The h Bar - 2025-02-04

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naturallyInconsistent

03:04

@JohnRennie All books are bosonic in nature; evidence: piles of books are statistically likely to grow in number, just like how the presence of photons induces greater and greater probabilities of emission. It is definitely still an open problem to try and make a laser out of books, but few people doubt the possibility. i.e. engineering problem, not theoretical physics problem.

Allie

good timing

i just impulsively bought 3 cheap books :P

naturallyInconsistent

see~

Allie

i like getting exercises right

naturallyInconsistent

03:44

yay

DIRAC1930

04:01

Finding good profound books is difficult

Allie

look harder

DIRAC1930

I've looked

Allie

04:45

yay i got numerous problems right today

physics is cool

2 hours later…

Tobias Fünke

06:34

morning

qwerty

06:54

gluten tag 🍞

Tobias Fünke

07:31

haha

Slereah

07:58

web.archive.org/web/20210130052439/https://…

qwerty

08:19

oh dear

qwerty

08:31

did other people also hear about the zizian cult (an offshoot of the rationalist bros) recently?

Tobias Fünke

08:59

what the heck are "rationalist bros"

naturallyInconsistent

@TobiasFünke have you not heard about the New Atheists?

qwerty

@TobiasFünke they've been brought up a few times in the chat, mostly whenever we bring up Bayesian stats

qwerty

09:32

maxread.substack.com/p/the-zizians-and-the-rationalist-death

@naturallyInconsistent I didn't know they had roots in new atheism

naturallyInconsistent

@qwerty the irony wasnt lost on their critics. It was super frustrating seeing them turn to xtianity after Hitchens' death

qwerty

0.o this is the lesswrong and starslate codex crowd?

ACuriousMind

09:50

@naturallyInconsistent while there is a certain overlap in personnel, it's not really New Atheism that turned into rationalism/EA (arguably the phenomenon is more that both funnel(ed) significantly into neoreaction or alt-right) . If you want to spend probably more time than necessary on the history, see e. g. aiascendant.substack.com/p/extropias-children - the transhumanist/longtermist agenda is older and more obscure than NA

2

qwerty

@ACuriousMind I'm getting "page not found" :(

John Rennie

@qwerty This

There was a rogue n in the URL.

I've read Harry Potter and the Methods of Rationality and I enjoyed it. I hadn't realised it was linked to these sorts of views.

qwerty

10:09

my friend was telling me about effective altruism a few years back and I associated it with Peter Singer

did not realise it was a Rationalist movement thing

ACuriousMind

10:25

Rationalism and EA are not synonymous, but there's large enough overlap in practice you can't really cleanly separate them anymore

Tobias Fünke

10:36

sorry, recently I try not to spend time on social media or the internet for such topics. :d

so no, I've not heard of anything of that kind ^^

well, I know EA ^^

naturallyInconsistent

@JohnRennie miao miao even went to a local meetup when HPMoR finally ended. A guy I met there is now a girl. Needless to say, we were sooooo disappointed with how that crowd went.

John Rennie

I think the problem is that rationality is no use on its own. It always needs some assumptions, i.e. some ideology, to start from.

naturallyInconsistent

@ACuriousMind it is the whole "there is sufficient nazi vibes to start looking for the door" That's what I'm also worried about hbar as you're not moderating enough.

John Rennie

@naturallyInconsistent Really? The hbar has always struck me as a remarkably balanced place.

I find myself regularly humbled by the insight that our members show.

naturallyInconsistent

@JohnRennie there is no lack of physics insight. But we always need to be wary of the Lubos rabbithole.

Or Maimon, if you will

Signor Feynman

10:44

hello guys, I've just learned that mixing ham and jam is not a good idea just because they rhyme

naturallyInconsistent

@SignorFeynman you mean that it is a slimey rhyme?

John Rennie

@SignorFeynman Have you tried chilli jam?

naturallyInconsistent

chilli jam on chilled ham in the style of thanksgiving turkey with berry jam?

Signor Feynman

I've tried none. I just wanted to make a gag contributing with a no-brainer "insight" :P

John Rennie

Or bacon jam. That can be absolutely delicious if it's made well.

