFT 2D materials before

Tobias Fünke

thanks

Arjun

13:22

@naturallyInconsistent XD

Tobias Fünke

@naturallyInconsistent may I ask why you changed?

Arjun

@naturallyInconsistent Are you on the experimental side?

naturallyInconsistent

@TobiasFünke the research project ended; my wonderful advisor decided to try the commercial world (and get permanent residence, and finally some spare cash), and so miao miao jumped ship to quantum computing. When miao miao described what miao miao was doing in QC to my current colleagues, quite a few of whom also came from QC, they said miao miao dodged a bullet in QC. They also have their own QC horror stories. Anyway, it is rare to find a nookooliar fooshun job, so it is worth spending some time

Arjun

what a life..xD

Tobias Fünke

@naturallyInconsistent okay, interesting. Thanks for sharing

naturallyInconsistent

13:34

@Arjun theorist by training, but if an experiment needs extra hands, miao miao can do it. Miao miao is the rare kind that shut the experiment sour grapes up in the lab, because miao miao aced both. Not the brightest at everything, but will get things done to a level that people take note.

@TobiasFünke It was only when miao miao left DFT that miao miao realised why the Wannierisation kept failing. For the most stupid rookie mistake: insufficient pseudopotential wavefunctions. But at least miao miao could point out that even advisor didn't know, and the person who was supposed to teach meow meow about Wannierisation, also abruptly left academia before having enough time to warn meow meow about pitfalls like that.

it's soooo gahhhh

Arjun

@naturallyInconsistent wow and on the other hand there are people like me who mistake a transistor for a capacitor lol

naturallyInconsistent

@Arjun it's ok; people just need to shine in their specialty. There is no need to be great at everything.

3

Tobias Fünke

@naturallyInconsistent Amen

Arjun

:D

Ryder Rude

13:56

i am more into theoretical physics than experiments

Tobias Fünke

there seems to be a preference here on physics SE :d... also reflected by the type of questions, at least this is what I experience

Ryder Rude

the top voted questions are experimentalist

i like theory because I like simplified view of the world

Nairit Sahoo

Is Gross Neveu model the same as Four Fermi but in 1+1 D?

naturallyInconsistent

Experimental questions are difficult to convert into a form that is of general utility, unlike theoretical questions.

Quite often the experimental questions would be tied to the specific type of experiment, or even the specific experimental equipment.

Slereah

14:49

The topoi have been ordered

I hope anyway

Arjun

15:06

@RyderRude Same here,even mathematical physics interests me,I hope to learn it someday : )

Ryder Rude

15:17

@Arjun i don't like too much rigor but I like abstraction

i will also learn some computation ideas like Church Turing thesis. think it is relevant for the physical world

Arjun

15:30

Well knowing that mathematicians have logically derived known physics from axioms rigorously helps me sleep peacefully lol

ACuriousMind

@Arjun Don't do QFT then if you value your sleep :P

3

Herr Feinmann

@TobiasFünke Well, I'm not even one :P

ACuriousMind

...but you're two PhD students?

Herr Feinmann

I'm not a PhD student :P

I have to get my MSc

Arjun

@ACuriousMind But I also wanna learn physics the physicist way first ; ) ,mathematical physics I feel like is an extra perk that I get : )

Herr Feinmann

15:35

Why did I get a star over that? :P

Arjun

@HerrFeinmann Oh so you're from Europe?

Herr Feinmann

No, I'm Italian.

I'm from New Jersey

(I've been thinking about this joke since yesterday)

Arjun

Cool,I thought Americans directly go for a phd after their BS degree,didn't know they also had an msc

Herr Feinmann

(I'm seriously Italian, so yes. I'm from Europe)

Arjun

@HerrFeinmann lol

@HerrFeinmann I thought you were of Italian descent living in New jersey,yes I didn't read the ps below your comment xD

Herr Feinmann

15:41

@Arjun I said that because there is a common joke about it

A: "I'm an authentic Italian."
B: "Oh, where are you from?"
A: "New Jersey"
B: "Wait, what?"
A: "Yeah, my grand-grandma was Italian"

