hiiiiiiiii

@SignorFeynman i dunno of a kiddo who liked to learn the characters

morning

hi

solidarity means support while solitarity means alone

@naturallyInconsistent I'm not a kiddo, but I do :P

@TobiasFünke buongiorno 🤌🏻 (please don't believe to that sterotype, Italians don't do that gesture randomly :P)

@SignorFeynman that's because you're probably not being forced to copy characters literally 100 times in a row for homework :p

@SignorFeynman Imagine having to learn the hanzi song

It takes forever

@qwerty Perfection requires sacrifice

Apparently, Hegel and Schelling are Christians

Kant too

is it strange how people can be so careful with reasoning and evidence, and dismiss those things when it comes to religion belief

He lived in Prussia, of course he was a Christian

It wasn't even legal to not be until the 1850's

oh

but their philosophies still subscribe to Christianity

You could be a Christian or you could be a jew (and have severely restricted rights)

wow

maybe these people just pretended to be Christian then

Mr. Hegel did not seem to be a sunday christians

He wrote whole books on the topic

Oh

i think these people just paid lip service to Christianity. They wanted to write about god in general. they just included Christianity to not piss off people

Hume came before Kant and he is openly atheist

but he is not from Prussia

@RyderRude If you have no idea about the historical context or what these people actually said, maybe do some research first before you randomly speculate? The Prussian censors multiple times supressed Kant's writing on religious topics, cf. e.g. Wiki, and those writings were not in support of the organized Christian churches

some sources do say that Hegel is effectively an atheist

Spinoza's writings on god were considered so horrible that he was one of the rare man to be excommunicated from judaism

i researched on philosophy SE

Tense times to write about God

Kant is against the church Christianity but is in support of Christian philosophy apparently

@Slereah oh

yes. Spinoza was braver than Hegel, Schelling and Kant

he was persecuted

If we're just going to do silly ranking of historical personalities again, please do that somewhere else.

and he had a group of followers . he didn't stop publishing his ideas

@ACuriousMind sorry

Especially if you just base this off random tidbits you learn from SE instead of actually investigating the topic in any depth

this idea that they pretended to be Christian makes more sense to me

@ACuriousMind i am going to learn their ideas in depth

@ACuriousMind have you read critique of pure reason

@Slereah have you

i think I will start with a basic philosophy book

Critique of pure reason is probably not a good starting point

yeah... i am going to start with a recent book which summarise all philosophy

there are a few from Russell

sometimes i think most idealist are Christian, which makes me question my idealism :P

but there are some atheist idealists like Spinoza and Wittgenstein. so i think my perspective is skewed

Spinoza wasn't an atheist

@SignorFeynman ;d

@Slereah effectively..

i mean effectively he was

the pantheism stuff is mostly naturalism

And also Spinoza is more often described as a materialist (cf. Stanford). Can you please stop just saying things that are wrong as if they were universally accepted facts?

By your own admission you haven't even read a "basic philosophy book". Why do you keep trying to discuss it in scholarly terms that require much more familiarity with the subject?

> Spinoza is often though controversially thought to defend a form of materialism

it is controversial

This is what the "amateur philosophy" complaints were about and after you said you will discuss it less you still come here every day with some uninformed comments about philosophy. What do you hope to achieve here?

@ACuriousMind i have not read other people's ideas but I myself have thought deeply about questions and the answers I've arrived at are often confirmed by some previous thinker

philosophy can be done independently it is just the art of thinking

@RyderRude You can believe that but that doesn't mean you need to type all of that thinking into the text box of the chat, and you especially don't need to present your thoughts as if they are facts. It is exhausting for other people in the chat to either let your musings stand uncorrected or to engage in these circular discussions. I'm asking you one last time to consider that this chat isn't your personal journal, it's a space to engage with other people.

