The h Bar

0celo7

12:00 AM

although I'm not sure that makes much sense.

that seems like a really big contradiction

even if $f$ blows up I don't see how one can get that...

NeuroFuzzy

12:59 AM

@BernardMeurer :(

Bernard Meurer

@NeuroFuzzy It's a compliment :p

vzn

1:47 AM

@Secret et al hows this for a video game? OE Cake! fluid dynamics simulator! have been looking for something like this for yrs! just discovered it wanna try it out! anyone heard of it? anyone else wanna do some serious research on it? think it could be used to experiment with solitons =D

OE-CAKE! Taffy Mixer

►

NeuroFuzzy

@BernardMeurer d'awww, thanks

@vzn I love OE cake!

vzn

OE-Cake!

OE-Cake, OE-CAKE! or OE Cake is a 2D fluid physics sandbox which was used to demonstrate the Octave Engine fluid physics simulator created by Prometech Software Inc.. It was one of the first engines with the ability to realistically process water and other materials in real-time. In the program, which acts as a physics-based paint program, users can insert objects and see them interact under the laws of physics. It has advanced fluid simulation, and support for gases, rigid objects, elastic reactions, friction, weight, pressure, textured particles, copy-and-paste, transparency, foreground a...

@NeuroFuzzy awesome what have you done with it? how long have you been using it?

NeuroFuzzy

@vzn Let's see... I remember messing with pressure, waterfalls, and fire...

but it was a long time ago. Maybe six or seven years, so I don't really remember

It's awesome as a more physically accurate falling-sand game

vzn

yikes their web site is down maybe defunct now? wonder if it is still supported prometech.co.jp/english/products/physicafe.html

oh maybe this is ok prometech.co.jp

NeuroFuzzy

Yes, and if I remember correctly, I had to change the date on my computer because OE cake was supposed to be a demo that would be disabled after a period of time :(

Have you seen dan-ball.jp/en/javagame/dust

and dan-ball.jp/en/javagame/ee

it definitely could support solitons easily (because all you really need is to have some time dependence and discretized diffusion, right?) but I don't know if it's possible in either OE-cake or that dust game

Secret

1:59 AM

As far I recall, being a long term powder gamer myself, powder game does not really have a diffusion like algorithm written into it. The liquids in powder game are sort of dots that move back and forth and subjected to gravity

NeuroFuzzy

@Secret I mean more along the lines of the fluid dynamics in that kind of game

@Secret Like how in the dan-ball one air pressure looks continuous (I assume)

@Secret You really just need a timer for particle extinction, and something that effects adjacent cells. Like maybe a rule for a particle that says: particles of type A turn into type B after 10 steps, particles of type B turn into type A if they are adjacent to type A.

I would bet you get lots of cool reaction-diffusion-like patterns with that rule.

DanielSank

@SirCumference Clearly the English one is the sexiest in this case.

Right?

Sir Cumference

2:39 AM

Darn it!

Where is Chris White when you need him?

0celo7

hiding from you

Sir Cumference

@0celo7 My bounty is gonna run out in 3 days...

;-;

0celo7

lol

DanielSank

4:36 AM

@SirCumference which one?

@Pulsar I'd be interested to hear your analysis of why that question is on topic.

John Rennie

5:18 AM

@dmckee Monty Python?

peterh

5:49 AM

@ACuriousMind It is a good to see that your suggested edit reviews got a positive direction, although you aren't really active in this queue.

John Duffield

7:48 AM

@vzn : rockets.

@peterh : I don't have a better theory. I'm not some my-theory guy.

Secret

9:41 AM

I am actually quite interested in what you guys think for this question

user116211

11:29 AM

Engineering?

user116211

0

Q: Does 'Snicko' really work? - Sound generated by object passing without touching

(Those that don't understand cricket, please ignore this context, I will get to the physics...) England are playing Pakistan at Lords and a decision has once again been overturned based on evidence from the 'snickometer'. (see over 1.4 ) It's always bothered me slightly that there seems to be a ...

Physics Meta

0

Q: Replacing the homework policy 1b: what is our scope anyway?

