The h Bar

0celo7

00:03

what direct evidence of spacetime curvature is there

Slereah

Stellar parallax around the sun

0celo7

no, that's direct evidence of light bending

Slereah

what would be evidence of spacetime curvature

0celo7

circles don't have 2pi circumference

ACuriousMind

Right, they have tau circumference ;)

Slereah

00:07

The bible says that a circle is 6 r

0celo7

where

@ACuriousMind has the usage of tau ever....

Slereah

"And he [Hiram] made a molten sea, ten cubits from the one rim to the other it was round all about, and...a line of thirty cubits did compass it round about....And it was an hand breadth thick...." — First Kings, chapter 7, verses 23 and 26

ACuriousMind

@0celo7 I don't even like tau all that much, just wanted to make a joke :P

Slereah

obvious evidence of space curvature

0celo7

@Slereah uh, what

Slereah

00:10

10 cubits diameter

30 cubits around

ACuriousMind

They had quantum computers back then?

Slereah

rimshot

ACuriousMind

::bows::

Slereah

Babylonian math also had $\pi = 3$

0celo7

@ACuriousMind have quantum computers ever

Slereah

00:13

Indian math had the area of a circle as $(d - d/9)^2$

ACuriousMind

The Babylonians also had a better fractional expression for it

Slereah

yeah

$3 \frac{1}{8}$

ClassicTelevisionBlog - Comedian Rodney Dangerfield

►

No respect at all

0celo7

$\pi=22/7$

NeuroFuzzy

$\pi=10$

Slereah

Pi Song [PMV]

►

ACuriousMind

00:15

$\pi = 3$ for large values of $3$.

Slereah

I had a professor who told us the physicist secrets for rounding pi

$\pi = 2, \pi^2 = 10$

NeuroFuzzy

@Slereah my eyeeeeessss

ACuriousMind

Great, now youtube will suggest MLP clips to me in the future :P

Slereah

Perfect

And Rodney Dangerfield, hopefully

Rodney Dangerfield My Wife

►

0celo7

@Slereah I should watch the third season of that.

related, but very NSFW -- audio)

good song btw

ACuriousMind

00:19

@Slereah Yeah, him too. I don't find him that funny.

Slereah

He is very old school comedian

Not really any overarching gag, just a bunch of jokes

ACuriousMind

@0celo7 lol, blocked in Germany due to GEMA.

0celo7

ARGH

Slereah

"I looked into my family tree, I found out I'm the sap!"

ACuriousMind

(don't worry, I don't wanna hear what's behind that title, anyway :P)

Slereah

00:21

"In the civil war, my great grandfather fought for the west!"

0celo7

@ACuriousMind D:

good song tho

also why is Germany 3rd world when it comes to music

ACuriousMind

@0celo7 Your taste in music is...not mine.

0celo7

@Slereah what

@ACuriousMind First two seasons were good.

ACuriousMind

@0celo7 I'll take your word for that.

0celo7

Does anyone here think my tastes are very strange?

I'm starting to think they are.

ACuriousMind

00:26

@0celo7 Yeah, you're a strange nerd like the rest of us ;)

0celo7

Seriously, what kind of person likes hard dance and gangster rap??

And I like linear shooters!!

D:

At least I don't like terrorcore.

Now that would be troubling.

Slereah

Guys

Let's make a law

If you write a paper with the goal of showing a new solution to some equation

You have to put a border around said equation

0celo7

"quantum fluctuation" = gulag

@Slereah why

Slereah

I am too lazy to read a whole paper for just a solution :V

0celo7

lol

Radical Redemption - The Black Demon (Full) [HD]

►

hard dance sampling rap = 10/10

ACuriousMind

00:34

Not blocked. I guess we don't consider that music :P

0celo7

It's Dutch, in case that matters.

Can something be "not music?" Is that even a thing?

ACuriousMind

Well, e.g. paintings are definitely not music ;) But you're correct, as long as it's sound that someone thinks is music, it's music.

