The h Bar - 2019-07-21 (page 2 of 3)

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5:00 PM

@RyanUnger We would be pretty silly if we told them how we caught them, wouldn't we? ;P

2

@EmilioPisanty I mean to be fair, he isn't present-tense abusing the system right now, in that he hasn't posted a well-received answer in the last 3 years

For halloween I will make a post about spooky physics

Not sure if that's a good thing tho

ghost fields, phantom fields, skeleton diagrams, demons and jinns

2

Mithrandir24601

@RyanUnger Magic smoke and a sprinkling of unicorn dust ;)

5:01 PM

@RyanUnger They can

right so if I get banned now I can then create a new account when at grad school

and there's no way you could find out

or use a proxy

or use your phone

@SirCumference He's present-tense using the rep+badge results obtained in trivial classical-mechanics questions as cover on his present-tense posting of misinformation.

or just say that you live in the same block

@ACuriousMind It's pretty well known on SE meta how they do it, especially when explaining how users are sockpuppeting :P

danielunderwood

5:02 PM

I mean IP changes are pretty easy these days

@Slereah free vpns are definitely shady

what about expensive VPNs

those are, as you said, expensive

@SirCumference can you link

I thought you believed in capitalism

I do

doesn't mean I want to spend money on everything

5:04 PM

@RyanUnger well, if they successfully cover all their tracks and start posting good content with a new account, it's a bit like xkcd 810

@RyanUnger Someone throw this pinko out of America

danielunderwood

I'd bet some paid VPNs are pretty shady too. I'm sure a lot of companies would be happy to take your money in order to see your browsing habits

do you have xkcd memorized by number @Loong

@Slereah wot

if I don't need something that badly, I won't buy it

@RyanUnger I trained a neural net to do it.

number one rule of capitalism

5:05 PM

Spending money on everything is the American way

yeah everything costs money but that doesn't mean I spend my money on frivolous things

-60

Q: Just lost 210 reputation. My answers (7 upvotes and 8 upvotes) were removed

I just lost 210 reputation, and two of my answers yesterday were removed. They had 7 upvotes and 8 upvotes each. Could someone take a look at this? How can I get those answers re-posted? Thanks. Here's my account: https://stackoverflow.com/users/3808877/steve Here are the links to the deleted qu...

discussion support deleted-questions deleted-answers upvotes

@Steve Your "friend", who is asking academic questions from different languages, for which you just happened to have lengthy, well-formatted (props on that, at least) answers stolen from other people preloaded in the chamber. Listen, this isn't tumblr, we're not stupid. Come on, you'll do fine in the long run. Don't try to rush to the finish line. Jon Skeet has that wrapped up. — Will Jan 5 '15 at 19:30

@Loong I was just about to post that one

user image

For the record, looking through the most downvoted Meta SE/SO posts is pretty fun :)

E.g.

-252

Q: Shop system. Reputation points buyable for real currency

Make a shop system, in which we can buy reputation packs for real money. There should be daily limit on how much of reputation we can buy a day. There could be also other features to buy. Here are my proposals: Golden frame around questions and answers. Bigger font of our comments or ability to...

feature-request status-declined reputation

5:09 PM

how do you find the most downvoted

and

-54

Q: Why was I suspended from chat for a fairly harmless message?

I just posted this message with bold text on http://chat.stackoverflow.com/rooms/10/loungec . Immediately some one suspended me for half an hour. Here is my message MIRACLES HAPPENS WHEN YOU ACTUALLY HAVE A STRONG WILL Why did I get suspended for that?

@RyanUnger You sort by votes and go to the last page?

@RyanUnger Sort by votes

didn't know you could sort by votes

I don't use this website

@SirCumference They aren't all from SE/SO employees?

5:10 PM

-14

Q: Should we discourage "canonical" questions with "canonical" answers?

We've recently had John Rennie asking "canonical" questions which he's answered himself: What is time, does it flow, and if so what defines its direction? What is time dilation really? What is the proper way to explain the twin paradox? He says his answers are intended to be definitive and au...

Hm

Something by John Duffield

I'd better downvote it

haha

Even thoguh that is AGAINST THE RULES

@RyanUnger Have you not found this infamous question (mods please don't remove it)

-25

Q: If there is no gravity on the moon, why is the american flag waving?

If there is no gravity on the moon, how could this flag be flapping in the wind? (source)

What is it about physics that pushes people to go down rabbit holes ignoring stuff in first year textbooks

5:12 PM

"closed as unclear what you're asking"

It's very clear what he's asking

@SirCumference We do not delete questions merely for being low quality.

