The h Bar

7:00 PM

@0celo7 You can simulate any Turing machine inside it

@BalarkaSen saw that in a fun doc recently that has a lot on notch, recommend it, bet youll like it. have you ever tried minecraft? imdb.com/title/tt2087878

0celo7

@ACuriousMind Ugh, help

John Duffield

I do think Gerardus 't Hooft is making a mistake putting things like this up on the internet: staff.science.uu.nl/~hooft101/gravitating_misconceptions.html

no_choice99

turing complete means you can program windows 10 in it

ACuriousMind

@0celo7 What's up?

no_choice99

7:06 PM

what do you mean john duffield, it's error 404 not found

ACuriousMind

If it's anything technical I'm afraid my brain is burnt out for the day :P

0celo7

@ACuriousMind my thesis is taking too long. I found a big mistake that no one knows how to fix

no_choice99

how so @ACuriousMind ?

vzn

@JohnDuffield its "[text](url)"

0celo7

my advisor won't let me ask the author or MO though

ACuriousMind

7:06 PM

@0celo7 ???

Why on earth not?

no_choice99

how did you get a brain burnt AcuriousMind?

vzn

@JohnDuffield he is too ~~old~~ established to care, cf smbc "aging physicists" :P

John Duffield

@no_choice99 : yeah sorry, I got the brackets back to front.

0celo7

@ACuriousMind "I wouldn't ask MO about this specific issue either. ... In general, it is a very bad idea to advertise to the world (or even to your colleagues) what you're thinking about. You should really try to exhaust every possibility of settling questions on your own (or with people at your department) before asking the internet
or people elsewhere. It's a competitive profession, and good questions are few and far between."

ACuriousMind

@no_choice99 By jumping between half a dozen different topics all day

Balarka Sen

7:08 PM

@vzn Admittedly not

ACuriousMind

@0celo7 That right there is what's wrong with academia :P

Balarka Sen

^

ACuriousMind

But tough luck for you, I guess

John Duffield

@vzn : he will care when he finds out he's got some strange misconceptions of his own.

vzn

@BalarkaSen worlds 1st $2.5B video game and notch is worlds 1st $1.3B coder o_O

ACuriousMind

7:09 PM

@0celo7 Is that big mistake somewhere "early" so you don't have anything at all to show without it being fixed?

If not, you might still have enough for a thesis, just not the complete work you wanted to have

vzn

@JohnDuffield (have ~~cyberstalked~~ tracked him some...) he has an SE acct & some posts on Physics, now maybe inactive, look up the one where he complains nobody takes him seriously, its my favorite :P

0celo7

I have more than enough for two theses already.

I was going to make it a triple, but maybe not now.

no_choice99

I see @ACuriousMind but you're a genius :)

ACuriousMind

@0celo7 Well, then I don't see an immediate problem. After the thesis is done you can still consider going against your advisor's advice and asking the author directly.

0celo7

But it's a very worrying error. The paper is very famous in my field.

Well, "error." I'm trying to come up with a counterexample but it's hard.

I think I can prove all of the "usual" things are true by using some newer results.

John Duffield

7:12 PM

@0celo7 : welcome to my world.

ACuriousMind

@0celo7 If you want to be "competitive" and you find a counterexample, you could also try to publish the counterexample. Although I personally would very much dislike doing that without asking the author first.

0celo7

@ACuriousMind My advisor said a counterexample would be publishable.

ACuriousMind

So you don't have an actual problem, just more work ahead of you ;)

0celo7

The author of this paper has no competition. His name rhymes with Yau.

vzn

@0celo7 are you joking? only 1 of the most important math concepts from 20th century dude, strongly running into 21st :P vzn1.wordpress.com/2016/01/22/…

0celo7

7:14 PM

@vzn Why would I be joking?

Can't be too important if I don't know what it is.

vzn

2 days ago, by Slereah

@0celo7 is incapable of expressing any genuine sentiment

2 days ago, by Slereah

He has caught the irony flu

0celo7

@Slereah How dare you spread vicious rumors

vzn

@0celo7 lol, said the drunk searching for his keys under the streetlight :P

ACuriousMind

@0celo7 Oh, so you can be the young upstart who found an error of Yau...or the young upstart who thought he found an error but overlooked something and embarrased himself by publishing it - and that's precisely why I'd ask the author first, but maybe make sure somehow to establish that it was you who found the counterexample first.

vzn

@0celo7 try reading about hilberts 10th problem if youre allergic to Computer Science :P

ACuriousMind

7:18 PM

@no_choice99 I'm...really not, but thank you for the flattery nevertheless :P

vzn

@0celo7 BM has mentioned it in here quite a few times & has some nice refs eg a recent one by aaronson re ZFC consistency etc

0celo7

@ACuriousMind My advisor sent me a list of counterexamples to try -- none of them are actually counterexamples. We've basically exhausted all of the "standard" manifolds. So maybe there's not an error with the conclusion, but the proof is definitely shady. This is why I think I should ask on MO. The paper has a billion citations so someone has probably thought about it in some detail -- I can't be the first.