@ACuriousMind like I had said back then, i sometimes do get discussions. the current discussion was a two-way discussion. this idea that no one else never wants to discuss philosophy is completely wrong

Slereah did want to discuss rn

it was a completely fine discussion. you are escalating things for no reason

@RyderRude To be perfectly blunt I would have preferred to not have this discussion at all rather than the frustrating corrections of your misconceptions that we had. You should not mistake people engaging with you with them enjoying it.

@ACuriousMind i don't mean you. i meant Slereah

@Slereah did you feel bad about anything i said

@ACuriousMind also, there is another presupposition that one is only allowed to discuss something if one expertises in it. this is also wrong

@RyderRude You can discuss things you're not an expert at. But not by just stating stuff as if you were an expert and then letting others correct you, which is what your mode of starting "discussions" is.

@ACuriousMind so what is the thing i was corrected upon rn? you said that Spinoza is widely called a materialist, leaving out the word "controversial". i started the discussion with Hegel, Kant and Schelling being Christians, which I had looked up before saying. Slereah then said they probably were pretending

it was not a correction. it was a contribution that I hadn't considered

it would be a completely normal discussion if u hadn't escalated things for no reason

@RyderRude Where did you "look that up"? If I type "was Kant a Christian" into a search engine, every result discusses how that's a somewhat difficult question. All the nuances that were brought up here and more are already there if you actually look it up. That's what I find frustrating.

Respectfully - Ryder - I don't mean any offense, but these philosophical discussions rarely have engagement, and when it happens it's negative engagement, be it someone who makes a correction or someone who asks you to reduce this kind of interaction here. Now, I'm not a fan of such discussion with these modality and frequency myself and I can just ignore them, like it happens for many discussion that are physics related too. Nonetheless, I think you should be more careful reading the room.

I hope he didn't quit for this message D:

mew mew

@qwerty To my great regret I had to learn that Outlook has a "recall" feature where the email just vanishes from the recipients' inboxes if no one has replied yet; I took to long to craft my reply :P

ah, for when your message is as dangerous as expired cheese!

I have kind of mixed feelings here. Anyone who gets annoyed by some user can click "ignore"... where is the problem? Sometimes people also write random math or physics things in here, I don't see a difference to random philosophy things (in both cases whether or not they are true or not)

@TobiasFünke do you not get annoyed when people say wrong things around you as if they are true?

That being said, I think one should always try to read the room and check if it is really the right time to discuss this specific topic, especially if other discussions/conversations are ongoing

@naturallyInconsistent the good thing in online communication as here is that you can simply ignore persons if needed

i don't know if my 2 cents will truly add anything or not but I feel like many times these "problems" come up in hbar... RR, and in the past with others, it's honestly imo not so much about the intellectual or academic stuff (although yes it is a part of it) as much as a problem with social skills. basically I agree with Tobias

@TobiasFünke That means you are letting wrong stuff go unchecked. It is not a solution to a problem.

@ACuriousMind philosophy.stackexchange.com/questions/6615/… this thread

it is agreed upon here that Kant disagreed with church Christianity but was kind of doing Christian philosophy

@ACuriousMind oh noooo lol

Also, there are those of us who do not wish to have missing convo, where you see other people interacting with someone that is blocked, all over the place, and frequently so.

@naturallyInconsistent I also don't agree with everything written about physics or math here

@TobiasFünke what has this got to do with the convo at hand?

You get to respond and correct people if they are wrong.

> That God, independent of our inability to recognize his nature, is postulated as the Christian God (at least I think so, should probably check that out)

> Kant proposes a totally different approach to religion and God,, but his morality cannot be thought independently of them.

this is why i thought that Kant believed in the Christian god

@RyderRude See, my problem is that even your source there is equivocating ("at least I think so") and there are other answers with different takes. But instead of looking up more on the topic, you come in here with the unqualified statement that "Kant was a Christian" and start talking about how Kant "dismissed reasoning and evidence what it comes to religion belief". That's not even a fair paraphrase of the only source you've read!

You're making everyone else do the work of figuring out what's actually going on. That's the frustrating part.

@SignorFeynman i don't know how to approach this situation. is completely stopping to mention philosophy the way?