Abstract: Analyzing the data from the last replace-the-homework-policy question was inconclusive. So back to the drawing board, or really back to this question: what do we really mean when we vote to close questions as homework-like? As some/many/most people are aware, we are in the midst of a...

discussion scope homework insufficient-effort

user116211

12:07 PM

So many close votes review:

user116211

Sir Cumference

12:55 PM

@DanielSank This one

4

Q: Understanding "dex"

Hi I am trying to understand the concept of dex and how to use it in calculations. The usual definition is that it is the order of magnitude, so $10^{0.1}$ is $0.1$ dex. I want to do a simple exercise of calculating the value of the RHS of Eqn 4 in this paper arxiv paper, the gammas are incompl...

supermassive-black-hole magnitude initial-mass-function

peterh

@MAFIA36790 Over 1000 we have 40 reviews/day

peterh

1:16 PM

30

Q: What is the smallest positive multiple of 450 whose digits are all zeroes and ones?

What is the smallest positive multiple of 450 whose digits are all zeroes and ones? I tried guess and check but the numbers grew big fast. Thanks in advance!

elementary-number-theory divisibility number-systems decimal-expansion

I think it is a very interesting question, despite that it is clearly a high school level one.

It seems, others had similar opinion on the MathSE. They didn't downvote and close it in minutes saying that it is homework.

Secret

http://meta.physics.stackexchange.com/questions/9086/replacing-the-homework-policy-1b-what-is-our-scope-anyway

I think I started to understand why I dreamt about a tensor of grids (or grids of tesnors, give or take) last night (to be elaborated later)

those correlation chart and their color distirbution somehow got stuck in my mind

and became tiled fields in a farmland

peterh

@ACuriousMind Guten Tag! :-) Dark Sun has also a lot of frightening characters. For example, Borys, the 30th level dragon. Or different stages of the defiler/psionicist 20/20 -> dragon 30 transformation. It is only a tip, if you start to think on your next avatar :-)

ACuriousMind

@PhysicsMeta The linear regression @DavidZ attempted there is highly reminiscent of the most recent xkcd ;)

Secret

1:38 PM

I basically see 3 blobs in the scatter diagram. While not so much of a correlation, I am not sure if that means anything (unless the order of points in the axes don't matter)

0celo7

@ACuriousMind Maybe we need the distances to be elongated

so that if $f$ blows up, the distance blows up

meaning if we bound something, $f$ can't have blown up

@ACuriousMind does that make sense?

Although I'm pretty sure if we elongate distances everywhere, we get a contradiction

Because convergent Cauchy sequences wrt. the "larger" metric are also for the "smaller" metric

but the smaller one isn't generally complete

Sir Cumference

YEEEEAAAAAHHHH

Someone gave me an answer

To that damned question I bountied

0celo7

fucking Harambe

@SirCumference what is wrong with our generation

David Z

1:56 PM

@ACuriousMind I did consider putting some thought into what constellation was represented ;-)

Sir Cumference

@peterh That's what happens when you moderate one of the biggest SE sites

peterh

What should I vote here? physics.stackexchange.com/review/low-quality-posts/144139

John Duffield

@peterh : you don't have to vote.

ACuriousMind

2:13 PM

0

Q: Eavesdropping Far Sound Waves

What is the maximum distance for eavesdropping pure sound waves? And what kind of device i need to use for eavesdropping? Actually a microphone with a parabolic reflector or laser reflected listening devices available on the market but is there any other devices on the planet which should allow ...

waves acoustics

I am slightly concerned about the motivation behind this question :P

@0celo7 Somewhat, yes

peterh

@ACuriousMind The KGB once used a tiny steel membrane in the Moscow U.S. Embassy, and then measured its vibrations with focused radio beam.

0celo7

2:26 PM

@ACuriousMind Is the "invariance of domain" theorem really hard to prove?

ACuriousMind

@0celo7 I don't know that theorem.

0celo7

@ACuriousMind Ah, here's why

you need it to link the "classical" definition of $\Bbb R^n$ to the modern one, I think

e.g. Spivak defines a manifold as one where each point has an nbd homeo to all of $\Bbb R^n$

and you need to make that nbhd open

that requires some work, apparently

but if you just define manifolds with open sets from the beginning, all is well

ACuriousMind

I have no idea what you are talking about

0celo7

Is that a common occurrence?

