The h Bar

Bernardo Meurer

19:00

the only example I know is Minix 3

John Rennie

@DanielSank who did the Windows install on your laptop, and from what source?

Emilio Pisanty

> In a microkernel the kernel is tiny

I could not have guessed that

Bernardo Meurer

@dmckee Darwin is a microkernel?

DanielSank

@JohnRennie I bought it from newegg. Dunno who did the install. Someone at Asus, I guess.

So yeah, I could redo it, but guess what? Then I have to buy Windows again.

Bernardo Meurer

@dmckee If you run Minix you're a bigger nerd than me :P

DanielSank

19:00

I already paid the Windows tax when I bought the damn computer.

John Rennie

@DanielSank There you go. Asus loaded it up with crap and you're blaming the OS for it being slow.

dmckee

@BernardoMeurer Well, it's a hybrid. But it has a lot of Mach at the core.

DanielSank

@JohnRennie No, I'm blaming the OS for running its own updater all the time.

Bernardo Meurer

@DanielSank You can extract the license key and reuse it

dmckee

@BernardoMeurer Ran, not run.

Slereah

19:01

To be fair, I can't complain that much about 90's Windows effort to have backward compatibility

DanielSank

@BernardoMeurer Reuse it how? Where do I get Windows8 to re-install?

John Rennie

@DanielSank Download the Windows 10 installer onto a USB stick, wipe the disk and do a fresh clean from scratch install and it will gibve you no more problems.

DanielSank

Will the motherboard let me do that or did Asus do some shit to make sure I can't install my own OS?

Slereah

Without it there would have been a lot of programs I wouldn't have been able to run back in the days

DanielSank

I don't know!

Bernardo Meurer

19:02

@DanielSank Download the ISO somewhere, I think MS has some tool. Never use W8 it's crap

@DanielSank I can help if you want

I will be your third world tech support

DanielSank

@BernardoMeurer I don't have a W10 license.

I'd rather install Ubuntu, honestly.

Bernardo Meurer

No, not ubuntu plz

ACuriousMind

@BernardoMeurer My system crashes perhaps once a year, if that often. Not sure I should care about microkernel as a not-designer.

DanielSank

Why not?

Bernardo Meurer

Canonical is shitty

DanielSank

19:02

@BernardoMeurer There's a lot of help online though.

dmckee

Apple built Darwin on mach to make it easier to switch architectures (something they've done three times in the history of the company and twice for "macintosh").

Slereah

"They reported this to the Windows developers, who disassembled SimCity, stepped through it in a debugger, found the bug, and added special code that checked if SimCity was running, and if it did, ran the memory allocator in a special mode in which you could still use memory after freeing it."

DanielSank

You want me to use Arch?

Slereah

My sides

Bernardo Meurer

@ACuriousMind You don't :) It's a thing for kernel-loving people I think

DanielSank

19:03

@Slereah yeah

Bernardo Meurer

@DanielSank Arch, Majaro, Antergos, Gentoo

ACuriousMind

@BernardoMeurer Kernophiles?

John Rennie

@DanielSank: you can get the Windows install image here

Bernardo Meurer

@ACuriousMind Yes!

Slereah

Windows XP and on were much less backward compatible and trust me it was a right ass to run anything old

Bernardo Meurer

19:03

@dmckee I have dreams that Hurd will work one day

John Rennie

@BernardoMeurer OSX is based on the Mach microkernel, but they rewrote it to make it monolithic.

Slereah

it still is

dmckee

@BernardoMeurer So doe RMS.

Slereah

Most old .exe won't run at all on windows 7

Bernardo Meurer

@JohnRennie So it's a hybrid kernel? kewl

@dmckee Lol, RMS is a bit of a goof

John Rennie

19:04

As far as I know there is no mainstream app using a microkernel because the performance hit is too great.

Slereah

I have to fire up the DosBox to run them

Bernardo Meurer

@JohnRennie Minix runs okay :(

ACuriousMind

Hm, the proper word would be karyophile, I guess

DanielSank

Hey @BernardoMeurer I'll need your help getting into my file server.

Bernardo Meurer

@ACuriousMind Why?

dmckee

19:05

@BernardoMeurer He's ... dedicated.

John Rennie

@BernardoMeurer no, it's monolithic but they stole all the code from Mach.

