The h Bar

2:47 AM

0

Q: why don't we remove tag homework like questions?

The number of homework like questions is increasing. People justput their homework questions(that too without explanation. They also just open stackexchange just for asking their homework like questions. Isn't it a good idea that noone can ask question until he/she get a decent reputation and rem...

Sir Cumference

5:11 AM

...anyone know what letter than is on the LHS?

looks like some music note

RewCie

@SirCumference That's the symbol for christoffel's gamma. I think that formula is valid for only flat space time... (I'M NOT SURE, I'VE BEEN AWAY FROM GR FOR SOME TIME, OUT OF TOUCH)

perhaps wait for more time for @JohnRennie @ACuriousMind @Slereah .... I don't remember much of these now...

John Rennie

6:36 AM

@SirCumference a weirdly written lower case sigma?

Or a weirdly written lower case delta?

Nihar Karve

8:32 AM

That would be a Minkowski metric, right? Although it doesn't really look like an eta

123

Hi All...

skullpatrol

hi

More Anonymous

10:41 AM

Hey all

skullpatrol

10:53 AM

hi

Sir Cumference

12:21 PM

howdy all

ACuriousMind

12:32 PM

@SirCumference that's an impressive case of "just draw a squiggle and hope it's a Greek letter" :P

5

skullpatrol

it says it came from somewhere, could we see the "where"?

ACuriousMind

but I'd it's likely that John is right and it's someone who didn't quite get how to write a delta

skullpatrol

true, I'm just grasping for context

have you read the story about the 102 year old woman who received her PhD from the university of Hamburg?

ACuriousMind

12:51 PM

no

Nihar Karve

To whoever was asking about the Havana syndrome, turns out it's most likely due to microwaves

skullpatrol

Dec 2 at 11:27, by Kenshin

@JohnRennie any idea what caused the Havana Syndrome?

@Kenshin

Sir Cumference

1:14 PM

skullpatrol

Thanks, pal @SirCumference

Sir Cumference

welp if that's any help lol

I think that might be a gamma?

Nihar Karve

@SirCumference a zeta, maybe?

The one in the previous equation could be a zeta

Sir Cumference

i feel like it's probably not a delta because it's usually reserved for the kronecker delta

skullpatrol

could be just made-up

like Feynman used to do

re:

50 mins ago, by ACuriousMind

@SirCumference that's an impressive case of "just draw a squiggle and hope it's a Greek letter" :P

Jack Rod

1:23 PM

why this happen?

sciencedaily.com/releases/2020/11/201130113527.htm

@JohnRennie

ACuriousMind

2:09 PM

@JackRod It would probably help if you were more precise what exactly you want to know about the article you linked...

Jack Rod

they said about how the dark energy disappeared!

ACuriousMind

"why this happen?" is (beside its wrong grammar, should be "why does this happen") not really a meaningful question because nothing "happened" there - they found an explanation for why some galaxies seem to have less dark matter than we would naively expect

@RewCie English, please

RewCie

@ACuriousMind Woops! That was some other translation. I thought it was emoji! :P

Btw, if anyone is interested to know, that's a pretty ancient Indo-Sino script!

🤦]

@SirCumference Am not able to find references, but crystoffel symbol reduces to that kinda something or something other in a special kind of flat spacetime... I'm not sure, don't believe me till I find references...

ACuriousMind

It's not a Christoffel symbol, a Christoffel symbol has three Greek indices. The tetrad analogue is the spin connection coefficients with one Greek and two Roman indices, but this one has just two indices, so it's neither of them.

Nihal already said it, it's the (Minkowski) metric in the moving frame of the tetrad

RewCie

There are crystoffel symbol with 2 indices... it's called reduced crystoffel or something like that.

ACuriousMind

2:17 PM

There are literally 3 hits on Google for "reduced Christoffel symbol", that's not a standard thing.

where are you getting all this nonsense from?

RewCie

woops

my bad

Faded Giant

@ACuriousMind "Just In"

RewCie

lmao!

hahahahahaha...

I'm embarrassed to death this time...

Okay, this must be sigma... I don't find anything similar being used in book either in Induced Metric stuff...

No idea ()/

Sir Cumference

2:47 PM

lmao I have no idea

it keeps showing up in tons of other places

RewCie

@SirCumference That looks familiar to Schwarzschild's middle term...

so, lambda is r?

not sure...

so whatever that is, if $\lambda = r$, then $\text{unknown thing}_{AB} d\theta^A d\theta^B$ might be referring to $dl^2$

Wait! I know a OCR software that recognises greek letters... lemme check it..

That must be the metric tensor for hypersurface then... (I'm throwing balls out of air...)

usually denoted as $\tilde g_{AB}$

ACuriousMind

@SirCumference can't you just ask whoever wrote these notes? :P

RewCie

Ah yes... You can anyways ask the writer...

Nihar Karve

Zeta is my final answer, Regis

RewCie

@NiharKarve Zeta Tensor?

But, I'm damn sure it's not Cauchy Tensor where sigma is used... It's not used like that here.

Slereah

3:01 PM

That letter looks like a Б

Is it from a Russian dude

ACuriousMind

do Russians actually use Cyrillic letters as variable names?

RewCie

Okay, here's my final answer if I have to lock somewhere, it's metric tensor for hypersurface... I know I'm wrong, but whatever...

Slereah

@ACuriousMind Sometimes?

John Rennie

@JackRod hi :-)

Slereah

I've seen Щ used occasionally

RewCie

3:03 PM

If anyone wants to know the unicode, it's u+0411

ACuriousMind

...why would anyone want to know that and not just look it up?

