The h Bar

0celo7

15:00

Hmm, this is strange. JD's answer is -7 but why isn't mine +7?

David Z

yeah, seriously, let it go

skill patrol

^

OG

with a night stick :P

0celo7

Extended comment discussions are to be moved to chat.

I'm moving it to chat.

skill patrol

Have fun

ACuriousMind

@0celo7 Then, uh, move it out of the main chatroom?

skill patrol

15:02

^

GG

German Gangsta

ACuriousMind

The entertainment value of watching these "discussions" has long become smaller than any positive real number :P

David Z

@0celo7 doesn't mean anything goes in chat. But yeah, if you keep stuff out of the main chatroom you get more leeway. (where "leeway" should be interpreted as "people not caring what you're discussing")

skill patrol

good point

less chance of getting flagged

but JD flags stuff too

0celo7

@ACuriousMind hmm

I'm not entertained either

obe

I think the discussions are funny.

skill patrol

15:06

6 mins ago, by skill patrol

@0celo7 let it go

Danu

Don't make me post that video again...

obe

@0celo7 I am, though it's kind of like arguing with a rock.

David Z

@skillpatrol well, if things go south in a separate chat room, it at least doesn't bother anyone who isn't interested. When it comes to chat, a lot of moderation decisions come down to deciding what counts as disruptive behavior. Something that isn't disrupting other people's conversations is not such a big deal.

It's also a lot easier to tell anyone who doesn't like what's going on in a separate chat room to just leave.

0celo7

what's the topology of FLRW? Is it globally hyperbolic?

obe

hmm is it bad to go and answer old unanswered questions?

skill patrol

15:10

no, if you have a good answer you should share it :-)

ACuriousMind

@obe No, that is good!

David Z

@obe it's encouraged, and there's even a badge for it (if you get some upvotes)

0celo7

> Energetic students may compute the Riemann tensor

David Z

Actually I never quite understood the prohibition on "necroposting" that exists at many forums. I mean, given how a traditional forum works, I guess it makes some sense, but it seems like a silly thing to have to forbid.

0celo7

Anyone volunteering to be energetic?

@skillpatrol I don't want to.

skill patrol

15:14

@0celo7 that, my friend, is your choice :-)

0celo7

@skillpatrol Of course it's my choice.

I'm a voluntarist, you're going to have to try hard for me to not admit that...

skill patrol

just show some respect

0celo7

@skillpatrol Oh I'm a dumb kid, I don't show respect

I'm smarter than Einstein after all

skill patrol

wooo

0celo7

Bet Einstein couldn't do quadratic equations either

skill patrol

15:15

wooo wooo

0celo7

Bubb Rubb and Lil Sis: "Tha whistles go WOOO"

►

woo woo

skill patrol

you see that head band?

0celo7

@skillpatrol yes :D

skill patrol

respect THE nation

:D

skill patrol

15:28

Hi @ChrisWhite

0celo7

@ChrisWhite you're from CA, right?

Raiders, 49ers or Chargers?

skill patrol

np

0celo7

whoops :P

user54412

@0celo7 I'm from Caltech. Those words have no meaning to me.

skill patrol

he was probably at cal tech when the raiders were in LA

where we won a sb

0celo7

15:34

@ChrisWhite What?

user54412

Did you know Caltech is undefeated in football since 1993? ...when it disbanded the team

0celo7

UTK is undefeated since...fuck

Slereah

@0celo7 No pix yet

But basically

0celo7

Ricci scalar?

Slereah

The torus metric is already pretty trig heavy

I need to add a bump function to make the inside shorter than the outside (may involve trig)

0celo7

15:38

jesus wtf are you doing

Slereah

I need to make the other mouth asymmetric (involves $\cos(\theta)$)

And I need to make that assymetry time periodic $\cos(\omega t)$

Making the metric isn't too difficult but I fear trying to solve any equations in it

0celo7

what are you doing??

Slereah

Moving wormhole mouth

This is not the assymetry I had in mind

0celo7

@Slereah wtf

Slereah

Making assymetrical shapes isn't easy

Basically I need to vary the position with respect to z, so it depends on $\cos \theta$

And it needs to change with respect to the radius

Hm

0celo7

15:50

aren't wormholes woo?