As a counterpoint to the hard dance rap or what exactly that was, have some Vikings:

Amon Amarth "Twilight Of The Thunder God" (OFFICIAL VIDEO)

►

In unrelated news, why do we have youtube and xkcd oneboxing, but still no arXiv oneboxing?!

0celo7

@ACuriousMind You do know I listen to stuff that could be considered pleasant, right?

@ACuriousMind arXiv is garbage.

The real question: WHERE IS VIXRA ONEBOXING

@ACuriousMind oh god the vocals

I liked it until then

also why is the hair so long

actually, that's very catchy @ACuriousMind

ACuriousMind

00:52

@0celo7 Do they not have metal in America? Long hair is a very frequent sign of metalheads here.

0celo7

@ACuriousMind bites tongue

you did this on purpose

to get me riled up

ACuriousMind

Hmmm? You mean that I posted a band with long hair? Seriously, if you pick metal bands at random, I think you get long hair more often than not.

0celo7

::looks through album covers::

skull petrol

Oakland Raiders - The Autumn Wind

►

0celo7

what's the common factor?

skull petrol

00:56

That is music boy.

0celo7

ACuriousMind

Yeah, I get it, long hair is not frequent in the music you listen to :P

0celo7

@ACuriousMind interesting how that works

also all of these are scrawny Dutch dudes

hmm

another interesting observation

ACuriousMind

Perhaps you have a secret crush on @Danu? :D

0celo7

eh, Audiofreq is Aus

@skullpetrol lol

REAL MUSIC

Osborne Brothers - Rocky Top

►

skull petrol

01:00

:P

0celo7

ACM probably wondering what kind of barbarism American colleges foster

:D

skull petrol

...and never wants to be a raider

ACuriousMind

@0celo7 Mostly confused what those Osborne Borthers have to do with anything right now :D

That you foster barbarism over there is not news to me ;P

0celo7

first instance of long hair in my collection:

ACuriousMind

No Alicia Keys?

0celo7

01:04

Hmm

Not on this computer

besides, she has short hair on the "girl on fire" cover

something which AK would know

Damn, you're finally exonerated yourself.

ACuriousMind

B)

0celo7

It seems I did not transfer my Britney Spears, Cascade, Lady GaGa, etc. from my old laptop. I should do that.

So there's like no long hair now.

skull petrol

Hooray for chicks with long hair :P

0celo7

TS has long hair on the 1989 cover

so yeah, @ACuriousMind, no long hair

wonder why that is

I listen to a lot of European music, but no long hair

skull petrol

Like he said its a heavy metal thing now.

ACuriousMind

01:10

It definitely is

Although hippie types into reggae and stuff also tend to have it, but as dreadlocks

0celo7

ah

Lil Wayne has long hair

you got me!

skull petrol

And a face tattoo

0celo7

I'm a hypocrite

4

ACuriousMind

@0celo7 Ha!

0celo7

I think T-Pain has dreads too

damn, astronomer

you got me good there

perfect timing and everything

skull petrol

01:15

I don't think you can wash your hair in dreads D:

ACuriousMind

@skullpetrol If they're done right, you can.

Just not for like a week when they're fresh, I think

0celo7

ewwwww

they gross me out like nothing else

skull petrol

They are kinda creepy.

Especially the really long ones.

ACuriousMind

I think they're cool :|

skull petrol

Yep, if styled right.

But if not. Eeeeeew

imho

ACuriousMind

01:20

Hm, is it ewwwww or eeeeeew?

skull petrol

Which would you choose?

0celo7

@ACuriousMind they're nasty

ewwwwww

::shivers::

just straight up long hair is better than dreads

skull petrol

Some girls like the Nasty boys :P

0celo7

indeed

does long hair facilitate intelligence?

ACuriousMind

Of course, where else are the extra brain cells supposed to be

0celo7

01:27

:(

so that's why I can't math

@ACuriousMind does category theory have any real world applications?

