The h Bar

ACuriousMind

12:00 AM

@0celo7 You mean $G= \{\sum_{i=1}^r n_i x_i \vert n_i\in\mathbb{Z}\}$, but alright

You can already show from that that $G \cong \oplus_r \mathbb{Z}$ by explicitly giving the isomorphism

0celo7

@ACuriousMind I do?

ACuriousMind

@0celo7 What else is the notation $\oplus^r n_i x_i$ supposed to mean?

0celo7

@ACuriousMind Well why can we write $G=\oplus^r Z$ but not $G=\oplus_i^r n_ix_i$?

ACuriousMind

@0celo7 Because the direct sum is an operation defined on groups, not on elements.

0celo7

Derp $x$ is not a group.

Ok that was dumb.

infinitesimal

12:04 AM

@KyleKanos IBL = Moore method

in Mathematics, 15 mins ago, by Ted Shifrin

skull: Moore method = no textbook; you are given a list of definitions and theorems and told to prove them yourselves. Socratic is actual teaching, with discourse between student and teacher. Moore, in principle, the teacher is a bystander.

0celo7

@ACuriousMind Can I take each $x_i$ to generate a cyclic group or something?

ACuriousMind

@0celo7 Sure, each $x_i$ generates a copy of $\mathbb{Z}$.

0celo7

@ACuriousMind So each $x_i$ generates an infinite cyclic group, which is isomorphic to $\mathbb{Z}$?

Or does it generate $\mathbb{Z}$ directly?

ACuriousMind

Depends how strict you are with the distinction isomorphism/equality ;)

But to be safe, you say that the group generated by $x_i$ is by definition cyclic, and is infinite since it sits inside a free group. Then you can give the isomorphism $x_i\mapsto 1$ to show that it is just a copy of (i.e. isomorphic to) $\mathbb{Z}$

0celo7

@ACuriousMind So how do we see that each $x_i$ generates an infinite cyclic group? (reading)

Infinite because it sits inside a free group?

ACuriousMind

12:09 AM

A finite group would have the relation $n x_i = 0$ for some $n$, but such elements do not exist in free groups

0celo7

A finite cyclic group you mean?

ACuriousMind

@0celo7 Yeah.

But even for non-cyclic finite Abelian groups you can find an $n$ for each element $g$ such that $ng = 0$

0celo7

@ACuriousMind even for $n\ne0$?

ACuriousMind

@0celo7 Yes, of course $n\neq 0$, that would be boring

0celo7

@ACuriousMind I don't get how $ng=0$ if $n\ne0$.

Is $n$ just a c-number?

ACuriousMind

12:14 AM

@0celo7 It's in $\mathbb{Z}$, and we are using additive group notation here, so $ng := g + g + g + g + \dots$ with $n$ summands on the right

In multiplicative notation, you would write $g^n$, but since you started with $n_i x_i$, your text seems to use additive notation

0celo7

@ACuriousMind But $g+g=0\implies g=-g\implies g=\operatorname{id}_+$, no?

Which is just 0

ACuriousMind

@0celo7 No, being its own inverse does not imply that an element is already zero.

Also, I did not say that $g+g = 0$, I said you can find some $n$ such that $ng= 0$.

0celo7

@ACuriousMind But what if $n=2$?

If something equals its inverse, it has to be identity element.

Right?

ACuriousMind

No

$-1$ is its own inverse with respect to multiplication, but it is not $1$.

0celo7

Huh.

Stan Shunpike

12:24 AM

@ACuriousMind So my book Tensor Analysis on Manifolds indicates that the Exterior Algebra is like the analogue to symmetric product between tensors. Does that match your understanding? I also have read that the exterior algebra is just an algebra whose product is the wedge product. I don't really get how that relates to your approach to explaining the exterior algebra to me.

0celo7

@ACuriousMind So the difference between a (just) finite and a free (and finite) group is just that the generators of the free groups are all linearly independent?

