The h Bar

Quatre Cent Coups, directed by Truffaut

Exceptionally strong!

(Four Hundred Blows, in English)

Absolutely amazing movie

The 400 Blows

The 400 Blows (French: Les Quatre Cents Coups) is a 1959 French drama film, the debut by director François Truffaut; it stars Jean-Pierre Léaud, Albert Rémy, and Claire Maurier. One of the defining films of the French New Wave, it displays many of the characteristic traits of the movement. Written by Truffaut and Marcel Moussy, the film is about Antoine Doinel, a misunderstood adolescent in Paris who is thought by his parents and teachers to be a troublemaker. Filmed on location in Paris and Honfleur, it is the first in a series of five films in which Léaud plays the semi-autobiographical character...

user54412

sounds like exactly the type of movie the local ~~theater~~ theatre would show

@HDE226868 Hah!!!!

Gotta love Pearls.

12:07 AM

I prefer Tom the Dancing Bug

@Danu Do you take great joy in being hipster

I do, in fact.

Mike Miller

reminds me of

clickhole.com/article/…

lol

Though I have to say that you guys make it very easy to be "hipster" in comparison ;)

We're so unhip it's a wonder our bums don't fall off.

12:15 AM

@HDE226868 Bum?

Not my joke.

You're a BRIT

@0celo7 Nah, I only quote 'em.

@0celo7 Do you prefer "caboose"?

Also, I try to stay as true as possible to THGTTG quotes as possible. Adams used "bums".

@Bass Well it is the engine that I want to write myself. The kind of things I'd need would be like libraries to plot etc. I could I guess just code C++ and emscripten that, but not sure if there are any SDL libraries out there that are quick and easy to use for interactive plotting (and I would probably prefer something vector based anyway).

@DanielSank As for TypeScript, will that be here and working in 5 years for the code I write today? I'd hate it to have it break or have to look after the code after its done and working.

12:32 AM

@HDE226868 On the other hand Zaphod is so cool you can keep a side of beef in him for a month and so hip he has trouble seeing over his own pelvis.

Oh and I should make clear that by a physics engine I don't mean it like as a rigid body system like the term is used in games. I'd like to be able to plot isosurfaces or fields etc.

And he comes in sixpacks, now

@dmckee I get stranger references than that free in my breakfast cereal.

@HDE226868 what

@HDE226868 No

I remember like 10 years ago I was looking at the simulations by Falstad, but now none of them work with my browser with Java disabled. Those and the simulations here are the sorta stuff I'd like to do, hopefully with something that will still "natively" run in 10 years.

3:08 AM

@DanielSank so I asked my question and you have nothing to say?? The problem is NOT the code!

The Hamiltonian is right...the lindblad operators are right...

7:00 AM

@alarge Programming stuff to work in browsers sucks. javascript is a nightmare. Typescript (and actually ES6) makes it much, much less of a nightmare.

I think typescript is worth it for a couple reasons: 1) It's backed by Microsoft so it probably won't die soon, unless 2) javascript may evolve such that what is now typescript becomes the standard, or at least similar.

In any case, writing code for the web that needs absolutely no looking after is probably pretty hard unless you want to write everything in vanilla javascript with no external libraries.

Heck, even the build systems for browser apps are complicated moving targets.

The one thing you might consider is GWT. It lets you replace the hell that is javascript with java, and it's heavily used by Google so it won't die.

@TanMath I'm only going to say this one more time: unless you show that the code is correct with a simple, fast running test example, nobody is going to be interested in helping.

Also, you seem to assume that I'm intentionally ignoring you. Have you considered that I don't spend all my life in front of a computer?

7:23 AM

@DanielSank huh? explain please...

@DanielSank you visited a few times today, but never replied...I am sorry...I forgot this is a Saturday...no seriously!

Unit testing

In computer programming, unit testing is a software testing method by which individual units of source code, sets of one or more computer program modules together with associated control data, usage procedures, and operating procedures, are tested to determine whether they are fit for use. Intuitively, one can view a unit as the smallest testable part of an application. In procedural programming, a unit could be an entire module, but it is more commonly an individual function or procedure. In object-oriented programming, a unit is often an entire interface, such as a class, but could be an individual...