ACuriousMind

@0celo7 Hm...not really answerable I'd say because almost all math you can do with it you could also do without it. (Unless you think math has no real world applications, then the answer is definitely no)

0celo7

>math has no real world applications

ACuriousMind

You could try asking that in the math chat if you really want an answer

0celo7

no, I think stuff like calculus can be used to...

you know :)

ACuriousMind

@0celo7 Ew, I've never used calculus for that

0celo7

01:35

@ACuriousMind there are calculus pickup lines :)

@ACuriousMind done

47

Q: Most striking applications of category theory?

What are the most striking applications of category theory? I'm trying to motivate deeper study of category theory and I have only come across the following significant examples: Joyals Combinatorial Species Grothendieck's Galois Theory Programming (unification as computing a coequalizer, Tatsu...

they think algebraic K theory is an application

o.o

ACuriousMind

@0celo7 They don't speak of application as in "real-world application" there

They speak of the application of category theory to a particular branch of math

0celo7

in Mathematics, 4 mins ago, by 0celo7

Hey guys, does category theory have any real world applications? Has it ever been used in an industrial process, etc.?

industrial process, etc. = ...

skull petrol

@ACuriousMind excellent use of the hyphen :-)

ACuriousMind

wat

0celo7

^

skull petrol

01:42

Real—world

ACuriousMind

still wat

0celo7

^

skull petrol

nvm :/

0celo7

still don't know what's up

ACuriousMind

I can't even decide if that was ironic or a compliment

skull petrol

01:46

A compliment

0celo7

still wat

skull petrol

Exact use of punctuation should be complimented.

ACuriousMind

!

0celo7

;

)

skull petrol

.

0celo7

01:49

laplace transforms tomorrow

yay

I can't stop thinking how handsome my avatar is

crazy

ACuriousMind

@0celo7 Is that an euphemism?

0celo7

only if you want it to be

are you really not a ginger

ACuriousMind

wat

My beard has a slight red tint, but no, I'm not ginger

0celo7

hmm, almost ginger

ACuriousMind

Why is that relevant?

0celo7

01:55

need to obtain math talent

-1

Q: How to determine whether two participants in the same event had equal instantaneous four-velocities at that event?

If two participants, $A$ and $B$, had met each other at one event $\varepsilon_{A B}$ then, for $A$ and for $B$ separately the values of average four-velocity, with respect to event $\varepsilon_{A B}$, can be determined for any other event which had been visited by $A$, or (separately) by $B$;...

general-relativity spacetime

holy crap

how many people in the world understand his ramblings

ACuriousMind

Meh, looks just like the others

0celo7

-1

Q: Are mass and angular momentum related at a quantum level?

Is the mass of an atom related to the amount of angular momentum it contains? It makes sense to me that since the waveform of an electron is much much larger than a particle in the nucleus that its relative angular momentum would be much less and thus its mass would be much less.

quantum-mechanics general-relativity mass angular-momentum

@ACuriousMind uh, what is that regge slope thing

is that mass and spin?

or some other relationship

ACuriousMind

@0celo7 Huh? Regge slope is the inverse string tension.

0celo7

it's called slope for a reason

it's the slope of some graph

now you think I'm insane

it's a real thing, I swear

arxiv.org/pdf/0903.5183v2.pdf

ACuriousMind

@0celo7 Hm, Regge trajectories can have slopes. Perhaps this is a relic from the times when the string theorists were trying to explain the strong force?

0celo7

02:05

@ACuriousMind yes!

that's why we have inverse string tension as a thing

if you read the dutchman's string theory notes he shows that if we have regge trajectories then the tension is the inverse of the slope

ACuriousMind

Ah, yes. The relation isn't really a relation between angular momentum and mass though, but between the angular momentum and the energy in the center of mass frame in a high energy collision.

0celo7

@ACuriousMind on page 249, what does he mean by "envelope of the fronts" (in the theorem)

@ACuriousMind angular momentum of what?

ACuriousMind

@0celo7 Total angular momentum in the center of mass frame, I think.

Since the experimental aim was to get a dependency between a scattering angle and the energy.

0celo7

ignore the envelope thing

there's a purty picture on the next page :)

how does one get nice looking diagrams like Arnold has

artistic graduate students?