@RyderRude to a first approximation, yes

the way i approach it rn is that I post prompts sometimes which only take a few messages and sometimes I get discussions

@RyderRude your "post prompts sometimes" is every day. Your "sometimes I get discussions" is, on the vast majority, corrections and rebuttals. That's not a discussion.

@ACuriousMind i meant to write "apparently, these people are Christian. i mentioned "apparently" in the preceding message. but i should've elaborated more

@naturallyInconsistent can you show me seven prompts from the past week??

@RyderRude That would not have helped. The essence of what so many people are here trying to tell you isn't that you have to sprinkle "apparently" into the discussion.

@RyderRude no, because I know you have less than that, due to getting banned.

i wasn't banned

for adjacent reasons

i think I will take a break from chat

@RyderRude As I said, I personally do not care enough about these discussion to suggest any such measures. That being said, I just described the external perception I have of such interactions

i will participate sometime later. see u all

@SignorFeynman it is fine

@TobiasFünke Incidentally, this is something I hate about being online. I never ignore people and I don't want to be ignored (I mean totally ignore). Ghosting is just evil :P

I hope cucumber comes back sometime

:(

I'm pretty sure that will happen someday, just wait

I saw several very unfriendly or even hostile reactions to RR. I just want to point out that it is perhaps better to simply ignore users with whom you do not want to engage with, rather than "discussing" the same thing over and over again.--- And by saying this, I don't mean to encourage RR (or anyone else) to just proceed with their behavior. I want to say what I've said some times before already: we should be more kind to each other... just my two cents

...

I've been in that position in the past. Now I switched to the neutral side :P

@TobiasFünke Look, there is kindness to inadvertent mistakes, and then there is kindness to recalcitrant behaviour. You are missing out on years worth of such behaviour that even the ever-patient ACM is no longer tolerating. Maybe you should consider that people are not intending to appear to be unkind by choice.

nI, I feel that RR isn't doing this out of spite, I agree that it's "problematic" but I feel he genuinely seems confused by the reactions/requests and the social interactions he's having on here. I'm not saying it should be "tolerated" nor that right now I have a "solution" but I want to point this out

@qwerty I've been a teacher. I've succesfully dealt with autistic, ADHD, epilepsy, what have you. It is much more difficult trying to get a cohort to be kind to students with special needs. This is definitely not out of spite. But at the same time, he is not so ignorant as to not realise that what he is doing is akin to scraping a blackboard. It is very much intentional by this point, especially with the extremely direct ways that ACM is telling him what is tolerated and what is not.

> ever-patient ACM

Who is that? I've never met them. :-)

I mean, ACM is a pretty patient guy :P

You can scroll up for countless examples of that.

lol

@naturallyInconsistent I agree that he "should" know and be taking on board the extremely direct feedback but he isn't. maybe he's not doing that because he doesn't understand the reasoning behind the direct feedback (even though it's obvious to all of us). I don't know if I or anyone else can explain it any better, though I've been thinking. but reacting in a hostile way hasn't made RR stop either!

@qwerty Well, sufficient moderation can force it to come to a head. However, ACM is not willing to do that.

Why are coherent states called coherent, though?

Glauber seems to be guilty

And coherent states do not spread because they are in phase

So, this part makes sense now. Probably it becomes bogus if you try to insist too much on giving a fundamental meaning to these things

@SignorFeynman I'd be slightly more precise about this. Coherence always has something to do with phase being kept. In these almost-classical states that are still quantum states, the phase is constant even after having the annihilation operator act on them (because they are eigenstates of the annihilation operator), and so calling them that way is tolerable.

Note also the context. If you are dealing with BCS, it probably is more confusing. But think in terms of lasers, where it first appeared, and you will realise that this naming is perfectly fine.

Which is also why it took root.

So what was your reason to loathe the term? :P

I dont loathe the term...