ACuriousMind

@0celo7 There are no free finite groups

By definition, a free group is one that has no relations among its generators, but $ng = 0$ would be a relation on the generators, and it holds in every finite group

0celo7

@ACuriousMind What? The definition states a free group of rank $r$ is finitely generated by $r$ linearly independent generators.

Is "finitely generated" not the same as "finite"?

ACuriousMind

@0celo7 No

0celo7

OK

ACuriousMind

12:27 AM

F.g. means "has finitely many generators"

Finite means "has finitely many elements"

NeuroFuzzy

May I ask which book this is? My abstract algebra knowledge is poorly applied to physics.

ACuriousMind

Every finite group is f.g, but most f.g groups are not finite

0celo7

I see.

ACuriousMind

@StanShunpike I have no idea what a "symmetric product" is supposed to be

0celo7

@NeuroFuzzy Nakahara, Geometry, Topology and Physics

ACuriousMind

12:28 AM

And yes, the exterior algebra is an algebra with the wedge as its multiplication.

Stan Shunpike

@ACurioiusMind A tensor product between tensors with tensors with non-mixed indices.

I think...

I'll go verify

NeuroFuzzy

WOW. That looks like a good book @0celo7 . Thanks.

0celo7

@NeuroFuzzy I'm liking it so far. I got it for the stuff on Chern classes but I was pleasantly surprised to see that it covers homology, homotopy groups, Kahler geometry, index theorems and fiber bundles.

Stan Shunpike

@ACuriousMind books.google.com/…

Bottom of the page

user54412

The above conversation is I think the perfect example of how weirdly inverted self-learning is. About 5 people in my undergrad class took full-blown QFT, and exactly 1 signed up for the full year of GR. Meanwhile the scores of people who took group/ring/module theory did so as freshman, or sophomores at the latest.

ACuriousMind

12:36 AM

@StanShunpike Okay, it's the symmetrized tensor product. The wedge is the antisymmetrized tensor product, and we have $s\otimes t = st + s\wedge t$, so, in a sense, $st$ is the "symmetric part" and $s\wedge t$ is the "antisymmetric part" of $s\otimes t$.

Kyle Kanos

@infinitesimal Interesting. I wonder how successful a method that is. Likely depends on student interest.

0celo7

@ACuriousMind Use something creative like $\boxtimes$!

Stan Shunpike

@ACuriousMind What does $st$ stand for?

0celo7

@StanShunpike Symmetric part.

ACuriousMind

@StanShunpike I'm just using the notation from your book for the symmetric product!

Stan Shunpike

12:39 AM

@ACuriousMind what I mean is, what operation?

@ACuriousMind lolol I look at the page and see gibberish. You look at it and see insight. I think my lens must be smudged. :p

ACuriousMind

@StanShunpike Just the operation that your book defines there, i.e. $st = \frac{1}{2}(s\otimes t + t\otimes s)$

We would have to actually define the wedge with a $\frac{1}{2}$ in front, too, so that $s\otimes t = st + s\wedge t$ holds, but no one is stopping us from that

Stan Shunpike

OH, lol. I get it

I polished up my lens

Oh, that's silly. Why does he use $\frac{1}{2}$ notation?

ACuriousMind

@StanShunpike So that we can write $s\otimes t = st + s\wedge t$ :P

Stan Shunpike

Ah, okay.

That seems redundant doesn't it?

ACuriousMind

@StanShunpike That is a feeling you often get when dealing with such definitions ;)

But, yeah, there's nothing deep about defining $st$ in that way

Stan Shunpike

12:46 AM

No, clearly.

At least, now it is.

NeuroFuzzy

doing the basic 4-vector stuff involving the boosted parallel plate capacitor: How did I never realize there was a 'between the sheets' pun staring me right in the face this whole time! All this time I've been doing electrodynamics and this is the first time I realized it.

ACuriousMind

@NeuroFuzzy lol

NeuroFuzzy

"I don't like talking about fringe fields. Personally, I prefer to talk about the field between the sheets if you know what I mean."

ACuriousMind

Does the field between the sheets lead to charged interaction?