ACuriousMind

"invariance of domain" seems to refer to $\mathbb{R}^n$ and $\mathbb{R}^m$ not being homeomorphic (or injective maps $U\to\mathbb{R}^n$ for open $U$ having open image)

What has any of this to do with manifolds?

0celo7

2:36 PM

@ACuriousMind Forget it.

David Z

@peterh Like John said, you can skip it. I would say "looks OK" but then I might downvote it for not being useful. I suspect you'd get a variety of opinions on how to vote on that review.

peterh

3:04 PM

@DavidZ Finally it got "Looks OK", downvote and a comment to the poster.

vzn

3:35 PM

@JohnDuffield lol & you have a better idea? having trouble following, 1-word-at-a-time :(

@ACuriousMind saw that, hilarious, touche! and how much different is that than what they do at LHC? re "bumps disappearing... in the night..." lol

John Duffield

@vzn : yes.

vzn

@peterh a common refrain... yet obviously theories take/ require development, they do not arrive instantaneously gift wrapped in ones lap, falling magically from the sky o_O

@JohnDuffield so maybe send musk an email on that :P

John Duffield

@vzn : no.

dmckee

3:56 PM

@JohnRennie Yes. The Holy Grail youtube.com/watch?v=dOOTKA0aGI0 'round about two and a half minutes in.

Bernard Meurer

4:17 PM

@dmckee Did you ask for PSE shirts for us?

dmckee

@BernardMeurer I got no positive response from anyone.

Bernard Meurer

@dmckee Let's make them an offer they can't refuse

amzn.com/B003G4IM4S

dmckee

There was for a short while a Stack Exchange shop, but it was apparently marginal in terms of money and more trouble than expected.

Bernard Meurer

Dang it

Make SE Great Again

0celo7

4:49 PM

@BernardMeurer have you been reading abbott

Bernard Meurer

@0celo7 No, I'm reading Larson

Secret

5:08 PM

Last night dream is some kind of documentary of a project by two uni students (not sure if they are freshman or sophomore). The story begins with two boys

Bernard Meurer

Oh god :p

Secret

one is a tall guy with a hairstyle that look like this

another is a guy with blonde hair that look like this

They are best known for their theoretical and experimental investigation of tensor arrays

Over the past years, they have been reshaping and rearranging farmland to represent these and investigate these mathematical objects

Bernard Meurer

Thom Yorke is awesome

Secret

and endless whiteboards get doodled with boxes, grids circled red markers and some scribbles

The documentary then showed one of the bird's eye view of the farmlands

(which pardon my sketchy drawing skills...)

Most of the farmland is tiled into grids

Here there are two distinct column and rows of tiled farmlands to the left and top of the main grid. They are the index arrays and they notate the range of inidex of the tensor array

In some tiles, there's a swirl of dirt mount, they represent components with nonzero curl

and in others grass grew

Two blue steel bars were visible laying across the grid, holding up a triangle pool of water

Next in an interview, they mentioned that experimentally the process is uite simple. The tall guy is seen using a large crowbar to pry away a screw that held a road sign under a skyway, i.e.

ocassionally, misshaps can happen, such as too much force applied and the sign snapped in the middle. The boys will then be forced to take the broken sign to the nearest roadworks workshop to mend it

At the end of the documentary, near a university lodge area

I walked towards the boys and expressed interest in joining their project. They then said that you will be spending quite a bit of time on the theoretical side and doddling on whitebaords. They also ask about my recent trip to London and Belgium. Dream ends

Secret

5:30 PM

Reality check: I have been to London, but not Belgium

Idea extraction: The tensor array mentioned in the dream is a multiindex object where each component can be tensors of different order

Presumably one can formulate it (using an example of a 4th order tensor) as follows:

$$A^{\alpha}_{\beta}_{\gamma,\delta,\epsilon}$$

and then allow the index $\alpha,\beta$ to run from 0 to the size of the matrix representation of the whole array

while for the indices $\gamma,\delta,epsilon$ it can be taken from a subset which the $\alpha,\beta$ indices are. For example to encode a patch of nonzero curl vector field in this object, one might set $\gamma$ to be from the set $\{4,9\}$ and $\delta$ to be $\{2,3\}$