The discussion we've had about "quantum coherence"...?

yes, but coherent states are proper

Oh, yes, coherent state are. I was talking about using them as a motivation for "quantum coherence" :P

The funny thing is that my SC course has an arrow with some red text saying "MACROSCOPIC QUANTUM COHERENCE" every two slides or so

uugh

im seriously counting upon you to give them a rude awakening that they just sound like cold fusion diehards, after they are no longer able to crunch your grades.

to be bending over backwards level of fair, there are actually plenty of quantum behaviour writ to be macroscopically large that somehow the pioneers are cognitively blocking away. However, just to avoid being construed to be the same as cold fusion diehards, we would just find another name than macroscopic quantum coherence for it

@naturallyInconsistent I don't want to be cruel, I already gave my prof trouble just because I asked what magnetic field we were talking about ($B$ or $H$), since the notation kept changing deceptively

That's also a thing to stab people in the face for making mistakes over

I didn't mean to stab, I was genuinely confused like everyone else there

At first the prof was befuddled, then told me I would get my reply in the next lecture. I did, but it was more confused than before. Then she told another prof (now my advisor) that I'm too nitpicky :P

There is no way to fix it, if the confusion is deep enough. In particular, B satisfies the no-monopole rule whereas H does not, and if there are sufficient confusion, there is no way to disentangle a particular expression over which is actually being meant.

I think that was a very basic question and I confirm it after learning some SC. You need to know well what magnetic field you're talking about, whethe $\mathfrak{H}, H$ or $B$

@SignorFeynman there's a bit of discussion over that at physics.stackexchange.com/q/300034/50583; generally I think it's one of those words (another example being "quantum fluctuations") that's often just used to vaguely gesture at something being "more classical" or "more quantum" than one might generically expect but there isn't really a deep technical definition that applies to all instances

In that case we were being presented a bunch of equation at a phenomelogical level, i.e. not derived from a microscopic theory

which compounds the confusion

Indeed

at some point in all these phenomenology, the disentangling becomes literally impossible

@ACuriousMind I read that question before, I like CR Drost's answer. Now that you rub salt in the wound, "quantum fluctuations" have confused me too in the past

They told me I would understand the name after learning about path integrals

lol

I mean, the only sense I can make of it is as fluctuations around the classical evolution $\delta S/\delta \phi=0$

@TobiasFünke I don't really want to extend this discussion, but: If my impression was that this was just my personal opinion I would just have kept it to myself. But what I see is that different people have been trying for a long time to say something similar via subtext that's then ignored (stuff like "maybe you should read a book for once" - "thanks, maybe I will!"), and I was trying to make it as much explicit text as possible for once. I don't intend to make this a recurring feature :P

But there are some things like "fluctuation operator" that are just too much

@SignorFeynman as I said: There's different instances where you can make sense of the phrase in rather straightforward ways (like sometimes all that's meant is non-zero variance of some operator, i.e. the measured value will "fluctuate")

but then you get people who talk about virtual particle pairs popping out from the vacuum (another one of my pet peeves) and that this must happen because of quantum fluctuation and it's impossible to decode that into a cohesive picture in terms of the actual formalism

and then there's again a rather different meaning when the term comes up in contexts like the fluctuation-dissipation theorem

Personally I think the right solution is to just avoid these ambiguous and overloaded terms, but clearly not everyone out there agrees :P

@ACuriousMind wait is there an SE answer or something talking about this? I'm curious

I'm always down for an ACM pet peeve lecture

@qwerty Sure, I have several rants about virtual particles, e.g. physics.stackexchange.com/a/275099/50583, physics.stackexchange.com/a/274374/50583

hiiii

hi nI

hummm I'll park this for another day

hi Allie

hiya tobias

im gonna try to get some reading done today

My problem with the term is mostly that it's extremely popular in pop-sci presentations of QFT to claim that "QFT says these virtual particles are created all the time" and then you get all kinds of (justified, from what they know) follow-up questions from the interested layperson that really make no sense because that picture of virtual particles makes no sense

i would love to get to the photon chapter

phonon*

physicists use it as a shorthand but aren't so often misled by it - I still remember the mix of hilarity and despair I felt when I read Hawking's original paper on Hawking radiation and he gives the picture of a virtual pair being created at the horizon and one of them falls in and the other becomes real only to say directly after that that that's just a metaphor and you shouldn't take it literally

cue every popular presentation on Hawking radiation taking it literally

how r u tobias?

