The h Bar

12:30 AM

@JohnRennie is liable to know this

12:58 AM

@0celo7 AFAIK, relativistic polytropic solutions aren't used that often for white dwarfs. Certainly not compared to implementations for neutron stars.

HDE 226868

1:09 AM

@0celo7 Try something like $\sim10^8\text{ g cm}^{-3}$ for central density. No complaining about units. Also, writing $\gamma$ is pretty much unimportant. Work with $n$ instead.

Out of curiosity, how are you integrating your models? RK4?

0celo7

3:06 AM

@HDE226868 Whatever mathematia uses for NDSolve. As I understand it, it selects a method based on what the equation is.

@HDE226868 No complaining about units? I don't even know what cgs is, those units are bad.

I need inch-slug-second.

Sir Cumference

@0celo7 Can you answer a cosmology question?

0celo7

3:37 AM

@SirCumference maybe

0celo7

5:59 AM

@JohnRennie I need to overclock my CPU

like, badly

my single core performance is not good enough

John Rennie

The trouble is that overclocking is only going to give you a small percentage increase

Maybe 10% at best

Unless you go for crazy measures like liquid nitrogen cooling

0celo7

@JohnRennie I should have gone for the mofo CPU!

John Rennie

A Ryzen 7?

0celo7

Yeah

John Rennie

Is that really that much faster?

0celo7

6:02 AM

Who knows

but I am getting 100% usage

John Rennie

Which R7 would you go for?

0celo7

look at this carnage

those 100 spikes are noticeable

I get a ~5 fps drop

I don't need a massive boost

John Rennie

If it was me, I'd live with it for now and upgrade to a Ryzen 7 at some point.

In fact there are rumours of a Ryzen 9 being released ...

0celo7

@JohnRennie Ryzen 7 has two more cores

it's twice as expensive though :o

John Rennie

How much are those 5 fps worth to you? :-)

0celo7

6:09 AM

@JohnRennie A few MHz of overclocking, clearly

what good is the water cooler if I don't overclock?

@JohnRennie So, how does one do it?

I have the AMD overclocking tool right here

What do I crank it up to?

John Rennie

There must be overclocking guides out there in Googlespace ...

I've never overclocked a Ryzen so I don't know what would be sensible increments

0celo7

@JohnRennie People are allegedly overclocking to 4GHz

John Rennie

I'd try 5% steps. For each step run a particularly demanding bit of TW3 and then check the core temperature. As long as the temperatures remain sane and it doesn't crash keep going.

0celo7

@JohnRennie I wasn't running TW3

Battlefield 1 multiplayer

GPU load was not bad, but the CPU was hit pretty hard

John Rennie

Anything that maxes out the CPUs. You could just use EatCPU.

Though a game would be a better test as it will present a more varied load.

0celo7

6:22 AM

Good lord

they needed a $140 cooler to get a 4.1GHz clock

does the temperature just explode when you overclock?

@JohnRennie I would probably run a graphics benchmarking program

John Rennie

4.1GHz

That's only a 14% increase

It's not exactly transformational ...

0celo7

Hmm, idk

Maybe it's not worth it

I should go to bed, cheers

John Rennie

Goodnight

0celo7

@JohnRennie I just don't understand how people are running 144fps rigs

If my CPU is bottlenecking, how do these other people get over twice the performance?

You can roughly double or triple GPU power, but the CPU is basically fixed

John Rennie

The top end Intel CPU has some ridiculous number of cores. 12 cores or somethign like that.

But it's 2000 dollars

0celo7

6:30 AM

@JohnRennie a sizable portion of the PC communitt runs 144Hz setups

I doubt they all have $5000 to spend on a computer

Seems a little extreme

John Rennie

Good grief, look at this

All the top end i7s are 10 core, so that's double the CPU of your Ryzen.

GPhys

that reminds me how hopeless one of our first several computational physics assignments was that was over computational QM

John Rennie

If it's CPU limited it's not hard to see how they're doubling the FPS

GPhys

I had the brilliant idea of doing it all in my 16 GB of RAM with numpy. (I ran out of RAM immediately the first time I tried it)

0celo7

@JohnRennie my benchmark is 13,000

GPhys

6:35 AM

iirc we were numerically estimating the energy levels of a harmonic oscillator using an infinite square well basis

and 95% of the assignment was programming code that would run and finish before the due date

John Rennie

@0celo7 well that i9 scores 23,000!

