In the Schrodinger picture, say if I have a 2nd quantized operator $\hat{O}=\sum_{ij}\langle i| \hat{o} |j \rangle \hat{a}^\dagger_i \hat{a}_j$ where $\hat{o}$ is a single particle operator, will the time dependence of the operator just be given by how the single particle states $|i>$ evolve?

I think this question shouldn't have been closed.

There's a Meta discussion to be had about where the boundary is between engineering questions and experimental-technique questions.

I'm not sure whether I'll have time to start that discussion on Meta in the next few days.

But perhaps if I grunt about it in here, someone else will be inspired to do the heavy lifting.

[grunt]

@ACuriousMind Well, does one situation show up more often than the other.

Also, can the time derivative be understood as an operator in QM? I am trying to understand how to derive equation (2.8) in this paper: michaelberryphysics.files.wordpress.com/2013/07/berry415.pdf.

I am trying to understand how to derive equation (2.8) by differentiating equation (2.1) w.r.t. time.

@rob When I first saw the question I read it as a question about experimental technique and thought it was a valid question. However on a more careful reread it's about quality control on a production line, and that seems like engineering to me.

@DIRAC1930 I don't really have the leisure right now to work to understand a paper just to answer questions about it, and this isn't really in my specialty anyways

@SillyGoose that depends on whether you work with cylinders a lot or not ;)

@SillyGoose the time derivative is not an operator on Hilbert space, if that's what you're asking, see physics.stackexchange.com/q/17477/50583, physics.stackexchange.com/a/199846/50583

you know, it's kind of weird that we have a backup of the kidney of all things

like why can't that be the case for something like the heart

I suspect it's an accidental side effect of bilateral symmetry.

i.e. kidneys evolved after bilateral symmetry so we got two of them.

@SirCumference we start out with two hearts, they just fuse

@DIRAC1930 in the Schrodinger picture operators are not time-dependent (unless they are explicitly so)

@ACuriousMind Gosh, that's disgusting :P

welcome to biology

Have you ever seen deformed fruit?

I don't know why but I can't stand it

Not talking about shape deformation but things like an orange that contains a little orange (well, it is not fruit but that's an example)

why would an orange not be a fruit?

but yes, I understand what you mean - I also feel some sort of primal revulsion at these oddities

@ACuriousMind In my language fruit and citrus fruit are considered different things

huh

Maybe scientifically speaking they are fruit just like a tomato is

ah, I see what's happening

@Feynman_00 Is your language not Italian?

Sì

I mean at least on a non-scientific level we distinguish fruit (frutta) and citrus fruit (agrumi)

your native language has some sort of subdivision of plant foods that is usually translated into English as "fruit" but doesn't actually mean "fruit" in the scientific sense

That is the main difference between jam and marmalade

yeah, German has that too where Obst is translated as "fruit" but not all fruit are Obst (e.g. most people wouldn't call a tomato Obst but it's definitely a fruit)

@ACuriousMind most people would not call a tomato a fruit in English either

hmmm

that's just the same word having different meaning in different context, and biologists wanting to impose their meaning

Same goes for eggplants

We tend to call fruit only sweet stuff

I mean, German does have two different words - the botanical meaning is Frucht, the colloquial one is Obst

It seems like the word fruit has manifold structure in German

I found the name of those repulsive oranges: navel oranges

btw I don't agree that "agrumi" are not considered fruit in Italian, it's a sub-category, but an orange would definitely count as fruit

they both get mapped to "fruit" in English and I guess I somehow assumed the "normal" English meaning would be the botanical one because its cognate to the German botanical word :P

That's a point but they surely occupy a special place if they are what makes "confettura" (jam) and "marmellata" (marmalade) two different things just for their composition

I hate when the maps between languages are not bijections

@Feynman_00 interestingly this distinction theoretically exists in German but most people will just call everything a Marmelade even if it's not made of citrus

The same things happens here

I found out there was a difference only after questioning why there were two different words meaning the same thing

well, but that tells you that most people probably don't think the distinction between citrus fruit and other fruit is relevant, no?