Arjun

15:58

2

@HerrFeinmann Saw this long time ago lol

also this xD

(pls don't take offense lol it's just light-hearted humor ;)

think_meaning_buildß

16:13

Why 50% of The World Live in these 6 OVERCROWDED Countries

►

Silly Goose

16:39

@naturallyInconsistent what QC horror stories 0.0

naturallyInconsistent

@SillyGoose entire research directions that obviously arent going to work

at least, that was before the recent nice breakthroughs

Silly Goose

@ACuriousMind I mean to write it down $\pi \circ \Psi$ locally where $\pi$ is the local cartesian product projection and $\Psi$ is some section of the bundle

blebolus it is hard to choose a research direction, even broadly :P

Relativisticcucumber

@Arjun saying 'pls dont take offense' doesnt make what you say inoffensive, it just shows that u r aware of ur potential to offend, which is somehow worse.

@HerrFeinmann this relates to a super weird trend in the states that ive noticed. ppl will ask me like where r u from and i say im american and they are like no where are you really from and im always like ??? i just told you im from here. some people in the states seem to have a fetish for insisting that you cannot describe your heritage as american. outside the US, i have never experienced this sort of thing.

also what makes it esp. weird is theres nothing ab me to indicate that i even might be from somewhere else

i know you will read this and be like "ur chinese what r u talking ab" @HerrFeinmann

Arjun

16:56

@Relativisticcucumber Damn,that's some depth

Relativisticcucumber

i guess the conclusion is that despite all evidence pointing to the contrary people refuse to believe i am not chinese xD the funny thing is ive even been to meet family members of asian people i know and they say "you look alike" when i literally look the OPPOSITE @HerrFeinmann what is it about me pls help me understand xD

@Arjun is this sarcasm

Arjun

No I mean it,I never thought about it that way

Relativisticcucumber

@Arjun oh i actually couldnt tell lol sorry

ACuriousMind

@Relativisticcucumber Some people get hung up on the weirdest things. I have an Indian colleague who kept asking me where I'm from and he really didn't want to accept "Germany" (or any of the specifics I gave him) as an answer because I "didn't sound like a German" to him :P

Arjun

@Relativisticcucumber it's not your fault lol, it's hard sometimes to get the tone on the internet

Herr Feinmann

17:16

@Relativisticcucumber or they think that US=World :P

In a literal sense

@Relativisticcucumber wait, are you not Ch- just kidding :P

@ACuriousMind did you waste the opportunity to troll? :P

Arjun

@ACuriousMind Well I've had a fellow Indian ask me which part of the country I was from,when I said I'm from the south he was like no you don't look like that at all lol,then he asked me where my parents are from,I said they are from the same region and then he even asked me about my grandparents lol

Herr Feinmann

@Arjun yeah, Chinese has 4 tones

Arjun

@HerrFeinmann I won't laugh at this..

(I don't want my social credit go down xD)

Slereah

@ACuriousMind just lay on the accent

Arjun

Gtg gn guyz (-_-)..zZ

ETHAN COUSINS

17:38

hello

Relativisticcucumber

@HerrFeinmann LOL

ETHAN COUSINS

hi

Relativisticcucumber

@ACuriousMind lmao what the. yeah one time it went all the way back to my great great great grandma. thats as far as i can recount

we did make some progress there tho bc at least at that point there was some migration. supposedly from oklahoma to california.

ETHAN COUSINS

is this all about physics?

hello?...

think_meaning_buildß

hi

ETHAN COUSINS

17:52

hello finally a response

think_meaning_buildß

11

A: The h Bar is always open! (Chat Guidelines)

Chatroom guidelines Be nice. Although chat is a place for casual conversation, swearing is generally frowned upon on SE, so be polite too. This is something you need to be particularly careful about when discussing sensitive topics like politics, sex, and religion. Don't use chat as a 'replacem...

ETHAN COUSINS

okay

think_meaning_buildß

welcome

ETHAN COUSINS

:D

hows everyones day?

ETHAN COUSINS

18:09

....

qwerty

19:38

@Relativisticcucumber imo "where are you from" and "what is your heritage" are different questions. I think a lot of the time people just dont have the vocab to ask you what they might actually mean. or they're conflating different things, like physicists talking to mathematicians lol

Silly Goose

@ACuriousMind by the way, what defines a “classical field”?

ACuriousMind

@SillyGoose what triggered this question?

