The h Bar

12:53 AM

@bolbteppa that’s not quite right. You can turn on link sharing and allow anyone to view the file by sharing the “view only” link. To edit a file one needs an account, even through the link sharing. For someone (not the owner) to access the file through her or his directory (which implies an account), the file must be shared. It is a step back from Overleaf_v1, especially as one can only share the file with a single collaborator unless you have a pro account (not i expensive).

Sir Cumference

2:21 AM

What ever happened to 0celo?

Slereah

3:45 AM

man

That book has an article exactly on the topic I've been writing about

I should read more experimental books!

Sir Cumference

just realized i've been mispronouncing lie groups up till now

textbooks ought to have the pronunciation in the definition

Slereah

Did they...

lie to you

Sir Cumference

arrgh

Sir Cumference

7:53 AM

@ACuriousMind I mean that seems like a way to make math feel arbitrary and confusing

not that i claim more knowledge about the subject than von neumann

but that quote always seemed weird to me

Knight

9:05 AM

@JohnRennie In that video the narrator says that nobody knows where those dark theme came from in Waters’ mind. What are your speculations about the origin of dark thoughts in his mind?

John Rennie

@Knight I don't know Roger Waters so I can only guess.

I don't think he had a happy childhood, and I suspect he's a bit prone to feelings of angst.

And being in a famous rock band is enormously stressful. Lots of rock stars have had breakdowns under the pressure. In fact many have committed suicide.

Johan Liebert

-5

A: Cause of weightlessness

I AM Making a Good Salary from Home $6580-$7065/week , which is amazing, under a year ago I was jobless in a horrible economy. I thank God every day I was blessed with these instructions and now it's my duty to pay it forward and share it with Everyone. go to home media tech tab for more detail r...

Is this what we call spam? The first spam I have seen on this site.

John Rennie

Yes. Flag as spam if you have enough rep. If there enough spam flags it will automatically delete the post.

Knight

9:26 AM

@JohnRennie Wow my spam has deleted the answer, I never thought I hold so much of the power.

John Rennie

@Knight :-)

Knight

@JohnRennie Was his childhood something similar to Jake Lamotta?

John Rennie

One of the key ideas of the SE system is that as your rep increases you can start helping to moderate the site by doing things like flagging spam posts.

Knight

Yes. I think it would take me just one and only one millennium to get reputation equal to yours (the current reputation of yours) :)

John Rennie

:-) My reputation just builds by itself these days. I hardly answer questions any more because I'm busy all the time in the chat, but old answers keep attracting upvotes.

Knight

9:32 AM

have you ever thought of doing some philanthropy? I mean like donating some of your reputations to people like me?

John Rennie

:-)

I suppose I could start awarding random bounties to transfer rep.

Knight

HAHAHHA

I think you could write my name in your will of reputations of SE

Will

9 mins ago, by Knight

@JohnRennie Was his childhood something similar to Jake Lamotta?

@JohnRennie

John Rennie

I don't anything about Jake Lamotta's childhood.

Knight

He was born in a locality where killing, murdering and what not was a common thing. When he became 6 years old his father used to exhibit him in front of all locality by making to fight vigorously with other kids (bigger than him).

John Rennie

Waters came from a reasonably wealthy family so he didn't suffer from poverty. But his father was killed in the second world war so he grew up with no father.

He was sent to boarding school from a young age and I think he didn't like school.

And I'd guess, though I'm not sure, that he didn't get on with his mother.

So, completely unlike Jake Lamotta!

Knight

9:43 AM

So having such a good life (Waters was married also) what caused him such dark thoughts. Was he same as philosophers? You will find that most of the philosophers were wealthy therefore they never did any work.

John Rennie

Waters has been married and divorced multiple times. I suspect he's a hard person to live with :-)

Knight

It may be that his voice is so heavy and eardrums may need to be operated time to time for his partners.

John Rennie

No, I suspect he's just a hard person to live with.

Knight

You're always right, reality may be occasionally wrong.

John Rennie

:-)

I must make it clear I don't know Roger Waters. I have never met him (though I have seen him on stage) so I have no personal knowledge of what he's like.

But the other big name from Pink Floyd is David Gilmour, and in contrast to Waters David Gilmour seems a relaxed and likeable chap.

Knight

9:51 AM

If you ever get time then please just listen this song

John Rennie

@Knight yes, it's a nice song.

Knight

@JohnRennie What did you feel by the song?

John Rennie

@Knight it's a nice song. It isn't really my sort of music.

Knight

@JohnRennie Oh! Do you like screamo?

John Rennie

Screamo?

Knight

10:03 AM

Shouting

with full strength

John Rennie

I'm not sure how to best characterise the music I like. I like lots of different styles of music but I have a taste for music that is a bit weird. Some of the music I like is loud, but some is soft.

Knight

okay

John Rennie

For example I like Black Sabbath and I also like Tangerine Dream, and they are about as different as you can get.

Knight

I have to listen to them, I have never heard about them,

John Rennie

There are more bands than you could listen to in a lifetime, so I wouldn't worry about having to listen to everything other people mention.