John Duffield

@vzn : I found 't Hooft's his answer to [Does any particle ever reach any singularity inside the black hole?] "Look at what happens in a space-time diagram. At the spacetime point where your astronaut passes the horizon... the observer just continues on, and in a finite amount of time, very quickly unless the black hole were more than millions of times heavier than the sun, he is killed by the central singularity..."

"In a black hole with high angular momentum (Kerr black hole), the singularity takes the form of a ring along the equator, and the astronaut might try to sail past it safely, and he would be able to enter into a strange new universe where he may or may not leave a negative mass black hole behind him..."

ACuriousMind

@DanielSank Why a cube though? A pun on qubit?

@0celo7 I see. Yeah, if it's possible the result is correct but just the proof wrong then searching for a counterexample is obviously futile.

Ask on MO under a different account and hope your advisor doesn't realize it's you :P

John Duffield

@vzn : sorry I mucked up a hyperlink again. It's physics.stackexchange.com/a/34607/76162

0celo7

7:26 PM

spoiler alert i guess

@ACuriousMind It's (definitely?) correct under slightly stronger curvature and topology restrictions.

So I have to construct some pathological things to check for counterexamples.

@ACuriousMind What does it mean to "obtain a manifold by doing surgery on a codimension $\ge$3 sphere"

ACuriousMind

@0celo7 Well, one usually does surgery on a $p$-sphere where $p\leq \dim(M)$ and this means that $p\leq \dim(M)-3$, I guess

0celo7

@ACuriousMind No, what does "doing surgery on a sphere" mean

I know what codimension is

ACuriousMind

@0celo7 Oh, I think "doing surgery on a $p$-sphere" just means doing the surgery where you cut out $S^p \times D^{\dim(M)-p}$. Or is the question what surgery is?

Sir Cumference

@diobuceulb Please stop deleting your account...

We enjoy having you here

DanielSank

7:43 PM

@ACuriousMind It's the site logo. I have no idea why.

0celo7

@ACuriousMind I guess surgery means something different to topologists than to geometers.

John Duffield

Who wants to talk about my book sitting on my table? It's The Principle of Relativity by Albert Einstein. Apparently it's accelerating upwards at 9.8m/s². Funny, I don't seem to be able to see any change of velocity there.

0celo7

@JohnDuffield Ugh, I thought having you back would be nice...

ACuriousMind

@0celo7 I don't know what it means to you but to me it means what Wiki says

0celo7

Yeah, I read that.

John Duffield

7:49 PM

@0celo7 : Be nice. It was quiet. I thought I'd volunteer something. If you'd prefer to talk about something else no problem.

0celo7

Well, that sucks.

no_choice99

@Pieter are you here? I'm wondering about the difference between a perfect conductor and a superconductor. I know the latter can expell an already present B field inside it, while the former can't. is that the only difference (ignoring phase transition) ?

ACuriousMind

@no_choice99 A perfect conductor is an idealization of a real classical conductor, while a superconductor is not an idealization, and not really a classical conductor.

no_choice99

yeah I know

ACuriousMind

Then what exactly do you want to know?

0celo7

7:52 PM

@ACuriousMind How to glue together psc manifolds to get a new one.

no_choice99

a perfect conductor is a conductor with rho = 0 or sigma = infinity. as a consequence, its skin depth is 0

0celo7

Preferably to do so countably many times and get a result that makes sense

But noncompact please

no_choice99

i want to know if the only difference between a superconductor and a perfect conductor is the ability to expell a B field inside it

ACuriousMind

@0celo7 I'm afraid that's outside of what I can help with :|

no_choice99

I mean macroscopically

ACuriousMind

7:53 PM

@no_choice99 Depends on how you define "difference". For instance, clearly a "perfect conductor" still has ordinary electrons moving through it while a superconductor has Cooper pairs.

But of course that's not something one could directly mesure

no_choice99

right, i mean macroscopically

are Cooper pairs bosons?

