The h Bar

7:56 AM

Morning

8:41 AM

Damn that post I made blew up

John Rennie

God bless the HNQ :-)

9:02 AM

Someone edited my post to remove the spaces before the colons

That is the French way dammit >:|

9:39 AM

physics.stackexchange.com/review/close/291088

@JohnRennie have a look at this (👆). I think the close vote limit has been reduced.

John Rennie

@JohanLiebert no, five people voted to close. The list at the top shows only close votes in the last 24 hours - or something like that.

Q: Question closed as opinion based, that is unusual but clearly not opinion based

@JohnRennie OK!

Loong

@Slereah exactly

Physics Meta

0

The question in consideration is Actual eletronic games (as in, games played using electrons)? I understand that this question is different from other questions on this site, but I think it can be objectively answered. Not in the sense of a complete answer, but surely we could comply a list of f...

discussion

John Rennie

10:02 AM

0

A: Question closed as opinion based, that is unusual but clearly not opinion based

I was one of the close voters. The reason I voted to close is because it isn't a question about physics. That doesn't mean it's a bad or uninteresting question, it just means it isn't an appropriate question for the Physics SE. I still think this and will probably vote to close again if the quest...

PM 2Ring

11:01 AM

@AbhasKumarSinha "I believe that there is a kind of radiation/wave emitted by Quantum Objects whose intensity is inversely proportional to the size of the object (Like Gravity is directly proportional to mass)" It's a crazy idea, but is it crazy enough to be true? :)

@AbhasKumarSinha And what do you mean by size? In the Standard Model, all particles are points. And if you mean mass, then that implies that neutrinos would emit your quantum waves with very high intensity, but neutrinos rarely have much of an effect on stuff, unless the flux is very high & the neutrinos have a lot of energy, eg in a supernova.

I just realized that jacobi fields are also bitensors

Well kind of

PM 2Ring

@AbhasKumarSinha "Dark matter causes expansion of universe." No it doesn't. Dark energy causes the expansion to accelerate. There's virtually no connection between dark matter and dark energy, apart from the word "dark" in the names.

11:29 AM

^Those are common medicines given in a standard 9th grade Textbooks

I believe the way of working out the photon bouncing problem without using coordinates is to use the JACOBI FIELD

Huzzah

Loong

18 hours ago, by Loong

@AbhasKumarSinha Please don't give unsolicited medical advice.

@PM2Ring smaller size more pronounced effect in slit experiment.

Gamma radiations will kill the corona virus

this is a medical fact

@Slereah humans too

11:31 AM

Well you have to pick your battles

@PM2Ring okay, didn't knew that those are different terms....

@Slereah I believe that there is one way to kill any single strand RNA Virus, it's to take them to the antimatter machine and annihilate them.

@tpg2114 true

My plan for the corona virus is a gamma ray burst

it should sterilize the earth

@Slereah green gamma rayburst...

@Slereah good idea. You should make a movie on it.

11:35 AM

Just turn CERN up to 11 and make a black hole. But I think being crushed into a singularity violates the social distance guidelines...

@tpg2114 does CERN has blackhole

?

No... but that didn't stop poor journalists and crackpots from thinking that turning it on would create black holes that consumed the Earth

home.cern/resources/faqs/will-cern-generate-black-hole

@tpg2114 seriously!? People do really take western media so serious!? Im amazed!

Enough that they had to answer it apparently

Ugh, a google search for "cern black hole" turns up very depressing results.

This ((--> . <--)) will turn into a blackhole in 24 hours.

@tpg2114 if you look into western media, then everything would be depressing.

11:40 AM

It's not just western media. And it's not all depressing -- but it takes effort to separate the quality reporting from the... not quality reporting

A good rule of thumb -- if a news report confirms every one of the things you already think are true, then it's probably a good idea to look for more reports.

@tpg2114 compare our Media... You'll realise what I'm talking about. Even in politics, western media is biased.

If some politician in India claims that he will create a black hole then he'll win majority with this claim.

All media everywhere is biased -- anything produced by humans, designed for consumption by humans, is biased. But if you take the "law of large numbers" approach and seek out many unique reports on a particular topic, then the truth lies in the combined reporting

The unique part is key, because lots of places just echo or pull reports from one place and don't do original reporting on something, so it's easy to see the same stuff in 10 places and think it's 10 reports, when really it is only 1

@tpg2114 don't agree. There exist media who put more fact than opinions from respected authorities. They are more reliable. You can apply your law of large numbers there too.

For example - Swarajmag

@AbhasKumarSinha Sure -- but it's still biased. The report itself may be neutral/fair, but some editor somewhere decided story A is more important to report than story B. And therein is a bias, because for somebody else, B is more important

Bias doesn't imply something isn't fairly done, or holding people accountable. But in the mere selection of what to report or not report, somebody's perspective comes into play

@tpg2114 we don't do that here ;)

@tpg2114 you can ask them about the reports and they make it in a week, can you get this done by some western ones? Probably no.

@tpg2114 you may ask, why my opinions are biased? See, I was an UPSC Aspirant.