It's dumb but very clear

@bolbteppa Plenty of people vote and yet probably don't understand economics or whatever else

@ACuriousMind Well there was a question about werewolves on this site that got removed :P

I don't know at all what policies would be best for society

And yet

Something along the lines of a physical "theory" explaining them

5:13 PM

Bam!

@SirCumference It was deleted by the roomba since it was closed, negatively scored and had no upvoted answers

"unclear" is code for "you're stupid"

Just put a stupid option in the reason for closing

@ACuriousMind Yeah but it was pretty funny :P

I'm just saying that the moon question is in no danger of being deleted

5:14 PM

@SirCumference actually I have seen that question

Bad SE posts get me through mondays

when I clicked on it, it had an upvote from me

...

2011

wow

could have been from a long time ago

@ACuriousMind is that @ me

Yes.

5:16 PM

I don't see what's so shocking about that. It's an entertaining question

I am a moon landing theorist

> This happened on Apollo 11 and they liked the effect so much they replicated it on subsequent missions.

Very convenient.

The question is stupid but it generated interesting answers. Hence an upvote.

Is that so wrong?

yes

It is a line of thinking with which you are not alone but with which I disagree :P

I do think votes on the question should be disjoint from whether or not there are good answers

@ACuriousMind can you actually see my voting history explicitly

No

There are tools for moderators to detect voting patterns, but we cannot see individual votes on posts

Lucky you :P

I'm not ashamed of my voting patterns

I rarely vote anyway

5:26 PM

I only use my powers to downvote Duffield

Saying his name is a good way to get ACM angry

@Slereah Please stop saying that. Do we have to have the "let's not talk about chat-suspended users if we can't avoid it" spiel again?

→ 16 messages moved to Trash

uh-oh

@ACuriousMind hmm so are we allowed to discuss voldemort in the trash room

The trash room should be a gallery where you can't talk at all

did they ever bring back the sci fi chat

> you've got a photon going round and round

> light travels in a straight line so if it's going round and round, the space has to be curved

that sounds right to me

help

5:32 PM

You spin me right round, baby

danielunderwood

isn't there a name for orbiting photons?

@danielunderwood the photosphere?

@RyanUnger The main sci-fi chat is the restaurant at the end of the universe nowadays

@ACuriousMind what

I'm not a nerd, I don't get the reference

It's the name of the room, and it's a Douglas Adams reference

Mithrandir24601

5:34 PM

@RyanUnger You've never read Hitchhiker's Guide to the Galaxy?

danielunderwood

@Slereah yeah, that's right. I was thinking of kugelblitz...which isn't right

@Mithrandir24601 no, don't know what it's about either

Kugelblitz is a geon I think

Geons are annoying

I think there's no exact solution of a geon

Do people actually say kugelblitz in practice

In practice people don't really talk about geons

But usually they just say geon yeah

5:42 PM

@Mithrandir24601 His education is severely lacking in pop culture

Mithrandir24601

@ACuriousMind I wouldn't even call it 'pop culture', just 'modern culture'

what was Ryan even doing when he was a kid

Mithrandir24601

maths?

He wasn't doing math, that I know

Mithrandir24601

ah

5:43 PM

When I met him he didn't know how a logarithm worked

@Slereah playing battlefield

How utterly plebeian

Check out the speed and precision of young Japanese drummer, Senri Kawaguchi playing Ladies Talk. Yes, it's jazz fusion, but I don't think you need to be a jazz fan to appreciate her playing.

@Slereah what

@ACuriousMind what?

Pretty sure I understand post 2000 pop culture

He's calling us old

the cheek

Novalium Company

5:46 PM

Good evening humans

Anything before that is baffling to me. It’s strictly inferior to modern stuff

It runs purely on nostalgia

Apr 9 '16 at 20:27, by 0celo7

is $\ln x^y=y\ln x$ correct

Lol 2016

Sep 9 '15 at 14:05, by 0celo7

after 900 hours in battlefield and 1000 in CoD

Ok battlefield 3

Yeah I played that a lot

The CoD number is a guess

The crazy thing is that my aiming skills with a controller have atrophied an insane amount since then

It’s not like riding a bike

Novalium Company

5:50 PM

@RyanUnger I have 200+ hours

Aren’t you like 15

Novalium Company

:( 17

It’s an 8 year old game

Novalium Company

time passes

@RyanUnger I played it years ago

900 hours over 3 years isn’t really that much is it

5:53 PM

I would say it's not much, but then again I'm an avid gamer :P

@ACuriousMind did you see the Witcher trailer

@Slereah I recommend a serious first principles write-up of BRST for point/spinning particles and EM, YM, Bosonic and Fermionic strings instead

@bolbteppa I am planning to do it yeah

For the article on extended objects

Still not happy with it at all, e.g. why you'd even think of it from YM

I would like to find some source for constraint mechanics done from like

a math perspective

6:05 PM

Constraint mechanics?

