The h Bar

0celo7

12:02 AM

@ACuriousMind Is, by some miracle, $M\setminus\{p\}$ always orientable?

ACuriousMind

Don't think so - at least the Möbius band being orientable if you remove a point feels weird to me

0celo7

$M$ is a closed manifold.

what is $\Bbb RP^2$ minus a point?

Just a disk, right?

that can't be, because putting the point back shouldn't change the orientability

The punctured RP2 is a mobius band

well, that's not good.

@ACuriousMind Ok, I have another doubt

Suppose $\tilde M\to M$ is a double covering. Is there a way to pull back $M\# T^n$ to get $\tilde M\# T^n\# T^n$ or something?

0celo7

1:22 AM

(yes, there is)

DanielSank

@ACuriousMind o_O

0celo7

1:35 AM

@DanielSank That's not true, he's saying it would be strange if it were.

Cows

2:21 AM

Heading to the beach for a run and quick swim

ACuriousMind

@0celo7 Sure - you just take the preimage under the covering map of the disk you're cutting out from $M$, and that gives you two disjoint disks in $\bar{M}$ you can use to do $\#T\#T$, no?

Bernardo Meurer

@ACuriousMind Make me minister of memes for Namibia

0celo7

@ACuriousMind Yeah, see the comment right after.

@ACuriousMind I want to draw this for a seminar talk. What's a good double covering?

ideally a 2-manifold

ACuriousMind

@0celo7 $S^2$ and $\mathbb{R}P^2$?

0celo7

@ACuriousMind Well sure, but if I could draw the latter I'd be a topologist.

ACuriousMind

2:33 AM

Well, I think the only double cover I can draw is $S^1\to S^1$ :P

0celo7

(although I do want it to be an orientation covering in the end)

@ACuriousMind lol

I wish I knew where my algebraic topology homeworks were

there was some neat stuff in there

Bernardo Meurer

@ACuriousMind Buy the Dragon Book

ACuriousMind

@BernardoMeurer Huh?

Bernardo Meurer

amazon.com/Compilers-Principles-Techniques-Tools-2nd/dp/…

ACuriousMind

Ah

Bernardo Meurer

2:35 AM

It's the reference on compiler construction

0celo7

@ACuriousMind For reference, I am studying manifolds of the form $M\# T^n$ where $M$ is orientable. If it isn't, then I can do that unfolding to work with $(\tilde M\# T^n)\# T^n$ instead and it works just as well.

$M\# T^n$ is a natural compactification for AF spaces

Bernardo Meurer

2:55 AM

@dmckee o/

0celo7

@BernardoMeurer I have a fortran group project

dmckee

@BernardoMeurer Everyone should read the Crenshaw Tutorial before embarking on the dragon book.

0celo7

how much do I have to pay you to write the pseudocode

Bernardo Meurer

@0celo7 How large is the project?

@dmckee Oooh, I didn't know that

dmckee

It puts the whole subject on a grounded an nonmysterious footing.

Bernardo Meurer

3:01 AM

I bought the book

0celo7

I haven't looked too carefully, but it seems like something with the heat equation

dmckee

@BernardoMeurer It's my opinion rather than a general rule.

But I stand by it.

Bernardo Meurer

@dmckee Link?

dmckee

@BernardoMeurer You can find the tutorial on line, and its a quick read.

Looking...

compilers.iecc.com/crenshaw

Bernardo Meurer

compilers.iecc.com/crenshaw

Aha

Alright, I'll read it :)

Good lord this is unreadable

I'll format it in LaTeX

0celo7

3:03 AM

kek

@BernardoMeurer do you want to see the typesetting in my thesis? It's top notch

Bernardo Meurer

@dmckee Thanks for the recommendation! Anything else I should know before starting to write my C compiler?

dmckee

I think I used the plain text files.

Bernardo Meurer

@0celo7 ye

dmckee

@BernardoMeurer Uh ... get a subset working first. It's not a huge project, but it's nice to have something to show halfway along.

Bernardo Meurer

@dmckee Alright, got it :)

How's the kid?

0celo7

3:06 AM

@BernardoMeurer for example i.gyazo.com/40bfb4a92f72706949b28c7e21558c8d.png

dmckee

@BernardoMeurer She's grasping, rolling over, and very sure of what she wants. Sleeping pretty well, though.