ACuriousMind

Well, the largest macroscopical difference is that perfect conductors don't exist :P

no_choice99

what would be the resistance of a perfectly crystalline 1 mm wide 1 cm long Cu wire?

its residual resistance would be only due to electron/electron scattering, at 0K ?

i should speak of resistivity so the dimensions don't matter

much more universal

oh wait there would still be surface effect. i guess this causes some resistance but im not 100% sure

no_choice99

8:14 PM

from hyperphysics.phy-astr.gsu.edu/hbase/Solids/meis.html#c1 , I'm unable to show "If there were no change in the applied magnetic field, there would be no generated voltage (Faraday's law) to drive currents, even in a perfect conductor. " I start with dB/dt =0 and this is equal to the curl of E. or curl of -grad(V) =0 . im not able to see that V = 0 like it's stated

Pieter

@ACuriousMind One can see that there are Cooper pairs by doing Andreev reflection. And one can measure the superconducting gap, which is a measure of the pairing energy.

ACuriousMind

@Pieter And that's why we need more condensed matter people here :)

0celo7

"Physicists apply this lemma with compactly supported variations"

maybe

maybe the physicists are gangsters and don't

Pieter

@no_choice99 Yes, Cooper pairs are bosons. But I am not much of an expert about the superconducting state.

0celo7

8:35 PM

@ACuriousMind "an $n-j$-dimensional subfold may be viewed as the intersection of $j-1$ hypersurfaces" is that really true?

no_choice99

thanks @Pieter

Bernardo Meurer

I goddamn hate libpsl

ACuriousMind

@0celo7 Well, it's true in $\mathbb{R}^n$ and I don't see a global obstruction to gluing the local hypersurfaces you get in balls around points on the subfold.

0celo7

@ACuriousMind why is it true in R^n? Is it the "locally cut out by functions" theorem?

probably not because that's local

ACuriousMind

@0celo7 Uhh...well, I meant "My intuition says it's true in $\mathbb{R}^n$" ;)

0celo7

8:41 PM

@ACuriousMind is this how you run SAP

ACuriousMind

@0celo7 No, this is how I do math after a long day at work :P

Bernardo Meurer

@0celo7 He's not a good CEO

ACuriousMind

@BernardoMeurer it's true I'm not

Bernardo Meurer

@ACuriousMind Did you read my crazy essay?

ACuriousMind

@BernardoMeurer I saw an...intriguing discussion about it but I didn't read it yet

0celo7

8:51 PM

it was never sent to me

Bernardo Meurer

Sec

send.firefox.com/download/3b13be6202/#2g60jvUTzibrNU9naT_N8g

@ACuriousMind @0celo7 ^

0celo7

@ACuriousMind btw if the argument in the paper is right, the main theorem is still not :)

it relies on a conjecture that is still unproved

I'm working on that too tho lol

stephen hawking quote!

I've got a great one

ACuriousMind

> In his meditations on the topology of Borromean knots, and in particular throughout his seminar of 1974–1975, the French psychoanalyst Jacques Lacan exposes the interrelation between the Symbolic, the Imaginary, and the Real in terms of link-topology

Bernardo Meurer

Yes

It's bonkers

ACuriousMind

Is this a Sokal? :P

vzn

8:56 PM

@JohnDuffield ok but (not following) how is 't hoofts answer different than what any other physicist would describe?

0celo7

I can't find the quote!!

Bernardo Meurer

@ACuriousMind The lacanian part requires some faith

It's just there because I wanted to read Lacan

vzn

@BernardoMeurer hey! 0celo7 needs tutoring on turing completeness think youre the man tag youre it :P (although maybe wasnt listening previously) :|

Bernardo Meurer

@vzn Lol

@0celo7 It's really easy to check for Turing Completeness. You just put me next to it and if I get aroused it's turing complete

0celo7

"It is self contained apart from requiring a knowledge of simple calculus, algebra, and point set topology."

::proceeds to do nonlinear hyperbolic PDE::

Bernardo Meurer

8:58 PM

Lol

vzn

@BernardoMeurer lol! TM completeness descr by a brazilian nonmathematician :P

Bernardo Meurer

@0celo7 In any way, I describe turing machines, which are TC, in the first pages of my paper

So read that

Or the references :)

0celo7

I'm stealing your dedication, but not the quote

My parents complained about my dedication to them

so screw them

John Duffield

@vzn : it's similar to what a lot of physicists would describe. But it came out of what you might call Misner-Thorne-Wheeler general relativity, which exhibits some marked differences from what you might call Einstein's relativity. When you stick to the latter, you get a very different picture of what happens to the infalling observer.

