The h Bar - 2015-11-06 (page 4 of 4)

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6:00 PM

Also has one about insects in an asteroid orbiting a black hole discovering Newton's laws

Stephen Baxter did some nice books, too

An interesting physics one is "Flux"

About neutron star people

He made up a whole ecology of neutron star critters

Eureka: A Prose Poem, an essay written in 1848, included a cosmological theory that presaged the Big Bang theory by 80 years,[122][123] as well as the first plausible solution to Olbers' paradox.[124][125] Poe eschewed the scientific method in Eureka and instead wrote from pure intuition.[126]

Edgar Allan Poe

Edgar Allan Poe (/poʊ/; born Edgar Poe; January 19, 1809 – October 7, 1849) was an American writer, editor, and literary critic. Poe is best known for his poetry and short stories, particularly his tales of mystery and the macabre. Widely regarded as a central figure of Romanticism in the United States and American literature as a whole, he was one of the country's earliest practitioners of the short story. Poe is generally considered the inventor of the detective fiction genre and is further credited with contributing to the emerging genre of science fiction. He was the first well-known American...

6:37 PM

@ACuriousMind I think I've conned my LA TA to meet with me later and look over all of my extremely boring and tedious Arnold proofs :D

let's see if he's as patient as you

I'd say no

@Huy f u

Michael is a nice guy

ACM too

ACM is a serial shanker!

Shankist?

ACM?

6:39 PM

I'm not Shankar

Shawshank Redemption?

@ACuriousMind never said you were

@Ghost That would be me :P

One of you knows quantum mechanics ;)

ah yes! of course!

6:40 PM

who coined ACM

@vzn apparently

it seems you have a fan club, ACM!

Jan 19 at 17:10, by vzn

hi ACM. ok. thats basically it right there. its based on a question by TK cited at the very beginning of the chat. & other brief intro there etc.

vzn did

@ACuriousMind I can search, too. Hence why I said vzn

@0celo7 Yeah, but you didn't show us the evidence ;)

@ACuriousMind @Huy what does a little circle on top of a set mean?

6:42 PM

ah, but ACM can search and quote!

interior @0celo7

@Huy ::attempts to figure out why the author is taking the interior of an open set::

odd

can you give context?

oh, he defines the ball as closed.

that explains it!

lol

6:43 PM

Anyone ever try special relativity on a cylinder?

who has closed balls

It's really weird.

My coworker and I messed around with it yesterday.

is the cylinder an affine space

@Slereah spent the last days doing GR on the worst torus.

@0celo7 I dunno. Who cares?

6:44 PM

Which worst torus

@DanielSank you need an affine space to do SR!

@0celo7 What's an affine space?

@DanielSank beats the hell out of me!

that's why I'm asking :P

looked it up?

@DanielSank: What, exactly, do you mean by "doing SR"?

6:45 PM

@Ghost I do know what it is

I just don't know how to tell if a space is affine or not

I see

@DanielSank care to report results?

researchgate.net/profile/Tatiana_Livshits/publications

very unfortunate transliteration of the last name

@ACuriousMind Er, trying to figure out what happens if you have a constant speed of light but you live on a cylinder.

@DanielSank Is the cylinder my space or my spacetime?

@ACuriousMind Spacetime. We made space periodic and time the infinite axis.

6:48 PM

what is in the cylinder?

@0celo7 Well, I think there's a preferred frame in which you age the fastest.

@Ghost I mean, space is 1D, but you make it periodic. Then adding a time axis makes a cylinder.

@Ghost $S^1\times R^1$?

oh in

There is a paper about the twin paradox on a circle

the cylinder in this sense has no "interior" to speak of

@Slereah Yeah, so what we found is that the twin paradox still isn't a paradox.

6:50 PM

Inside the cylinder is azathoth

could azathoth kill Cthulhu?

spooky (and awesome)

Who knows

Lovecraft never really developped the mythos

For him it was just flavor text

the point was that they were unknowable

although I think Azathoth created this universe, so probably

is Cthulhu's classical image the way humnans perceive him or is he really an octopus dragon

I dunno

6:52 PM

well start knowing!