I am fine so far, thanks. I was quite unmotivated the last days, so I did not really make any progress...but it is better now

And you? :)

@ACuriousMind I also got it in answer to a question I had about some inconsistency I noticed in high school physics, back in the day

I forgot what it was

...I have the problem that once I understood some things or solved a problem, it becomes quite "uninteresting", in the sense that I am too lazy to put everything in a nice publishable form lol

now I really wish I remembered because it's be nice to know what the rigorous answer was

@ACuriousMind The second one is the version I was talking about, I think. Well, they didn't say it in terms of particles popping out, but in terms of vacuum polarization

I think it was something about energy conservation...

Still, I think it's the same think you are talking about

@ACuriousMind omg D:

@TobiasFünke I have the problem that once I solve a problem, I have to write it down in detail, with sources and steps because I think my future-self will be too dumb to understand

@SignorFeynman "Vacuum polarization" is another of these terms :D

@SignorFeynman me too

Unfortunately it is, yes

There's a technical meaning (e.g. Haag often phrased Haag's theorem as being "due to vacuum polarization") and the weird handwaves people use it for

That's... NASTY

@SignorFeynman yes, me too. But to publish something requires more effort, because you do not write it for yourself. At least this is my perspective

Oh, you meant publish as a paper, then yes.

jup

@SignorFeynman see, the opposite problem is thinking you're smart enough to remember the solution but you don't and then you have to rederive it every time you need it :P

I still remember mildly annoying ACM one of the early times I wandered into hbar thinking he would need to make notes to remember or understand things like the rest of us mortals xD

also since I use non-standard notation in my notes (compared to my field)

@qwerty it is not only remembering, but to spell out an argument in a precise and concise manner.

@TobiasFünke yup

@TobiasFünke im alright i suppose

@ACuriousMind I mean, if the solution requires me to consult 20 papers the first time...

@ACuriousMind yeah but it takes you only 5mins right? ;) but also the last time I did that one of my mentors said "just rederive it, it's good for the soul" lol

it depends on what it is, sure

@qwerty It's a mix of good memory and also good search, which is suggested by the fact that he often provides links

Well, there are also answers he can't forget, like the "fetish" answer

the $eta$s here define an example of what to my understanding is a usual and simple bogoliubov transformation

gauge fetish

the computation below shows that there does not exist a nontrivial vacuum for both $\eta_q$ and $\eta_{-q}$ in the $\{\Phi_0, \Phi_{-q,q}\}$ subspace, but this seems wrong?

lol

again, $\xi$ is another fermionic operator and $\Phi_0$ is its vacuum. the $\eta$ are also fermionic.

@SignorFeynman I mean arguably some of my answers are just me writing down stuff just like you would in your personal notes :P

i assume that means its not a fetish for symmetries

@SignorFeynman ehh do I get a link? :)

@ACuriousMind Yes, indeed

the fetish answer

@qwerty here you go mate

He's so damn fast...

(I usually search for it via "red herring" and not "fetish" :P)

I find "fetish" more effective and unique

lollll ive been to this answer at least ten times in the past year

@SignorFeynman Ty fratello

@SillyGoose What was you expression for the Bogoliubov vacuuma and where did you get it?

lol

@SignorFeynman I mean you're technically right - I have 5 posts mentioning red herrings and only 1 mentioning a fetish :P

I have to admit that "red herring" is one of those phrases which ring the ACM bell in my mind

@SignorFeynman from journals.aps.org/rmp/abstract/10.1103/RevModPhys.36.856

the expression is $c_q \Phi_0 + s_q \Phi_{-qq}$

@SillyGoose I'm asking because in the case of BCS (which I don't think is unlike yours) the Bogoliubov vacuum is a coherent state for the fermionic operators

@SillyGoose Indeed, this is a coherent state

@qwerty haha, true that

@SignorFeynman for the untransformed fermionic operators? (any vacuum is a coherent state by definition for its own operators, right?)

