The h Bar

12:54 AM

lol

feeling lost can be the beginning of finding something :)

ok now I think you're either drunk or pulling my chain

just in a zen mood at moment, somewhat like bohr was occasionally

bolbteppa

@vzn you should read the QM book of Bohr's PhD student to get more of that zen

amazon.com/Quantum-Mechanics-Third-Non-Relativistic-Theory/dp/…

it seems some of bohrs philosophizing has been airbrushed out of scientific history... just found a great book to counteract that. actually found it years ago, have been meaning to read it, got vague urge recently, dug it up

amazon.com/Einstein-Buddha-Parallel-Thomas-McFarlane/dp/…

@vzn I don't think that's true. I think people read Bohr's papers nowadays and just find it very hard to read.

bolbteppa

1:00 AM

@vzn do you know much of the scientific part of that history as you would find in the book I linked to? The first chapter has more words than equations

some of bohrs actual ideas (some even written) have been swept aside by history, they were not all that different than bohms. just found a staggering/ jawdropping quote by bohr in this book, have to share it with anyone....

> For a parallel to the lesson of atomic theory, [we must turn] to those kinds of problems with which thinkers like the Buddha and Lao Tzu have been confronted, when trying to harmonize our position as spectators and actors in the great drama of existence. --bohr

Why is that jaw-dropping?

My jaw is firmly in place.

Are you being just a tad dramatic, @vzn?

meurer.xyz/post/my-new-iphone-sucks

@DanielSank Bam

have read mountains of accts on bohr and never heard that he said anything about buddhism, taoism... long had some suspicion though.

@vzn You might enjoy that too

1:10 AM

@Slereah are you a villani fan? this book has been on my to-read pile for awhile, some of the hardcore mathgeeks in here might like it... even nearly )( popsci :)

amazon.com/Birth-Theorem-Mathematical-C%C3%A9dric-Villani/dp/…

@BernardoMeurer 2nd blog in a quarter year, youre on your way :) ... my sig other got an iphone somewhat recently... still slowly figuring it out... eg the contact mgt seems to be a bit unintuitive/ tricky am sure theres lots else o_O

@vzn I have two more that I just haven't gotten to finish yet

1. is a short essay about tragedies in the US

2. is an overview of Spinoza's concept of God

lol youre a natural man :)

I'm a what?

natural blogger... a raconteur :)

Aaaah

Thanks :P

1:17 AM

> it fatefully died after being mistaken for a shoyu tray in a dimly lit Japanese restaurant

(reminds me of how my ipad mini got cracked in a dramatic incident last summer) o_O

@bolbteppa which book are you talking about? kaku on string theory?

Me: Can I use heroin?
@DanielSank: Sure
Me: Can I jump from this bridge?
@DanielSank: Head first
Me: Can I drink kitchen alcohol:
@DanielSank: Chug! Chug! Chug!
Me: Can I use git submodule?
@DanielSank: STOP RIGHT WHERE YOU ARE

2

LOLOLOLOL

1:37 AM

@DanielSank dont understand this sentiment or why its starred. what is ooolbs "bs rhetoric"? he said its not easy to build QFT? or renormalize? its not even clear what hes talking about...

1:51 AM

Yo @JakeRose.

Yo @DanielSank

I was typing that message just as you sent yours what a coincidence :')

Does latex work in this?

Ok so we start off with $$\ddot{x} + 2\gamma \dot{x} + \omega^2 x = f(t),$$ right?

@JakeRose Yes, but you have to run a javascript script to make it work.

Mhm

A: Should chat have TeX support?

116

There are four bookmarks which are located on this installation page: start ChatJax installs MathJax and starts a loop that renders $\LaTeX$ as needed. This is intended for use in chat, where the contents of the page are not static. Reloading the page will stop the loop, so the bookmark needs t...

At my level we haven't introduced complex numbers into the equation

1:53 AM

oops

Cambridge teach everything weird I suppose

Nope, I was just thinking in frequency space. Ignore that i. It's gone now.

Like magic :')

Ping me when you get chatjax working.

Its working

Pretty sure I have it installed from a while back

Yep I have

1:56 AM

great

So we have $$\ddot{x} + 2 \gamma \dot{x} + \omega^2 x = 0,$$ yes?