Italy on lockdown over coronavirus

11:54 AM

►

The reporter looks so panicked. 😨😨

livemint.com/elections/opinion/…

Secret

The only thing I don't get about the COVID-19 is how on earth Italy have such a rapid buildup of infections

@JohanLiebert she should not have done reporting. Public reporting doesn't has that.

@Secret 70% of Infected prople in India are Italians

Secret

ok I see

@Secret the virus kept spreading unnoticed for quite some time and now we are seeing the effect.

11:58 AM

@JohanLiebert read somewhere that Indians who were infected recovered without medications, except paracetamol. (Check that one too)

indian Medical Board has isolated the virus and will start making Vaccines.

I see Israel very close to Vaccines now, they'll make it much before.

Chinese have identified the 2 sets of viruses and are working on the aggressive one.

^(I still dun know what set means there)

@AbhasKumarSinha don't take it too easy bro. It's not that simple. Those who are healthy would soon recover, but the problem is what would happen to those who have serious medical conditions. Also vaccines aren't coming in less than 9 months.

Private firms like GSK in India are very active. Will need one more month.

@JohanLiebert for vaccines - 2 months. Dun worry it won't spread in India now. MEA has suspended all Visas except official ones and UN.

So, Indians are isolated now. See the graph, we are doing good... I'm happy with the isolation process.

@JohanLiebert also MEA is also bringing all Indian citizen back to country from affected areas free of cost

qz.com/india/1800640/…

Dedicated labs in India helping neighbors free of cost ^

Related : rt.com/news/482908-india-coronavirus-chatam-china/amp/…

India is only country to have 0 killed due to virus till now. The NITI Ayog has uploaded a real-time dashboard and upload their 200 page approach to tackle this epidemic in 6 months!

12:22 PM

@JakeRose Jake without Rose is same as Physics without mathematics.

1:06 PM

What's a bitensor

Semiclassical

something something geometric algebra?

wikitionary defines it as "a tensorial function of pairs of points."

@bolbteppa see also this: google.com/books/edition/Bryce_DeWitt_s_Lectures_on_Gravitation/…

in which case it's just a synonym for "rank 2 tensor"

Synge's world function

In general relativity, Synge's world function is an example of a bitensor, i.e. a tensorial function of pairs of points in the spacetime. Let x , x ′ {\displaystyle x,x'} be two points in spacetime, and suppose x {\displaystyle x} belongs to a convex normal neighborhood of x {\displaystyle x} so that there exists a unique geodesic γ ( λ ) {\displaystyle \gamma...

Semiclassical

yeah, those two descriptions don't seem entirely compatible

Q: Defining the covariant derivative on bitensors

5

Bitensors (tensors defined on two different points) are an extension of tensors found in some applications of general relativity, where objects such as the world function, parallel transport operator, heat kernel or propagator are bitensors of some kind. It is unfortunately not commonly done in t...

general-relativity differential-geometry differentiation

hmm

Oh look who asked that

Semiclassical

or, maybe it is? I guess Dewitt's first example is to show that the delta function is a trivial example

so a Green's function is an obvious example of a bitensor

and an n-point correlation function would be an n-tensor in that sense

...which he also says. boy, i need to read stuff i cite

1:18 PM

What is pseudotensor? this $T^r_s = V^* \times V^* \times \dots \times V^* \times V \times \dots V$?

^that thing or what?

$r$ times $V^*$ and $s$ times $V$

@Semiclassical So that's also a pseudotensor?

@Loong are you there?

That is a mixed tensor. A pseudo-tensor is a tensor which transforms as a tensor except up to factors of the determinant of the transformation. For example, the volume element in an integral transforms by Jacobians and so is a pseudo-scalar

Okay...

@bolbteppa $P^{abc}_{def}$ is a type (3,3) tensor na? Then why some book say it's (0.1) type tensor....

1:35 PM

Looks like a (3,3) tensor

bitensors are tensors on $M \times M$

to me too

@Slereah Correction $M^* \times M$ or $M \otimes M^*$, for $M \in \mathbb R^n$ and $M^* \in \mathcal R$

$\mathcal R$ is a dual space.

No they're not.

$M$ is the manifold

it has no dual space.

okay then

It's the tensor bundle $\pi : E \to M \times M$

1:42 PM

$\rightarrow$

coool

@Slereah What's your favourite physics equation?

Where did the balantly off-topic close reason go? I can't find it in the set of close reasons.

@bolbteppa @Slereah Do you know any software to automatically download all citations mentioned in a paper...?

I recommend less pings

6

@bolbteppa didn't get it? Pings is related to internet connection...

You don't need every reference in every paper when you're still studying the material, pings are the @'s

1:51 PM

I prefer reading the whole thing, being a new guy, I need to check all biblography in order to understand the paper

@JohanLiebert You can always just go to the "Other" off topic reason, and replace the comment with "ME NO SEE PHYSICS!"

2

"ME NO SEE PHYSIKS" XD

Yuvraj Singh...

3:03 PM

I hope that one day there would be a community on stack exchange on styling and fashion!

3:13 PM

copy that^

I failed in my fashion and hairstyle

Just took that for marks!