NeuroFuzzy

this is the best pun.

ACuriousMind

1:20 AM

General question: Does anybody think history questions are on-topic? For one, there's now HSM, and regardless of that, they aren't about physics as such - I've seen several such recent questions being closed, but the tag exists and gives the impression they are on-topic.

Stan Shunpike

@ACuriousMind I feel like they should be

Here's my reasoning: history of physics often is important to understanding the motivations for creating the original theories. So I think it's important to understanding the theories themselves. And therefore on topic

0celo7

Are you ready? Are you ready?

►

Werster has issues.

ACuriousMind

@StanShunpike I think asking "What is the motivation for this kind of theory?" is perfectly fine, and not even a {tag:history] question, but asking "Who discovered this first?" or "When was this or that done?" has nothing to do with the physics, and should be off-topic.

@0celo7 My poor ears.

Good thing I wasn't using headphones

0celo7

@ACuriousMind Werster is hilarious. He has 11 Pokemon world records.

He's like the Unreal Tournament kid but with good strats.

Stan Shunpike

1:37 AM

@ACuriousMind I agree. I think the factual questions don't belong here.

@ACuriousMind So the gauge covariant derivative is related to the covariant derivative from Riemannian geometry?

ACuriousMind

@StanShunpike Just like the "Riemannian" covariant derivative is induced from the Levi-Civita connection on the tangent bundle, the gauge covariant derivative is induced from the gauge connection on the principal bundle. They are, in a sense, not different concepts.

dmckee

2:05 AM

@ChrisWhite I'm honored by the shout-our, Chris, but I'm not aware of a uniform notation for branching ratios. Sorry. I've used $\mathrm{BR}$ possibly with subscripts on the few occasions I've needed to assign symbols in formal writing.

Stan Shunpike

@ACuriousMind @0celo7 im not a Pokemon fan but my sister just told me there is an actual animal called a pika...like pikachu

ACuriousMind

Random fact: .wtf is an allowed top-level domain

Stan Shunpike

Lolol

physicsoverflowmeta.wtf

ACuriousMind

I stumbled across it because a member of Academia has algorithms.wtf

Stan Shunpike

I've never used Academia

NeuroFuzzy

2:21 AM

@StanShunpike I like to read linked posts on it, mostly for gossip about crummy reviewers/professors/students

dmckee

@ACuriousMind And .sux has been approved, as well. But contrary to the spirit in which it was proposed, companies are going to be allowed to grab up the .sux urls that might refer to them and shield themselves from that particular variety of criticism. Not sure how I feel about that.

Stan Shunpike

Wow

@NeuroFuzzy so they just post general questions about academic life? There are just wide differences between what academics do

Kyle Kanos

@dmckee Hmm, so I can get physics.stackexchange.sux and they can't stop me!? Muahahahaha!

Stan Shunpike

Our brand is doomed.

dmckee

@KyleKanos Well, there will be a period when companies can pre-purchase their own trademarks for US$2500. When general registration open those domains will start at US$10.

Stan Shunpike

2:28 AM

@KyleKanos is secretly a PO agent

Kyle Kanos

@StanShunpike I was thinking pro-actively: they might want it, so I take it first

@dmckee Doesn't seem to be a whole lot of money for a company

dmckee

@KyleKanos No. It's dirt cheap.

Kyle Kanos

I find the way you phrased that funny though: they can pre-purchase their own trademarks

ACuriousMind

Dollar currency signs don't play well with ChatJaX :(

DanielSank

@ACuriousMind USD

;)

Stan Shunpike

2:31 AM

Smart

ACuriousMind

@NeuroFuzzy Yeah the gossipy posts or the ones that put the questioners in their place who ask stuff like "Can I pay someone to write my PhD?" are usually the most fun to read

Kyle Kanos

@ACuriousMind Of course you can!

ACuriousMind

@KyleKanos Yeah, you can, true.

Stan Shunpike

@ACuriousMind Are you a Lord of Rings fan?