The point that some authors didn't get was that the mythos wasn't about spooky monster gods

what was it about

It was about powerful entities in an indifferent universe that we cannot comprehend

boring

I like the first version better

In modern terms it's not very spooky

"Oh no the universe isn't about us"

6:53 PM

@Slereah ahhh mathematicians then

@Ghost oh please

Basically the elder gods were aliens more than gods

we all know the sociologists are the nutcases

@DanielSank By results I meant some math. What did you do?

How did you do SR on the torus?

@0celo7 : Carefully

IIRC the Lorentz group doesn't work anymore

user image

6:55 PM

@0celo7 I don't understand the question. We just tried to figure out what happens if you apply the postulates of SR to a 1D periodic space with infinite extent time axis.

@DanielSank Pls do that here. I'm interested.

@0celo7 I believe the result is that there is a preferred "rest" frame.

In that frame, the universe is of length $L$.

@DanielSank Proof?

In all other frames it is shorter.

@0celo7 Well, note that a cylinder is flat.

It's just a flat sheet where you roll it up along two of the edges.

So, you can make your world lines on the flat sheet, transform them as you normally would with the Lorentz transforms, and then roll it up to see what you get.

Lines parallel to the edge which gets rolled up are at "rest".

Other lines will wrap around the cylinder and eventually meet back up with the rest line.

This is odd, because if I'm moving relative to you, you would predict that my time goes more slowly.

Yes, at different proper times.

6:59 PM

But because space is periodic, we can meet up again without me accelerating.

It's not odd, it's relativity with a compact dimension :P

1

Q: Proper times of two observers in a three-torus

Consider two observer in a tree-torus space of size $L$. Observer $A$ is at rest, while observer $B$ moves in the $x$-direction with constant velocity $v$. $A$ and $B$ began at the same event, and while $A$ remains still, $B$ moves once around the universe and comes back to intersect the worldlin...

special-relativity symmetry reference-frames topology

@DanielSank Let us continue this later. I have to eat lunch and meet with a TA.

Going through all of this carefully we came to the conclusion that someone in a "moving" frame sees space as being shorter in length.

@0celo7 k

Anyone going to APS March meeting?

Abstracts are due today.

@DanielSank Well according to Lubos Motl everything you did is wrong?

7:02 PM

@DanielSank Length contraction is normal though, isn't it?

@ACuriousMind Yeah but normally space isn't compact.

@ACuriousMind What Lubos is saying there confuses me. Are we not allowed to have RxS spacetimes?

@0celo7 Why is there a question mark on that sentence?

@0celo7 When you live on a ring you can associate a total length to it.

I think there are inertial frames on the ring which actually reduce its length.

@DanielSank have you heard of Ted Shifrin before?

who is Ted Shifrin?

7:06 PM

@0celo7 He's saying the resulting spacetime has no notion of Lorentz invariance

MSE user

@skullpetrol Yes.

@Ghost Author of math books, among other things.

ahh very nice indeed! great to have an author on board!

Well there is Lorentz invariance

But the group isn't $SO(3,1)$

I think you need a fancy group on a torus

@Slereah Well, "Lorentz invariance" usually means invariance under the Lorentz group :P

7:09 PM

I dunno

Should be at least locally invariant under Lorentz

I think it's a restriction of the Lorentz group

$O(3,1)/\mathrm{some shit}$

best equation ever

I think the cylinder one is $\mathrm{SO}(1,1;\mathbb{Z})$

Where...I'm not sure what $\mathrm{SO}(1,1)$ actually is, checking...

De Sitter invariant special relativity

In mathematical physics, de Sitter invariant special relativity is the speculative idea that the fundamental symmetry group of spacetime is the indefinite orthogonal group SO(4,1), that of de Sitter space. In the standard theory of general relativity, de Sitter space is a highly symmetrical special vacuum solution, which requires a cosmological constant or the stress–energy of a constant scalar field to sustain. The idea of de Sitter invariant relativity is to require that the laws of physics are not fundamentally invariant under the Poincaré group of special relativity, but under the symmetry...

^Special relativity for De Sitter space

Dunno about cylinder, though

Isn't $1,1$ just like

Hyperbolic rotations

also what is the $;Z$ here

@Slereah Coefficients in $\mathbb{Z}$.

@Slereah And yes

Is it like $SO(1,1)/\mathbb{Z}$

7:15 PM

No

Hm

It's the matrices from $\mathrm{SO}(1,1)$ which only have entries in $\mathbb{Z}$.

