The h Bar

vzn

12:18 AM

@pZombie lol you might have a future studying QM interpretations. or not :P

Physics Meta

2:13 AM

0

Q: Remove my post from the 'on hold' status!

I have a question about my Physics Stack Exchange post: SHM Sound Waves Problem My question was placed on hold, and I just corrected it (I believe it is fine now). Please help me, I urgently need help with that homework.

John Rennie

8:00 AM

@Mithrandir24601 for some reason I love eating ribs when I'm out for a meal, but I rarely cook them at home.

Mithrandir24601

@JohnRennie I don't often do either - I've made enough for two nights though, so more again tonight :)

John Rennie

@Mithrandir24601 I'm in my weekday healthy eating phase, but plans for the weekend meals are coming along nicely. I've bought some Polish smoked sausage which will probably be the basis for Saturdays meal.

Mithrandir24601

@JohnRennie Never had polish sausage before... Sounds good though - I'm fortunate(?) enough that I'm able to just eat what I like when I like and if I don't stuff myself with biscuits or something semi-regularly, will just loose weight

John Rennie

@Mithrandir24601 you too will be middle aged one day, and on that day I will laugh scornfully - assuming I'm still alive :-)

Mithrandir24601

@JohnRennie People keep telling me this and all that's happened so far is that I need to eat more in order to not loose weight

then I loose weight anyway! :P

John Rennie

8:10 AM

I was just like you. Actually I still eat copious amounts at the weekend - I just need to use a bit of moderation during the week. My BMI is still the same as when I was 18, but maintaining it takes more attention these days.

Mithrandir24601

Well... I'm not sure I want to 'maintain' my BMI - last I checked, the GP was like 'you should eat more' so...

John Rennie

I'm unconvinced it's a problem if your BMI is low. Assuming you're still fit, i.e. you can run or cycle, being skinny isn't an issue.

Mithrandir24601

I'm not into cycling or running to be honest :P I do have various medical problems that could be related in some way though - one part of one of these is that I get lightheaded way to easily

John Rennie

That's probably low blood pressure, which apart from the irritating tendency to faint at least means you're less likely to drop dead of a heart attack or stroke.

Zerix

Exercising or fasting. What's best way to reduce weight? Scientifically it's fasting but are we supposed to not eat everyday or just a routine

John Rennie

8:16 AM

@Zerix the only successful way to control weight is to eat the correct amount every day. Fasting is a poor way to do it because the temptation is just to eat more the day after the fast because you're extra hungry.

Mithrandir24601

@JohnRennie Nope. My blood pressure is perfectly fine. Even when going from sitting to standing, everything about my blood pressure is perfectly normal and expected

John Rennie

Exercise is important for keeping fit, but exercise uses surprisingly few calories. Running a mile - really running not just jogging - uses only 100 calories.

Zerix

Yes. I can maximum fast for 1and 1/2 day but I will eat more than 2 days food after that xD

Mithrandir24601

@JohnRennie A mile isn't that far, as far as running is concerned though

John Rennie

@Zerix exactly. The key to controlling weight is to check every day what you're eating and eat just a little less than you need. Not a lot less or you'll get hungry and feast again. Just eat a little less every day for a lot of days.

@Mithrandir24601 well look at it this way. Just maintaining your body temperature uses as many calories as running 20 miles.

Zerix

8:20 AM

Yep. I skip lunch usually. Basically I eat food only on mornings and evenings and I am seeing a lot of positive changes

John Rennie

Alternatively fasting for one day is as effective as running a marathon when it comes to reducing weight.

Zerix

I suck at running xD

John Rennie

@Zerix ideally you make it part of your everyday routine, so it doesn't feel as if you're actively dieting. You want the controlled calorie intake to feel normal so you do it instinctively.

Mithrandir24601

@JohnRennie But I'm always cold

John Rennie

@Mithrandir24601 you're an alien from the planet Zarg. Clearly swapped at birth.

