The h Bar

Bernardo Meurer

00:28

@JohnRennie I have to say, for all my dislike of Windows, it does handle hardware failures really well

Emilio Pisanty

00:47

@0celo7 that's interesting

did they run out of old ships to shoot at?

Artificial reef

An artificial reef is a man-made underwater structure, typically built to promote marine life in areas with a generally featureless bottom, to control erosion, block ship passage, or improve surfing. Many reefs are built using objects that were built for other purposes, for example by sinking oil rigs (through the Rigs-to-Reefs program), scuttling ships, or by deploying rubble or construction debris. Other artificial reefs are purpose built (e.g. the reef balls) from PVC or concrete. Shipwrecks may become artificial reefs when preserved on the sea floor. Regardless of construction method, artificial...

News Alert - The U.S. Navy ships sunk in 3 minutes by TORPEDO attack!

►

this kinda thing

Bernardo Meurer

Pro tip fellas: never, never, NEVER unplug a drive or allow system failure during low-level operations.

It's harder to fix than I imagined

After two days I finally recovered this bricked drive

Emilio Pisanty

01:05

@BernardoMeurer unlike you, we actually listen to the folks like you who tell us not to do stupid shit like that

¯\ _(ツ)_/¯

Bernardo Meurer

@EmilioPisanty I am the guy who tells you not to do it :P

Someone has to try it :P

Emilio Pisanty

@BernardoMeurer Like you didn't know it was a bad idea

Bernardo Meurer

In my defense it was half-needed

Emilio Pisanty

just sayin'

Bernardo Meurer

I was creating a ZFS pool on a drive and my girlfriend decided she had other plans than waiting

I ain't confronting her because I need to wait on ZFS ;P

Shit I broke it

again

AH

I'm throwing this drive away

it's dead

Emilio Pisanty

01:15

@BernardoMeurer quitter

Bernardo Meurer

@EmilioPisanty I know how to fix it

Emilio Pisanty

You gonna give up that easily?

Bernardo Meurer

Boot into a vanilla kernel with the default scheduler, dd /dev/zero into the block device, and wait

problem is writing 500GB through a USB2 link takes like 16h

This drive costs like $10, my 16 hours is worth more than $10

The problem is that the bfq IO scheduler causes the -ck kernel to panic when a block-dev driver hangs; which this drive does because it has a corrupt superblock somewhere that I cannot get rid of

[ 1226.710194] INFO: task kworker/u16:3:28760 blocked for more than 120 seconds.
[ 1226.710200]       Tainted: P        W  O     4.15.18-1-ck-ivybridge #1
[ 1226.710201] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 1226.710203] kworker/u16:3   D    0 28760      2 0x80000000
[ 1226.710218] Workqueue: events_freezable_power_ disk_events_workfn
[ 1226.710221] Call Trace:
[ 1226.710236]  ? __schedule+0x7d3/0xe20
[ 1226.710243]  schedule+0x32/0xc0
[ 1226.710249]  io_schedule+0x12/0x40

See ^

Oh, I know what to do!

I have a NetBSD machine!

Bernardo Meurer

01:38

Yeah, apparently my custom kernel was the issue

preliminary results

Yep, the problem is bfq :)

Pro-tip: If you have a drive with shitty sectors, don't use an asynchronous scheduler :)

Abhinav

02:01

I have 18 reputation but I can still talk here

0celo7

@EmilioPisanty this reef is crazy

these people just dumped 2,000,000 tires in the ocean

complete madlads

and now when there's a big storm they get scattered everywhere and destroy all of the natural reefs

dmckee

02:14

I'm temped to start collecting statistics about questions that involve the concept of centripetal force/acceleration. I conjecture that nine of of ten times they can be resolved by (getting the the OP to believe/understand that) "the system is not in equilibrium!"

rob

@Abhinav You also have reputation on Mathematics. That's the difference.

vzn

@0celo7 lol since when are you concerned about the environment? your chat record shows quite the opposite sentiments repeatedly :P

Bernardo Meurer

@EmilioPisanty There, now I have a raspberry pi wiping the drive for me

Abhinav

02:35

@rob So it works like that.Thanks for telling me

Cows

I feel a warmth inside

I am going to be live studying category theory later

I feel like I will make a lot of progress tonight. Will begin in an hour

Ok let me grab a bottle and start. Will be making strides in the associated fora.