@ACuriousMind I really like this answer :p gj

since vacuum is an eigenstate of the annihilation operator with eigenvalue $0$

is this an incorrect definition of coherent states?

I am confused as to what is vector currect? The charge or particle current density is a vector. Am I misunderstanding something here?

Wait, you're right

But it's a degenerate case

@SignorFeynman do you have a textbook reference which goes through an example of using fermionic bogoliubov transformation?

i have been trying to get out of these contradictory computations for a few days now :P

@imbAF That's what they're saying: The current is a 4-vector, a "vector current". The name is to distinguish it from "axial currents" that are pseudovectors.

@SillyGoose Although it's the context of BCS, you could check Annett, the chapter on BCS but I don't know your knowledge about the context

@ACuriousMind I see

I have one more thing I want to ask

That being said, even if vacuum is a coherent state, it's one with quantum $\alpha=0$, we don't care about it now.

Do you know what $\Phi_{q,-q}$ is?

In our lecture, when we tried to calculate the matrix element between proton electron interaction, when we considered the proton as a point particle, we couldn't because the proton has sub structure. So a suggestion was given where the term $\langle p'|j_\mu|p\rangle$ was suddenly introduced

Can you explain to me what exactly this is?

Because this term was introduced in the matrix element

ph wow this is beautiful

brillouin zone magic

And it was just suggested to attempt such a solution. I don't understand it

I want to give a better explanation as to what I mean.

@SillyGoose in case you reply, ping me, since I am changing tabs

I don't understand what \langle p'|j_\mu|p\rangle is and where does it come from

And I am having truble solving the exercise

@imbAF You have to observe that your first expression can also be written as $\langle k'\vert j_e \vert k\rangle\langle p' \lvert j_\text{pr}\lvert p\rangle$, where $j_e$ is the electron current and $j_\text{pr}$ the proton current (for pointlike particles). Why are these called currents? Because they're exactly the expressions that appear in the EM coupling terms in the Lagrangian $A^\mu j_\mu$ as the currents

all your ansatz is doing is saying "okay, now suppose we don't know the microscopic form of $j_\mu$ (i.e. the expression in terms of the fermion fields $j^\mu = \bar\psi \gamma^\mu \psi$), what can we still say?"

Honestly, maybe I should have deduced this

but until this very moment

we never wrote entities/structure I don't know the correct phrase in the matrix element as currents

It comes as a new thing for me

And also do you make the distinction between current and current density?

I feel like in most texts and in general people are not accurate with what they precisely mean

generally I'm too lazy to type "density" :P

probably the majority of "Lagrangians" I talk about are properly Lagrangian densities

it's usually clear from context

In QFT you have only Lagrangian densities, I would say

For Hamiltonians, you also care about the true one (the integral of the Hamiltonian density), but I don't think I have seen an instance of Lagrangians in QFT

And is the gordon identity another way of saying gordon decomposition?

Because to my understanding the decomposition can be used to express the matrix elements in form factors

But I don't understand how that would, eventually, in the end give me tensor form of the four vector

when the four vector is a vector quantity

so k vectors lying on the boundary of any brillouin zone satisfy the bragg diffraction condition, right

for elastic scattering

since you can draw a k' with equal length such that delta k ends up on a reciprocal lattice point G (which comes from the fact that the Brillouin zone boundaries are formed by planes bisecting the reciprocal lattice points)

@imbAF by "tensor structure" they just mean proving eq. (1), i.e. show that there are two independent terms with a $\mu$ index in there, i.e. the $q^\mu$ and the $\sigma_{\mu\nu}q^\nu$, and that it is only their coefficients $F_i(q)$ that are unknown.

