The h Bar

Avantgarde

00:33

The number of people celebrating the discovery of virtual particles at the LHC is too damn high.

danielunderwood

01:11

@DanielSank Nice! I like the level of technicality. Are you guys associated with tensorflow or just happen to be on their channel?

vzn

03:40

colder than deep space! :o

DanielSank

05:07

@danielunderwood The association with TensorFlow is totally incidental. We're piggy-backing on their channel.

dmckee

05:34

Last week I offered a few lightly considered thoughts on a some fairly basic topics. Pay-off in rep: 10-20 per post.

This week the same kinds of offerings, and the same kinds of responses. Except the one that's netted me +175 so far, despite being no different that I can see from the others.

All you can say is that the site is fickle and unpredictable.

John Rennie

@dmckee HNQ?

dmckee

Not that I noticed, but I haven't been on the site much since posting the answer.

John Rennie

This one. That was on the HNQ.

dmckee

Ah. And apparently someone tweeted it as well.

John Rennie

The HNQ isresponsible for this :-)

dmckee

05:52

I think you could have put the full-stop after the third word.

John Rennie

:-)

Actually there have been some pretty good questions n the HNQ recently.

dmckee

Oh, I like noodling around the HNQ to find questions on other sites ...

... but that's different. Entirely different.

HDE 226868

@DanielSank That's a pretty awesome video. I definitely learned a couple things there.

Unknown MathMan

06:55

Griffith's book doesn't contain the matrix method, is there any good book which explains the matrix method for solving hamiltonian?

DanielSank

@HDE226868 Glad to hear that.

Unknown MathMan

I got this note online, but it doesn't explain how we are getting $\langle n|x|m\rangle=x_{nm}$ in the matrix etc.

young.physics.ucsc.edu/115/matrix_qm.pdf

Physics Meta

08:00

0

Q: Why can't we connect virtual ground to real ground in an inverting amplifier op amp?

I was posed with this question and I don't have a definite answer for it. Why can't we connect the virtual earth of an inverting op amp to ground ?

Avnish Kabaj

09:48

@JohnRennie Interesting

Physics Meta

10:08

-1

Q: When "too broad" is really too broad?

Referring to this question, and the discussion at meta. In a nutshell the original question was closed as "non-mainstream" physics, but after the meta question, it was reopened. However, there are suggestions that it should be closed as "too broad": This is not or less going to require a ...

discussion close-reasons too-broad

John Rennie

@AvnishKabaj Thomas More was born in the 15th century. Even then it was obvious that vigilantes are a bad idea.

I think it's a general rule that people who are sure they are right are usually dangerous.

Avnish Kabaj

Don't you dare demean spider Man

Slereah

Well that was before the invention of Batman

Avnish Kabaj

:P

PM 2Ring

I'm not quite sure why this was closed. Sure, it's homework, and on a first glance it looks like a "check & complete my work" plea, but the core of the question is "how to calculate the diffracted radius", and the OP has posted their thoughts related to that. What else does the OP need to do to make it eligible for reopening?

ACuriousMind

10:21

@PM2Ring Ask a question that is not simply "How do I correctly compute the radius?"

ACuriousMind

10:34

In some cases, there isn't really a way to make a homework-like question on topic. In this particular case, there isn't really any trick or physical insight to the question that one could ask about - the width of a Gaußian beam simply falls out of the wave equation if you plug in a Gaußian ansatz and chug through

Slereah

Look at @ACuriousMind flaunting his ß

$$\Huge{\ss}$$

Hm, apparently not available by default

ACuriousMind

@Slereah I'm fabulouß!

Slereah

What an aß

2

PM 2Ring

Fair enough. I don't know how to solve questions like that, but I guess that convolution is involved, somehow. :) So is the OP misleading themself with thoughts of the Dirac delta?

ACuriousMind

I don't know about convolution - as I said, you plug in a Gaußian ansatz into the wave equation, out falls the Rayleigh length. It's a bit of an annoying derivation, see e.g. the first part of this

PM 2Ring

10:49

@ACuriousMind Thanks. I'll read it later. I may even absorb some of the info. :)

@Slereah I like big ẞ and I cannot lie.

