The h Bar

Slereah

15:02

Am I

0celo7

@Slereah yes

$\mathrm{SL}$ is a functor

Slereah

But

What map am I

Vector spaces to what

0celo7

@Slereah their special linear group

Slereah

Wait

Is it a functor

Isn't it just a map within the category

0celo7

@Slereah Is the special linear group a vector space

I know it's not

FenderLesPaul

15:10

@GPhys indeed

still no official word of UChicago

the wait intensifies

0celo7

@FenderLesPaul why do you care

FenderLesPaul

@0celo7 why do I care about UChicago?

0celo7

@FenderLesPaul si

David Z

1

Q: How much light is necessary to form a black hole

I suppose that enough light in a small enough volume could create a black hole. What is the good quantity that can tell when light can or cannot make a black hole? Energy density? But there must be some importance of the time it stays in that volume. So is it irradiance? How much of it is requi...

one to review for reopening

dmckee

Lots of philosophers on the site this week.

0celo7

15:15

I like how libgen has free, legal pdfs in addition to the free, illegal ones.

Slereah

Well why not

The point isn't illegalness

dmckee

I blame LIGO: they came to get their questions answered (bringing their popsci notions with them) and are trying to take part like good kids. But they have a confused idea of how scientists actually think.

Slereah

It's just to gather ressources

FenderLesPaul

@0celo7 yeah I don't care about going there

but it'd be nice to hang with Bob Wald for a bit haha

0celo7

@Slereah hmm, how does the $\mathrm{SL}$ functor work on the morphisms of $\mathsf{Lin}$?

FenderLesPaul

15:20

@DavidZ that's an interesting question though

why was it closed?

Slereah

If it's one I guess it's a morphism to itself?

0celo7

@Secret Please interpret what that is

FenderLesPaul

@0celo7 dude what the fuck

Slereah

Isn't that Pingu's mouth

dmckee

@FenderLesPaul John R. duphammered it. As the proposed duplicates has an answer that links to papers showing that either gravitational waves or light can form BH it at least links to the answer to the current question.

FenderLesPaul

15:23

@dmckee Ah ok

that's fair

didn't see that

0celo7

@FenderLesPaul language

dmckee

I note that the OP of the current question is unhappy with that result.

Slereah

Well

From Wald, I remember that black holes do emit gravitational waves as part of Hawking radiation

So I guess it is possible

also generally gravitational wave collisions can form singularities

David Z

@dmckee I think the argument that it's a different question is technically valid, but it's really close. I don't consider the content of the answers when checking for duplicate-ness.

0celo7

@Slereah can a black hole radiate radiation that causes a black hole to form

does that not violate the "no splitting" theorem?

Slereah

15:27

Fuck if I know

FenderLesPaul

@0celo7 writing

@Slereah I think the question isn't whether BH's can emit gravitational radiation

as this is certainly true

but rather whether a bath of radiation can collapse to form a BH

Slereah

Well I'm thinking of the time reversed case

Of course it would be a white hole

But still

FenderLesPaul

Can geons undergo gravitational collapse?

0celo7

white holes are just porn star black holes

FenderLesPaul

they are already unstable so I would figure no

but still curious

David Z

15:29

@0celo7 racist :-P

Slereah

Well as said

Some solution of gravitational wave collisions produce singularities

So I think it's doable?

Maybe

0celo7

algebra prof is making us participate in a poll, and it's required

I can't access it

great...

FenderLesPaul

@Slereah but aren't those naked singularities that disappear in finite time?

I guess you're talking about colliding pp-waves?

Slereah

Well it's only an example I had in mind

I don't know about like

Collapsing spherically symmetric g-waves

FenderLesPaul

Yeah that's what I had in mind

Slereah

15:35

For a start you can't have a vacuum solution with that

Because Birkhoff and all

So it's gonna be a bitch to solve

FenderLesPaul

Are Geon space-times stationary?

Slereah

I think they can be?

I know there's spacetime solutions that are vacuum and static

0celo7

wtf is a geon

Slereah

and not Minkowski

A little ball of gravity

Gravitational or EM waves held together by their own gravity

FenderLesPaul

@0celo7 a solution of Einstein equations for a compact bundle of EM or gravitational waves

0celo7

15:38

never heard of them

FenderLesPaul

@Slereah Ok I guess they can be stationary

maybe not spherically symmetric?

geons that is

Slereah

The solution I have in mind has an awful awful name

FenderLesPaul

@Slereah what is it?

