The h Bar - 2016-02-12 (page 1 of 3)

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12:00 AM

Stephen, I have edited in the reference. I find it extremely disingenuous that you attempted to hide your authorship of that document behind the link. Going beyond that, I don't think this is really the venue for the type of debate that you're looking for; we are not a substitute for the discussion that is currently taking place in the literature (cf. Johnson and Robitaille in the latest issue of Progr. Phys.). We are also not a substitute to peer review of your paper from last year. (You can try your luck at physicsoverflow and see what they say, maybe?) — Emilio Pisanty 5 hours ago

@Danu what

^^for others interested. Great comment

@0celo7 Which book is it.

Oh, Diff Geo by R.W. Sharpe.

Thanks.

Subtitle Cartan's Generalization of Klein's Erlangen Program.

@Danu Chern wrote the preface.

12:04 AM

Looks very interesting. Thanks a lot for the reference.

I like the idea of focusing on group actions

(that is what it does, right?)

How would I know? I'm planning to read this in years

Chap 1 kicked my ass already

Well, the first few chapters are on related topics

homogeneous spaces

what book are you looking at?

first few chapters are basic geometry, foliations and maurer-cartan stuff

But the first chapter, while basic in a sense, is written for a far more mature audience than e.g. Lee

Funny; I saw a summary while googling---you're right that the contents seem different.

@Danu It's also charitable to call a paper in Progr. Phys "discussion in the literature", since that's reputed to be viXra in journal form.

12:08 AM

@0celo7 I like that! Lee is starting to be a bit "too explicit" sometimes

Maybe I'll see if I can get anything out of this book some time

...but I'm already swamped in other shit of course :\

I should be doing problems in Bredon right now

^good idea

I did that too, last summer :D

't was fun

@Danu Problem is, my prof also wants me reading this PDE book and some nonlinear analysis shit

I can't absorb stuff instantly :(

Maybe Milnor this summer would be too ambitious

What other interesting stuff could I get him to do a reading course on

@Danu what's some interesting geometry stuff that doesn't need as much algebraic topology as Milnor

@Danu now that I vehemently disagree with

user54412

@ACuriousMind it's a new day :p

boy we are getting a lot of gravitational waves in SE aren't we?

12:24 AM

@gonenc Well, what did you expect?

@ChrisWhite Good timing, that

@ACuriousMind I just didn't expect this much

@gonenc It's almost worse than when Planet Nine was proposed.

how do we go about simultaneous-duplicate questions

@gonenc Choose the better written one, close the other as duplicate.

Or choose the one which already has answers, if one of them is still unanswered

@ChrisWhite I hadn't considered those. I always think Type II when thinking about supernovae, or Type Ia.

user54412

12:27 AM

Of course, with 70,000 questions asked on the site, even if we got 100 new questions on a topic, it would affect anything at all

@0celo7 Guillemin & Pollack

It's differential topology $\simeq$ geometry

(the homotopy equivalence is obtained by slowly forgetting all about what differential structure means)

I just finished reading the entire Blumenhagen book in about 4 days

-_____-'

Exam time tomorrow!

@Danu Yes, that's also one of the books on his list

Hori et al. - Mirror Symmetry

Physics AND super deep math

all in one 1000 page book :D

(also i will read this for my thesis prep.!)

Uh

bye for now

12:37 AM

He's never mentioned that

bye

@0celo7 It's not a standard math curriculum thing :P

Where's the party at, yo?

@ManishEarth Frat row is that way

user54412

There are so many times I wish I had a gif of confetti on hand...

12:53 AM

@ChrisWhite name one other time

1:20 AM

@ACuriousMind Can one prove the convergence/divergence of $\sum n^{-p}$ without using the integral test?

0

Q: Proving the convergence of the $p$-series without using the integral test?

I'm having trouble figuring out how to prove the convergence of the $p$-series, that is, $$\sum_{n=1}^{\infty}{\frac{1}{n^p}}$$ where $p > 1$. I'm in a real analysis course and I have a midterm coming up. I think I might need to prove this on the midterm, but without using the integral test. ...

@Secret yay my hunch for solving it was right

I don't understand any of those.