Bernardo Meurer

@0celo7 Mine?

To S.H.?

0celo7

9:00 PM

to hawking

Bernardo Meurer

Ah, yeah, use the quote tho

It's nice

0celo7

no, I've got my evans quote

Bernardo Meurer

Dedicate this bitch to me

I told you already

0celo7

Mathematicians are like theologians: we regard existence as the prime attribute of what we study. But unlike theologians, we need not always rely upon faith alone.

Bernardo Meurer

"To Bernardo, without whom I wouldn't be comfortable with my alcoholism"

vzn

9:02 PM

@JohnDuffield ok. think somebody should just write all this up (maybe you!) as "different interpretations" much like in QM. which btw there are some very excellent papers out now surveying that. & btw think "what really happens™" is probably as unanswerable as it is "currently" with QM...

Bernardo Meurer

@JohnDuffield Hello darkness, my old friend :)

ACuriousMind

@0celo7 ...do they not like your math? :/

John Duffield

@vzn : See the 2013 AMPS paper an apologia for firewalls. Tucked away in the conclusion on page 27 is footnote 31, containing a reference 87 to Friedwardt Winterberg’s 2001 paper gamma ray bursters and Lorentzian relativity.

0celo7

@ACuriousMind my dad doesn't, but they thought it wasn't correct

I guess I misinterpreted their parenting for 20 years

vzn

@JohnDuffield possibly your debate with slereah is just over 2 different substantial "interpretations"...

ACuriousMind

9:04 PM

@BernardoMeurer I have to say that I find the idea of the graph of semi-signifieds interesting, but can't discern the reason all the other philosophy is there :P

Bernardo Meurer

@ACuriousMind To satisfy the professors that need to read it ofc

0celo7

@BernardoMeurer this is confusing. in the definition of $\delta$, should it be a $\to$ and not $\mapsto$

ACuriousMind

@BernardoMeurer ::heavy sigh::

Bernardo Meurer

@0celo7 Oops

I'll fix it, thanks

@ACuriousMind Come on, you know how this goes

John Duffield

@vzn : no, it's much more than two different interpretations. You end up with very different predictions about what happens when it comes to black holes and the like.

ACuriousMind

9:06 PM

@BernardoMeurer I actually don't, there is no "general education" requirement here, so I never had to take a university course on anything besides math and physics.

Bernardo Meurer

@ACuriousMind Ah, well, imagine how it goes then

ACuriousMind

Btw, I also am skeptical of the idea that one should suppose the existence of a single "correct" signified (death of the author and all that...).

Bernardo Meurer

Also, I need the philosophy in Section 3, which is what this whole thing was about anyway

vzn

chat.stackexchange.com/users/340822

Bernardo Meurer

@ACuriousMind Balarka mentioned that, I don't get it. Of course when people say something they mean something, even if they mean to not mean anything

vzn

9:09 PM

@JohnDuffield the point is that even mainstream physicists have ideas with different nuance and theres no airtight consensus on certain topics. its the scientific equivalent of the zen question, what is the sound of one hand clapping? what happens when an astronaut falls into a black hole?

ACuriousMind

@BernardoMeurer What if they were delighted by the ambiguity of their statement, not fully intending any particular meaning?

And why is what they meant privileged over what others understand?

you could have a graph of all possible signifieds, without the "intended" signified being special at all. Right now it looks as if the graph terminates at the correct signified for some reason

John Duffield

@vzn : What happens when an astronaut falls into a black hole? He doesn't even make it to the event horizon. It's like Winterberg said. Winterberg was the guy who came up with the idea for GPS, he's no joker. The astronaut is destroyed and turns into a gamma-ray burst. I am confident that Winterberg is right, and 't Hooft is not.

ACuriousMind

@0celo7 They thought your math wasn't correct, or that it wasn't correct to dedicate it to them?

vzn

@JohnDuffield lol if humans want to destroy themselves in space all they have to do is get sucked out of the airlock just like what happened to the traitorous spy in the last gerard butler movie last summer geostorm :P imdb.com/title/tt1981128

0celo7

@ACuriousMind I expressed thanks to them for something

ACuriousMind

9:17 PM

Oh.

0celo7

but they thought what I said was wrong

and I misinterpreted their actions

ACuriousMind

Oh. Welp.