ACuriousMind

@PM2Ring That's funny, because the ß traditionally had no capital form :P

Slereah

But then how do you write it when you're really angry on the internets

the big dude

ACuriousMind

Capital ß is often rendered as 'SS' in all-caps

Slereah

Didn't Germany have enough SS back then

PM 2Ring

@ACuriousMind Indeed. I was just about to link that page, but you beat me to it.

Captain Bohemian

12:33

Google+ will be abolished in the beginning of April, but strangely it can still be posted.

Anonymous

12:59

@Slereah Lol, aß rhymes well with Gauß. :D

Anonymous

(I AM STEALING IT.)

user351417

13:13

> The fumes above a gasoline pool are macroscropic gluons caused by the negative pressure created by the being known as YHVH-pi and do not conform to the standard model of atomic physics.

user351417

Wow. Just wow.

Slereah

Is that Deepak Chopra

user351417

@Slereah No, it's physics.stackexchange.com/users/11696/thedoctor, the author of a post @JMac linked a while back

Slereah

"Quantum Mechanics needs to expand its model so as not to prefer any particular scale or ''reference frame''. See my paper "The Nature of the Quantum Field" at linkedin.com."

🚨🚨🚨

user351417

I have never heard of people posting papers on linkedin, but I'm quite sure that isn't peer-reviewed.

Slereah

13:16

it gets worse the further you read

user351417

His location is "Suicidalburg". I find that joke somewhat lacking in taste.

user351417

He actually has some totally sparkling questions and answers though. All thoroughly non-mainstream.

Captain Bohemian

I posted others' papers in LinkedIn.

LinkedIn looks boring, so I just use it to post my notes.

ACuriousMind

13:33

@Blue ....the two words do not rhyme at all...

PM 2Ring

13:52

@Chair Ah, that guy.

17 hours ago, by PM 2Ring

@JMac Damn. Now I have to recalibrate my crank index calculator. Again.

@Chair That may be worth a custom flag. I didn't notice it before because location isn't visible in the mobile view.

Anonymous

14:12

@ACuriousMind Wait, for some reason I was reading it as auß. :P

Anonymous

Gauß Auß!

Anonymous

@CaptainBohemian You use LinkedIn to post "notes"? O_O

user351417

14:43

@PM2Ring Nah, I don't find it particularly intolerable/indecent. It's just... lacking in taste.

PM 2Ring

@Chair Ok. And I guess there's no need for a flag, since any mods who visit here can make up their own minds about it.

ACuriousMind

@PM2Ring If you wish to bring something to moderator attention, you should never rely on us reading anything in chat.

But in this case, I do share the evaluation as "distasteful, but not in breach of the policy formerly known as Be Nice".

user351417

I really hate the term "code of conduct". Such a mouthful.

ACuriousMind

Yeah, I thought that Be Nice was a pretty good name.

user351417

15:01

Quora's Be Nice Be Respectful is a pretty nasty mouthful too. Just so many words, no appropriate punctuation, and so much redundancy.

PM 2Ring

@ACuriousMind Understood

user351417

@PM2Ring Hehe I used to do that a bit (chat for uncertain flags), but then they mentioned that flags are also pretty convenient for tracking issues which could progress over time.

PM 2Ring

Consider it an informal communication over an unreliable channel, rather than official complaint. ;)

ACuriousMind

The main point is that if you tell us something in chat and we forget to follow up on it, then it's just gone. If there's a flag and we don't handle it, it'll sit there, reminding us

PM 2Ring

Yep. We have a couple of mods who are regulars in the Python room. For serious stuff, they prefer we use the flag system, but they don't mind thd informal method for the occasional low priority tentative thing.

user351417

15:11

@ACuriousMind How did the kets at physics.stackexchange.com/a/164219 happen? Did mathjax have ket support at the time? Is it just failing on my device? I would have thought someone would edit that one; it has a score of 13 (now 14 :P), so it has definitely received some attention.

ACuriousMind

@Chair The question contains a \newcommand for ķet

user351417

Huh, it shows up with red \ket text on my computer.

user351417

Perhaps SE made the newcommand stuff apply only to the post which contains it?

ACuriousMind

That's why one shouldn't rely on \newcommand at all in MathJax - there are no proper scope rules, you can't rely on any particular \newcommand definition extending to any other MathJax block on the page

In other words: Nice that you edited it out, but you should also edit it out of the question while you're at it

4-year-ago me was careless in using it at all

user351417

I'll edit the question then.