I'm still not 100% sure everything is all proper in the sources I've seen

@RyanUnger Gauge stuff for hamiltonians

Henneaux Teitelboim...

The Henneaux book is probably the best bet

yeah I got that one

Also got the Dirac book

Those videos calmed me down about this stuff, feel like the main point was conveyed modulo minor 'details'

But BRST is an animal unto itself

Novalium Company

6:07 PM

I used to make minecraft servers when I was 12. I actually made some bucks from them.

I had like 40+ players. It was the minecraft bubble then

I think doing BRST quantization of the dumb non-relativistic Dirac particle will be a good exercize

Since its quantization should just be free particle

@NovaliumCompany I don't remember minecraft too well, except that figuring out how to set up servers was a legit nightmare

all that port fowarding bs

Novalium Company

6:22 PM

@SirCumference I was a pro at it :D I even programmed custom plugins for my server in Java

I also recall MC being the only thing Java was good for :P

2

Novalium Company

I mean, I never had much friends so I had to find a way to fill my time or I'll go crazy

@SirCumference yup :D

I think BRST might really just be the analogue of Gupta-Bleuler for non-abelian gauge theories at the end of the day and that's why you'd think of trying to find such a thing, though I don't see how going backwards from GB would lead you to such a crazy symmetry

@Qmechanic ditto with physics.stackexchange.com/questions/480574/… and physics.stackexchange.com/questions/473937/… =)

"However, the Gupta–Bleuler approach cannot be generalized to Yang–Mills non-Abelian gauge fields. The BRST method of quantization is a modern formulation of the Gupta–Bleuler approach that is equally valid for the Yang–Mills fields."

6:39 PM

@AaronStevens can I ask why there's a non-rendering ${}$ at the end of physics.stackexchange.com/a/452358/8563 ?

@EmilioPisanty 6 character edit limit

@EmilioPisanty I will wager it's a hack to get around the character limit for suggested edits (the last edit was a suggested edit)

@Loong ah, got it

Dammit, too slow in typing out a full sentence :P

I just caught this from a query and was confused

(link, for the curious)

6:43 PM

@SirCumference Not true. There's lots of mediocre software out there written in Java! :P

wuzz popin

i know i should not waste time but i came here with the intention to

You should waste time!

It's one of the great pleasures of life

get that hedonist out of my sight

@Slereah it all makes so much sense when you view it this way compared to the craziness regarding BRST brought up in here before (Feynman cancelling things at one loop etc)

@BalarkaSen You...can't actually see me

6:55 PM

That's a fair argument

Novalium Company

In partial derivatives, the variables we hold constant are basically turning into 0? And we simply differentiate the focused variable?

The variables we hold constant aren't turning into 0, they're just not changing. You change one variable at a time, and see the rate of change of the function when you do that.

No wonder the BRST charge for a relativistic point particle ends up being the KG equation applied to a state (i.e. the classical constraint $p^2 + m^2 = 0$ applied to a state)

For a two-variables function $f(x, y)$ think of what $f_x(a, b)$ (partial derivative of $f$ wrt variable $x$ at the point $(x, y) = (a, b)$) means in the graph of $z = f(x, y)$.

Novalium Company

brb sorry

6:59 PM

@BalarkaSen Hey, now you're teaching someone. That's not wasting time!

I'm tricking myself into believing I am doing something productive by teaching someone whereas I should be figuring some math out

That may be inherently not wasting time, but it falls in the general umbrella of procrastination

Just how big brains people procrastinate

Everyone in this room is familiar with this process ;)

I looked back at the transcript and one thing that hasn't changed here is @Slereah humor

They are :italianchefhand:

Novalium Company

In $x^+y^3$ with respect to x, y turn into 0 and doesn't stay a constant as you say

What is $x^+$

@bolbteppa Yes, the BRST charge is an "aggregation of constraints", that's why the physical states are in its cohomology (its kernel is the proto-states on which the constraints hold true, the image is the image of gauge transformations)

Novalium Company

@BalarkaSen I'm from phone

7:08 PM

"physical states are in its cohomology"

lol

@BalarkaSen a cation

Novalium Company

$x^2+y^3$

@NovaliumCompany The partial derivative at $(x, y) = (a, b)$ is $2a$. That's the rate of change of $x^2 + y^2$ if you moved $x$ slightly from $x = a$ and kept $y = b$ constant

Just because a "$y$ term" doesn't exist in the resulting thing doesn't mean it's going to vanish

I basically just need to figure out (or just see) how to work backwards from Maxwell to ending up with the BRST symmetry as natural now and then another BaRSTrier broken

Take $xy$. The partial derivative of that wrt $x$ at $(x, y) = (a, b)$ is $b$.