David Z

@GPhys Funny, that doesn't seem like the kind of thing that would eat up 16 GB of RAM

John Rennie

@DavidZ You shouldn't underestimate the ability of students to write fantastically inefficient algorithms :-)

GPhys

^^^ Indeed. This was one of the first assignments, and we were also using our own Python code to do the integrals.

@DavidZ (I just pulled up the question): It was asking how many terms and how wide of square well we needed to correctly determine the first 40 energy levels. It looks like the next question was about a finite square well. (I don't quite remember which part I overran memory on)

David Z

@JohnRennie fair point

I guess 40 energy levels isn't exactly trivial anyway

GPhys

6:51 AM

I recall fairing better than people who didn't code gaussian quadrature or romberg integrators

David Z

ha :-P I can imagine that not going well for them

John Rennie

0

Q: If we bet, that the world is a matrix, is it possible to break ourselves out of it?

I don't enjoy reading physics books any more because I am almost convinced that we are in a computer simulation (I feel like I lost my passion to study physics) I'm not alone in this issue, even tech billionaires are convinced that we live in the matrix. You know, they are billionaires، They have...

Sigh

David Z

I presume that would have been without Numpy?

GPhys

@DavidZ It was with numpy, but used only as a matrix library essentially

David Z

Oh, because I was thinking you can still do numerical integration and get decent performance using vectorized arithmetic

GPhys

7:01 AM

my simpson's rule for one of the first assignements

(fully vectorized essentially)

David Z

Yeah, that's what I meant (I'm assuming f itself is vectorized)

GPhys

I remember using my romberg integrator for most of the rest of the semester if only because I programmed it with adaptive error

David Z

nice

GPhys

7:18 AM

For my final project in that class I made a high order symplectic integrator and did a Newtonian n-body simulation of ~2000 particles (merging of two 'galaxies')

David Z

ooh that sounds fun

GPhys

@DavidZ final rendering youtube.com/watch?v=Qp0M3gj23YY

code is entirely numpy (used just for vectorization again) and matplotlib

David Z

It looks pretty good

user228700

@JohnR: Morning :-)

GPhys

I'm told disc galaxies do actually merge into elliptical galaxies like that, but I didn't put too much effort into the initial conditions of the disc galaxies actually being realistic

John Rennie

7:28 AM

@Kaumudi.H Morning :-)

user228700

How was the meeting?

John Rennie

@Kaumudi.H Good, though several of the people who usually attend were away on holiday so it was a bit quieter than usual.

David Z

@GPhys It seems to have worked out well enough. Galaxy mergers are definitely a thing, and that looks about right for how they would go down.

John Rennie

Good discussion though. We were discussing The Magic Toyshop by Angela Carter.

user228700

@JohnRennie Ah, I see.

user228700

7:34 AM

@JohnRennie Right, right, u mentioned her before. Was it good?

John Rennie

I'm not a huge fan of the book. Angela Carter is one of those cult authors whose name is mentioned with reverence, but I find her books hard to read.

user228700

Huh. How come?

John Rennie

You need to read her books to understand what I mean.

It's ard to explain her style.

user228700

Oh, OK...

John Rennie

She's more interested in characters and the scenery than the plot, so her books contain lots of descriptive text where nothing much happens.

user228700

7:36 AM

Huh, I see...

user228700

Her boos haha :-)

John Rennie

That's not necessarily a bad thing, but I felt she didn't do a very good job of it in The Magic Toyshop. It felt a bit forced sometimes and also a bit inconsistent.

But if you Google for reviews of the book you'll find lots of people rate it as very good, so I appear to be in a minority.

user228700

Ohh, OK, I see...

John Rennie

Anyhow, it's always fun to meet up with friends, so even though I wasn't keen on the book the meeting was still enjoyable.

user228700

Right, right :-)

John Rennie

7:40 AM

And I have a curry appointment this afternoon, so the weekend is far from over!

user228700

Yes, I remember :-)

user228700

Where are u going?