Slereah

Ozsváth–Schücking metric

The Ozsváth–Schücking metric, or the Ozsváth–Schücking solution, is a vacuum solution of the Einstein field equations. The metric was published by István Ozsváth and Engelbert Schücking in 1962. It is noteworthy among vacuum solutions for being the first known solution that is stationary, globally defined, and singularity-free but nevertheless not isometric to the Minkowski metric. This stands in contradiction to a claimed strong Mach principle, which would forbid a vacuum solution from being anything but Minkowski without singularities, where the singularities are to be construed as mass as in...

that's the one

FenderLesPaul

@0celo7 they are gravitationally unstable so they aren't realistic

so you don't see them often

0celo7

15:42

@Slereah lol

that's worse than Picardy Lindelhofer

what is the worst theorem name

Slereah

Probably something by a Polish dude

Or worse

Georgian

Is there any georgian mathematician

there's a Revaz Gamkrelidze

Did he do a theorem

0celo7

haha

Slereah

Andrzej Grzegorczyk

D:

"He became the first to describe the Grzegorczyk hierarchy"

0celo7

Hah!

Slereah

Indian dudes don't have complex names but they are very long, though

0celo7

15:51

Like Chandrasekaran

Who the hell has a name like that

Slereah

Or Raychaudhuri

You know who I like?

Bose.

0celo7

Yes.

A decent Indian name.

Slereah

Short and sweet

Well except for his first name

satyendra

0celo7

Venkatanarasimharajuvaripeta railway station

Venkatanarasimharajuvaripeta or Venkatanarasimha Rajuvaripet is a railway station in Andhra Pradesh on the border with Tamil Nadu, India with the distinction of having the longest name among all stations on the Indian Railway system. It is on the Renigunta-Arakkonam section of Southern Railway. Venkatanarasimharajuvaripeta is sometimes referred to with the prefix "Sri", making the name three letters longer. In railway parlance, it is a flag station. It is unsignalled and passenger trains halt here. The actual station name for this station is: "Venkata Narasimha Raju vari Bahadur vari Peta". �...

Someone with this name needs to prove the Riemann conjecture

That way everyone will know that name

Slereah

The Japanese guys also have short names

Yukawa

Bam

0celo7

15:54

Or maybe they'll call it the V-peta proof

Slereah

Well Tomimatsu is a bit long

0celo7

Matushima

Kobayashi

Slereah

Nambu

Goto

0celo7

Action

Slereah

all good names

0celo7

15:55

kaku

sounds like the German word for poop

Slereah

Neil DeGrasse Tyson, do you really need three names

0celo7

G.F.R. Ellis

He has four

Yvonne Choquet Bruhat

Slereah

Kolmogorov is also a bit long

0celo7

you know who has the best name

Jack Lee

Probably the shortest and easiest name ever

Slereah

I'm sure there's a chinese physicist with a shorter name

0celo7

15:57

@Slereah actually the shortest name might be H. Wu

the H stands for Hung-Hsi

I think Wu is the shortest you can get

There are probably no one letter names

Slereah

Wu, Li

0celo7

Oh shit analysis test gotta go

Slereah

There's a Di Liu on Arxiv

0celo7

The best name is Vladimir Vladimirovich

Slereah

Carl Carlson

0celo7

16:04

Lereah Lereahvichson

Slereah

Have you got an ocelot

I've got lots of ocelots

Give me all the ocelots you've got 'cause I like ocelots a lot

And I want lots and lots and lots of ocelots

0celo7

Are you trying to seduce me

ACuriousMind

Has the design of the review queue bottons changed recently? They look...flatter to me than a few weeks ago.

Slereah

I like how on Physics SE, you get one line questions by some layman

And then the top voted answer is CONSIDER THE IRREPS OF THE LORENTZ GROUP

blablabla

dmckee

16:19

@GPhys Factoid that might be interesting to you. If you break down MCAT results by college major, physics tops the list as most successful followed by math.

ACuriousMind

Wait...you only study medicine after already getting a another, unrelated degree in the USA?

I'll never understand your education system

David Z

@ACuriousMind yep

Medicine is a graduate-level degree

although many colleges do offer an undergrad-level concentration in premedical studies

which could be something like a minor

ACuriousMind

@DavidZ Well, here they flat out refused to split medicine into an undergraduate and graduate degree (since that split is only quite recently introduced through the Bologna process). It's one single six year long course here that usually (but not necessarily) awards you a doctorate in medicine at the end.

David Z

Ah, I see (also: only six years?!)