Slereah

Well yes, but "woo" sounds fun

0celo7

maybe you should raise GDP or something

Slereah

Futurama: Fry's Woo

►

ACuriousMind

@Slereah Mathematica.SE is full of experts in assymetrical shapes.

Slereah

@ACuriousMind : Yes I know that thread :p

0celo7

15:51

@ACuriousMind lol

Slereah

I'll go ask them if I can't jury rig something

math.stackexchange.com/questions/301632/…

Also of interest

Not quite what I want but close

Dupin cyclide

In mathematics, a Dupin cyclide or cyclide of Dupin is any geometric inversion of a standard torus, cylinder or double cone. In particular, these latter are themselves examples of Dupin cyclides. They were discovered by (and named after) Charles Dupin in his 1803 dissertation under Gaspard Monge. The key property of a Dupin cyclide is that it is a channel surface (envelope of a one-parameter family of spheres) in two different ways. This property means that Dupin cyclides are natural objects in Lie sphere geometry. Dupin cyclides are often simply known as cyclides, but the latter term is also used...

The ring cyclide is pretty interesting, actually

Basically I have two things to put in

0celo7

those looks like the spinor dirac belt things

but they aren't blue

Slereah

Assymmetric mouth and shorter path distance on one side

bolbteppa

So that's what an electron really looks like :\

Slereah

This shape looks a bit naughty

0celo7

16:04

Well, now things are getting removed. Should I expect an email?

How many days?

Slereah

A tad better!

0celo7

Is that a donut?

obe

I barely see fenders here, what happened to him?

ACuriousMind

No one knows

Slereah

Hm

Might need to go in cylindrical coordinates to make it work

Slereah

16:36

Man that shape has like no symmetry

How to do it

Slereah

16:52

Not to bad

Could be better tho

skill patrol

have you tried the mathematica room?

Slereah

I probably should yeah

NeuroFuzzy

@Slereah what is that??

skill patrol

don't hold your breath...

Slereah

@NeuroFuzzy the worst donut

3

skill patrol

17:02

looks quiet in there

21 hours with no chat

Slereah

Hm

Thing is that I don't even know where to look

"Asymmetric torus" did not bring up a lot of results

skill patrol

you could ask on their main site

or search their questions

Slereah

Already did

math.stackexchange.com/questions/301632/…

closest I could find

Maybe I should throw in a bump function

So that the influence of the slant decreases with distance

But then it's gonna be pretty abstruse

skill patrol

I meant the mathematica site

ask there

Slereah

I suppose

skill patrol

17:09

mathematica.stackexchange.com/search?q=+torus+

John Duffield

17:23

@0celo7 : it's because my Einstein and the evidence trumps your Wald. As for Strauman, it's likely to be derivative. AFAIK the problem goes back to Wheeler.

@0celo7 : er, no, you aren't smarter than Einstein.

ACuriousMind

@JohnDuffield As we also told 0celo7, please do not continue this discussion in the main chatroom. Open your own if you want to discuss this further.

0celo7

@ACuriousMind Do daughter chats inherit the "be nice" policy?

Or can it be suspended by the owner of the room?

@ACuriousMind I know where he lives. I could find out.

@Slereah Do you know what the null geodesics of FLRW are?

ACuriousMind

@0celo7 The "Be nice." policy holds network-wide, AFAIK.

0celo7

@ACuriousMind Fine.

Slereah

I do not

0celo7

17:32

@JohnDuffield Give me your Skype so we can discuss this properly.

John Duffield

@ACuriousMind : it's a physics chatroom. If somebody wants to talk to me about some physics matter, I feel duty bound to respond. Or have I got that wrong? Is this a place where physics discussion is forbidden? Such that when David Z tries to start a discussion, it goes nowhere and gets knocked on the head after 18 minutes?

ACuriousMind

3 hours ago, by David Z

@0celo7 doesn't mean anything goes in chat. But yeah, if you keep stuff out of the main chatroom you get more leeway. (where "leeway" should be interpreted as "people not caring what you're discussing")

I'm pretty sure that was saying you two should take this discussion elsewhere, but you can ask him directly if you like.