(Do the opposite of the proof of divergence of the 1/n sum. The one that's like 1/2+1/2+1/4+1/4+1/4+1/4+ whatever)

@0celo7 do you know the proof for divergence of sum 1/n I'm talking about?

No

1:29 AM

The first answer in secrets linked q is that, in reverse

Oh then google it. There are a ton of better explanations

And I'm on my phone and dont want to type slashes :D

0

Q: Can a photon be captured at a fractional Planck distance in space?

Consider a photon, positioned in space in a finite portion of a grid. Any point of the grid is vertically or horizontally aligned, each distanced by a Planck unit. $l_P = 1.616 199(97) × 10−35 m$ The speed of the photon is, in this grid, $v = l_P/t_P$ The photon is first captured at its orig...

particle-physics spacetime distance

@GBeau yeah I got an email from UCLA

and MIT

I sometimes wonder about things similar to these when thinking about planck units, but I guess the uncertainty principle would take care of that

no Harvard

1:53 AM

Below is an example on why it is so easy for my maths question to get tread into things like category theory or even metamathematics:

This question is generated by generalising the above question in the MSE
What are the criteria that a mathematical object $M$ has to satisfy in order for the question "Proof some properties in $M$ without using some properties $A$" to have a nonempty solution

The funny thing is that, most of the time, these questions while hard, actually makes sense

Which then caused me to wonder about an even philosophical question:

Why are things seemed to have properties independent of the scope and scale of the context

@DanielSank I'm reasonably sure that's the hard part of new thermo text.

that is, it seems the same set of principles can be used whenever you are talking subatomic particles, or the cosmos, whenever you are talking about a number or a category etc.

2:13 AM

@dmckee Let's hope I get on payroll tomorrow

2:55 AM

@ChrisWhite are you around

user54412

maybe

user54412

depends how entertained I am

$\frac{1}{\sqrt{2}}|\text{around}\rangle+\frac{1}{\sqrt{2}}|\text{away}\rangle$

@ChrisWhite If $E\to M$ is a vector bundle, have you seen the notation $\Omega^p(M;E)$ before?

user54412

poor \lvert forever neglected

3:00 AM

Wouldn't that be the pullback?

I think it should be illegal for a book to not have a comprehensive list of symbols

@dmckee is that at me?

@ChrisWhite Since I've started using the physics package I haven't had to recall that stuff.

@0celo7 Yes. But not because I'm an expert. Just because I've a vague feeling I;ve seen it before.

user54412

"vector bundle" -- do I look that much like a mathematician? (no I haven't seen the notation)

@ChrisWhite you have a degree in math!

@dmckee ok, what is being pulled back by what

user54412

only a bachelors

3:01 AM

So, ACM doesn't have any math degree

Ah!

user54412

also, my degree in physics detracts from my math degree I'm pretty sure

@0celo7 Not a clue. But it could be a general abstract nonsense thing.

$\Omega^k(M;E):=\Gamma\left(E\otimes\bigwedge^k T^*M\right)$

That makes sense

@dmckee no, this is not category theory

user54412

everything is category theory

2

but every book should have a comprehensive list of symbols >:(

@ChrisWhite Hmm, $\Gamma$ is a functor.

So is $\bigwedge^kT^*$.

user54412

3:04 AM

One thing I'd really like to do (perhaps the wizards at tex.SE can help) is have a document where all symbols automatically hyperlink back to their first use (with possible overriding to link to specific uses).

user54412

@0celo7 So have your German nuc profs been talking about Wendelstein?

@ChrisWhite I only have one and he doesn't give a shit about fusion :P

user54412

too bad

user54412

they've definitely put themselves back in the race to break even

@ChrisWhite He's a solid state physicist, not a plasma guy.

And his research tends to have more fission applications.

Although we're looking at solid state fuel cells now because of an accidental discovery a grad student made.

user54412

3:14 AM

also, stellarators are apparently the brainchild of my academic great great grandfather

@ChrisWhite Chandrasekhar?

Eddington?

user54412

Spitzer

Never heard of him.