Just listen to what you like.

Knight

10:09 AM

@JohnRennie But I hope that eventually you will like Poets of the Fall.

Knight

10:20 AM

@JohanLiebert Do you know @AbhasKumarSinha at any other site?

Johan Liebert

@Knight no I never asked him about that. Though it is possible that might have a fb account.

Knight

@JohanLiebert Would you please search for him?

Johan Liebert

@Knight OK! But I don't know how he looks like. So I would search for his city related info.

Knight

@JohanLiebert Which city is he in?

Johan Liebert

@Knight Bandhabahal

@Knight I searched though I wasn't able to pin point his account

Secret

11:07 AM

The mystical experience of the ghosting emotion:

whenever I detected an instance of (usually Facebook) ghosting, the following experience is felt:

1. There is a loud tinnitus that floods the background

2. Time stops in its track, visual field locked in the current zoom

3. Vision turned pitch blood red as an intense feeling of freefall more than 3 g is felt

4. The redness fades back to normal, along with the ceasing of the freefalling, with an aftertaste of intense dread, now felt extremely tangible black cubic soot, locked in a rocky cavern

John Doe

11:21 AM

@Mithrandir24601 Note sure if you recall my previous Big-O notation query. You stated the following: $$\partial_\theta\left(\mathcal O(\theta^2) + \mathcal O(\theta^3)\right) = \partial_\theta\mathcal O(\theta^2) + \partial_\theta\mathcal O(\theta^3) = \mathcal O(\theta) + \mathcal O(\theta^2)$$Am I correct in stating that the derivative of these big-O terms can only be proved to exist at $\theta = 0$, hence we assume the above holds only for small $\theta$?

Johan Liebert

-4

A: Cause of weightlessness

This question is answered really well by the answers above. Of course, as explained in all answers the statement quoted from your textbook is incorrect. The phenomenon of weightlessness could be explained in two different ways: The object orbiting the planet is in free fall (as described in oth...

John Rennie

@JohanLiebert the question has been protected now so that should stop any more spam answers.

Johan Liebert

@JohnRennie yes I looked at the edit history and it looks like the community user has protected it (due to the fact that two spams were deleted today?)

John Rennie

@JohanLiebert yes. I didn't realise there was a mechanism to automatically protect questions.

PM 2Ring

11:54 AM

@JohnRennie That feature is rather handy, especially on SO, where popular questions often attract a bunch of low quality or copycat answers (eg answers that duplicate code in existing answers, but with no explanatory text). In extreme cases we clean them up, but you can chew up a lot of delete votes rather quickly that way.

tpg2114

Feel free to flag questions for moderators to look at, if worried that they need protecting

The spam ones tend to get caught quickly and auto-protected, but drive-by VLQ answers tend to accumulate

PM 2Ring

My theory is that new answerers use such questions for practice, figuring that they can't do too much harm if they're wrong, and they might even score an upvote or two if they're lucky... or if they have school friends reading their posts...

Mithrandir24601

12:26 PM

@JohnDoe I mean, technically, $\mathcal O$ means that it's upper bounded in the limit of $\theta \rightarrow \infty$ (and yeah, I could and will below argue that they're abusing this notation in that paper, but practically, I think it's understandable), but that statement is still right $\forall \theta$. However, that equation given in the paper is only true for small theta

So, what they did in equation 25 is technically wrong (but understandably correct, if that makes sense?)

They gave that $$\langle S_m \rangle = 1-(\theta^2/2)\mathcal{Q}(G) + \mathcal{O}(\theta^3)$$

Yuvraj Singh...

Can anybody confirm that absolute state of rest in space is impossible.

That, s what Einstein has said to us!

Mithrandir24601

But they also gave that $$\langle S_M\rangle = \sum_{m=0}^\infty \frac{(i\theta)^m}{m!}\text{tr} \left(\left(\sum_{i=0}^n X_i\right)^m G\right)$$

So, unless all terms with $m>0$ cancel, saying that this is $= \mathcal O(\theta^3)$ is actually technically false

So, this only applies in the limit of small $\theta$

And using $\mathcal O$ is using this notation in a regime where it just doesn't apply

So the equations they give only apply in the limit of small $\theta$

@YuvrajSingh... I'd argue that the statement should be more along the lines of saying that 'absolute rest' as a concept is wrong. It's not 'possible' or 'impossible', rather the concept itself is just not a thing. I picking very fine hairs here though. Like, to say it's impossible to me is implying that it can be defined, whereas I'd argue that being at 'absolute rest' isn't something properly definable. Might just be my odd way of putting things though

John Doe

12:48 PM

@Mithrandir24601 You state " that statement is still right $\forall \theta$"...but how would you show that $\partial_{\theta}\mathcal{O}$ exists for all $\theta$?