0celo7

@ACuriousMind That's what I got out of it, too. @JohnDuffield we should take this to Skype and have a man-to-man talk.

David Z

@ACuriousMind no, that's not what I was saying. If I were saying to take this discussion elsewhere, I would have said "Take this discussion elsewhere." (more or less)

ACuriousMind

@DavidZ So, you're fine with these endlessly repeating discussions which regularly lead to flagging and need for mod intervention happening in this room?

David Z

17:44

I didn't say that either

0celo7

"need"

bolbteppa

lol

Slereah

Mathematica gave me a pretty good way to do it

Nice plot

But formula is a bit terrible :p

ACuriousMind

Well, what did you expect? :P

David Z

Let me say this: from my point of view this amounts to little more than a minor annoyance. But, @0celo7 and @JohnDuffield, it does seem that taking your discussion elsewhere would be a good idea. (Again, note that I'm not "ordering", just suggesting)

Slereah

17:56

Not gonna be too nice for calculations

Oh well

I'll stick with the one that looks okay

0celo7

@DavidZ Ok.

Slereah

Hoping that it will contains the correct physics

0celo7

Let it be known that I have invited @JohnDuffield to a Skype discussion. Username: revolver_0celo7

David Z

@0celo7 I don't think anyone else cares

0celo7

@DavidZ That's fine.

Slereah

17:58

Also maybe I should do a less awful one

Current equation has $e^{\cos(\theta)}$

Not too nice

0celo7

@Slereah $\mathrm{e}$

Slereah

Really I don't even need it to be particularly fancy

I just need to have one pole moving and the other stay relatively still

Ugh, and I need to stick a $\cos(\omega t)$ too in there

Dunno if I should use the Dupin cyclides

They look very nice for what I want

But they are kind of awful

ACuriousMind

I don't think you can expect something nice when you are searching for such strange things

0celo7

@ACuriousMind GR is strange?

Slereah

Yeah that is a problem

0celo7

18:03

Quantum supremacist!

Slereah

The less symmetrical it is, the more functions are in there

And I fear for the geodesic equation being solvable

ACuriousMind

@0celo7 No, I didn't say that at all

But, like Slereah says, setting asymmetry as a goal and expecting nice stuff to turn up is...optimistic.

Slereah

Just finding the metric from the parametric equation isn't fun :p

And that's just derivatives

obe

I need to e-mail a prof though I'm scared he will deny me.

Huy

don't be scared

obe

18:08

lol though

only 1 chance

then it's over forever

bolbteppa

I have a similar situation, terrified

Slereah

Hey look

I made a triangle

ACuriousMind

@obe Well, not emailing him won't get him to agree ;)

obe

hmm

do you think

I should wait until a few days before his lab work begins?

like in january?

ACuriousMind

Any actual reason to wait?

0celo7

18:18

@obe if you're doing well in school and in your university classes he won't deny you

obe

@0celo7 idk really.

@ACuriousMind to build more background.

0celo7

@obe what don't you know

obe

@0celo7 i'm bad at doing well and being successful.

ACuriousMind

@obe Well, if you think he could require specific things (not just in the vague "What if I don't know enough?" way) you don't have yet but will have then, it's reasonable to wait.

Slereah

18:31

Uh

Actually found a reasonably short expression for my thing

Well

It's still awful

Ghost

@tpg2114 let me know if the answer to your question can be awarded the bounty I set - physics.stackexchange.com/q/83671/94040

Slereah

Had to put a few sigmoid functions to reign it in :p

Oh well

I'll try the physics without the sigmoids first

See what happens

0celo7

@Slereah gg

0

A: Homotopy proof of the lack of foliation of the Gödel metric

What motivates the assumption that a closed timelike curve must cross a spacelike slice an odd number of times? Well, it isn't true as stated. Consider $\mathbb S^2\times\mathbb R^2$ as a subset of $\mathbb R^6,$ or just $$\{(a,b,A,B,y,z)\in\mathbb R^6:a^2+b^2=A^2+B^2=1\}$$ with the metric $...

Was so excited for a split second

Slereah

Yeah the metric has a tad fucked up signature

0celo7

see my second comment

Slereah

18:39

Let's write zee metric with a generic function $f(t,\theta,\phi)$ for the asymmetry

0celo7

Zee? Like A. Zee?