DanielSank

I haven't updated the OS in forever, and it's been powered off. I don't remember the password.

Bernardo Meurer

@DanielSank That's never a good thing :P

Jesus

ACuriousMind

@BernardoMeurer Because karyon is the Ancient Greek word for "kernel"

DanielSank

Nah, it's cool. It's been off.

Bernardo Meurer

19:05

@dmckee He's crazy, but I love him

dmckee

Sometimes that comes across as fanatical or goofy, but he's right enough often enough that it's a mistake to dismiss him out of hand.

DanielSank

I'll turn it on, back up the data, and then deal with it, yeah?

Bernardo Meurer

@JohnRennie Sweet

DanielSank

(no network, obviously)

Slereah

"In fact if you poke around in the AppCompatibility section of your registry you’ll see a whole list of applications that Windows treats specially, emulating various old bugs and quirky behaviors so they’ll continue to work."

Bernardo Meurer

19:06

@DanielSank Yep :)

John Rennie

@BernardoMeurer Windows NT 3.1 was originally designed as a microkernel, and the alpha builds were classic microkernel design.

Bernardo Meurer

@ACuriousMind karyophile, cool

@JohnRennie I think one day we will have computers fast enough to use microkernels and not care

Slereah

"For example, a lot of developers used to try to make their Macintosh applications run faster by copying pointers out of the jump table and calling them directly instead of using the interrupt feature of the processor like they were supposed to.

Even though somewhere in Inside Macintosh, Apple’s official Bible of Macintosh programming, there was a tech note saying “you can’t do this,” they did it, and it worked, and their programs ran faster… until the next version of the OS came out and they didn’t run at all. "

This article is always a fun read

"a veritable panoply of external dependencies each one of which is going to be a huge headache when you ship your application to a paying customer and it doesn’t work right. The technical name for this is DLL Hell."

dmckee

Inside Machintosh was full of warnings not to take the current implementation as a license to do things. It sometime took years for an update to kick cheaters in the butt, but it happened many times.

John Rennie

The no. 1 problem with Windows is that MS have to let OEMs do their own installs and piss about with the install as they do it. Even the big names like Dell overload the Windows install with crap, and the box shifters do installs that should earn them a long spell in jail.

dmckee

19:09

In fact, every time I tried to take a shortcut I was eventually caught by an update.

Slereah

Crime doesn't pay @dmckee!

dmckee

@JohnRennie Android does that crap too. Grrrr...

John Rennie

This doesn't affect Apple because they have complete control over the hardware and OS, and it doesn't affect Linux because everyone does their own install;s.

Slereah

you know what else has a crazy amount of backward compatibility?

John Rennie

@dmckee Buy a Nexus!

Slereah

19:10

x86 processors

Bernardo Meurer

x86_64 was a mistake

Slereah

They start in 16 bits mode, just in case you want to install a program from the 1970's on it

dmckee

^ Those (x86 processors) are just full of cruft.

Bernardo Meurer

At least it's not that Itanium BS

IA-64 GRRRRRRR

Slereah

I mean backward compatibility is fine but maybe we don't need 16 bits mode anymore

Bernardo Meurer

19:10

Makes me angry just to think

John Rennie

@dmckee Eh?

Bernardo Meurer

It's BS

Slereah

I don't think anyone has seriously used it in 20 years

Bernardo Meurer

To think we still use BIOS!

dmckee

@JohnRennie They didn't fit in the right spot in features-price-performance space last time we were shopping for phones.

John Rennie

19:12

Then a OnePlus, or any of the brands that do a minimal install. Motorola are pretty good for this.

dmckee

Ended up with moto-gs which are nice, except for the stuff I can't de-install and keep gone.

I've considered jailbreaking them just for that reason.

And the G doesn't have an SD card slot, so the on-board memory is it and when it gets full...

Bernardo Meurer

Is it faster to run a sieve of erasthotenes or to apply miller rabin to all odd numbers to find primes?

OnePlus is cool

I'm stuck with Apple and iMessage though

dmckee

You know what the web needs? An architecture for web-authors to justify their use of external scripts to people trying to load a page.

I'm looking at a page that doesn't actually display anything unless I enable at least 7 separate thrid-party scripts.

Bernardo Meurer

Scripts are cancer

dmckee

And I don't know what they do or why I should trust them.

Ghaw!