It's really just an asymptotic upper bound statement, this is not enough to conclude differentiability for all $\theta$

Mithrandir24601

@JohnDoe Doesn't need to be differentiable $\forall\,\theta$ though, does it? it's just saying that it's differentiable $\forall\,\theta > \theta_0$ for some $\theta_0$

But what they appear to mean in this paper (this is physics remember!) is that $\mathcal O(\theta^m) = x\theta^m$ for some matrix (or number or something) $x$ that's independent of $\theta$ and this is why I'm saying that it's technically an abuse of notation

John Doe

@Mithrandir24601 Yes the abuse started with the approximation of the higher order Taylor series terms using the Big-O notation to begin with...but as you say it is physics...

dsm

1:48 PM

Does anybody understand the "Killing form"? I'm trying to show that the $(2,0)$ Killing tensor is invariant under the $\text{Ad}$ homomorphism: $K(\text{Ad}_A(X),\text{Ad}_A(Y))=K(X,Y),$ with $X,Y\in \mathfrak{g},\hspace{1mm}A\in G,$ and $K(X,Y)=-\text{Tr}(\text{ad}_X\text{ad}_Y)$. I currently have no idea how to interpret that trace.

Trying to peer into it, I'd write $\text{Tr}(\text{ad}_X\text{ad}_Y) = \text{Tr}([X,[Y,\cdot]]),$ which just heightens my feeling that this needs an argument to make any sense. How am I to interpret that trace??

@ACuriousMind

Knight

Find the magnetic field at point P on the axis of a tightly wound solenoid (helical coil) consisting of n turns per unit length wrapped around a cylindrical tube of radius $a$ and carrying current $I$ (Figure 25). Express your answer in terms of $\theta_1$ and $\theta_2$ (it's easiest that way). Consider the turns to be essentially circular, and use the result of example 6. What is the field on the axis of infinite solenoid (infinite in both directions) ?

My doubt is how $\theta_1$ gonna become 0 and $\theta_2$ $\pi$ as the length of solenoid gonna go to infinity. Please help me in seeing that.

Yuvraj Singh...

@Mithrandir24601 OK then how do we measure age then?

Mithrandir24601

@YuvrajSingh... Number of oscillations of a caesium-133 atom that you're stationary relative to

PM 2Ring

@YuvrajSingh... No, I'm not angry with you. And I wasn't angry with you yesterday either, as I said before. I was upset & disappointed with you, but I forgave you after you apologized, deleted the plagiarised material, and promised not to do it again.

Yuvraj Singh...

@Mithrandir24601 actually I do not know about that, I heard about it that we use wavelength of caseium,!

@PM2Ring ah, thanks sir, I was in stressed from yesterday! That I might angry you.

dsm

2:04 PM

@PM2Ring Do you understand the "Killing form"?

PM 2Ring

@YuvrajSingh... We use the frequency of a caesium oscillation, not the wavelength. I suppose we actually use the period of that oscillation as the basis for our definition of the second.

@dsm Not well enough to answer your question properly.

dsm

Alright no worries. I have no clue how to interpret what is meant by that trace...

Yuvraj Singh...

@PM2Ring make me correct that mean excitation of electron from ground to higher orbit is that what it mean?

Semiclassical

@Knight it becomes infinite in both directions, not just one. Hence the ends are infinitely forward from the origin (theta = 0) and infinitely backwards (theta = pi)

PM 2Ring

There's a nice description here that gives the main details without getting too technical: NIST-F1 Cesium Fountain Atomic Clock

Semiclassical

2:09 PM

If you make it infinite in only one direction, then you’re at one end of an infinite solenoid rather than at the center of one

Yuvraj Singh...

@PM2Ring it is not opening sir!

Semiclassical

It opens for me just fine, for reference

Yuvraj Singh...

One more question it is quite basic one what make ice to change it s phase, is it heat or is it the temperature difference. Question can be little bit stupid when one can say heat depend upon temperature difference but still if we look at the graph of ice Vs temperature graph is initially straight and then become parallel to axis then again go straight.

JMac

@YuvrajSingh... Well heat is what actually drives it to change phase. That's what the latent heat of fusion measures. The temperature determines when the added heat goes into changing phases instead of changing temperature, but it's the actual heat that melts it.

PM 2Ring

@YuvrajSingh... The caesium clock uses transitions between the two hyperfine ground states of caesium-133 atoms. It's a bit hard to explain exactly what that means, but roughly speaking, instead of there being a single ground state for the valence electron of caesium there are 2 states caused by the interaction between the electron's magnetic dipole & the electric field created by the nucleus & the other electrons. See en.wikipedia.org/wiki/Hyperfine_structure

Semiclassical

2:21 PM

Having said the above, I’m having a hard time getting the trig to work out properly

Yuvraj Singh...

@j Mac @PM2Ring Thanks.

PM 2Ring

@YuvrajSingh... That's a shame. It's a USA government site, I don't think it would be blocked in India. Wikipedia has an article, but it's not as good, and it doesn't have the nice diagrams that the NIST site has. en.wikipedia.org/wiki/Atomic_fountain

Knight

@Semiclassical Sir if you don’t mind much can you please make a sketch of it?