Slereah

Woops

Ghost

thank you @HDE226868 :)

0celo7

@HDE226868 Did you delete that >:(

Ghost

hope so

0celo7

18:56

@ACuriousMind indices i.gyazo.com/5135f89b67e0e699c25bd260fc92a88b.png

HDE 226868

@0celo7 I have no comment at this time.

0celo7

@HDE226868 As a Canadian citizen you must answer!

HDE 226868

@0celo7 Ah, but I'm not Canadian.

0celo7

@HDE226868 You can't fool me.

You're as Canadian as frostbite!

or maple syrup

or meese!

@ACuriousMind Does the variability of the fine structure constant imply the constants it is defined in terms of are variable?

Slereah

Phew

Metric is calculated

NeuroFuzzy

19:09

"The worst donut"

That explains everything I need to know

thank you

Ghost

@NeuroFuzzy mmmmm donuts....

Slereah

$ds^2 = -(\dot{f} + 1) dt^2 + ((c + f + a\sin(\theta))^2 + f_{\phi}^2 d\phi^2 + (a^2 + f_\theta^2 + 2a\cos(\theta) f_\theta) d\theta^2 + f_\phi (a\cos(\theta) + f_\theta) d\phi d\theta + (a\cos(\theta) + f_\theta) \dot f dt d\theta + \dot f f_\phi dt d\phi$

Pretty awful

Though it just reduces to the torus metric if $f = 0$

Ghost

hello @TanMath!

Slereah

$ds^2 = - dt^2 + (c + a\sin(\theta))^2 d\phi^2 + a^2 d\theta^2 $

f is the ugly asymmetry function

Let's check the Frobinius condition for a laugh!

ACuriousMind

19:27

@0celo7 What do you mean by "variability of the fine structure constant"?

TanMath

@Ghost hello!

Ghost

@TanMath how are you?

Slereah

Hm

The inverse matrix is a bit too hideous

grumble grumble

Gonna have to simplify it

0celo7

@ACuriousMind It runs with the energy level, no?

ACuriousMind

@0celo7 No, the fine structure constant is the value of that running coupling at zero energy scale.

Calling it "the fine structure constant" at other energy scales is misleading.

But, if you want to know which of its constituents is the one that also runs with the energy scale, it's the "elementary" charge.

Since that charge is basically just the coupling of the electron field to the gauge field, and couplings are the things that run

Slereah

19:42

heheh

Did the Einstein tensor of the raw wormhole spacetime

It has $\rho = \frac{\sin(\theta)}{a (c + a \sin(\theta))}$

The energy is positive for $\theta > 0$

Which is indeed the outside of the wormhole, technically

Hm, I wonder if I can change the metric by hand by fiat

Maybe a good first thing to do would be to find out a simple CTC spacetime with this

Add some cross terms, and find out if a line of constant $\theta$ is timelike

Err constant $\phi$

Let's see

Curve with vector field $(0,1,0)$ and some $f dt d\theta$ crossterm

Hm no, that doesn't work

the $d\theta^2$ terms needs to be changed

Either that or the curve needs to be slightly askew

0celo7

20:01

@ACuriousMind Good. Looks like another thing I'm right about that you know who isn't.

Ghost

"you know who"?

0celo7

Voldemort

Ghost

right

Slereah

Hm, even with the asymmetry thing no integral line of $\theta$ seems to be a CTC

Maybe I fucked up somewhere

or you need not integral lines

0celo7

@Slereah there's new comments on Timaeus' answer

Ghost

20:11

link

0celo7

Ghost

hilarious

0celo7

@0celo7 I only isometrically embedded the 4d manifold $\mathbb S^2\times\mathbb R^2$ into 6d in order to have a global coordinate system and avoid having to do a quotient, have multiple coordinate charts, and have the 3d surface naïvely/wrongly appear to have a boundary. $\mathbb S^2\times\mathbb R^2$ is a 4d manifold. And it is an answer because the first bullet point isn't a general phenomena, and so there isn't a general explanation. And I didn't even go for the trivial mistake in the post where obviously a CTC can cross zero times (because that error clearly isn't in Hawking and Ellis) — Timaeus 1 hour ago

ikr

uh

the thing that that comment is attached to

I still don't get it.

