The h Bar

Silly Goose

02:43

@Relativisticcucumber it should be 0

Relativisticcucumber

yes i realize my error was elsewhere

Relativisticcucumber

03:33

@SillyGoose thank u

Tobias Fünke

06:43

@Relativisticcucumber in finite dimensions this is true indeed

in infinite-dimensional cases too, if everything is well-defined

ACuriousMind

07:26

@Relativisticcucumber this is the simplest argument for why representations of the canonical commutation relations have to be infinite-dimensional! See e. g. my answers physics.stackexchange.com/a/149792/50583 and physics.stackexchange.com/a/783327/50583

Slereah

08:06

Discovering trace-class operators

Ryder Rude

08:25

hi

Slereah

Think I found a neat version of the reduction of GR to SR in a smoll neighbourhood

The diffeomorphism group of an infinitesimally thickened point (that stabilizes the central point) is the jet group

To first order? That's the general linear group

you can just look for the subgroup that leaves the metric invariant

math.ru.nl/~landsman/scriptieTim.pdf

Fuck :V

Looks like I'm late to the party

Ryder Rude

08:41

i feel the bot here knows physics well chat.stackexchange.com/rooms/155368/thinking-out-loud

i asked it some technical questions

about AdS/CFT

naturallyInconsistent

@Relativisticcucumber Miao miao looked up the many definitions of the word "functionalist" and have no idea which it is that would apply in this situation.

@Relativisticcucumber a wave packet is usually not an eigenstate of the Hamiltonian. The eigenstates of the Hamiltonian are maximally delocalised (crystal-)momentum eigenstates

I mean, Mr. F gave a very good summary

@Relativisticcucumber delocalised Bloch waves are physical solutions, just like plane waves are! But if you want "hovering around a particular atom", you want Wannier functions.

@SillyGoose If you read the Landau levels wikipedia page, it references and links to the de Haas-van Alphen effect, the wikipedia page of which states how it can be used to image the Fermi surface. This is illustrated beautifully in Ashcroft & Mermin.

@TobiasFünke never actually understood Landau levels because the derivation required strong fields but we don't seem to actually work with that strong. Also, the whole degeneracies part are just left as exercise to the reader. But Ashcroft & Mermin at least plotted de Haas-van Alphen effect beautifully. Not sure how much is understood, but pretty pictures~~

Tobias Fünke

09:09

@naturallyInconsistent Well, the only thing I remember is what we've covered in a lecture some years ago :d... yesterday I checked my german version of Ziman, and some other famous german solid state book. The latter pointed to the work of Onsager regarding the Haas-van Alphen effect, where it seems he worked within the semi-classical framework

naturallyInconsistent

@Mr.Feynman I'd have chosen to say instead that it is not that the support is so important. It is rather that the ISW has beautifully simple results: equally spaced spectrum (and thus infinite) that is thus also extremely easy to work with, because the results are analytic. The reason why we do FSW right after that, is precisely to justify the use of ISW: we show that the non-analytical ugliness of FSW actually mostly give the same answers (for deep levels) near that of ISW, and only near the

highest, i.e. last few possible energy states, that the energy shifting is important. You can also estimate how many actual energy states there should be (as opposed to the ISW's infinitely many), and so that approximating the FSW with ISW is often justifiable.

Mr. Feynman

@naturallyInconsistent the context was that of an old question of mine

naturallyInconsistent

@TobiasFünke didn't almost everybody do basic solid state stuff using semi-classical? The initial theories are all hodge-podge ones.

@Mr.Feynman without a link or something, that is too much work to unearth

Mr. Feynman

No no, no need to. Basically Tobias commented and I was lazy to reply to a comment, so I replied here

naturallyInconsistent

omg main site shenanigans? naughty you

Ryder Rude

09:18

9

Q: "No local gauge invariant observables in gravity"... Is it a classical or quantum statement?

