@ACuriousMind Ligo, I'd assume. Otherwise, no-one can vote on this!

Democracy ftw

@Danu The process is not symmetrical - look on the synonym page of ligo, there's no grav-wave-detectors there. So I think that if A is proposed as a synonym of B, you need the score in B, not in A.

@ACuriousMind Hmm... :P

(proposing grav-wave-detectors as a synonym of ligo, however, doesn't really make sense because the former is broader than the latter)

@ACuriousMind : Hmm, and there are only two grav-wave-detectors questions for now, so that's impossible. Ok, I'll create the synonym now unless there are protests?

Done.

@Danu egad, insufficient rep to vote on the tag merger. It's been a while since that happened to me :-) I'll try and answer a few LIGO questions then vote for the merger.

Guys I need some help

I remember once finding an example of a solution to Newton's Laws for a ball on top of a solid half-ball where the ball starts to spontaneously move at some point.

Maybe it was on Baez's pages, but I'm not sure.

Norton's dome

Thanks.

(that was fast) :)

@ACuriousMind oh you bugger! I was about to post that!

Needed it for this:

@Danu Well, are the wormhole and while hole solutions of the type of Norton's dome (i.e. they are solution for some initial conditions where a "simpler" solution also exists)? Otherwise I don't see the relevance.

@JohnRennie Think about how often that has been thought after you answered a question ;)

@ACuriousMind I think he's arguing that every possible situation must be realized. This counters that.

But I see your point. It's not 100% the same.

@Qmechanic Finished going through the entire gravitational-waves list.

@Danu : Good job!

Thanks.

@ACuriousMind :-)

I'm close to my next golden badge :D (review though, so not very exciting)

I'm 50/100 to my first golden badge on Math.SE (visit 100 days in a row)

I'll probably manage to screw that one up, though

A have a math question I gotta post there...

I've just checked the review queue and there are 26 posts in the close queue that I can't vote on because I've reached my limit. 26!

Yeah, the close queue has been very busy for a while now

We have either a shortage of 3k users, an excess of idiots or both :-)

Random question but im confused how this works - how do the stats not add up to 100%

like how are they getting 61% from that graph

it clearly doesnt add up to 61%

@JohnRennie An excess of 3k idiots?

@ChrisWhite : Noted. Do other agree with Chris White on this?

@Qmechanic yup absolutely

@ChrisWhite Staying true to myself, then ;)

@HariPrasad : OK, then I'm breaking the synonym for now with possibility to vote for the selected few.

@Qmechanic I think that we shouldn't have a tag for every notable experiment in the long run, but they make sense over the short run.

@dmckee : I agree.

What if we use a three step process. (A) Make a tag for detectors that hit the news.

(B) When there are several devices in a class we make a tag for that class, and ...

(C) eventually make the specific tags synonyms for the general.

@dmckee : That's was my thinking as well.

The one thing to watch out for is questions that really do address a particular instrument but rely on the tag to make that clear. They are going to have to be edited so that the device in question is part of the title or text lest the tag synonym render them ambiguous.

@ChrisWhite Is that alien stuff

@Qmechanic @ChrisWhite we just have one successful detection of gravitational wave and one known (true) source that produces it. i think we should find some other sources and reproduce the experiment either with the current technology or maybe advanced ones before we can generalize it

@Qmechanic I agree with this too

@ChrisWhite How many people actually write a LIGO/LHS tier paper

@ChrisWhite It looks like a peak. The skew toward the left could easily just be random, so I wouldn't put much faith in it unless there is a reason to expect a structure to that side.

Just on the size of the error bars and density of the bins that looks a lot like typical particle data from the mid to late 1980s. Much better than the previous generation and a bit crude by modern standards.

@0celo7 While @ChrisWhite is right that a relatively small number of people actually provide text, a non-trivial fraction of the collaboration will have made specific comments on earlier drafts.

I written comments for more than half the papers I'm named on, and only write a "looks good" comment if (a) I'm the first people to so responds or (b) I've been specifically asked for my feedback on a particular section and I don't have anything to criticize.

I've suggested alternate phrases, made editorial remarks about punctuation, suggested changes to plots or captions, ask for clarifications and so on.

You don't want hundreds of people actually touching the paper, but instead designate a team and send feedback on particular section through the person in charge of that section.

So, when you are using a LIGO even to set the window the "we're plotting thousands of bins so it's likely that we'll see some three or four sigma events" problem is strongly suppressed.

In the absence of some other explanation that is very suggestive.

Ive downloaded by not read the preprint.

I suppose that amount of expected high-energy E&M radiationdepends strongly on the matter environment around the holes when the inspiral finishes.

Has anyone produced simulations or BoTE calculation? How bright should that be in the gamma?

Ah ha! Is the difference in arrival times consistent with a guess at the intergalactic index of refraction over those distances?