RewCie

On windows, type the number "0411" (without quotes) and then immidiately hit Alt + x

@ACuriousMind ^

On linux, Ctrl + shift + u, an underlined u will appear then type 0411 and hit spacebar

John Rennie

Some codes are convenient to remember i.e. ° is alt-248 and I use it frequently enough to make it worth committing to memory.

RewCie

It's u+2103 for Linux.. I guess...

ACuriousMind

@JohnRennie German keyboards just have a ° key for that :P

RewCie

3:06 PM

type 2103 then then hit alt+x without any space, just immediately after the number

John Rennie

@ACuriousMind that's absolutely true and also entirely unhelpful. Are you by any chance a theoretical physicist?

RewCie

In C, one uses 2 word casting techniques to do it.

lol

Nihar Karve

@ACuriousMind where are your diacritics located?

RewCie

Wow! German Keyboard looks cool!

ACuriousMind

@JohnRennie hey, that's the joke we tell about mathematicians!

RewCie

3:08 PM

It has a omega too! type w

For AE it's A

ACuriousMind

@NiharKarve Which ones?

RewCie

Okay, Elon Musk uses German Keyboard, I think.

Nihar Karve

ä et al

RewCie

Keep pressed a on android, that's it.

ACuriousMind

@NiharKarve There's just keys for the umlauts öüä directly, there is no key for the diacritic itself

RewCie

3:10 PM

@ACuriousMind How are you switching from german to english?

ACuriousMind

@RewCie why would I need to switch?

English has no symbols I can't type with a German keyboard

RewCie

@ACuriousMind So how are you typing german within english so quick?

Nihar Karve

Dude

ACuriousMind

what

RewCie

Aahh! That's how it's done...

127

Q: How to switch language keyboard combination?

I would like to type Hebrew in Ubuntu. I tried downloading the Hebrew language pack and then setting alt-shift as my layout-change shortcut in the Options section of "Keyboard Layout". However, when I actually press alt-shift, nothing happens. How can I switch my keyboard layout to Hebrew?

keyboard-layout language

ACuriousMind

3:12 PM

...what are you talking about? I don't need to switch to an English layout to type English, the two languages are using the same letters!

RewCie

@ACuriousMind So you have english letters 26 + german ones? That requires too many keys then?

@ACuriousMind How? No extra keys?

apart from 26 english ones?

ACuriousMind

there's just three extra keys for the öüä umlauts

RewCie

So german language alphabets have 3 extra additions to 26 letters?

ACuriousMind

I believe that's what I just said, yes

RewCie

Okay...

John Rennie

3:15 PM

It's a little known fact that English has extra letters as well. In priciple, though not in practice, some letters are modified by adding a diaeresis.

RewCie

But diaeresis ones are not used in english? right?

ACuriousMind

@JohnRennie you mean like some people write "coördinates"?

RewCie

So, phonetical letters should also be considered english.

I think, as we do it.

@JohnRennie Hello sir, do you have this book?

Classical Electrodynamics (book)

Classical Electrodynamics is a textbook about that subject written by theoretical particle and nuclear physicist John David Jackson. The book originated as lecture notes that Jackson prepared for teaching graduate-level electromagnetism first at McGill University and then at the University of Illinois at Urbana-Champaign. Intended for graduate students, and often known as Jackson for short, it has been a standard reference on its subject since its first publication in 1962.The book is notorious for the difficulty of its problems, and its tendency to treat non-obvious conclusions as self-evident...

John Rennie

@ACuriousMind yes :-)

Nihar Karve

Do people really write that? Or am I being naïve?

John Rennie

3:23 PM

@NiharKarve only people with far too much free time

Nihar Karve

Actually I don't anyone after the 2000s has consciously written the word "naïve" with the diaeresis

RewCie

Café too

John Rennie

That's a Frech loan word.

RewCie

Oh ok... I see

What if I go to some snowy hilly area after retirement and start a cafe there.

It'd be fun!!!

John Rennie

And now you'll have to excuse me. I have, as usual, made far too much to eat for Sunday lunch but I'm going to attempt it anyway.

RewCie

3:27 PM

@JohnRennie Eat well sir!

Charlie

4:04 PM

Does AdS/CFT have a lot of applications in non-perturbative qft? I'm currently writing my research proposal/interests for phd places, and I'd like to do something relating ads/cft to string theory and non-perturbative qft. We're obviously not expected to know everything about the field at this stage, but is applying ads/cft to non-perturbative qft a thing that is done?

I'm trying to get at least some idea of what is and isn't being researched over the last few days, but ofc a lot of this stuff goes over my head

I will understand if the answer is "go ask somewhere else" :P

ACuriousMind

4:29 PM

@Charlie well, the correspondence is between string theory on AdS backgrounds and CFTs, so it has no obvious applications to generic "non-perturbative QFTs" that are not either CFTs themselves or effective theories of string theories.

so I'm not quite sure what one would mean by "applying AdS/CFT to non-perturbative QFT"

Charlie

oh

damn

ok thanks I might need to rethink some things in that case

Physics Meta

5:07 PM

0

Q: Languages of references

I understand that Physics Stack Exchange "is an English language site", but I'm wondering whether it's acceptable to provide a generic reference (such as a link) to a source, written in a language other than English, whose translation would be very time-consuming. Would its acceptability be gene...

discussion

Physics Meta

6:23 PM

0

Q: Network-wide feature request to support TeX in tables

Many of us here frequently use MathJax, whether for this site or another site on the SE Network. Recently SE added support for tables, but ignored the needs of the TeX community, who wish to be able to type TeX symbols/formulas/etc. as well. This is the feature request on Meta.SE, to support Math...