The "$y$ term" doesn't vanish.

Novalium Company

7:10 PM

Sorry I'm from phone and reading LaTex is nightmare. I'll read it/continue later when on my pc. Thanks @BalarkaSen anyways

@bolbteppa it's pronounced breast

@ACuriousMind alchemy in this game is impossible

you have to do things in a specific order with timing

what game?

kingdom come

What exactly is the BRST cohomology

7:12 PM

cracks knuckles

@BalarkaSen I've got you covered

All the math speak you could want in that one

Excellent, thanks!

I bet money you wont know what it is after reading that :p

then you dont know balarka

he loves awful things

'Poisson superalgebra'

7:14 PM

I like it so far; I have thought about Lie algebra cohomology a bit, so it's a good starting point.

"There's an ugly differential in our complex, spoiling the fun!"

what?

Oh, so Chevalley-Eilenberg cohomology with twisted coefficients is BRST?

You seem to say the differential is the BRST operator

@BalarkaSen Yes

hey, someone mind having a look? physics.stackexchange.com/questions/492881/…

Or, well, the bracket with the BRST operator is the differential

7:15 PM

I don't get it, how does the differential spoil the fun

Novalium Company

Guys, you are awesome.

hard to have a cohomology theory without that

Oh wow the second half is even more interesting.

This is a great answer, have a +1

@RyanUnger I wrote that almost 5 years ago, no idea what I was thinking with that phrase :P

I don't know the symplectic geometry enough. The moment map sounds like the function whose "$\mathfrak{g}$-valued Hamiltonian" is the representation $\rho : \mathfrak{g} \to T_{\text{id}} \text{Symp}(M)$ in the Poisson algebra.

That's what $d\mu_g = \omega(\rho(g), -)$ reads to me

7:22 PM

@BalarkaSen It is! And again, I've got an answer about that

Lmao here we go into the rabbithole

"The heart of the Gupta-Bleuler formalism is the observation that two states which differ by a state of zero norm can be mapped into one another by a gauge transformation; hence, one can define the physical theory by factoring the Hilbert space of states into equivalence classes, defining all states that differ by a gauge transformation as the same state."

seems reasonable

@ACuriousMind This makes a lot of sense. Isn't $0$ being a regular value of $\mu$ an issue, though? I think it's not the case in general?

Namely, how does one symplectically reduce in those pathological cases?

@BalarkaSen I think it will be the case in all physical applications! Although you are right that nothing I've said there shows that

7:32 PM

Yes, I suspect in physical scenarios it's not that important

The reason I think it will always be regular is that reducing a gauge theory is "the wrong way around" - it is the reduced space that is truly physical, and the extended space is just in our descriptions. If the reduction is impossible or does not yield the physical phase space, then we did something wrong in our description.

But I don't know if symplectic reduction is of independent interest to mathematicians

Reminds me I always wanted to read through Abraham/Marsden but never got around to it

There's some work by Sjamaar which deals with the issue by describing $\mu^{-1}(0)/G$ as a stratified symplectic space.

I think these are as follows: $X$ admits a filtration $X_0 \subset X_1 \subset \cdots \subset X_n \subset X$ such that $S_n = X_n \setminus X_{n-1}$ are smooth manifolds, and there is a sheaf $\mathscr{C}$ of subalgebras of continuous functions on $X$ which makes $(X, \mathscr{C})$ a locally ringed space and each of the restrictions $(S_k, \mathscr{C}|_{S_k})$ are isomorphic as locally ringed spaces to a symplectic manifold with it's sheaf of Poisson algebras.

I don't know how interesting this setup is to physicists, though

I do think that stratified spaces probably (should) underlie quite a bit of physics where we usually just talk about "singularities"

I have heard that term mostly used in context to geometric setups, where usually a physicist calls a singularity to be something where the metric is blowing up

Are topological singularities, in the ambient space itself, interesting to you all?

@BalarkaSen I'm not sure about "ambient space", but definitely not all singularities in physics are metric

7:42 PM

I see

@ACuriousMind I might have to read it someday

String theory tries a lot to talk about manifolds with different topologies "smoothly" morphing into one another - the singularity at the point where the topology changes is definitely not purely metric

Ah OK

By that description I'd generally think you're describing a smooth cobordism between smooth manifolds, but maybe you want to talk about a cobordism "fibering" over $[0, 1]$ and the various time-slices (these may not be manifolds, but mostly are)

So eg, the pair of pants projecting to $[0, 1]$ and at the $t = 1/2$ mark there's a wedge of circles.