Emilio Pisanty

19:18

well, I'll be, OP has gone and deleted their account not one hour after asking

0

Q: Do quantum linked rings of quantum knots have energy?

There has been an experiment where infinite quantum linked rings were created to make a quantum knot.The structure is topologically stable and the knot can't be untied without breaking the rings. If these rings have energy and allow the structure to be stable, wouldn't there be infinite energy ...

dmckee

Come to that, I wish more android app authors would explain all the permissions they are asking for.

Emilio Pisanty

second time this happens, too: physics.stackexchange.com/questions/319986/…

DanielSank

This is really interesting:

Microsoft grew up during the 1980s and 1990s, when the growth in personal computers was so dramatic that every year there were more new computers sold than the entire installed base. That meant that if you made a product that only worked on new computers, within a year or two it could take over the world even if nobody switched to your product.

Emilio Pisanty

@dmckee load Privacy Badger and if it doesn't display it's its own fault

dmckee

I'm using noscript right now. What advantage does the badger offer?

Emilio Pisanty

19:21

@dmckee it only blocks stuff that looks like it's tracking you

dmckee

Though I do simple kill the tab for sites that won't come up during casual browsing.

Emilio Pisanty

specifically by attempting to measure the entropy of any IDs in whatever they're sending

dmckee

I need to be able to see enough to decide I want to see more before I'll even consider what scripts I might be willing to temporarily enable.

Emilio Pisanty

Here, I'll link to it

Privacy Badger - also on the Chrome Webstore and as a Firefox extension

dmckee

Hmmm ... cool.

Emilio Pisanty

19:24

it does break some pages on occasion, but it's overall pretty good

btw @dmckee can mods see whether the OP in that one above deleted their account voluntarily, or what went on there?

ACuriousMind

@EmilioPisanty We can, but I think that's not information we should disclose unless there is demonstrable need for it.

Emilio Pisanty

@ACuriousMind ok, fair enough

I'm annoyed that I put up with that paper's ridiculous intro only for OP to scamper, but ultimately whatevs

I asked in case e.g. they were having trouble getting their account to work correctly or something

particularly since the very next user has the same username

but then again google has a hit for a much older deleted user of the same name

0celo7

what's going on?

@ACuriousMind I like how this result is attributed to Goldstine

That name makes no sense

Skyler

19:44

whats this event about ladies?

ACuriousMind

@EmilioPisanty Aptly observed, Sherlock ;) It's good that you're looking out for new users, we're aware of the situation and handling it.

@Skyler ...what?

There's no event here, and certainly none about ladies.

Skyler

i just saw a message about some kind of event on the h bar

Emilio Pisanty

@ACuriousMind good to know

Skyler

it was showing in other chat rooms i had open

0celo7

Bajoran, can you be less cryptic

ACuriousMind

19:46

@Skyler Uh, that was the chat session a few hours ago

@0celo7 No, I can't I'm afraid.

Skyler

@ACuriousMind oh ok well that makes sense, grandpa here was in nappy poo land until recently

Run like hell

@ACuriousMind Thanks, now I can finally see :)

Slereah

"When they tried to “End Of Life” Windows 98, it turned out there were still so many people using it they had to promise to support that old creaking grandma for a few more years."

heh

0celo7

The coffee machine in the office doesn't seem to work anymore

I am taking suggestions on how to fix it

Bernardo Meurer

@0celo7 Install Linux on it

2

ZeroTheHero

20:01

@EmilioPisanty I hope I'm not muscling into your conversation but I did notice a number of new users trying to vandalize the site by posting garbage questions, answers or comments.

Emilio Pisanty

@ZeroTheHero possibly, but from what I see it's not the case here

ZeroTheHero

@E

oups...

Emilio Pisanty

that person asked a terrible question, had it closed and deleted, and then came back and asked a much better version

Slereah

joelonsoftware.com/2000/04/06/things-you-should-never-do-part-i

Emilio Pisanty

there's always a steady stream of garbage posts. I haven't seen an increase in the rate lately but it's entirely possible.

ZeroTheHero

20:03

@EmilioPisanty thanks for the clarification. The accounts and posts have been deleted so t'was difficult for me to fully assess the context.

Slereah

"Third, the code may be doggone ugly. One project I worked on actually had a data type called a FuckedString."