John Rennie

Haven't decided yet, but probably an Indian restaurant in Chester rather improbably named Barton Rouge. I've been there lots of times and it's generally very good.

user228700

Improbably named? I don't understand...

John Rennie

Well Baton Rouge is a famous city in the US.

GPhys

7:43 AM

@DavidZ Indeed! I was quite happy with it

I found it interesting when coding it that even though the 'Force' matrix is skewsymmetric (i.e. $F_{ij}=-F_{ji}$) it was faster to calculate the force twice than to take advantage of this. (Every scheme I could come up with to take advantage of the above relation had a numpy overhead more than the speedup.) I'm sure if I had programmed it in C or the like that wouldn't be true, though.

John Rennie

And I assume Barton Rouge is derived from it's name.

user228700

Ah, lol, I see.

John Rennie

But Baton Rouge is famous for the French cuisine, not Indian.

user228700

Right...

John Rennie

Baton Rouge, Louisiana

Baton Rouge ( BAT-ən ROOZH; French for "Red Stick", French: Bâton-Rouge [bɑtɔ̃ ʁuʒ]) is the capital of the U.S. state of Louisiana and its second-largest city. It forms the parish seat of East Baton Rouge Parish and is located on the eastern bank of the Mississippi River. As the capital city, Baton Rouge is the political hub for Louisiana, and is the second-largest city in the state after New Orleans, with an estimated population of 228,590 in 2015. The metropolitan area surrounding the city, known as Greater Baton Rouge, is also the second-largest in Louisiana, with a population of 830,480 people...

user228700

7:44 AM

Say, do u have pretty canals in Chester?

John Rennie

There is a canal, the Shropshire Union canal.

user228700

(I'm looking at their menu now and wow, there seem to very few veg. dishes)

user228700

@JohnRennie Shropshire is a little funny sounding :-)

John Rennie

It passes near to my house so I sometimes walk into town along the canal path. It's nice, though I'm not sure I'd say it was beautiful.

user228700

Ah, OK...

John Rennie

7:46 AM

@Kaumudi.H It's an English county.

I'm used to it, so I guess it doesn't sound strange to me.

user228700

Right :-) I bet Tirunalveli sounds just as funny to you.

user228700

Oh, no, I take that back! There are lots of veg. dishes on the menu!

John Rennie

Where the Shropshire Union canal goes through the middle of Chester it passes through a deep cutting that is really spectacular. I don't have any photos though.

user228700

> I don't have any photos though

user228700

:-( OK.

John Rennie

7:48 AM

It's very narrow with vertical sides that go up for maybe 20 metres.

user228700

Oh, wow, I see...

John Rennie

This gives some idea

user228700

Oh, sheesh, that is beautiful.

John Rennie

Though it doesn't really capture the feeling when you're standing in the canal path.

user228700

Of course :-) Kakkanad (a settlement near MEC) is also quite beautiful.

John Rennie

7:51 AM

Or this, looking down on the canal

user228700

@JohnRennie Wow. You live in a beautiful town!

John Rennie

Chester is nice. I ended up here mostly by accident, but it has turned out to be a nice place to live.

user228700

Say, how did you end up there?

user228700

My goal is to be able to move to a Norwegian fjord when I retire.

user228700

7:54 AM

One second!

John Rennie

When I left university I got a job at a research lab about 20 miles from Chester, and I needed to find a house in the area. I was staying in a hotel in Chester, so I looked in a local estate agent and bought pretty much the first house I saw. I intended it to be just temporary but ... I'm still here :-)

@Kaumudi.H you might wish to check the average temperatures in Norway before you decide to move there :-)

user228700

@JohnRennie Ohhh, wow :-)

user228700

@JohnRennie Eek, I hadn't thought of that! In any case, I hope to have lived in enough countries by the time I retire to have gotten used to colder temperatures.

David Z

@GPhys Huh, that's interesting. I guess that's vectorization. If you can share code that demonstrates that effect I'd be interested to see it (though not now, I'm very busy this weekend).