Yep

You still there? @DanielSank

yes

Internet chat is an asynchronous communicaiton protocol.

Anyway, so ok your prof did what next?

I wish I could downvote chat comments

me too

isn't that what a flag is?

a form of down vote, I mean

2:10 AM

@JakeRose

no, I want the world to know that Daniel's asynchronous line is wrong and harmful

Okay so next the driving frequency is equal to the natural frequency of the system (a mass and spring) and so =k/m

oops

$\root {k/m}$

Crap

Ok wait a second.

how so?

Let's define $\omega_0 \equiv \sqrt{k/m}$ yes?

2:11 AM

Yes

So the equation of motion is $$\ddot{x} + 2 \gamma \dot{x} + \omega_0^2 = F(t)/m \, ,$$ where $F(t)$ is the driving force.

enumaris

fix it felix

Yes (you missed x on the %\omega^{2}$)

fuck

But yes I agree other than that

cursing is bad

enumaris

This is a Christian chat I'm told

2:15 AM

^

says the pot to the kettle

Dangit

$$ \ddot{x} + 2 \gamma \dot{x} + \omega_0^2 x = F(t)/m$$

THERE

Ok so now the prof said $F(t) = f \cos(\omega_0 t)$?

"Arrives between Dec. 28 - Jan. 16.
Ships from NJ, United States."

how does that even work

Yah thats coorect

it's like a 5 hour drive

2:17 AM

@0celo7 Yes well, you're not important enough to get a personalized shipment, driver, and delivery, I'm afraid.

^

@JakeRose Ok so then $$\ddot{x} + 2 \gamma \dot{x} + \omega_0^2 x = f \cos(\omega_0 t)$$

@DanielSank point being NJ is close so that shipping time is insane

Yes

Amazon?

2:18 AM

amazon used

@0celo7 How do you know it's not the seller-doesn't-guarantee-when-they'll-decide-to-ship-your-item time?

The Amazon is a jungle of red tape.

@DanielSank that's probably it, which is also insane

Or the seller-doesn't-actually-have-the-item-in-stock-and-is-going-to-buy-it-on-ebay-an‌d-rip-you-off time?

@DanielSank uhh

that's clever

does that happen?

2:20 AM

yup

why not

@0celo7 Of course. It's a free market.

@JakeRose Ok so what's next?

Aka the most "efficient" market

Lecturer then stated that $\ddot{x}+\omega^{2}x=0$

Well in a way, yes. The rip-off is a charge you're paying to have someone shop for you.

@JakeRose Hm, ok. That's true for an undamped, undriven oscillator.

Agreed

2:23 AM

If they decided to just forget the damping, then I think I understand what they're doing here.

I don't understand how he does this

How he does what?

Are you familiar with homogeneous and inhomogeneous parts of the solution of a differential equation?

If not, explaining that will probably clear this up for you.

No we haven't covered differential equations in our maths course yet

The damping has definitely not been ignored by the looks of the rest of the notes from this part

What? Cambridge maths has not covered differential equations yet?

@JakeRose oh

ok

2:26 AM

Nope we cover it later in the year

So, let's just throw out the damping and move on.

And I dont do maths I do physics

Ok this is going to make sense now.

Natural Sciences

@JakeRose are you aware that the derivative is a linear operation?

2:27 AM

Not a clue what that means

i.e. $(d/dt)(f + g) = df/dt + dg/dt$

Oh yes

A thing is linear if its action on a sum is the same as the sum of the thing acting on each item individually.

Yeah so the derivative is linear in that sense. Similarly, the second derivative is also linear. This should be obvious.

Yes?

Yes

Ok so check this out: we can rewrite the oscillator differential equation:

$$\ddot{x} + 2 \gamma \dot{x} + \omega_0^2 x = F(t)/m$$

as

$$(D^2 + 2 \gamma D + \omega_0^2)x = F(t)/m$$

where here $D$ means "time derivative".

2:30 AM

Yes

Ok now note that the thing in parentheses is linear!

It's a sum of things that are linear, and is therefore itself linear. You can easily check this.

Okay

Ok so now here's the important part:

Be wise and linearize :-)

Suppose $y(t)$ is a solution to the equation $(D^2 + 2 \gamma D + \omega_0^2)y = 0$.

i.e. $y$ is a solution if there's no driving force.