ACuriousMind

@StanShunpike No. While liking fantasy, I never got to like Tolkien, I find his writing style tedious and boring, and the black-and-white morality also gets on my nerves.

Stan Shunpike

2:45 AM

So not a fan of the movies either?

ACuriousMind

@StanShunpike Mh, I don't think they're bad, but I'm not a fan of them, either.

Stan Shunpike

They take a lifetime to watch...

ACuriousMind

I don't think I've ever seen a fantasy movie I really liked, with the possible exception of the very faithful Discworld adaptations.

user54412

@ACuriousMind A host of nerds just shed a single collective tear, but not one so potent as those of Nienna.

ACuriousMind

@ChrisWhite I know my opinion is unpopular :D (Also, I had to google Nienna, as you might have guessed)

DanielSank

2:51 AM

@ACuriousMind I really really like Tolkien, and I agree with everything in this statement :)

Stan Shunpike

Why did he write such long books?

user54412

"The mission of the .VODKA top-level domain is to provide consumers of vodka an easy way to find and evaluate information about vodka, and in some cases to purchase it online"

ACuriousMind

@DanielSank Interesting - I guess the intricate world building outweighs it for you?

Stan Shunpike

I tried to read it when I was a kid and fell asleep each time

user54412

@StanShunpike well, the Hobbit is basically a children's bedtime story ;)

Stan Shunpike

2:53 AM

lol

DanielSank

@ACuriousMind That's definitely part of it.

user54412

@ACuriousMind the languages!

Stan Shunpike

The language part is awesome

DanielSank

The other thing is that by avoiding the Great Sin of Scifi I automatically put Tolkien above most everything else I've read.

@ChrisWhite Yeah, those too.

Stan Shunpike

How did he know how to make a language?

DanielSank

2:54 AM

The Great Sin of Scifi (GSS) is explaining the rules of your world to the audience. None of the great works do this.

user54412

@StanShunpike he was a linguist; also, his invented languages are heavily inspired by real-world ones

ACuriousMind

@StanShunpike He was a linguist by trade, I think

DanielSank

Tolkien just dumps you in Middle Earth with a map, some lembas, and an appetite for elevensies tea.

He doesn't bother about explaining magic, wizards, trolls, etc. They just are.

user54412

basically, he was writing an alternate history/literary legacy of northern Europe

DanielSank

The other great works of Scifi also do this. Consider The Matrix. There's only one scene in the entire film which stoops to blatant exposition and it's the worst scene in the film.

@ACuriousMind Firefly is another example of avoiding the GSS. There are spaceships, and horses, and that's just how it is.

ACuriousMind

2:57 AM

@DanielSank Firefly is great

DanielSank

@ACuriousMind Yup.

ACuriousMind

And I definitely agree with your classification of the GSS

Kyle Kanos

I still can't grasp the Silmarillion, but I've read LotR a few times, the Hobbit a few times, and then some of the lesser stories (i.e., The Children of Hurin)

ACuriousMind

Suspension of disbelief is actually made more difficult when the work attempts to "explain" the way its world works.

user54412

^ tell that to all the worldbuilding.SE questions that ask "how can I explain this setting of mine?"

ACuriousMind

3:00 AM

@ChrisWhite Huh, there is a single person, the Independent Objector that decides whether to formally object against proposed TLDs or not.

You go there thinking it's some abstract entity, and - nope, it's just a single guy

@ChrisWhite Heh, yeah. I don't understand that desire. Except when you are some crazy person like Greg Egan and try to actually write in a world with internally consistent alternative physics.

user54412

I was kinda hoping the person's identity was top secret

ACuriousMind

That would have been awesome

Stan Shunpike

3:18 AM

@ACuriousMind so what counts as fantasy?

btw, have you ever listen to War of the Worlds?

The original broadcast was genius

ACuriousMind

@StanShunpike Elves are generally a good indicator ;) More broadly, anything that involves magic in some form.

Stan Shunpike

So does Harry Potter qualify?