John Rennie

@Kaumudi.H Lots of people have this notion that it would be great to move out into the countryside when they retire. Well my mother lives in the countryside and it's rubbish.

David Z

8:05 AM

@JohnRennie Oh it's not that countryside that people are talking about :-P

John Rennie

From her village there's two buses a day into the nearest town, and a taxi costs about £15 for the round trip.

Sid

I would prefer the natural beauty of countryside and the easy availability of stuff in cities to be found in one single place

user228700

I know, I know.

John Rennie

@Sid then move to Chester :-)

user228700

But still, I hope to be in a state of mind OK with living at a fjord and all.

Sid

8:07 AM

@JohnRennie It's that great, is it?

John Rennie

@Kaumudi.H And after you've gazed at the amazing scenery for a couple of days you'll start thinking now what do I do?

@DavidZ No?

user228700

Right, right, but I'll think up something to do before I move; I'll work on a book or something!

user228700

@JohnRennie Lots of places in Kerala are like that :-)

Sid

@JohnRennie Do you see those temperatures? Nothing>20 degrees

I don't think I can survive

David Z

There will always be another countryside. If people go to one and find they don't like it, they'll just get wistful about somewhere else.

Balarka Sen

8:08 AM

And you may tell yourself
This is not my beautiful house!
And you may tell yourself
This is not my beautiful wife!

[Chorus]

David Z

@Sid celsius? Sounds nice to me (though I didn't think it would be that cold)

John Rennie

@Sid In Chester? At the moment the temperature during the day is around 20 - 25C, which I'd say is about perfect.

Sid

We get 15-20 degree Celsius in Winters.

John Rennie

Warm enough to be nice but not so hot that it's uncomfortable to do anything strenuous.

user228700

> Perfect

user228700

8:10 AM

::Scoffs::

Sid

For us, Warm=30+ but less than 35

The West calls it suffocatingly hot. Which it is not.

user228700

^

David Z

More like the north, I would think? E.g. Mexico is "west" and it gets pretty hot too

user228700

@JohnR: Going out for lunch!

user228700

Will have the usual: fried rice and chilli potatoes.

Balarka Sen

8:12 AM

same as it ever was :3

John Rennie

@Kaumudi.H anywhere special? i.e. a special restaurant?

user228700

@BalarkaSen Hmm?

Balarka Sen

Talking Heads - Once In A Lifetime (HQ)

►

John Rennie

@Kaumudi.H Talking Heads song.

user228700

Ohh, OK.

Balarka Sen

8:13 AM

I should limit my vocabulary to the large word data collection in James Joyce's Finnegans Wake and various song lyrics.

user228700

@JohnRennie Nah, it is a place we've haunted for almost two decades now.

Sid

*haunted?

You mean, hunted?

Balarka Sen

Maybe I will spend 17 years writing a book with that vocabulary

user228700

@Sid No, I mean haunted. Visited, I mean.

user228700

I should edit that.

John Rennie

8:16 AM

No, I think haunted is a perfectly good word to use.

David Z

"haunted" is fine, I got it

user228700

I was going to edit that to "It has remained one of our haunts for...".

Balarka Sen

It's a comic way to say it's a common place of visit for a group of people or an individual

Sid

To me, haunted=Scary.

user228700

@BalarkaSen Right, right, and this is how I meant for it to read but for a moment, I didn't think haunted would translate as another version of haunts.

David Z

8:19 AM

Scary is definitely the most common sense in which it's used, but I do also know it as meaning "frequently visited or occupied", albeit uncommonly used that way. It might come from the idea that ghosts tend to be "attached" to one place. (Or maybe the other way around)

user228700

^

John Rennie

I need to work for a few minutes. Back in a bit ...

user228700

Man, I am so hungry! I haven't eaten anything in close to 17 hours :-(

user228700

Right, we're here! Toodleoo!

John Rennie

9:37 AM

Wow, it's national ice cream day. Who knew? Not that I need an excuse to eat ice cream :-)

user228700

9:59 AM

@JohnRennie Haha wow :-)

user228700

I didn't order the usuals after all! I had masala kulcha with paneer butter masala and a fruit salad with ice cream! :-) It was lovely.