I have seen different explanations to understand why there are no local gauge invariant observables in gravity. Some of them explain that diffeomorphisms are a gauge symmetry of the theory and thus any observable evaluated at a spacetime point will be gauge dependent and therefore not an observab...

i think one needs to re-define observables in quantum gravity

Tobias Fünke

@naturallyInconsistent yeah

Ryder Rude

but, as the answer shows, this is also true in classical GR. Nothing specific to quantum gravity

if we visualise diffeomorphism invariance as a symmetry about co ordinate transformations, then it is a gauge symmetry and the observables must be diffeomorphism invariant

observables in any QFT are attached to the manifold itself. it has nothing to do with co ordinates. so i don't think any problem arises in GR

but in the quantum GR case, problems may arise as the causality condition cannot be written down

as the metric is dynamical

Tobias Fünke

10:00

general question: is the website with the friendly crow delivering papers down only for me?

naturallyInconsistent

@TobiasFünke the south east one is working

Tobias Fünke

thanks

Ryder Rude

3

A: Did John Wheeler retract himself on the participatory universe claims?

Not exactly. In late years, Wheeler did not go back on observer participancy, but was agonizing over reconciling it with shared reality for different observers. That led him to some doubts about the role of consciousness, but not over the informational underpinnings of the universe folded into "i...

Wheeler had this idea that the observer shapes the universe by the choice of what to measure. this is a participatory universe, in which observers play an active role

but this idea is extremely difficult to reconcile with science. Wheeler struggled a lot with it :The last entry Wheeler ever wrote was in 2006, age 95, nearing death, his life now bookended by questions. It consisted of a single sentence, left behind for the community: “Hope produces space and time?”"

Slereah

14:20

A lot of the nlab weirdness is really just due to them not specifying when they use the Yoneda lemma

They just think it is so natural

Relativisticcucumber

15:08

@naturallyInconsistent well in the subects of phil of mind functionalists believe mental states are characterized by what they do, not what they are made of/what physically constitutes them. so i extrapolated this notion to imply that the value i find in smth is based on what it does, not about the actual experience of engaging w that thing. perhaps a bit of a stretch idk

Slereah

15:27

> SAY MORE ABOUT HOW!!!
DEFINE “LAZY SURFACE”!!!

I like how so many physics papers have these

Just writing [REMEMBER TO DO THIS SECTION YOU LAZY PIECE OF SHIT]

naturallyInconsistent

16:26

@Relativisticcucumber still confused but ok?

ACuriousMind

17:42

@naturallyInconsistent they're saying the function of the book in teaching the subject well by being self-contained is more important to them than it's experiential quality of being nice to read

Relativisticcucumber

17:57

@ACuriousMind yes

also look acm its ur favorite:

SvNT

ACuriousMind

I do love me some SvN

Tobias Fünke

18:49

hello everybody

Silly Goose

19:25

hello

qwerty

morning

Michael

Afternoon

DanielSank

Why do people refer to relativity as "Einstein's relativity"?

Tobias Fünke

@DanielSank Well, isn't there also "Galilean relativity"

DanielSank

Not that I've heard of.

Tobias Fünke

19:31

Galilean invariance

Galilean invariance or Galilean relativity states that the laws of motion are the same in all inertial frames of reference. Galileo Galilei first described this principle in 1632 in his Dialogue Concerning the Two Chief World Systems using the example of a ship travelling at constant velocity, without rocking, on a smooth sea; any observer below the deck would not be able to tell whether the ship was moving or stationary. == Formulation == Specifically, the term Galilean invariance today usually refers to this principle as applied to Newtonian mechanics, that is, Newton's laws of motion hold in...

ACuriousMind

alternatively they might be taking a side in the relativity priority dispute :P

DanielSank

If I say "I'm studying relativity", don't you interpret that as the theory devised by Einstein?

@ACuriousMind The ":P" means this is not to be taken seriously, right?