0celo7

the math is wrong too, damn yau

well, some of it at least

Sir Cumference

@0celo7 obe is deleting his account again :(

0celo7

@SirCumference how do you know

also I figured, I think he deleted his discord

@BernardoMeurer using iff for definitions is poor form

Sir Cumference

9:21 PM

5 hours ago, by diobuc eulb

@Secret im deleting my account, do you have a discord or other thing i can add you on?

5 hours ago, by diobuc eulb

@SirCumference you too

0celo7

he's doing the usual periodic meltdown. pretty hard to keep track

John Duffield

@vzn : the point is that light curves because the speed of light is spatially variable. That's what Einstein said. That's why optical clocks go slower when they're lower. That's why your pencil falls down. And when you drop it into a black hole, it falls faster and faster and faster, through space where the speed of light is getting slower and slower and slower. Something has got to give.

Bernardo Meurer

@ACuriousMind Well, I'm stating that there is an intended signified

Which I believe

I don't think you can do anything without a master signified that is your intention with it

Even if you say something just to be amused my how nonsensical it is, then your signified is your amusement

@0celo7 Why?

0celo7

why what

Bernardo Meurer

@0celo7 Why is using iff poor form

0celo7

9:26 PM

it just is. my authoritative source is a lecture by J.P. Serre

ACuriousMind

@BernardoMeurer But in such cases, it's hard to see how anyone trying to understand a statement is supposed to ever generate that signified in the graph to begin with. Do all statements always have "all possible" (whatever that means) signifieds in their graphs?

vzn

@JohnDuffield let me try to cook up an analogy. think some of the terminology problems are related to this. imagine a fluid with varying density regions. now someone is trying to "describe" those density variations. now is the observer himself inside or outside the fluid? you seem to have an outside of fluid pov. but maybe physics is still using an inside of fluid pov descr. but maybe theres not much difference mathematically as ACM once pointed out in comment (cf earlier)...

Bernardo Meurer

@ACuriousMind Well, yes, for any statement you make, someone (omniscient) could produce a graph with all the possible signifieds. You might only be able to produce those which your contextual knowledge allow

And even the originator (of the sentence) might not be able to construct his true signified, maybe he doesn't know it consciently

ACuriousMind

@BernardoMeurer Well, I mean, won't the omniscient version simply include all signifieds. I.e. the omniscient graph always has the same nodes and they just differ in their connection? The interesting part here is the construction of the graph more than finding a way through it, imo.

Bernardo Meurer

So maybe I tell Ryan I love him, and I think the master signified of that is a true feeling, but in reality i subconsciently just want his money or w/e

ACuriousMind

9:32 PM

That is, what is the process that determines how close a signified is to the sentence in the graph?

Bernardo Meurer

Ah

ACuriousMind

In your essay, the graph just...appears.

Bernardo Meurer

Wait, what's the question

How the graph is constructed?

ACuriousMind

@BernardoMeurer I think I'm working that out while I babble at you ;)

Bernardo Meurer

Hehehe

ACuriousMind

9:34 PM

But yes, currently my main problem with saying that "understanding" is finding the route through that graph is where the graph comes from in the first place.

Balarka Sen

He assigns some fucking weights I don't believe but I think passes off okay

It's a philosophy essay. He did good mathematics in it. I'm okay with that

It's probably a simplified model of things

John Duffield

@vzn : my pov is that the photon is a soliton wave in space, we can make an electron and a positron out of photons in gamma-gamma pair production, and we have hard scientific evidence of the wave nature of matter. So the electron is a wave in space, and the observer is more of the same. The difference is that people like 't Hooft think you can dive into a black hole and emerge in some parallel universe. Whilst I think there's a BOOM and you're just a gamma-ray burst.

The difference is massive.

Balarka Sen

By probably I mean very likely

Bernardo Meurer

@ACuriousMind Well, the graph depends on 3 things:

1. There is a sentence, which is a groups of signifiers

2. There is a true (master) signified

Balarka Sen

As an example of that graph, think of linguistics. Think of signifiers as adjectives or adverbs (of adverbs or of adjectives) and signified as nouns

Noam Chomsky style

Oppa Chomsky style Op Op Op

Bernardo Meurer

9:37 PM

3. There are intermediate virtual signifieds that allow you to reach 2 from 1

vzn

@JohnDuffield we may have similar picture/ pov, but havent thought about black holes that much except like a highest-possible-density area in a space fluid, maybe something like what youre sketching out (where "speed" is inversely related to density). it appears to me photons are like solitons but are spherical and expanding, not spatially localized like solitons. (have been talking about solitons in here/ elsewhere for ages, still not much reaction so far...)