John Rennie

masala kulcha - stuffed bread?

user228700

Essentially, yes.

user228700

Mine were stuffed with spiced mashed potatoes!

John Rennie

My friends have just mailed me with details of the meetup, but we aren't eating until 17:45. That's seven hours from now. I'll be dead of starvation by then.

user228700

10:35 AM

@JohnRennie Wtf, so you're really only having an early dinner, not lunch...

user228700

(Sorry about the latency; I've just received Rs. 2000 from an aunt for having gotten into MEC!)

John Rennie

@Kaumudi.H Yes, I thought we were meeting up for lunch, but the others are going to see a film and we're eating after the film.

user228700

Oh, no :-(

user228700

Eat some apples, then, at lunchtime.

John Rennie

I'll survive. I'll be thinner, but still alive :-)

The trouble is that I'm not very good at eating a small snack. Small snacks tend to turn into large meals, then I'll be full and won't want any curry.

The safest option is not to eat at all until the meal.

user228700

10:39 AM

Wow, your body is quite mean to you!

user228700

3 mins ago, by Kaumudi. H

(Sorry about the latency; I've just received Rs. 2000 from an aunt for having gotten into MEC!)

user228700

And now I've got Rs. 5000 in my purse!

John Rennie

I saw. Buy a headphone adaptor!!!

user228700

I will but for that, I will ask my mum; I'm saving this lot for later.

user228700

@JohnRennie I used to be worryingly thin. So much so that my friends and family used to joke that if I started eating any less than I used to, I'd vanish completely :-)

John Rennie

10:42 AM

I'm thin, but I stopped worrying about it a long time ago :-)

user228700

:-)

Balarka Sen

Damn I could quote another line from the same album right now

user228700

Sigh, I'm quite tired from having gone out for lunch; how I will survive college I dunno.

user228700

@BalarkaSen So why don't you?

Balarka Sen

"I'm so thin"

user228700

10:44 AM

Took my breath away :-P

Balarka Sen

Well it's a fantastic line

@0celo7 I think I am going to spend the next four days learning from Milnor's red book, chapter 2

user228700

At this rate, I'm not going to get through even half a day of classes.

John Rennie

@Kaumudi.H I wouldn't worry about it. I always feel sleepy after eating.

I tend to eat late in the day so I can get everything done before I eat then conk out.

user228700

Right, but this isn't exactly about eating alone; I feel more tired than ever if I socialise for a little more than an hour.

user228700

Mixed with the eating and all, it's proving to be disastrous, even though I slept for 11.5 hours last night!

Balarka Sen

10:50 AM

that's easy to fix

John Rennie

Why disastrous? What you describe sounds like fairly typical teenge behaviour to me.

user228700

@BalarkaSen Yeah, not socialising is not an option at college.

user228700

@JohnRennie It's not fairly typical in my experience.

user228700

Disastrous because it drains my sap right away.

ACuriousMind

It's typical for introverts - you just need to figure what makes you feel energetic again (e.g. reading, exercise)

John Rennie

10:52 AM

@Kaumudi.H I wouldn't be so quick to predict catastrophe. Go to college and take it as it comes.

user228700

@ACuriousMind I know, I know. I'm merely predicting that college is going to be a tad exhausting.

John Rennie

If you need to sleep for 11.5 hours then sleep for 11.5 hours.

ACuriousMind

@Kaumudi.H Life is "a tad exhausting" :P

user228700

@JohnRennie Haha, I don't think I'm going to be able to sleep for this long in college; I'm going to try and stick to a 7-hour sleep schedule...

Balarka Sen

well, the use of the adjective "introvert" is overrated

user228700

10:54 AM

@ACuriousMind :-P Right.

John Rennie

@Kaumudi.H Seven hours is not enough sleep for an 18 year old.

At that age you need somewhere in the range 8-10 hours.

user228700

:-/ I might not be able to do all of the things if I sleep for that long.

user228700

@BalarkaSen Sure. Why do u point this out now?

John Rennie

@Kaumudi.H then prioritise things and omit the low priority ones. Getting too little sleep is not a viable long term strategy.

user228700

Hmm, yes, you're right. I will try to figure it out.