Anonymous

15:59

@Chair Yes.

Anonymous

14

A: The scope of \newcommand is the entire page

It pains me to break this thread by fixing the issue, but here we are. :) We are now inserting \begingroup and \endgroup directives into post and comment bodies, so all command definitions should be scoped to individual posts. For now, I'm only enabling this on Math (and here on meta), but barr...

Anonymous

@djsmiley2k Does your cat know how to delete messages in chat?

Mo_

16:50

@Chair It shows \ket red for me everywhere (even on the posts)

Abcd

@JohnRennie Hello

ACuriousMind

@Mo_ What do you mean - Chair edited out the kets, there are none left

John Rennie

@Abcd hi :-)

Abcd

@JohnRennie which quality to choose for best printing?

John Rennie

@Abcd I doubt the media setting will make any difference.

Captain Bohemian

17:00

@Blue otherwise I don't have an idea of what LinkedIn should be used for. Every time when I see the feeds in my LinkedIn, they are something boring. In Facebook, my feeds have something interesting, like EarthSky, QuantaMagazine, Cosmology, SPACE, Symmetry Magazine, but LinkedIn never has something like these.

Abcd

@JohnRennie i know...what to choose from Quality settings

John Rennie

@Abcd ah. FastRes 1200 is best quality, but the difference between 600 and 1200 dpi is probably very small.

ACuriousMind

@CaptainBohemian LinkedIn is not supposed to be "interesting" - it's a "professional" social network some people use to present themselves as employable and to network with other professionals

Anonymous

@CaptainBohemian Well, you need to follow interesting people for that. But yes, if you're looking for science stuff there, you'll not find much. It's mainly for job searching and keeping in touch with your professional acquaintances.

ACuriousMind

Unless you're printing high resolution photography with an excellent printer, you won't ever need more than 600 dpi :P

Captain Bohemian

17:05

@Blue But every time I see the connection suggestion, they are people in business or engineering. Like today, I get a sugestion to follow some MBA. I have never had interest in that, so I decline it.

ACuriousMind

...why, exactly, did you sign up for the site in the first place?

Captain Bohemian

@Blue indeed, what motivates me to register LinkedIn is I found my ex-boss is there, but I found I can't send message to people who are not connected to me.

Abcd

@JohnRennie What do I do about the pictures being too light? Here is an example:

PM 2Ring

@EmilioPisanty Nice work on physics.stackexchange.com/a/459580/123208 ! I was beginning to despair that that question wouldn't get a decent answer.

Anonymous

@CaptainBohemian I think you can send them a message along with the "connect" request. Alternatively, you can upgrade to the premium version which allows you to message members outside your direct network.

vzn

17:10

The Endgame for LinkedIn Is Coming medium.com/@lancengym/…

Abcd

@JohnRennie c^

Anonymous

Your printer seems faulty...

John Rennie

@Abcd I don't think there is a lot you can do about that, except possibly to go back to the original picture and use some image processing app to make the text darker.

Abcd

@Blue No see this:

ACuriousMind

Why are you printing out a picture of a textual output rather than actually printing the text?

Anonymous

17:14

Wait, you're printing a picture?

Anonymous

That makes sense now.

John Rennie

@ACuriousMind I think it was a screen grab

Anonymous

There's a print option from within BlueJ. Use that.

Abcd

fish it had my name lol , did any one see?

ACuriousMind

@JohnRennie Still results a picture, which is responsible for the poor quality. Don't print text as pictures, print it as text!

Anonymous

17:15

@Abcd I did... :P

Anonymous

Dun worry...we'll keep it a secret. ;)

Abcd

@Blue :(

John Rennie

@ACuriousMind that's assuming it is possible to get the info as text. That may or may not be easy depending on what app was being used.

Abcd

Who else?

Anonymous

@Abcd Do you want me to redact it? Mods and room owners can always see deleted messages (unless it's redacted).

Abcd

17:17

@Blue please do so.

ACuriousMind

@JohnRennie What sort of standard text field doesn't allow you to Ctrl-C the text?

Abcd

PM 2Ring

Oh, that's much better!

Abcd

@PM2Ring yeah.

PM 2Ring

Sorry, I'm a bit slow. I'm on my phone, and it's after 4AM.