Bernardo Meurer

@dmckee Glad to hear all is well, specially wrt to sleep!

0celo7

ready for diff geo yet?

Bernardo Meurer

That is indeed top notch

No

I left that life behind me

0celo7

I meant her

@BernardoMeurer what??

Bernardo Meurer

3:08 AM

Oh, good

0celo7

3:52 AM

@Semiclassical So I've managed to wrap my head around the positive mass theorem literature. I'm about to offer to give more talks next semester. Is that a mistake?

ZeroTheHero

4:29 AM

allo... just wonderin’ if the chat community could identify subfields of physics where the majority of submissions for peer review are NOT in LaTeX. I mean: are there subfields of physics where the bulk of manuscripts are submitted in MSWord for instance? Anecdotally LaTeX is completely dominant in theoretical physics, and a simple survey of arXiv submissions suggests most of these are in LaTeX... but there might be exceptions.

Physics Meta

5:05 AM

0

Q: A moderator understood and answered my question but put it was put on hold as unclear?

I asked this question Zero Radiation Nuclear Bomb Possible? and a moderator completely understood my question, provided an answer and mention he would like to see other answers, but it still got put on hold for being unclear after he posted. How is this? I believe that it was too quickly dismis...

0

Q: After Three years .......:p

After three years I returned to stackexchange to ask one question...Because it was not recieved well, I am now banned from asking with this account. Really ? Three years on and there is no room for one honest question? I have had a few poorly recieved questions in the past but I have also had a ...

support suspensions

0celo7

5:45 AM

@JohnRennie I can't tell if I'm contrarian, insane, or both

John Rennie

Everyone's insane except for the two of us - and I'm not so sure about you ...

Cows

@0celo7 you're fine. Just do you bro

:)

John Rennie

@0celo7 why the sudden crisis of sanity?

If you're wondering if it's normal to be fascinated by abstruse maths then then the answer is clearly no, but by that measure we're all too many standard deviations from the mean

0celo7

@JohnRennie my personal philosophy is against net neutrality

I think I’m in a very, very small minority on the issue

John Rennie

That doesn't make you insane :-)

(just wrong :-)

0celo7

5:51 AM

I can’t find a single argument for it that’s not an argument by entitlement or whining

John Rennie

You don't seem to believe in a caring society.

... but then that's not compulsory

0celo7

@JohnRennie not a single bit.

I am perhaps the greatest misanthrope ever, but not crazy enough to do anything about it.

John Rennie

I think in general Europeans believe we make the world a better place by helping the less privileged.

This varies from country to country.

0celo7

Oh, that’s probably true.

But I don’t consider “making the world a better place” to be a part of government policy

John Rennie

The sad reality is that people don't do it on their own. It's not that we're all bastards, but that there is always something more important to spend our money on closer to home.

0celo7

5:58 AM

It’s all about the initiation of violence. And in this case, net neutrality is violence against the ISPs, whereas the converse is...no one really knows.

@JohnRennie I know, hence my misanthropeness

John Rennie

The ISPs are just companies. They take money from us, spend some of on running their business and keep the remainder as profit. Net neutrality isn't doing violence against the ISPs, but you can argue it raises the charges the ISPs levy on us.

0celo7

Jesus Christ the reddit posts are awful. “We don’t wanna pay for reddit”. Literally.

John Rennie

In effect we all pay a bit more to keep the Internet a level playing field.

0celo7

@JohnRennie if you ban someone from doing something you’re threatening violence if they don’t comply.

John Rennie

All companies are subject to regulation, and for good reason.

0celo7

6:01 AM

Maybe a good reason for you, but I find it indefensible.

John Rennie

This is just one aspect of the regulation.

Actually I might well have agreed with you when I was 18. You really do mellow as you get older - it isn't just a saying.

0celo7

I am very mellow

I am so mellow that i don’t think anyone should be telling anyone what to do

That’s about as mellow as it gets

I am the ultimate hippy. And with that, I’m going to bed

John Rennie

You're telling government that they can't require net neutrality

i.e. you're telling them not to do something

In effect you're saying everyone should live the way you consider best. That isn't not telling anyone what to do.