* a bottle of water that is * I don't drink alcohol (anymore hehe)

alright

Cows

03:02

Actually, let me just read and scribble first

Sid

06:10

@JohnRennie HELP required!!

John Rennie

@Sid whats up?

Sid

I hope you are okay with magnetic circuits..

John Rennie

Magnetic circuits. Hmm. Well, what's the question?

Sid

Suppose, we are given flux through the airgap and Area of Cross section of the air gap. Then, we can find flux density. And from a table given to us, the corresponding values of Magnetic field strength for different values of flux density are given

John Rennie

OK ...

Sid

06:17

From this, we can find the permeability. However, the flux density that I get from calculation is, say 0.5. But, the value of H (Magnetic field strength) corresponding to 0.5 isn't given in the table. But that of 0.4 and 0.6 are given.

How do I calculate the value of H corresponding to 0.5?

John Rennie

Graph the figures you are given then estimate the value for 0.5 by interpolation?

Sid

Won't that be approximation?

John Rennie

I'd draw the graph and see what it looks like. It might be linear in which case you'd get a pretty accurate value.

Sid

No, it's not linear. If it had been, I wouldn't have been asking you..

I did draw the graph and approximated the value of H. My final answer of current came out to be about 2mA more than the answer given in the book

John Rennie

Unless you know some formula that relates H to the flux density I'm not sure what more you can do. Does the curve look like anything obvious? A parabola for example?

Sid

06:32

Well, it's sort of straight line.

(How do you upload pictures in mobile version of chat?)

John Rennie

06:51

@Sid Upload to imgur and post the link?

Or use the desktop version of the web site

Sid

07:07

I will post once I am in the vicinity of a laptop

Slereah

Morning my dudes

Abhinav

How to write a good answer so to get votes....my answers are not good results

getting*

user228700

09:23

@JohnR: Hi! :-) You around?

John Rennie

Morning :-)

user228700

How's it going?

John Rennie

Though i'm only around for a few minutes as I have deliver a laptop (one I've fixed)

@KaumudiH Mondays aren't my favourite day, but it's OK. The weather is nice :-)

user228700

@JohnRennie Ah, haha, yet another has fallen victim! :-)

user228700

@JohnRennie Cool :-)

John Rennie

09:25

I do the washing on a Monday morning but it's mostly done so that's Ok too :-)

How is life in Kochi? I guess the exams are about to start - or shouldn't I mention that? :-)

user228700

Actually, in a stunning turn of events, I find myself in Chennai again!

John Rennie

Ah, do go on ...

user228700

(That's why my replies aren't coming in minutes later, haha.)

user228700

@JohnRennie Well, it turned out that I had a few days of study holidays left, so I came back home with my parents.

John Rennie

Presumably the theory is that you'll use the peace and quiet to get lots of work done? :-)

user228700

09:28

I will be leaving on Wednesday, and they will follow either this Sunday, or the next Saturday.

user228700

@JohnRennie Sort of :-)

John Rennie

How are the plans for the move to Kochi going?

user228700

Great! We've found an excellent apartment, my Father's been looking into Packers & Movers options, and I'm vacating my room at the hostel this Friday, right after my exam, and taking my stuff to the new house!

user228700

I'll be staying there on my own until my parents move in with all the stuff, but I'll still have a few essentials from hostel to live on till then- a bed, a bucket, soap, etc.

John Rennie

@KaumudiH have they sorted out the Internet connection? You have to take care of the important things first!!!

user228700

09:32

No, no, they have not :-) Not to worry, I'll be able to use my mobile as a hotspot till they do.

user228700

You're not adequately excited about "I'm vacating my room at the hostel this Friday..."

John Rennie

How far is it from MEC? What's the travel time like?

user228700

VACATING MY ROOM AT THAT WRETCHED HOSTEL, JOHN!

John Rennie

@KaumudiH Free! Free, at last!! :-)

user228700

:-D Yes!

user228700

09:33

@JohnRennie Around 5 Kms, so roughly 20 minutes (on a scooter my parents are going to buy me soon!), give or take.

John Rennie

You'll be able to go out after 6 p.m. How will you cope with the freedom after your long incarceration? :-)

@KaumudiH Cycle distance?

user228700

@JohnRennie :-D Hahaha, yes!

user228700

The apartment's on the 17th floor, inside a gated community of four other buildings. So, they have a gym, a swimming pool, a shopping complex, a cafeteria, etc.

user228700

@JohnRennie True, but the roads are too hilly to cycle on.