ACuriousMind

I don't seriously think that's the case in most cases

DanielSank

mm

Tobias Fünke

@DanielSank I do, but that doesn't preclude that it makes sense to talk about "Galilean relativity", too

ACuriousMind

19:34

but they might be mirroring the phrasing of someone who was using that phrase to make clear they credit Einstein

but more realistically I think the most common reason will just be a not particularly mindful reference to authority - everyone knows Einstein was a genius, so calling it "Einstein's relativity" increases the perceived importance of the subject

Tobias Fünke

just found this article, but I've only read the abstract:

pubs.aip.org/aapt/ajp/article-abstract/88/3/207/148995/…

DanielSank

mmm, in protest I will start saying "Heisenberg's quantum mechanics" just to annoy people.

ACuriousMind

we love making history about individual people, it's a subconscious reflection of the Great Man theory of history in action

@DanielSank around 6000 google hits for that exact phrase, you're not the first

Tobias Fünke

sure not. it is a common phrase lol

...to distinguish it with Schrödinger's quantum mechanics, in a historic context

ACuriousMind

well, "Heisenberg's matrix mechanics" would be the more common way to say that, I think

Tobias Fünke

19:42

okay, I agree. And similarly Schrödinger's wave mechanics or so

qwerty

@ACuriousMind definitely this. and it also seems a little dated in fashion.

Tobias Fünke

the analogue to "Einstein's relativity" could be something like "von Neumann's quantum mechanics" (?)

ACuriousMind

@TobiasFünke probably not - the level of functional analysis at which von Neumann engaged with quantum mechanics is not how QM is done in practice :P

Tobias Fünke

@ACuriousMind Dirac's? :d

ACuriousMind

yeah, that's more fitting

qwerty

19:46

@ACuriousMind I would also say it's just name dropping to increase the perceived important of the author at times too

I was looking through Weber's book on gravitational waves and the number of [insert famous name] (personal communication) references was a little alarming

Tobias Fünke

If one wants to emphasize the difference to e.g. "Galilean's relativity" or if one wants to emphasizes Einstein's role in the development, then I don't think it is unusual or "inappropriate" to say "Einstein's relativity"...

qwerty

@TobiasFünke that's why I said "at times" :p

Sir Cumference

@DanielSank ey it's been a while

how's life

DanielSank

@ACuriousMind Yes. It's a thing I do not much like :-)

Hero worship never ends well.

Mr. Feynman

@Relativisticcucumber whenever he mentions SvN I feel so weak in QM :P

@ACuriousMind I mean, saying "Hilbert's relativity" would be like saying that a kind stranger who helped me on the streets is my dad :P

ACuriousMind

19:58

how do you know the kind stranger isn't your dad?

(I'm not really following the metaphor :P)

qwerty

ooo shots fired

Mr. Feynman

@ACuriousMind Incidentally, I find that if on the one hand many people do that, on the other hand you have many people apparently loathing this tendency to a fault, which I never understood

qwerty

also why did SvN get starred, is there some kind of joke?

ACuriousMind

@qwerty not that I'm aware of

Mr. Feynman

I mean, I think it is ok to glorify some individuals in science, as long as you understand that their words is not absolute

I don't like when people have to tell you every time that Einstein or Feynman or whoever else was "a person like us". I don't like thinking that all scientists are equal

qwerty

20:02

@Mr.Feynman well we've discussed a bit before: is is reflective of reality firstly, and secondly is it beneficial to the culture in science ( i mean students and academics as well as popular culture) to think that way

Mr. Feynman

@ACuriousMind I was trying to say that Hilbert did something important, but the fundamental idea of GR (as we know it today) is Einstein's (or at least not Hilbert's :P)

Tobias Fünke

omg roasted

ACuriousMind

@Mr.Feynman Well, see, in even saying this you're implicitly saying that it's somehow important to get right whose idea it was. I'm not saying this is wrong in all possible meanings, but the question is: Why do you think it's important?

Tobias Fünke

@Mr.Feynman All scientists are equal, but some are more equal than others.

Mr. Feynman

I think it is important, yes. Not for science, but for history of science.

ACuriousMind

20:05

And why is the apparently most unpopular answer to reject the notion that these kinds of inventions have to belong to a single person or a very small group of people?