ACuriousMind

17:20

"Yo, I heard you like QuizResults so I put some QuizResults in your QuizResults..."

ACuriousMind

Dammit, Rust, I'm just trying to pass a string to a method! How complicated can that be! I'm starting to think this was the wrong language to choose to learn for relaxation... :P

Abcd

which language are you learning for relaxation.

ACuriousMind

Rust.

Anonymous

@Abcd Done.

Abcd

lol I thought 'rust' is a mild swear word

ACuriousMind

17:25

@Blue Should I mention that was a bit pointless because the picture is still on imgur and accessible to anyone with the URL? :P

Captain Bohemian

@Blue Does upgrade to the premium version require money? I don't know if my ex-boss actually logins LinkedIn often because he is also a physicist; I seem not to see many physicists in LinkedIn.

Anonymous

@ACuriousMind Tbh, I made the offer mostly because it's fun to use the redaction script. :P

Anonymous

@CaptainBohemian Yup.

Anonymous

(I'm secretly wishing that someone leaks their contact details on QCSE so that I can practice redacting on the main site too. Hmm, I could actually try it on any existing post too...)

Avnish Kabaj

Pssst

What's abcd's name

These Are The Best Vaccination Alternatives Already On The Market

Emilio Pisanty

17:40

@PM2Ring thanks

I vacillated a good deal about whether to write it

after spending that much work on getting it right I do kinda want it to go on HNQ

particularly given how many answers it has

but I suspect it's some twelve hours too old for that, now

Avnish Kabaj

clickmonkeys.com

Where there is will there is way

Emilio Pisanty

what?

John Rennie

@EmilioPisanty what question is that?

Emilio Pisanty

7

Q: So is quantum entanglement actually FTL "communication" or is it mundane pre-determination?

I have to say right off the bat, I'm a little frustrated that there seem to be very contradictory answers about this, at least to a layman like me. If two particles are entangled and you separate them by some huge distance, and you measure one of the spins, you know the other particle must be sp...

quantum-mechanics quantum-information quantum-entanglement definition faster-than-light

Anonymous

@EmilioPisanty Someone didn't want to type much...

ACuriousMind

18:05

@EmilioPisanty Not a bug, the user actually typed '.......' as the close reason, then deleted the auto-generated comment. We're looking into it.

Emilio Pisanty

@ACuriousMind oh, I didn't think it was a bug

I thought it was a user abusing the close-vote privilege by voting to close without bothering to give any reason at all

ACuriousMind

@EmilioPisanty For the record, that's worth a mod flag next time you see it. There are always some strange close reasons in the tools overview but it's pretty hard to find the post where they were cast, especially if the comment is deleted

Emilio Pisanty

@ACuriousMind ok, good to know.

Anonymous

@ACuriousMind We could ask Glorfindel to write up a userscript for that.

Anonymous

It would be pretty useful for the mods.

Anonymous

18:19

(I wish I knew how to write them myself.)

dmckee

@AvnishKabaj And wow are they working out in Washington state, US just now...

ACuriousMind

@Blue For what? How is that script supposed to find the location of the close vote from the aggregation in the tools overview?

dmckee

I mean, a measles epidemic in a supposedly advanced society in the 21st century. What's not to like?

ACuriousMind

Scripts are not magic, there needs to be a way to find out the information they're supposed to retrieve :P

Anonymous

@ACuriousMind A script for keeping track of the custom close reasons written by users (should be extractable from the timelines) in a separate page. It doesn't need to be from the tools overview.

ACuriousMind

18:24

And...what exactly do I do with that script?

Anonymous

@ACuriousMind Check for close privilege misuse as in the above case?

Anonymous

I mean, custom close reasons are not used that often. I could definitely check them once a day like I check the chat message flags.

ACuriousMind

I'm sceptical that the custom reasons can be extracted from the time line. The timeline features two entries for a custom close vote - one with "close - custom reason" and one with "comment added - ..." where '...' is the custom close reason.

You'd need to be willing to bet that the comment that follows a custom close vote in the time line will always be the reason

If you're unlucky, you get two comments added at the same time, sowing confusion

Anonymous

@ACuriousMind Well, I guess that'd be pretty rare...

Anonymous

18:32

Better to take some assumptions rather than having nothing at all to deal with such misuse. And oh, look, you get the timestamp to the precision of a second.