Zerix

8:22 AM

@JohnRennie yes. I don't feel hungry for lunch now. That's the effect you must be talking about.

I have made the routine I guess

John Rennie

But then I've long suspected that no-one who likes quantum computing is entirely human :-)

@Zerix good work :-)

Mithrandir24601

@JohnRennie Bahaha! We're a growing bunch and ~~soon~~ maybe someday we will have achieved our goal of ~~building a quantum computer~~ ~~world domination~~ building a quantum computer!

Mo_

8:57 AM

@Mithrandir24601 Are you doing theoretical or experimental work?

How does a typical day in an experimental PhD look like? Does it mean your job is just fabrication and measurement of others' theoretical work?

Mithrandir24601

@Mo_ I think the closest description would be 'theory of experiment' (although my supervisor does want me to get in the lab at some point, which I should do soon)

Slereah

morning

Mithrandir24601

Essentially, I come up with ideas and go through the theory of those (and some other people's) ideas to see if/how well they work in theory, then go through this with other relevant experimental people in my office to see if it makes sense/I haven't gone way off/it's reasonably doable as an experiment, then they go and do the experiment (this is an extremely simplified version of what happens but hopefully gets the gist across)

@Slereah Rytsas!

Slereah

9:15 AM

@Mithrandir24601 sure

Anonymous

9:33 AM

Interesting thread:

Anonymous

38

Q: Consequences of lack of rigour

The standards of rigour in mathematics have increased several times during history. In the process some statements, previously considered correct where refuted. I wonder if these wrong statements were "applied" anywhere before (or after) refutation to some harmful effect. For example, has any br...

soft-question ho.history-overview

3

Anonymous

On the HNQ today.

Anonymous

10:25 AM

5

A: Melting point of unsymmetrical dimethylhydrazine vs 1,2-dimethylhydrazine

According to the Carnelley’s Rule: That of two or more isomeric compounds, those whose atoms are the more symmetrically and the more compactly arranged melt higher than those in which the atomic arrangement is asymmetrical or in the form of long chains If we attend to the structure ...

Anonymous

@Chair This one is pretty close.

user351417

11:39 AM

@Blue Indeed, even the other answer did have a somewhat interesting argument, though it wasn't particularly well-supported.

user351417

I'll wait a couple of days before accepting an answer though.

Anonymous

11:55 AM

@Chair Yeah, I too will wait the whole 7 days before awarding the bounty.

Secret

12:48 PM

-2

Q: Have I empirically falsified the "law" of non-contradiction?

In the 2nd half of the 20th century the American mathematician Haskell Curry and logician William Alvin Howard discovered an analogy between logical proofs and working computer programs. This is known as the Curry-Howard correspondence. Mathematical proofs are working computer programs. https://e...

quantum-mechanics spacetime time

@vzn I wonder if the collective consciousness can help

user351417

1:03 PM

@Secret (with reference to the comments) I'm sure that the word "paradigm" shows up many times in Baez's index.

Secret

well...

JMac

1:28 PM

Well, I tried to see if they were genuinely curious about if their reasoning makes sense, or if they are just trying to find other people to say "wow that's amazing this will change everything"; based on the word-salad I just got as a reply... I'm guessing they are only trying to have someone reinforce what they are saying

Slereah

1:40 PM

you know

it's been a while since we've had a

cough cough

unorthodox theory man

on chat

Well except @vzn I guess

But no new one for a while

Anonymous

1:54 PM

@Slereah Speak of the devil and he doth appear.

Anonymous

:P

Slereah

doth he

Hm

Given a manifold $M$, with some set of isometries, is it fair to say that an open submanifold $M' \subset M$ will have at most the same isometries

PM 2Ring

2:12 PM

@Secret On xkcd, we call that a theroy.