Signor Feynman

10:46

But apparently that's a thing D:

John Rennie

Well yes, I regularly eat both!

Chilli jam works well with anything that has been subject to a Maillard reaction.

Signor Feynman

Now that I think of it, it was not really a good example. Prosciutto is good with cantaloupe, so it makes sense that it could be good with jam

naturallyInconsistent

om nom nom

John Rennie

@SignorFeynman You underestimated how literally we would take your post :-)

qwerty

11:13

I have actually been sufficiently happy with ACM's moderation of hbar that I briefly wondered whether plato had a point with the whole philosopher-king thing ;)

Signor Feynman

@qwerty We've discussed something like that :P

Dec 28, 2024 at 19:07, by Slereah

@imbAF do you think if the politicians had PhDs they'd be less so

around here

qwerty

@SignorFeynman oh but ACM doesn't have a PhD :p

Ryder Rude

hi

Signor Feynman

@qwerty that was not the point

The discussion was more about having more academically educated politicians :P

Ryder Rude

@JohnRennie i am thinking that reasoning is not sufficient for navigate the world

Signor Feynman

11:24

You also need a good ship

And a good navigator, look what happened to Columbus

John Rennie

I think it is easy to underestimate how educated and intelligent a typical politician is. However they tend to be driven by an ideology that underpins any rational reasoning they do. Ideologies are fundamentally not rational.

qwerty

@SignorFeynman tbh I'm not sure that my train of thought had any criteria other than "is ACM" xD

Tobias Fünke

Hi RR

Signor Feynman

Power would eventually corrupt him and he would become a sith

Darth gauger

Ryder Rude

@JohnRennie i think one should be using a combination of intuition and reasoning and evidence.

qwerty

11:27

LMAO

Ryder Rude

maybe ideology is part of intuition

@TobiasFünke hi

reasoning need not capture intuition

so these r apriori separate resources

qwerty

@JohnRennie I keep hearing this word "ideology" these days and I don't actually know what the precise definition is

Signor Feynman

@JohnRennie That's why I made sure to write "academically educated"

Which would be the modern version of Plato's noocracy, I suppose

Tobias Fünke

@JohnRennie most if not all people are driven by some sort of "ideology"

Signor Feynman

My ideology is to fight condensed matter from the inside

from the BULK

Tobias Fünke

11:34

haha

if you cannot beat them, join them

come to the dark side

Signor Feynman

Indeed, it's like the Flood

Tobias Fünke

it is cozy inside the bulk!

Signor Feynman

Please, Tobias, tell me you know Halo

Tobias Fünke

nope, sorry :d (I mean I know it, but never played it seriously)

Signor Feynman

silence is a sharp blade

Oh, that was not silence :P

Tobias Fünke

11:36

hehe

qwerty

lol

Signor Feynman

Eh, I have had some issues with ghosting recently, so I freak out easily :P

qwerty

hugs

Tobias Fünke

:/

Signor Feynman

Thankies :)

I guess that's really the true plague of the 3rd millennium

ACuriousMind

12:07

@SignorFeynman People really did forget quickly about the 'rona, huh? :P

Signor Feynman

12:24

is that Corona? I would argue that it's too localize to be a millennium problem, on the other hand ghosting is a social mechanism that will plague humanity for a longer time

Ryder Rude

12:52

@MoreAnonymous i myself agree with putnam

More Anonymous

Doesn't EPR sort of destroy the argument though?

Ryder Rude

why is that

More Anonymous

Here's why I say so

Let's say I have 2 particles and they are entangled.

I separate them and have 2 experimentalists (A and B) measure them such that these events are spacelike.

This means there exists an observer who will say A is measured the particle spin up which caused the particle of B to be spin down. But it also means there exists an observer who will say B measured the particle spin down which caused A's particle to be spin up. This is because they events (both measurements) are spacelike there is no ordering of which event came "first."