Secret

5:46 PM

$A^{\alpha}_{\beta}\vcenter{\scriptstyle{\gamma\delta\epsilon}}$

typo: sorry 5th order

However even if taking indices to have certain values only, it is unsure if it is of any use since most tensor expressions have indices taken from a set of consecutive numbers rather than random integers

DanielSank

6:51 PM

@DavidZ in the recent meta post about the homework policy there is the following statement:

> We want to make it sure because people want those questions closed. Evidence: people are closing them. If people are closing questions that have no valid reason for closure, we have bigger problems.

This is an interesting statement.

I wonder to what extent not having a homework close reason would simply force would-be close-voters to either edit the post, down-vote, or think more carefully whether there is another more specific reason for closure, e.g. "unclear what you're asking".

I'm not saying I think simply dropping the homework close reason and doing nothing else is a good idea.

I did suggest that previously in chat, and as I recall there were good objections (which are echoed in @ACuriousMind's meta answer's comments).

peterh

7:51 PM

Wow! Ron Maimon was network-wide suspended until 2026!

What could have he done?

It is so sad, that I didn't have the possibility to communicate with him. :-(

As he had only a yearlong cage, I wished he will get once back. Now this hope is gone :-(

Emilio Pisanty

8:31 PM

@MAFIA36790 Meh. Try having a peek at the StackOverflow close review queue. This is apparently now considered to be relatively under control, at maybe 10% of its historical peak.

DanielSank

@peterh I've noticed you have a lot of complaints and negative feelings about this site.

Emilio Pisanty

@peterh Does it really matter? He went on several extended campaigns of trying to get himself banned, and knew (or could have known) that ten-year bans are on the cards.

DanielSank

@EmilioPisanty Why are we even talking about this?

Emilio Pisanty

@DanielSank Mostly in a (probably vain) attempt to get @peterh to recognize that it's not a particularly helpful topic.

@peterh That said, he used to be fairly active on physicsoverflow, so if you really pine for the opportunity to communicate with him, you can go on ahead there. But seriously, bringing it up, particularly in that way, is not all that constructive.

peterh

8:49 PM

@DanielSank No, the site mods could have caged him only in the PSE, and only for a year. That he got. After that his cage was extended to a 10 year long network-wide one, it couldn't be the result of the site mods. Only the CMs can do this, typically for network-wide bad deeds.

@EmilioPisanty Yes, but I had liked to talk to him here.

@DanielSank I am only curious, what he did. Maybe he attacked the whole network? Or he toke a site-level conflict to the IRL world? As I know, network-wide bans happen for such things.

Emilio Pisanty

@peterh It. Doesn't. Matter.

peterh

@EmilioPisanty No, site-level things result only single-site, 1yr bans. It is unfortunate, that the majority of his campaigns are probably deleted now, thus there is no way to know, what he did.

@EmilioPisanty I can only hope, that not I will be the next.

Emilio Pisanty

@peterh That is pure fear-mongering. Unless you plan on going on extended campaigns to get yourself suspended, in which case I wish you speedy luck.

4

Seriously, suspensions are never handed out without warning, and you will not be ten-year-banned out of the blue. Ron had very clear choices and a very clear picture of the consequences of his choices, and he made his decision. There is nothing more to see here, and bringing it up again (and particularly in such a dewy-eyed manner) is far from helpful.

peterh

@EmilioPisanty Although it is already not about Ron Maimon, but I can't see here the meaning of "campaign" enough well-defined. And yes, it is a little bit of source of fear for me, that maybe my behavior can be also measured as if "I would campaign for my caging".

Emilio Pisanty

@peterh OK, sorry, I'm going to side with Daniel and go with "why am I even discussing this?". Good night.

peterh

9:00 PM

@EmilioPisanty Sorry, I didn't want to annoy you. Also I stop this topic. Good night!

Bernard Meurer

10:49 PM

@dmckee Are you around?

dmckee

11:02 PM

@BernardMeurer Kinda.

Bernard Meurer