Secret

I have many pet theories, it's just the wavefunction have shifted from the h bar

Slereah

phew

Secret

which is why I am mostly a scrodinger cat in this chat now in terms of (non)existence

danielunderwood

2:54 PM

So if $e$ are your basis vectors and $\omega$ are basis vectors in the dual space, is $\omega^a (e_b) \ne \delta^a_b$ equivalent to your dual metric not being the inverse of the metric? And is it ever useful to make such a choice or does it just lead to more calculation?

Slereah

@danielunderwood I mean you can pick whatever basis you want

But it is more practical to use a dual basis

danielunderwood

Like always? Or is there some crazy situation where a different choice ends up being better?

Slereah

3:23 PM

Not that i can think of

bolbteppa

3:49 PM

Who wants to talk about the covering group of $GL(n,R)$

4

Q: Does $GL(N,\mathbb{R})$ own spinor representation? Which group is its covering group? (Kaku's QFT textbook)

In Kaku's QFT textbook page 54, there is a saying: $GL(N)$ does not have any finite-dimensional spinorial representation. This implicates that $GL(N)$ owns infinite-dimensional spinorial representation. While in my opinion, a group's spinorial representation is the representation of its uni...

group-theory group-representations lie-algebra representation-theory

vzn

4:18 PM

@Slereah "unorthodox theory man"? lol nicest comment on me in here in months... ps how about this for a esteemed/ illustrious comrade-in-arms :P calvinandhobbes.fandom.com/wiki/Transmogrifier

Slereah

4:29 PM

you know what you did :V

"Let $\pi : \mathfrak{E} \to \mathfrak{M}$ be a vector bundle"

Oh god

the Fraktur

it hurts

danielunderwood

The more I learn, the more is sounds like math is just the study of maps

vzn

@Slereah nice writeup SL lol spking of "unorthodox theory man"... Minkowski space as "non pathological spacetime" :P

Slereah

It's the non-pathologicest

@danielunderwood it has a lot of it

depending on the field of math

You can even replace all of set theory with a pure function-based logical system

vzn

@Slereah know what you mean(t) but think that honor goes to... euclidean/ newtonian...!

Slereah

although it's not super popular

@vzn not the best example of a spacetime

Geroch's papers are usually fun

He's always writing weird stuff

like a paper on singularities starring Simplicio and Salviatti

vzn

4:35 PM

@Slereah are you coding for job these days?

Slereah

Sure am

vzn

May 18 '18 at 17:17, by vzn

@Droleulb ah! found it with some googling, did you like the galileo dialogue? if so you might like this, am now thinking need to read it sooner rather than later... Are quanta real/ Jauch https://en.wikipedia.org/wiki/Are_Quanta_Real_(book)

@Slereah just like the rest of us it seems, what kind of coding?

Slereah

the same kind as everyone

using existing libraries to vaguely perform tasks

vzn

@Slereah so, like ACM, cobol? :P

Slereah

and most of the job is just figuring out how a non-documented library works with the rest

A variety of languages

mostly Python

vzn

4:39 PM

any data science?

pZombie

i find myself not understanding my own code when i look at it a few months later

Slereah

It is indeed "data science"

If you call using a data science library data science

vzn

IMPLEMENTATION SECTION lol

@Slereah yes... which library?

danielunderwood

He just does import datascience

Slereah

A few

Mostly sklearn and statsmodels

vzn

4:46 PM

Nov 1 '17 at 12:34, by pZombie

@Semiclassical I assume that if we had powerful enough computers to simulate fluids on a quantum level without any simplications, you would expect for the simulation to deliver the proper results, right?