Ryder Rude

i think entanglement is not a causality phenomenon. It is just correlations. so i disagree with the premise that anyone could say that one event caused the other

but also, we don't understand the right formalism of wavefunction collapse yet. u r assuming an objective collapse theory here

More Anonymous

@RyderRude Yes.. but when you do a measurement the wavefunction no longer evolves unitarily so you have to account for the change in the description

I think the point remains there is no global structure?

Ryder Rude

12:57

@MoreAnonymous yes, but in relative state theories (like QBism or Rovelli's relational interpretation or even MWI), the change in state is subjective and relative to the observer. so the third observer will not witness any wavefunction collapse according to these theories

also, one of two meanings of Copenhagen interpretation also says that collapse only happens in the mind of the observer

More Anonymous

@RyderRude Yea I never got that ... Like if all the observers meet up and exchange information ... what do they conclude?

Ryder Rude

the story they share does look like an objective collapse theory

suppose u r one of the observers. and u believe in QBism (say). then ur description of the measurement conducted by any of the other observers had resulted in that observer going into a superposition

but when u ask that observer, they would report not being in a superposition

however, there is no way to experimentally verify their story

assuming QBism is true

More Anonymous

I mean there are paradoxes one gets when you start putting the observer in superposition

Ryder Rude

i have come across some papers which describe problems with the idea

but those papers involved performing a measurement on another human's brain and modifying their memory

if memories get modified, then we do get inconsistent stories across observers

other than that, i don't think there r any problems with this idea yet

More Anonymous

I share the same contention as scott

scottaaronson.blog/?p=3975

“it makes (no) sense to chain together statements that involve superposed agents measuring each other’s brains in different incompatible bases, as if the statements still referred to a world where these measurements weren’t being done.”

Thats one of the paradoxes I was thinking of

Anyway gtg

Ryder Rude

13:10

@MoreAnonymous yes. Scott is criticising the paper by Frauchinger and Renner. This is the same paper I was referencing

note that Scott is not criticising the relative state idea. Scott is criticising the criticism of the relative state idea

Scott believes in MWI (which is epistemologically the same as a relative state theory)

i think the relative state idea has some conceptual problems ,but the objective collapse idea has much more concrete problems, as in, the dynamics of these theories are not known to be reconciliable with relativity

i believe we should keep both ideas on our radar as we try to solve the measurement problem. it is likely that neither is the full story

Putnam'a argument is made on the level of classical SR. within that context, i agree with him. within the QM context, i think spacetime probably doesn't exist in quantum gravity

Slereah

14:03

> As Bell wrote in [6]: ‘When the Queen dies in London (may it long be delayed) the Prince of Wales, lecturing on modern architecture in Australia, becomes instantaneously King’

2 hours later…

More Anonymous

16:03

@Slereah lol

ACuriousMind

16:17

@SignorFeynman I was making a joke about the literal meaning of "plague" :P

But more seriously, "ghosting" is not even in my top 10 things wrong with humanity currently; if it's in yours we live in very different worlds :P

@TobiasFünke the history of the word ideology is interesting, no one uses it in its original meaning anymore, it's either a pejorative term for "worldview I do not agree with", a somewhat neutral term for "worldview" or a specific term used by Marxists and/or continental philosophers who then smugly complain you have to read Lacan to understand what they mean :P

Tobias Fünke

16:42

Hi

thanks for the link, ACM. I will have a look :)

naturallyInconsistent

17:40

@ACuriousMind oh nice this is a great read, thanks. Starred

User198

17:53

Everything went downhill after the trial of Socrates... :/

"I believe that I'm one of a few Athenians—so as not to say I'm the only one, but the only one among our contemporaries—to take up the true political craft and practice the true politics. This is because the speeches I make on each occasion do not aim at gratification but at what's best." -Socrates

Questions:

1.) In mechanics (both quantum and classical) is it correct to say that the Path integral formulation is the "most fundamental one" and from that one all other formulations can be "derived" via. math manipulations and for CM we do the classical limit?

2.) Is the Path integral formulation connected somehow to the Moyal equation (Moyal bracket), that is the phase space formulation of QM?

naturallyInconsistent

(1) every formalism can derive all the other formalisms; they are equivalent, not more fundamental than any other. (2) yes

User198

@naturallyInconsistent So path integral formulation is on the same footing as say newtonian or lagrangian?

naturallyInconsistent

In classical, yes. But Newtonian framework was the first to die in the quantum revolution and will never be revived.