2:32 AM

are you teaching him how to solve ODEs

Suppose $x(t)$ is a solution to the full equation with the driving force.

What can you say about $x(t) + y(t)$?

::raises hand::

@0celo7 Just some basics about linear ones.

Must also be a solution?

@0celo7 Please go away.

2:33 AM

That was a guess

@JakeRose Yes, why?

@DanielSank rude

Remember, the stuff in parentheses is linear...

You can act it on each term in the sum individually and add the results.

@0celo7 So is ::raises hand:: You're being a smart-ass.

So if you input y(t) + x(t) the differential operator acts on both seperately

@JakeRose Yeah...

2:35 AM

And so you get the y(t) solution coming to 0

And being eliminated

because $D(x+y) = Dx + Dy$.

@JakeRose Yes!

The key concept here @JakeRose is linearization.

The point being that you can always add in the solution to the no-driving case and still have a perfectly acceptable solution.

@skullpatrol Eh, I dunno. This equation is linear from the start.

I think your prof was using this idea.

For learning purposes :-)

@skullpatrol eh? Very linear systems exist in nature all the time.

2:38 AM

Ah I see

Remember, he has not covered differential equations yet.

Not even in high school? @JakeRose

Right, @JakeRose this whole idea only works when the differential equation is linear.

Nope

:-/

British education system at its finest

2:40 AM

Not sure why you're so surprised, @skullpatrol. I have never taken a differential equations course.

I went to quite a poor quality school so the maths course at A-level which probably would have contained it wasnt available to me

Well, I had a math teacher in high school who tried to teach us differential equations in my senior year, but I don't think any of us absorbed it at all. It was too advanced at that point. She was trying to do multivariable differential equations.

In my opinion, learning the mathematical manipulations first makes the physics easier to see.

Just from a more physical standpoint if we say $m\ddot{x}=-kx$ how does that work?

Bea=cause the overall force isnt just the spring

Its the driving force too?

@skullpatrol I agree entirely. I just don't think it's surprising when physics/math curricula fail to teach math early enough.

@JakeRose That equation simply represents the case with no friction and no driving.

(let's forget friction entirely from now on) Suppose I have a solution with driving, $x(t)$. It is the case that physically the motion $x(t) + y(t)$, where $y(t)$ solves the equation without driving, is a possible motion of the oscillator.

2:48 AM

In the lecture though he says that there is 'perfect balance between spring force and acceleration'

Can't interpret lecturer's words :-\

What do you mean sorry?

@JakeRose sorry?

@JakeRose looks like AlfredCentauri figured out what's going on.

Im confused :')

Check your post on the main site. Someone gave an answer that looks right.

I couldn't tell exactly what you were asking, but Alfred got it!

2:59 AM

Yeah I get it

Just having trouble with the physical intuition

hmmm

Im pretty tired and probably gonna sleep so Ill let this go for now

Hey @DanielSank mind if I just ask some general questions?

3:50 AM

@JakeRose go for it

Secret

5:29 AM

[Some rambles]
Esoterists and most spiritual people love to use the term "energy", when they are in fact trying to quantify a complex mixture of good or bad mental, environmental etc. influences into a scalar value.
In a rough sense the analogy kinda cuts because we are often expect to be more productive when under influences that make us happy stable or (insert any positive emotions), and in 1st year physics, energy is often defined as the readiness to do work.

Caution is to be taken not to conflate these two notions when conversing with a spiritual friend

To a spiritualist, the influence from the environment on my emotions is effectively zero as most of my emotions are very similar to tranquility and nothingness thus don't readily get perturbed like the more common emotions

5:48 AM

what's your point?

or just don't talk to spiritualists.

Secret

There is no point for the 3rd starred message

As for the 2nd, this is to be able to have a conversation with these groups without accidentally introducing pseudoscience, and to be able to talk about these things without using science wrongly

That will ensure some conversation in the common ground between scientists and spiritualist to not having misinformation generated and keep the conversation relevant

alright but why is that important?

y'know there's lots of groups of people like spiritualists with their own weird worldviews

Secret

Well, I just want to say the core messages from their conversations can be understood once you recognise all the (possibly misused) terminology. There are times these people have interesting advices on how to arrange your workload and organise things to make yourself happier and efficient

I have a claim (which I am not sure if it can be demonstrated, my need to check later) that almost everything the spiritual people said that is not misinformation are just psychology

I felt that when being careful enough, you can find something useful from them in terms of life advices.