@TanMath Saturday, Monday, Tuesday... it doesn't matter. Do you think people are paid to help here? It is a purely recreational activity.

@DanielSank so according to this, I should check if all the matrices are correct...

@TanMath No.

@DanielSank i am basing this on your regular visits...sorry...

Well, yes, but that's not enough.

7:27 AM

i am sorry if this is late btw...

I don't feel like teaching you how to test code.

Here's a project I did which includes tests:

github.com/DanielSank/observed

It's probably not a good example though because the project does something kind of complex.

Is concept of absolute space as newton proposed in principia necessary to study and understand the law of inertia

Or if one should be straightaway introduced to inertial frames which are not like the former unknowable !

8:02 AM

@DanielSank just tell me what to test...

10:37 AM

Hey @0celo7

What was that analysis book u were reading

Oh, found it

Real Analysis by Carother

Do you recommend it

@TanMath Please, just stop trying to have people tell you how to solve your problems.

11:09 AM

@Slereah No, it's too hard

Is it PhD level math

No

Prof. Emeritus level

11:44 AM

@TanMath Your code gives the wrong answer; Yes the problem is the code. I don't know how the library you are using is supposed to work and I'm not going to read the documentation for you. Start with a simpler problem that you can get to work properly and slowly add more complexity to it.

@DanielSank Well that's why I floated the idea of coding in C++ and compiling that to the web. I would imagine that that won't be getting any less stable over the years. Your thoughts?

12:12 PM

@alarge if you can find a good C++-2-JS compiler, this might be an option, however I doubt that such a thing exists. Have a look at the first paragraph of this FAQ of Google's Dart team: dartlang.org/support/… C++ is even more different to JS than Java is.

For the same reason I would advise against using GWT. AFAIK even at Google the trend goes away from GWT and towards Dart or TypeScript

Typescript is a strict superset of JS, which can be an advantage during debugging, since it's easy to look at the compiled JS code and see what Typescript is doing. On the other hand, Dart is a completely different language, which might also have some advantages, but I have no experience in using Dart.

Oh my god r/exmormon_nsfw is a thing

@Bass What's wrong with emscripten? And I imagine that the push to get C++ working on browsers in a more efficient way (SIMD etc) is just going to increase in the future. Not that I know much anything about web programming, which is why I'm asking about this stuff in the first place.

@alarge If you write the engine yourself, then I think it's best writing directly against an HTML5 canvas. This is an HTML element on which you can draw lines, corcles, points, basic 3D objects. It also supports linear transformations which can make the rendering much easier. If you need complex 3D rendering like OpenGL or DirectX, you might give WebGL a try, but note that its browser support is limited.

Guys let's name all the representations of the Lorentz group

Scalar, spinor, vector, schwingor, gravitor

@Bass are there plotting libraries that would be suitable for physics kinda purposes?

12:31 PM

@alarge First time I heard about emscripten. Sounds interesting. I would be careful for the following reasons: 1) Community seems to be quite small (292 questions on stackoverflow, comparing to ~7000 for TypeScript and Dart). 2) Compile-to-Javascript languages are limited by the capability of Javascript, so LLVM features that are not supported by Javascript have to be "simulated", which can hurt performance badly.

@alarge By SIMD, you mean hardware acceleration? I suppose modern browsers use the GPU to render canvas operations, but for a full-fledged hardware acceleration you would need WebGL, see above.

@alarge I suppose there are, but I'm not the expert there. And, it really depends what you mean by "physics kinda purposes", that's a very large definition.

Most important distinction, are we talking about 2D or 3D rendering?

12:49 PM

Apparently we have a "National Postal Museum"

0D rendering

@Bass As far as I remember, emscripten was what was used to get Unreal Tournament etc. 3D games to run in browsers. So while performance degragation may be an issue, it should be fast enough.