John Rennie

@KaumudiH Wow, that's a step up from the hostel!

Do you have free use of the gym and swimming pool, or do you have to pay?

user228700

09:36

@JohnRennie "Free". We'll be paying Rs. 3000 for maintenance every month, which includes all this stuff.

John Rennie

@KaumudiH ah, I just noticed you said in an earlier post that you were getting a scooter.

user228700

Second hand, but still!

John Rennie

@KaumudiH In the UK that would be really cheap - I don't know how it is in Kochi.

user228700

Eh, it's not too cheap by modern standards over here, but not too expensive, either. Affordable.

John Rennie

@KaumudiH I don't think I've ever owned a brand new motorcycle or car. I actually quite like driving a slightly battered car as I feel I don't have to be ultra careful with it.

user228700

09:39

Oh, what, I thought your car was new when you bought it!

John Rennie

@KaumudiH No. I do so little driving these days that it wouldn't be worth spending lots of money on a new car. I tend to look for cars that are about ten years old but with a low mileage.

user228700

Ah, I see!

John Rennie

Those tend to be cheap, and as I said it allows me to be careless with them without feeling guilty.

With a brand new car I'd be terrified of scratching it.

Nehal Samee

Can anyone tell me how can I represent acceleration in respect to distance $x$ ...? Like , *x double dot *...

user228700

@JohnRennie Right, like that time it hit that tree in your driveway :-P

John Rennie

09:41

@KaumudiH ah, erm .. yes :-)

And I managed to back into a wall so the corner of the rear bumper is bent now. Oh well :-)

But the car just passed its MOT with no repairs needed so it's good for another year.

user228700

@JohnRennie x'D When did this happen?

John Rennie

@KaumudiH A while back. I was at my Mum's and we were visiting a friend of hers who is in a care home. When I was backing out of the parking space there was a low wall - so low I couldn't see it through the rear window.

user228700

@NehalSamee x double dot is quite correct-acceleration is the double derivative of distance with respect to time.

user228700

@JohnRennie Oh, dang.

John Rennie

But it's OK - just a slightly bent bumper. Hardly noticable given all the other dents on the car :-)

user228700

09:44

:-) Right...

John Rennie

That's the thing about an old car. You don't care if you add another dent or two.

user228700

I like your car. It's cute :-)

Nehal Samee

@KaumudiH Ah , sorry... I couldn't complete it ... Using Math jax ...

Of course ...

user228700

@NehalSamee Ah, you wanted the MathJax for it?

John Rennie

It is a nice car. I don't get attached to cars like some people do, but I will be sorry when it finally dies of old age.

user228700

09:45

@JohnRennie :-) How old is it now?

Nehal Samee

@KaumudiH yeah ...

John Rennie

@NehalSamee $\ddot{x}$ or $\frac{d^2x}{dt^2}$

@KaumudiH 15 years!

Nehal Samee

@JohnRennie Thanks ...😄

user228700

@JohnRennie Wow! :-o That's not normal for a car, no?

John Rennie

Modern cars last ages. It's not uncommon to see 20 year old cars.

What tends to happen is they get gradually more expensive to keep running, then eventually something big and expensive goes wrong and it's cheaper to buy a new car than fix the old one.

user228700

09:47

Wow, I see. My Dad's car is now...almost 10 years old, and works just fine! Guess we'll be seeing loads more of him (the car), thank God! It's such a good car.

user228700

@JohnRennie Ah, right, right.

John Rennie

Anyhow I need to go. My drier has just pinged to say it's finished, and I need to get the clothes out then dash off with the laptop.

user228700

How's the new cycle doing?

user228700

Ah, OK :-) Catch you later!