Emilio Pisanty

> As if source code rusted.

is pretty good

@ZeroTheHero no worries. Even I can't see deleted users (presumably mods can? who knows), and I could only find the old question because I voted to close it.

0celo7

I took it apart

Slereah

"Have you ever heard of SEMA? It’s a fairly esoteric system for measuring how good a software team is. No, wait! Don’t follow that link! It will take you about six years just to understand that stuff."

0celo7

it seems to be working now

MartianCactus

20:12

when a light ray falls perpendicularly on a transparent object from vaccum, then does it bend?

like if the angel of incidence is 0

Slereah

One of the article on that blog is from 2000 and it has a link to a software company, except it doesn't exist anymore and now the link is to a tree removal company

Ben Niehoff

by symmetry, which way would it bend?

0celo7

@BenNiehoff All ways at once

Ben Niehoff

there you go!

0celo7

and don't even try that symmetry crap

what direction does the ball on that dome fall

and at what time

Norton's dome

Ben Niehoff

20:14

arccos 2/3

or something like that

Slereah

to the right

0celo7

@BenNiehoff what?

Ben Niehoff

the azimuthal angle at which the ball, rolling down the dome, experiences zero normal force (and thus flies off the surface)

0celo7

do you know what I'm actually taking about :P

Ben Niehoff

no

but I see it's time for another episode of Will It Bend?

0celo7

20:16

try solving $x''=\sqrt x$

Ben Niehoff

no

0celo7

fine, be like that

Ben Niehoff

I will

I won't attempt random-ass nonlinear ODEs unless they are first-order

it's a rule I have

MartianCactus

when a light ray falls perpendicularly on a transparent object from vaccum, then does it bend?
like if the angel of incidence is 0

ACuriousMind

7 mins ago, by Ben Niehoff

by symmetry, which way would it bend?

MartianCactus

20:20

oh sorry didnt see that

ACuriousMind

Also, it's the angle of incidence, I doubt there's a divine creature responsible for incidence.

MartianCactus

by symmetry nothing would bend

but it moves nearer to normal

Slereah

@0celo7 not a very good retort

0celo7

$\mathfrak{Proof}$?

MartianCactus

what?

Slereah

20:21

most people will solve it but fail to see the multiple solutions

MartianCactus

wait wait wait

lemme refo the question

when a light ray falls perpendicularly on *vaccum from a transparent object*, then does it bend?
like if the angel of incidence is 0

Ben Niehoff

same answer

or you can just use Snell's law...is it confusing?

0celo7

@BenNiehoff Sorry, I meant $x''=x^{3/2}$

There are two families of solutions

Clearly $x\equiv 0$

Slereah

Use Snell's law, yes

0celo7

But then there are solutions that start moving after an arbitrary amount of time

Slereah

20:30

hint : $\sin(\pi/2) = 1$

0celo7

and there's no reason why it should move in an particular direction either

so it's perfectly valid for the ball to wait for a while and then just roll in a random direction

Someone should make a perfectly non-Lipschitz dome and try the experiment

Slereah

Hint : you can't

Because reaction forces aren't real in the real world

0celo7

reaction forces?

Slereah

Norton's dome is based on the concept of reaction forces

0celo7

what?

Ben Niehoff

20:32

by "start moving after an arbitrary amount of time", what do you mean? x is some non-analytic function?

0celo7

@BenNiehoff Almost all functions are not analytic

Slereah

The surface on which the ball is exerts a force perpendicular to the surface

Ben Niehoff

of course

0celo7

The soltutions of $x''=x^{3/2}$ are not unique

Ben Niehoff

but what do these solutions look like? literally flat until they transition to a nonzero function?

0celo7

20:33

There are solutions that are $x(t)=0$ for arbitrarily large $t$

Ben Niehoff

or with some sort of small tail?

0celo7

@BenNiehoff Yeah

Slereah

The solution is like $\approx t^4$

0celo7

$x''=x^{3/2}$ corresponds to a ball sitting on a dome of some particular shape

then apply Newton's law

Slereah

The exact class of solution is $$x(t) = \Theta(t - T) \frac{1}{144} (t - T)^4$$

Ben Niehoff

20:34

so x would have to have things in it like e^{-1/t}...is that what you're saying?

Slereah

For every value of $T$

0celo7

what @Slereah said looks right

Emilio Pisanty

@BernardoMeurer around?