Stan Shunpike

Why do we use operators in quantum mechanics? Suppose I have a wave function $\psi(x)$. What exactly does an operator do physically? Are there restrictions on operators allowed?

@Bass By SIMD I mean just old fashioned SIMD; vector instructions like SSE, AVX.

@Bass So I want to be able to plot the kind of things you might plot with matlab or matplotlib, gnuplot etc. interactively (so I can resize stuff and this can be communicated back to the engine). Most plotting libraries I've found for JS don't do this.

@StanShunpike The operators have to be finite

12:54 PM

See e.g. Falstad for an example of the stuff that I'd like to plot.

And observables are hermitian

Oh and they are linear operators, obviously

@alarge Seems emscripten converts OpenGL code to WebGL, which has (or had, for long times) limited browser support. I'd say, give it a try.

And the operators are basically to extract informations out of the wavefunctions

For charts and plots, you might also have a look at d3js.org

@Bass Right, that's what I've used in the past in my slides. But at least a few years back plotting (just simple physicsy graphs, like x vs. y) was very cumbersome.

There were other libraries meant for plotting wrapping over d3js, but they were mostly for time series plots etc.

(the reason I wanted to use HTML5 to do my slides over beamer was that I wanted videos, and having those in a pdf is always a pain)

1:10 PM

@Slereah Obviously?

Yes.

1:29 PM

How is it obvious

1:56 PM

On the buuuuuuussss

2:21 PM

How can we say that clocks measure time ??? IT'S confusing or they measure themselves..

3:00 PM

"ARE we AI Algorithms in a COMPUTER SIMULATION running on QUANTUM Computing Technology?"

Why is the computer being quantum relevant

Non-quantum computers can run the same class of algorithms as quantum ones

@Slereah It's way cooler

You know what could run more algorithms?

GR computers.

Although actually no but still

(No because they would need infinite memory)

What is a GR computer

there's a few papers on running SUPER TURING computers by using black hole infinite time dilatation to run infinite computations

It is a bit dubious, though

I suspect it is written by math people who don't know GR that well

Hmm. So the computer is just outside of the event horizon?

What about a quantum GR computer

@ACuriousMind Good one ;)

(Assuming you were referencing that q computers are supercooled)

3:10 PM

Although considering that the structure of a black hole is that timelike infinity is in the singularity

I am doubtful this would work

@0celo7 Accidental pun :D

Starting analysis in a few days. Can't wait.

Anal ISIS?

@Slereah Uh timelike infinity is not in the horizon

No, it is the singularity!

Hm, wait

Blah, too tired to think about this

3:16 PM

Bullšit. There are timelike curves which never hit it.

Been awake for 16 hours so far

I need a little sleep

Trying to fix your sleep schedule?

yeah

Back to work on the 15th

Gotta be roughly on normal people schedule

@ACuriousMind you still in vampire mode?

Or are you roughly normal

Vampire

3:25 PM

by the way have you seen "What we do in the shadows"

It's a pretty fun movie

@ACuriousMind Isn't it time for an avatar change? We've had the redeemed salarian for a while now

@Slereah Nope

Give it a looksie

@0celo7 Yes, but I didn't have a flash of inspiration whom to choose

Btw your avatar is why I played ME, thanks for that

So pick someone from another series that I should play

5:10 PM

@alarge You know, I've never run across a system for C++ --> javascript. Link?

Does Qt provide that sort of thing?

Also please clarify: do you want something that runs in browser, or something that runs as an installable application on e.g. mobile devices?

@DanielSank Emscripten (asm.js). And I thought WebAssembly etc were all the rage now and that's where things in general were headed. Not that I would really know, I don't code web.

And something that runs in browser is what I'm looking for.

5:35 PM

@alarge OH! I didn't realize you were interested in that route.

Yeah, that can work.

I've never tried it though, and I'm not sure how well supported asm is on various browsers.

If you try it, put your stuff somewhere public?

I'd be interested to see a simple demo.