ACuriousMind

Yes, of course

Kyle Kanos

I think most fantasy genres, for whatever reason, always have swords as the primary weapon

Or sharp, stabby things

ACuriousMind

@KyleKanos That's, fittingly, called Sword & Sorcery

Stan Shunpike

3:24 AM

I really like The Dark is Rising. I read that when I was a kid. I have the audiobooks. The fourth books is cool because it has a lot of welsh words in it.

book*

ACuriousMind

Never heard of that

Kyle Kanos

@ACuriousMind Interesting. Further reading gives me High Fantasy, in which LotR lies

DanielSank

3:37 AM

@StanShunpike My teacher read that to us when I was quite young.

I don't remember the plot at all, but for some reason I have a very strong notion in my head that it's a very awesome book.

Stan Shunpike

I love them. Two of them won Newbery awards.

@DanielSank the audio books are even better.

DanielSank

@StanShunpike I can haz?

Stan Shunpike

Any fans of the Godfather by Mario Puzo?

@DanielSank was that English? Lol

DanielSank

@StanShunpike Yes. It's a reference to this.

Stan Shunpike

"In a style popularized by 4chan"

says wikipedia

I had never heard of 4chan before SE

some guy mentioned it on Math SE I think

ACuriousMind

3:46 AM

@StanShunpike Yiou found SE before you heard of 4chan?

You've been living a sheltered life ;)

DanielSank

@ACuriousMind I think I probably did too.

Not sure.

4chan is... well you know.

Stan Shunpike

lol I live in a bubble.

Kyle Kanos

@DanielSank One reason why I hate it when someone doesn't know any particular website

Stan Shunpike

@ACuriousMind random fact, usually half the time it takes to make a song is spent adjusting the volumes.

I don't know why its so hard to optimize them, but I waste so much time listening over and over to the song making sure its not too loud or too soft.

I would think this should be easy to do algorithmically somehow.

But I have no idea

@ACuriousMind I still don't get why rings are important.

Like what can a ring do that a field cannot?

I can accept the definition / axioms. I just don't see why people care about them. Like what situation would rings come up in physics for instance? We always work with things where for instance if $\hat{v} = (3,4,6)$ then $2\hat{v} = \hat{v}2$. Where $\hat{v}$ is velocity. See right there we use fields. It would be nonsense not to have commutativity.

Ah, math chat answered. Sweet. Rings are so cool

Stan Shunpike

5:15 AM

@ChrisWhite do you think studying black holes is likely to help us formulate a theory of quantum gravity?

Or rather, one with testable predictions...

David Z

5:42 AM

Someone posts a nonsensical theory of everything on reddit's /r/askscience that predicts the end of the world in a month, and the community's immediate reaction is... 2 upvotes

*facepalm*

user54412

@StanShunpike I enjoyed that series too. Also because of the Welsh.

user54412

@StanShunpike Real black holes? No. Not a chance.

user54412

They're too far away and absolutely overwhelmed by all sorts of other physics going on around them (really cool physics too -- my entire thesis in on this in fact)

user54412

Theoretical black holes? maybe

user54412

But while I may understand standard black holes inside and out, I bowed out of the quantum world years ago and haven't looked back ;)

user54412

5:47 AM

I also never understood most "quantum gravity is necessary" arguments based on black holes, especially the ones that get all worked up over the singularity

user54412

@DavidZ So I still have never even visited reddit (or quora or any similar site), and from what I can tell, my life is all the more stress free for it ;)

user54412

though perhaps this is just a corollary to "more internet exposure is more stress"

David Z

Yeah, your life would probably be even more stress-free if you weren't on PSE either

/r/askscience is pretty good actually, for a subreddit. They have a similar "no crap" mindset to what we have here.

user54412

Aha -- astronomy has finally run out of English acronyms. Introducing NIHAO (Numerical Investigation of a Hundred Astrophysical Objects)

David Z

lol

maybe it's just because all the scientists are Chinese these days

user54412

6:03 AM

also from astro-ph today, this gem of honesty: "We offer only a highly tentative proof of this "Pulsar No-Hair Theorem". Our analytics, while convincing in its non-triviality, is incomplete, and counts only as a plausibility argument. Our numerics, while complete, is dubious."