Nowadays however, finding spiritualists that are not scammers is so hard that it might be impractical to waste time on them, but I don't know.

Anonymous

6:14 AM

Aha. This is an excellent way to teach Fourier transforms: betterexplained.com/articles/…

6:47 AM

@Blue Better explained often does a great job making mathematics intuitive

Anonymous

@SirCumference Yeah, I'm quite happy to have found that site :D

@Blue Honestly the nicest thing back in Calc I and II was this article:

betterexplained.com/articles/…

Anonymous

Oh, yes. That is a good analogy

Anonymous

Before learning any topic I tend to check out the related youtube videos

Anonymous

That helps a lot

7:25 AM

Note: vote today to receive a limited hat

@SirCumference the Solstice hat?

@JohnRennie Yep

Got that yesterday :-)

Huh...

You get it for participating when it's the 21st anywhere in the world, so from about 10:00 UTC yesterday.

7:29 AM

@JohnRennie Although I notice you haven't put any hats on?

I'm not that active on the main site these days so I only have ten hats

I thought that wasn't enough to be worth taking part in the hat wearing.

"Not that active", "only ten hats"

Welp, shows how inactive I've been, only having 8.

@JohnRennie Ah, it's fun, you don't need to race for the most hats

They're gonna be gone in a few weeks anyway

We'll see ..

7:50 AM

whoever gets the most hats has my respect and admiration.

Fawad

I have 0 hats :( 😢

Anonymous

@Fawad If you can maintain 0 hats till the end of Winter Bash, even after visiting the site everyday, that would be an achievement in itself :P

2

who is the lively astronomer tonight?

@Fawad The Islam SE doesn't appear to be taking part in the Winter Bash. Is that a deliberate choice by the site?

8:06 AM

@JohnRennie I see some users on Islam with hats

Anonymous

Medi1Saif ♦

17.7k 4 27 82

Anonymous

There are people wearing hats there

Anonymous

@JohnRennie winterbash2017.stackexchange.com/leaderboard/…

@Blue Oh yes. Ignore me :-)

Anonymous

Perhaps you don't see many hats because the activity is low on that site

Anonymous

8:08 AM

And it's still in beta :)

It was just I know Islam forbids portrayal of people (I've probably oversimplified that) and I wondered if putting hats on avatars was frowned up. Clearly not.

Q: Is that permissible to participate in the Stackexchange Winter Bash?

@Blue Oh neat, I didn't know there were leaderboards

winterbash2017.stackexchange.com/leaderboard/…

:)

Anonymous

2

Is that ok to celebrate with Winter Bash on Stack Exchange? Stack Exchange invites you to celebrate the end of a great year …with HATS! As you use your site, you'll discover hats and other items hidden behind certain actions. Collect all of them, some of them, or none of them, but be quick – ...

halal-haram celebration

Anonymous

There was a discussion on that it seems

If you do in some way worship the hat / site, you have some serious introspection to make

I love the phrasing of that. Very English somehow :-)

Anonymous

8:12 AM

Hehe

Even with only ten hats I'm fourth on the leaderboard. Maybe I'll don a hat after all. I assumed I'd be way behind.

Anonymous

@JohnRennie Put on a funny hat, maybe. The "Just Jesting" one would suit you well :'D

Why is there no crackpot hat? It would get awarded for having your question closed as non-mainstream :-)

Ooh, my hat has just appeared ...

Anonymous

@JohnRennie Both crackpot and nutcase hats should be added :P

Anonymous

@JohnRennie Yay!

Anonymous

8:17 AM

It looks cool :D

The trouble is that I'd love a nutcase hat. I'd probably post a crank question just to get one :-)

Anonymous

:P

BTW I have one last point about Visual Studio ...

You know how it puts in it's own header "stdafx.h"?

Anonymous

@JohnRennie Oh, no, I don't

Anonymous

How?

8:20 AM

The office people liked the gift

good

Anonymous

@Slereah Congrats. You worked hard!

That's what you get when creating a new project.

@Blue Those burns were not in vain!

Anonymous

@JohnRennie Right

Anonymous

Then?