All I know about him is that his name means "pencil sharpener" in German.

user54412

lol

user54412

he (and Chandra) have space telescopes named after them

user54412

3:16 AM

Eddington doesn't even get one of those

@ChrisWhite Hmm, what's a vector bundle called where the fiber is a Lie algebra?

user54412

algebra bundle?

Did you guess that?

I...think that's right.

user54412

which will impress you more, saying I knew it or saying how good I am at google?

The latter, honestly.

@ChrisWhite What happens if one does GR on bundles other than $TM$

Can one define the Einstein equations for a general vector bundle geometry?

Hmm, how would one get a Ricci tensor...nevermind.

3:43 AM

I seem to become grumpier and curmudgeonier every year.

@dmckee Me too.

I'm mostly staying away as the least stressful way to not shout "You didn't give a shit last week! So come back when the big kids are less busy, already!"

Which even I recognize as neither constructive nor entirely fair.

What?

What's the context? What kids?

You have kids?

user54412

I'm not sure I've seen a self-consistent, well-defined notion of "fair"

user54412

which is one way of saying that's entirely fair as far as I care

3:51 AM

@ChrisWhite Nothing is fair.

@ChrisWhite The turnabout rule is at least a working heuristic.

At least, it works between saneish people.

@0celo7 The way to analyze that is to think about who could be accused of "not [giving] a shit last week" who might be annoying me and work from there.

Chris got it.

@dmckee Your wife?

Them's fightin' words pad'ner.

Well I don't know what the hell you're talking about and you won't tell me.

Just trying to help.

user54412

3:57 AM

@0celo7 doesn't have many points in perception

Apparently not!

@dmckee A failing student?

A philosopher?

What did Chris get? He didn't say anything!

I'm so confused.

A student is wrong but a better guess. A philosopher is correct but it always is and I don't care about giving them a fair shake.

Chris said he thought I was being fair implying that he knew who had in mind and at least partially agreed. So it has to be someone Chris might be annoyed with too.

Ah, someone on PSE.

Now you're on the scent.

user54412

I bet @dmckee and I could come up with a list of people not on this site we're both annoyed with

4:02 AM

Sometimes I forget you're a mod -- you're too nice.

@ChrisWhite Well, maybe on or two. Dozen.

Can we start with science journalists?

Why not start with terrorists and dictators?

Too ubiquitous. You get numb to the evil.

@dmckee I bet it's not hard.

You just have to get your head out of your butt and stop regurgitating the same ill defined garbage that books have been regurgitating for decades.

I hear Callen's book is better though.

I'd be hard for me. I can muddle through but clarity is not my gift on the matter.

4:07 AM

@dmckee The real problem, of course, is that even if someone does write it up nicely, that's not enough to publish a book.

The barrier to publication is enormous.

@DanielSank I hated Callen so much as an undergrad that I sold it back. Then I had to buy it again for grad school and I fell in love.

This is why we need modular open source textbooks.

user54412

There is currently more direct evidence for the existence of gravitational waves than for the existence of a good thermo text.

4

Each module explains one thing and links to its prerequisites (multiple) and next steps (multiple).

I'd say it shouldn't be a first text on the subject. Now if you could write Callen lite I'd adopt it.

4:08 AM

Wow, predictable star much

user54412

it's an astronomer thing, what can I say

In the imaginary parallel universe in which I quit my job and dedicate five years to writing pedagogical texts, this would be one of the steps.

@ChrisWhite ffs

It's my current plan for retirement...

but by then I'll have forgotten everything.

you're not even an astronomer

4:09 AM

@DanielSank I've been writing some notes like that for myself. Original working title "Forgotten Grad School Physics". Now I'm trying to adapt the earlier parts for my students, so the new working title is "A Physics Student's Companion".

you're a programmer

@dmckee Oooh, can I edit the section on GR

more bundles!

@dmckee I have an enormous set of detailed modules on various important physics and math topics.

I don't have a section on GR and I never knew bundles.

@dmckee Noooo

My little plan that I'll never execute is to put them into a website that admits further additions and interlinks as described above.

4:10 AM

@DanielSank is there a git file with all of that

Imagine you were reading an E&M book and you could click a link to "wtf are all these vector symbols".

@DanielSank That had occured to me too, but the administration would be a nightmare.

So I, too, will probably never go that way.