Semiclassical

Can’t. I’m on mobile

Knight

Okay. Let’s say that distance from forward center to point P is $d$.

Jake Rose

2:25 PM

@Semiclassical what was that book you recommended for me again? Can’t find it in the transcript :p

Semiclassical

I’ll suggest $z$ instead, to avoid conflating with differential d

@JakeRose shankar

Jake Rose

Gracias

Knight

Okay. Let’s call it $z$

Semiclassical

It’s a standard grad QM book. Big thick and red

Seemingly we should have $\tan \theta=a/z$

Knight

$\sin \theta_1 = \frac{a}{a^2 + z^2}$

Semiclassical

2:27 PM

But that goes haywire for small $z$

PM 2Ring

@YuvrajSingh... I remember "discovering" this when I was a child, playing with icecream in a cardboard cup. I discovered that if I quickly stirred the icecream it would start to melt but it also made the cup feel much colder: it was pulling heat out of my hand so it could do the phase transition.

Knight

@Semiclassical Means?

$\tan \theta_2 = a/l $

l is the length of the solenoid.

Semiclassical

no. $\tan(\theta_2)=a/(l/2)$

Yuvraj Singh...

@PM2Ring then how you find the reason?

Semiclassical

We want it to be infinite in both directions, so half is in front of the origin and half is behind

So $\tan(\theta_1)=a/(-l/2)$

Knight

2:31 PM

But I think $\theta_2$ is the angle that the farther end makes with the point P, ?

Semiclassical

Yes, but the front end is $+l/2$ away from the origin and the back end of $-l/2$ away

Otherwise you’d be stretching it in one direction, not both

Jake Rose

@Semiclassical any particular sections? Just got it from the mathematical library so all is good

PM 2Ring

@YuvrajSingh... Well, I didn't understand it when I was 9 years old, but it made sense a few years later when I learned about latent heat.

Semiclassical

Don’t remember off the top of my head

It’s a big book tho

Knight

Sir, I thought that I should calculate for the normal case and then take the limit as $l \to ~ \infty$

Semiclassical

2:34 PM

So probably look up the sections on spin 1/2

Yes, and that’s what I’m doing.

Knight

But I didn’t get when you wrote $l/2$ in the present case of the picture

Semiclassical

The normal case has both ends equidistant from the origin. For it to have length $l$, that means one end is at $z=+l/2$ and the other is at $z=-l/2$.

Yuvraj Singh...

@PM2Ring it feel especial to learn something new at early age, I M not sure about how Australian schools are. But Indian school they teach with no logic just mug up all the thing irrespective what actually they mean I must say our high school teacher pattern is pathetic.

Semiclassical

If you take $z=l$ and $z=0$ as the ends of your solenoid, then your observation point is at one end of the solenoid. That’s an interesting problem in itself, but it isn’t what the question is asking

Knight

@Semiclassical Yes I agree. But we agreed to call the distance from the center of forward end to P as $z$?

PM 2Ring

2:38 PM

The reverse process is responsible for generating heat inside the Earth. The inner core of the Earth is solid, mostly iron. It's surrounded by the liquid outer core. As liquid iron crystallises onto the inner core latent heat is released, which heats up the outer core and slows down the crystallisation process.

Semiclassical

Ah. I’ve been using $z$ as the coordinate along the axis, not as a particular position

Yuvraj Singh...

@PM2Ring wow. Does this hest have significant effect!

Knight

@Semiclassical My mistake was that I was considering this a real problem.

Semiclassical

What?

JMac

@YuvrajSingh... Bad teachers seem pretty universal. I had some great teachers and some terrible ones in high school. An anecdote I like to share is about my grade 11 "advanced" math teacher. The teacher didn't even understand rounding. We were expected to round 0.45 up to 1 because 0.45 rounds up to 0.5 and that rounds up to 1... Bad teachers exist everywhere.

Knight

2:41 PM

@Semiclassical What question is saying ? I understood it that one end is at $z=0$ and the other at $z=l$

Semiclassical

. The question tells you to take the solenoid to be infinite in both directions

PM 2Ring

@YuvrajSingh... I don't know what it's like in Australian high schools these days, I went to school several decades ago. Back then, we did have to memorize some facts, but there was always a strong emphasis on understanding the principles and logic. In exams, you might lose a mark or 2 if you got the memorized facts wrong, but if you demonstrated that you understood the principles then you'd generally get good marks.

Semiclassical

That means the origin is at the middle, with one end in the positive direction and the other in the negative direction

Yuvraj Singh...

@j Mac yes that, s problem I recently passed high school and I have gone through this experiences.

Knight

@Semiclassical okay.

Semiclassical

2:43 PM

“ What is the field on the axis of infinite solenoid (infinite in both directions) ?”

For specificity

Yuvraj Singh...

@PM2Ring that, s very much good.

JMac

@PM2Ring To add on to this, and what I was saying about some teachers being bad, my experience was quite a mixed bag. I had several teachers (thankfully precalc/calc and science teachers mostly) who put heavy emphasis on understanding the concepts and applying that understanding. I had other teachers who heavily emphasized just knowing the procedure and applying it blindly. It all depended on the teacher, not the system in general.