↑ unorthodox theory man lol :P

pZombie

i believe only in what i can simulate

any numerical simulation is fine as long as it approaches the real result the smaller the steps to take are set

vzn

@pZombie so what are you coding anyway?

pZombie

nothing at all. I only code something once in a year or two, whenever i have an idea and i cannot find any implementation of it already, like my twin paradox simulation

which is basically why i have to relearn java every time i start a new project

vzn

(java rocks!) :) have seen you in Mathematics are you a math student?

pZombie

no, i am not studying at all at the moment

just interested in physics and math from time to time but not motivated enough to go through all the math required. I did not really like how universities teach really. It felt like they are just writing down their script and you are then supposed to spent all day figuring out what they wrote down non-stop in 2 hours

vzn

4:56 PM

@pZombie certainly can relate to that. o_O did you graduate or drop out? dont answer if you dont like

pZombie

i abandoned ship pretty early, less than 6 months. I did not even go and fetch my first physics test i passed

vzn

@pZombie lol you did pass it? was this in US?

pZombie

the first one yes. Physics came always easy to me but the math part was a bitch

nah, europe

vzn

which country?

pZombie

vzn - Are you a student?

vzn

5:01 PM

@pZombie "always learning"... went to school a long time ago in galaxy far away. BS software engr US, took a bunch of physics + math classes etc... ps welcome to the room :)

pZombie

i would like to write a numerical relativistic quantum particle simulation but unfortunately i lack the knowledge. I would not mind if i could only simulate 1 trillions of a femtosecond with multiple particles involved, as long as my simulation would get more accurate the more computing power/steps it took

vzn

@pZombie strange/ synchronicity it was just occuring to me to inquire if you were interested in pursuing physics simulations. :) ... there is a lot of off-the-shelf stuff available now for anyone enterprising. do you have a day job?

pZombie

interested yes, but not capable of pursuing the simulations i would like to code at my current state

vzn

@pZombie my point is that surprisingly little coding may be required for some types of potentially rewarding prjs... esp fluid mechanics which youve expressed repeated interest in... but yeah it may tend to be computationally intensive...

pZombie

it is strange there are not more simulations out there similar to the one i wrote for the twin paradox, which i could improve further i guess to simulate all paradoxes related to SR and even extend it to 2 space and 1 time dimension and allow people to write their own scripts on what they want to simulate

vzn

5:09 PM

@pZombie think that science is slowly (at times) adapting itself to the idea of simulations which are relatively new technology so to speak.

pZombie

@vzn you seem predestined to write such simulations based on your studying history

vzn

@pZombie yes indeed have toyed with some over the years, have a lot of affinity for it to say the least. its a big prj though. need assistan(ce/ts). :|

pZombie

@vzn yes but from someone on your level, speaking your language.

vzn

@pZombie (lol) you mean, human? :P

pZombie

i assumed you are human, so yes :D

vzn

5:18 PM

← speaks english :P

pZombie

i meant more the language of math and physics you speak on a level different to mine for example

just throwing more coders at a project does not help. They have to be at the same level

vzn

@pZombie to me these are no more foreign languages other than english. years ago some colleges even allowed coding to count as a foreign language. being from europe do you know a language other than english?

@pZombie coding skillz are a big part of it but really the scarce resource(s) are volunteers/ motivation/ commitment/ free time/ incentives etc

pZombie

hard to imagine we live on a planet with 7-8 billion people sometimes

it should be easy to find enough people to launch such projects now that almost everyone has access to the internet

vzn

@pZombie yes. open source has changed the planet in a sense. however open science is far more rare it seems. it is building slowly. the "resource allocation system" aka (late stage) capitalism plays a very big role and leaves "much to be desired" even in highly advanced/ technological countries.

Anonymous

5:46 PM

@EmilioPisanty @Chair:

Anonymous

Anonymous

https://physics.stackexchange.com/posts/463327/revisions

Anonymous

We will have the HNQ status of questions displayed from today onwards (in the timeline and history). :)

Avnish Kabaj

6:01 PM

in The Periodic Table, Apr 2 '18 at 14:21, by orthocresol

@Abcd Manish has contributed a great deal to chem.SE especially when the site was new. Although he isn't around much anymore, he still offers us some occasional advice. It is true that today there would not be much difference if he was no longer a mod, but the same can be said the other way round: there is no harm in him remaining as a mod, and on top of that, he deserves some recognition for the work he has done. If he steps down at some point in time, it will be of his own accord.

bolbteppa

Spin connection

In differential geometry and mathematical physics, a spin connection is a connection on a spinor bundle. It is induced, in a canonical manner, from the affine connection. It can also be regarded as the gauge field generated by local Lorentz transformations. In some canonical formulations of general relativity, a spin connection is defined on spatial slices and can also be regarded as the gauge field generated by local rotations. == Definition == Let e μ a ...