This is what we really need, and consistent notation would make it amaaaaaaazing.

vector symbols are trivial, @DanielSank

@dmckee There has to be a way to make it work.

A review procedure and unbreakable notation rules would be very important.

4:11 AM

@0celo7 Oh, good. I'll tell my students tomorrow. I"m sure they will all feel relieved to hear it.

@dmckee nice!

what are they confused about

There needs to be ONE differential geometry book

@0celo7 That varies from student to student as does the degree of self-awareness about the difficulty. Which is par for the course in the teaching business.

This is what the world needs

Fortunately, the charging one has been solved now that we've all standardized on mini-USB. Or is it micro-USB? Shit.

it needs to go from point-set topology to Cartan geometries and prove EVERYTHING

I don't care about the notation

I just hate that I have to go to this book from 1983 to find a proof

and in that book I'll have to go to Steenrod, inevitably

but he doesn't explain any algebraic topology

so I'll ask ACM

I wonder if there are any geometry books that don't reference Steenrod

@dmckee what's the "average"

maybe I don't get it either

I am just a Freshman, after all

4:16 AM

Right now they prefer to write things out long hand rather than try to grok the expressions in sum form. All the proofs I've graded from M&T's chapter one so far are doing it. Well, my solutions are in the compact form, so they'll have to think about it to ask me questions.

Oh, well I've done enough GR that sums are second nature

I had that problem is class yesterday too, when telling them about the extension of the exponential function to the complex domain.

They wanted to see the first few terms of the odd and even groups in order to identify them as sin and cos respectively.

Did you prove absolute convergence of the sum?

No. I referred them to the math department. I know I've done that proof once, but class time is too valuable for that stuff.

The proof is an exercise in my analysis book -- I don't know how to do it yet.

So it's safe to say it's nontrivial, unless we're willing to accept the fact that I suck at math.

Well, we have a whole unit on power series, so that will be fun.

4:28 AM

Not as fun as today's LIGO announcement was :-)

user54412

@DanielSank So I'm reminded of a conversation we've had about astro and the things we do for signals. Now we're entering an era where 10^{-21} strength signals will be the norm. How many of those have you measured lately? :p

@guest I still don't care about that.

How can you not care about entering a new era?

It doesn't do much for me

Or anything, really.

user54412

and algebra bundles do?

4:35 AM

What did they teach you in high school about "measurement"? Give me their definition.

user54412

is this a quantum question in disguise?

nope, I just want to find out why the lack of interest.

0celo7 and you call yourself a physicist? or physicist in training? more like a scientific nihilist...

the math professor who teaches my cryptography class is a funny guy

You are weak?

They all say that :P

4:46 AM

@GBeau I'm still waiting to hear about a crypto class taught by some guy named Mallory. I mean, sure, Bob is a little funny but Bob's are a dime a dozen while Mallorys are pretty scarce and would be funnier to begin with.

Professor Eve would be a good runner up, of course.

@dmckee Hah! Get a load of the messages my professor leaves:

user image

Congrats on NYU @GBeau :-)

Classic.

@vzn I don't call myself a physicist.

I'm sure @ACuriousMind will be happy to provide you with the evidence.

The man who can outcypher Vizzini can plan my key distribution system any day!

4:50 AM

@ChrisWhite They get me excited in a special way.

^ TMI

@dmckee We were told the primes for that RSA were chosen poorly. As it turned out, very poorly: that was the first thing I tried.

Rule 34 consequence: HotAlgebraicBundles.com

You must have really liked algebra and trigonometry in hs. @0celo7

@guest Hated it. Why?

4:53 AM

^ Bored, I assume.

No, algebra 2/trig was the hardest damn class I've ever taken.

quadratic equations ::shivers::

there's a reason why I have a CAS now

You quoted trig as the heart of science.

@guest Yeah, that was T. Paine!

From 17--

I think fiber bundles are the heart of science -- classical science anyhow

@ChrisWhite 10^-21 what?

i.e. non-quantum

4:55 AM

Like, signal to noise ratio of 10^-21?