But I'm not sure if this is the one for the cylinder

yeah can't find a lot of details about SR in a cylinder

You need to find all hyperbolic rotations which preserve the boundary conditions

Let's say the boundary condition is identifying $x = x+1$

Then a hyperbolic rotation $H$ needs to send $\binom{t}{x}$ and $\binom{t}{x+1}$ to $\binom{t'}{x'}$ and $\binom{t'}{x'+n}$ for some integer $n$.

true

Discrete Lorentz group or somesuch

7:21 PM

Why does physics suck

This is too complicated

Physics is the best and this is not that complicated (have been following this discussion)

Now, the hyperbolic rotation does $x' = \sinh(\alpha)t+\cosh{\alpha}x$ and $(x+1)' = \sinh(\alpha)t + \cosh(\alpha)x + \cosh(\alpha)$. This gives $\cosh(\alpha) = n$. Now, since $\cosh^2-\sinh^2 = 1$, we have $\sinh(\alpha) = \sqrt{n^2 - 1}$, and so the cylinder group is matrices $\left(\begin{matrix} n & \sqrt{n^2 -1} \\ \sqrt{n^2-1} & n\end{matrix}\right)$ for integer $n$.

neat

Wish Chatjax worked on phone

What is (x+1)'

@0celo7 You should've been faster deriving that on a piece of paper than me typing that in LaTeX :P

7:26 PM

@ACuriousMind I don't like reading TeX code is all

I can do it, of course.

But wait

If not all frames are lorentz doable, what happens if the speed of the spaceship isn't a rational number of the length of the cylinder :O

I guess then it is not invariant

@Slereah Interestingly, for irrational speed the ship never returns to its original position ;)

'irrational speed' - sounds like when my brother drives

3

7:40 PM

Things get even worse if you also compactify time :p

especially if you do it poorly

You can see that that completely destroys every invariance since $\sqrt{n^2-1}$ is never an integer for $n\neq 0$.

@ACuriousMind Proof?

Hm, well, you can probably save one transformation by choosing the time radius correctly, but you're right, probably not a good idea

@0celo7 Left to the reader.

Bullšit there's no one throwing a bra at you

Although that should read $n>1$ instead of $n\neq 0$.

@0celo7 How do you kno

7:45 PM

You would have not responded if there were :P

not necessarily

Lol now he's gonna leave

maybe he has something to be completed, or a TV show to be watched...

@ACuriousMind What about $n= 1$ :p

@ACuriousMind : IIRC for toroidal spacetimes the identification length of time and space must be rational

Otherwise you encounter troubles

Basically no field can exist except for constant fields

and tribbles

7:52 PM

7 mins ago, by ACuriousMind

Although that should read $n>1$ instead of $n\neq 0$.

:P

@Slereah Nothing exists, so no troubles. Looks alright to me.

good times

@Ghost Well, as fast as they reproduce, they are going to fill the entire spacetime

Also, irrational speed sounds more like

user image

@MarkMitchison long time no see!!

@ACuriousMind so very true

@Slereah and that is definitely my brother's driving

7:56 PM

Hm, so anyway

The only paper on non-time orientable spacetimes gives the metric as $X_1 = \cos(\pi x) \partial_x + \sin(\pi x) \partial_y$, $X_2 = -\sin(\pi x) \partial_x + \cos(\pi x) \partial_y$, $g(X_1,X_2) = -1$ and $g(X_1,X_1) = g(X_2,X_2) = 0$

So $cos^2 g_{xx }+ sin^2 g_{yy} = sin^2 g_{xx} + cos^2 g_{yy} = 0$

heheh

That's tricky! :P

Damn, what did he remove

So... $g_{xx } = - \tan^2 g_{yy}$

I feel like he's hiding something from me

@Slereah How did you get that?

8:04 PM

Oh wait

I guess I do divide by zero possibly while doing it

No matter, let's push on and see what happens!

$g_{xx} = -\cot^2 g_{yy}$ on the flipside

Hm

When is the tangent equal to the cotangent

user image

Apparently various multiples of $\pi/4$

I don't see how you get any of these equations

$\cos^2 g_{xx} + \sin^2 g_{yy} = 0$

$\cos^2 g_{xx} =- \sin^2 g_{yy}$

$ g_{xx} = -\tan^2 g_{yy}$

oO

wot

Wait. What is the argument to the $\cos$ or $\sin$?