ACuriousMind

I think there are/were people who specialize in producing such illustrations

0celo7

02:17

@ACuriousMind you should write a GR book with @Slereah and me

ACuriousMind

Today, if you're really determined, you can get TeX to draw them

0celo7

it would be fun

@ACuriousMind seriously

can you do that?

ACuriousMind

@0celo7 Yes, the tikz package is made for illustrations

0celo7

@ACuriousMind how long would it take someone to draw the diagram on page 493?

ACuriousMind

@0celo7 No idea since I don't know tikz that well

0celo7

02:19

@ACuriousMind so the calculus of variations class at my school has Arnold listed as a reference

ACuriousMind

Or any other graphics package

I can barely draw commutative diagrams

0celo7

and my ODE teacher recommended it for me...he also teaches that class

so tomorrow I'm going to annoy him about some exercises

give you a break

@ACuriousMind it's just arrows!

(yes, I've tried doing it before)

(I gave up)

ACuriousMind

That's what tikz-cd is for

0celo7

I have that in my standard TeX header

or whatever it's called

@ACuriousMind do you know anything about Morse theory?

ACuriousMind

Sadly not

0celo7

02:23

sadly?

is it interesting?

Riem. Geom. 2 Electric Boogaloo is all about Morse Theory

ACuriousMind

Yeah, it is interesting, the little I've heard

No lecture here on it

0celo7

We had a lecture two years ago on Ricci flow and the Millennium problem

now that I would have enjoyed

@ACuriousMind the main text for RG2 is amazon.com/Comparison-Theorems-Riemannian-Geometry-Publishing/…

oh my god

Hawking-Ellis is on the book list for RG2

...I must take this class

so the Riemannian geometry class covers most of HE, most of Wald and all this Morse theory crap :O

guess Freire likes GR

0celo7

02:43

@ACuriousMind "In differential topology, Morse theory enables one to analyze the topology of a manifold by studying differentiable functions on that manifold." wow

Galois in the Field

06:54

Pretending that $r^{-5}q_mq_mq_j$ was a real operator, can we simplify it somehow?

Huy

07:16

is it just me or do you need to specify what you mean

Galois in the Field

@Huy Hmm I originally thought so, but yesterday everyone just knew what I meant haha

Oh wait, I did say I was doing computations for the non-relavatisic hydrogen atom yesterday

Huy

ok

I need to go to some Lie groups lecture

see you later

Galois in the Field

Okay cya later

skill patrol

08:42

@ACuriousMind I think I figured out how the program selects the "highlights." It uses a combination of starred messages and if there are no starred messages then it uses the specific user requesting for highlights @ messages to highlight.

Hi @yuggib

Slereah

09:44

@Qmechanic : Hey are you 'round

Qmechanic

10:03

@Slereah : Hi.

Slereah

Hey

About your answer on compact support for tachyonic fields

Do you happen to know if there's any bibliography on the topic

I always end up on Baez's page

Which is weird

Is there no paper on the topic

Qmechanic

@Slereah : Concerning my answer here, I also ended up in Baez's page and links therein. I don't know of any reference on top of my head.

Slereah

There seems to be a pretty big blank of papers on classical tachyonic field after the original 70's papers

I know it's not a particularly useful field and all but I've seen way more obscure topics with a lot more papers

Also everyone always bases their answer on Baez which is a bit limited in scope

(not to mention that people conflate tachyons with tachyonic fields even when the question doesn't mention them)

I am wondering how well it generalizes to a more general case

Danu

10:43

@dmckee Heh, nice to see you on History of Science and Mathematics ;D

Slereah

11:07

"The fact causality is not violated no matter the sign of m2 is trivial: Causality properties of solutions of linear PDEs are always described by the principal part of the equation. It is gμν∇μ∇ν here, in all cases. The sign of m2 is irrelevant"

Whaaat

I am curious now

Danu

@Slereah Ask a question about it---I saw it too and was as intrigued!