John Rennie

Bye :-)

Bernardo Meurer

10:38

ZFS is kind of amazing

@0celo7 50% confirmed for Brazil

Just getting things set-up with Standard Cognition

Should be in Rio from August 2-25

Rumplestillskin

11:08

Can anyone help me out with some index notation: I've got the following expression $$ -4/c^2 \mathbf{v} \times (\nabla \times \mathbf{w}).$$ So far I've re-written it as $$ \mathbf{v} times (\epsilon_{ijk} \partial_j w_k)$$ but I'm not really sure how to handle the rest any suggestions. I know I want to get it so that we can write it in terms on Kroneckers deltas but I currently having a brain fart. $$ \mathbf{v} $$ is used to denote a boldface vector and the $$-4/c^2$$ is just a constnat

Slereah

You can rewrite the levi-civita tensor as a sum of Kronecker symbols

Also I don't know what you want to prove so that doesn't help

Rumplestillskin

11:34

Ah I got it! When you don't use something for a while the tricks fade away! Thanks @Slereah

0celo7

12:03

@BernardoMeurer sick dude I’m going earlier than expected

We’re gonna have 4 days to ruin my life before the conference

@vzn that shows you just don’t know anything about me

@ACuriousMind unexpected porno imgur.com/a/uB4aPIW

Balarka Sen

is this the new post apocalyptic waifu simulator that you're playing

0celo7

replaying the witcher 3

Slereah

Witcher than what

0celo7

admittedly the name doesn't make sense

especially because you're not a witch hunter

Mockingbird

13:20

Hello, everyone.

Can you people suggest me some resources (books, webpages etc.) to learn physical simulation?

Emilio Pisanty

13:32

Michael Mcintyre talks 'hanky panky' - The Graham Norton Show 2016: Episode 7 Preview – BBC One

►

Semiclassical

@EmilioPisanty oh, I remember you wondering what I was talking about when I brought up finite-gap potentials at one point. while looking up something else, I found a pretty good discussion (or at least one which isn't completely obscure) in one of Arnold's books: books.google.com/…

Emilio Pisanty

@Semiclassical goodness

Semiclassical

yeah, i came upon that pretty randomly

but it's about as good as one would hope for

the lead-up to it is some inverse scattering transform stuff, but if you take that eigenvalue problem for granted then I think it's pretty self-conntained

Emilio Pisanty

that's horrifying

but more importantly

lunch calls

Balarka Sen

14:01

@BernardoMeurer

Cannibal Ox - The Cold Vein 2001 (FULL ALBUM)

►

0celo7

@EricSilva tfw Sougi shows up in research

It’s a small world

Oh no this is P. E. Soug

False alarm

Balarka Sen

Lol

0celo7

What

Balarka Sen

It's a Sougi meme created by the UCians

Alex K Chen

hello balarka

Balarka Sen

14:16

h

Slereah

Help

Alex K Chen

>

ffahim

Hello there

Slereah

My current job mission is working on some VBA application developped by some company

The help I need is for someone to shoot me

Balarka Sen

is assisted suicide legal in france?

i won't do it otherwise

Slereah

14:17

come and find out

Balarka Sen

im a law-abiding citizen

Slereah

Have you ever analysed VBA code on an excel file written by people who don't know anything about programming

Balarka Sen

Admittedly not

Alex K Chen

i am reading torque and stuff like that from hrk

but they only consider tension force, but not lateral force in rod

so ain't the calculations a bit off ?

Balarka Sen

those calculations that you deleted did seem off

Alex K Chen

14:19

lol

no I mean for two particle rod configurations like this, shouldn't lateral force produces a change in calculations ?

0celo7

@BalarkaSen yo i hrd you like indices

Balarka Sen

Besus Brist

Sir Cumference

Morning folks

Eric Silva

@0celo7 souganidis is p.e. soug

Takis is his nickname

Balarka Sen

(hence why the meme was relevant)

0celo7

14:31

@EricSilva oh

He has an MCF paper

Nehal Samee

14:42

Can anyone tell me if a charged particle is in motion in a place where both electric and magnetic field exist , then will its path be circular ? And if yes , then will I count only magnetic force for finding its radius ?

Slereah

depends on the electric and magnetic field.

There's a famous setup where the path will be helicoidal

John Rennie

@Slereah VBA in Excel? That's what I get paid £500 a day to do :-)

Slereah

@JohnRennie You poor man

John Rennie

It's all money :-)

Slereah

Those people don't use any variable names for rows and columns for the most part

I'd rather prostitute myself

John Rennie

14:51

@Slereah Shooting is too good for them

Either use named cells or ranges, or at least define some const values with the row/column numbers.

Slereah

Alas not

John Rennie

@Slereah me too, but I fear there would be little demand for my services

Slereah

It's a giant seething mass of "if" statements with random numbers for rows and columns

Debugging it is fairly tough

also they don't seem to understand factorization

John Rennie

Excel has a primitive object system. There's no inheritance but it does a decent job of encapsulation.