0celo7

you obtain a solution for any value of $T$, it's quite amazing

Ben Niehoff

oh, right, because x only needs to be C^2, not C^\infty

0celo7

20:35

Is that there actually not smooth?

I'd have to plot it

Ben Niehoff

and the problem is basically because x=0 is some kind of singular point

Slereah

It's not smooth, no

0celo7

I think it's fine...all the derivatives are equal to zero at $t=T$

@Slereah why not?

Slereah

But the problem isn't that it's $C^2$

Ben Niehoff

no, it's obviously not smooth, its 4th derivative is discontinuous

Slereah

20:36

The problem is that the problem isn't Lipschitz continuous

0celo7

I don't see how that's obvious, but ok

The third derivative gives a kink, ok

In any case, there's no physical reason for things to be Lipschitz or smooth

Slereah

Do you think you can have a non-Lipschitz continuous metric

0celo7

Yes.

$g=x^2\mathrm dx^2$

$x\mapsto x^2$ is not Lipschitz

Slereah

Hm

Does it give rise to issues though?

0celo7

No, why would it?

Slereah

20:44

Is $x'' = x^2$ ill defined

0celo7

@Slereah Oh, for ODE you only need locally Lipschitz

Slereah

Well can you have a metric that isn't locally Lipschitz

0celo7

$x^{3/2}$ fails to be Lipschitz on any neighborhood of $0$

Slereah

$\sqrt x$ isn't gonna work

Would fuck up the signature

Maybe a root on one of the off-diagonal terms?

Can you have a $C^2$ function that fails to be locally LC though

0celo7

No, all $C^1$ functions are LL.

Slereah

20:47

yeah I guess it would be a pretty fucked up metric anyway

although some metrics are just $C^0$

0celo7

You can define metrics with values in Sobolev spaces

If you do it correctly you can get Sobolev-valued Christoffels and curvature

Slereah

gross

0celo7

Indeed

You need something called the Sobolev multiplication theorem

It says that certain Sobolev spaces can be paired via a generalized multiplication operator

MartianCactus

21:01

@BenNiehoff doesnt snell's ;aw break when angel of incidence is zero?

Ben Niehoff

no?

MartianCactus

it does

or thats what my notes say anyway

sin of angel of incidence / sin of angel of refraction is no longer constant so..

ACuriousMind

@MartianCactus Not when you write it in a form without fractions

I.e. $n_1\sin(\theta_1) = n_2\sin(\theta_2)$

Also, it's still angle, not angel.

Slereah

I can be your angle or your devil

ACuriousMind

Don't you mean devli? :P

Ben Niehoff

21:06

devle

Jaime Gallego

Send me an angel ohohohohohhhhhh

Send me an angeeeel

Ben Niehoff

@0celo7 I did a GR problem once where the curvatures ended up with second derivatives of Dirac delta :P

Jaime Gallego

Real Life - Send Me An Angel

►

Ben Niehoff

propagating gravitational shock wave, basically

Slereah

Shock waves are pretty shit

0celo7

21:20

@BenNiehoff you're a terrible person

Slereah

"The story goes that one programmer, who had to write the code to calculate the height of a line of text, simply wrote “return 12;” and waited for the bug report to come in about how his function is not always correct. "

Help, i have died of laughter

(this was code for Microsoft Words)

ACuriousMind

@Slereah Word or Works?

Slereah

Word

Bass

21:40

@ACuriousMind For a Dirac spinor $\psi$, what are $u$ and $v$, if they are defined by $(\gamma^\mu p_\mu - m)u=0$ and $(\gamma^\mu p_\mu+m)v=0$? Are they the Weyl spinors which constitute the Dirac spinor? Or are they the sums and differences of the Weyl spinors like $\psi = (u,v) = (\psi_L + \psi_R, \psi_L - \psi_R)$?

The latter are normally written as $\psi = (\phi, \chi)$, and the former are usually called $\psi_L$ and $\psi_R$, so I believe they are neither.

ACuriousMind

@Bass They are the positive and negative frequency solutions. For any constant Weyl spinor $\xi$, $u = (\sqrt{p\cdot \sigma} \xi,\sqrt{p\cdot \bar{\sigma}}\xi)$ and $v = (\sqrt{p\cdot \sigma}\xi,-\sqrt{p\cdot \bar\sigma}\xi)$ are such solutions.