Yes, that's correct

languages don't work with any kind of logic :P

Oranges are referred to as "fruit" in the "Obst" German sense colloquially

by the modern pedantic definition, the original marmelade wouldn't be a marmelade because the word is for something made from quinces, which aren't citrus fruit

@ACuriousMind And they tell you Latin helps you understanding logic D:

If anything it's very useful with etymology and it's cool

no, it helps you understand a lot about Romance languages - but that doesn't make the stuff that happens any more reasonable :P

Did you study Latin by any chance?

yes

I didn't think you did that in Germany

my school had an "ancient languages" track: Everyone learned Latin, and people could also choose Ancient Greek and Hebrew

Think of it, in Italy most students dislike studying Latin :(

many schools offer Latin as an elective, but most people don't choose it (because it's usually offered as an alternative to another more immediately useful language like French)

(though, when I say "many schools" I only mean many of the upper track of the weirdly tri-forked school system we have)

@Feynman_00 that's no different here: most of my friends disliked studying Latin, too!

Subjects in Italian School are completely established by the type of school. I've seen people choose a "Liceo Scientifico" and hate Math and Latin lol

And you already know beforehand you'll be studying those subjects

tbf many of those who disliked it had that choice made by their parents, so I don't really blame them?

Well, that's a point too

Is Differential Geometry used in QFT (considering Lie Groups separately)?

(Introductory QFT)

typical introductions to QFT don't use differential geometry (even for gauge theories they sweep a lot of it under the rug), but surely there are also people/books teaching it with a more geometric approach

I understand, thanks

@Feynman_00 I did that, and I certainly hated every second of the Latin classes =)

but if you want the "scientific" track, it's not like you get to choose an alternative which doesn't include latin. Well, maybe now you do, idk. When I did it Latin was pretty much in any kind of liceo

@glS Yeah the point was about hating both Latin and Math

@ACuriousMind wow, never knew that

@fqq This is why I'm confused. In that paper the guy says that the time dependence is just given by $U n_U U^\dagger$ where all those operators are single particle space operators

It's in this paper arxiv.org/pdf/0804.1377.pdf in the 2nd paragraph above equation 6

Hello all users of this chat room The h Bar, I'm curious about the post with identifier 10759 on Physics Stack Exchange and title Possibility of "graviballs"?. If I refer well, gravitational geons are an hypothetical solution of general relativity (Einstein's equations).

I add as general reference that Wikipedia has the article Geon (physics). I would like to know if it is known how the search for these hypothetical objects could be (I ask as curiosity about a reference request or an idea of some user of this chat room). Many thanks.

...why would you give us the hard-to-use description "the post with identifier 10759 on Physics Stack Exchange and title Possibility of "graviballs"" rather than just a link to the post?

You are right, I don't like to add links @ACuriousMind But I add it since you're a moderator physics.stackexchange.com/questions/10759/… Many thanks for your help and attention. And I'm waiting your response if you know the theory about gravitational geons.

I'm afraid I don't know anything about geons

what's wrong with links? They're what makes hypertext superior to text!

It is sad that you don't know about geons. Yes your right, the next time I add a message in this chat, if necessary I add the link. No problem @ACuriousMind

@user250478 Why is it sad that they don't know about geons? Not every physicist studies theoretical particles.

I chose to read that as user250478 being sad I don't know about them because that means I can't talk to them about it :P

A tensor is something that transforms as a tensor

Looks like it has no effect :P

hm?

That was an attempt to get you triggered with my "definition"

I made peace with that definition years ago :P

it's my least favourite way of defining diff. geo. objects, but unfortunately it works

if you want to annoy me, start talking about how GR is "diffeomorphism-invariant" :P

I'm studying tensors right now, so it's time to know my enemies from the beginning :P

That was my next move but I know no GR and I don't know what that means

Talking about GR, my program has no differential geometry course, that's why I'm studying it. Next year I might suffer during the brief differential geometry introduction in the GR course

@ACuriousMind In terms of migrations, I've frequently seen diamond moderators initiate discussions in chat before making decisions. I thought it might have been good for MoreAnonymous to see whether or not the migration would be appropriate before flagging the question. Anyway, next time I won't ask the user to ping anyone if you prefer that!