Combined programs are relatively rare in the US

ACuriousMind

@DavidZ It's well-known that the doctorate in medicine is generally not equivalent to a doctorate in other sciences (i.e. they mostly only spent the better part of a year on their thesis, if that much). Also, they are not yet specialists after those six years - for their specialty, there's another multi-year training period after that.

That training is not academic, however - it happens while they are already working as a general physician

ACuriousMind

16:50

What's going on at the moment? I run out of close votes every day, the queue is fuller than usual, and I see quite a few questions that are off-topic, but don't have any close votes. Have some people stopped voting to close or are we flooded with sub-par questions?

0celo7

Turns out half of my analysis class only brothers showing up on test day

I must be pretty stupid then, I would not be able to do that test without the lectures...

John Rennie

17:23

@ACuriousMind I suspect there are only a few of us dedicated enough to go through the queues every day, and we are just being swamped.

Unless we get the number of reviews per user increased (I vaguely recall SE are against this) or increase participation in reviewing the situation won't change.

dmckee

@ACuriousMind The question rate is up substantially since the LIGO announcement and many of those questions are from new users so I imagine that the rate of poor questions is up by at least the same fraction.

John Rennie

@dmckee Not good for the site though, is it?

357

@0celo7 :(

dmckee

If it persists that was I'd say it was very bad. In the past it has shaken out after a while with some the new users drifting off and a few accumulating rep and joining the ranks of the reviewers.

ACuriousMind

@dmckee But...many of those crap questions aren't even about gravitational waves! That's a weird correlation

Do people just start wondering randomly about physics when any kind of physics hits the news?

dmckee

17:27

@ACuriousMind Yep. I envision two scenarios. (A) A user comes to ask about gravitational wave and stays to asking everything else on their mind, and (B) a user googles about gravitational waves, find an answer on Physics and thereby becomes aware or us.

John Rennie

Chocolate and cleavage!

0

Q: Chocolate bar and cleavage

Why does chocolate bar usually break at the cleavages? The chocolate bar is less thick at cleavages.How can we relate thickness and fracture point of chocolate bar?

stress-strain

ACuriousMind

Far less exciting than the title promises :P

skull petrol

:P

ACuriousMind

@dmckee It's kinda sad to think that the fact that we're highly ranked on Google and have good answers is working against us in that way...

dmckee

@JohnRennie Great title.

@ACuriousMind Such is the price of fame.

skull petrol

17:36

Exactly^

0celo7

@dmckee $bucks burnt the crap out of this dark roast

I should have gotten French Vanilla

Danu

Yikes... Did the font change?

ACuriousMind

@Danu I think the promised serif font has arrived

Danu

Yikes... I don't really like it.

Is this supposed to go better with the math?

0celo7

Font on mobile has not changed.

At least not on iOS.

ACuriousMind

17:40

The math does blend in a lot better, imo

It'll just take a bit getting used to the different look

Look at comments with math in them in particular. I like it

skull petrol

hmmm...good point

Itachí Uchiha

Is this chat open for anyone?

skull petrol

Yup

Welcome

Itachí Uchiha

Thanks :)

skull petrol

:-)

Itachí Uchiha

17:47

what type of topics of discussion are not allowed?

ACuriousMind

@ItachíUchiha There's no restriction on the topics as such. You're just expected to behave like a decent human being

John Rennie

@ItachíUchiha I would avoid anything offensive or slanderous. Other than that talk about anything you want.

Itachí Uchiha

alright.gotcha

John Rennie

I love your question title by the way :-)

skull petrol

it has been appropriately edited

John Rennie

17:52

@ItachíUchiha And actually your question about the triple point is a good one. For a long time I've struggled to find an intuitive explanation for the existence of a liquid phase but never succeeded.

Physics Meta

1

Q: Is this question about the meaning of derivations on topic?

Are derivations of physical laws less important than the laws themselves? This question is attracting a lot of attention, but there is a significant disagreement about whether it's on topic. I want to bring it up here to give the issue more exposure. I don't think I can give any summary that wou...

discussion scope specific-question

John Rennie

@skullpetrol Boo :-(

skull petrol

not by me @JohnRennie

ACuriousMind

@JohnRennie I know, I'm a spoilsport, but question titles should be as informative as possible, so I phrased the title as the actual question

The cleavage is still there, just the potential for misunderstanding is less now

Danu

What??

ACuriousMind

17:55

@Danu What "What??"?

John Rennie

@ACuriousMind I would have made it Why do chocolate bars usually break at the indentations?, but cleavage is good :-)

David Z

@ACuriousMind just noting that in the long term, giving more reputation to deserving contributors is the "right" way to solve this. So in addition to whatever else we might do about it, go out and vote up some good posts!