Balarka Sen

10:58 AM

When one claims something is typical for introverts, one is claiming that outside a small subset of exceptions, the mass of people, tagged as "introverts", have that something in question as properties. I'm just pointing out that the suggested mass is vague; it's not clear what or who an introvert is.

Mithrandir24601

For me, the whole introverted/extroverted thing is a relative term - if you stick me at home with a bunch of friends from school and make me interact with them, I'm going to get tired and fed up pretty quickly, but if you stick me in a room with a few of my friends from Uni, that doesn't happen, so how introverted I am depends a lot on who I'm with. Also, 7 hours was a nice, long sleep in undergrad :P

Balarka Sen

Thereby any adjective imposed upon that given mass is going to be, in turn, vague.

John Rennie

@Kaumudi.H wait and see what the workload is like at college before worrying. I bet it will be a lot lighter than your revision schedule was.

user228700

@JohnRennie Are u aware, BTW, that even the number of hours of sleep u get everyday comes with an inherent sense of shame in these parts? At school, some used to scoff at others for sleeping for any more than 6 hours.

John Rennie

@Kaumudi.H some people are arseholes. That's life.

Mithrandir24601

11:00 AM

@Kaumudi.H I would turn round and call them silly and shallow for not having any real interests

Balarka Sen

I bear no shame for pickling my owls

John Rennie

Though I guess if you nap during the day then your overnight sleep will be shorter ...

user228700

No, I don't usually nap during the day because if I accidentally nap for any more than half an hour, I can't get myself to fall asleep at night anytime before 3 AM.

John Rennie

pickling my owls - that's sounds like one of those suspicious euphemisms :-)

user228700

But I'm going to risk it and take a quick nap now! @JohnR: Enjoy ur late lunch/early dinner! :-)

user228700

11:04 AM

I hope u don't die of starvation by then :-P

John Rennie

I'm doomed ...

user228700

Drink water. LOADS of water.

John Rennie

Not many calories in water

user228700

That's what I do anyway, when I'm starving and have nothing to eat at home.

user228700

@JohnRennie No, but it makes ur brain feel like ur stomach is full for a very short while.

John Rennie

11:07 AM

I generally drink coffee to stave off hunger pangs.

Caffeine is a reasonably effective appetite suppressant.

user228700

Coffee then! Copious amounts!

John Rennie

And you get all that exercise running up the stairs to the bathroom :-)

Balarka Sen

coffeous amount

John Rennie

I'm contemplating buying another PC, so that will give me something to pass the time ...

user228700

@JohnRennie Ah, we live on one floor :-) The bathroom is 5 feet away from where I'm currently sitting.

user228700

11:09 AM

@JohnRennie Jesus Christ, you're literally the only person who buys computers to pass the time! I wonder if there's someone else like you, but with cars...

user228700

@BalarkaSen x'D

John Rennie

@Kaumudi.H If you've got a good aim you could probably reach the toilet from where you are :-)

@Kaumudi.H This one but I won't pay much more than £250 for it and I'm guessing the price will go a lot higher than that.

user228700

@JohnRennie Ahem. I'm a girl! Why do people keep forgetting that? My profile picture is that of a girl! ME!

user228700

@JohnRennie Wow, £250 is still a lot of money.

John Rennie

It is a very, very powerful PC though. It's considerably more powerful than the laptop I'm using to type this.

user228700

11:12 AM

Hmm, I see...

user228700

Again, I ask: What on Earth will u do with it?

John Rennie

We'll see. In any case it will almost certainly sell for more than I want to pay.

Mithrandir24601

@JohnRennie The hard drive's a bit small though. Not that that's a hard problem to fix :P

John Rennie

@Mithrandir24601 when I buy computers on eBay I always factor in the cost of replacing the existing disk by an SSD.

In fact this computer has an SSD already, though as you say a small one.

user228700

@JohnRennie Pass ur time and donate rice at the same time.