Bernardo Meurer

And then Figure 6 is just my vizualization of it

But it can look like anything

Later on I thought that a network graph might be better wuited

ACuriousMind

@BernardoMeurer Although I approve of the usage of "virtual" likening it to Feynman diagrams - where do these intermediate signifieds come from? How do you determine how far they are from the originator's actual imtermediate signifieds?

Balarka Sen

Nobody's going to star that Gangam style joke? Ok well

Bernardo Meurer

Okay, so 1. Where do they come from? 2. How do you measure their distance from the originator's

John Duffield

9:39 PM

@vzn : IMHO a photon isn't spherical and expanding. And it isn't spatially localized either. IMHO the best analogy for a photon is a seismic S-wave. But whatever you think of it, it has a wave nature, so do buckyballs, and so do you.

vzn

@JohnDuffield particles ≈ 3d solitons

Bernardo Meurer

1. I don't know, I've been thinking about it. I think the virtual signifieds come from the originator's thought process in the production of the sentence, but I haven't been able to formalize it yet. So, right now, they come from the originator's thinking that generates s

vzn

@JohnDuffield yes exactly. p-waves/ s-waves are a form of matter "polarization"... its so bizarre that there seems to be no physicists describing the analogy! re photons, think you will have to revise that. (have a fairly simple experiment in mind.)

Bernardo Meurer

2. I don't know how to do it properly yet. Right now I'm modeling it as a boolean distance, where there's a cost of 1 if the virtual signified is not the originator's and 0 otherwise

ACuriousMind

I'm just thinking that generating the tree on the part of someone trying to understand the sentence seems even harder than finding the correct path through it, i.e. "most" of the effort of understanding in your model would be in that generation.

Bernardo Meurer

9:45 PM

Yeah, I agree, I think

No wonder we misunderstand each other all the time :)

0celo7

@ACuriousMind Maybe I should mention that my advisor was a student of Yau's.

So that might have something to do with this as well.

ACuriousMind

@0celo7 That's certainly possible

John Duffield

@vzn : IMHO this physicsFAQ article is worth a read. Note the general relativity section. The speed of light at the ceiling is greater than the speed of light at the floor. So the ascending photon speeds up. In a very strong gravitational field, it speeds up more.

vzn

@JohnDuffield nice article but could use more eqns & diagrams. a key idea is that "reference frames" are similar to coordinate systems. etc and the whole theory is about 3d linear/ nonlinear translations etc... actually have found a very nice analogy that others have missed. speed of sound in gases

John Duffield

@vzn : Compare and contrast with what some highly-regarded authors say: "We may think of C as being in such a strong gravitational field that even the ‘outgoing’ light rays from it are dragged back". In a very strong gravitational field the ascending light beam speeds up more. It doesn't get dragged back.

Bernardo Meurer

9:55 PM

@ACuriousMind I guess an interesting point too is that even if you're capable of constructing a graph with all the virtual signifieds needed for understanding the originator, doing so is still extremely hard

0celo7

@BernardoMeurer I'm going to read this now

it better not have any fucking set theory

Bernardo Meurer

It doesn't

I swear

Unless you say Complexity Classes are sets

Which I guess they are

Crap

0celo7

reeeeeeeeeeeeeeeeeeeeee

vzn

Aug 8 '16 at 23:21, by ACuriousMind

@vzn "etc."? What is this et cetera that no one but you and JohnDuffield have access to? Stop weaseling around and write down a single equation substantiating any of the claims you made.

Aug 9 '16 at 4:02, by vzn

@ACuriousMind hint: velocity of sound in an ideal gas + dimensional analysis

0celo7

"As is well known"

John Duffield

9:59 PM

@vzn : I prefer to use the analogy of the speed of a shear wave in a solid. There's a shear-stress term in the stress-energy-momentum tensor.

0celo7

@BernardoMeurer use $\setminus$ for set difference

vzn

@JohnDuffield yes. tenev + horstemeyer. some of the math is similar to speed of sound in gases.

Bernardo Meurer

@0celo7 In Def. 1.1?

ACuriousMind

@0celo7 No, an ordinary minus is much better

0celo7

@ACuriousMind are you being ironic?

ACuriousMind

10:00 PM

Maybe

You need to find my true signified

0celo7

I can't get past the definition of a Turing machine

Bernardo Meurer

@0celo7 How come?

0celo7

I thought a spacetime $(M,g,\nabla,\mu,\tau,T)$ was bad enough

this thing has 9 components!