Anonymous

If you see some other kind of comment at the same time (i.e. other than a close-vote-reason), you could check out the corresponding post manually.

Mo_

19:01

@ACuriousMind ah, I didn't read the discussion; I just meant I occasionally see red \kets on the main site

ACuriousMind

Yeah, that's either people who didn't look at their output at all or whose posts were broken by the change to \newcommand's scope Chair linked

djsmiley2k

19:27

@Blue it was a small child, hense me deleting them

Anonymous

@djsmiley2k Hehe. :)

Emilio Pisanty

20:41

oh, by the way

@ACuriousMind $\renewcommand{\int}{\text{why not?}}\int$

rob

21:05

@EmilioPisanty These kinds of shenanigans are one reason that I've never installed ChatJax.

Emilio Pisanty

21:21

@rob $\Huge 😶$

@Blue hmmmm. I saw the statement and thought of this

45

Q: Is the non-triviality of the algebraic dual of an infinite-dimensional vector space equivalent to the axiom of choice?

If $V$ is given to be a vector space that is not finite-dimensional, it doesn't seem to be possible to exhibit an explicit non-zero linear functional on $V$ without further information about $V$. The existence of a non-zero linear functional can be shown by taking a basis of $V$ and specifying th...

axiom-of-choice set-theory linear-algebra dual-pairs lo.logic

user222141

hey thanks again for the great answer

Emilio Pisanty

and then you go to the proof in the accepted answer, and you get this

> Indeed let $E$ be a basis for $V$...

... because every vector space has a basis?

Anonymous

Feb 5 at 17:56, by ACuriousMind

Caveat, the proof requires the axiom of choice :P Without choice, you can have non-trivial vector spaces whose dual is trivial.

Anonymous

Yup, ACM had pointed that out. :P

Anonymous

I still haven't gone through the whole proof.

Emilio Pisanty

21:29

@Blue yes, this is a frequent touchstone with ACM

@user222141 no worries.

user222141

what is the general consensus on self-teaching physics? impractical?

Anonymous

@user222141 That sounds like a very vague question...

user222141

vague how?

what I mean is how realistic is it to try to self-educate in physics without having formal training or classes or professors etc, just reading books and such

PM 2Ring

@user222141 How's your calculus? And linear algebra?

Emilio Pisanty

@user222141 Self-teaching physics, and particularly quantum foundations, without at least someone with a solid understanding that you can talk to in real life, does carry the danger that you'll fool yourself into thinking that you've understood more than you've actually understood

a bunch of crackpots got to where they are via that route

5

which is not to say that self-teaching physics implies that you'll become that

but it is certainly something that needs to be actively mitigated

As for practicality - depends on how much time, patience and discipline you have.

it's certainly feasible, given enough of those

Anonymous

21:45

I guess learning from proper sources helps too. There are also plenty of classroom-recorded lectures on the internet these days. Of course, they won't be research-level physics, but they cover at least up to the graduate level.

Anonymous

I remember JR mention that he learnt GR and parts of QFT from scratch after retirement, which is pretty motivating. Sticking around knowledgeable folks also helps. SE is a great resource for self-learning. That said, definitely, it's better to take formal courses. But not everyone has that privilege.

user222141

22:08

@PM2Ring Could probably use some work on both, as I never did formal classes in either

Anonymous

@user222141 Are you enrolled in any course currently?

user222141

@EmilioPisanty If it's any consolation, the constant crackpottery is what led me to make that question on the site... I got tired of the crap explanations that one sees over and over and over again

@Blue No, not a student anymore

Anonymous

@user222141 I see.

user222141

I would absolutely love to go back to school and stuff my face with math, computer science, physics, etc, but it's not a realistic possibility for me

I'm good at problem-solving in general, just lacking in the formal stuff

Anonymous

I can understand. Anyway, "I want to learn all of physics" isn't a good goal. You'd have to first decide on what exactly you want to learn, first.

user222141

23:17

@Blue I guess just a better understanding of physics as it might apply to electronics, getting better at newtonian physics, better at quantum physics and relativity just to better understand the universe... just a wide variety of topics

somewhat of a wide net

Anonymous

23:58

@user222141 ...that's not much of an improvement over "I want to learn all of physics". :P

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