@imbAF you could answer this question yourself by comparing the German and English Wikipedia articles on the topic :P

I was reading QFT from mandl shaw, trying to see if there was a more detailed explanation of this topic, but it wasn't mentioned. Which means, what was said in the lecture

was taken from another book

Do you know where I can read about the theory regarding this exercise, because I am thoroughly confused with this topic

As we made several claims without proof i.e that $\langle p'|j^\mu|p\rangle$ can be equal to an expression that contains some form factors, a majority of them proven to be zero. Then we proceed with gordon decomposition as a tool that help us show that several FFs are zero, without ofc explaining what the decomposition is

if you just search for something like "proton formfactor gordon" you can find many resources discussing various derivations of this; I don't have any favourites, but e.g. web2.ph.utexas.edu/~vadim/Classes/2019s-qft/FormFactors.pdf looks perhaps more like the level of detail you want

Thanks for the link

@imbAF You can probably find a derivation on Greiner QED too

Just never forget this: if a particle is so disrespectful it has a momentum-dependente vertex, it doesn't deserve your attention.

hi guysssss

i have a question!

so im learning about the stress tensor for the first time (a brief discussion in my solid state book) and i guess my first quesiton is, if the stress in the solid is non-uniform, you basically have a stress tensor at each point in the solid, right? where the stress tensor is acting on a infinitesimal volume element in the solid

and same for the strain

also, strain has to do with the geometry, while stress has to do with the forces, right?

@Allie What physicists call tensors, are really tensor fields. Even in the uniform case you have one at each point, just that it's the same tensor (thus uniform) :P

ok cool! i assume we mean field in the sense that each point in space is associated with a tensor?

@Allie Indeed

thanks :3

@SignorFeynman I don't know what this means

@ACuriousMind If I understand what you are saying, the exercise wants me to show the formula that it displays ?

yes?

It's such a confusing way of asking that. Or, maybe because this entire topic with form factors, gordon identities etc, comes as a total surprise to me,I don't understand what it wants me to do

it's the current $j^\mu = \bar\psi\gamma^\mu \psi$ where $\psi$ is a Dirac field

so, what we called vector current a while back

@imbAF A joke

I checked the book you mentioned, but I didn't find the derivation. You sure is in there?

@ACuriousMind In the link you provided, it says something about "on-shell" momenta of the proton. I know on and off shell masses. What are on and off shell momenta ?

@imbAF It's just momenta $p$ with $p^2 = m^2$, i.e. the on-shell mass.

\ok

@imbAF Greiner?

yes

Mhh, let me check. I haven't read that in a long time

(unlike @ACuriousMind I can't remember the sections after years :P)

@imbAF Rosenbluth’s Formula, exercise 3.5

Ok

Toast is not bread

@SignorFeynman ...okay?

I didn't know Italians cared about bread :P

hello

ciabatta, focaccia... are they not Brot? ;p

now I want bread D:

@ACuriousMind It was from a skit and this apparently triggered Germans :P

most Germans do seem to love toast, yeah

@ACuriousMind Oh, we do. In many parts of Italy bread is essential

I'm not its biggest fan but I don't eat a lot of bread in general

(The trigger was that according to Brits, toast is not bread)

This is one of Italy's most famous breads

@qwerty Oh, you seem to know some bread names. I know an English girl who's lived here for years and speaks Italian at a native level but she finds the name of the different types of bread to be extremely difficult :P

I myself do not know the names and I always point. I think I got the same shape of bread for a year because I remembered the name

slipper bread

I'm never sure about which one is a ciabatta :P

me neither :\

@SignorFeynman just those two really! hahaha it helps that it's labelled here. and it's true that here you can get very nice food from all over the world, it's quite normal to eat a different cuisine every meal. and we like to use the proper language names for foods unlike in the USA (eg they rename pasta shapes over there on packaging.) But I think focaccia was also popular on social media for a while, during the pandemic maybe

@qwerty yes, my Australian cousin told me all the time that many cuisines are popular in Australia

@SignorFeynman the true Mr Feynmate ;)

Ahahaha indeed