PM 2Ring

@YuvrajSingh... Definitely! IIRC, it's more important than the heat released by the radioactive decay of uranium, thorium, and potassium (which are the main sources of radioactive heat inside the Earth). David Hammen has written some great answers that mention this.

Knight

All right. So, how $\tan \theta_2 = \frac{a}{l/2} $ please explain

From my thinking $\tan \theta_2 = \frac{a}{l+z}$

@Semiclassical Are you here?

Novalium Company

How to capture my ideas and thoughts at the moment?

Like, let's say I'm outside and I think of something brilliant or just a thought/idea I want to have in a database. How do I do that?

I don't have the time to stop and type on my little phone.

PM 2Ring

2:52 PM

@JMac Understood. I was lucky to have some pretty good maths & science teachers. But I'm pretty sure that the syllabus in my state had a strong emphasis on teaching concepts and not just rote memorization of facts. For a couple of years, my science teacher was actually one of the co-authors of our science textbook, which was pretty cool. He was the principal author of the astronomy & chemistry sections.

@NovaliumCompany Doesn't your phone let you record audio?

Semiclassical

I’ve given my reasoning already. One end of the solenoid is $+l/2$ from the origin, so $\tan\theta_2=a/(+l/2)$

Yuvraj Singh...

@PM2Ring have you done a science project during school days?

JMac

@NovaliumCompany Carry around something to take notes on. I was watching an interview with a writer last night where he talked about that exact problem. Sometimes it's hard or impossible to actually leave a note at the time. I don't know if there's a good solution besides just thinking of some way to record ideas. Taking notes with Siri (or whatever android has) is one possible workaround.

Semiclassical

The endpoints can’t be functions of $z$ if $z$ is to denote the coordinate along the axis

Yuvraj Singh...

@PM2Ring on what topic it was

Knight

3:01 PM

@Semiclassical Please elaborate.

Yuvraj Singh...

@JohnRennie rennie sir, what was your experience. Of high school teaching.!

Semiclassical

I’ve elaborated multiple times. If what I’ve said so far isn’t enough, then I don’t see how further repetition is going to help

Knight

Okay.

Yuvraj Singh...

@JohnRennie how is UK high school teaching.?

John Rennie

@YuvrajSingh... you mean what was the teaching like when I was at school? If so, I was lucky because the teachers at the school I went to were very good.

Knight

3:03 PM

@JohnRennie Sir please help

1 hour ago, by Knight

Find the magnetic field at point P on the axis of a tightly wound solenoid (helical coil) consisting of n turns per unit length wrapped around a cylindrical tube of radius $a$ and carrying current $I$ (Figure 25). Express your answer in terms of $\theta_1$ and $\theta_2$ (it's easiest that way). Consider the turns to be essentially circular, and use the result of example 6. What is the field on the axis of infinite solenoid (infinite in both directions) ?

Yuvraj Singh...

@JohnRennie very good! On what basis?

Knight

1 hour ago, by Knight

John Rennie

@YuvrajSingh... they knew their subject well, and they were good at encouraging the pupils.

Knight

1 hour ago, by Knight

My doubt is how $\theta_1$ gonna become 0 and $\theta_2$ $\pi$ as the length of solenoid gonna go to infinity. Please help me in seeing that.

PM 2Ring

@YuvrajSingh... Not really. But I did science stuff at home. I started playing around with electronics when I was around 9 or 10. A year or so later I had a small chemistry lab in the basement. At school, in the science labs, we had access to much more dangerous chemicals than they let kids handle these days.

I was on good terms with the science master, and had permission to use the chemistry lab for my own experiments during the lunch hour, as long as I didn't do anything stupid. I was mostly sensible, but I did get banned for a week one time for making a large "volcano" with ammonium dichromate, which was rather messy :)

John Rennie

3:06 PM

@Knight the field on the axis of an infinite solenoid is the usual $B = \mu_0 n I$, where $n$ is the number of turns per unit lenth.

Novalium Company

I'm too lazy to search for my phone or take it out of my pocket to record my idea/thought. Not only that, but I need it as text, so I can read it out later easily. (and not listen to my jibberish)

Knight

Yes. My doubt is how $\theta_2$ gonna become $\pi$ as length goes to infinity

Yuvraj Singh...

@JohnRennie wow your teacher allowed you to use lab as if you want, when I was in high school we are not allowed to enter in lab without teacher permission.

@JohnRennie what kind of dangerous material are you referring for.

Novalium Company

I think I have a solution for my problem. BOOM business idea.

Yuvraj Singh...

@PM2Ring I haven, t ask you what kind of course you had done during University days.

PM 2Ring

3:14 PM

@YuvrajSingh... I started doing science & computer stuff, but I didn't last very long, for various reasons (which I don't wish to discuss). I dropped out in less than 6 months. :(

Yuvraj Singh...