0celo7

@JohnRennie low effort argument

dmckee

@ZeroTheHero I have a former student doing grad school in space science, and in her end of things most stuff is MS because of NASA.

John Rennie

6:04 AM

No, it's a perspective failure on your part.

0celo7

The government is an illegitimate group

John Rennie

You're failing to see the beam in your own eye

0celo7

no

Bernardo Meurer

6:26 AM

@0celo7 I really wish you weren't so unbearable sometimes

I don't know what the h-bar does to you

dmckee

7:04 AM

There is a kind of purity to libertarian theorizing that is very appealing—I desperately want to believe in it myself and think that more than a few thing in the way the US is organized could be improved by a applying a more libertarian approach.

John Rennie

The problem is that libertarianism would work well if people were basically nice. Sadly we aren't.

dmckee

And of course real working governances violate the deepest core ideas at some level. (Or like most of the real life pockets of anarchy that do or have existed in place they are embedded in a polty with such a governace and get some support services from it).

John Rennie

In Europe we elect governments to make us do the things we should do if we were caring human beings but that we wouldn't do if it were down to us.

dmckee

Which leads the theorizer to question if those governing structures are morally supportable.

Been there done that.

John Rennie

I think Americans generally have a belief in their own infallibility that seems naive to us Europeans.

dmckee

7:08 AM

@JohnRennie The theororizers like to imagine a social structure that reinforces the good tendencies and thereby controls the ill. See Vinge's "The Ungoverned" for instance.

But at best we don't have examples of those structures that work at scales bigger than a few time the human monkey group size.

Dunbar's number

Dunbar's number is a suggested cognitive limit to the number of people with whom one can maintain stable social relationships—relationships in which an individual knows who each person is and how each person relates to every other person. This number was first proposed in the 1990s by British anthropologist Robin Dunbar, who found a correlation between primate brain size and average social group size. By using the average human brain size and extrapolating from the results of primates, he proposed that humans can comfortably maintain only 150 stable relationships. Dunbar explained it informally...

At worst such things are not possible.

John Rennie

Vinge, Heinlein et al have proposed lots of social arrangements that would work brilliantly if all humans were like Vinge/Heinlein's protagonists. But we aren't.

dmckee

So, the question for the disillusioned still kinda a libertarian is "How to make this mess we have suck a little bit less?"

Bernardo Meurer

The solution is simple: kill everyone

dmckee

But it can take a while to get the idealism beaten out of you, and in the mean time ...

John Rennie

@BernardoMeurer that is certainly an effective solution :-)

Bernardo Meurer

7:27 AM

Sid

7:45 AM

@dmckee the sleeping part. Who is sleeping well? You or She?

Anonymous

@0celo7 For the sequence space $s$, if $|\xi_i-\eta_i|$ blows up as $i\to\infty$, does the metric $d=\sum_i\frac{1}{2^{i}}(|\xi_i-\eta_i|)/(1+|\xi_i-\eta_i|)$ still remain defined (always)? I mean the limit as $i\to\infty$, could be infinite (for $|\xi_i-\eta_i|$), and we'd then get a $\frac{\infty}{\infty}$ for the distance function's terms (ending terms)...which may either be finite or undefined. Is there something more to the definition of the metric (which is implicit) ?

Anonymous

@Sid Lol, use your common sense :P

Sid

I read this extremely funny article on cats vs babies a few days ago. I wonder if that is also dmckee's experience

Cows

9:48 AM

Ok done coding for this session

going to grab food, watch tv and then head to bed

John Rennie

10:27 AM

I managed to spill some epoxy hardener while repairing the laptop I bought yesterday, and it's horrible sticky stuff. So to clean it up I tried (in increasing order of desperation):
- alcohol
- white spirit
- trichloroethylene
and nothing worked.

Then I do what I should have done at the outset and Google for how to clean epoxy hardener and ...

... it turns out it's water soluble. Warm water does the trick! Doh :-)

Mithrandir24601

@JohnRennie Lesson learned for today :)

John Rennie

Indeed :-)

The laptop is great by the way. One dab of epoxy and a replacement disk later and it's as good as new. That was £54.78 well spent :-)

user929304

10:44 AM

hahaha :)

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