@ETHANCOUSINS don't take it personally, the chat isn't always active at all times

ETHAN COUSINS

20:01

lol I just thought because the thing said always open

Silly Goose

@ACuriousMind Your response that you wouldn't call the $\Psi$ in Leinaas & Myrheim a classical field

ACuriousMind

@SillyGoose I mean - it's not a classical field, it's a wavefunction. That's not a statement about its mathematical nature but about its physical meaning.

ETHAN COUSINS

....*quietly observes*....

qwerty

@ETHANCOUSINS the bar may be open, doesn't mean there's patrons inside ;)

ETHAN COUSINS

@qwerty what that means?

@ACuriousMind cheese powder.....

new feed interesting

Allie

20:07

Hi guys. Quick and simple question :)

ETHAN COUSINS

Helloooo

I'm active:D

Allie

So the C=O IR stretch usually shows up at wavenumber 1600-1700 cm-1

And I know that in the quantum harmonic oscilator model the energy of your vibrational modes are given by $h\nu (v + 1/2)$

ETHAN COUSINS

ya I'm sorry but I'm in eith grade and I just froze in my chair trying to comprehend that.@qwerty can you help?

Allie

In this case, $\nu$ is the frequency of the vibration in the molecule right?

ETHAN COUSINS

hmmmmmmmmmmmm this is what Google said lol (4.95\times 10^{13}) s$^{-1}$

Allie

20:12

Or, sorry. Would it be $\nu (v + 1/2)$?

Silly Goose

@Allie is your $v = 0, 1, 2, ...$?

Allie

Yeah

Silly Goose

@Allie I imagine $h\nu$ can be described as the characteristic energy gap between two adjacent energy levels in the system. For a harmonic oscillator, the energy gap is literally always $h\nu$.

ETHAN COUSINS

phew thank you finally daomen else took over

Allie

I get that

I'm more asking about the vibration in the actual bond

Unless that doesn't really make sense because we're not dealing with a classical harmonic oscillaotr

Silly Goose

20:17

I would have to look back at some notes, but I imagine classically you can approximate an atomic bond between two atoms as two masses connected by a spring, which can then be treated as a harmonic oscillator. Then, quantum mechanically you just treat it like a quantum harmonic oscillator. But I don't recall if there is just one "fundamental" frequency associated with a given atomic bond (in the simple classical model).

Allie

the main reason Im asking is because of a homework question but Ive also always been curious....

I'm just wondering whether that nu_0 would be my nu in this case?

and I'd also add the first anharmonic term

ACuriousMind

@Allie yes, the $\nu_0$ is the notation for the "base" frequency of an oscillator, it's your $\nu$

Allie

Yay thanks bestie

ETHAN COUSINS

:D I tried

Allie

So I should write $E = \nu_0 (v + 1/2) + \nu_0 x_e (v + 1/2)^2$

Tobias Fünke

20:25

during day (some hours ago) this chat is condensed matter focused, and during night (now) it is the math and high energy physics people :d

Silly Goose

time to ask questions that mix both

ACuriousMind

@TobiasFünke the logical conclusion is that the math/hep folks have jobs while the CM folks don't ;) (no, I have never heard of time zones)

3

or perhaps the conclusion should be the inverse, depending if you think people access the chat more or less while at work :P

Tobias Fünke

:d hehe

ETHAN COUSINS

Oooooo thats why it got all sicentific

well does school count as work?

Tobias Fünke

that's exactly the point in my case haha. but every now and then I have only some "easy" stuff to-do...plotting etc...

@ETHANCOUSINS sure ;)

ACuriousMind

20:27

I mean...you are in the chat of the physics.SE site, getting scientific is kinda what you'd expect :P

Tobias Fünke

@SillyGoose go ahead :d

ETHAN COUSINS

ya lol

Silly Goose

how about axiomatic condensed matter theory 🥴

Tobias Fünke

xD good joke

I am happy if any book properly defines their symbols and conventions lol

Loong

@ACuriousMind I'm too busy at work and too tired after work.

Silly Goose

20:29

@TobiasFünke lol

@TobiasFünke i am plotting right now...hehe

Tobias Fünke

of course a bit exaggerated...but there is some truth in my statement ^^

qwerty

@Loong +1 to this. 2 more days til my Christmas break!