@DanielSank no, the amplitude is 10^-21 m

@guest Seriously, trig is just the study of the frame bundle on $(\mathbb{R}^2,\delta)$.

everything is a damn bundle

Measurements are not bundles.

measurements are sections of bundles

Someone ought to also write a self QA about how the interferometer at LIGO works. It uses a very subtle quantum mechanics trick to improve the noise coming from the so-called "photon shot noise" (terrible phrase, but whatever).

How so?

4:59 AM

@guest You can make everything into a bundle ;)

Just attach the space of measurements to each point of spacetime, voila, measurements are sections

I'm not saying that's useful, but you can force a bundle anywhere

I'm beginning to see why LIGO means nothing to you.

why

You just don't care.

@guest what

I said that earlier

I don't care about the LIGO experiment

There's no mystery there, nice observation

You don't find it mysterious that two black holes can merge into one?

5:08 AM

No?

Are you saying I don't care in general?

What if Mars merged into the Earth?

Am I alive or dead when this happens?

Alive.

Well, I don't want to die just yet.

What kind of question is that?

A cosmic question.

5:12 AM

me on LIGO: youtu.be/WgZRUHJ-FNg?t=22s

Until today black holes were just equations on paper; today they are measurable which makes them a real object.

So they claim

With evidence.

Where can i get the paper that einstein published describing gravitational waves

5:31 AM

scitation.aip.org/content/aip/magazine/physicstoday/article/68/…

@guest I haven't seen black holes in the night sky

but it doesn't matter whether they're real or not :)

I'm not excited because nothing has changed.

Heh, Ben Franklin says your mistress should be old so there's no chance of errant children appearing.

When people found out that the world was not flat nothing had changed for them either.

Ok?

I don't see the issue.

5:58 AM

Nobody can make you see.

@guest What

The issue.

@guest I don't see the issue.

0

Q: Is there a connection between Space-Time Vortex and Gravitational Waves?

Is there a connection between Space-Time Vortex and gravitational waves ? Space-Time Vortex

gravitational-waves

Beautiful

6:15 AM

The Science of Internet Trolls

More beautiful.

6:33 AM

Very high temptation to post a Rocky Horror Picture Show link under the question about gravitational waves and time.

Let's do the timewarp again!

6:44 AM

::the horror, the horror ::

wait till they start asking "what are the waves waving in?"

2 hours later…

8:23 AM

@Danu Confusion in a problem

btw how sure are we of gravitational waves? ie. is there a possibility that they goofed like the speed-of-light-thing in italy

@gonenc Unlikely.

The waves were detected in two locations hundreds of miles apart at the same time.

Very unlikely that this would be an accident.

They said 5 sigma.

That's quite a lot.

@DanielSank I know that would be very unprobable accident

I didn't know it was 5 sigma. I knew it was alot :D

Then what are you trying to ask?

@DanielSank that wasn't a clear formulation of mine...

8:33 AM

Thoughts on a LIGO tag?

Too transient? Or useful?

@dan it's probably way more than 5 sigma, that's a lower bound on the significance. In there sampling distn for the test statisitc, they couldn't generate any events in the tail beyond test stat =13 or so. The event was at about 20.

Simulating tails of distn s to find p-values is tricky when the p-value is so so tiny.

@innisfree too transient (imo)

Are we condemned to 2 months of questions on gravitational waves

GR is really much simpler than QFT

When I see GR questions on SE I always know what they're talking about

When I look at the QFT tag half the time I don't fucking know what's going on

9:05 AM

user image

2 hours later…

10:58 AM

user image

2 hours later…

12:31 PM

@DanielSank Do you really want to, tho

The mathematical theory is GEOMETROTHERMODYNAMICS

It has CONTACT MANIFOLDS

@Slereah Hi

hey

12:51 PM

@Slereah Are you a physics student?

Not in a while

@Slereah I'm trying to convert to physics from pure maths, quite tricky because there are a lot of basics that I missed out on :/ but it's interesting anyway...

Ahahah

I did that once

Did a year of pure math after my physics master

Did not end well

@Slereah Yeah the conversion seems easier until you actually get into it. But I'm working through Griffiths QM book at the moment. Will look at more advanced books later if I survive.

Yeah the trick is

Mathematicians have a very different definition of what "calculus" or "differential geometry" means

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