ACuriousMind

The question doesn't really make sense because there is no classical "path integral formulation"

naturallyInconsistent

You cannot compare path integral formalism, which is necessarily quantum, to a classical theory.

Why do you have to be seconds faster...

ACuriousMind

17:59

:)

User198

@ACuriousMind I didn't mean path formulation for classical , I meant for quantum. But you can get to classical in the classical limit from it.

ACuriousMind

@User198 why did you say "both quantum and classical" if you didn't mean classical :P

also "the classical limit" is far more subtle and less general than you might think

User198

@ACuriousMind I wanted to write: "The most "fundamental" way one can derive equations of motion."

You can derive EOM using newton, lagrange, schrodinger...

ACuriousMind

there is no general procedure to extract a classical limit from an arbitrary quantum system, more a bunch of heuristics that may or may not work

User198

Hm

ACuriousMind

18:02

@User198 No, this is a bizarre claim. The "e.o.m." of QM's Schrödinger picture is not the same e.o.m. as that of classical Newtonian mechanics at all

User198

It is not the same, but they are both EOM

Signor Feynman

@ACuriousMind my my, I am so slow

naturallyInconsistent

@SignorFeynman its ok, we thought you caught the joke

Signor Feynman

I hope I don't catch the joke, since in this case the joke is plague

ACuriousMind

@User198 sure, but since they are about completely different things I don't really know what the question is

Signor Feynman

18:04

@ACuriousMind beware, I consider ghosting that of people close to you, not that of a random SE user or someone else you've never talked to

Like a friend who ghosts you and cuts you off

ACuriousMind

if you need to do some basic classical mechanics like compute a cannonball's trajectory you use Newtonian mechanics, if you need to describe an electron passing through a double slit you use QM; you could not substitute one for the other in either direction (even though in principle you may believe the classical trajectory should emerge in some sense from the quantum description, no one does it that way)

naturallyInconsistent

@ACuriousMind technically, you can do the cannonball in QM; it is just not practical...

ACuriousMind

just edited that in ;)

@SignorFeynman I understood that :P

User198

Can you not use the Path integral formulation, and say , all the paths "cancel" instead the one for which the action is stationary, hence we get the canonball trajcetory.

@naturallyInconsistent that is what I am asking

naturallyInconsistent

@User198 not practical

User198

18:07

@ACuriousMind Ok ok. So you can conceptually (even if it would be not practical) derive classical EOM using path integral formulation.

@naturallyInconsistent ofc

But you can not do vice versa. Say start from some classical theory and derive the EOM for some quantum system.

@naturallyInconsistent That is what I meant by "more fundamental", but you said that they are all "equivalent".

naturallyInconsistent

@User198 that's on you

User198

@naturallyInconsistent You would say Newtonian mechancis is as fundamental as the Path integral formulation?

naturallyInconsistent

@User198 actually you can; it is just not necessarily correct

ACuriousMind

@User198 Careful: Saying that you can derive the classical physics from the quantum physics is a completely different claim from saying one of the formalisms of mechanics is more fundamental than the other (with the exception of Newtonian mechanics which has no quantum analogue)

DIRAC1930

I haven't read all the comments but an interesting point is that the Schrodinger equation is the EOM for the non-relativistic field operators

User198

18:10

@naturallyInconsistent ? I can say F=mv but it is not necesarrily correct. I don't understand your sentence?

naturallyInconsistent

@User198 there is no classical theory that is fundamental compared to quantum theories. That's the only relationship about fundamentality that you can draw; it is, however, not what I interpreted your vague question to be.