Mr. Feynman

@TobiasFünke Yes, basically what I think about our farm :P

qwerty

@TobiasFünke oink

ACuriousMind

@Mr.Feynman Then you should oppose calling the Einstein-Hilbert action that, since that was mostly Hilbert's doing!

if it's Einstein's relativity, then it's Hilbert's action

now, I think that's a silly argument, but I think that people would add Einstein to the action but not Hilbert to the relativity hints strongly towards a less-than-purely-historical thing going on

Mr. Feynman

@ACuriousMind 100% agree

@ACuriousMind mhhh, no. I probably phrased it incorrectly. Of course that holds true in many cases. Most of the theories as we know them today come from the effort of multiple people. I was talking about the fact that many people seem to dislike when one single scientist is glorified (not talking about anyone here specifically, irl experience) and need to remind you that he was human or that he is not a god. Of course I know that :P

qwerty

@ACuriousMind it is "historical" - history is a narrative written by victors :p

ACuriousMind

20:09

I'm not buying that someone calling himself "Mr. Feynman" isn't talking about someone specific :P

Mr. Feynman

If you wonder why I mention that now it's because these same people also tend to find any possible caveat to give credit to someone else in order to downplay someone more famous :P

@ACuriousMind not specific here

I always get into fights about this with a friend of mine, okay? :P

qwerty

@Mr.Feynman i think there's a difference in downplaying contributions and not buying into fanboy/girl-ing culture, don't you?

Mr. Feynman

@ACuriousMind In fact I always wondered why it's the EH action and not the H action. I think that the most accurate representation is Einstein's relativity+Hilbert's action. Anything else is wrong

qwerty

honestly the history of science seems rather complicated and diving into it seems like a full-time academic pursuit

Mr. Feynman

@qwerty yes, that is correct and I admit that I have a strong fanboy tendency myself

ACuriousMind

20:12

@Mr.Feynman ::shocked Pikachu face::

4

Mr. Feynman

As you can guess from my parasocial behaviours :P

Damn, the chat is roasting me hard tonight

Tobias Fünke

yeah indeed

Mr. Feynman

Anyways, as I said I think that calling it just the "Hilbert action" and "Einstein's relativity" is the way to go. Now the question is: why do people call it EH action and refuse to say "Einstein-Hilbert's relativity"? Well, I think because the action is an important contribution but it's almost more of a tool, an alternate derivation of the EoM, which ontologically (?) wouldn't have the same importance as the whole theory.

In other words, putting Einstein's name in the action is in this sense more acceptable than putting Hilbert's name in relativity

Tobias Fünke

Stigler's law of eponymy

Stigler's law of eponymy, proposed by University of Chicago statistics professor Stephen Stigler in his 1980 publication "Stigler's law of eponymy", states that no scientific discovery is named after its original discoverer. Examples include Hubble's law, which was derived by Georges Lemaître two years before Edwin Hubble; the Pythagorean theorem, which was known to Babylonian mathematicians before Pythagoras; and Halley's Comet, which was observed by astronomers since at least 240 BC (although its official designation is due to the first ever mathematical prediction of such astronomical phenomenon...

Mr. Feynman

@ACuriousMind C'mon, don't tell me it's just the username :P

ACuriousMind

20:21

@qwerty I'm hesitant to use that phrase or to agree too much with its implication that history is a one-sided parade of propaganda. Think of all the atrocities of victors we do know about, and all the failings of great historical people - if they wrote that, they did a pretty bad job at hiding their faults!

(Remember, I grew up in a country where "history is written by the victors" is a phrase with a very different historical weight than in most other Western countries)

@Mr.Feynman not exclusively, but it's certainly not helping!

Mr. Feynman

Oh God, I thought I was hiding it well :P

ACuriousMind

@Mr.Feynman my brother in physics, you made the starred post about tattooing Qmechanic's favourite quasisymmetry on your body

4

Tobias Fünke

lmao

Mr. Feynman

And you snakes keep starring that!

It was a moment of weakness

Tobias Fünke

@Mr.Feynman Anything you say can and will be used against you (it seems)

qwerty

20:30

@ACuriousMind yes, you're right, of course. there is indeed nuance; but broadly I feel like the general message of being sceptical of what the historical narrative is (with the nuance you mention, and not just going into... history denial? is that the term?) is still defensible as "correct".