@ChrisWhite The big one, I suppose. Unless the index of refraction is unknown at a scale that admits that kind of range for the difference?

Then it's big but not huge. In my ignorance I'm willing to entertain the idea that it is real.

That makes life harder.

I was imagining something pretty non-specific. So you'd expect a lot of light across a lot of bandwidth.

My latest creation.

@Danu That's not a covering in the usual sense.

@ACuriousMind The result?

No, that's the point

@Danu No, the first map

I actually didn't have time yet to think about what the prof. meant ,exactly.

About the first map.

Something has to be done about the "lines in between" and maybe even more

The fiber of the red point is the entire real line (or at least it looks to me as if it is meant to), which is not discrete, hence the map is not a covering.

(see above)

I'll think about it later; for now I'm going to have some drinks. Tell me if you come up with something good :)

@Danu No one asked him when he described that? oO

Or rather, how do you know you drew the right thing there? :P

@Danu found it, the map doesn't do what it naively looks like - it sends the $n$-th circle on the left the the $n+1$-th circle on the right, and the unit interval between the integers to the outer circle on the right.

Just drawing that picture without stating that is highly misleading, imo

I think the "proper" visualization is spiral-like like that of $\mathbb{R}\to S^1$, but that probably looks really confusing when trying to draw it in this case.

@FenderLesPaul slow day

@GPhys yeah

expected more

UChicago is still keeping people at the edge of their seats

@ACuriousMind We did a damped wave equation in PDE today, I don't get this step in my notes imgur.com/a/4FAel

Very funny :P

@ACuriousMind No really, that's my PDE lecture notes from today...

@ACuriousMind So I showed my proof of Heine-Borel --> least upper bound property and he pointed out that I didn't use Heine-Borel anywhere

But he couldn't find the mistake

I think I nerd sniped him...but sadly we were interrupted because there's a test on Thursday and people are bad at analysis

Why would you ask me a question to which you know the answer?

I work in mysterious ways, Bajoran.

should I read nakahara or a topology and diffgeo book if I want to understand orbifolds?

Yes

@FenderLesPaul is that a reply to my comment?

why would you want to understand them

Idk they're cool.

I like the name.

Fair enough

well which one is it?

would I be better off reading munkres?

or lee?

@bd-3 yes

Just read the orbifold book + wiki

@FenderLesPaul amazon.com/Teletubbies-Hide---Seek-Lift---Flap/dp/0590386174/…

yes PLEASE

yes

@bd-3 yes

I used to love those things

@0celo7 are you sure it will be enough prerequisite to learn about orbifolds?

Yes

Exercise: Compute the fundamental group of each teletubby

in all seriousness though, you're suggesting I just read the book and wikipedia whatever I don't understand?

Get the book, maybe it explains everything you need

If you're hell-bent on reading it, get it

You can always read it later...

ok.

it doesn't explain anything.

gyazo.com/f0f13b2f89700c2ff9ce984375fdbcc9

I only know some of those words. :P

does nakahara cover the rest? (as prerequisite)

Well how do they define the orbifold atlas

@0celo7 gyazo.com/902d7209c7b0a7310e9f9b50ff10db8c

Wtf AMS books from the AMS website are softcover

will nakahara prepare me to understand all of that?

or should I read other books?

Probably.

do you understand it?

I think so.

ok.

and the only topology book you read was nakahara

right

@dmckee : if you'd like to ask a question about spin angular momentum I'll be only too happy to answer it.

@ACuriousMind What is "tropical geometry"?

The theory of coconut bundles.

@ACuriousMind I honestly don't know if you're kidding or not

@0celo7 If only there was a freely accessible repository of human knowledge that you could consult to find out...

@ACuriousMind Yeah, you, I'm asking you.

guys I need career advice.

Idk what to study in university

what do they offer in Canadia

everything they offer in the usa...

what about something exotic like moose care?

@bd-3 they have nuke engi?

@0celo7 yeah

I'm debating between compsci and physics.

I suck at compsci though.

and I don't know anything about it which makes me want to study it.

I did compsci. Do physics instead.

@ACuriousMind Is $E:=\mathrm{id}$ a European thing?

@JohnDuffield why?

Damn Germans. The book is in "graduate studies in mathematics" but the author says it's accessible to third year undergraduates.

@0celo7 why does that matter though?

@bd-3 Because the Germans are too smart

@bd-3 : computer science is where you learn about things like transistors and NAND gates and parallel adders and processors, and about software and other things too. But it's mundane. It isn't interesting and exciting like physics is.

@JohnDuffield There's a lot more money in CS than in physics.

@0celo7 Uh...not that I'd now. It's personal preference as far as I'm concerned , although $E$ stresses more that it's the unit (the $E$ comes from the German Einheit for unit) of composition, while $\mathrm{id}$ stresses more that it is the identity on whatever space you're considering.