Loong

At least I am not on on-call duty this Christmas.

Tobias Fünke

@Loong may I ask what your job is?

ACuriousMind

@Loong I feel you - I've been on break since Monday and I'm slowly starting to remember how it feels not to be tired :P

Loong

20:32

@TobiasFünke The short version is that I have Homer Simpson's job.

Tobias Fünke

OK

ETHAN COUSINS

RADIATION

Tobias Fünke

that's kinda cool, no? :d

ETHAN COUSINS

THE PAOWER

qwerty

I was planning to read and write a lot of physics over the break but instead I have life admin and the potential to turn into a pile of goo

Silly Goose

20:33

XD

Loong

@TobiasFünke Well, it's mostly a huge responsibility.

Tobias Fünke

I see

Loong

Or as we say: always with one foot in prison.

Tobias Fünke

oO

ETHAN COUSINS

any of you say about the physics of stuff like honey?

ACuriousMind

20:37

@Loong that can't be so bad, we all know that can be automated ;)

Loong

Y Y Y Y Y

Tobias Fünke

@ETHANCOUSINS what do you mean? viscosity?

Loong

@ACuriousMind And we don't even have any radioactive gases for venting anymore.

One of our subcontractors distributed Heidelberg Monopoly games to everyone today.

imbAF

In the $\phi^4$ interaction, the coef. $\frac{1}{4!}$ is there to account for all the possible contractions of the same type?

ACuriousMind

@Loong now you can buy my house in your game D:

Loong

20:42

What's the Schlossallee of Heidelberg?

Silly Goose

Has anyone had problems with laggy typing in Overleaf when using Safari?

qwerty

@Loong ah so you can make the "one foot in prison" joke when playing together

Silly Goose

I have never had this issue when using Chrome, but I recently switched to Safari and noticed this to be the case. The problem is independent of the document, but the lag seems to go away if I zoom far enough out of the document.

Tobias Fünke

@SillyGoose nope

but the last time I typed in Safari is a few weeks ago, so...

BTW: How do you like the new integrated AI? is it any worth?

Silly Goose

i finally made the switch back to safari...since chrome kills my laptop's battery too quickly

i am not sure if i have integrated AI turned on or not. if i do have it turned on i guess i haven't noticed XD

qwerty

20:46

@TobiasFünke oh no when did they roll that out? I was on overleaf only 2weeks ago and didn't notice

ACuriousMind

@Loong uhhh...perhaps the Philosophenweg?

Silly Goose

oh wait the AI tool for overleaf? I turned that off, so I actually do not think I have used it at all yet

Loong

@ACuriousMind Apparently, they used Schloss-Wolfsbrunnen-Weg. Does that make sense?

Tobias Fünke

yeah, its really new

it suggests improvement for language, grammar and so on

qwerty

nooooo

I hate when robots try to write for me

ACuriousMind

20:48

@Loong yeah, that fits, too

Loong

okay

Silly Goose

okay i've got to finish my final project i will see u guys later

qwerty

they are always wrong and not only that, what happened to having your own thoughts and style on paper?

@SillyGoose have fun and good luck!

ACuriousMind

But I don't think I've ever been there - the Philosophenweg is a similarly rich neighbourhood but there's also some physics institutes there so I'm more familiar with it

@qwerty "AI" isn't for people who have their own thoughts or style :P

Tobias Fünke

@SillyGoose good luck, see you soon

Loong

20:50

@ACuriousMind Ah yes, they used the Philosophenweg instead of the Parkstraße.

qwerty

@ACuriousMind I hate how in many products they make it very difficult to find the settings to turn it off. in the most recent android update on my phone, it turned on some new "smart reply" function that was absolutely infuriating and the off toggle was buried 3layers deep in the obscure unsearchable settings

as searching "smart reply" gave you two other smart reply settings but not the actual setting for the update

ACuriousMind

@qwerty That's because they need you to use it so they can justify the investment to their bosses ("look how many users are using our new feature!")! They know it's garbage.

or, conversely, they only built it because the bosses wanted it and if the bosses don't see the feature being used they'll just blame the people who built it instead of admitting they don't understand what they're doing

(can you tell I'm jaded about the topic? :P)

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