It's so simple

Got huge doing it some other way compared to this

Emilio Pisanty

6:31 PM

@Chair please remind me later that there's another chem.se follow-up question about p. 137 from Ignition

@Blue well, that's new

Is that retroactive?

Kyle Oman

999 LQP reviews, and nothing in the queue, oh well.

2

Emilio Pisanty

... no, it doesn't seem to be.

@Blue will it mark the exit from the list?

Is it discussed somewhere on meta?

@Blue %@#)(&)#!!!&@)!!!!!!

I mean, I guess utterly and ridiculously late is better than never

By some slim margin

@Blue looking forward to that announcement

ACuriousMind

@KyleOman 999 LQ re-views on the wall, 999 LQ re-views...

Anonymous

6:57 PM

@EmilioPisanty It seems I'm not allowed to share that message publicly yet. Apologies!

Anonymous

Also, it was slightly inaccurate. Which is why redacted it. Hope you don't mind.

ACuriousMind

@knzhou The "argument" you just edited in sounds to me very much like "We have to assume this for frame dragging to account for the entire Machian effect, so we have no option but to assume it", I have to say. At least, I don't know what else "Only so can $\omega_\text{drag}$ retain its inescapable identity with $\omega$" is supposed to mean - that very identity is what we want to show, isn't it?!

knzhou

@ACuriousMind I know!!

MTW is such an authoritative reference though. I hope there's more behind it.

ACuriousMind

It's so authoritative everyone assumes they are just too dumb to understand the argument there :P

bolbteppa

The wiki has a sign error
\begin{align}
\omega_{\mu a b} &= e_{\mu}{}^c ( \Omega_{bca} + \Omega_{abc} - \Omega_{cab} ) \\
&= e_{\mu}{}^c ( e^{\rho}{}_b e^{\nu}{}_c \partial_{[\rho} e_{\nu] a} + e^{\rho}{}_a e^{\nu}{}_b \partial_{[\rho} e_{\nu] c} - e^{\rho}{}_c e^{\nu}{}_a \partial_{[\rho} e_{\nu] b}) \\
&= \dfrac{1}{2} e_{\mu}{}^c ( e^{\rho}{}_b e^{\nu}{}_c \partial_{\rho} e_{\nu a} - e^{\rho}{}_b e^{\nu}{}_c \partial_{\nu} e_{\rho a} + e^{\rho}{}_a e^{\nu}{}_b \partial_{\rho} e_{\nu c} - e^{\rho}{}_a e^{\nu}{}_b \partial_{\nu} e_{\rho c} - e^{\rho}{}_c e^{\nu}{}_a \partial_{\rho…

This looks pretty scary when books just throw the final result at you

ACuriousMind

7:02 PM

Oh no, stop the presses! A physicist has made a sign error in an area muddled by myriads of different sign conventions! :P

bolbteppa

I just made a $\dfrac{1}{2}$ typo so I mean :p

ACuriousMind

@knzhou I've traced too many formulae in popular "authoritative" papers back through their citation chain to "[private conversation with N.N:]" to not be cynical about that ;)

bolbteppa

(Not a sign error, a factor of 2 error)

danielunderwood

Just find what you need to redefine that that fixes the sign issue

I'd wager that there's some way to do it

But it's an exercise for the reader

Emilio Pisanty

7:21 PM

@Blue I hope by "slightly inaccurate" you meant "they're in fact recording some (suitably time-coarse-grained) information about all HNQs leaving the list, with the full thing made available on SEDE for analysis, like they should've done three years ago when this was first brought up"

I mean, in the interest of them living up to their promise to fix this mess

Anonymous

@EmilioPisanty I'm not allowed to confirm or deny that. :P

Anonymous

Tbh I don't know the details either. Guess we'll see soon when it's on Meta SE.