Bernardo Meurer

@ACuriousMind We will never know :P

ACuriousMind

@0celo7 It's a pencil on a tape :P

John Duffield

10:03 PM

@vzn : the crucial point is that a black hole is a place where the speed of the wave is zero. Einstein thought a black hole could therefore never form, but he forgot about hailstones. They form from the inside out. That's what Winterberg said about black holes. You're a water molecule, and you can't pass through the surface of the hailstone. But you can alight upon the surface and get buried by other water molecules. So the surface can pass though you.

vzn

@0celo7 think of the tape as a topological obj :P

@JohnDuffield am not familiar with einsteins ideas on black holes but its not surprising they need revision lol ... anyway think avoiding ref to speed (which is intra-fluid) and thinking more about density (extra fluid) may actually be helpful.

0celo7

"With Definitions 1.2 and 1.1, the reader now has a clear, formal, understanding of what
a Turing machine is,"

what bullshit writing is this?

ACuriousMind

There's also a lot of "trivial" things in there... :P

Bernardo Meurer

What?

ACuriousMind

@BernardoMeurer You like to say "trivially" :P

John Duffield

10:07 PM

@vzn : speed is crucial. See Robert Oppenheimer and Hartland Snyder's 1939 "frozen star" paper on continued gravitational contraction.

Bernardo Meurer

@ACuriousMind I was taught that if you don't make the reader feel like a moron you're not a good writer

0celo7

@BernardoMeurer This is not clear, and I do not have an understanding

Bernardo Meurer

@0celo7 Balarka understood it

0celo7

Balarka is Yau 2

Bernardo Meurer

What do you not understand about TM?

0celo7

10:07 PM

I don't know what a state, alphabet, tape, or transition function is

I basically understand nothing

and what does "trivially understandable" mean

vzn

@0celo7 did you look at wikipedia? have you ever seen a typewriter? or ticker tape? they existed when Turing came up with the idea & think probably nearly inspired it... en.wikipedia.org/wiki/Turing_machine

Bernardo Meurer

A tape is a collection of cells, each of which can hold a state, the state is represented by a symbol in the tape alphabet

0celo7

I was born in 1997, no I have not seen a typewriter

Bernardo Meurer

an alphabet is a collection of symbols

0celo7

you don't define what polynomial time means

vzn

10:11 PM

@JohnDuffield there is a "natural speed" connected to density its that permitivity/ permissivity eqn you cited in here once

Bernardo Meurer

Nope, because it doesn't matter, the important part there is the definition of tractability and the Cobham-Edwards thesis

Sir Cumference

What is a tensor

0celo7

something that transforms like a tensor

Bernardo Meurer

@SirCumference chat.stackexchange.com/transcript/message/43490301#43490301

0celo7

@ACuriousMind beat you

Bernardo Meurer

10:12 PM

7 hours ago, by Slereah

Let's stop right there, it's not really worth it

^ w.r.t. tensors

Sir Cumference

@BernardoMeurer What

ACuriousMind

@0celo7 You beat me at what?

vzn

Aug 8 '16 at 20:59, by John Duffield

@WilliamBulmer : the way the electromagnetic stress tensor resembles the continuum-mechanics Cauchy stress tensor. And the way the expression for the speed of a shear wave in a solid c = √(G/ρ) resembles c = 1/√(ε0μ0). The reciprocal is there because permittivity is a "how-easy" measure rather than a "how-hard" measure.

0celo7

@ACuriousMind defining tensors

ACuriousMind

Oh.

I would've said it's a multilinear map on vector spaces :P

Sir Cumference

10:14 PM

I just need a quick explanation

John Duffield

@vzn : yes, see this recent answer. When the speed varies, the wave curves.

Sir Cumference

I know of course what a vector is, but how is a tensor a generalization of them?

Is it a member of some space?

0celo7

@BernardoMeurer you seem to always use $\mapsto$ over $\to$

Sir Cumference

Or is it some kind of linear transformation?

John Duffield

-2

A: Equivalence principle for test fields

We all know that, for a test particle (classical) in a gravitational field, the motion is only determined by the geodesic lines Actually, that isn't quite right. The geodesic lines don't actually exist in any objective sense. They're abstract things that are used to model particle motion, but's ...