Mithrandir24601

11:16 AM

@JohnRennie Seems like a good idea :) When I got the one I'm using, I somehow managed to get a 500GB SSD drive for an extra £20 (was on offer or something at the time :) )

(and that was on top of the 1TB HDD :P )

John Rennie

The Optiplex 9030 has two drive bays, so I can always put in a large second disk if I need a lot of space, and put the OS and apps on the SSD.

Mithrandir24601

@JohnRennie This is a very good idea. But you obviously know this already :P

John Rennie

@Kaumudi.H I'm not sure I see the point of that freerice web site.

Initially I thought it was some form of crowdsourcing, but I can't see the point of the questions it asks you.

user228700

@JohnR: What's ur will going to be like? You've already given laptops and stuff to pretty much everyone you know x'D

user228700

@JohnRennie They're too easy, yes, but hey, donating rice!

John Rennie

11:22 AM

The computers I own don't add up to very much because I always buy them cheap on ebay. 0celo7's new gaming machine probably cost more than all my computers combined.

My brother probably spends more on one family holiday than all my computers are worth.

user228700

Ah, hmm.

user228700

@JohnR: That website has a variety of subjects to choose from, BTW! It even has one for SAT prep.!

John Rennie

No section on Physics though

user228700

No :-(

Mithrandir24601

Or you could always pass your time messing with IBM's quantum computer

John Rennie

11:26 AM

Hmm, it appears to be part of the UN food programme.

Balarka Sen

Hmm. If I have a Riemannian surface $S$ and a vector field $X$ on a chart at $p$ in $S$ that is parallel (that is $\nabla_{\partial/\partial x} X = \nabla_{\partial/\partial y} X = 0$), does that mean $S$ is flat at $p$? In general if I have a Riemannian manifold $M$ of dimension $n$ and $n$ independent parallel vector fields on a chart at $p$, does that mean $M$ is flat at $p$?

user228700

Omg...

Balarka Sen

(@ACuriousMind Do you know this?)

user228700

That number was incorrect; they've actually donated 70,225 Kgs of rice.

user228700

@JohnRennie It is, yeah. It's legitimate and all.

Bernardo Meurer

11:29 AM

Back to Brazil :^)

@JohnRennie Had to leave the Amplifier for my gf to ship to California

That will be one travelling amp :P

John Rennie

Yes, it's a big heavy lump to be carrying around the world!

Careful though ... you might get charged import duties by US customs.

Bernardo Meurer

I know

That would suck

I'm shipping my darned speakers too

What a headache

John Rennie

It would be worth checking with the US customs to see what the situation is. I'm fairly sure you're allowed to bring in your own property without incurring charges.

Bernardo Meurer

Hopefully that's the case

and I had to sell my turntable to cover moving costs :(

John Rennie

I'd check before you get the stuff shipped.

Bernardo Meurer

11:32 AM

::nods::

John Rennie

@BernardoMeurer bummer. But to be fair turntables are delicate and the chances of it surviving the shipping weren't that high.

Bernardo Meurer

@JohnRennie I had it on the original box though with all the packing

John Rennie

By contrast the amp is built like a tank and could probably survive being thrown across the Atlantic :-)

Bernardo Meurer

That thing is like a tank

and weighs 6Kg :P

Balarka Sen

@ACuriousMind Nevermind, that should be true.

The chart parametrization should be an isometry.

Slereah

12:47 PM

$$\odot \smile \odot$$

Sid

@JohnRennie For the last week, I have slept for 3-4 hours everyday. Pretty sure, I am sane and doing my everyday chores quite well.

Physics Meta

0

Q: violation of energy conservation in retarded interaction of magnet and coil

If i move a magnet towards the coil than magnet will experience resistive force because of the lenz law. This way mechanical energy will convert into electrical energy. But what if magnet and the coil are sufficiently large distance apart. The change in magnetic field travels at the speed of lig...

discussion support

0celo7

@BalarkaSen Yes, it is true.

@BalarkaSen Just use the vector fields to compute the Riemann tensor. All of the derivatives vanish. Since the vector fields span the tangent space at each point, all of the component vanish.

Balarka Sen

2:40 PM

@0celo7 yeah.... i'm super dumb

0celo7

2:59 PM

@JohnRennie 3.8 was stable

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