8:21 AM

So it turns out molten solder stings

The "stdafx.h" is used to support a feature called precompiled headers that significantly speeds up compilation of big apps.

Anonymous

@Slereah And, so what gift did you get in the secret santa? :D

a box of chocolate

Anonymous

@JohnRennie Interesting

Anonymous

Which headers in particular?

8:22 AM

You can remove it and use the usual <stdioh> <string.h> etc, but you need to go into the project settings and turn off precompiled hearders.

I mention this in case you want to use VS for course work where the lecturer won't be expecting you to use MS specific headers.

Anonymous

@Slereah Sad.....they didn't work hard to gift you :P Anyway, chocolates are always a good gift...:)

Very true. You can't eat Arduinos :-)

Anonymous

lol

Anonymous

@JohnRennie Ah, gotcha! Thanks

@JohnRennie Well technically you can

It's just not very good

8:25 AM

:-) They aren't very nourishing though.

Might be a useful source of trace elements I suppose ...

Anonymous

@JohnRennie Which Setting menu actually? I have VS open (new project)

Anonymous

Ok,opened that

Anonymous

Then?

Change the setting to not using precompiled headers. Then you can delete the stdafx include and replace it by the stadnard include files.

Anonymous

8:31 AM

I get that screen. But I can't understand how to set it to "not using precompiled headers"

Anonymous

Where is that option? (Hope I'm not overlooking things)

Click on that line to select it, and a drop down arrow appears

Anonymous

It says Edit. So should I just edit and delete what's written?

(where I've outlined in red)

Anonymous

And then "Apply"?

8:34 AM

Anonymous

@JohnRennie That option was not given

Anonymous

I just edited and deleted whatever was written and then clicked "Apply"

Hmm, can you post a screen grab?

Anonymous

That's the wrong line! You want the top line!

Shing

8:36 AM

I don't get any cool hat :(

Look at my screen grab.

Anonymous

Oh, sorry

Anonymous

Done now

Students these days ... :-)

Anonymous

Lolol

8:38 AM

OK. Now look at the Solution Explorer pane at the top right.

Anonymous

Yes, I see that

You can right click the files I've outlined and exclude them from the project. So your cpp file is the only source file.

You don't have to do that as leaving those three files part of the project doesn't do any harm, but it's neater to remove them.

Anonymous

@JohnRennie Ah, done!

Anonymous

Thanks

It's just that your course will probably expect you to use the standard headers.

This allows you to do that and still use VS.

Anonymous

8:42 AM

True. I was looking for a way to do this earlier :)

Shing

I don't understand why all the downvotes?

Q: If all matter ceased movement, would time still pass?

Or you can compile from the command line and just use VS as a text editor. But then you can't use the debugging facilities.

Shing

-4

I was reading The Black Hole War, by Leonard Susskind, when I came across a section describing the moving and relative bending of time. If time is a property of the movement of all matter in relation to one another, would time cease to exist if all movement stopped? Is this absolute zero?

time matter

Anonymous

From this semester I don't think we'll have pure C programming (like in the first semester). But got to use it for the algo and numerical analysis class

Anonymous

@JohnRennie Hehe, using command line for compiling is always a bit painful

8:46 AM

gcc --sillyflagsIcantremember helloworld.c

Anonymous

XD

To be fair you'd use a makefile as soon as the app got big

Anonymous

Makefile

A makefile is a file containing a set of directives used with the make build automation tool. == Overview == Most often, the makefile directs make on how to compile and link a program. Using C/C++ as an example, when a C/C++ source file is changed, it must be recompiled. If a header file has changed, each C/C++ source file that includes the header file must be recompiled to be safe. Each compilation produces an object file corresponding to the source file. Finally, if any source file has been recompiled, all the object files, whether newly made or saved from previous compilations, must be linked...

Anonymous

I didn't know what this is

Anonymous

Interesting

Anonymous

8:57 AM

I'll ask you to teach me that, someday :)

Anonymous

"These instructions with their dependencies are specified in a makefile. If none of the files that are prerequisites have been changed since the last time the program was compiled, no actions take place. For large software projects, using Makefiles can substantially reduce build times if only a few source files have changed."

@JohnRennie just put all the flags

Back when I did C coding I used to just put all the flags on high alert to try to write the 100% COMPLIANT C PROGRAM

when I got bored

100% C compliance isn't easy