4

user54412

@DavidZ That might be observer bias :P

David Z

sure, but it was already a thing before I came to China :-P

user54412

@DavidZ I don't suppose you'll be in Shanghai the first week of June? I'll actually be there for an astro conference. (Yeah, I know, Shanghai from Wuhan is like Detroit from Princeton)

David Z

Nope, not unless I find out about some currently unknown travel plans

and honestly, given that I know about 20 words in Chinese, anywhere that's not on or immediately adjacent to campus may as well be the north pole

user54412

that's about twice as much as me, but I feel I know all the important stuff, like the difference between beef and pork, or rice and dumplings :)

David Z

6:16 AM

that's actually something you don't need to know

well, something I don't need to know, at any rate

user54412

because you go grocery shopping, or because food places near campus speak English?

David Z

because adapting to Chinese food requires a mindset of not caring what you're actually eating as long as it tastes okay :-P

scratch that. As long as it's not moving.

dmckee

If I had to pick just one thing that bugs me about people who've read a couple of pop-sci books and want to discuss what they think they learned it is their blindness to the scale of various effects.

Stan Shunpike

@dmckee example?

dmckee

I know, it's not their fault, but stilll.

@StanShunpike physics.stackexchange.com/questions/170962/… is what brought it back to mind.

But something on Physics.SE reminds me of this every few days. Well, maybe once a week.

That said, teaching students to pay attention to scales is a multi-year battle, so I guess I shouldn't be surprised.

Stan Shunpike

6:33 AM

People ask really weird questions sometimes.

Like I don't know what that guy is asking.

David Z

-1

Q: Is this a frequency domain plot for audio?

I have a program "spectrum" that draws an chart for an audio file (a short .wav with an human voice recorded on it). I believe it is a frequency domain chart. The problem is, when I play the audio, for each given second of playback there is a separate chart (here are 3 print screens from the pr...

off topic?

Stan Shunpike

@DavidZ Yes, completely

There's an SE for that already also I think

David Z

yeah, Signal Processing, but that's not relevant to the decision of whether to close it

Stan Shunpike

That's the most clearly off topic one I've seen in a few days

Isn't there an audio processing SE?

I thought there was

Maybe that's just an area 51 proposal

I mean, that's not physics. That's audio analysis.

It uses the same math as physics in some ways, but its not physics.

Was @KyleKanos serious about buying the .sux domain?

I have no idea. The whole PO thing is weird. The meta section is crazy

David Z

7:03 AM

@StanShunpike yeah, [av.SE] or something

actually it's Video Production now. The video and audio editing sites merged a while back.

but I think this is more in the domain of DSP

Stan Shunpike

7:20 AM

@ChrisWhite what's the difference between real black holes and theoretical black holes? Should reality and theory be the same?

David Z

8:23 AM

Random thought: it would be really cool to have a machine learning algorithm that identifies low-quality homework questions. I know some work on this has been done on SO and other sites, but I'm envisioning tuning it to this site.

Inspired by this:

15

Q: Why isn't more being done to avoid facilitating copy/paste homework questions?

I'm relatively new to this site, but I've noticed a disturbing trend during my time here: many of the questions are simply copy / pasted or even scanned and show little to no effort on the part of the asker. Personally, I downvote such questions and move on, but it is frustrating to have to sift...

discussion homework

Danu

10:24 AM

Is it me, or is mathjax not working?

None of the math on the site renders for me ATM

ACuriousMind

@Danu It's you.

Danu

FML

Also, obligatory "what are you doing awake at this hour?"

ACuriousMind

@Danu Haha...organisatory stuff, I've got some documents to hand in and can only do so between 1 and 2 pm

Danu

So... how do I fix this? I've already done Shift+F5 and restarting my browser (Chrome)

Physics Meta

0

Q: Is it possible to implement the physics package of latex into mathjax?