Physics Meta

0

Q: 2nd place gets the bounty

In Physics I asked a question and got 3 answers, 1 from a moderator and 2 from users. All 3 are good answers, but the moderator is spot on. I can tell 1 of the users are close in quality and took some thought. Since the moderator has 56k reputation and the user 300 would it be ok to award a bount...

@DanielSank I thought asm.js was just standard JS, or a subset thereof, where the subset is so chosen that those operations can be easily optimized by the browser vendor (i.e. the browser recognizes that asm.js is loaded and bit of code from there will end up calling native functions or whatever)

It's the interactive graphics bit that I'm most worried about and in general support for math libraries.

I don't want to code my plotters with SDL, I'd much rather take and use someone else's (JS) library.

Do clocks measure psychological time ?

@HiteshPathak I don't know what "psychological time" is, but clocks measure arc-length.

Do we define time so that motion becomes simple to represent or something like that

How we measure time ..it's confusing

5:45 PM

What is confusing about it? I'm not sure what your question is.

How to measure time ? Is simply what i am asking

With a clock. But you already seem to know that.

We intuitively know what time is then we can say that time is passing by bla bla..
But it's qualitative not quantitative..

How clocks measure time

How does a ruler measure length?

@alarge As I understand it, emscripten uses WebGL for rendering LLVM stuff that uses OpenGL (which is 99% of all 3D applications). Here's a summary of the browser support for WebGL: caniuse.com/#feat=webgl

5:51 PM

But i can't convince myself that the time passed in a tik of clock is the same as the next tik

@HiteshPathak How do you convince yourself that the markings on a ruler are equidistant?

@HiteshPathak buy a swiss watch

They look equidistant to me ..I guess

@HiteshPathak So...if the clock seems to be ticking regularly, why would that not convince you, if it does for a ruler?

@Bass Well to my understanding it is just a LLVM backend emitting asm.js (a subset of JS), so it has nothing to do with OpenGL per se (yes, I imagine that it gets special treatment so as to be translated into WebGL, but still). So in principle I believe I should be able to interface with the program (C++) using an HTML5 canvas wrapper if that is indeed the most sensible way to plot.

5:56 PM

YEAH but it happens sometimes that an hour ( of the clock ) seems like more than an hour and sometimes it just passes swiftly..

@HiteshPathak So? Distances can also seem long or short to you depending on what you're doing.

@HiteshPathak That's just perception of time. It's all in your head.

Yes therfore there's some ambiguity in measuring these things

Uh, no. We humans are just bad at measuring them "by feeling" :P

@HDE 226868 That's what I meant by psychological time

So how we are doing it

6:00 PM

@HiteshPathak It's not physical. It's an illusion.

Perhaps there is a better way

Then we can't depend on intuitions for this I guess

@alarge Looks good. Seems like Firefox, Chrome and soon IE have specific performance optimizations for asm.js code, so this should indeed result in better performance than normal JS.

LLVM code uses various APIs, so when translating LLVM bytecode to Javascript, they don't just have to translate the code, they also have to find Javascript replacements for the native APIs. WebGL is the replacement for OpenGL.

Why does this have homework close votes? I don't see why it counts as homework or an exercise. I can see other close reasons maybe being applied, but the homework one?

@HDE226868 Solving the Kepler problem sure looks like an exercise to me.

@ACuriousMind Sure, but I don't feel like he's going for that, just asking if certain properties can be used to create a model. It's possible I'm misinterpreting that, though.

6:08 PM

@ACuriousMind Do you know how we really measure it... It would be helpful if ypu could mention a source to read from

@HiteshPathak We measure time with clocks. I suspect you want some "deeper" stuff about that but that's not physics, imo.

@Bass Well yes I would imagine that any function call to any external library would have to be translated to something that you can actually call in the browser's sandbox (OpenGL->WebGL being one of the few things that you can call). Not that I know much about browser architecture.

It's probably metaphysics philosophy and all that ..