8:08 PM

$\pi x$

Ah. Carry on then

It's always the same so I'm not writing it

Your notation is confusing because people commonly omit the brackets in arguments to $\sin,\cos,\tan$.

I.e. they write $\sin^2\theta$ and mean $\sin^2(\theta)$.

So we have $g_{xx} = -(\frac{\pi}{4} + n \frac{\pi}{2}) g_{yy}$

For the cross term now...

$g(X_1,X_2) = - g_{xx} \cos \sin + g_{yy} \sin \cos + g_{xy} (\cos^2 - \sin^2) = -1$

$\cos \sin (g_{yy} - g_{xx} )+ g_{xy} (1 - 2\sin^2) = -1$

Hm

Getting complicated

$\cos \sin g_{yy}(1 + \frac{\pi}{4} + k \frac{\pi}{2} )+ g_{xy} (1 - 2\sin^2) = -1$

Why didn't he just write the metric

Hm

Let's use

AN ANSATZ

I'm pretty sure $g_{xx}$ and $g_{yy}$ are trig functions

$\cos^2 (a \cos + b \sin) + \sin^2 (c \cos + d\sin)= 0$

bluh bluh bluh

$a\cos^3 + b \cos^2\sin + c \sin^2 \cos + d\sin^3= 0$

Hm

Not overly illuminating

Really it just seems to be rotating counterclockwise as $x$ increases

Pretty sure $g_{xx}$ should just be $\sin(\pi x)$

So that product should be... $\sin\cos(\cos + \sin)$?

That is not 0 tho

Hm

user image

I forget where I got this picture

Hm, there's a bit on time orientation in Hawking-Israel

But no metrics either

8:48 PM

user image

That's how you start a book :p

user54412

9:09 PM

"By Lorentzian is meant..." -- English not is.

user54412

@0celo7 Freeman did. He said he was sort of a crotchety old man by that point. Probably would have been better to settle down at a university rather than the IAS, since he wasn't forced to have students or interact with anyone.

Oh right, Freeman is still alive

user image

Well, I suppose

It's hard to tell from the photo

9:42 PM

@Slereah : That sounds a bit disrespectful to the old.

I one day too will be old

And will feel the chilly breeze of death

user54412

9:56 PM

Pretty sure Freeman could GR-ify your torus, while simultaneously sipping tea and fighting Nazis.

5

@Qmechanic What have the old done for me lately

Probably

Hey Freeman, are you on Stack Exchange

We need your wisdom

@0celo7 why should the old do anything for you?

Wait what did Freeman do in GR?

I only know his QFT contributions

@ChrisWhite Caltech has brainwashed you

Was Feynman even a physicist

9:58 PM

Freeman

Freeman Dyson

user54412

@Slereah I don't know of anything actually. He probably considered it too easy.

Or Gordon Freeman, possibly

user54412

The Free-man.

I do love Gordon Freeman's thesis title

"Observation of Einstein-Podolsky-Rosen Entanglement on Supraquantum Structures by Induction Through Nonlinear Transuranic Crystal of Extremely Long Wavelength (ELW) Pulse from Mode-Locked Source Array "

Although it means he is a filthy experimentalist

Fu too

10:00 PM

'filthy experimentalist"?

He is not part of the glorious theoretical physicists

Says the ~~engineer~~ programmer

Like Dr. Kleiner, probably

Although

I think most people at Black Mesa were experimentalists

vignette3.wikia.nocookie.net/half-life/images/d/d2/…

experimentalists and theoreticians have equal importance and their work is of equal respect

10:17 PM

@Ghost really?

any idiot can measure things

@ACuriousMind lol

if you say so

so experimentalists not welcome here, according to you, @0celo7?