ACuriousMind

@DavidZ Most people who are able to VTC and review just don't do it. (And I do upvote good posts! But lately I'm also haivng the issue that just voting on questions lets me run out of my daily 40 votes...)

Danu

@ACuriousMind I've been slacking for a few months now

But I, too, noticed the fuller queues recently

skull petrol

Why don't they give more votes to users over 30K @DavidZ?

David Z

18:00

@ACuriousMind that's true, of course. But the more people there are with sufficient rep, the more reviewers there will be.

@skullpetrol beats me, maybe check Meta Stack Exchange?

ACuriousMind

@skullpetrol The reviews and closures are supposed to be community actions. Giving more votes to very few users defeats the idea of the community moderating itself.

John Rennie

@PhysicsMeta Off-topic. It might make a useful discussion in chat, but it isn't a question about physics.

David Z

@JohnRennie of course that feedback would probably be more useful on the meta post :-P

John Rennie

@DavidZ but then I have to provide a reasoned and coherent answer! :-)

skull petrol

Derivation is not a question about physics?

David Z

18:04

haha

Well, I have an answer there, you can just vote on that if you're feeling lazy

John Rennie

@skullpetrol it's not about derivation. It's about the fact that for experienced physicists some things seem too obvious to be worth wasting time on

The OP is concerned because it's not obvious to less experienced physicists - which is a fair point.

0celo7

Is there a chat session right now?

ACuriousMind

@DavidZ I think your answer focuses on the wrong aspect. If there was a universally agreed upon standard of rigor across the physical disciplines, then the question would have a unique answer that is specific to physics. I'll write that as an answer later, but right now I have to go

John Rennie

@0celo7 No

David Z

@ACuriousMind sure, that's probably another discussion to have (I mean, among various reasons for considering the question off topic)

skull petrol

18:10

One could argue it is more a question of math.

Not that I would argue that way :)

David Z

Well, one could argue anything

skull petrol

True.

John Rennie

Have to go. Our SF discussion group is reviewing Darwin's Radio this weekend and it's 600 pages! I have some frenzied reading sessions ahead.

0celo7

@JohnRennie and I complain about 20 pages at a time for my lit class

skull petrol

See you later :)

David Z

18:17

I also have to go because it's after 2 AM :-/

skull petrol

Later pal

John Rennie

@0celo7 yeah, but I bet they don't read SCIENCE FICTION!!!

0celo7

@JohnRennie no, we read Puritan sermons and poetry

I'm painfully aware that we don't read Sci fi

dmckee

@JohnRennie Easy enough to convince some lit teachers to read Le Guin or Butler. It got some history at this point and takes on "serious" themes.

0celo7

@dmckee what about an early American survey course

dmckee

18:34

@0celo7 You're out of luck.

Danu

Is there any way to see the top users by number of helpful flags?

I'm curious how I do in comparison to other highly active users, but wasn't able to quickly find a relevant Stack Exchange Data Explorer query.

@ACuriousMind By the way, now that I went through my 20 votes of the day, the queue is small.

(maybe it wasn't just me going through, but I noticed a lot of 4-vote questions)

Itachí Uchiha

@JohnRennie Thank you sir. :)

0celo7

18:50

@dmckee I know I'm out of luck

skull petrol

Luck favours those that are prepared.

0celo7

@skullpetrol what

skull petrol

That is an old proverb.

fortune favors the prepared mind." - Louis Pasteur

0celo7

19:07

@skullpetrol I know

I don't see how that applies to my being in an early American lit class

user54412

@ACuriousMind @Danu Indeed it does blend well:

user54412

Danu

@ChrisWhite The texed version is much nicer though ^^

Yeah, mathrm is almost identical to this, I guess :)

user54412

Well, the lowercase e is a bit wonky in that image, but that's pixel aliasing

user54412

@Danu Yes, the non-tex numbers especially are a bit weird

Danu

19:10

even then

@ChrisWhite Yeah, the $0$ is way too round :P

user54412

They feel like what I'd expect in an accountant's log book from the 19th century or something

Danu

The font here hasn't change (yet?), though :)

I guess they don't change that, on any site

0celo7

@yuggib How does one actually read PDE books? I checked out that nonlinear stability of Minkowski space book that you said I should look at. There's pages and pages of equations.

Is one supposed to verify each of those?

How common is it for a book to randomly have 32 pages printed upside down?

skull petrol

Really?

I've never even seen one page like that.

32 out of how many?

I guess I don't read as much as you :P

0celo7

19:31

@skullpetrol 514

skull petrol

That's a significant percentage.