@Slereah does it make sense to you?

ACuriousMind

Why does everyone think "phenomena" is singular :(

Slereah

Well it certainly doesn't help with my question :p

0celo7

20:15

@ACuriousMind Humans are a strange phenomenae.

@Slereah THE ANSWER

he changed it

@ACuriousMind Do you understand the new answer?

ACuriousMind

@0celo7 No

0celo7

@ACuriousMind but you edited it :(

Did you try to understand it?

Or just brushed over it?

ACuriousMind

@0celo7 Look what I did - TeX and typo fixes

0celo7

@ACuriousMind That implies you read it.

And smart people read things and understand them.

ACuriousMind

@0celo7 Yes. That does not imply I understand it

0celo7

20:23

@DilithiumMatrix Wiener in the house!

ACuriousMind

I'm particularly missing the actual argument why the curve should cross an odd number of times.

@0celo7 wat?

0celo7

@ACuriousMind Exactly.

We have a surface embedded in the sphere and a closed curve...somehow this means an odd number of crossings?

Is that the gist of what he wrote?

@ACuriousMind Look at his profile picture.

Pornography, just like @Sofia said.

ACuriousMind

Jul 30 at 21:27, by 0celo7

I'm not even an adult.

confirmed again.

2

Ghost

Yup, noticed that too

0celo7

Literally an adult.

You ppl don't know what you're talking about

Ghost

20:27

yeah right

0celo7

...you doubt that I'm 18?

Ghost

don't care

0celo7

@ACuriousMind you're a meanie

Slereah

Guys

What's the signature convention in 2+1 D

And the determinant

If I pick $(+--)$, it will be $g=1$, but if I pick $(-++)$ then $g = -1$

Both are fine as long as it is consistent I suppose?

0celo7

probably

Physics Meta

20:36

0

Q: List of answers to "why can't ____ be explained by ____ instead?"

There are many questions which come up again and again, virtually every day, trying to propose an alternative explanation for a well-established principle. I think it would be very useful to keep a list of best-explanations for why the established principle is the established principle, for quic...

TanMath

@Ghost fine..

You?

Ghost

@TanMath very well - having a good day

TanMath

Great!

Slereah

Hm

Trying to think of a spacetime that's topologically trivial and has a Cauchy horizon before CTC formation

And no event horizons

I think that's only Ori

Because I am wondering how that works

I'm working with only 4 components so I guess subtleties might be involved

Oh wait, the TARDIS spacetime, maybe

Ghost

20:53

wibbly wobbly timey wimey stuff

0celo7

tardis spacetime?

what's tardis?

Slereah

$ds^2 = [1 - h(x,y,z,t) (\frac{2t^2}{x^2 + t^2})] (dx^2 + dt^2) + h(x,y,z,t)(\frac{4xt}{x^2 + t^2}) dx dt + dy^2 + dz^2$

ACuriousMind

@0celo7 I cannot fathom how many pop culture references you must miss in daily life :P

Slereah

Hm

0celo7

@ACuriousMind maybe?

is that the Dr who thing

ACuriousMind

20:55

Yes

0celo7

never seen it.

Slereah

Determinant is $[1 - h(x,y,z,t) (\frac{2t^2}{x^2 + t^2})]^2 - h^2(x,y,z,t)(\frac{16x^2t^2}{(x^2 + t^2})^2$

0celo7

f that!

Slereah

Second part is pretty negative I suppose

0celo7

@ACuriousMind Ok apparently my extremal problem --> geodesic problem via Maupertuis was the right answer

Slereah

20:56

And h is $\in [0,1]$

0celo7

@ACuriousMind Freire told me I need to convince myself of the details.

He also said I should read

amazon.com/Differential-Geometry-Symmetric-Graduate-Mathematics/…

Slereah

Which is... Not negative??? >:\

Dammit

0celo7

My reading list is stupidly long.

Slereah

Now I have to check by hand

Oh wait

Minus sign from the $dt^2$

It's all good

Hm

$x$ is never timelike, though

You need a fancy curve

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