Yes, that's one way to look at it

0

Q: Help to edit my question/answer/tags

Not being native English speaking, I ask with such friendliness to all users to be able to edit my answers or questions or tags because, apparently, the translation (https://www.deepl.com/translator) is not always perfect and the question or answer is not always clear in English. I hope very much...

support feature-request

@ACuriousMind Thanks a lot for that, by the way. I might get into symplectic geometry very soon, so I'll ask various things so that you can explain it to me (in physics if you want).

The two answers were very relevant to me

7:55 PM

Happy to help :)

I can't guarantee anything for symplectic geometry - I mostly know exactly the bits of it that were relevant to gauge theory and nothing more

@ACuriousMind hey

Yeah I realize; but I think your bits overlap with mine

if a body is glued to an accelerating frame of reference and then enters free fall, does it have an initial velocity by virtue of its having been moving in a uniformly accelerated way?

@BalarkaSen Not saying you can't ask me, just saying I might not have the answers ;P

(also it's been almost two years since I've done anything with this kind of physics/math)

@Luyw I don't know what it means to be "glued" to a frame of reference

A frame of reference is a mathematical abstraction, not a physical object. You can't be glued to a coordinate system.

moving with it

consider a body glued to the ceiling of an elevator whose ascending in an accelerated way

$a$ constant

8:03 PM

Okay. So what is the question?

if that body goes into free fall, would it have an initial velocity by virtue of its previous acceleration?

@ACuriousMind All the more reason to find a discussion along those lines refreshing :)

@Luyw A velocity relative to what?

1) the ground 2) the elevator

1) yes 2) no

@BalarkaSen Sure :)

8:10 PM

thank you, I agree about the ground, but why not the elevator? if the elevator's vertical coordinate w.r.t the ground is $y_e(t)$ and that of the body is $y_b(t)$, then the $y$ of the body w.r.t the elevator is $(y_b-y_e)(t)$ and since $y_b(t)$ includes an initial velocity, then surely the difference also will.

@EmilioPisanty Ah you found my secret.

@Luyw Yes, and for that distance w.r.t. the ground only the velocity w.r.t. the ground plays a role.

@EmilioPisanty Just kidding, I don't know why that is there. How did you happen across that?

The velocity of the object w.r.t the elevator doesn't play any role there

2 hours ago, by Emilio Pisanty

I just caught this from a query and was confused

why? it's included in $(y_b-y_e)(t)$

8:13 PM

2 hours ago, by ACuriousMind

@EmilioPisanty I will wager it's a hack to get around the character limit for suggested edits (the last edit was a suggested edit)

@Luyw The difference is that $y_b(t)$ does not include an acceleration after the body detaches from the elevator

gravity?

weak force?

but no, in my problem i am to take gravity into account*

Sorry, if we're not just naming fundamental forces you'll have to explain a bit more in detail what you're thinking about here

after the body detaches from the elevator, it's subject to gravity's pull

8:17 PM

It's also subject to gravity's pull before that!

If we take the time when the body detaches as $t_0$, then we have that $y_e(t) = (a-g)t^2$ and $y_b(t) = at_0^2 + at_0 t - gt^2$

That's all you need to know about the movement of the body

Damn I'm hungry and it's the middle of the night so there's no food

i have it as $y_b(t)=-1/2g(t-t_0)+(y_e)'(t_0)t+y_0$

Guess I'll chug water and smoke

@Luyw I forget the 1/2 and assumed $x_0 = 0$.

@BalarkaSen I approve of one of those things

$y_b(t)-y_e(y)=-1/2g(t-t_0)^2+(y_e)'(t_0)t+y_0-1/2(a-g)t^2$

what's wrong in here?

this is for $t\geq t_0$

8:26 PM

It's probably right, I didn't think properly

it's not actually, it's yielding me incorrect results

@ACuriousMind I naturally assume it's the latter.

can i link you to my question on phys stack exchange?

@BalarkaSen 'course, water is for wimps

@Luyw Nothing of this is actually necessary - just explain why you think the body should have an "initial velocity" w.r.t to the elevator

The very definition of "being attached" means moving at the same velocity

when it is detached i meant

8:29 PM

So at the moment between being attached and being not attached, the two bodies have to have the same velocity

Otherwise velocity wasn't continuous.

i mean, in the frame if reference of the elevator, when it does get detached, it should have an upward velocity

No

In the moment it gets detached, the body has exactly the same velocity as the elevator

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Jul '1921

The h Bar

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