0celo7

@skullpetrol how much exactly?

user116211

19:47

@dmckee: Aren't the fonts in the main page looking different?

user116211

the new:

user116211

skull petrol

2 hours ago, by Danu

Yikes... Did the font change?

user116211

@skullpetrol They are quite beautiful!

skull petrol

20:00

Yup.

@0celo7 don't you have a calculator?

0celo7

@skullpetrol nope

user116211

@0celo7: You've Siri ;/

skull petrol

use google

0celo7

@user36790 in class

Also Siri is retarded

user116211

o.O

0celo7

20:06

I told her to call dad and she called the wrong Robert

I said "dad"

user116211

lol

user116211

Then?

0celo7

She called the wrong Robert!

user116211

siri is dumb!

0celo7

She's also called the wrong mom before as well

skull petrol

20:08

I like her answer to "divide by 0"

user116211

WTF!

0celo7

She goes to the first "Robert" and "Susan" in the phone book

Doesn't bother getting the last name right.

user116211

@0celo7: Ask her about Cortana.

user116211

@0celo7 Epic disaster from Siri :P

GPhys

@FenderLesPaul He emailed me back to schedule lunch while I'm visiting :D

0celo7

20:15

@user36790 I don't want Siri hating on my main bitch Cortana

Slereah

20:31

"The 2016 edition will be published in summer. PDG Books containing
Summary Tables and review articles as well as Booklets will be mailed in
fall. Starting this year, the Data Listings will only be published online."

Damn

I did good to register

This year's may be the last print edition of the particle data group book

0celo7

So?

Slereah

I want a big ass reference book in me library

skull petrol

Old school^

:)

0celo7

I want Beem et al in mine but don't have $300 for one book

John Duffield

21:39

@Slereah : an electromagnetic wave is not confined by its own gravity. If it was, we'd call the result a geon. Only we don't. Gravity is waaay too weak. We call it an electron.

0celo7

@JohnDuffield We've been over this

John Duffield

A geon is "an electromagnetic or gravitational wave which is held together in a confined region by the gravitational attraction of its own field energy". So what would you call an electromagnetic wave which is held together in a confined region by the electromagnetic attraction of its own field energy?

0celo7

@JohnDuffield I've never seen such an object

Physics Meta

1

Q: Was the new font incompletely implemented?

As you all might have noticed, our posts appear in a brand new font since today (as requested long ago. However, there are some places where the font has not been implemented, and this leads to some silly "design bugs". I took a screenshot of one of them (note the two different zeros), but I'm su...

discussion feature-request bug

0celo7

0

Q: Mistake in deriving the evolution equation for the shear of a congruence of timelike geodiscs in general realtivity

I need to give a bit of background before I come to my question: We are considering a congruence of timelike geodesics. The geodesics are parameterized by proper time $\tau$, so that the vector field, $V^a$, of tangents is normalized as: $V^a V_a = - 1$. The "spatial metric" $h_{ab}$ is defined ...

general-relativity geodesics

Wow!

Is that the longest question we've ever had here?

John Duffield

21:54

@0celo7 : what would you call it?

0celo7

@JohnDuffield I don't know what I could call it

I've never heard of such a thing

What would you call a unicorn that has a turtle shell and Einstein hair?

John Duffield

The g in geon stands for gravity. If the wave was confined by electromagnetism instead of gravity, what might you call it? Let's see now, how about something beginning with electro-, and ending with -on?

This is of course one of the tragedies of physics: "Matter tells space how to curve. Space tells matter how to move". Because curved space is not curved spacetime. The distinction is crucial.

OK I'm off to bed. Night all.

skull petrol

bye

0celo7

@JohnDuffield electron?

That's confusing -- why would we call that thing you described an electron

it's too close to the particle electron

Secret

22:10

@0celo7 All I see is there's a manifold R being glued to a torus . The gaussian curvature marked there requires R to be known, I guess

0celo7

@Secret Uhhh, what is $R$

Secret

I don't know, it is not written as $\mathbb{R}$ thus whatever it is it is not eucliduean

0celo7

@Secret Well, at least you identified a torus.

I didn't see that :P

Bernard Meurer

22:38

Hallo

skull petrol

hi

The writing of textbooks and making them freely available on the web is an idea whose time has arrived.

0celo7

23:12

physics.stackexchange.com/questions/238261/…

Seems interesting, too bad it got deleted

HDE 226868

23:26

@0celo7 At which point it went to Worldbuilding.

0celo7

@HDE226868 cool!

Transcript for