I don't know if you know the package physics in LaTeX but it is a really good one especially if one writes something about physics. e.g. I hate writing |\Psi\rangle\ which is as simple as \ket(\Psi) in this package or \left( \right) which is just \qty(). I know that we are using MathJax and not L...

feature-request mathjax formatting

ACuriousMind

10:31 AM

@Danu I'd just wait, MathJaX randomly stops rendering for me sometimes, too. It usually comes to life again quickly.

Danu

:\

John Rennie

Goddamn bastard MathJax rendering bug. Do you have any idea how hard it is to get equations right when you can't see the preview? :-)

Danu

@JohnRennie Hey, you're experiencing the same thing?!

My mathjax is not rendering on the main

John Rennie

Plus I've just written another of my awesome GR answers and none of my adoring fans can see my equations or graph :-)

Danu

Now that's a shame ;)

ACuriousMind

10:34 AM

My MathJaX is working fine.

That's weird

Danu

It's not just me! Puh! :)

Clearing cache also didn't work (to be expected if it's not just me)

Also @ACuriousMind I've been listening to the music from those games for the past days, loving it :D

ACuriousMind

@Danu Heh, very good :)

Danu

Also, finished the chapter on elementary group theory in Vinberg---as expected he pretty much only discusses finite groups so not very useful (except for classifying crystals, I'd assume) but very fun! Especially the part on quotients and homomorphisms

John Rennie

Hmm it's OK in IE11

Danu

@JohnRennie I refuse to re-enable IE :P

ACuriousMind

10:40 AM

@DavidZ Oha, seems the situation on math is heating up.

John Rennie

Ah, I've just tried again in Chrome and it looks like it's working now.

If you want to be amazed and awed see ...

4

Q: Could we send a rocket to the Moon without general relativity?

I'm wondering if it's possible to send a man to the Moon using equations consistent with Newtonian gravity and without the elaborate tools of Einstein gravity. Are the predictions made by Newtonian gravity sufficiently precise to plan a successful voyage? If not, where would the Newtonian equatio...

newtonian-mechanics newtonian-gravity rocket-science moon space-travel

Danu

@JohnRennie Not working for me again :\

@ACuriousMind I spent a lot of time reading on math.se meta yesterday

They've had much... "hotter" situations haha

ACuriousMind

Oh. Well, I like the peace and quiet of our little place far better, I think ;)

Danu

Especially when Bill Dubuque left for a while, that was hectic stuff

@ACuriousMind Yeah, I guess it's because we just (pre-emptively) use a set of much stricter rules

John Rennie

On a vaguely related topic, I saw the comments yesterday about the Physics Overflow.

Do I gather it is finally dying?

Danu

10:45 AM

Well, appears not to be doing so great

ACuriousMind

@JohnRennie Apparently, they're having troubles. Many users from their beginning seem to have left, and the moderators are/were fighting among each other, as I gather.

Danu

Apparently, both Dilaton (forced to resign) and Ron already stepped down as mods

And yeah... very low activity (quite comparable to HSM atm, although I have hopes on this comparison improving in favor of HSM over time haha)

John Rennie

But Dilaton and Ron Maimon are such easy going and un-opinionated people. How could it have come to this?

Danu

@JohnRennie Mmm the dripping sarcasm is delicious

ACuriousMind

::wipes drink off monitor::

Danu

10:47 AM

@JohnRennie Did you see the quote of Ron's I posted? It kinda made me laugh

16 hours ago, by Danu

@KyleKanos Ron's writing is juicy as usual: "The story here is essentially the same policy as anywhere, with different people on top. There's no "community moderation", there's moderation by arbitrary fiat, and official warnings, and official blocks. That's not what I signed up for. I have refrained from advertising the site further, and I think it's time to call the experiment a failure. You really can't trust anyone at all. "

John Rennie

@Danu No, or at least I don't think so. Have you got a link?

Danu

...but he himself was one of the mods (at the time), I think. Pretty good

John Rennie

Oh yes, I did see it.