@PM2Ring oh!

Novalium Company

nvm my idea sucks

apparently amazon echo loop exists

they've integrated f*cking Alexa into a ring...

you literally have the whole internet and many apps on your finger

you can record, take notes, take calls, google...

Slereah

3:50 PM

9

Johan Liebert

4:19 PM

Please describe what kind of mice you want to catch otherwise your question would be closed.

PM 2Ring

4:34 PM

Yes, it's ~~too broad~~ needs more focus. Or primarily opinion based.

PM 2Ring

5:23 PM

The new CEO has just made his first post on the network:

34

Q: A Note To Meta on my 2020 Kickoff Blog Post

Hello members of the Meta community - I wanted to share the blog post I wrote to kick off 2020 and reflect on my first 90 days at the company. It’s intended for a wide audience, the tens of millions of people we serve, but also because I know you all want to hear directly from me. My style is to ...

Loong

I am not going to read all that stuff in that blog post.

It's only about Stack Overflow anyway.

Sir Cumference

do users who haven't been here in months still get pinged if you reply to their messages?

Slereah

No, at some point this doesn't work anymore

Sir Cumference

aw man

Knight

5:49 PM

@JohanLiebert If possible make a Facebook account with name Johan Liebert Stackexchange and send a friend request it to all Abhas Kumar Sinha in the list (with the name of the city which you told me). We should bring him back.

I can do it but there are more chances of you to find him because you are his paisano

Johan Liebert

@Knight actually today i talked to him a bit.

@Knight we are friends now on fb

Knight

@JohanLiebert Wow! What happened then?

Johan Liebert

@Knight he came here for some time in general chat and shared his fb profile (which is there till now).

Knight

@JohanLiebert Please give me the link here. Why he is not coming to the h bar?

Johan Liebert

@Knight you know all that( what happened yesterday ). There is no point in repeating it.

Sir Cumference

5:59 PM

2 days ago, by ACuriousMind

@AbhasKumarSinha You may come back tomorrow, provided you can abstain from advocating Nazi ideology then.

Slereah

I guess he couldn't stop advocating for nazi ideology

Knight

Actually he was unaware of what he actually did and so he got punished for that.

Sir Cumference

well he'll come back if he wants to

Knight

But he shouldn’t leave like this, I cannot understand what hurts him?

Sir Cumference

not sure how you can be unaware of advocating Nazi ideology

that's a pretty extreme ideology

Slereah

6:03 PM

Or wanting someone who advocates nazi ideology to come back

JMac

@Knight He made a very poor reference to Nazi ideology. I don't think it was actually trying to promote it (IIRC it was a bad joke); but it wasn't the right thing to say at the time. I think he might be overreacting to the ban too though. From my understanding, it was a slap on the risk to get him to think about saying things like that; but he seems to have taken it more seriously.

Semiclassical

If they’re willing and able to come back, they will

Johan Liebert

@Slereah @SirCumference he wasn't spreading any ideology. He just made a sarcastic comment on it (and intended it to be a joke and nothing serious).

Knight

@JMac @Slereah @SirCumference I have read his chat in the other room and the main problem with him is that he still doesn’t know what was his mistake, that’s immensely terrible but if you take his age into consideration you will find that he didn’t mean what his words meant.

@JohanLiebert Just send this chat transcript to him on Facebook and I’m sure he will come back for giving clarifications (I know him)

Johan Liebert

in General chat, 5 hours ago, by Abhas Kumar Sinha

@tpg2114 thanks sir, I agree to the point that the joke was tasteless and terrible.

Knight

6:09 PM

He just said it for formality

He should come back here and learn from a real German I.e. ACM about what actually went wrong with his reference of that book to me.

@JohanLiebert

JMac

@Knight I think that might be part of the problem. He "didn't know what his words meant"; but he said them, and they had pretty significant meaning.

Johan Liebert

@Knight I don't think he will come back. And by the way its his decision why should I interfere?

Sir Cumference

i think it's a little early to tell

it's only been a day or two

Knight

Yes it’s early but I should convince him to come back before eeveything fades away

@JMac So what you propose?

Sir Cumference

give him a day or two to cool off?

Johan Liebert

6:15 PM

@Knight why do you think there is a necessity for him to come back? I mean he can always make a new account if he wants to ask a question.

Knight

Okay.

@JohanLiebert I’m not feeling good without him.

JMac

@Knight What the heck am I supposed to propose here? He said something he shouldn't have, got a 1 day time-out, and then decided to not come back. I propose that if that's what he decided, it's his choice to make.

Knight

@JMac I solemnly reject your proposal

JMac

@Knight You reject that it's his own choice to make...?

Johan Liebert

@Knight try to accustom yourself to this. You should nor try to force people against their will.

Knight

6:20 PM

@JMac “ I propose that if that’s what he decided, it’s his choice to make” I reject this proposal of yours

JMac

@Knight On what grounds?

Knight

@JMac In all human sorrows nothing gives comfort but love and faith.

On this ground

Aaron Stevens

@Knight So you think it is not his choice, so we should force him back into the chat?