@0celo7 Your point being?

@ACuriousMind you should know by now. lol

@bd-3 It does actually matter because it's hard to judge what one needs to read the book.

@0celo7 : if you've got a physics degree you won't have any problems getting a job in IT if that's what you want. Or a job as a Quant.

A book on stuff including Seiberg-Witten theory and it's accessible to juniors? Either the author is a god of pedagogy or we have the standard German education where their second year students can outperform grad students over here.

A friend of mine actually did a seminar on Seiberg-Witten theory in his third year, it was quite well-attended.

See?

Completely ridiculous.

And then it pisses me off when profs say I know a lot of math.

@0celo7 but he's in his third year.

you're a freshman.

and people evolve really fast in university.

I'm taking third and fourth year classes.

@0celo7 that doesn't mean you're third year.

I'm classified as a junior in the school's database.

@0celo7 I think you'd be a lot less stressed about all of this if you stopped assigning "xth year" labels to knowledge or courses. We don't do that here, either.

@ACuriousMind Because you move extremely rapidly.

How are people who didn't take calculus in high school supposed to become mathematicians in this country?

I skipped two years of math and I'm still way behind German students.

is algebraic topology algebra or topology?

@dmckee Do you think that this book is accessible to the average junior or senior in mathematics and physics?

@0celo7 The generic German student doesn't do all this stuff, either. When someone says "it's accessible to X" they don't mean "everyone in group X is able to understand this without problems", they mean "interested and able members of X will be able to understand this after possibly quite a bit of work".

@ACuriousMind The preface clearly says that the perquisite material "should" be provided by the second or third year.

I'm shocked that in Germany one "should" have seen $G$-bundles by the second year.

According to @DanielSank, most grad students here haven't even heard of forms.

@0celo7 Definitely not true (many people don't care for bundles in any case) - but if you are interested in that direction, it is also definitely possible.

Ok, topic change, this one is too depressing.

Hmm, I don't have anything to change the topic to.

Yep, you painted yourself into a corner :P

"The Hodge star acting on 2-forms on a 4-dim manifold is conformally invariant"

@ACuriousMind Is there some clever way to check this or just brute-force calculation?

@skullpetrol Well, I could ask ACM if he thinks I should do topology or actually useful math next semester, but we all know the answer to that

Argh, that book is still $300

@0celo7 : IMHO there's something else that's a too depressing. Like, I know why light curves. And I know why an electron falls down. But I don't know why a black hole falls down. You will forgive me if I don't go on about it too much at this juncture. OK, since it's 11pm here in the UK, I'm off to bed.

Here's a star for your efforts pal :)

@0celo7 If $F,G$ are forms in the middle dimension $D/2$, $F\wedge{\star}G=\langle F,G\rangle\omega$ by definition. The r.h.s. is conformally invariant because $\omega$ changes by $\Lambda^{-D/2}$ under a Weyl transformation, and the $\langle F,G\rangle$ has exactly $D/2$ metric tensors in it each giving one factor of $\Lambda$, so they cancel. Since $F,G,\wedge$ on the l.h.s. don't change at all, $\star$ can't change either for the whole expression to be invariant.

@ACuriousMind Neat-o! It's probably in Hatcher...

Thanks for searching.

@ACuriousMind Ah, nice.

has paul davies written any physics papers recently?

Is he still active?

Is he even alive?

lolz yes he is at ASU

@Danu You're welcome (would've bothered me the whole time if I didn't search for it ;) )

@ACuriousMind It's actually the obvious modification

I'll indicate it with color-coding in my diagram, I guess...

I think Leeb must've lifted it from a book---he would've said something if he had properly inspected it.

@Danu He's got the lifting property w.r.t. books?

@ACuriousMind Exercise 1.6 from Hatcher... Yup.

...

@ACuriousMind (also lol, I see what you did there)

@ACuriousMind His lecture is fully contained in the characteristic projection of Hatcher ;)

LIGO’s black holes may have lived and died inside a huge star / new scientist

> It’s too soon to know whether this idea is right. Even Fermi’s results are in doubt: researchers analysing data from the European gamma-ray spacecraft, INTEGRAL, couldn’t corroborate Fermi’s finding, and concluded that the gamma ray signal is not real.

arxiv.org/abs/1602.04180

@Danu I think this book is also in the spirit of Sharpe.

Thanks for the link

@Danu Np, I'm hunting for geometry things for a summer reading course under my adviser.

what a time

@Danu So if you could throw something interesting my way it would be much appreciated

Ideally something that doesn't require algebraic topology -- I'm reconsidering Milnor because of that

@0celo7 Haven't I given you all I have to give? :P

@Danu I can't join.

Oh, haha