@HiteshPathak One of the simplest clock is the pendulum clock. Its measuring is based on the fact that one swing of the pendulum takes about the same time as the next one. Why should one be faster than the other one? Our modern clocks like wrist-watches or atomic clocks are basically just refined versions of the pendulum clock. Instead of a pendulum, they use some atomic oscillator like quartz crystals.

7:01 PM

Silly people. A clock measures duration.

We need user12264 to give us the full story on what a clock is.

@Bass and why NOT the other swing takes less time than previous ?

Here I found , feynman also says in his lectures we only know that a regularity of one kind fits together with a regularity of another kind , we can just say that we base our definition of time on the repetition of some APPARENTLY periodic event

But still I'm sure I've not understood this thing completely..

@0celo7 can you clarify what do you mean by duration here.

7:23 PM

@HiteshPathak What should cause the difference? But if that does not satisfy you, consider it empirically. Say you have two pendulum clocks. One day, you measure the duration of clock 1 in terms of clock 2: how many times does clock 1 swing while clock 2 swings 1000 times. Then you get some ratio $c_1/c_2$. The next day you measure again, and get the same ratio. The next day again, etc. One day you are convinced that those clocks swing regularly.

Then you repeat it with more clocks, maybe compare it with a solar clock or a wristwatch, and get again constant ratios. The more you measure, the more you get convinced that the clocks swing regularly, which means they really are clocks. This way humanity started to trust clocks.

7:37 PM

@Bass Anything can cause the difference if one is sceptic enough noone can have exactly the same state of universe(or rather say that even if somehow everything was same ) even if everything was same one thing is different for the successive swings and that is instant of time they started
But emperically it is true

Feynman puts it like this "Someone might question whether there might not be some omnipotent being who would slow down the flow of sand every night and speed it up during the day ".

@Bass Thank you for providing that empirical stuff i was thinking that if i am onlyone who doubts his instinct that the pendulum swings might be of unequal duration..

@0celo7 Oddly enough that the one point he goes on about that I find useful at times. I tried it out on my Modern Physics class last semester and it helped clarify some difficult statements.

8:37 PM

@dmckee Huh, example please?

user54412

@alarge I've personally found beamer+videos to work well for my purposes. I'm curious what doesn't satisfy you.

8:57 PM

@0celo7 It's the same as the distinction between position and displacement. Normally we rely on each other to sense what meaning (the reading of the clock or the elapsed time during some process) we intend through understanding the sweep of the problem, but making the verbal distinction allows clarity.

Of course, for simple events we can just reset the zero and both are the same, but for compound events you may want the ability to be precise.

I used it when talking about the resolution of the twin paradox.

11:04 PM

@ChrisWhite Well things might have changed in the past few years, but I do remember having issues in particular when using different readers and codecs.

no_choice99

one question. sometimes I see very old questions as "active" (such as physics.stackexchange.com/questions/13611/…) despite no new comments nor answers in years. Why is it so? Is it because someone pressed "up" or something like that?

11:26 PM

@no_choice99 Possibly, but there's a bot called "Community" that bumps old questions.

11:46 PM

@Danu do you write theses without any help? no mentor, no professor, nothing? because your advice makes it seem so...

@alarge how are you so sure the problem is with the code?

@TanMath Is it not by definition that if the code doesn't work, it's broken. Now naturally you could also have issues in your equations, meaning that the code actually works, just your inputs or your expectation of the output is wrong. You claimed this not to be the case.

> You claimed this not to be the case.

when?

@TanMath I thought you'd checked that the matrices you were inputting were correct. Why in the world are you even asking for help if you haven't? I mean I haven't even seen you explain where you got your data from and now you're saying that there might be an error in it? What do you need help with?

@TanMath We all had mentors. Several mentors generally, but having a mentor and leaning on your mentor are very different things. From where I sit you seem to come back to the advice well very quickly and without having invested enough time and effort in obtaining your own progress and insight.

Certainly there are stylistic differences between people, but a typical successful grad student is not eager to go back to their boss and say "I still don't understand" without being able to show some real progress.