JMac

@Knight How is that a reason to reject my proposal? As far as I can tell, it's a non sequitur.

Knight

@JMac That’s a very nice reason for rejecting your proposal. You can see it clearly.

Aha! ACM is here.

Aaron Stevens

6:27 PM

So anyway, anyone learn anything cool recently?

Johan Liebert

@Knight I don't this is good to continue this discussion.

JMac

@Knight No, it's not a reason at all. It's a non sequitur. It doesn't follow from what I said. How is "In all human sorrows nothing gives comfort but love and faith" the grounds to reject that we should respect his choice? For one thing, I don't even necessarily agree that the quote is correct, let alone that it's relevant.

ACuriousMind

@Slereah I'm offering a 500 point bounty for the tiger's answer.

JMac

@ACuriousMind I mean really though, the tiger has it figured out. The cat had an X Y problem.

ACuriousMind

I think some sites call that sort of answer a "frame challenge"

JMac

6:29 PM

@ACuriousMind Yeah X Y problem might not be the exact right wording

Johan Liebert

But the OP has not done any proper research on this topic. So its off topic.

JMac

@JohanLiebert Depends on where you ask sadly. Some SE sites might eat that up.

Johan Liebert

@JMac lucky cat though!

ACuriousMind

Lack of research has never been conclusively settled as an off-topic reason on most sites - certainly not on ours! People occasionally vote to close because of "no prior effort" as a custom close reason, but we've never really gotten a consensus on that one as far as I know

Aaron Stevens

@ACuriousMind I feel like it becomes more of an issue if the answer can easily be found

Novalium Company

6:37 PM

I just finished watching 1917

Everything was great but I expect a better ending.

Aaron Stevens

@NovaliumCompany I thought the edit was fitting. But that is all I will say since it is a movie that just came out

ACuriousMind

@AaronStevens Yeah, that's one of the reasons consensus on this is hard because people have wildly differing standards for what "easily found" means

JMac

@AaronStevens I saw the question titled "W = Fd does not explain anything!" and just knew I was in for a great misunderstanding.

Aaron Stevens

@JMac Yeah I am trying to think up a better title now

ACuriousMind

Sure, if I paste the title of your question into google and get the answer, it's clear you didn't do any research. But does that mean the same question with the same amount of prior research gets on-topic if OP just chooses a bad title (and is generally bad at expressing themselves)?

Aaron Stevens

6:44 PM

@JMac I have come across questions like these recently. "Why is this term not defined this way instead?" It could be a good question if the OP makes the case that the definition has a certain goal in mind, but another definition would achieve that goal in a better way. But questions like that never go like that

Slereah

@ACuriousMind Rawr >:3

Aaron Stevens

@ACuriousMind On a somewhat related note, what is the current view on questions that are mostly likely only to be useful for the person asking and not useful to a broader audience? Based on the very limited old posts I have seen, it looks like that used to be a reason to close a question. I think more recently it was mentioned in the homework close banner (the one before the current one). Now it seems like that is not as much of a reason anymore, or maybe I am just missing something?

JMac

@AaronStevens Probably because if a different definition would achieve a goal in a better way, that definition likely already has a word associated with it and is being used in that context. Especially with classical mechanics questions, where most topics have been studied extensively for centuries.

Aaron Stevens

@JMac Right. And that happens in this question, which is why I discuss impulse in my answer :)

ACuriousMind

@AaronStevens It used to be a standard close reason as "too localized", but it was abandoned years ago. We use "questions should be useful to a broader audience" as one reason to try and motivate people to make the HW questions more about concepts and less about how to solve a specific problem, but it's not seen as a close reason on its own anymore

JMac

6:49 PM

@AaronStevens Personally, I often like answering questions like that. If I can show the person that they actually were kinda onto something; just maybe not exactly what they expected, I have hopes that it will encourage them to keep thinking about the concepts and maybe feel some pride that they were thinking about it at all.

Aaron Stevens

@JMac True, that is a good point. I think it also is something a lot of students get hung up on. They think they need to understand "why is this called work?", when instead they need to take the definition as a given and learn how to apply it. I suppose it is a difference of trying to arrive at a definition vs. starting at a definition.

Often learning how to apply it shows how the definition is useful, which then shows why it was given a special definition in the first place

Knight

@ACuriousMind My respect for you is increasing day by day. Even today your maturity (by not saying a single in that discussion) has won my heart.

Aaron Stevens

7:41 PM

"I was traveling exactly the same speed as the other guy. There's no way we could have collided!" — WillO 16 mins ago

lol

JMac

@AaronStevens I think it's even worse than that. It's like, "the guy in front of me was driving and spilling oil the whole time. If we were going the same speed, how the hell did I wind up being affected by the oil skid left behind"

Aaron Stevens

@JMac Haha right, exactly.

I wish I had the ingenuity to come up with questions like that

Ones where you can kind of see where it came from, yet where the question ends up is very odd.