@ACuriousMind Michael gave up trying to explain AoC/Zorn's lemma

I'm biologically incapable of understanding it

@Ghost I get reminded of my place in the order of things on a daily basis

I think that theorists secretly believe themselves to be higher

openly...meh? not sure

@0celo7 not really, other than @Slereah's nonsense statement above

23 mins ago, by Slereah

Although it means he is a filthy experimentalist

@Danu I asked a grad student about a geometry proof, his immediate reaction was to grab Lee and see what he said about it :D

@Ghost he's not very subtle, the others are

user image

10:24 PM

so am I wasting my time with this site then?

user image

maybe

dunno, I'm still here and I'm a mere engineer

I'm literally shit at life

and I think I get stuff out of this site

Reminder: People are bad at telling irony through the internet.

@ACuriousMind not all of that is ironic though

@0celo7 Did I say that? Precisely if you didn't mean all of that to be ironic/serious it's difficult to tell.

@Slereah lol, not sure if conference organizers are demigods or poor bastards based on that

10:29 PM

interesting

@ACuriousMind what does that even mean

@0celo7 What it says. Stop questioning my utterances :P

in any case, I like to think of my chat comments as interpretive art

interpret it any way you want, but I'm not liable for any f'ed up stuff you do in response or whatever

Ah, the motto of the troll.

dude

why do I get called a troll everywhere I go

user54412

10:33 PM

...

user54412

So there's a job posting that's right up my alley at MPE Garching...

@ChrisWhite go for it!

MPE Garching?

@ChrisWhite What would you do there?

Germany!

@ACuriousMind physics

user54412

10:34 PM

@ACuriousMind theory and computation of black hole accretion, apparently

does that have any applications?

user54412

@0celo7 At least as many as whatever ACM is up to these days :P

greater than or equal to 0, got it

@HDE226868 hello

@0celo7 Hi there.

Are you ever off of chat?

@HDE226868 Yes, what kind of question is that

I'm cleaning my room now

user54412

10:38 PM

@ACuriousMind Does extraterrestrische have the same connotations in German as extraterrestrial in English?

just got back from my TA's office

@ChrisWhite Not sure what the connotations in English are, but the average German will directly associate that word with "Aliens"

Note that "aliens" does not mean "illegal immigrants" in German

afaik

might have changed

Ah, yes, it means beings from outer space, not from next door :P

but of course "extraterrestrials" means "space aliens" in English

user54412

10:40 PM

@ACuriousMind Ok so MPE sounds just as strange in both languages.

@ACuriousMind ew where are you living that there are aliens next door

Area 51?

does Germany have an Area 51?

Not as far as I know, but perhaps ours is just better in being secret

Flächeninhalt ein und funfzig

Germany has the nazi UFO

@ChrisWhite Probably

And the nazi time machine

Lots of nazi stuff in Germany

10:43 PM

> Flächeninhalt

Yeah, I don't think they'd call it that :P

Perhaps they didn't want to be just another institute for Astrophysik

@ACuriousMind or you're a sheep

The nazi time machine thing is pretty hilarious

Flächeninhalt 51 is gold :D

Die Glocke (pronounced [diː ˈɡlɔkə], German for “The Bell”) was a purported top secret Nazi scientific technological device, secret weapon, or Wunderwaffe. Described by Polish journalist and author Igor Witkowski in Prawda o Wunderwaffe (2000), it was later popularized by military journalist and author Nick Cook as well as by writers such as Joseph P. Farrell and others who associate it with Nazi occultism and antigravity or free energy research. According to Patrick Kiger writing in National Geographic magazine, Die Glocke has become a popular subject of speculation and a following similar to...

"According to Witkowski, he was shown the allegedly classified transcripts in August 1997 by an unnamed Polish intelligence contact who said he had access to Polish government documents regarding Nazi secret weapons"

pretty legit

Really how do the people who write those books even come up with it

10:45 PM

imagination

user54412

Hmm, looks like there are also recent postings for jobs in Heidelberg and Zurich...

Well yes but why use even things that stupid

I mean if you're gonna make it up

At least go big

Lie the hell out of it

each to their own

Say that there are plenty of nazi documents about it

Not some unamed polish SS officer

adds an air of mystery

11:04 PM

@ChrisWhite Anything at ORNL?

Hmm, I can't access PSE

@0celo7 :

We are investigating an issue with our Load Balancers

Tweeted by StackStatus on November 6, 2015 at 11:04 PM

@Loong kk

11:55 PM

Oh no

I added a term to that wormhole thing and now the geodesic eq is slightly more difficult

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