Emilio Pisanty

7:46 PM

@Blue well, imma raise some hell on meta if what they come up with is as bad as what your deleted message said. The only way I can explain that kind of 1%-hearted solution is that they just don't care much, and the meltdown from last year didn't particularly worry them.

</ mild hyperbole >

But we'll see on meta

Qmechanic

2

Q: Exponential model fits my data, but only if I don't consider the integration time

I have a problem with fitting some of my experimental data. It is the time evolution of a signal, and because it is based on chemical reactions, it first grows quite quickly but then decays after reaching a maximum. It looks like this: I first modeled the data with the formula $$ I(t) = A e^{-B...

experimental-physics physical-chemistry models

Revoke the bounty and close as being homework? Migrate to more approapriate SE site?

Anonymous

It doesn't appear that off-topic to me (fits well in the experimental physics category). But I guess a site regular would be able to say better. I personally wouldn't migrate it single-handedly. If there are any flags asking for migration then perhaps.

JMac

It seems to be a question focused purely on differential equations, and the data comes from a chemical reaction; it's not really physics at all IMO, especially because you could ignore the chemical reaction part and it's still practically the same question about math

ACuriousMind

@Qmechanic 1. I just left a comment why I think this isn't really a physics question. 2. I don't see why it would be homework-like, it's just off-topic because they don't give us any physics to work with.

DanielSank

Hi, everybody.

Anonymous

7:57 PM

Holla.

DanielSank

Здравствуй!

Anonymous

8:16 PM

@EmilioPisanty There you go!

Anonymous

I didn't know it's available via the API.

ACuriousMind

@Blue That's just an ordinary user asking about it, not an official announcement/explanation.

Sir Cumference

8:30 PM

Come on Spivak, who tf uses $D_i f(a)$ as notation for a partial derivative

Anonymous

@SirCumference Umm, that's common notation...

Anonymous

Partial derivative

In mathematics, a partial derivative of a function of several variables is its derivative with respect to one of those variables, with the others held constant (as opposed to the total derivative, in which all variables are allowed to vary). Partial derivatives are used in vector calculus and differential geometry. The partial derivative of a function f ( x , y , … ) {\displaystyle f(x,y,\dots )} with respect to the variable x {\displaystyle x} is variously...

Sir Cumference

Welp nvm then

Still annoying to distinguish between it and the linear approximation of a function, which he denotes $D f(a)(v)$

ACuriousMind

@SirCumference The partial derivatives are the components of the linear approximation, hence the notation!

Sir Cumference

@ACuriousMind The partial derivatives are the components of the Jacobian, which as far as I understand generalizes the coefficient in a linear approximation, $f'(a)$. Whereas $Df(a)(v)$ generalizes the notion of the linear approximation, i.e. $f'(a) x$.

ACuriousMind

8:35 PM

@SirCumference The Jacobian is just the representation of $Df(a)$ in matrix form.

We do not generally sharply distinguish between a matrix and the linear transformation it represents

Sir Cumference

I mean from what I can tell, it's the difference between considering a slope and a linear approximation. $\partial f/\partial x$, $f'(x)$, etc. usually denote a slope or coefficient, whereas $Df(a)(v)$ does not.

Idk maybe i'm overthinking it

ACuriousMind

What is a "linear approximation" if not just multiplication by a slope (=1x1 matrix)?

Sir Cumference

Nothing really. But the linear approximation is different from the slope. The term "derivative" in the 1D case usually refers to $f'(x)$, which need not be linear. On the other hand this use of "derivative" $Df(a)(v)$ refers to something else, which is necessarily linear.

From how I've viewed it, the Jacobian is a function mapping from the domain to the set of $m \times m$ matrices. It's not necessarily linear

Anonymous

Ted's blue book explains this topic beautifully. You really should get hold of it. :P

Sir Cumference

Name?