Novalium Company

9:16 PM

every time you play this it will sound like it's getting higher in pitch

►

what the actual f*ck

psa

In the context of statistical mechanics, does the classical limit start to disappear within low or high temperature ranges?

ACuriousMind

@dsm $\mathrm{ad}_X$ for fixed $X$ is a linear map from the algebra to itself (if you choose a basis you can represent it as a matrix), and $\mathrm{ad}_x \mathrm{ad}_Y$ is just the composition of two of these (matrix multiplication!). Linear maps from vector spaces to themselves (square matrices) have traces.

enumaris

@ACuriousMind sent you an email XD

ACuriousMind

I'll see it tomorrow, then :)

enumaris

sounds good :D

Hope I didn't send it to the wrong person lol

ACuriousMind

9:26 PM

A colleague of mine gets about a wrong email a day because he's got a name in common with about five other employees, so...it happens xD (my name is unique as far as I know, though)

enumaris

Would be awkward for this email since I said like "Greetings from Enumaris" on it

Sir Cumference

9:49 PM

@psa you start to approach the classical mechanics at high temperatures

not sure what you mean by "disappear"

psa

poor wording, I didn't know how else to ask it

thanks though, that's what I had figured

Jake Rose

10:49 PM

You know what I still don't get?

Viewing differential operators as unit vectors in a vector space

enumaris

they don't gotta be unit

psa

11:08 PM

why is "vibrational" kinetic energy distinct (i.e. we count it as another degree of freedom) from "translational" kinetic energy?

there's two quadratic degrees of freedom in $\frac{1}{2}kx^2 + \frac{1}{2}mv^2$, but haven't we already accounted for $\frac{1}{2}mv^2$ by just calling it a translational degree of freedom?

enumaris

energy and degree of freedom are not the same things

psa

sure, but I'm talking about the equipartition theorem here

Jake Rose

@enumaris even just vectors then

psa

are we just distinguishing CM motion from internal motion?

enumaris

Yes

motion of center of mass vs individual motion of particles

Jake Rose

11:14 PM

@psa vibrations, and translations are two distinct things. i.e. they have no dependence on each other. Thus they each get an additional bit of energy by equipartition theory

psa

cool okay thanks

enumaris

which could be rotational or vibrational w.r.t. CoM

@JakeRose They form a vector space so you can consider them as vectors

psa

right, thanks both of you

enumaris

np

Jake Rose

Mhmm. Is there any more intuitive explanation

Or should I bend my intuition to the axioms of vector spaces

Do they technically form a hilbert space?

enumaris

11:17 PM

no

an inner product is not defined naturally on all manifolds

Jake Rose

Such as?

enumaris

well you generally have to define a metric to have an inner product

giving rise to Riemannian or Semi-Riemannian manifolds

but you need not define a metric...in which case the inner product is not defined

A generic vector space need not have an inner product defined in it.

Jake Rose

Ah. But you can define a Hilbert space from them, just not generally?

enumaris

Are you trying to deal with infinite-dimensional manifolds or something?

Why the focus on Hilbert spaces?

Jake Rose

I'm not dealing with anything. Just generally interested.

Sir Cumference

11:22 PM

@enumaris huh, i thought i heard that we can always find an inner product on a real/complex vector space

nvm apparently that needs the axiom of choice

enumaris

o.o

@JakeRose You can probably intuit, using Euclidean geometry, that for any vector, there is an associated derivative operator that "goes along with it". So e.g. $\partial _{\vec{v}} = \sum_i \vec{v_i}\cdot \partial _{x_i}$. Then you can just choose the $\partial_{\vec{v}}$ as "vectors" and $\partial _{x_i}$ are your basis vectors

Sir Cumference

37

A: Is there a vector space that cannot be an inner product space?

I'm assuming the ground field is ${\mathbb R}$ or ${\mathbb C}$, because otherwise it's not clear what an "inner product space" is. Now any vector space $X$ over ${\mathbb R}$ or ${\mathbb C}$ has a so-called Hamel basis. This is a family $(e_\iota)_{\iota\in I}$ of vectors $e_\iota\in X$ such t...

enumaris

@SirCumference There's a difference between "a vector space that cannot be an inner product space" versus "are all vector spaces inner product spaces?"

Sir Cumference

well yep, a (real/complex) vector space isn't an inner product space until we choose an inner product

enumaris

yes

Sir Cumference

11:29 PM

crud misread the conversation

sorry

enumaris

np :)

psa

11:41 PM

if I'm trying to approximate $\sum_{j=1}^{\infty} (2j+1)e^{-j(j+1)\beta\epsilon}$ with $\int_{0}^{\infty} (2x+1)e^{-x(x+1)\beta\epsilon} dx$, I should be taking very large $\beta$, right?

because if so I'm confused on the physics

Jake Rose

11:58 PM

@psa if you're approximating it with a Riemann sum then you to evaluate it at some point, and have some width $\delta x$.

So it looks like $\int f(x) \approx\sum\limits_n (2x_n +1)e^{-x_n(x_n + 1)} \delta x$

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