Actually, I can also ask that question if you don't feel like typing it

Slereah

Well I already asked about tachyon fields in general

Feel free to ask

Danu

Aight.

skill patrol

hi pal

yuggib

@skillpatrol Hi ;-)

skill patrol

11:21

@yuggib how are you?

yuggib

Fine...a lot of work to do, but that's better than nothing to do ;D

skill patrol

yep

:-D

yuggib

how are you?

skill patrol

fine thanks

Slereah

Also this specifies linear solutions

But what about interacting tachyons D:

Which are the most interesting ones!

I should make some $Z^2$ theory of tachyons interacting with massive particles

See what happens

0celo7

11:29

@Slereah Riemannian Geometry 2 is based partly on Hawkinf-Ellis

Slereah

but HE isn't riemannian :O

0celo7

Course description is topics in Riemannian and Lorentzian geometry

Danu

0

Q: Can one classify partial differential equations according to the causality properties of their solutions (and if yes, then how)?

Recently, I bumped into this interesting comment by Valter Moretti which made me wonder about the following, more general question: Can we easily tell, just from the operators appearing in a differential equation, whether the solutions to this differential equation will turn out to violate causa...

mathematical-physics causality differential-equations

@0celo7 That sounds not very mathematical :P

Is it taught by a mathematician or a physicist?

0celo7

Mathematician

Apparently RG2 is just "Lorentzian geometry"

But the bookstore has a Morse theory book listed

Confus, will ask prof today

Slereah

11:45

Lorentzian geometry is just geometry of signature (p, q)

0celo7

@Danu How is it not very mathematical? My understanding is that HE is quite rigorous. At least, the first 6 chapters seemed rigorous to me.

0celo7

12:00

@ACuriousMind Freire refers to Hawking-Ellis as HE in the syllabus :)

ima.umn.edu/2006-2007/T9.15-16.06

seriously!?

Slereah

@Danu all hyperbolic equations are locally causal

But globally who the fuck knows

Danu

@0celo7 It's not a typical mathematician's choice.

Slereah

I think anyway

Might be specific rules about linearity or well behaveness

Danu

@Slereah if you can answer (part of) the question I'd like to encourage you to do so

Slereah

I would rather a math people actually answer

I am curious too

Danu

12:12

@ValterMoretti I'd be really interested in your view on this question I posted (if you think it's worth answering)

30 mins ago, by Danu

0

Q: Can one classify partial differential equations according to the causality properties of their solutions (and if yes, then how)?

Recently, I bumped into this interesting comment by Valter Moretti which made me wonder about the following, more general question: Can we easily tell, just from the operators appearing in a differential equation, whether the solutions to this differential equation will turn out to violate causa...

mathematical-physics causality differential-equations

Galois in the Field

Lie algebra $gl(n)$ is spanned by $n^2$ generators with $[a_j^i,a_l^k] = \delta_j^k a_l^i -\delta_l^i a_j^k$ but is that the commutator bracket in the first place?

I imagine it is since all matrix lie algebras have used the commutator bracket in the past

John Duffield

@Slereah : curved spacetime isn't curved time and curved space. It's inhomogeneous space. Einstein referred to it here. If you plotted the inhomogeneity using eg light clocks at various elecvations, your plot would be curved.

Slereah

Oh hush

John Duffield

@0celo7 : I've just been busy. I've got a lot on next week too.

skull petrol

Hello Sir.

John Duffield

12:20

Hi skull patrol.

@Sleareah : you keep confusing curved spacetime with curved space.

skull petrol

Is there curved time?

Can space exist without time? @JohnDuffield

Or vise versa?

What does Einstein and the evidence say about this question?

Seriously, if you @JohnDuffield read his book for high schoolers you would know his answer to these questions.

0celo7

12:58

@Danu Semi-Riemannian geometry is also used.

The book by Oneil

ACuriousMind

@GaloisintheField Yes

Galois in the Field

@ACuriousMind Thanks

ACuriousMind

It is an exercise to show that the Lie bracket of matrix groups is just the commutator, though

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