Slereah

there's a bunch of If sheet1.Cells(i, n).value = "" Then
sheet2.Cells(i, n).value = 0
Else
sheet2.Cells(i, n).value = sheet1.Cells(i, n).value
End If

Like dozens of them

Semiclassical

15:16

@EmilioPisanty lol, I don't think it's that bad

especially if you look specifically at the case considered at the bottom of page 274, where $L=-\partial_x^2 +u(x)$ with $u(x+T)=u(x)$. (the second operator in that case is the discrete translation operator)

ffahim

Hey guys while reading an article about the unusual characteristic of Projectile motion I came to know that for angle greater than 70.5288 ° the projectile starts oscillating. And we can find two points where the radial vectors magnitude is same. When I was reading the proof of this phenomenon I saw they used radial velocity =dr/dt= 0 then kept proceeding. But how could the radial velocity be zero? See the pictures

Semiclassical

then being finite-gap amounts to "the dispersion relation is $\epsilon^2=f(k)$ with $f(k)$ being a rational function"

ffahim

Semiclassical

@ffahim They're looking for the moment of time where the distance of the particle from the origin is maximum

so you want to find the critical point for the function $r(t)$.

ergo, you want the time at which $dr/dt=0$

That's no different than saying that, if you toss a particle vertically upwards, then the height is maximum at the moment when $v_y=dx/dt=0$

it's true for some particular moment in time, not for all times

Eric Silva

@0celo7 I am aware

ffahim

15:25

@Semiclassical what zero velocity has to do with the maximum radial distance since the radial velocity never becomes zero only the vertical component of velocity is zero at maximum point still there is no zero velocity. Can you please elaborate more

Semiclassical

if i'm throwing it straight up, then there certainly is zero velocity when the particle's height is maximized

presumably, though, what they mean is precisely that the radial component of the velocity is zero

that's why they write $dr/dt$ not $d\vec{r}/dt$

$r$ is the distance from the origin. it's not a vector. hence dr/dt is not a vector quantity.

ffahim

Oh I see. I am sending another picture, what does that mean by the line I circled

@Semiclassical "" radial velocity goes to zero and changes sign""?

Semiclassical

radial velocity = radial component of velocity

so the distance from the origin goes from increasing to decreasing or vice versa

ffahim

Radial means vertical component?

Semiclassical

radial means distance from the origin

but they're not really spelling that out

if you want to think in terms of vectors (as they're language suggests) you really need to think of your vectors as being in polar coordinates rather than Cartesian coordinates

ffahim

15:36

So how does it change sign? Since it's not a vector

I got that r represents here the radial distance fine, and when finding out two equal radial distance and showing that the change in distance is zero hence the radial velocity (speed) is zero, but what sign flip has to do anything with that

Semiclassical

because the distance goes from being increasing to decreasing, i.e. dr/dt>0 to dr/dt<0, or vice versa

ffahim

Thank you so much, now it's clear :) @Semiclassical

Semiclassical

the point is that, initially, the distance of the particle from the origin is definitely increasing

and if you wait long enough, then it'll also definitely be moving away from the origin

but, apparently, if the initial angle is steep enough then there'll be a time interval in which the particle's radial distance is decreasing. for that to happen, you need for dr/dt to go from being positive to negative (and ultimately back to positive)

Emilio Pisanty

15:58

this is....

Semiclassical

yeah...

Emilio Pisanty

not all that informative

Semiclassical

it's a bit disappointing, yes. I more meant that the context they're setting is not so strange

Emilio Pisanty

@Semiclassical not an unsurmountable problem though

Semiclassical

ya

and if you look at the stuff they do ahead of that, you can imagine where they're going with it

Emilio Pisanty

16:00

I guess it's a matter of time before IT catches on and kills that route to the secret Russian cache of wisdom

but for the time being, life is good

Semiclassical

loool

Emilio Pisanty

@Semiclassical used to be gen.lib.rus.ec worked, but then it ~~stopped~~ was killed by IT

currently the .io domain still works

@Semiclassical It doesn't accent Lamé correctly

srsly wtf

but more seriously now

> There is a large class of periodic or quasi-periodic finite-gap (algebro-geometric) potentials $u(x)$ such that all but finitely many of their forbidden zones have length zero. Then the Riemann surface $\Gamma$ of the corresponding Bloch-Floquet function has genus $g$, where $g$ is the number of forbidden zones of finite length.

they're kidding, right?

that's ridiculously strong

Semiclassical

:)

Emilio Pisanty

or maybe not?

heck, maybe it's just exactly what you'd expect from simple examples?