3:26 PM

A spacetime observer would be fully defined by its parametrization, rotation, acceleration, and initial position, velocity and frame

The horror

I shudder to think what this will all give for entire networks of observers

@YuvrajSingh... if you wish then you can propose such sites on area 51!

dun't think

Aaron Stevens

4:54 PM

@JMac I'll write up a meta post requesting this reason gets added to the list of close reasons

@AaronStevens Check for a dupe first. This can't be the first time "Me no see physics" has been suggested as a close reason.

@AaronStevens Unfortunately, sites can only have up to 3 close reasons and we already have a full set. #WeHateFunHere

That explains why physics SE has been the most boring video game I've ever played.

Aaron Stevens

@JMac Wait, my rep points don't represent my total HP?

They do, but they're worthless because imbalanced boss monsters can cast "suspension" and reduce you immediately to 1 HP without a saving throw

5:01 PM

@AaronStevens I thought it was my experience at first, but I never leveled up. I'm starting to think it's some sort of gold or something. I don't know though. This game is too text based. There should at least be 2D graphics or something.

I haven't even seen a single mushroom powerup.

Aaron Stevens

Aaron used "Critical Thinking".... It was immediately shut down

5:59 PM

goOd eVenIngs genders

I come here to spread love and peace for everybody

May your dreams come true

and your banks go full

what if I dream of a world without banks

then u r not a true gender

I don't know what that's supposed to mean. Please try to make at least a little sense.

@ACuriousMind a person hired me to freelance code some stuff and he refused to pay and blocked me. I feel tricked :( He was a Bulgarian so... I should've expected it (I did but still...)

Q: Thought experiment closed as off-topic and better suited for engineering. But thats a thougt experiment

@NovaliumCompany Seems like you learned a lesson - never hand over a product without an enforceable way of getting paid! :P

Physics Meta

6:16 PM

0

The question in consideration is: Could there theoretically exist a material so light, that it can levitate in the air just due to the in height decreasing air pressure? I think thats definitely a thought experiment discussing the underlying physical principles. If I understand it right, then th...

support scope specific-question close-reasons reopen

6:46 PM

break his legs

ZeroTheHero

or his nose.

8:07 PM

Just watched The Lego Movie 2... it's amazing

In my opinion, it's even better than the first one.

The movie has deeply embedded moral values, easter-eggs and it's so fun to decipher it while watching

It touched me emotionally and I like that it doesn't focus so much on being "logical" (like most self-proclaimed movie critics would insist on) but on delivering the right conclusions and values in the right way. It makes you wonder, ask questions and it's very involving.

Toy Story 4 is good as well (although it's mostly funny, not necessarily emotional)

I don't know who banned me temporarily 2 hours ago but please tell me why so I know what not to do because this chatroom is really important to me.

@NovaliumCompany I kicked you for a minute because you posted complete nonsense right after me asking you to not do exactly that.

@ACuriousMind I get it but it was supposed to come out as joking around a bit. Not everything has to be serious and professional and plus there was no one online. I may not be right but still, don't ban me please. Next time just tell me "stop or I'll kick you" and I'll stop.

"Not everything has to be serious and professional" is true, but that doesn't mean we have to devolve into posting barely grammatical nonsense here. If other users complain about something you're doing (and the complaint is not completely without merit), you should consider what they're saying without an explicit threat of being kicked.

8:23 PM

@ACuriousMind Okay, that makes sense. I'll try :----)

"Don't take life so seriously, you're not gonna get out of it alive anyways' - John Rennie

Not sure how correct and applicable that saying is but it has it's uses.

Black Thursday (2020)

Black Thursday is an ongoing global stock market crash on March 12, 2020. Global stock markets suffered from the greatest single-day fall since the 1987 stock market crash. Following Black Monday three days earlier, Black Thursday was caused by the coronavirus pandemic and investors feeling concerned after US president Donald Trump imposed a 30-day travel ban against the Schengen Area. The Dow fell 2,352 points. == Background == On March 9, 2009, the stock market hit its lowest close during the Great Recession. Since then, the US stock market was a bull market and held an 11-year streak despite...

2

@bolbteppa the heck

let's just hope a second global economic depression doesn't come

It's funny (and originally from someone named Elbert Hubbard, apparently), but it since it contains no actual argument it would indiscriminately apply to your choice of text editor or the decision to start a nuclear war :P

@ACuriousMind yep

...why do we call stock market crashes "Black X", anyway?

A: What good is the Einstein de-Sitter model?

8:34 PM

@ACuriousMind I guess you're supposed to fill up the X with whatever's black

Don't mind me, I'm being illogical, it's late

M.N.Raia

11:49 PM

Goodmorning/ evening/night for everyone!

Hey, is it possible to apply d'alambertian operator on Vector and Tensor fields? Like

$\square A_{\mu}$ or $\square T^{\mu\nu}$

Sir Cumference

2

EdS universe represents a matter-dominated universe. Since the universe is currently matter-dominated and evolving towards lambda dominated, its a good approximation to use the EdS model to calculate the age of the universe.

I maybe super tired rn but the universe has been lambda dominated for several billion years now, right?