Anonymous

8:42 PM

I and Balarka had an extensive 1 week chat on this and related topics. Lemme see if I can find the transcript.

ACuriousMind

@SirCumference But in Taylor series, $f'(x)$ is the coefficient of the linear term! So the linear approximation to $f(x)$ at $x_0$ is $x_0 + f'(x_0)x$. The notion of $D'f(a)$ is just the generalization of that, the linear approximation to $f(v)$ at $a$ is $a + D'f(a) v$

Anonymous

@SirCumference amazon.in/Multivariable-Mathematics-Algebra-Calculus-Manifolds/…

ACuriousMind

And just like the single "component" of $f'(x)$ is the actual derivative of $f$, the components of $D'f(a)$ as a matrix are the partial derivatives, i.e. it is the Jacobian

Sir Cumference

@ACuriousMind Spivak does it differently then

This notation refers to the linear term, what you referred to as $D'f(a) v$

ACuriousMind

Oops, I meant $Df$, of course. $D'f$ is redundant :P

But I don't see where you think I and Spivak disagree

Sir Cumference

8:45 PM

Your definition seems to imply $Df$ is a not necessarily linear function, whereas Spivak's is necessarily linear :P

Anonymous

Sir Cumference

In the same way $f'(x)$ need not be linear, e.g. $f'(x) = x^2$

Anonymous

@SirCumference Here's the transcript.

ACuriousMind

@SirCumference You are misunderstanding what "linear" means.

It is not the expression of $Df(a)$ as a function of $a$ that is linear, it is that $Df(a)$ is a linear map for every value of $a$ that can act on vectors $v$.

When I write $Df(a)v$ that expression means "apply the linear transformation $Df(a)$ to the vector $v$"

Also, I didn't say it was a definition, it's just a fact about the derivative. You might take it as a definition, and it is of course then equivalent to Spivak's and everyone else's

Just like $f'(x)$ is not a linear function of $x$, but the function $x\mapsto f'(x_0) x$ is linear.

Sir Cumference

Wait, I may be misunderstanding this. Spivak denotes $\lambda (h)$ as the best linear approximation at $v$. Then does $Df(v)$ refer to the same thing as $\lambda (v)$ in that context?

ACuriousMind

8:51 PM

@SirCumference Yes, $Df(a)v = \lambda(v)$.

Spivak just didn't write the dependence of $\lambda$ on $a$ explicitly

Sir Cumference

Sigh I'd been completely misunderstanding, I thought $Df(a)=\lambda (a)$

Welp thanks then

ACuriousMind

You're...welcome? :)

Sir Cumference

Jesus I feel like facepalming, now everything in this chapter makes way more sense

ACuriousMind

It happens

user301074

10:11 PM

can observed black-holes be Einstein-rosen bridges i.e. black-holes with two congruent "sheets"?

user301074

Einstein-rosen bridges reproduces the same results of "normal" black-holes (i guess)

Emilio Pisanty

10:36 PM

@Blue thanks for the pointer. I'll hold off on raising hell until they post an official announcement. You know, to give them a chance to explain the unsurmountable technical barriers that prevent the drop-off data from being recorded.

bolbteppa

Seems like the argument is: $GL(2,R)$ does not admit finite dim spinor reps because $SL(2,C)$ is simply connected yet the rotations $\begin{bmatrix} \cos \theta & - \sin \theta \\ \sin \theta & \cos \theta \end{bmatrix}$ live in $SL(2,C)$ and cause a spinor to go from $\psi$ to $- \psi$ under a $2 \pi$ rotation which is impossible because $SL(2,C)$ is simply connected

vzn

11:42 PM

via reddit for the ML/ AI fans in here, remarkable

in theory salon, 44 secs ago, by vzn

https://thispersondoesnotexist.com/ https://www.lyrn.ai/2018/12/26/a-style-based-generator-architecture-for-generati‌ve-adversarial-networks/

Transcript for