ACuriousMind

you can do quantum physics with the operator or the path integral formalism, and the latter both with the Lagrangian and the Hamiltonian version

you're simply throwing very different things in the same category here, there are at least three axes of distinction here: classical/quantum, Newtonian/Lagrangian/Hamiltonian, operator/path integral

naturallyInconsistent

hence why the wrongness is on you; you needed to first have enough clarity to state a question that can be correctly answered if you wanted a correct answer

ACuriousMind

with the exception of "quantum Newtonian" or (purely) "Lagrangian operator", arguably all other combinations of these describe some way of approaching (a subset of) physics

User198

Ok

naturallyInconsistent

18:13

@ACuriousMind I know you know this, but the reader might not: there is also a lot of nuances in how we organise the differences. It is not just Newtonian Lagrangian Hamiltonian, but also Maxwellian. And maybe symplectic. Phase space v.s. configuration space v.s. momentum space. So many things to consider.

User198

1.) So can we agree that Quantum mechanics is more fundamental than classical mechanics?

2.) In the QM, there are various formalisms, they are all equivalent?

I thinnk yes for both questions.

naturallyInconsistent

Yes. On top of that, in CM, there are also various formalisms, and they are, amusingly, not always equivalent, though for the bulk of it, you can prove the equivalence.

User198

@naturallyInconsistent How so? In CM I think that all formalisms are equivalent.

ACuriousMind

@User198 1, Yes, in the sense that classical mechanics is supposed to be a limit of quantum mechanics, not vice versa. 2. In ordinary QM, yes. In QFT, it's an open question since there is not even a rigorous formulation of path integrals in that case.

naturallyInconsistent

@User198 Try handling both linear and quadratic air drag in Hamiltonian formalism

Worse, Hamilton-Jacobi

ACuriousMind

18:18

@User198 It starts to depend on what you mean by "equivalent" already between only Lagrangian and Hamiltonian when the Legendre transformation is singular (i.e. naively not invertible). Everything is much more subtle than the short statements you want to reduce it to

User198

Okok. Thanks.

@naturallyInconsistent Is Hamilton-Jacobi actually used anywhere? Or is it just a nice example of a CM formalism "simmilar" to QM?

I know about Hamilton-Jacobi-Bellman (HJB) equation. But is HJ used anywhere in strictly CM anywhere?

naturallyInconsistent

you'll see this in a TONNE of places. For example, the maximally generalised Riemannian style integral can integrate stuff that the maximally generalised Lebesgue integral cannot, and vice versa, and their properties differ; only in the very restricted intersection do you have agreement. By having different formalisms, you are always getting more out than when you only take one viewpoint as the end-all and be-all

User198

@naturallyInconsistent Nicely put. I agree.

The Empty String Photographer

@naturallyInconsistent Never seen the British spelling in that figure of speech

DIRAC1930

@Slereah I remember on your bookshelf you had Schrodingers book Space-Time Structure. What were your thoughts on it?

Slereah

18:24

Haven't read much of it

naturallyInconsistent

@User198 It is another formalism that is equivalent to basic Hamiltonian formalism and treated as so too in many textbooks. It is also widely considered to the point of closest approach between classical and quantum mechanics. It is used. I dont know what your issue with it is.

DIRAC1930

I think it is a masterpiece

Short and sweet

User198

@naturallyInconsistent Do you have any concrete example of where it would be benefitial to use Hamilton-Jacobi equation, than say Hamiltonian mechanics or Lagrangian?

naturallyInconsistent

@TheEmptyStringPhotographer I'm the one writing it, I get to choose. It is fun

The HJE's action is the thing that path integration's semiclassical limit is supposed to get you. It is not about beneficial. It is about seeing connections.

But it also happens to be Goldstein's go-to way to find the most parsimonious way to deal with celestial mechanics. The maximally convenient variables are found by working on the HJE, and when you have perturbations, those variables become secular and automatically become the important slowly-varying parameters that must be treated properly

Like, you'll see all these things if you would just study from the standard textbooks. They are highly recommended textbooks for good reasons

User198

Ok thank you

Signor Feynman

18:42

@naturallyInconsistent I think I've never asked and I'm not sure you are willing to disclose it... I wonder what's your field/expertise. I only know it's somewhere in condensed matter

naturallyInconsistent

@SignorFeynman Ive talked about it a few times. I'm in nookooliar. Jumped ship from 2D materials