Mr. Feynman

@TobiasFünke Yeah, since qwerty joined the gang, I get more roasts :P

Which is funny because it's not the only online place where people like to roast me 💀

ACuriousMind

@qwerty Yes, skepticism is good - a blanket assumption that it's one-sided is not, I feel

qwerty

@Mr.Feynman I'm sorry mr F :P it's very much not targeted!

@ACuriousMind I suppose it depends on what level you're learning or studying history as well? if you get the cliffs-notes version (which I what I feel happens in physics when you get told "Einstein came up with relativity") I think that tends to be more one-sided as it's been simplified/reduced. If you're an actual historian, you know more details, more sources and "sides" to put it that way

ACuriousMind

yes, certainly

imbAF

Can anyone explain the relation between the solution to the klein gordan equation and harmonic or quantum harmonic oscillator? What does this mean for the particle?

Tobias Fünke

20:46

@imbAF sorry, can you be more specific? what exactly do you mean?

Mr. Feynman

@qwerty I have a thick skin :P

imbAF

In my lecture we started with the klein gordan eq. and we arrive at the following point:
$(\frac{\partial}{\partial^2} + \vec p^2 + m^2)\phi(t,\vec p)=0$
And this was said to be the harmonic oscillator equation or is related to it, no idea what the notation (harmonic oscillator ) in the notes is supposed to mean. Anyway, because in QM we dealt with the algebraic and analytical solution of the QHO, the equations there, those of motion (I assume) did not look like what we wrote in the lecture

So in conclusion I don't know the tie made between KG equation and qho or harmonic oscillator

@TobiasFünke

ACuriousMind

@imbAF See chapter 1.5 in Weigand's notes [pdf link] for a properly written explanation of the analogy.

imbAF

Mode expansion ?

ACuriousMind

yes, you have correctly read the title of chapter 1.5. :P

imbAF

20:54

I mean I am asking because I don;t read klein gordan

And I though I was at the wrong chapter

But ok

thank you

ACuriousMind

Do you not see that eq. (1.58) is the KG-Hamiltonian, i.e. what you are asking about?

Mr. Feynman

Very good notes, btw

imbAF

@ACuriousMind I see it. Thanks

I think that the notes are good, but I believe that their purpose is to remind someone who was already a good understanding of QFT, in other words, has read the books Weingard recommends, about a concept. Unless I am wrong and reading this would suffice. I am talking in general now, not particularly for the KG equation question that i posed earlier

ACuriousMind

@imbAF They are most definitely not, these are the notes of the course in which I learned QFT and I did not read any of the books while I was taking the course.

imbAF

@ACuriousMind Then that's awesome. I won't have to read 800 pages of schwarz during break time from uni

really thanks

ACuriousMind

21:06

I mean, that doesn't mean there aren't some things that some of the books explore in more depth or topics left out, but for an intro to hep-th QFT it is reasonably complete

Mr. Feynman

@imbAF you can trust ACM, as he took the course on which the notes are based :P

Iirc

ACuriousMind

@Mr.Feynman I literally just said that :P

Mr. Feynman

You know I don't read the chat (I was about to type "ah, he said that")

imbAF

Yeah of course. I also believe that what I am doing is into of QFT

and will be doing it until the end of semester

So the book will do

Mr. Feynman

@ACuriousMind actually there is more in those notes about Wilsonian renormalization than in many intro QFT books

DanielSank

21:54

@SirCumference It's pretty good. We are making a lot of progress in quantum computing.

I am slowly making progress on a "book" about engineered quantum systems.

imbAF

23:33

I have a question regarding atomic orbitals of two atoms

If one atom is at a certain position in the coordinate frame e.g origin, and the 2nd one is at distance R at some angle $\phi$ from the x axis. Would a rotation of the frame so that the new x' "contains" both atoms, change or simplify the calculations for a matrix element of the Hamiltonian?

In condensed matter theory

It was said that a change of the coordinate system does affect the calculations of a matrix element

How would that be the case?

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