Sir Cumference

10:15 PM

I dunno how to interpret the matrix-ness

Bernardo Meurer

@0celo7 Yep, mistake

0celo7

u n i v e r s a l p r o p e r t y

@SirCumference

Sir Cumference

@0celo7 What

0celo7

"In his meditations on the topology of Borromean knots,"

wtf am i reading

Bernardo Meurer

I know

Lacan is a weird fuck

Also note that the Borromean Knot is a link, and not a knot

ACuriousMind

10:18 PM

@SirCumference It is...both. Just like a matrix can be seen both as a linear transformation and a "vector of vectors", so a tensor is both a kind of linear map and a "vector of vectors of .... vectors"

Sir Cumference

:43499978

Bernardo Meurer

@ACuriousMind ur mom is a vector of vectors of vectors...

0celo7

ban him please

Bernardo Meurer

@0celo7 I'm technically right

ACuriousMind

For instance, you can say that a 4-tensor consisting of components $T^{abcd}$ is a vector of vectors of vectors of vectors by parsing it like $(((T^a)^b)^c)^d$, and also that it is a (multi-)linear map in four arguments by interpreting it as the map $V\times V\times V\times V\to \mathbb{R}, (v,w,x,y)\mapsto T^{abcd}v_a w_b x_c y_d$.

0celo7

10:23 PM

ACM using abstract index notation? What the hell?

Although using lower indices for vectors should really be cause for a stoning.

ACuriousMind

@0celo7 I explicitly said components! It's not abstract!

@SirCumference Did you fall asleep trying to respond to me? ;)

Bernardo Meurer

@ACuriousMind He's not being able to construct your master signified

You need to provide more contextual cues

0celo7

10:37 PM

lol this typo

"is a union of two spheres"

he means "two-spheres"

I think!

Bernardo Meurer

Not me, right?

0celo7

no

Bernardo Meurer

I was about to search where tf I use spheres

0celo7

@ACuriousMind from my advisor: "Either the answer is 'yes', or it is 'no', and it's a classical result." wise words!

/s

ACuriousMind

lol

Akiva Weinberger

10:41 PM

Hello

Is this the room where we learn the laws of physics so as not to accidentally break them

Bernardo Meurer

@AkivaWeinberger Only Lacanian psychoanalysis here, wrong room

0celo7

@ACuriousMind are you good with multiple complex variables

ACuriousMind

@0celo7 nope

0celo7

@ACuriousMind Hmm. Who is?

Bernardo Meurer

@0celo7 I am

0celo7

10:48 PM

@ACuriousMind I seem to have proved that for $k\ge 2$, $\Phi:\Bbb C^k\to\Bbb C^k$ holomorphic means $\Phi$ is injective. This seems very wrong!

ACuriousMind

Hm, yes, that does seem wrong

0celo7

@ACuriousMind Do multivariable holomorphic functions preserve angles like in 1 complex dimension?

ACuriousMind

I don't think so

For instance, the projection $(z_1,z_2) \mapsto (z_1,0)$ is holomorphic and just forgets everything that happens in the second component, doesn't it?

John Duffield

@AkivaWeinberger : no, this is the room where we learn how to repair them.

0celo7

@ACuriousMind Hmm, yeah, what even is the definition of holomorphic for $C^k\to C^k$

ACuriousMind

10:56 PM

@0celo7 Each component of the function in the target space is holomorphic as a function of each component in the source, I'd say

0celo7

@ACuriousMind Right, well like in 1D you've got that a holo fcn is a local diffeo, right? So I guess that's not true in more dimensions.

ACuriousMind

I agree

Bernardo Meurer

guise dis number no exist

y boder

leave complecs alone, is imaginari!

no exist

0celo7

@ACuriousMind Thanks. Now I'm at square -1 in my counterexample hunt.

Oh well, I can read these other Yau papers in the meantime...

@ACuriousMind "That's a pretty degenerate example, though."

Bernardo Meurer

@rob Long time no see!

rob

11:27 PM

@BernardoMeurer Yeah, rough year. How are you?

Bernardo Meurer

@rob Oh no, anything in particular? :/

I'm alright, kind of reached that mid-semester exhaustion

rob

@BernardoMeurer It's personal stuff. I know what you mean about the middle of the semester.

Bernardo Meurer

@rob Sorry to hear it, I hope it gets better / you feel better soon

rob

@BernardoMeurer Thanks.

Bernardo Meurer

I also kind of just want to go home, California is tiring :P

Life without beer is much harder than I expected

0celo7

11:31 PM

you should have detoxed by now

Bernardo Meurer

@0celo7 Nope, I'm still in withdrawal

I dream I'm sitting in the couch having a beer sometimes

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