Semiclassical

It's a strong condition, but so is a high-order polynomial having rational solutions

Emilio Pisanty

16:05

[91] P. Pechukas et al. Analytic structure of the eigenvalue problem as used in semi-
classical theory of electronically inelastic collisions. J. Chem. Phys. 64 no. 3, pp.
1099–1105 (1976).
[92] J.-T. Hwang and P. Pechukas. The adiabatic theorem in the complex plane and
the semiclassical calculation of nonadiabatic transition amplitudes. J. Chem. Phys.
67 no. 10, pp. 4640–4653 (1977).

^ i.e. the stuff in those papers

particularly the first one

dx.doi.org/10.1063/1.432297 and dx.doi.org/10.1063/1.434630 for convenience

Semiclassical

can you see the discussion on page 278?

the point is more or less that, in that scenario, the variational aspect of the problem basically forces you to get a finite-gap solution

Emilio Pisanty

@Semiclassical I've got the full pdf now

Semiclassical

nice

Emilio Pisanty

which part of p278?

Semiclassical

the P-F model

specifically the point about the 'first case' they considere

Emilio Pisanty

16:10

@Semiclassical that's horrifying

Semiclassical

lol

it's basically an electronic lattice with elastic energy as well

so that the lattice can lower its energy either by organizing the charge in a certain way or by deforming the lattice

I dunno why they use that interaction function though if I'm honest

this is something you definitely hear about in solid state courses, but i dunno how much play it gets outside of that

The other thing I'll confess is that the analytical details for these stories always slew me

just too much

Emilio Pisanty

18:12

Yo @Semiclassical that Riemann-surface thing

any chance for a 2D treatment?

i.e. the Riemann surface of the eigen-energies of graphene & related materials?

theDoctor

18:48

Is pi=2.0 on a sphere?

Slereah

On a sphere, the relation between the perimeter and area of a circle depends on its radius

Consider the three cases : an infinitesimally small circle ($A \approx \pi r^2$), the circle that covers half a sphere ($A = 2\pi$ for $r = \pi / 2$, so $A = 4 r$)

And the circle that covers the entire sphere

Wait that sounds wrong

Hm

Semiclassical

@EmilioPisanty wish I knew tbh. At the very least you’d now have the k-vector as 2D rather than 1D, which would seem to mean you’d end up not with a surface in C^2 but in C^3...which, yikes

Slereah

Ah yes, the area of the sphere is $4 \pi R^2$, so the half sphere is $2 \pi R^2$, with a radius of the circle of $(\pi/2) R$

Emilio Pisanty

@Semiclassical yes, that =/

alas, saddle-point analysis for HHG in graphene has landed on my plate

Slereah

So the relation would be... $A = 8 R^2 / \pi $?

Semiclassical

19:01

in this vein you might like : arxiv.org/pdf/0901.0050.pdf

Slereah

4

Q: Area of a circle on sphere

On a (flat) Euclidean plane, the area of a circle with a radius $r$ can be described by the function $A(r) = \pi r^2.$ But how can one describe the area of the same circle on a spherical manifold? Assuming that the radius of the sphere is an Euclidean distance of $d,$ how would $A(x)$ look? I'm...

Here's the relation apparently

Semiclassical

But how to get a Riemann-surface type logic...

(One idea which I think would work is to take one of the k-components as fixed. But that’s quite a strong restriction)

Slereah

and apparently the perimeter is given by

$$P = 2\pi R \sin\left(\frac{r}{R}\right)$$

So if you define $\pi' = P / 2R$, then $$\pi' = \pi \sin(r/R)$$

So the value of $\pi'$ is anywhere between $\pi$ and $0$

Since in the limit $r \to 2\pi$ (a circle that is the entire sphere), the perimeter goes to zero

Semiclassical

19:37

I bet Ayou get a similar idea when you look at the perimeter of a spherical triangle vs it’s area

Though that’s a bit involved since the area is governed by the angles of the triangle and it’s perimeter by the sides

Lozansky

20:17

What's an example in classical physics where operators do not commute?

Balarka Sen

20:31

@0celo7 u there

0celo7

maybe

Balarka Sen

flip we pinged each other simultaneously but in the wrong rooms

dude check out the math mod's office chat room

so much spice and curry there

0celo7

link?