Slereah

$u$ and $v$ are the particle and antiparticle solution

They are not Weyl spinors

Weyl spinors don't split particles and antiparticles all that well, IIRC

and especially not Majorana spinors

Bass

Ah, so they are not anything specific from a group theoretic viewpoint?

Slereah

well positive and negative frequency solutions are pretty specific

you don't get that without the $T$ part of the Lorentz group

ACuriousMind

@Bass The terminology is a bit confusing here - one should distinguish between Weyl and Dirac spinors, which are just elements of their specific group representations, and there are the spinor-valued fields. $u$ and $v$ are specific spinor-valued fields, but not special as mere spinors.

Slereah

21:48

Like without time orientability you can't get those I think

Bass

But in which Lorentz irrep do they transform?

ACuriousMind

@Bass Both $v(\vec p)$ and $u(\vec p)$ are Dirac spinor-valued fields.

Slereah

$(0,1/2) \oplus (1/2, 0)$

Bass

Ah, I see.

What's the difference between $u,v$ and $\phi,\chi$?

Emilio Pisanty

This is so cool

Mars’ moons could be remnants of earlier rings, destined to form a new one

Bass

21:50

with $\phi = \psi_L+\psi_R$ and $\chi = \psi_L - \psi_R$.

Slereah

Well for a start there's no $u$

It's $u^s$

Bass

@Slereah OK, go on.

ACuriousMind

@Bass You need to be more explicit whether you're writing down spinors or spinor-valued fields here. First, the $u,v$ depend on the choice of a Weyl spinor $\xi$, so they're Dirac-valued fields $u_\xi(p)$ with a Weyl-spinor parameter $\xi$.

Slereah

I think you have $$\frac{u + v}{2} = \psi_L$$

or at least something proportional to it

Bass

@ACuriousMind OK, I'm trying: $\phi$ and $\chi$ are just spinors, they are defined by their transformation under the Lorentz group. $u$ and $v$ are spinor fields, i.e. solutions to the Dirac equation.

ACuriousMind

21:54

Now, if you look at my formulae up there, for the choices $\psi_{L,\xi}(p) = \sqrt{p\cdot \sigma}\xi$ and $\psi_{R,\xi}(p) = \sqrt{p\cdot \bar\sigma}\xi$, then you have indeed that $u_\xi(p) = \psi_{L,\xi}(p) + \psi_{R,\xi}(p)$ and $v_\xi(p) = \psi_{L,\xi}(p) - \psi_{R,\xi}(p)$.

Slereah

Yeah that sounds reasonable

Bass

Oh, of course.

Cool, thx!

Slereah

I am slightly annoyed that the Einstein notation for spinor never stuck

I find it usually more clear

though spinor calculus has weird rules

Ben Niehoff

which spinor notation is the "Einstein" one?

and I think you mean Grassmann calculus has weird rules

Bernardo Meurer

@EmilioPisanty Now I am, what up?

0celo7

22:11

Is grassman calculus anything more than purely formal?

Is the grassmann integral actually an integral in the MT sense?

Slereah

@BenNiehoff $\psi^\dot A \sigma_{\dot A}^A \psi_A$

That kind of stuff

Emilio Pisanty

@BernardoMeurer on that qsub thing

I write a shell script and hand it off to the queue manager

I suspect the issue is that the shell inside the thing isn't bash

How do I find out what shell is interpreting my .sh file?

Sir Cumference

22:33

@OBE So...is this Astro design idea not happening or...?

OBE

22:56

@SirCumference wait im working on a different graphics project right now.

all my free time is on that

Sir Cumference

All right

OBE

should be done soon

Sir Cumference

Oh, by the way, should I learn how to make music digitally?

OBE

sure

Sir Cumference

I'm thinking of learning a new skill of some sort

OBE

22:58

physics is a pretty useful skill

Sir Cumference

I'm already majoring in it

That ain't new

Qmechanic

0

Q: How to define complex mechanics problems mathematically correct?

I asked a similar question in the math section but no one answered , hopefully I will find the answer here.I am an engineering student and I often face mechanics problems which involves usings concepts like infinitesimal and limits . I have a clear idea of those concepts ,however applying them on...

classical-mechanics mathematical-physics

Too broad?

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