I do wonder about whether it's possible to have a physics equivalent of the Math Overflow. The natural level seems to be around the undergraduate level. That's what we seem to have stabilised at.

ACuriousMind

@Danu Nevertheless, one user there answered my question.

Danu

@JohnRennie I'm fairly certain it is not possible

It seems that (1) The amount of graduate level questions is simply insufficient (2) Professional physicists are somehow just not interested enough to really build a commuinty like this

I wonder whether it has to do with the fact that, in physics, one can really be "right", which might introduce a general unwillingness to share all knowledge (especially on research topics) freely and stuff

ACuriousMind

10:54 AM

Which is a bit weird since the mathematicians have successfully done so. Are there more mathematicians, or are the physicists less sociable/interested in online communities?

Danu

@ACuriousMind See the above

ACuriousMind

Yeah, you answered my question preemptively, it seems ;)

Danu

I feel like physicists may be less altruistic

ACuriousMind

Which is a sad answer if it is true

John Rennie

You say:

I wonder whether it has to do with the fact that, in physics, one can really be "right"

But actually I'd say this was the problem.

ACuriousMind

10:55 AM

Ah, well. Time to jump to hurdles of bureaucracy. See you later!

John Rennie

In maths you choose your axioms and all competnat mathematicians will agree you're right or wrong

The axioms can't be incorrect because they're just chosen starting points

Danu

Yeah

John Rennie

The trouble with physics is that your axioms need to be physically reasonable or what you're doing isn't physics.

And I think the big arguments come over disagreements about the initial assumptions.

Danu

True, true

Maybe we just wouldn't be able to get people to agree

John Rennie

Since the assumptions often aren't easily testable the arguments rapidly approximate a religious war.

Anyhow, I'd better go off and do some work now. Though since the Physics SE is apparently working again ...

Danu

10:59 AM

Yes, MathJax has revived even for me :)

Nice talking to you, John. I wish you'd be in chat more often ;)

Sabre Tooth

in experimental physics, we can test whatever we hypothesise (within reason)

Danu

@SabreTooth Clearly. If you hypothesize A and from that derive (rigorously) result B, and show that B is not true (experimentally) then certainly A was wrong.

Sabre Tooth

it may be that I am too tired, but I lost focus after the first A

Danu

@SabreTooth It's one of the most basic methods of proof

Sabre Tooth

got ya... give me a bit of leeway here, I have just worked 14 hours

and notice what I said, we can test what we hypothesise, I said nothing about proving etc

Martin

11:13 AM

Let me add another perspecitve: Mathoverflow started at a graduate school and was (by design) supported by a lot of graduate students at that institution. It seems to me that quite early on, a few high profile mathematicians such as Tao or Gowers have joined the site, who are also otherwise very outspoken on community efforts. This led mathoverflow to pass the "critical mass" of enough people staying on the site so that it is constantly populated with questions and answers. So I feel it may also have been a bit of luck. You'd need a similar amount of physicists to achieve this - even then, …

Danu

@Martin I didn't know that about the history of MO. What university does it originate from?

Sabre Tooth

@Danu forgot to answer this - what made me think I was 'bad' is actually what made me feel like I was a 'bad fit for the site' - a mix of things, namely being an experimental physicist, being mocked in the final question I wrote (by the way, my method worked - getting published soon); comments against me in chat (e.g being called 'pathetic' and the suggestion that I deal drugs to cover costs etc)... the bandwagoners who chimed in - got a bit too much, so I thought - time to go

Martin

@Danu: Apparently Berkely (with Geraschenko and a few others).

Danu

@Martin Very interesting.

@SabreTooth Okay. As you probably recall, I've said time and again that these perceived mockeries etc. did not need to be taken seriously (and weren't meant to be even by those who wrote them) and I think everyone could've benefited from you continuing your contributions, but oh well. It's your life, obviously ;)

LOL:

The Bible describes an early application of the Banach-Tarski paradox. — Rahul May 15 '14 at 18:59

David Z

11:54 AM

@SabreTooth you know you can flag mocking for moderator attention, if it's serious.

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