Balarka Sen

click

0celo7

@BalarkaSen I dont get iot

Balarka Sen

20:37

Me neither. It's too much condensed drama

My brain doesn't have enough water to liquify it in the right proportion

0celo7

are those bots in there

wtf is that conversation

Balarka Sen

our collective IQ is too low for us to understand the conversation, admit it

0celo7

my brain is kind of fried rn

so idk

Balarka Sen

21:03

@0celo7 looool @ math mods office

vzn

Apr 14 at 14:29, by 0celo7

From my perspective the climate scientists are evil

0celo7

Low tier argument, there's more to environmentalism than climate science

I can care about people polluting the ocean but dispute global warming

Not saying that I am, but I could do that

Balarka Sen

Lol

vzn

hypothetically speaking. anyway maybe should know better than to take any of your stated positions seriously, incl/ maybe esp on "serious" issues... based on my knowledge of you...

Balarka Sen

Indeed.

You should change your name to vsn

Very Serious Name

vzn

21:14

← actually was slightly )( triggered by the glimmer )( of conscience, maybe should forget about the whole thing... whatever

Lozansky

Do you always write your comments with bra-ket notation?

vzn

@Lozansky hi, probably more when bored/ aimless. so are you physics student?

Lozansky

No, just a lowly engineering student

vzn

@Lozansky cool question, wonder myself the answer to that question, think itd be great if you could formulate it for the main site, dont think it has been studied much, suspect there are examples/ analogies. have found "at least 1" from long research over yrs.

@Lozansky what kind

Lozansky

@vzn Physics!

vzn

21:26

@Lozansky great, what year/ country? studying QM already?

Lozansky

3rd year/Sweden. Yeah, it's only an introductory course tbf

vzn

@Lozansky still worthwhile am sure

Semiclassical

22:20

@Lozansky the usual example is for rotations, namely that the order in which you rotate a solid object with respect to the x-, y-, z-axes makes a difference as to the final orientation

Another analogue is passing light through polarizing filters at angles

Suppose you have three polarizing filters: one horizontal, one vertical, and one at 45 degrees to both

If you put the filters in that order, no light passes through the first two and so nothing comes out

But if you put the 45 degree filter between the two others, then light will pass through all three. (The intensity will low—only 1/8th of the initial incident intensity if I remember right—but it’s not zero.)

So the order in which you place the filters makes a difference to whether all the light is filtered

(People like to use this as an analogue for the Stern-Gerlach experiment. It’s not a perfect analogy but it does have merit.)

@vzn oh. Does the name John Bush ring a bell with you?

vzn

22:35

@Semiclassical yes, found his excellent survey on PWH, cited in here, have been calling it the Couder-Bush theory recently, real pioneers =D math.mit.edu/~bush/?page_id=484

Semiclassical

Then you’ll probably wish you were on campus here Thursday: physics.umn.edu/events/calendar/spa.all/thisweek/index/…

vzn

@Semiclassical way cool, another rabbit out of the hat, youre going for sure right? you really picked an outstanding school for physics =D ... wondering, did you look at any others? did you do your undergrad degree there too?

Semiclassical

Yeah, I am, and I may get a chance to talk with him separately. (I did my degree at a liberal arts college which was within walking distance)

I will point out that this is a bit of a one-off—pwh is not a common topic of study in physics

vzn

@Semiclassical he seems to be sufficiently conservative in his claims/ demeanor/ reputation to not arouse any serious opposition so far :P

@Semiclassical the lecture is a one-off for you to attend or the dept to hold?

Semiclassical

So I wouldn’t read_ too_ much into the school’s view on it from their invitation. It’s complicated

The latter

I’m an easy mark for talks like that

vzn

22:43

@Semiclassical not sure what you mean by "its complicated". its physics, period. (and have strong feeling, much more in the future.) as for "easy mark," (lol) either that or youre way ahead of the curve™ :P

Semiclassical

I mean that Bush being invited isn’t synonymous with an endorsement of such work, either in terms of its meaning or in terms of whether anyone here will start exploring it

So the institutional aspects are a bit harder to gauge

vzn

@Semiclassical "endorsement"? the university probably does not really "endorse" any work except their own, so to speak. & isnt that really a peripheral issue anyway? :|

Semiclassical

True enough

vzn

thx for the good news =D

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