Signor Feynman

19:40

@naturallyInconsistent Oh, so you had a phase transition

Ryder Rude

@User198 i think this is not settled..

i asked this question a while ago physics.stackexchange.com/q/834627/156987 . it is not settled

but I do think QM is more fundamental cuz there r theories like the Dirac field theory where the classical field makes no sense. so it is all quantum

basically, classical fields make no sense for fermions

as in, those classical fields don't describe anything experimentally. their only job is to be quantised

but @bolbteppa believes that classical and quantum mech r equally fundamental

Tobias Fünke

20:19

-33

Q: AI-generated Answers experiment on Stack Exchange sites that volunteered to participate

Answer Assistant is an experiment in which AI-generated answers are verified, edited, and curated by the community before becoming publicly visible. We want to test if this feature could help improve the answer experience and encourage knowledge sharing by helping users get unstuck or get a jump-...

discussion featured announcements generative-ai answer-bot

qwerty

21:03

@TobiasFünke noooo

Tobias Fünke

... yeah

Signor Feynman

21:28

It's time for the hbar to declare independence

I always try to imagine what it would look like if it were a real bar

Tobias Fünke

hehe

Sine of the Time

@TobiasFünke violence is not the answer, it's the question and the answer is yes

Signor Feynman

21:48

@SineoftheTime we are Italian physics students the most violent? I've heard this from a physics fellow :P

Or... Probably I was the one to say it

qwerty

@SignorFeynman is ACM the bartender? he's carving up a quantum apple for someone's quantum apple martini whilst simultaneously gauging someone else's beer

Signor Feynman

@qwerty YES! Absolutely. The bar is one of those old west saloon, and it's dimly lit, in my imagination

The mod powers are actual superpowers. Something like the Force in Star Wars. ACM lifts his arm and throws people out

qwerty

hahaha

Signor Feynman

Now I'm wondering if ACM actually has mod powers in real life. Like, can he ban people from existence?

ACuriousMind

@TobiasFünke physics.SE has not volunteered to participate :P

Tobias Fünke

22:00

ACM, yes; fortunately

however, I am pessimistic about the general future of the network itself

...let's see

qwerty

all sites rise and fall. maybe not Wikipedia, hopefully.

Signor Feynman

@TobiasFünke at this point I don't know if we should even be. I'm only sorry for the serious contributors, but the network itself (I mean the top brass) will only get what is deserved

For making such choices

@qwerty and Slereah's blog ;)

Tobias Fünke

I am not sure if I understand you correctly.. I am sorry for all of us, who try to contribute to this site (and its original purpose)... But okay... Let's see

ACuriousMind

@TobiasFünke Actually it gives me a little bit of hope to see that we as a community at least overwhelmingly downvote and clown on these posts (this is in stark contrast to the ratios I experience e.g. at work on these topics :P). Remember the formatting assistant? Never saw that thing again!

Tobias Fünke

I just get reminded to better back up some threats lol

@ACuriousMind yeah, my impression is actually that the very most "featured" posts on meta are downvoted, especially those regarding AI stuff

I might be wrong...but that is what I remember from the last times checking those posts

ACuriousMind

22:12

there was once a time where the featured stuff would gain upvotes, but yes, those times are gone :P

Tobias Fünke

:d

Signor Feynman

@TobiasFünke I mean this maneuver (or anything of sorts) backfires, that's what they deserve for hypocritical coming up with these things and claiming to be "Committed to the Stack Exchange network being a place for human-curated knowledge". Nonetheless, I would be sorry for those users who have been contributing seriously so far

Tobias Fünke

yes

qwerty

22:25

it just occurred to me to wonder if Wikipedia has mechanisms to prevent AI generated edits

and if this is a problem for them

Signor Feynman

Next me is definitely Mr. fAInman

qwerty

=_=

DIRAC1930

I absolutely hate AI

It was impressive at first when they could show how it could fake certain videos

But now its just really annoying

Signor Feynman

AI can't even get gauge symmetry breaking right

Oh, wait :P

ACuriousMind

@qwerty best I can find is the AI cleanup project but I find it really hard to navigate Wikipedia's "meta" parts so I don't know if there's more

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